1
|
Brandt AM, Kania JM, Gonzalez ML, Johnson SE. Hepatocyte growth factor acts as a mitogen for equine satellite cells via protein kinase C δ-directed signaling. J Anim Sci 2018; 96:3645-3656. [PMID: 29917108 PMCID: PMC6127786 DOI: 10.1093/jas/sky234] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Accepted: 06/13/2018] [Indexed: 12/26/2022] Open
Abstract
Hepatocyte growth factor (HGF) signals mediate mouse skeletal muscle stem cell, or satellite cell (SC), reentry into the cell cycle and myoblast proliferation. Because the athletic horse experiences exercise-induced muscle damage, the objective of the experiment was to determine the effect of HGF on equine SC (eqSC) bioactivity. Fresh isolates of adult eqSC were incubated with increasing concentrations of HGF and the initial time to DNA synthesis was measured. Media supplementation with HGF did not shorten (P > 0.05) the duration of G0/G1 transition suggesting the growth factor does not affect activation. Treatment with 25 ng/mL HGF increased (P < 0.05) eqSC proliferation that was coincident with phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and AKT serine/threonine kinase 1 (AKT1). Chemical inhibition of the upstream effectors of ERK1/2 or AKT1 elicited no effect (P > 0.05) on HGF-mediated 5-ethynyl-2'-deoxyuridine (EdU) incorporation. By contrast, treatment of eqSC with 2 µm Gö6983, a pan-protein kinase C (PKC) inhibitor, blocked (P < 0.05) HGF-initiated mitotic activity. Gene-expression analysis revealed that eqSC express PKCα, PKCδ, and PKCε isoforms. Knockdown of PKCδ with a small interfering RNA (siRNA) prevented (P > 0.05) HGF-mediated EdU incorporation. The siPKCδ was specific to the kinase and did not affect (P > 0.05) expression of either PKCα or PKCε. Treatment of confluent eqSC with 25 ng/mL HGF suppressed (P < 0.05) nuclear myogenin expression during the early stages of differentiation. These results demonstrate that HGF may not affect activation but can act as a mitogen and modest suppressor of differentiation.
Collapse
Affiliation(s)
- Amanda M Brandt
- Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg VA
| | - Joanna M Kania
- Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg VA
| | - Madison L Gonzalez
- Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg VA
| | - Sally E Johnson
- Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg VA
| |
Collapse
|
2
|
FAK phosphorylation plays a central role in thrombin-induced RPE cell migration. Cell Signal 2017; 36:56-66. [DOI: 10.1016/j.cellsig.2017.04.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Revised: 04/21/2017] [Accepted: 04/22/2017] [Indexed: 02/06/2023]
|
3
|
Pinzon-Guzman C, Xing T, Zhang SSM, Barnstable CJ. Regulation of rod photoreceptor differentiation by STAT3 is controlled by a tyrosine phosphatase. J Mol Neurosci 2014; 55:152-159. [PMID: 25108518 DOI: 10.1007/s12031-014-0397-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2014] [Accepted: 07/30/2014] [Indexed: 11/25/2022]
Abstract
Signal pathways that reduce the levels of tyrosine-phosphorylated STAT3 (pSTAT3) allow late retinal progenitors to exit the cell cycle and enter a terminal differentiation pathway into rod photoreceptors. In the mouse retina, we previously identified PKC-β1 and PKC-γ isoforms as essential components of a key signal pathway and IGF-1 as a major extrinsic factor regulating rod formation. In this manuscript, we demonstrate that PKC decreases phosphotyrosine but not phosphoserine on STAT3 in neonatal mouse retinas. Neither IGF-1 nor PMA induced a significant change in the levels of STAT3 or in the levels of the key proteins regulating STAT3 degradation, SOCS3, and PIAS3. Treatment of neonatal mouse retinal explants with sodium orthovanadate inhibited the PKC-mediated reduction in pSTAT3, indicating a role for a phosphatase. Addition of the PTEN inhibitor bpV(phen) to explant cultures treated with IGF-1 or PMA had no effect on the reduction in pSTAT3 levels, but the effect of both IGF-1 and PMA was blocked by a concentration of the inhibitor NSC87877 that is selective for the phosphatases Shp1 and Shp2. Inhibition of Shp1/2 phosphatases was also sufficient to abolish the IGF1-mediated induction of rod photoreceptor differentiation in the retina explant cultures. We conclude that one or both of these phosphatases are key components regulating the formation of rod photoreceptors in mouse retina.
