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Akaniro-Ejim NE, Smith PA. Intracellular Ca 2+ in Mouse White Fat Adipocytes: Effects of Extracellular Anions, Growth Hormone, and Their Interaction with Ca 2+ Influx. Bioelectricity 2021. [DOI: 10.1089/bioe.2021.0020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
| | - Paul A. Smith
- School of Life Sciences, University of Nottingham, Nottingham, United Kingdom
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Bentley DC, Pulbutr P, Chan S, Smith PA. Etiology of the membrane potential of rat white fat adipocytes. Am J Physiol Endocrinol Metab 2014; 307:E161-75. [PMID: 24865982 DOI: 10.1152/ajpendo.00446.2013] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The plasma membrane potential (Vm) is key to many physiological processes; however, its ionic etiology in white fat adipocytes is poorly characterized. To address this question, we employed the perforated patch current clamp and cell-attached patch clamp methods in isolated primary white fat adipocytes and their cellular model 3T3-L1. The resting Vm of primary and 3T3-L1 adipocytes were -32.1 ± 1.2 mV (n = 95) and -28.8 ± 1.2 mV (n = 87), respectively. Vm was independent of cell size and fat content. Elevation of extracellular K(+) to 50 mM by equimolar substitution of bath Na(+) did not affect Vm, whereas substitution of bath Na(+) with the membrane-impermeant cation N-methyl-D-glucamine(+)-hyperpolarized Vm by 16 mV, data indicative of a nonselective cation permeability. Substitution of 133 mM extracellular Cl(-) with gluconate-depolarized Vm by 25 mV, whereas Cl(-) substitution with I(-) caused a -9 mV hyperpolarization. Isoprenaline (10 μM), but not insulin (100 nM), significantly depolarized Vm. Single-channel ion activity was voltage independent; currents were indicative for Cl(-) with an inward slope conductance of 16 ± 1.3 pS (n = 11) and a reversal potential close to the Cl(-) equilibrium potential, -29 ± 1.6 mV. Although the reduction of extracellular Cl(-) elevated the intracellular Ca(2+) of adipocytes, this was not as large as that produced by elevation of extracellular K(+). In conclusion, the Vm of white fat adipocytes is well described by the Goldman-Hodgkin-Katz equation with a predominant permeability to Cl(-), where its biophysical and single-channel properties suggest a volume-sensitive anion channel identity. Consequently, changes in serum Cl(-) homeostasis or the adipocyte's permeability to this anion via drugs will affect its Vm, intracellular Ca(2+), and ultimately its function and its role in metabolic control.
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Affiliation(s)
- Donna C Bentley
- School of Life Sciences, University of Nottingham, Nottingham, United Kingdom
| | - Pawitra Pulbutr
- School of Life Sciences, University of Nottingham, Nottingham, United Kingdom
| | - Sue Chan
- School of Life Sciences, University of Nottingham, Nottingham, United Kingdom
| | - Paul A Smith
- School of Life Sciences, University of Nottingham, Nottingham, United Kingdom
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Bakillah A, Guillot R, Urios P, Grigorova-Borsos AM, Sternberg M. Stimulating effect of growth hormone on type IV collagen production by endothelial cells cultured in normal and high glucose. Amino Acids 2011; 43:697-707. [PMID: 22002796 DOI: 10.1007/s00726-011-1118-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2011] [Accepted: 10/01/2011] [Indexed: 10/17/2022]
Abstract
Collagen IV accumulation is characteristic of diabetic angiopathy. To test the possible contribution of GH, we studied its effects on collagen IV production by human umbilical vein endothelial cells at 5.5 and 16.7 mmol/l glucose. GH (100 ng/ml) markedly increased collagen IV level in the culture supernatant and in the insoluble extracellular matrix and cell fraction at both glucose concentrations. This stimulating effect of GH was additional to that of high glucose. It was more pronounced on collagen IV than on total protein synthesis. GH increased free latent gelatinase activity slightly at normal and markedly at high glucose. Using GF109203X, a PKC inhibitor, we observed that high glucose, but not GH, activated PKC. These two factors stimulating collagen IV production appear to work through different pathways, favoring an additivity of their effects. This supports the contribution of high plasma GH in diabetic vascular basement membrane thickening.
