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Njeim R, Merscher S, Fornoni A. Mechanisms and implications of podocyte autophagy in chronic kidney disease. Am J Physiol Renal Physiol 2024; 326:F877-F893. [PMID: 38601984 DOI: 10.1152/ajprenal.00415.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2023] [Revised: 03/27/2024] [Accepted: 03/27/2024] [Indexed: 04/12/2024] Open
Abstract
Autophagy is a protective mechanism through which cells degrade and recycle proteins and organelles to maintain cellular homeostasis and integrity. An accumulating body of evidence underscores the significant impact of dysregulated autophagy on podocyte injury in chronic kidney disease (CKD). In this review, we provide a comprehensive overview of the diverse types of autophagy and their regulation in cellular homeostasis, with a specific emphasis on podocytes. Furthermore, we discuss recent findings that focus on the functional role of different types of autophagy during podocyte injury in chronic kidney disease. The intricate interplay between different types of autophagy and podocyte health requires further research, which is critical for understanding the pathogenesis of CKD and developing targeted therapeutic interventions.
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Affiliation(s)
- Rachel Njeim
- Katz Family Division of Nephrology and Hypertension, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida, United States
- Peggy and Harold Katz Family Drug Discovery Center, University of Miami Miller School of Medicine, Miami, Florida, United States
| | - Sandra Merscher
- Katz Family Division of Nephrology and Hypertension, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida, United States
- Peggy and Harold Katz Family Drug Discovery Center, University of Miami Miller School of Medicine, Miami, Florida, United States
| | - Alessia Fornoni
- Katz Family Division of Nephrology and Hypertension, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida, United States
- Peggy and Harold Katz Family Drug Discovery Center, University of Miami Miller School of Medicine, Miami, Florida, United States
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Chen B, Jefferson DM, Cho WK. Impaired Regulatory Volume Decrease and Characterization of Underlying Volume-Activated Currents in Cystic Fibrosis Human Cholangiocyte Cell Line. J Membr Biol 2022; 255:261-276. [DOI: 10.1007/s00232-022-00216-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2021] [Accepted: 01/11/2022] [Indexed: 11/29/2022]
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Yuan Z, Wang S, Tan X, Wang D. New Insights into the Mechanisms of Chaperon-Mediated Autophagy and Implications for Kidney Diseases. Cells 2022; 11:cells11030406. [PMID: 35159216 PMCID: PMC8834181 DOI: 10.3390/cells11030406] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2021] [Revised: 01/14/2022] [Accepted: 01/18/2022] [Indexed: 02/04/2023] Open
Abstract
Chaperone-mediated autophagy (CMA) is a separate type of lysosomal proteolysis, characterized by its selectivity of substrate proteins and direct translocation into lysosomes. Recent studies have declared the involvement of CMA in a variety of physiologic and pathologic situations involving the kidney, and it has emerged as a potential target for the treatment of kidney diseases. The role of CMA in kidney diseases is context-dependent and appears reciprocally with macroautophagy. Among the renal resident cells, the proximal tubule exhibits a high basal level of CMA activity, and restoration of CMA alleviates the aging-related tubular alternations. The level of CMA is up-regulated under conditions of oxidative stress, such as in acute kidney injury, while it is declined in chronic kidney disease and aging-related kidney diseases, leading to the accumulation of oxidized substrates. Suppressed CMA leads to the kidney hypertrophy in diabetes mellitus, and the increase of CMA contributes to the progress and chemoresistance in renal cell carcinoma. With the progress on the understanding of the cellular functions and uncovering the clinical scenario, the application of targeting CMA in the treatment of kidney diseases is expected.
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Rojas-Canales DM, Li JY, Makuei L, Gleadle JM. Compensatory renal hypertrophy following nephrectomy: When and how? Nephrology (Carlton) 2019; 24:1225-1232. [PMID: 30809888 DOI: 10.1111/nep.13578] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/24/2019] [Indexed: 12/16/2022]
Abstract
Following surgical removal of one kidney, the other enlarges and increases its function. The mechanism for the sensing of this change and the growth is incompletely understood but begins within days and compensatory renal hypertrophy (CRH) is the dominant contributor to the growth. In many individuals undergoing nephrectomy for cancer or kidney donation this produces a substantial and helpful increase in renal function. Two main mechanisms have been proposed, one in which increased activity by the remaining kidney leads to hypertrophy, the second in which there is release of a kidney specific factor in response to a unilateral nephrectomy that initiates CRH. Whilst multiple growth factors and pathways such as the mTORC pathway have been implicated in experimental studies, their roles and the precise mechanism of CRH are not defined. Unrestrained hypoxia inducible factor activation in renal cancer promotes growth and may play an important role in driving CRH.
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Affiliation(s)
- Darling M Rojas-Canales
- College of Medicine and Public Health and Medicine, Flinders University, Adelaide, South Australia, Australia.,Department of Renal Medicine, Flinders Medical Centre, Adelaide, South Australia, Australia
| | - Jordan Y Li
- College of Medicine and Public Health and Medicine, Flinders University, Adelaide, South Australia, Australia.,Department of Renal Medicine, Flinders Medical Centre, Adelaide, South Australia, Australia
| | - Leek Makuei
- College of Medicine and Public Health and Medicine, Flinders University, Adelaide, South Australia, Australia
| | - Jonathan M Gleadle
- College of Medicine and Public Health and Medicine, Flinders University, Adelaide, South Australia, Australia.,Department of Renal Medicine, Flinders Medical Centre, Adelaide, South Australia, Australia
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Mishra R, Upadhyay A, Prajapati VK, Mishra A. Proteasome-mediated proteostasis: Novel medicinal and pharmacological strategies for diseases. Med Res Rev 2018; 38:1916-1973. [DOI: 10.1002/med.21502] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2017] [Revised: 03/13/2018] [Accepted: 04/04/2018] [Indexed: 02/06/2023]
Affiliation(s)
- Ribhav Mishra
- Cellular and Molecular Neurobiology Unit; Indian Institute of Technology Jodhpur; Rajasthan India
| | - Arun Upadhyay
- Cellular and Molecular Neurobiology Unit; Indian Institute of Technology Jodhpur; Rajasthan India
| | - Vijay Kumar Prajapati
- Department of Biochemistry; School of Life Sciences; Central University of Rajasthan; Rajasthan India
| | - Amit Mishra
- Cellular and Molecular Neurobiology Unit; Indian Institute of Technology Jodhpur; Rajasthan India
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Souza-Menezes J, da Silva Feltran G, Morales MM. CFTR and TNR-CFTR expression and function in the kidney. Biophys Rev 2014; 6:227-236. [PMID: 28510183 PMCID: PMC5425698 DOI: 10.1007/s12551-014-0140-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2013] [Accepted: 03/04/2014] [Indexed: 10/25/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is abundantly expressed in the kidney. CFTR mRNA is detected in all nephron segments of rats and humans and its expression is higher in the renal cortex and outer medulla than in the inner medulla. CFTR protein is detected at the apical surface of both proximal and distal tubules of rat kidney but not in the outer medullary collecting ducts. The localization of CFTR in the proximal tubules is compatible with that of endosomes, suggesting that CFTR might regulate pH in endocytic vesicles by equilibrating H+ accumulation due to H+-ATPase activity. Many studies have also demonstrated that CFTR also regulates channel pore opening and the transport of sodium, chloride and potassium. The kidneys also express a CFTR splicing variant, called TNR-CFTR, in a tissue-specific manner, primarily in the renal medulla. This splicing variant conserves the functional characteristics of wild-type CFTR. The functional significance of TNR-CFTR remains to be elucidated, but our group proposes that TNR-CFTR may have a basic function in intracellular organelles, rather than in the plasma membrane. Also, this splicing variant is able to partially substitute CFTR functions in the renal medulla of Cftr-/- mice and CF patients. In this review we discuss the major functions that have been proposed for CFTR and TNR-CFTR in the kidney.
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Affiliation(s)
- Jackson Souza-Menezes
- Laboratório Integrado de Ciências Morfofuncionais, Núcleo em Ecologia e Desenvolvimento Sócio-Ambiental, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Av. São José do Barreto, 764, Barreto, Macaé, 27965-045 RJ Brazil
- Laboratório de Fisiologia Celular e Molecular, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21941-902 Brazil
| | - Geórgia da Silva Feltran
- Laboratório Integrado de Ciências Morfofuncionais, Núcleo em Ecologia e Desenvolvimento Sócio-Ambiental, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Av. São José do Barreto, 764, Barreto, Macaé, 27965-045 RJ Brazil
| | - Marcelo M. Morales
- Laboratório de Fisiologia Celular e Molecular, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21941-902 Brazil
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Abstract
Chaperone-mediated autophagy (CMA) is a lysosomal proteolytic pathway in which cytosolic substrate proteins contain specific chaperone recognition sequences required for degradation and are translocated directly across the lysosomal membrane for destruction. CMA proteolytic activity has a reciprocal relationship with macroautophagy: CMA is most active in cells in which macroautophagy is least active. Normal renal proximal tubular cells have low levels of macroautophagy, but high basal levels of CMA activity. CMA activity is regulated by starvation, growth factors, oxidative stress, lipids, aging, and retinoic acid signaling. The physiological consequences of changes in CMA activity depend on the substrate proteins present in a given cell type. In the proximal tubule, increased CMA results from protein or calorie starvation and from oxidative stress. Overactivity of CMA can be associated with tubular lysosomal pathology and certain cancers. Reduced CMA activity contributes to protein accumulation in renal tubular hypertrophy, but may contribute to oxidative tissue damage in diabetes and aging. Although there are more questions than answers about the role of high basal CMA activity, this remarkable feature of tubular protein metabolism appears to influence a variety of chronic diseases.