Collapse
Affiliation(s)
- Carolina Pinzon-Guzman
- Department of Neural and Behavioral Sciences, Pennsylvania State University College of Medicine, Hershey, PA, 17033-2255, USA
| | - Tiaosi Xing
- Department of Neural and Behavioral Sciences, Pennsylvania State University College of Medicine, Hershey, PA, 17033-2255, USA
| | - Samuel Shao-Min Zhang
- Department of Neural and Behavioral Sciences, Pennsylvania State University College of Medicine, Hershey, PA, 17033-2255, USA
| | - Colin J Barnstable
- Department of Neural and Behavioral Sciences, Pennsylvania State University College of Medicine, Hershey, PA, 17033-2255, USA.
| |
Collapse
|
4
|
Fogh BS, Multhaupt HAB, Couchman JR. Protein kinase C, focal adhesions and the regulation of cell migration. J Histochem Cytochem 2014; 62:172-84. [PMID: 24309511 PMCID: PMC3935447 DOI: 10.1369/0022155413517701] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2013] [Accepted: 11/21/2013] [Indexed: 12/18/2022] Open
Abstract
Cell adhesion to extracellular matrix is a complex process involving protrusive activity driven by the actin cytoskeleton, engagement of specific receptors, followed by signaling and cytoskeletal organization. Thereafter, contractile and endocytic/recycling activities may facilitate migration and adhesion turnover. Focal adhesions, or focal contacts, are widespread organelles at the cell-matrix interface. They arise as a result of receptor interactions with matrix ligands, together with clustering. Recent analysis shows that focal adhesions contain a very large number of protein components in their intracellular compartment. Among these are tyrosine kinases, which have received a great deal of attention, whereas the serine/threonine kinase protein kinase C has received much less. Here the status of protein kinase C in focal adhesions and cell migration is reviewed, together with discussion of its roles and potential substrates.
Collapse
Affiliation(s)
- Betina S Fogh
- Department of Biomedical Sciences, University of Copenhagen, Denmark
| | | | | |
Collapse
|
5
|
Kupcova Skalnikova H, Navarro R, Marsala S, Hrabakova R, Vodicka P, Gadher SJ, Kovarova H, Marsala M. Signaling proteins in spinal parenchyma and dorsal root ganglion in rat with spinal injury-induced spasticity. J Proteomics 2013; 91:41-57. [DOI: 10.1016/j.jprot.2013.06.028] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2013] [Revised: 05/31/2013] [Accepted: 06/28/2013] [Indexed: 12/12/2022]
|
6
|
Zeng L, Webster SV, Newton PM. The biology of protein kinase C. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 740:639-61. [PMID: 22453963 DOI: 10.1007/978-94-007-2888-2_28] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
This review gives a basic introduction to the biology of protein kinase C, one of the first calcium-dependent kinases to be discovered. We review the structure and function of protein kinase C, along with some of the substrates of individual isoforms. We then review strategies for inhibiting PKC in experimental systems and finally discuss the therapeutic potential of targeting PKC. Each aspect is covered in summary, with links to detailed resources where appropriate.
Collapse
Affiliation(s)
- Lily Zeng
- School of Medicine, University of California, San Francisco, CA, USA
| | | | | |
Collapse
|
7
|
Labbé DP, Hardy S, Tremblay ML. Protein tyrosine phosphatases in cancer: friends and foes! PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2012; 106:253-306. [PMID: 22340721 DOI: 10.1016/b978-0-12-396456-4.00009-2] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Tyrosine phosphorylation of proteins serves as an exquisite switch in controlling several key oncogenic signaling pathways involved in cell proliferation, apoptosis, migration, and invasion. Since protein tyrosine phosphatases (PTPs) counteract protein kinases by removing phosphate moieties on target proteins, one may intuitively think that PTPs would act as tumor suppressors. Indeed, one of the most described PTPs, namely, the phosphatase and tensin homolog (PTEN), is a tumor suppressor. However, a growing body of evidence suggests that PTPs can also function as potent oncoproteins. In this chapter, we provide a broad historical overview of the PTPs, their mechanism of action, and posttranslational modifications. Then, we focus on the dual properties of classical PTPs (receptor and nonreceptor) and dual-specificity phosphatases in cancer and summarize the current knowledge of the signaling pathways regulated by key PTPs in human cancer. In conclusion, we present our perspective on the potential of these PTPs to serve as therapeutic targets in cancer.
Collapse
Affiliation(s)
- David P Labbé
- Goodman Cancer Research Centre, McGill University, Montréal, Québec, Canada
| | | | | |
Collapse
|
8
|
Gomez MA, Alisaraie L, Shio MT, Berghuis AM, Lebrun C, Gautier-Luneau I, Olivier M. Protein tyrosine phosphatases are regulated by mononuclear iron dicitrate. J Biol Chem 2010; 285:24620-8. [PMID: 20519508 DOI: 10.1074/jbc.m110.107037] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The involvement of macrophages (Mvarphis) as host, accessory, and effector cells in the development of infectious diseases, together with their central role in iron homeostasis, place these immune cells as key players in the interface between iron and infection. Having previously shown that the functional expression of NRAMP-1 results in increased protein phosphorylation mediated in part by an iron-dependent inhibition of Mvarphi protein-tyrosine phosphatase (PTP) activity, we sought to study the mechanism(s) underlying this specific event. Herein we have identified the mononuclear dicitrate iron complex [Fe(cit)(2)H(4-x)]((1+x)-) as the species responsible for the specific inhibition of Mvarphi PTP activity. By using biochemical and computational approaches, we show that [Fe(cit)(2)](5-) targets the catalytic pocket of the PTP SHP-1, competitively inhibiting its interaction with an incoming phosphosubstrate. In vitro and in vivo inhibition of PTP activity by iron-citrate results in protein hyperphosphorylation and enhanced MAPK signaling in response to LPS stimulation. We propose that iron-citrate-mediated PTP inhibition represents a novel and biologically relevant regulatory mechanism of signal transduction.