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Affiliation(s)
- A Bakillah
- Equipe de Recherches sur la Biochimie et la Pharmacologie des Vaisseaux et du Rein, Protéines Modifiées, Protéases et Physiopathologie de l'Endothélium Vasculaire, Laboratoire de Pharmacologie, Faculté de Pharmacie, 4 avenue de l'Observatoire, 75006 Paris, France
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Smit LS, Meyer DJ, Argetsinger LS, Schwartz J, Carter‐Su C. Molecular Events in Growth Hormone–Receptor Interaction and Signaling. Compr Physiol 2011. [DOI: 10.1002/cphy.cp070514] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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Gevers EF, Hannah MJ, Waters MJ, Robinson ICAF. Regulation of rapid signal transducer and activator of transcription-5 phosphorylation in the resting cells of the growth plate and in the liver by growth hormone and feeding. Endocrinology 2009; 150:3627-36. [PMID: 19359380 DOI: 10.1210/en.2008-0985] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
GH has physiological functions in many tissues, but the cellular targets for direct effects of GH remain ill defined in complex tissues such as the growth plate in which the contribution of direct vs. indirect actions of GH remains controversial. The Janus kinase (Jak)-signal transducer and activator of transcription (STAT)-5 pathway is activated by GH, so we developed a method to visualize nuclear Stat5b and phosphorylated Stat5 in single cells in response to a pulse of GH. Hep2 cells did not show a Stat5 phosphorylation (pY-Stat5) response to GH except in cells transfected to express GH receptors. ATDC5 cells express GH receptors and showed GH-induced pY-Stat5 responses, which varied with their state of chondrocyte differentiation. In vivo, Stat5b(+ve) nuclei were seen in the resting and prehypertrophic chondrocytes of the growth plate. After a single ip pulse of human GH or mouse GH, but not prolactin, pY-Stat5 responses were visible in cells in the resting zone and groove of Ranvier, 10-45 min later. Prehypertrophic chondrocytes showed no pY-Stat5 response to GH. GH target cells were also identified in other tissues, and a marked variability in spatiotemporal pY-Stat5 responses was evident. Endogenous hepatic pY-Stat5 was detected in mice with intact GH secretion but only during a GH pulse. Fasting and chronic exposure to GH attenuated the pY-Stat5 response to an acute GH injection. In conclusion, pY-Stat5 responses to GH vary in time and space, are sensitive to nutritional status, and may be inhibited by prior GH exposure. In the growth plate, our data provide direct in vivo support for an early role of GH to regulate the fate of immature chondrocytes.
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Affiliation(s)
- Evelien F Gevers
- Division of Molecular Neuroendocrinology, Medical Research Council National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom.