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Affiliation(s)
- Harold A Franch
- Research Service, Atlanta Veterans Affairs Medical Center, Decatur, GA; and Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, GA.
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Advani A, Wiggins KJ, Cox AJ, Zhang Y, Gilbert RE, Kelly DJ. Inhibition of the epidermal growth factor receptor preserves podocytes and attenuates albuminuria in experimental diabetic nephropathy. Nephrology (Carlton) 2011; 16:573-81. [PMID: 21342330 DOI: 10.1111/j.1440-1797.2011.01451.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
AIM Early renal enlargement may predict the future development of nephropathy in patients with diabetes. The epidermal growth factor (EGF)-EGF receptor (EGFR) system plays a pivotal role in mediating renal hypertrophy, where it may act to regulate cell growth and proliferation and also to mediate the actions of angiotensin II through transactivation of the EGFR. In the present study we sought to investigate the effects of long-term inhibition of the EGFR tyrosine kinase in an experimental model of diabetes that is characterized by angiotensin II dependent hypertension. METHODS Female heterozygous streptozotocin-diabetic TGR(mRen-2)27 rats were treated with the EGFR inhibitor PKI 166 by daily oral dosing for 16 weeks. RESULTS Treatment of TGR(mRen-2)27 rats with PKI 166 attenuated the increase in kidney size, glomerular hypertrophy and albuminuria that occurred with diabetes. The reduction in albuminuria, with EGFR inhibition in diabetic TGR(mRen-2)27 rats, was associated with preservation of the number of glomerular cells staining positively for the podocyte nuclear marker, WT1. Immunostaining for WT1 inversely correlated with glomerular volume in diabetic rats. In contrast to agents that block the renin-angiotensin system (RAS), EGFR inhibition had no effect on either the quantity of mesangial matrix or the magnitude of tubular injury in diabetic animals. CONCLUSION These observations indicate that inhibition of the tyrosine kinase activity of the EGFR attenuates kidney and glomerular enlargement in association with podocyte preservation and reduction in albuminuria in diabetes. Accordingly, targeting the EGF-EGFR pathway may represent a therapeutic strategy for patients who continue to progress despite RAS-blockade.
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Affiliation(s)
- Andrew Advani
- Keenan Research Centre of the Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, Ontario, Canada.
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Wang WH, Yue P, Sun P, Lin DH. Regulation and function of potassium channels in aldosterone-sensitive distal nephron. Curr Opin Nephrol Hypertens 2010; 19:463-70. [PMID: 20601877 PMCID: PMC4426959 DOI: 10.1097/mnh.0b013e32833c34ec] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
PURPOSE OF REVIEW K channels in the aldosterone-sensitive distal nephron (ASDN) participate in generating cell membrane potential and in mediating K secretion. The aim of the review is to provide an overview of the recent development regarding physiological function of the K channels and the novel factors which modulate the K channels of the ASDN. RECENT FINDINGS Genetic studies and transgenic mouse models have revealed the physiological function of basolateral K channels including inwardly rectifying K channel (Kir) and Ca-activated big-conductance K channels in mediating salt transport in the ASDN. A recent study shows that intersectin is required for mediating with-no-lysine kinase (WNK)-induced endocytosis. Moreover, a clathrin adaptor, autosomal recessive hypercholesterolemia (ARH), and an aging-suppression protein, Klothe, have been shown to regulate the endocytosis of renal outer medullary potassium (ROMK) channel. Also, serum-glucocorticoids-induced kinase I (SGK1) reversed the inhibitory effect of WNK4 on ROMK through the phosphorylation of WNK4. However, Src-family protein tyrosine kinase (SFK) abolished the effect of SGK1 on WNK4 and restored the WNK4-induced inhibition of ROMK. SUMMARY Basolateral K channels including big-conductance K channel and Kir4.1/5.1 play an important role in regulating Na and Mg transport in the ASDN. Apical K channels are not only responsible for mediating K excretion but they are also involved in regulating transepithelial Mg absorption. New factors and mechanisms by which hormones and dietary K intake regulate apical K secretory channels expand the current knowledge regarding renal K handling.
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Affiliation(s)
- Wen-Hui Wang
- Department of Pharmacology, New York Medical College, Valhalla, New York 10595, USA.
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10
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Expression and localization of cystic fibrosis transmembrane conductance regulator in human gingiva. Cell Biol Int 2010. [DOI: 10.1042/cbi20090019] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Wang WH, Giebisch G. Regulation of potassium (K) handling in the renal collecting duct. Pflugers Arch 2009; 458:157-68. [PMID: 18839206 PMCID: PMC2730119 DOI: 10.1007/s00424-008-0593-3] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Accepted: 09/20/2008] [Indexed: 12/13/2022]
Abstract
This review provides an overview of the molecular mechanisms of K transport in the mammalian connecting tubule (CNT) and cortical collecting duct (CCD), both nephron segments responsible for the regulation of renal K secretion. Aldosterone and dietary K intake are two of the most important factors regulating K secretion in the CNT and CCD. Recently, angiotensin II (AngII) has also been shown to play a role in the regulation of K secretion. In addition, genetic and molecular biological approaches have further identified new mechanisms by which aldosterone and dietary K intake regulate K transport. Thus, the interaction between serum-glucocorticoid-induced kinase 1 (SGK1) and with-no-lysine kinase 4 (WNK4) plays a significant role in mediating the effect of aldosterone on ROMK (Kir1.1), an important apical K channel modulating K secretion. Recent evidence suggests that WNK1, mitogen-activated protein kinases such as P38, ERK, and Src family protein tyrosine kinase are involved in mediating the effect of low K intake on apical K secretory channels.
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Affiliation(s)
- Wen-Hui Wang
- Department of Pharmacology, New York Medical College, Valhalla, 10595, USA.
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12
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Souza-Menezes J, Morales MM. CFTR structure and function: is there a role in the kidney? Biophys Rev 2009; 1:3-12. [PMID: 28510151 PMCID: PMC5387792 DOI: 10.1007/s12551-008-0002-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2008] [Accepted: 12/19/2008] [Indexed: 12/27/2022] Open
Abstract
Cystic fibrosis (CF) is a lethal autosomal recessive genetic disease caused by mutations in the CF transmembrane conductance regulator (CFTR). Mutations in the CFTR gene may result in a defective protein processing that leads to changes in function and regulation of this chloride channel. Despite of the expression of CFTR in the kidney, patients with CF do not present major renal dysfunction, but it is known that both the urinary excretion of proteins and renal capacity to concentrate and dilute urine are altered in these patients. CFTR mRNA is expressed in all nephron segments of rat and human, and this abundance is more prominent in renal cortex and outer medulla renal areas. CFTR protein was detected in apical surface of both proximal and distal tubules of rat kidney but not in the outer medullary collecting ducts. Studies have demonstrated that CFTR does not only transport Cl- but also ATP. ATP transport by CFTR could be involved in the control of other ion transporters such as Na+ (ENaC) and K+ (renal outer medullary potassium) channels, especially in TAL and CCD. In the kidney, CFTR also might be involved in the endocytosis of low-molecular-weight proteins by proximal tubules. This review is focused on the CFTR function and structure, its role in the renal physiology, and its modulation by hormones involved in the control of extracellular fluid volume.
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Affiliation(s)
- J. Souza-Menezes
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Macaé, Brazil
| | - M. M. Morales
- Instituto de Biofísica Carlos Chagas Filho, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
- Av Carlos Chagas Filho 373, Centro de Ciências da Saúde Bloco G Sala 48, Cidade Universitária, Rio de Janeiro, 21941-902 Brazil
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Rajan V, Mitch WE. Ubiquitin, proteasomes and proteolytic mechanisms activated by kidney disease. Biochim Biophys Acta Mol Basis Dis 2008; 1782:795-9. [PMID: 18723090 DOI: 10.1016/j.bbadis.2008.07.007] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2008] [Revised: 07/27/2008] [Accepted: 07/30/2008] [Indexed: 01/08/2023]
Abstract
The ubiquitin-proteasome system (UPS) includes 3 enzymes that conjugate ubiquitin to intracellular proteins that are then recognized and degraded in the proteasome. The process participates in the regulation of cell metabolism. In the kidney, the UPS regulates the turnover of transporters and signaling proteins and its activity is down regulated in acidosis-induced proximal tubular cell hypertrophy. In chronic kidney disease (CKD), muscle wasting occurs because complications of CKD including acidosis, insulin resistance, inflammation, and increased angiotensin II levels stimulate the UPS to degrade muscle proteins. This response also includes caspase-3 and calpains which act to cleave muscle proteins to provide substrates for the UPS. For example, caspase-3 degrades actomyosin, leaving a 14 kDa fragment of actin in muscle. The 14 kDa actin fragment is increased in muscle of patient with kidney disease, burn injury and surgery. In addition, acidosis, insulin resistance, inflammation and angiotensin II stimulate glucocorticoid production. Glucocorticoids are also required for the muscle wasting that occurs in CKD. Thus, the UPS is involved in regulating kidney function and participates in highly organized responses that degrade muscle protein in response to loss of kidney function.