Collapse
Affiliation(s)
- Maria Adelaida Gomez
- Department of Microbiology and Immunology, McGill University, Montréal, Québec H3A 2B4, Canada
| | | | | | | | | | | | | |
Collapse
|
9
|
Grant S, Tran P, Zhang Q, Zou A, Dinh D, Jensen J, Zhou S, Kang X, Zachwieja J, Lippincott J, Liu K, Johnson SL, Scales S, Yin C, Nukui S, Stoner C, Prasanna G, Lafontaine J, Wells P, Li H. Discovery of a novel class of targeted kinase inhibitors that blocks protein kinase C signaling and ameliorates retinal vascular leakage in a diabetic rat model. Eur J Pharmacol 2009; 627:16-25. [PMID: 19850035 DOI: 10.1016/j.ejphar.2009.10.029] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2009] [Revised: 09/18/2009] [Accepted: 10/06/2009] [Indexed: 01/21/2023]
Abstract
Protein kinase C (PKC) family members such as PKCbetaII may become activated in the hyperglycemic state associated with diabetes. Preclinical and clinical data implicate aberrant PKC activity in the development of diabetic microvasculature abnormalities. Based on this potential etiological role for PKC in diabetic complications, several therapeutic PKC inhibitors have been investigated in clinical trials for the treatment of diabetic patients. In this report, we present the discovery and preclinical evaluation of a novel class of 3-amino-pyrrolo[3,4-c]pyrazole derivatives as inhibitors of PKC that are structurally distinct from the prototypical indolocarbazole and bisindolylmaleimide PKC inhibitors. From this pyrrolo-pyrazole series, several compounds were identified from biochemical assays as potent, ATP-competitive inhibitors of PKC activity with high specificity for PKC over other protein kinases. These compounds were also found to block PKC signaling activity in multiple cellular functional assays. PF-04577806, a representative from this series, inhibited PKC activity in retinal lysates from diabetic rats stimulated with phorbol myristate acetate. When orally administered, PF-04577806 showed good exposure in the retina of diabetic Long-Evans rats and ameliorated retinal vascular leakage in a streptozotocin-induced diabetic rat model. These novel PKC inhibitors represent a promising new class of targeted protein kinase inhibitors with potential as therapeutic agents for the treatment of patients with diabetic microvascular complications.
Collapse
Affiliation(s)
- Stephan Grant
- Department of Biochemistry and Primary Screening, Pfizer Global Research & Development, Pfizer La Jolla Laboratories, San Diego, CA 92121, United States.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
10
|
Halfter U, Derbyshire Z, Vaillancourt R. Interferon-gamma-dependent tyrosine phosphorylation of MEKK4 via Pyk2 is regulated by annexin II and SHP2 in keratinocytes. Biochem J 2009; 388:17-28. [PMID: 15601262 PMCID: PMC1186689 DOI: 10.1042/bj20041236] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
IFNgamma (interferon-gamma) binding to its cognate receptor results, through JAK (Janus kinase), in direct activation of receptor-bound STAT1 (signal transducer and activator of transcription 1), although there is evidence for additional activation of a MAPK (mitogen-activated protein kinase) pathway. In the present paper, we report IFNgamma-dependent activation of the MEKK4 (MAPK/extracellular-signal-regulated kinase kinase kinase 4) pathway in HaCaT human keratinocytes. MEKK4 is tyrosine-phosphorylated and the IFNgamma-dependent phosphorylation requires intracellular calcium. Calcium-dependent phosphorylation of MEKK4 is mediated by Pyk2. Moreover, MEKK4 and Pyk2 co-localize in an IFNgamma-dependent manner in the perinuclear region. Furthermore, the calcium-binding protein, annexin II, and the calcium-regulated kinase, Pyk2, co-immunoprecipitate with MEKK4 after treatment with IFNgamma. Immunofluorescence imaging of HaCaT cells shows an IFNgamma-dependent co-localization of annexin II with Pyk2 in the perinuclear region, suggesting that annexin II mediates the calcium-dependent regulation of Pyk2. Tyrosine phosphorylation of MEKK4 correlates with its activity to phosphorylate MKK6 (MAPK kinase 6) in vitro and subsequent p38 MAPK activation in an IFNgamma-dependent manner. Additional studies demonstrate that the SH2 (Src homology 2)-domain-containing tyrosine phosphatase SHP2 co-immunoprecipitates with MEKK4 in an IFNgamma-dependent manner and co-localizes with MEKK4 after IFNgamma stimulation in the perinuclear region in HaCaT cells. Furthermore, we provide evidence that SHP2 dephosphorylates MEKK4 and Pyk2, terminating the MEKK4-dependent branch of the IFNgamma signalling pathway.