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6
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Cammisotto PG, Bukowiecki LJ. Role of calcium in the secretion of leptin from white adipocytes. Am J Physiol Regul Integr Comp Physiol 2004; 287:R1380-6. [PMID: 15331383 DOI: 10.1152/ajpregu.00368.2004] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The mechanism by which calcium regulates leptin secretion was studied in adipocytes isolated from rat white adipose tissue. Incubation of adipocytes in a medium containing glucose, but no calcium, markedly inhibited insulin-stimulated leptin secretion (ISLS) and synthesis, without affecting basal leptin secretion or lipolysis. However, when pyruvate was used as a substrate, ISLS was insensitive to the absence of calcium. Likewise, the stimulatory effects of insulin were completely prevented by phloretin, cytochalasin B, and W-13 (3 agents that interfere with early steps of glucose metabolism) in the presence of glucose, but not in the presence of pyruvate. Thus calcium appears to be specifically required for glucose utilization. On the other hand,45Ca uptake and leptin secretion were not affected by insulin or by inhibitors of L-type calcium channels. However, agents increasing plasma membrane permeability to calcium (high calcium concentrations, A-23187, and ATP) increased45Ca uptake and concomitantly inhibited ISLS. Similarly, release of endogenous calcium stores by thapsigargin inhibited ISLS in a dose-dependent manner. ATP, A-23187, calcium, and thapsigargin inhibited ISLS, even in the presence of pyruvate. These results show that 1) extracellular calcium is necessary for ISLS, mainly by affecting glucose uptake, 2) insulin does not affect extracellular calcium uptake, and 3) increasing cytosolic calcium by stimulating its uptake or its release from endogenous stores inhibits ISLS at a level independent of glucose metabolism. Thus calcium regulates leptin secretion from adipocytes in a manner that is markedly different from its role in the exocytosis of many other polypeptidic hormones.
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Affiliation(s)
- Philippe G Cammisotto
- Faculty of Medicine, Department of Anatomy and Physiology, Laval University, Quebec, Canada G1K 7P4
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Marrero I, Déniz A. The phospholipase C-InsP3 pathway is involved in calcium mobilization induced by growth hormone in hepatocytes. Growth Horm IGF Res 2004; 14:85-90. [PMID: 15123167 DOI: 10.1016/j.ghir.2003.11.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/26/2003] [Revised: 11/03/2003] [Accepted: 11/03/2003] [Indexed: 10/26/2022]
Abstract
We investigated the effects of bovine GH (bGH) on Ca(2+) handling, phospholipase C (PLC) activation and inositol 1,4,5-trisphosphate [Ins(1,4,5)P(3)] formation in hepatocytes. bGH generates oscillations in cytosolic free Ca(2+) concentration ([Ca(2+)](i)) in single male rat hepatocytes microinjected with the photoprotein aequorin. In the absence of extracellular Ca(2+) these transients persisted for more than 10 min indicating a requirement for intracellular Ca(2+). Treatment of the hepatocyte with the phosphatidylinositol-specific phospholipase C (PI-PLC) inhibitor U-73122 removed the oscillations. These results suggest bGH-induced oscillations are due to PLC activation and generation of Ins(1,4,5)P(3). We measured the mass of Ins(1,4,5)P(3) in freshly isolated hepatocyte suspensions in response to bGH, and vasopressin as a control. Both agonists rapidly increased the levels of Ins(1,4,5)P(3). This is the first study to indicate that early events in the signal transduction pathways mediated by GH in hepatocytes involve intracellular Ca(2+) mobilization via activation of a PI-PLC and subsequent Ins(1,4,5)P(3) production.
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Affiliation(s)
- I Marrero
- Departamento de Fisiología, Centro de Ciencias de la Salud, Universidad de Las Palmas de Gran Canaria, Apartado 550, Las Palmas de Gran Canaria, 35080 Islas Canarias, Spain.
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Strous GJ, dos Santos CA, Gent J, Govers R, Sachse M, Schantl J, van Kerkhof P. Ubiquitin system-dependent regulation of growth hormone receptor signal transduction. Curr Top Microbiol Immunol 2004; 286:81-118. [PMID: 15645711 DOI: 10.1007/978-3-540-69494-6_4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The growth hormone (GH) receptor is a key regulator of cellular metabolism. Unlike most growth factor receptors, its downregulation is not initiated by its ligand. Like many growth factor receptors, specific molecular mechanisms guarantee that a receptor can signal only once in its lifetime. Three features render the GH receptor unique: (a) an active ubiquitination system is required for both uptake (endocytosis) and degradation in the lysosomes; (b) uptake of the receptor is a continuous process, independent of both GH binding and Jak2 signal transduction; (c) only the cell surface expression of dimerised GH receptors is controlled by the ubiquitin system. This system enables two independent regulatory mechanisms for the endocrinology of the GH/GHR axis: the pulsatile secretion of GH by the pituitary and the GH sensitivity of individual cells of the body by the effects of the ubiquitin system on GH receptor availability.