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Affiliation(s)
- Vik Rajan
- Nephrology Division, M/S: BCM 285 Baylor College of Medicine, One Baylor Plaza, Alkek N-520 Houston, TX 77030, USA
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Abraham P, Indirani K, Sugumar E. Effect of cyclophosphamide treatment on selected lysosomal enzymes in the kidney of rats. ACTA ACUST UNITED AC 2007; 59:143-9. [PMID: 17686619 DOI: 10.1016/j.etp.2007.05.003] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2007] [Accepted: 05/10/2007] [Indexed: 11/26/2022]
Abstract
The anti-cancer drug cyclophosphamide (CYP) is nephrotoxic besides being urotoxic thereby limiting its clinical utility. Since the nephrotoxicity of CYP is less common compared to its urotoxicity, not much importance has been given for the study of mechanism of CYP-induced nephrotoxicity. The aim of the present study is to investigate the possible role of lysosomal enzymes in CYP-induced renal damage. Adult female Wistar rats weighing 200-250 g were used for the study. The rats were administered single-intraperitoneal injection of CYP at the dose of 150 mg/kg body wt and sacrificed at various time intervals 6, 16 or 24 h after the dose of CYP. The control rats were administered saline alone. Nephrotoxicity was assessed by measuring plasma creatinine and urea and histopathology of the kidney. The kidney was weighed and used for the assay of lysosomal enzymes namely acid phosphatase, beta-glucuronidase and N-acetylglucosaminidase and total protein content. Histologically, the CYP-treated rat kidneys showed progressive renal damage with increase in time after treatment. Glomerular nephritis, cortical tubular vacuolization and interstitial edema were observed in the CYP-treated rats. Surprisingly, a significant drastic decrease (instead of an increase) in the activities of lysosomal enzymes was observed in the kidneys of CYP-treated rats at 16 and 24 h as compared with the control. A highly significant increase (270%) in protein content was observed in the kidneys of the CYP-treated rats as compared with the control. Decrease in the activities of lysosomal protein digestive enzymes may contribute to CYP-induced renal damage. The accumulation of abnormal amounts of the protein in the kidney may be due at least in part to defect in lysosomal enzyme activity and contribute to renal damage.
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Affiliation(s)
- Premila Abraham
- Department of Biochemistry, Christian Medical College, Bagayam, Vellore 632002, Tamil Nadu, India.
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Kidney growth during catabolic illness: what it does not destroy makes it grow stronger. J Ren Nutr 2007; 17:167-72. [PMID: 17462548 DOI: 10.1053/j.jrn.2007.01.018] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2006] [Indexed: 12/19/2022] Open
Abstract
The kidney undergoes hypertrophy under conditions that paradoxically cause a loss of lean body mass, such as diabetes, acidosis, and chronic kidney disease. What unique mechanisms account for kidney growth during negative nitrogen balance? One adaptation is that renal tubular cells substantially decrease protein breakdown during kidney cell growth. In this review, we discuss how acidosis and diabetes reduce protein breakdown within the kidney and the intracellular signaling pathways that may regulate protein metabolism. Our results suggest that in cell culture models and in acute diabetes, kidney cells specifically reduce protein breakdown by the lysosomal pathway of chaperone-mediated autophagy. This differs from the activation of proteolysis by the ubiquitin-proteasome system in muscle in acute diabetes and uremia. A shared signaling pathway regulates protein breakdown in both kidney and skeletal muscle, namely, phosphatidylinositol-3 kinase signaling. Diabetes mellitus activates signaling through this pathway in the kidney while down-regulating it in skeletal muscle. We conclude that similar signaling pathways may regulate distinct proteolytic pathways in different tissues.
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Sidani SM, Kirchhoff P, Socrates T, Stelter L, Ferreira E, Caputo C, Roberts KE, Bell RL, Egan ME, Geibel JP. ΔF508 Mutation Results in Impaired Gastric Acid Secretion. J Biol Chem 2007; 282:6068-74. [PMID: 17178714 DOI: 10.1074/jbc.m608427200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is recognized as a multifunctional protein that is involved in Cl(-) secretion, as well as acting as a regulatory protein. In order for acid secretion to take place a complex interaction of transport proteins and channels must occur at the apical pole of the parietal cell. Included in this process is at least one K(+) and Cl(-) channel, allowing for both recycling of K(+) for the H,K-ATPase, and Cl(-) secretion, necessary for the generation of concentrated HCl in the gastric gland lumen. We have previously shown that an ATP-sensitive potassium channel (K(ATP)) is expressed in parietal cells. In the present study we measured secretagogue-induced acid secretion from wild-type and DeltaF508-deficient mice in isolated gastric glands and whole stomach preparations. Secretagogue-induced acid secretion in wild-type mouse gastric glands could be significantly reduced with either glibenclamide or the specific inhibitor CFTR-inh172. In DeltaF508-deficient mice, however, histamine-induced acid secretion was significantly less than in wild-type mice. Furthermore, immunofluorescent localization of sulfonylurea 1 and 2 failed to show expression of a sulfonylurea receptor in the parietal cell, thus further implicating CFTR as the ATP-binding cassette transporter associated with the K(ATP) channels. These results demonstrate a regulatory role for the CFTR protein in normal gastric acid secretion.
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Affiliation(s)
- Shafik M Sidani
- Department of Surgery, Yale University, New Haven, Connecticut 06520, USA
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Shen W, Brown NS, Finn PF, Dice JF, Franch HA. Akt and Mammalian Target of Rapamycin Regulate Separate Systems of Proteolysis in Renal Tubular Cells. J Am Soc Nephrol 2006; 17:2414-23. [PMID: 16885413 DOI: 10.1681/asn.2005111157] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
EGF suppresses proteolysis via class 1 phosphatidylinositol 3-kinase (PI3K) in renal tubular cells. EGF also increases the abundance of glycolytic enzymes (e.g., glyceraldehyde-3-phosphate dehydrogenase [GAPDH]) and transcription factors (e.g., pax2) that are degraded by the lysosomal pathway of chaperone-mediated autophagy. To determine if EGF regulates chaperone-mediated autophagy through PI3K signaling, this study examined the effect of inhibiting PI3K and its downstream mediators Akt and the mammalian target of rapamycin (mTOR). Inhibition of PI3K with LY294002 prevented EGF-induced increases in GAPDH and pax2 abundance in NRK-52E renal tubular cells. Similar results were seen with an adenovirus encoding a dominant negative Akt (DN Akt). Expression of a constitutively active Akt increased GAPDH and pax2 abundance. An mTOR inhibitor, rapamycin, did not prevent EGF-induced increases in these proteins. Neither DN Akt nor rapamycin alone had an effect on total cell protein degradation, but both partially reversed EGF-induced suppression of proteolysis. DN Akt no longer affected proteolysis after treatment with a lysosomal inhibitor, methylamine. In contrast, methylamine or the inhibitor of macroautophagy, 3-methyladenine, did not prevent rapamycin from partially reversing the effect of EGF on proteolysis. Notably, rapamycin did not increase autophagasomes detected by monodansylcadaverine staining. Blocking the proteasomal pathway with either MG132 or lactacystin prevented rapamycin from partially reversing the effect of EGF on proteolysis. It is concluded that EGF regulates pax2 and GAPDH abundance and proteolysis through a PI3K/Akt-sensitive pathway that does not involve mTOR. Rapamycin has a novel effect of regulating proteasomal proteolysis in cells that are stimulated with EGF.
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Affiliation(s)
- Wen Shen
- Address correspondence to: Dr. Harold A. Franch, Renal Division, Emory University School of Medicine, W.M.B., Room #338, 1639 Pierce Drive, N.E., Atlanta, GA 30322, USA
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Ozdemir AM, Hopfer U, Erhard P, Monnier VM, Weiss MF. Processing Advanced Glycation End Product-Modified Albumin by the Renal Proximal Tubule and the Early Pathogenesis of Diabetic Nephropathy. Ann N Y Acad Sci 2006; 1043:625-36. [PMID: 16037286 DOI: 10.1196/annals.1338.071] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Diabetes is characterized by increased quantities of circulating proteins modified by advanced glycation end products (AGEs). Proteins filtered at the glomerulus and presented to the renal proximal tubule are likely to be highly modified by AGEs. The proximal tubule binds, takes up, and catabolizes AGE-modified albumin by pathways different from those of unmodified albumin. These differences were examined in polarized, electrically resistant proximal tubular cells grown in monolayer culture. In patients with type 1 diabetes, urinary excretion of a lysosomal enzyme predicted the development of nephropathy.