Collapse
Affiliation(s)
- Ursula M. Halfter
- Department of Pharmacology and Toxicology, University of Arizona, 1703 E. Mabel Street, Tucson, AZ 85721, U.S.A
| | - Zachary E. Derbyshire
- Department of Pharmacology and Toxicology, University of Arizona, 1703 E. Mabel Street, Tucson, AZ 85721, U.S.A
| | - Richard R. Vaillancourt
- Department of Pharmacology and Toxicology, University of Arizona, 1703 E. Mabel Street, Tucson, AZ 85721, U.S.A
- To whom correspondence should be addressed (email )
| |
Collapse
|
11
|
Jang SH, Hwang SA, Kim M, Yun SH, Kim MS, Karnik SS, Lee C. A protein tyrosine phosphatase inhibitor, pervanadate, inhibits angiotensin II-Induced beta-arrestin cleavage. Mol Cells 2009; 28:25-30. [PMID: 19711041 PMCID: PMC2823265 DOI: 10.1007/s10059-009-0104-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2009] [Revised: 05/20/2009] [Accepted: 06/09/2009] [Indexed: 10/20/2022] Open
Abstract
Beta-arrestins turn off G protein-mediated signals and initiate distinct G protein-independent signaling pathways. We previously demonstrated that angiotensin AT(1) receptor-bound beta-arrestin 1 is cleaved after Phe(388) upon angiotensin II stimulation. The mechanism and signaling pathway of angiotensin II-induced beta-arrestin cleavage remain largely unknown. Here, we show that protein Tyr phosphatase activity is involved in the regulation of beta-arrestin 1 cleavage. Tagging of green fluorescent protein (GFP) either to the N-terminus or C-terminus of beta-arrestin 1 induced conformational changes and the cleavage of beta-arrestin 1 without angiotensin AT(1) receptor activation. Orthovanadate and molybdate, inhibitors of protein Tyr phosphatase, attenuated the cleavage of C-terminal GFP-tagged beta-arrestin 1 in vitro. The inhibitory effects of okadaic acid and pyrophosphate, which are inhibitors of protein Ser/Thr phosphatase, were less than those of protein Tyr phosphatase inhibitors. Cell-permeable pervanadate inhibited angiotensin II-induced cleavage of beta-arrestin 1 in COS-1 cells. Our findings suggest that Tyr phosphorylation signaling is involved in the regulation of angiotensin II-induced beta-arrestin cleavage.
Collapse
Affiliation(s)
- Sei-Heon Jang
- Department of Molecular Biology, Daegu University, Gyeongsan 712-714, Korea
| | - Si Ae Hwang
- Department of Molecular Biology, Daegu University, Gyeongsan 712-714, Korea
| | - Mijin Kim
- Department of Molecular Biology, Daegu University, Gyeongsan 712-714, Korea
| | | | | | | | - ChangWoo Lee
- Department of Molecular Biology, Daegu University, Gyeongsan 712-714, Korea
| |
Collapse
|
12
|
Abstract
Protein-tyrosine phosphatases are tightly controlled by various mechanisms, ranging from differential expression in specific cell types to restricted subcellular localization, limited proteolysis, post-translational modifications affecting intrinsic catalytic activity, ligand binding and dimerization. Here, we review the regulatory mechanisms found to control the classical protein-tyrosine phosphatases.
Collapse
|
13
|
Krejci P, Masri B, Salazar L, Farrington-Rock C, Prats H, Thompson LM, Wilcox WR. Bisindolylmaleimide I suppresses fibroblast growth factor-mediated activation of Erk MAP kinase in chondrocytes by preventing Shp2 association with the Frs2 and Gab1 adaptor proteins. J Biol Chem 2006; 282:2929-36. [PMID: 17145761 DOI: 10.1074/jbc.m606144200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Fibroblast growth factors (FGFs) inhibit chondrocyte proliferation via the Erk MAP kinase pathway. Here, we explored the role of protein kinase C in FGF signaling in chondrocytes. Erk activity in FGF2-treated RCS (rat chondrosarcoma) chondrocytes or human primary chondrocytes was abolished by the protein kinase C inhibitor bisindolylmaleimide I (Bis I). Bis I inhibited FGF2-induced activation of MEK, Raf-1, and Ras members of Erk signaling module but not the FGF2-induced tyrosine phosphorylation of Frs2 or the kinase activity of FGFR3, demonstrating that it targets the Erk cascade immediately upstream of Ras. Indeed, Bis I abolished the FGF2-mediated association of Shp2 tyrosine phosphatase with Frs2 and Gab1 adaptor proteins necessary for proper Ras activation. We also determined which PKC isoform is involved in FGF2-mediated activation of Erk. When both conventional and novel PKCs expressed by RCS chondrocytes (PKCalpha, -gamma, -delta, and -epsilon) were down-regulated by phorbol ester, cells remained responsive to FGF2 with Erk activation, and this activation was sensitive to Bis I. Moreover, treatment with PKClambda/zeta pseudosubstrate lead to significant reduction of FGF2-mediated activation of Erk, suggesting involvement of an atypical PKC.