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Affiliation(s)
- G J Strous
- Department of Cell Biology, University Medical Center Utrecht, 3584 CX Utrecht, The Netherlands.
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Ling L, Zhu T, Lobie PE. Src-CrkII-C3G-dependent activation of Rap1 switches growth hormone-stimulated p44/42 MAP kinase and JNK/SAPK activities. J Biol Chem 2003; 278:27301-11. [PMID: 12734187 DOI: 10.1074/jbc.m302516200] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We demonstrate here that growth hormone (GH) stimulates the activation of Rap1 and Rap2 in NIH-3T3 cells. Full activation of Rap1 and Rap2 by GH necessitated the combined activity of both JAK2 and c-Src kinases, although c-Src was predominantly required. GH-stimulated Rap1 and Rap2 activity was also demonstrated to be CrkII-C3G-dependent. GH stimulated the tyrosine phosphorylation of C3G, which again required the combined activity of JAK2 and c-Src. C3G tyrosine residue 504 was required for GH-stimulated Rap activation. Activated Rap1 inhibited GH-stimulated activation of RalA and subsequent GH-stimulated p44/42 MAP kinase activity and Elk-1-mediated transcription. In addition, we demonstrated that C3G-Rap1 mediated CrkII enhancement of GH-stimulated JNK/SAPK activity. We have therefore identified a linear JAK2-independent pathway switching GH-stimulated p44/42 MAP kinase and JNK/SAPK activities.
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Affiliation(s)
- Ling Ling
- Institute of Molecular and Cell Biology, 30 Medical Drive, Singapore 117609
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Zhu T, Ling L, Lobie PE. Identification of a JAK2-independent pathway regulating growth hormone (GH)-stimulated p44/42 mitogen-activated protein kinase activity. GH activation of Ral and phospholipase D is Src-dependent. J Biol Chem 2002; 277:45592-603. [PMID: 12218045 DOI: 10.1074/jbc.m201385200] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have demonstrated here that growth hormone (GH) stimulates the formation of the active GTP-bound form of both RalA and RalB in NIH-3T3 cells. Full activation of RalA and RalB by GH required the combined activity of c-Src and JAK2, both kinases activated by GH independent of the other. Activation of RalA and RalB by growth hormone did not require the activity of JAK2 per se. Ras was also activated by GH and was required for the GH-stimulated formation of GTP-bound RalA and RalB. Activation of RalA by GH subsequently resulted in increased phospholipase D activity and the formation of its metabolite, phosphatidic acid. GH-stimulated RalA-phospholipase D-dependent formation of phosphatidic acid was required for activation of p44/42 MAPK and subsequent Elk-1-mediated transcription stimulated by GH. Thus we report the identification of a JAK2-independent pathway regulating GH-stimulated p44/42 MAPK activity.
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Affiliation(s)
- Tao Zhu
- Institute of Molecular and Cell Biology, Singapore, Republic of Singapore
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Abstract
Multiple signaling pathways mediate the diverse effects of growth hormone (GH) on growth and metabolism. The interaction of GH with GH receptors (GHR) on target cells promotes the association of the cellular tyrosine kinase JAK2 with the GHR, initiating tyrosine phosphorylation of GHR and JAK2, and activation of multiple signaling cascades. GH-stimulated activation of signal transducers and activators of transcription (STATs), mitogen activated protein kinase (MAPK) and phosphatidylinositol 3' kinase (PI3K) cascades have been shown to regulate the transcription of GH-responsive genes. Cross-talk among these signaling cascades in regulating specific genes suggests that GH signaling to the nucleus involves a GH-regulated signaling network.