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Affiliation(s)
- Aylin M Ozdemir
- Division of Nephrology, Department of Medicine, University Hospitals of Cleveland, 11100 Euclid Ave., Cleveland, OH 44106-5048, USA
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Peerce BE, Clarke RD. Renal cytoplasmic proteasome proteinase activities are altered in chronic renal failure. Arch Biochem Biophys 2005; 444:84-91. [PMID: 16293221 DOI: 10.1016/j.abb.2005.09.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2005] [Accepted: 09/27/2005] [Indexed: 10/25/2022]
Abstract
The effect of uremia on renal cortex cytoplasmic proteasomes was examined by comparing proteasomes isolated from 5/6th nephrectomy rats 3-months post-surgery and age-matched control rats with normal renal function. ATP-dependent proteasome activity was reduced 50% in chronic renal failure rats (CRF) 3-months post-surgery compared to age-matched control rats. Trypsin-like (T-like) proteasome activity was decreased 90% compared to 70% for caspase-like activity (PGPHase) and 30% for chymotrypsin-like activity (C-like). ATP-independent proteasome activity was decreased 60% in CRF rats 3-months post-surgery. ATP-independent renal cortex proteasome T-like activity in CRF rats was 4% of age-matched control rats. C-like and PGPHase activities were 60% and 50% of age-matched controls, respectively. Uremia was associated with decreased 26S proteasome beta subunits. CRF rat 26S proteasomes had decreased levels of beta1, beta3, alpha4, and alpha7 abundances. Compared to age-matched control rats with normal renal function, CRF rats had a 25% increase in ubiquitinated cytoplasmic proteins. Decreased renal cytoplasmic proteasome activity may play a role in renal tubule hypertrophy common to renal diseases associated with decreased functioning nephrons.
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Affiliation(s)
- Brian E Peerce
- Department of Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, 77555-0641, USA.
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20
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Wassef L, Kelly DJ, Gilbert RE. Epidermal growth factor receptor inhibition attenuates early kidney enlargement in experimental diabetes. Kidney Int 2005; 66:1805-14. [PMID: 15496151 DOI: 10.1111/j.1523-1755.2004.00955.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND Renal enlargement is an early feature of both human and experimental diabetes. Although the precise mechanisms underlying its development are incompletely understood, locally active growth factors have been suggested to have a key role. Having previously documented increased expression of the proproliferative and antiapoptotic growth factor, epidermal growth factor (EGF), in early diabetes-related kidney growth, the present study sought to evaluate its pathogenetic role by blocking its action with a specific inhibitor. METHODS Sprague-Dawley rats were randomized to receive streptozotocin (diabetic) or buffer (control) and then further randomized to receive either vehicle or the inhibitor of the EGF receptor tyrosine kinase, PKI 166 (100 mg/kg/day) for 2 days and 3 weeks following streptozotocin administration. RESULTS Experimental diabetes was associated with an increase in kidney weight and tubular epithelial cell proliferation as identified by increased expression of proliferating cell nuclear antigen (PCNA) and 5-bromo-2'-deoxyuridine (BrdU) incorporation. PKI 166 resulted in a 30% reduction in kidney weight in diabetic rats (P < 0.01) and reduced tubular epithelial cell proliferation (P < 0.01). In addition, EGF receptor inhibition also led to a 40% increase in tubular epithelial cell apoptosis at 3 weeks (P < 0.01). Diabetes-associated glomerular enlargement was similarly attenuated by PKI 166, although glomerular hyperfiltration was unaffected. CONCLUSION These findings suggest that the EGF-EGF receptor (EGFR) axis has a significant role in the development of early diabetes-related kidney growth. The impact of EGFR inhibition on the later development of renal dysfunction, however, remains to be determined.
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Affiliation(s)
- Lesley Wassef
- Department of Medicine, St. Vincent's Hospital, University of Melbourne, Victoria, Australia
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21
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Barrière H, Tauc M, Poujeol P. Use of knock-out mouse models for the study of renal ion channels. J Membr Biol 2005; 198:113-24. [PMID: 15216413 DOI: 10.1007/s00232-004-0665-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2003] [Indexed: 12/30/2022]
Affiliation(s)
- H Barrière
- UMR CNRS 6548, Université de Nice-Sophia Antipolis, 06108 Nice Cedex 2, France
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22
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Vankeerberghen A, Cuppens H, Cassiman JJ. The cystic fibrosis transmembrane conductance regulator: an intriguing protein with pleiotropic functions. J Cyst Fibros 2004; 1:13-29. [PMID: 15463806 DOI: 10.1016/s1569-1993(01)00003-0] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/16/2001] [Indexed: 12/19/2022]
Abstract
Cystic fibrosis is a frequent autosomal recessive disorder that is caused by the malfunctioning of a small chloride channel, the cystic fibrosis transmembrane conductance regulator. The protein is found in the apical membrane of epithelial cells lining exocrine glands. Absence of this channel results in imbalance of ion concentrations across the cell membrane. As a result, fluids secreted through these glands become more viscous and, in the end, ducts become plugged and atrophic. Little is known about the pathways that link the malfunctioning of the CFTR protein with the observed clinical phenotype. Moreover, there is no strict correlation between specific CFTR mutations and the CF phenotype. This might be explained by the fact that environmental and additional genetic factors may influence the phenotype. The CFTR protein itself is regulated at the maturational level by chaperones and SNARE proteins and at the functional level by several protein kinases. Moreover, CFTR functions also as a regulator of other ion channels and of intracellular membrane transport processes. In order to be able to function as a protein with pleiotropic actions, CFTR seems to be linked with other proteins and with the cytoskeleton through interaction with PDZ-domain-containing proteins at the apical pole of the cell. Progress in cystic fibrosis research is substantial, but still leaves many questions unanswered.
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Sooparb S, Price SR, Shaoguang J, Franch HA. Suppression of chaperone-mediated autophagy in the renal cortex during acute diabetes mellitus. Kidney Int 2004; 65:2135-44. [PMID: 15149326 DOI: 10.1111/j.1523-1755.2004.00639.x] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
BACKGROUND In the renal hypertrophy that occurs in diabetes mellitus, decreased proteolysis may lead to protein accumulation, but it is unclear which proteins are affected. Because the lysosomal proteolytic pathway of chaperone-mediated autophagy is suppressed by growth factors in cultured cells, we investigated whether the abundance of substrates of this pathway increase in diabetic hypertrophy. METHODS Rats with streptozotocin (STZ)-induced diabetes were pair-fed with vehicle-injected control rats. Proteolysis was measured as lysine release in renal cortical suspensions and protein synthesis as phenylalanine incorporation. Target proteins of chaperone-mediated autophagy were measured in cortical lysates and nuclear extracts by immunoblot analysis. Proteins that regulate chaperone-mediated autophagy [the lysosomal-associated membrane protein 2a (LAMP2a) or the heat shock cognate protein of 73 kD (hsc-73)] were measured in lysosomes isolated by density gradient centrifugation. RESULTS Proteolysis decreased by 41% in diabetic rats; protein synthesis increased at 3 days, but returned to baseline by 7 days. The abundance of proteins containing that chaperone-mediated autophagy KFERQ signal motif increased 38% and individual KFERQ containing proteins [e.g., M2 pyruvate kinase, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and pax2] were more abundant. LAMP2a and hsc73 decreased by 25% and 81%, respectively, in cortical lysosomes from diabetic vs. control rats. CONCLUSION The decline in proteolysis in acute diabetes mellitus is associated with an increase in proteins degraded by chaperone-mediated autophagy and a decrease in proteins which regulate this pathway. This study provides the first evidence that reduced chaperone-mediated autophagy contributes to accumulation of specific proteins in diabetic-induced renal hypertrophy.