Collapse
Affiliation(s)
- Pavel Krejci
- Medical Genetics Institute, Cedars-Sinai Medical Center, Los Angeles, California 90048, USA.
| | | | | | | | | | | | | |
Collapse
|
14
|
Zhou Y, Wang D, Li F, Shi J, Song J. Different roles of protein kinase C-betaI and -delta in the regulation of adipocyte differentiation. Int J Biochem Cell Biol 2006; 38:2151-63. [PMID: 16950644 DOI: 10.1016/j.biocel.2006.06.009] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2006] [Revised: 06/08/2006] [Accepted: 06/20/2006] [Indexed: 12/22/2022]
Abstract
Protein kinase C (PKC) is a member of serine/threonine protein kinase family that plays important roles in the control of vast variety of cellular functions. Nevertheless, the regulatory effect of PKC on adipogenesis remained not well understood. In this study, we investigated the effect of several PKC isoforms on the adipogenic conversion of 3T3-L1 preadipocytes induced by dexamethasone, isobutylmethylxanthine and insulin. Treatment of cells with broad-spectrum PKC inhibitor Rö318220 suppressed the adipogenesis. Gö6976, a selective inhibitor for PKC isoforms-alpha, -betaI and -mu, also inhibited the adipogenesis of cells. Pretreatment of cells with peroxisomal proliferator activated receptor-gamma (PPARgamma) agonist troglitazone abolished the inhibitory effect of Gö6976 on adipogenesis. The plasmic membrane translocation of PKC-betaI was observed at the first 2 days of differentiation. Whereas no translocation of PKC-alpha and -mu was observed. Overexpression of dominant negative PKC-betaI, but not wild-type PKC-betaI, blocked adipogenesis. This effect of dominant negative PKC-betaI can be reversed by troglitazone, suggesting that PKC-betaI is required for the initiation of adipogenesis. In addition, rottlerin, a specific inhibitor of PKC-delta, can reverse the suppression of adipogenesis mediated by 12-O-tetradecanoyl-phorbol-13-acetate, transforming growth factor-beta1, and epidermal growth factor. These data suggest that PKC-betaI is important in the induction of adipogenesis, while the PKC-delta has an inhibitory role for adipogenesis.
Collapse
Affiliation(s)
- Yiran Zhou
- Laboratory of Molecular Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | | | | | | | | |
Collapse
|
15
|
Specific protein kinase C isoforms as transducers and modulators of insulin signaling. Mol Genet Metab 2006; 89:32-47. [PMID: 16798038 DOI: 10.1016/j.ymgme.2006.04.017] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/05/2006] [Revised: 04/23/2006] [Accepted: 04/23/2006] [Indexed: 12/14/2022]
Abstract
Recent studies implicate specific PKC isoforms in the insulin-signaling cascade. Insulin activates PKCs alpha, betaII, delta and zeta in several cell types. In addition, as will be documented in this review, certain members of the PKC family may also be activated and act upstream of PI3 and MAP kinases. Each of these isoforms has been shown one way or another either to mimic or to modify insulin-stimulated effects in one or all of the insulin-responsive tissues. Moreover, each of the isoforms has been shown to be activated by insulin stimulation or conditions important for effective insulin stimulation. Studies attempting to demonstrate a definitive role for any of the isoforms have been performed on different cells, ranging from appropriate model systems for skeletal muscle, liver and fat, such as primary cultures, and cell lines and even in vivo studies, including transgenic mice with selective deletion of specific PKC isoforms. In addition, studies have been done on certain expression systems such as CHO or HEK293 cells, which are far removed from the tissues themselves and serve mainly as vessels for potential protein-protein interactions. Thus, a clear picture for many of the isoforms remains elusive in spite of over two decades of intensive research. The recent intrusion of transgenic and precise molecular biology technologies into the research armamentarium has opened a wide range of additional possibilities for direct involvement of individual isoforms in the insulin signaling cascade. As we hope to discuss within the context of this review, whereas many of the long sought-after answers to specific questions are not yet clear, major advances have been made in our understanding of precise roles for individual PKC isoforms in mediation of insulin effects. In this review, in which we shall focus our attention on isoforms in the conventional and novel categories, a clear case will be made to show that these isoforms are not only expressed but are importantly involved in regulation of insulin metabolic effects.