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Abstract
Rapid progress has been made recently in the definition of growth hormone (GH) receptor signal transduction pathways. It is now apparent that many cytokines, including GH, share identical or similar signalling components to exert their cellular effects. This review provides a brief discourse on the signal transduction pathways, which have been demonstrated to be utilized by GH. The identification of such pathways provides a basis for understanding the pleiotropic actions of GH. The mechanisms by which the specific cellular effects of GH are achieved remain to be elucidated.
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Affiliation(s)
- T Zhu
- Institute of Molecular and Cell Biology, 30 Medical Drive, Singapore 117609, Singapore
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Abstract
Growth hormone (GH) is not only the major regulator of postnatal somatic growth but also exerts profound effects on body composition through a combination of anabolic, lipolytic and antinatriuretic actions. GH enhancement of the lipolytic activity of adipose tissue in combination with a reduction of triglyceride accumulation via inhibition of lipoprotein lipase activity appears to be the major mechanism by which GH results in a reduction of the total fat mass. Recently, much progress has been made in understanding the molecular mechanism by which GH affects cellular function. This review provides a brief discourse and summary of the mechanism of effects of GH on preadipocyte/adipocyte function. It is intended to provide a functional understanding of the mechanism of action of GH as it relates to adipogenesis and adipocyte function.
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Affiliation(s)
- S Y Nam
- Department of Internal Medicine, Yongdong Severance Hospital, Yonsei University College of Medicine, Dogok-dong 146-92, Kangnam-Ku, Seoul 135-270, Korea
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Sjöholm A, Zhang Q, Welsh N, Hansson A, Larsson O, Tally M, Berggren PO. Rapid Ca2+ influx and diacylglycerol synthesis in growth hormone-mediated islet beta -cell mitogenesis. J Biol Chem 2000; 275:21033-40. [PMID: 10748000 DOI: 10.1074/jbc.m001212200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Growth hormone (GH) is an important mitogenic stimulus for the insulin-producing beta-cell. We investigated the effects of GH on Ca(2+) handling and diacylglycerol (DAG) and cAMP formation in the beta-cell. GH elicited a rapid increase in the cytoplasmic free [Ca(2+)], which required extracellular Ca(2+) and was also blocked by pertussis toxin or protein kinase C (PKC) inhibition. GH also elevated islet DAG content, which should lead to PKC activation. Pertussis toxin and PKC inhibitors obliterated the mitogenicity of GH, suggesting involvement of GTP-binding proteins. PKC activation stimulated beta-cell proliferation, and it also activated phospholipase D. Islet cAMP content was not elevated by GH. Addition of a specific protein kinase A antagonist failed to influence the mitogenicity of GH, whereas a stimulatory cAMP agonist stimulated beta-cell replication. We conclude that GH rapidly increases the beta-cell cytoplasmic free [Ca(2+)] and also evokes a similar increase in DAG content via a phosphatidylcholine-specific phospholipase C, but does not affect mitogen-activated protein kinases, phospholipase D, or the cAMP signaling pathway. This rise in DAG may be of importance in translation of the stimulatory signal of GH into a proliferative response by the beta-cell, which seems to occur through GTP-binding proteins and PKC-dependent mechanisms.
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Affiliation(s)
- A Sjöholm
- Department of Molecular Medicine, Endocrine and Diabetes Unit, Rolf Luft Center for Diabetes Research, Karolinska Institutet, Karolinska Hospital, S-171 76 Stockholm, Sweden.