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Affiliation(s)
- Sira Sooparb
- Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, and Atlanta Veterans Afffairs Medical Center, Decatur, Georgia, USA
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24
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Cho WK, Siegrist VJ, Zinzow W. Impaired regulatory volume decrease in freshly isolated cholangiocytes from cystic fibrosis mice: implications for cystic fibrosis transmembrane conductance regulator effect on potassium conductance. J Biol Chem 2004; 279:14610-8. [PMID: 14722124 DOI: 10.1074/jbc.m310855200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Various K(+) and Cl(-) channels are important in cell volume regulation and biliary secretion, but the specific role of cystic fibrosis transmembrane conductance regulator in cholangiocyte cell volume regulation is not known. The goal of this research was to study regulatory volume decrease (RVD) in bile duct cell clusters (BDCCs) from normal and cystic fibrosis (CF) mouse livers. Mouse BDCCs without an enclosed lumen were prepared as described (Cho, W. K. (2002) Am. J. Physiol. 283, G1320-G1327). The isotonic solution consisted of HEPES buffer with 40% of the NaCl replaced with isomolar amounts of sucrose, whereas hypotonic solution was the same as isotonic solution without sucrose. The cell volume changes were indirectly assessed by measuring cross-sectional area (CSA) changes of the BDCCs using quantitative videomicroscopy. Exposure to hypotonic solutions increased relative CSAs of normal BDCCs to 1.20 +/- 0.01 (mean +/- S.E., n = 50) in 10 min, followed by RVD to 1.07 +/- 0.01 by 40 min. Hypotonic challenge in CF mouse BDCCs also increased relative CSA to 1.20 +/- 0.01 (n = 53) in 10 min but without significant recovery. Coadministration of the K(+)-selective ionophore valinomycin restored RVD in CF mouse BDCCs, suggesting that the impaired RVD was likely from a defect in K(+) conductance. Moreover, this valinomycin-induced RVD in CF mice was inhibited by 5-nitro-2'-(3-phenylpropylamino)-benzoate, indicating that it is not from nonspecific effects. Neither cAMP nor calcium agonists could reverse the impaired RVD seen in CF cholangiocytes. Our conclusion is that CF mouse cholangiocytes have defective RVD from an impaired K(+) efflux pathway, which could not be reversed by cAMP nor calcium agonists.
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Affiliation(s)
- Won Kyoo Cho
- Department of Medicine, Division of Gastroenterology/Hepatology, Indiana University School of Medicine and The Richard L. Roudebush Veterans Affairs Medical Center, Indianapolis, Indiana 46202, USA.
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Volk T, Konstas AA, Bassalaý P, Ehmke H, Korbmacher C. Extracellular Na+ removal attenuates rundown of the epithelial Na+-channel (ENaC) by reducing the rate of channel retrieval. Pflugers Arch 2003; 447:884-94. [PMID: 14704795 DOI: 10.1007/s00424-003-1193-x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2003] [Revised: 09/20/2003] [Accepted: 09/26/2003] [Indexed: 11/30/2022]
Abstract
Regulation of the epithelial sodium channel (ENaC) is important for the long-term control of arterial blood pressure as evidenced by gain of function mutations of ENaC causing Liddle's syndrome, a rare form of hereditary arterial hypertension. In Xenopus laevis oocytes expressing ENaC a spontaneous decline of ENaC currents over time, so-called rundown, is commonly observed. Mechanisms involved in rundown may be physiologically relevant and may be related to feedback regulation of ENaC by intra- or extracellular Na+. We tested the effect of extracellular Na+ removal on ENaC rundown. Spontaneous rundown of ENaC was largely prevented by extracellular Na+ removal and was partially prevented by primaquine suggesting that it is due to endocytic channel retrieval. Liddle's syndrome mutation caused a reduced rate of rundown, and in oocytes expressing the mutated channel extracellular Na+ removal not only prevented rundown but even increased the ENaC currents (runup). Acute exposure to high extracellular Na+ drastically reduced whole-cell currents and surface expression of wild-type ENaC, while these effects were much smaller in ENaC with Liddle's syndrome mutation consistent with a stabilization of the mutated channel in the plasma membrane. Interestingly, the apparent intracellular Na+ concentration [Na+](i-app) was high (>60 mM) in ENaC-expressing oocytes but rundown was not associated with a further increase in [Na+](i-app). We conclude that the inhibitory effect of extracellular Na+ removal on rundown is due to an inhibition of endocytic ENaC retrieval.
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Affiliation(s)
- Tilmann Volk
- Institut für Zelluläre und Molekulare Physiologie, Universität Erlangen-Nürnberg, Waldstrasse 6, 91054 Erlangen, Germany
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26
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Owsianik G, Cao L, Nilius B. Rescue of functional DeltaF508-CFTR channels by co-expression with truncated CFTR constructs in COS-1 cells. FEBS Lett 2003; 554:173-8. [PMID: 14596935 DOI: 10.1016/s0014-5793(03)01162-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The most frequent mutant variant of the cystic fibrosis transmembrane conductance regulator (CFTR), DeltaF508-CFTR, is misprocessed and subsequently degraded in the endoplasmic reticulum. Using the patch-clamp technique, we showed that co-expressions of DeltaF508-CFTR with the N-terminal CFTR truncates containing bi-arginine (RXR) retention/retrieval motifs result in a functional rescue of the DeltaF508-CFTR mutant channel in COS-1 cells. This DeltaF508-CFTR rescue process was strongly impaired when truncated CFTR constructs possessed either the DeltaF508 mutation or arginine-to-lysine mutations in RXRs. In conclusions, our data demonstrated that expression of truncated CFTR constructs could be a novel promising approach to improve maturation of DeltaF508-CFTR channels.
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Affiliation(s)
- Grzegorz Owsianik
- Laboratory of Physiology, Catholic University of Leuven, Campus Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium.
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27
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Yoo D, Flagg TP, Olsen O, Raghuram V, Foskett JK, Welling PA. Assembly and trafficking of a multiprotein ROMK (Kir 1.1) channel complex by PDZ interactions. J Biol Chem 2003; 279:6863-73. [PMID: 14604981 DOI: 10.1074/jbc.m311599200] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The ROMK subtypes of inward rectifier K+ channels (Kir 1.1, KCNJ1) mediate potassium secretion and regulate NaCl reabsorption in the kidney. In the present study, the role of the PDZ binding motif in ROMK function is explored. Here we identify the Na/H exchange regulatory factors, NHERF-1 and NHERF-2, as PDZ domain interaction partners of the ROMK channel. Characterization of the basis and consequences of NHERF association with ROMK reveals a PDZ interaction-dependent trafficking process and a coupling mechanism for linking ROMK to a channel modifier protein, the cystic fibrosis transmembrane regulator (CFTR). As measured by antibody binding of external epitope-tagged forms of Kir 1.1 in intact cells, NHERF-1 or NHERF-2 coexpression increased cell surface expression of ROMK. Channel interaction with NHERF proteins and effects of NHERF on ROMK localization were dependent on the presence of the PDZ domain binding motif in ROMK. Both NHERF proteins contain two PDZ domains; recombinant protein-protein binding assays and yeast-two-hybrid studies revealed that ROMK preferentially associates with the second PDZ domain of NHERF-1 and with the first PDZ domain of NHERF-2, precisely opposite of what has been reported for CFTR. Consistent with the scaffolding capacity of the NHERF proteins, coexpression of NHERF-2 with ROMK and CFTR dramatically increases the amount of ROMK protein that coimmunopurifies and functionally interacts with CFTR. Thus NHERF facilitates assembly of a ternary complex containing ROMK and CFTR. These observations raise the possibility that PDZ-based interactions may underscore physiological regulation and membrane targeting of ROMK in the kidney.
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Affiliation(s)
- Dana Yoo
- Department of Physiology, University of Maryland School of Medicine, Baltimore 21201, USA
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Lin D, Sterling H, Lerea KM, Giebisch G, Wang WH. Protein kinase C (PKC)-induced phosphorylation of ROMK1 is essential for the surface expression of ROMK1 channels. J Biol Chem 2002; 277:44278-84. [PMID: 12221079 PMCID: PMC3047507 DOI: 10.1074/jbc.m203702200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
We carried out in vitro phosphorylation assays to determine whether ROMK1 is a substrate of protein kinase C (PKC) and used the two-electrode voltage clamp method to investigate the role of serine residues 4, 183, and 201, the three putative PKC phosphorylation sites, in the regulation of ROMK1 channel activity. Incubation of the purified His-tagged ROMK1 protein with PKC and radiolabeled ATP resulted in (32)P incorporation into ROMK1 detected by autoradiography. Moreover, the in vitro phosphorylation study of three synthesized peptides corresponding to amino acids 1-16, 174-189, and 196-211 of ROMK1 revealed that serine residues 4 and 201 of ROMK1 were the two main PKC phosphorylation sites. In contrast, (32)P incorporation of peptide 174-189 was absent. In vitro phosphorylation studies with ROMK1 mutants, R1S4/201A, R1S4/183A, and R1S183/201A, demonstrated that the phosphorylation levels of R1S4/201A were significantly lower than those of the other two mutants. Also, the Ba(2+)-sensitive K(+) current in oocytes injected with green fluorescent protein (GFP)-R1S4/201A was only 5% of that in oocytes injected with wild type GFP-ROMK1. In contrast, the K(+) current in oocytes injected with GFP-ROMK1 mutants containing either serine residue 4 or 201 was similar to those injected with wild type ROMK1. Confocal microscope imaging shows that the surface expression of the K(+) channels was significantly diminished in oocytes injected with R1S4/201A and completely absent in oocytes injected with R1S4/183/201A. Furthermore, the biotin labeling technique confirmed that the membrane fraction of ROMK channels was almost absent in HEK293 cells transfected with either R1S4/201A or R1S4/183/201A. However, when serine residues 4 and 201 were mutated to aspartate, the K(+) currents and the surface expression were completely restored. Finally, addition of calphostin C in the incubation medium significantly decreased the K(+) current in comparison with that under control conditions. Biotin labeling technique further indicated that inhibition of PKC decreases the surface ROMK1 expression in human embryonic kidney (HEK) cells transfected with ROMK1. We conclude that ROMK1 is a substrate of PKC and that serine residues 4 and 201 are the two main PKC phosphorylation sites that are essential for the expression of ROMK1 in the cell surface.