Collapse
|
16
|
Poole AW, Jones ML. A SHPing tale: perspectives on the regulation of SHP-1 and SHP-2 tyrosine phosphatases by the C-terminal tail. Cell Signal 2005; 17:1323-32. [PMID: 16084691 DOI: 10.1016/j.cellsig.2005.05.016] [Citation(s) in RCA: 131] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2005] [Accepted: 05/17/2005] [Indexed: 01/31/2023]
Abstract
Protein tyrosine phosphorylation is a ubiquitous signalling mechanism and is regulated by a balance between the action of kinases and phosphatases. The SH2 domain-containing phosphatases SHP-1 and SHP-2 are the best studied of the classical non-receptor tyrosine phosphatases, but it is intriguing that despite their close sequence and structural homology these two phosphatases play quite different cellular roles. In particular, whereas SHP-1 plays a largely negative signalling role suppressing cellular activation, SHP-2 plays a largely positive signalling role. Major sequence differences between the two molecules are apparent in the approximately 100 amino acid residues at the extreme C-terminus of the proteins, beyond the phosphatase catalytic domain. Here we review how the differences in the tails of these proteins may regulate their activities and explain some of their functional differences.
Collapse
Affiliation(s)
- Alastair W Poole
- Department of Pharmacology, University of Bristol, School of Medical Sciences, Bristol BS8 1TD, UK.
| | | |
Collapse
|
17
|
Müssig K, Staiger H, Fiedler H, Moeschel K, Beck A, Kellerer M, Häring HU. Shp2 is required for protein kinase C-dependent phosphorylation of serine 307 in insulin receptor substrate-1. J Biol Chem 2005; 280:32693-9. [PMID: 16055440 DOI: 10.1074/jbc.m506549200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The function of insulin receptor substrate-1 (IRS-1), a key molecule of insulin signaling, is modulated by phosphorylation at multiple serine/threonine residues. Phorbol ester stimulation of cells induces phosphorylation of two inhibitory serine residues in IRS-1, i.e. Ser-307 and Ser-318, suggesting that both sites may be targets of protein kinase C (PKC) isoforms. However, in an in vitro system using a broad spectrum of PKC isoforms (alpha, beta1, beta2, delta, epsilon, eta, mu), we detected only Ser-318, but not Ser-307 phosphorylation, suggesting that phorbol ester-induced phosphorylation of this site in intact cells requires additional signaling elements and serine kinases that link PKC activation to Ser-307 phosphorylation. As we have observed recently that the tyrosine phosphatase Shp2, a negative regulator of insulin signaling, is a substrate of PKC, we studied the role of Shp2 in this context. We found that phorbol ester-induced Ser-307 phosphorylation is reduced markedly in Shp2-deficient mouse embryonic fibroblasts (Shp2-/-) whereas Ser-318 phosphorylation is unaltered. The Ser-307 phosphorylation was rescued by transfection of mouse embryonic fibroblasts with wild-type Shp2 or with a phosphatase-inactive Shp2 mutant, respectively. In this cell model, tumor necrosis factor-alpha-induced Ser-307 phosphorylation as well depended on the presence of Shp2. Furthermore, Shp2-dependent phorbol ester effects on Ser-307 were blocked by wortmannin, rapamycin, and the c-Jun NH2-terminal kinase (JNK) inhibitor SP600125. This suggests an involvement of the phosphatidylinositol 3-kinase/mammalian target of rapamycin cascade and of JNK in this signaling pathway resulting in IRS-1 Ser-307 phosphorylation. Because the activation of these kinases does not depend on Shp2, it is concluded that the function of Shp2 is to direct these activated kinases to IRS-1.
Collapse
Affiliation(s)
- Karsten Müssig
- Division of Endocrinology, Metabolism, and Pathobiochemistry, Department of Internal Medicine, University Hospital of Tübingen, Tübingen 72076, Germany
| | | | | | | | | | | | | |
Collapse
|
18
|
Du Z, Shen Y, Yang W, Mecklenbrauker I, Neel BG, Ivashkiv LB. Inhibition of IFN-alpha signaling by a PKC- and protein tyrosine phosphatase SHP-2-dependent pathway. Proc Natl Acad Sci U S A 2005; 102:10267-72. [PMID: 16000408 PMCID: PMC1177356 DOI: 10.1073/pnas.0408854102] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Cytokine signaling by the Jak-STAT pathway is subject to complex negative regulation that limits the amplitude and duration of signal transduction. Inhibition of signaling also mediates negative crosstalk, whereby factors with opposing biological activities crossinhibit each other's function. Here, we investigated a rapidly inducible mechanism that inhibited Jak-STAT activation by IFN-alpha, a cytokine that is important for antiviral responses, growth control, and modulation of immune responses. IFN-alpha-induced signaling and gene activation were inhibited by ligation of Fc receptors and Toll-like receptors 7 and 8 in a PKCbeta-dependent manner. Neither PKCbeta nor PKCdelta influenced responses of cells treated with IFN-alpha alone. Inhibition of IFN-alpha signaling correlated with suppression of IFN-alpha-dependent antiviral responses. PKC-mediated inhibition did not require de novo gene expression but involved the recruitment of PKCbeta to the IFN-alpha receptor and interaction with protein tyrosine phosphatase SHP-2, resulting in augmented phosphatase activity. PKC-mediated inhibition of IFN-alpha signaling was abolished in SHP-2-deficient cells, demonstrating a pivotal role for SHP-2 in this inhibitory pathway. Together, our data describe a rapidly inducible, direct mechanism of inhibition of Jak-STAT signaling mediated by a PKCbeta-SHP-2 signaling pathway.