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Nofer JR, Junker R, Seedorf U, Assmann G, Zidek W, Tepel M. D609-phosphatidylcholine-specific phospholipase C inhibitor attenuates thapsigargin-induced sodium influx in human lymphocytes. Cell Signal 2000; 12:289-96. [PMID: 10822169 DOI: 10.1016/s0898-6568(00)00068-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Previously, we reported that the phosphatidylcholine-specific phospholipase C (PC-PLC) inhibitor tricyclodecan-9-yl xanthogenate (D609) potentiates thapsigargin-induced Ca(2+) influx in human lymphocytes. In the present study we examined the effect of D609 on the thapsigargin-induced Na(+) entry. We found that the early phase of the thapsigargin-induced increase in the intracellular Na(+) concentration (approx. 1-2 min after stimulation) was attenuated after preincubation of lymphocytes with D609. By contrast, thapsigargin-induced Na(+) influx was not affected in the presence butan-1-ol, which inhibits phosphatidylcholine-specific phospholipase D (PC-PLD). The thapsigargin-induced Na(+) influx could be mimicked by PC-PLC exogenously added to the lymphocyte suspension, whereas addition of PC-PLD had no effect. In addition, thapsigargin stimulated formation of the physiological PC-PLC products, diacylglycerol. Cell-permeable diacylglycerol analogue, dioctanoyl-glycerol (DOG), produced time- and concentration-dependent increase in the intracellular Na(+) concentration. Both thapsigargin- and DOG-induced Na(+) increases were not affected in the presence of Na(+)/H(+) antiport inhibitor, HOE609, or Na(+)/Ca(2+) antiport inhibitor, dimethylthiourea, as well as in the presence of Co(2+) and Ni(2+), which block store-operated Ca(2+) entry. By contrast, markedly reduced thapsigargin- and DOG-induced Na(+) influx were noted in the presence of flufenamic acid, which blocks the non-selective cation current (I(CRANC)). In conclusion, our results suggest that diacylglycerol released due to the PC-PLC activation contributes to the thapsigargin-induced Na(+) entry.
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Affiliation(s)
- J R Nofer
- Institut für Klinische Chemie und Laboratoriumsmedizin, Zentrallaboratorium, Westfälische Wilhelms-Universität, A. Schweitzer Str 33, 48-149, Münster, Germany.
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Mörk AC, Sun X, Liu X, Rodriguez D, Martinez JR, Castro R, Zhang GH. Regulation of (1-3)-beta-glucan-stimulated Ca(2+) influx by protein kinase C in NR8383 alveolar macrophages. J Cell Biochem 2000; 78:131-40. [PMID: 10797572 DOI: 10.1002/(sici)1097-4644(20000701)78:1<131::aid-jcb12>3.0.co;2-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Stimulation of (1-3)-beta-glucan receptors results in Ca(2+) influx through receptor-operated channels in alveolar macrophages (AMs), but the mechanism(s) regulating Ca(2+) influx is still undefined. In this study we investigated the role of protein kinase C (PKC) regulation of Ca(2+) influx in the NR8383 AM cell line using the particulate (1-3)-beta-glucan receptor agonist zymosan. PKC inhibition with calphostin C (CC) or bisindolymaleimide I (BSM) significantly reduced zymosan-induced Ca(2+) influx, whereas activation of PKC with phorbol-12-myristate 13-acetate (PMA) or 1, 2-dioctanoyl-sn-glycerol (DOG) mimicked zymosan, inducing a concentration-dependent Ca(2+) influx. This influx was dependent on extracellular Ca(2+) and inhibited by the receptor-operated Ca(2+) channel blocker SK&F96365, indicating that zymosan and PKC activate Ca(2+) influx through a similar pathway. NR8383 AMs expressed one new PKC isoform (delta) and two atypical PKC isoforms (iota and lambda), but conventional PKC isoforms were not present. Stimulation with zymosan resulted in a translocation of PKC-delta from the cytosol to the membrane fraction. Furthermore, inhibition of protein tyrosine kinases (PTKs) with genistein prevented zymosan-stimulated Ca(2+) influx and PKC-delta translocation. These results suggest that PKC-delta plays a critical role in regulating (1-3)-beta-glucan receptor activated Ca(2+) influx in NR8383 AMs and PKC-delta translocation is possibly dependent on PTK activity.