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Affiliation(s)
- DaoHong Lin
- Department of Pharmacology, New York Medical College, Valhalla, New York 10595
| | - Hyacinth Sterling
- Department of Pharmacology, New York Medical College, Valhalla, New York 10595
| | - Kenneth M. Lerea
- Department of Anatomy and Cell Biology, New York Medical College, Valhalla, New York 10595
| | - Gerhard Giebisch
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06511
| | - Wen-Hui Wang
- Department of Pharmacology, New York Medical College, Valhalla, New York 10595
- To whom correspondence should be addressed: Dept. of Pharmacology, New York Medical College, BSB Rm. 537, Valhalla, NY 10595. Tel.: 914-594-4120; Fax: 914-347-4956;
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Konstas AA, Koch JP, Tucker SJ, Korbmacher C. Cystic fibrosis transmembrane conductance regulator-dependent up-regulation of Kir1.1 (ROMK) renal K+ channels by the epithelial sodium channel. J Biol Chem 2002; 277:25377-84. [PMID: 11994290 DOI: 10.1074/jbc.m201925200] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The epithelial sodium channel (ENaC) and the secretory potassium channel (Kir1.1/ROMK) are expressed in the apical membrane of renal collecting duct principal cells where they provide the rate-limiting steps for Na(+) absorption and K(+) secretion. The cystic fibrosis transmembrane conductance regulator (CFTR) is thought to regulate the function of both ENaC and Kir1.1. We hypothesized that CFTR may provide a regulatory link between ENaC and Kir1.1. In Xenopus laevis oocytes co-expressing both ENaC and CFTR, the CFTR currents were 3-fold larger than those in oocytes expressing CFTR alone due to an increased expression of CFTR in the plasma membrane. ENaC was also able to increase Kir1.1 currents through an increase in surface expression, but only in the presence of CFTR. In the absence of CFTR, co-expression of ENaC was without effect on Kir1.1. ENaC-mediated CFTR-dependent up-regulation of Kir1.1 was reduced with a Liddle's syndrome mutant of ENaC. Furthermore, ENaC co-expressed with CFTR was without effect on the closely related K(+) channel, Kir4.1. We conclude that ENaC up-regulates Kir1.1 in a CFTR-dependent manner. CFTR may therefore provide the mechanistic link that mediates the coordinated up-regulation of Kir1.1 during the stimulation of ENaC by hormones such as aldosterone or antidiuretic hormone.
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Abstract
PURPOSE OF REVIEW Although the suppression of protein breakdown plays a major role in the growth of the adult kidney in conditions that cause renal hypertrophy, the pathways responsible for controlling proteolysis and the substrates being destroyed have only recently been investigated. This review focuses on the role of the ubiquitin-proteasome pathway in regulating specific substrates during kidney growth, and the role of the lysosomal pathways in the suppression of general protein breakdown and of the substrates of chaperone-mediated autophagy. RECENT FINDINGS New insights into the regulation of specific ubiquitin ligases demonstrate how the cell controls the destruction of particular substrates important for growth, including hypoxia-inducible factors and the cell cycle inhibitor, p27. In cell culture, growth factors suppress the lysosomal pathway of chaperone-mediated autophagy leading to the accumulation of specific cytoplasmic proteins containing KFERQ motifs. In a variety of systems, including cultured renal tubular cells, phosphoinositol 3 kinase activity and its downstream mediators control lysosomal proteolysis. SUMMARY Specific ubiquitin ligases and the pathways that control their substrate recognition may be key signalling intermediaries for cell growth, but global alterations in lysosomal pathways account for the decrease in general proteolysis. Functional KFERQ motifs mark proteins that are important in renal growth, including enzymes responsible for the characteristic shift to glycolytic metabolism during growth, transcription factors, and signalling molecules. As altering phosphoinositol 3 kinase changes patterns of vesicular trafficking, it is possible that the regulation of intracellular trafficking may underlie the changes seen in lysosomal proteolysis with growth.
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Affiliation(s)
- Harold A Franch
- Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia, USA; and Atlanta Veterans Affairs Medical Center, Decatur, Georgia, USA.
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31
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Franch HA, Wang X, Sooparb S, Brown NS, Du J. Phosphatidylinositol 3-kinase activity is required for epidermal growth factor to suppress proteolysis. J Am Soc Nephrol 2002; 13:903-909. [PMID: 11912249 DOI: 10.1681/asn.v134903] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Suppression of protein breakdown occurs commonly in cell growth, but the pathways responsible for controlling proteolysis are poorly understood. Protein breakdown in NRK-52E renal epithelial cells treated with epidermal growth factor (EGF) and intracellular signaling inhibitors or dominant negative signaling molecules contained in an adenoviral vector were measured. The tyrosine kinase inhibitor, herbimycin A, eliminated the suppression of proteolysis induced by EGF. In contrast, the Src inhibitor, PP1, had no effect. Expression of dominant negative H-RasY57 blocked the ability of EGF to stimulate downstream targets of Ras and also reduced the ability of EGF to suppress proteolysis. Inhibiting MEK did not influence the ability of EGF to suppress proteolysis, but the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor, LY249002, stimulated basal proteolysis and completely eliminated the proteolytic response to EGF. Use of an adenovirus that expresses a dominant negative p85 subunit of class 1 PI 3-kinase completely blocked the ability of EGF to suppress proteolysis, whereas use of an adenovirus expressing a K227E constitutively active p110 subunit reproduced the reduction in protein breakdown. It was concluded that EGF suppresses proteolysis by a mechanism that involves Ras and class 1 PI 3-kinase.
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Affiliation(s)
- Harold A Franch
- *Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia; and †Atlanta Veterans Affairs Medical Center, Decatur, Georgia
| | - Xiaonan Wang
- *Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia; and †Atlanta Veterans Affairs Medical Center, Decatur, Georgia
| | - Sira Sooparb
- *Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia; and †Atlanta Veterans Affairs Medical Center, Decatur, Georgia
| | - Nikia S Brown
- *Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia; and †Atlanta Veterans Affairs Medical Center, Decatur, Georgia
| | - Jie Du
- *Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia; and †Atlanta Veterans Affairs Medical Center, Decatur, Georgia
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Boucherot A, Schreiber R, Kunzelmann K. Role of CFTR's PDZ1-binding domain, NBF1 and Cl(-) conductance in inhibition of epithelial Na(+) channels in Xenopus oocytes. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1515:64-71. [PMID: 11597353 DOI: 10.1016/s0005-2736(01)00396-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) inhibits epithelial Na(+) channels (ENaC). Evidence has accumulated that both Cl(-) transport through CFTR Cl(-) channels and the first nucleotide binding domain (NBF1) of CFTR are crucial for inhibition of ENaC. A PDZ binding domain (PDZ-BD) at the C-terminal end links CFTR to scaffolding and cytoskeletal proteins, which have been suggested to play an important role in activation of CFTR and eventually inhibition of ENaC. We eliminated the PDZ-BD of CFTR and coexpressed Na(+)/H(+)-exchange regulator factors together with CFTR and ENaC. The results do not support a role of PDZ-BD in inhibition of ENaC by CFTR. However, inhibition of ENaC was closely linked to Cl(-) currents generated by CFTR and was observed in the presence of Cl(-), I(-) or Br(-) but not gluconate. Therefore, functional NBF1 and Cl(-) transport are required for inhibition of ENaC in Xenopus oocytes, while the PDZ-BD is not essential.
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Affiliation(s)
- A Boucherot
- School of Biomedical Sciences, Department of Physiology and Pharmacology, University of Queensland, St. Lucia, 4072, Brisbane, Qld, Australia
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33
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Franch HA, Sooparb S, Du J, Brown NS. A mechanism regulating proteolysis of specific proteins during renal tubular cell growth. J Biol Chem 2001; 276:19126-31. [PMID: 11262416 DOI: 10.1074/jbc.m101777200] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Growth factors suppress the degradation of cellular proteins in lysosomes in renal epithelial cells. Whether this process also involves specific classes of proteins that influence growth processes is unknown. We investigated chaperone-mediated autophagy, a lysosomal import pathway that depends on the 73-kDa heat shock cognate protein and allows the degradation of proteins containing a specific lysosomal import consensus sequence (KFERQ motif). Epidermal growth factor (EGF) or ammonia, but not transforming growth factor beta1, suppresses total protein breakdown in cultured NRK-52E renal epithelial cells. EGF or ammonia prolonged the half-life of glyceraldehyde-3-phosphate dehydrogenase, a classic substrate for chaperone-mediated autophagy, by more than 90%, whereas transforming growth factor beta1 did not. EGF caused a similar increase in the half-life of the KFERQ-containing paired box-related transcription factor, Pax2. The increase in half-life was accompanied by an increased accumulation of proteins with a KFERQ motif including glyceraldehyde-3-phosphate dehydrogenase and Pax2. Ammonia also increased the level of the Pax2 protein. Lysosomal import of KFERQ proteins depends on the abundance of the 96-kDa lysosomal glycoprotein protein (lgp96), and we found that EGF caused a significant decrease in lgp96 in cellular homogenates and associated with lysosomes. We conclude that EGF in cultured renal cells regulates the breakdown of proteins targeted for destruction by chaperone-mediated autophagy. Because suppression of this pathway results in an increase in Pax2, these results suggest a novel mechanism for the regulation of cell growth.