Collapse
Affiliation(s)
- Zhimei Du
- Graduate Program in Immunology, Weill Graduate School of Medical Sciences of Cornell University, New York, NY 10021, USA
| | | | | | | | | | | |
Collapse
|
19
|
Maniar R, Pecherskaya A, Ila R, Solem M. PKC alpha-dependent regulation of the IGF1 receptor in adult and embryonic rat cardiomyocytes. Mol Cell Biochem 2005; 275:15-24. [PMID: 16342423 DOI: 10.1007/s11010-005-7264-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
In both, the adult rat ventricular cardiomyocytes and the embryonic rat heart cell line, H9c2, acute exposure to IGF1 resulted in activation of the IGF1 receptor's internal tyrosine kinase, and this was completely blocked by the PKC alpha inhibitor, Gö6976. In addition, RNA interference using siRNA mediated gene silencing of PKC alpha-inhibited IGF1 receptor activity and blocked PKC alpha expression in H9c2 cells. Biochemical experiments demonstrate that PKC alpha is associated with the IGFlR (beta subunit) only after acute IGF1 exposure, and this may suggest that there is a direct interaction and possibly a PKC alpha phosphorylation site within the internal IGF1 receptor domain. The downstream effects of blocking PKC alpha activity by exposure to Gö6976 include inhibition of IGF1-stimuated PI3 kinase activity and reduced IGF1-stimulated c-fos expression in the adult cardiomyocytes. Previously, the laboratory has reported that IGF1 activates PKC alpha in adult rat cardiomyocytes, and that PKC alpha activity is required for IGF1-dependent Erk/Erk2 activity and protein synthesis. Here, it is shown that IGF1-dependent protein synthesis is completely blocked by PD98059, indicating that the Raf-Mek-Erk cascade is required for IGF1's anabolic activity. Pretreatment with LY294002, a specific inhibitor of PI3 kinase, blocked IGF1-stimulated Erk1/Erk2 activity; therefore, PI3 kinase may also be required for IGF1-dependent protein synthesis. In H9c2 cells, coincubation with PMA lead to an increase in the rate of the IGF1 receptor activation, and this may further implicate a role for PKC in regulating the IGF1R. In conclusion, PKC alpha plays an essential role in the IGF1-signaling cascade, including the regulation of key signaling proteins involved in cell signaling and gene expression, and this may primarily be due to PKC alpha directly regulating the IGF1R.
Collapse
Affiliation(s)
- Ruchita Maniar
- Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, 1020 Locust Street, Philadelphia, PA 19107, USA
| | | | | | | |
Collapse
|
20
|
Jones ML, Craik JD, Gibbins JM, Poole AW. Regulation of SHP-1 Tyrosine Phosphatase in Human Platelets by Serine Phosphorylation at Its C Terminus. J Biol Chem 2004; 279:40475-83. [PMID: 15269224 DOI: 10.1074/jbc.m402970200] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
SHP-1 is a Src homology 2 (SH2) domain-containing tyrosine phosphatase that plays an essential role in negative regulation of immune cell activity. We describe here a new model for regulation of SHP-1 involving phosphorylation of its C-terminal Ser591 by associated protein kinase Calpha. In human platelets, SHP-1 was found to constitutively associate with its substrate Vav1 and, through its SH2 domains, with protein kinase Calpha. Upon activation of either PAR1 or PAR4 thrombin receptors, the association between the three proteins was retained, and Vav1 became phosphorylated on tyrosine and SHP-1 became phosphorylated on Ser591. Phosphorylation of SHP-1 was mediated by protein kinase C and negatively regulated the activity of SHP-1 as demonstrated by a decrease in the in vitro ability of SHP-1 to dephosphorylate Vav1 on tyrosine. Protein kinase Calpha therefore critically and negatively regulates SHP-1 function, forming part of a mechanism to retain SHP-1 in a basal active state through interaction with its SH2 domains, and phosphorylating its C-terminal Ser591 upon cellular activation leading to inhibition of SHP-1 activity and an increase in the tyrosine phosphorylation status of its substrates.