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Affiliation(s)
- A C Mörk
- Department of Pediatrics, University of Texas Health Science Center, San Antonio, Texas 78284, USA
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Abstract
A growth-promoting principle of the pituitary gland was discovered in 1921, and bovine growth hormone (GH) was isolated in 1944. Since then, the structure of GH as it relates to its biological activities has been an exciting research topic. Equally fascinating is the relationship between GH structure and its metabolic activities. In attempts to define some of these activities, several investigators have used GH transgenic mice as models. In this review we summarize what is known about the molecular mechanisms of GH action. We then describe some of the GH transgenic models and point out potential targets for nutrition research.
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Affiliation(s)
- J J Kopchick
- Edison Biotechnology Institute, Konneker Research Laboratories, College of Osteopathic Medicine, Ohio University, Athens 45701, USA.
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Sugita K, Mörk AC, Zhang GH, Martinez JR. Modulation of Ca2+ mobilization by protein kinase C in the submandibular duct cell line A253. Mol Cell Biochem 1999; 198:39-46. [PMID: 10497876 DOI: 10.1023/a:1006925408055] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The expression of protein kinase C (PKC) isoforms and the modulation of Ca2+ mobilization by PKC were investigated in the human submandibular duct cell line A253. Three new PKC (nPKC) isoforms (delta, epsilon, and theta) and one atypical PKC (aPKC) isoform (lambda) are expressed in this cell line. No classical PKC (cPKC) isoforms were present. The effects of the PKC activator phorbol 12-myristate-13-acetate (PMA) and of the PKC inhibitors calphostin C (CC) and bisindolymaleimide I (BSM) on inositol 1,4,5-trisphosphate (IP3) and Ca2+ responses to ATP and to thapsigargin (TG) were investigated. Pre-exposure to PMA inhibited IP3 formation, Ca2+ release and Ca2+ influx in response to ATP. Pre-exposure to CC or BSM slightly enhanced IP3 formation but inhibited the Ca2+ release and the Ca2+ influx induced by ATP. In contrast, pre-exposure to PMA did not modify the Ca2+ release induced by TG, but reduced the influx of Ca2+ seen in the presence of this Ca2+-ATPase inhibitor. These results suggest that PKC modulates elements of the IP3/Ca2+ signal transduction pathway in A253 cells by (1) inhibiting phosphatidylinositol turnover and altering the sensitivity of the Ca2+ channels to IP3, (2) altering the activity, the sensitivity to inhibitors, or the distribution of the TG-sensitive Ca2+ ATPase, and (3) modulating Ca2+ entry pathways.
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Affiliation(s)
- K Sugita
- Department of Pediatrics, University of Texas Health Science Center, San Antonio 78284-7827, USA
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Gaur S, Schwartz Y, Tai LR, Frick GP, Goodman HM. Insulin produces a growth hormone-like increase in intracellular free calcium concentration in okadaic acid-treated adipocytes. Endocrinology 1998; 139:4953-61. [PMID: 9832433 DOI: 10.1210/endo.139.12.6387] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
In vivo, GH and insulin usually produce opposing effects on carbohydrate and lipid metabolism in adipocytes, even though their signal transduction pathways overlap. However, when added to rat adipocytes that have been made GH deficient, GH briefly produces responses that are qualitatively like those of insulin. Subsequently, GH induces refractoriness to this acute insulin-like response, in a sense restricting its effects to a unique subset of possible physiological actions. Okadaic acid is an inhibitor of type I and IIa phosphoprotein phosphatases and affects glucose metabolism in fat cells in a manner that is reminiscent of GH. Okadaic acid initially mimics the actions of insulin, and subsequently, even after it has been removed by thorough washing, blunts the ability of adipocytes to accelerate glucose metabolism in response to insulin or GH. Because refractoriness to the insulin-like effect of GH is associated with GH-induced increases in intracellular free calcium concentrations ([Ca2+]i), we examined the effects of insulin on [Ca2+]i in okadaic acid-treated adipocytes. Adipocytes were incubated with 0.25 microM okadaic acid for 1 h, washed, and