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Affiliation(s)
- H A Franch
- Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia, USA
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Malik B, Schlanger L, Al-Khalili O, Bao HF, Yue G, Price SR, Mitch WE, Eaton DC. Enac degradation in A6 cells by the ubiquitin-proteosome proteolytic pathway. J Biol Chem 2001; 276:12903-10. [PMID: 11278712 DOI: 10.1074/jbc.m010626200] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Amiloride-sensitive epithelial Na(+) channels (ENaC) are responsible for trans-epithelial Na(+) transport in the kidney, lung, and colon. The channel consists of three subunits (alpha, beta, gamma) each containing a proline rich region (PPXY) in their carboxyl-terminal end. Mutations in this PPXY domain cause Liddle's syndrome, an autosomal dominant, salt-sensitive hypertension, by preventing the channel's interactions with the ubiquitin ligase Neural precursor cell-expressed developmentally down-regulated protein (Nedd4). It is postulated that this results in defective endocytosis and lysosomal degradation of ENaC leading to an increase in ENaC activity. To show the pathway that degrades ENaC in epithelial cells that express functioning ENaC channels, we used inhibitors of the proteosome and measured sodium channel activity. We found that the inhibitor, MG-132, increases amiloride-sensitive trans-epithelial current in Xenopus distal nephron A6 cells. There also is an increase of total cellular as well as membrane-associated ENaC subunit molecules by Western blotting. MG-132-treated cells also have increased channel density in patch clamp experiments. Inhibitors of lysosomal function did not reproduce these findings. Our results suggest that in native renal cells the proteosomal pathway is an important regulator of ENaC function.
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Affiliation(s)
- B Malik
- Department of Physiology and Renal Division, Emory University, Atlanta, Georgia 30322, USA.
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Franch HA. Modification of the epidermal growth factor response by ammonia in renal cell hypertrophy. J Am Soc Nephrol 2000; 11:1631-1638. [PMID: 10966487 DOI: 10.1681/asn.v1191631] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Epidermal growth factor (EGF) causes proliferation in renal tubular cells but, when it is combined with transforming growth factor-beta1, it causes hypertrophy by a mechanism that requires the activity of the retinoblastoma family of proteins. In contrast, ammonia causes hypertrophy by decreasing lysosomal proteolysis; in some cell types, it also decreases cellular proliferation. These studies were designed to determine whether ammonia, like transforming growth factor-beta1, could convert EGF-induced hyperplasia to hypertrophy. Cultured NRK-52E cells were incubated with EGF and/or ammonia and the protein/DNA ratio was measured, as a marker of hypertrophy. Addition of ammonia to EGF-treated NRK-52E cells converted EGF-induced hyperplasia to hypertrophy, because of a decrease in DNA synthesis. The mechanism involved no change in EGF-induced protein synthesis. Inhibition of lysosomal function with a proton pump inhibitor or lysosomal protease inhibitors also converted the response of EGF-treated cells to hypertrophy. Expression of the human papilloma virus 16 E7 protein (which inactivates all members of the retinoblastoma family) prevented ammonia from converting EGF-induced hyperplasia to hypertrophy. It is concluded that ammonia converts EGF-induced hyperplasia to hypertrophy by a mechanism that involves suppression of lysosomal function and this response can be blocked by inhibiting the activity of the retinoblastoma family of proteins.
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Affiliation(s)
- Harold A Franch
- Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia, and Atlanta Veterans Affairs Medical Center, Decatur, Georgia
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Schreiber R, Pavenstädt H, Greger R, Kunzelmann K. Aquaporin 3 cloned from Xenopus laevis is regulated by the cystic fibrosis transmembrane conductance regulator. FEBS Lett 2000; 475:291-5. [PMID: 10869574 DOI: 10.1016/s0014-5793(00)01689-6] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is essential for epithelial electrolyte transport and has been shown to be a regulator of epithelial Na(+), K(+), and Cl(-) channels. CFTR also enhances osmotic water permeability when activated by cAMP. This was detected initially in Xenopus oocytes and is also present in human airway epithelial cells, however, the mechanisms remain obscure. Here, we show that CFTR activates aquaporin 3 expressed endogenously and exogenously in oocytes of Xenopus laevis. The interaction requires stimulation of wild type CFTR by cAMP and an intact first nucleotide binding domain as demonstrated for other CFTR-protein interactions.
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Affiliation(s)
- R Schreiber
- Department of Physiology and Pharmacology, University of Queensland, St. Lucia, Brisbane, Australia
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Cahill P, Nason MW, Ambrose C, Yao TY, Thomas P, Egan ME. Identification of the cystic fibrosis transmembrane conductance regulator domains that are important for interactions with ROMK2. J Biol Chem 2000; 275:16697-701. [PMID: 10748197 DOI: 10.1074/jbc.m910205199] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In addition to functioning as a cAMP-activated chloride channel, the cystic fibrosis transmembrane conductance regulator (CFTR) plays an important role in conferring regulatory properties on other ion channels. It is known, with respect to CFTR regulation of ROMK2 (renally derived K(ATP) channel), that the first transmembrane domain and the first nucleotide binding fold domain (NBF1) of CFTR are necessary for this interaction to occur. It has been shown that under conditions that promote phosphorylation, the ROMK2-CFTR interaction is attenuated. To elucidate the complex nature of this interaction, CFTR constructs were co-expressed with ROMK2 in Xenopus oocytes, and two microelectrode voltage clamp experiments were performed. Although the second half of CFTR can act as a functional chloride channel, our results suggest that it does not confer glibenclamide sensitivity on ROMK2, as does the first half of CFTR. The attenuation of the ROMK2-CFTR interaction under conditions that promote phosphorylation is dependent on at least the presence of the R domain of CFTR. We conclude that transmembrane domain 1, NBF1, and the R domain are the CFTR domains involved in the ROMK2-CFTR interaction and that NBF2 and transmembrane domain 2 are not essential. Lastly, the R domain of CFTR is necessary for the attenuation of the ROMK2-CFTR interaction under conditions that promote phosphorylation.
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Affiliation(s)
- P Cahill
- Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticutt 06520-8026, USA
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Jiang Q, Li J, Dubroff R, Ahn YJ, Foskett JK, Engelhardt J, Kleyman TR. Epithelial sodium channels regulate cystic fibrosis transmembrane conductance regulator chloride channels in Xenopus oocytes. J Biol Chem 2000; 275:13266-74. [PMID: 10788432 DOI: 10.1074/jbc.275.18.13266] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR), in addition to its well defined Cl(-) channel properties, regulates other ion channels. CFTR inhibits epithelial Na(+) channel (ENaC) currents in many epithelial and nonepithelial cells. Because modulation of net NaCl reabsorption has important implications in extracellular fluid volume homeostasis and airway fluid volume and composition, we investigated whether this regulation was reciprocal by examining whether ENaC regulates CFTR. Co-expression of human (h) CFTR and mouse (m) alphabetagammaENaC in Xenopus oocytes resulted in a significant, 3.7-fold increase in whole-cell hCFTR Cl(-) conductance compared with oocytes expressing hCFTR alone. The forskolin/3-isobutyl-1-methylxanthine-stimulated whole-cell conductance in hCFTR-mENaC co-injected oocytes was amiloride-insensitive, indicating an inhibition of mENaC following hCFTR activation, and it was blocked by DPC (diphenylamine-2-carboxylic acid) and was DIDS (4, 4'-diisothiocyanatostilbene-2,2'-disulfonic acid)-insensitive. Enhanced hCFTR Cl(-) conductance was also observed when either the alpha- or beta-subunit of mENaC was co-expressed with hCFTR, but this was not seen when CFTR was co-expressed with the gamma-subunit of mENaC. Single Cl(-) channel analyses showed that both CFTR Cl(-) channel open probability and the number of CFTR Cl(-) channels detected per patch increased when hCFTR was co-expressed with alphabetagammamENaC. We conclude that in addition to acting as a regulator of ENaC, CFTR activity is regulated by ENaC.
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Affiliation(s)
- Q Jiang
- Departments of Medicine and Physiology, University of Pennsylvania and Veterans Affairs Medical Center, Philadelphia, Pennsylvania 19104-6144, USA
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Steagall WK, Elmer HL, Brady KG, Kelley TJ. Cystic fibrosis transmembrane conductance regulator-dependent regulation of epithelial inducible nitric oxide synthase expression. Am J Respir Cell Mol Biol 2000; 22:45-50. [PMID: 10615064 DOI: 10.1165/ajrcmb.22.1.3789] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Recent evidence has shown that the inducible form of nitric oxide (NO) synthase (NOS2) has reduced expression in airway epithelia of patients with cystic fibrosis (CF) despite the presence of chronic inflammation. The goal of this paper is to determine whether NOS2 expression is regulated by the presence of functional CF transmembrane conductance regulator (CFTR). Using a human trachea epithelial cell line in which CFTR activity is blocked by the overexpression of the CFTR regulatory domain, we found that loss of CFTR activity reduces NOS2 messenger RNA expression as determined by reverse transcriptase/polymerase chain reaction and reduces overall NO production compared with mock-transfected controls. An in vivo model using mice lacking CFTR expression (cftr -/-), wild-type mice (cftr +/+), and cftr -/- mice that have had human CFTR introduced to the intestinal epithelium using the fatty acid binding protein (FABP) promoter (FABP-hcftr) was also examined. Electrical characterization confirmed that FABP-hcftr mice had corrected electrophysiologic properties compared with cftr -/- mice in the ileum, but FABP-hcftr nasal transepithelial potential difference measurements were identical to cftr -/- values showing specific intestinal correction. NOS2-specific immunostaining revealed that NOS2 expression is evident in sections of ileum and nasal epithelium of cftr +/+ mice but is absent in both tissues in cftr -/- mice. FABP-hcftr mice, however, show strong NOS2 staining in epithelial cells of the ileum but reduced staining in the nasal epithelium, suggesting a CFTR-related influence in the regulation of NOS2 expression in epithelial cells.
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Affiliation(s)
- W K Steagall
- Departments of Pediatrics and Genetics, and Center for Human Genetics, Case Western Reserve University, Cleveland, Ohio 44106-4948, USA
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Kunzelmann K. The cystic fibrosis transmembrane conductance regulator and its function in epithelial transport. Rev Physiol Biochem Pharmacol 1999; 137:1-70. [PMID: 10207304 DOI: 10.1007/3-540-65362-7_4] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
CF is a well characterized disease affecting a variety of epithelial tissues. Impaired function of the cAMP activated CFTR Cl- channel appears to be the basic defect detectable in epithelial and non-epithelial cells derived from CF patients. Apart from cAMP-dependent Cl- channels also Ca2+ and volume activated Cl- currents may be changed in the presence of CFTR mutations. This is supported by recent additional findings showing that different intracellular messengers converge on the CFTR Cl- channel. Analysis of the ion transport in CF airways and intestinal epithelium identified additional defects in Na+ transport. It became clear recently that mutations of CFTR may also affect the activity of other membrane conductances including epithelial Na+ channels, KvLQT-1 K+ channels and aquaporins (Fig. 7). Several additional, initially unexpected effects of CFTR on cellular functions, such as exocytosis, mucin secretion and regulation of the intracellular pH were reported during the past. Taken together, these results clearly indicate that CFTR not only acts as a cAMP regulated Cl- channel, but may fulfill several other cellular functions, particularly by regulating other membrane conductances. Failure in CFTR dependent regulation of these membrane conductances is likely to contribute to the defects observed in CF. Currently, no general concept is available that can explain how CFTR controls this variety of cellular functions. Further studies will have to verify whether direct protein interaction, specific effects on membrane turnover, changes of the intracellular ion concentration or additional proteins are involved in these regulatory loops. At the end of this review one cannot share the provocative and reassuring title "CFTR!" of a review written a few years ago [114]. Today one might rather finish with the statement "CFTR?".
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Affiliation(s)
- K Kunzelmann
- Physiologisches Institut, Albert-Ludwigs-Universität Freiburg, Germany
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Basile DP. The transforming growth factor beta system in kidney disease and repair: recent progress and future directions. Curr Opin Nephrol Hypertens 1999; 8:21-30. [PMID: 9914857 DOI: 10.1097/00041552-199901000-00005] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Transforming growth factor beta is a multifunctional polypeptide growth factor implicated in a variety of renal diseases. The expression of transforming growth factor beta is enhanced in renal diseases and available evidence suggests that its activity in promoting the synthesis of extracellular matrix plays a crucial role in fibrotic deposition and the decline in renal function. Transforming growth factor beta is, however, also expressed in response to renal injury and may play an important role in normal repair processes. It appears that renal diseases may result from the inappropriate regulation of transforming growth factor beta expression. The determination of the factors that mediate transforming growth factor beta activity will be of primary importance in elucidating the mechanisms leading to renal disease or repair after injury. Both in-vitro and in-vivo studies have demonstrated that proteolytic activity, thrombospondin-1, elevated glucose, angiotensin II, oxidant stress and hemodynamic forces regulate transforming growth factor beta activity through both transcriptional and post-transcriptional mechanisms. In some cases, therapies that may partly disrupt renal transforming growth factor beta activity have shown promise in slowing the progression to end-stage renal disease.
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Affiliation(s)
- D P Basile
- Department of Physiology, Medical College of Wisconsin, Milwaukee 53226, USA
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Schwiebert EM, Benos DJ, Egan ME, Stutts MJ, Guggino WB. CFTR is a conductance regulator as well as a chloride channel. Physiol Rev 1999; 79:S145-66. [PMID: 9922379 DOI: 10.1152/physrev.1999.79.1.s145] [Citation(s) in RCA: 334] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
CFTR Is a Conductance Regulator as well as a Chloride Channel. Physiol. Rev. 79, Suppl.: S145-S166, 1999. - Cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ATP-binding cassette (ABC) transporter gene family. Although CFTR has the structure of a transporter that transports substrates across the membrane in a nonconductive manner, CFTR also has the intrinsic ability to conduct Cl- at much higher rates, a function unique to CFTR among this family of ABC transporters. Because Cl- transport was shown to be lost in cystic fibrosis (CF) epithelia long before the cloning of the CF gene and CFTR, CFTR Cl- channel function was considered to be paramount. Another equally valid perspective of CFTR, however, derives from its membership in a family of transporters that transports a multitude of different substances from chemotherapeutic drugs, to amino acids, to glutathione conjugates, to small peptides in a nonconductive manner. Moreover, at least two members of this ABC transporter family (mdr-1, SUR) can regulate other ion channels in the membrane. More simply, ABC transporters can regulate somehow the function of other cellular proteins or cellular functions. This review focuses on a plethora of studies showing that CFTR also regulates other ion channel proteins. It is the hope of the authors that the reader will take with him or her the message that CFTR is a conductance regulator as well as a Cl- channel.
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Affiliation(s)
- E M Schwiebert
- Department of Physiology and Biophysics, Gregory Fleming James CF Research Center, University of Alabama at Birmingham, Birmingham, Alabama, USA
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Short DB, Trotter KW, Reczek D, Kreda SM, Bretscher A, Boucher RC, Stutts MJ, Milgram SL. An apical PDZ protein anchors the cystic fibrosis transmembrane conductance regulator to the cytoskeleton. J Biol Chem 1998; 273:19797-801. [PMID: 9677412 DOI: 10.1074/jbc.273.31.19797] [Citation(s) in RCA: 358] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The function of the cystic fibrosis transmembrane conductance regulator (CFTR) as a Cl- channel in the apical membrane of epithelial cells is extensively documented. However, less is known about the molecular determinants of CFTR residence in the apical membrane, basal regulation of its Cl- channel activity, and its reported effects on the function of other transporters. These aspects of CFTR function likely require specific interactions between CFTR and unknown proteins in the apical compartment of epithelial cells. Here we report that CFTR interacts with the recently discovered protein, EBP50 (ERM-binding phosphoprotein 50). EBP50 is concentrated at the apical membrane in human airway epithelial cells, in vivo, and CFTR and EBP50 associate in in vitro binding assays. The CFTR-EBP50 interaction requires the COOH-terminal DTRL sequence of CFTR and utilizes either PDZ1 or PDZ2 of EBP50, although binding to PDZ1 is of greater affinity. Through formation of a complex, the interaction between CFTR and EBP50 may influence the stability and/or regulation of CFTR Cl- channel function in the cell membrane and provides a potential mechanism through which CFTR can affect the activity of other apical membrane proteins.
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Affiliation(s)
- D B Short
- Department of Physiology, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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Ho K. The ROMK-cystic fibrosis transmembrane conductance regulator connection: new insights into the relationship between ROMK and cystic fibrosis transmembrane conductance regulator channels. Curr Opin Nephrol Hypertens 1998; 7:49-58. [PMID: 9442363 DOI: 10.1097/00041552-199801000-00009] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The structure of ATP-sensitive K+ (KATP) channels in excitable cells has been elucidated recently. These channels consist of a pore-forming inward rectifier K+ (Kir) channel and four sulfonylurea receptor proteins. In the distal nephron, Kir 1.1 (ROMK) channels probably contribute to the formation of epithelial (KATP) channels. Current findings suggest the possibility that these renal KATP channels consist of Kir 1.1 channel-CFTR complexes and therefore represent structural analogues of classical KATP channels.
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Affiliation(s)
- K Ho
- Washington University School of Medicine, Renal Division, St. Louis, MO 63110, USA.
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