reincubated without okadaic acid for 2 h before measurement of [Ca2+]i using fura-2 as a calcium indicator. Neither GH (500 ng/ml) nor insulin (100 microU/ml) affected [Ca2+]i in cells in which glucose metabolism was stimulated, but both hormones rapidly increased [Ca2+]i in adipocytes that were refractory to insulin-like stimulation. The characteristics of the increase in [Ca2+]i produced by insulin were identical to those previously reported for GH. The effect of insulin was mimicked by the dihydropyridine calcium channel activator BayK 5552 or depolarization of the cell membrane with 30 mM KCl and was blocked by the dihydropyridine calcium channel blocker, nimodipine (100 nM), implicating activation of voltage-sensitive L-type Ca2+ channels. The increase in [Ca2+]i was also mimicked by sn-1,2-dioctanoylglycerol and blocked by inhibitors of protein kinase C (staurosporine, chelerythrine chloride, and calphostin), and D609, an inhibitor of phospholipase C, as reported for GH. Acquisition of the ability to increase [Ca2+]i in response to insulin required a lag period of at least 2 h after removal of okadaic acid and was prevented by inhibitors of RNA and protein synthesis. Adipocytes that were incubated with inhibitors of protein kinase A (KT-5720), or protein kinase C (staurosporine) along with okadaic acid also failed to increase [Ca2+]i in response to insulin. Conversely, adipocytes that were incubated with dibutyryl cAMP, methylisobutyl xanthine, or phorbol ester instead of okadaic acid increased [Ca2+]i when treated with insulin 2 h later. These results suggest that phosphorylated substrates of protein kinases A and C may mediate the transcriptional event(s) that enable adipocytes to activate L-type Ca2+ channels in response to insulin. Blockade of protein kinases A or C or removal of calcium from the incubation medium did not restore the ability of okadaic acid-treated adipocytes to increase glucose metabolism in response to insulin, nor did pretreatment of adipocytes with dibutyryl cAMP or phorbol ester decrease insulin-induced stimulation of glucose metabolism. The failure of insulin to increase glucose metabolism in okadaic acid-treated adipocytes thus cannot be ascribed to the increase in [Ca2+]i. These findings indicate that just as GH can produce an insulin-like response, so too can insulin produce a GH-like response, and highlight the need to understand how specificity of hormone action is achieved in cells that respond to different hormones that share elements of their transduction pathways.
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Affiliation(s)
- S Gaur
- Department of Physiology, University of Massachusetts Medical School, Worcester 01655, USA
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Gaur S, Morton ME, Frick GP, Goodman HM. Growth hormone regulates the distribution of L-type calcium channels in rat adipocyte membranes. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:C505-14. [PMID: 9688605 DOI: 10.1152/ajpcell.1998.275.2.c505] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Earlier studies demonstrated that deprivation of growth hormone (GH) for >/=3 h decreased basal and maximally stimulated cytosolic Ca2+ in rat adipocytes and suggested that membrane Ca2+ channels might be decreased. Measurement of L-type Ca2+ channels in purified plasma membranes by immunoassay or dihydropyridine binding indicated a two- to fourfold decrease after 3 h of incubation without GH. No such decrease was seen in unfractionated adipocyte membrane preparations. The decrease in plasma membrane channel content was largely accounted for by redistribution of channels to a light microsomal membrane fraction. Immunoassay of alpha1-, alpha2/delta-, and beta-channel subunits in membrane fractions indicated that the channels redistributed as intact complexes. Addition of GH during the 1st h of incubation prevented channel redistribution, and addition of GH after 3 h restored channel distribution to the GH-replete state of freshly isolated adipocytes. The studies suggest that GH may regulate the abundance of Ca2+ channels in the adipocyte plasma membrane and thereby modulate sensitivity to signals, the expression of which is Ca2+ dependent.
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Affiliation(s)
- S Gaur
- Department of Physiology, University of Massachusetts Medical School, Worcester, MA 01655, USA
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