Collapse
MESH Headings
- Amino Acid Sequence
- Blood Platelets/enzymology
- Cell Line
- Electrophoresis, Polyacrylamide Gel
- Gene Expression Regulation
- Gene Expression Regulation, Enzymologic
- Glutathione Transferase/metabolism
- Green Fluorescent Proteins
- Humans
- Intracellular Signaling Peptides and Proteins
- Luminescent Proteins/chemistry
- Luminescent Proteins/metabolism
- Microscopy, Confocal
- Models, Biological
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Oncogene Proteins/metabolism
- Phosphorylation
- Precipitin Tests
- Protein Kinase C/metabolism
- Protein Kinase C-alpha
- Protein Structure, Tertiary
- Protein Transport
- Protein Tyrosine Phosphatase, Non-Receptor Type 6
- Protein Tyrosine Phosphatases/biosynthesis
- Protein Tyrosine Phosphatases/genetics
- Proto-Oncogene Proteins c-vav
- Receptor, PAR-1/metabolism
- Receptors, Thrombin/metabolism
- Recombinant Fusion Proteins/metabolism
- Sequence Homology, Amino Acid
- Serine/chemistry
- Serine/metabolism
- Substrate Specificity
- Thrombin/chemistry
- Tyrosine/chemistry
- src Homology Domains
Collapse
Affiliation(s)
- Matthew L Jones
- Department of Pharmacology, School of Medical Sciences, University Walk, Bristol BS8 1TD, United Kingdom
| | | | | | | |
Collapse
|
21
|
Romanova LY, Hashimoto S, Chay KO, Blagosklonny MV, Sabe H, Mushinski JF. Phosphorylation of paxillin tyrosines 31 and 118 controls polarization and motility of lymphoid cells and is PMA-sensitive. J Cell Sci 2004; 117:3759-68. [PMID: 15252114 DOI: 10.1242/jcs.01206] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Tyrosine phosphorylation of paxillin regulates actin cytoskeleton-dependent changes in cell morphology and motility in adherent cells. In this report we investigated the involvement of paxillin tyrosine phosphorylation in the regulation of actin cytoskeleton-dependent polarization and motility of a non-adherent IL-3-dependent murine pre-B lymphocytic cell line Baf3. We also assessed the effect of phorbol myristate acetate (PMA), a phorbol ester analogous to those currently in clinical trials for the treatment of leukemia, on paxillin phosphorylation. Using tyrosine-to-phenylalanine phosphorylation mutants of paxillin and phosphospecific antibody we demonstrated that IL-3 stimulated phosphorylation of paxillin tyrosine residues 31 and 118, whereas the tyrosines 40 and 181 were constitutively phosphorylated. Phosphorylation of paxillin residues 31 and 118 was required for cell polarization and motility. In the presence of IL-3, PMA dramatically reduced the phosphorylation of residues 31 and 118, which was accompanied by inhibition of cell polarization and motility. This PMA effect was partially recapitulated by expression of exogenous tyrosine 31 and 118 mutants of paxillin. We also demonstrated that PMA inhibited the IL-3-induced and activation-dependent tyrosine phosphorylation of focal adhesion kinase. Thus, our results indicate that phosphorylation of paxillin tyrosine residues 31 and 118 regulates actin-dependent polarization and motility of pre-B Baf3 cells, both of which could be inhibited by PMA. They also suggest that inhibition of upstream signaling by PMA contributes to the decrease of paxillin phosphorylation and subsequent changes in cell morphology.
Collapse
Affiliation(s)
- Larisa Y Romanova
- Molecular Genetics Section, Laboratory of Genetics, National Cancer Institute, NIH, 9000 Rockville Pike, Bethesda, MD 20892, USA.
| | | | | | | | | | | |
Collapse
|
22
|
Nozawa Y, Nishihara K, Akizawa Y, Orimoto N, Nakano M, Uji T, Ajioka H, Kanda A, Matsuura N, Kiniwa M. Protein Kinase C Activation by Helicobacter pylori in Human Gastric Epithelial Cells Limits Interleukin-8 Production Through Suppression of Extracellular Signal-Regulated Kinase. J Pharmacol Sci 2004; 94:233-9. [PMID: 15037807 DOI: 10.1254/jphs.94.233] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
Abstract
Helicobacter pylori (H. pylori) infection of gastric epithelial cells has been shown to induce interleukin (IL)-8 production, but the signal transduction mechanism leading to IL-8 production has not been clearly defined. Here, we investigate the role of protein kinase C (PKC) in the mechanism of induction of IL-8 release by H. pylori in human gastric epithelial cells. In MKN45 cells, H. pylori-induced IL-8 release was enhanced by treatment with PKC inhibitors (GF109203X and calphostin C) and PKC depletion, which completely inhibited PKC activity. Moreover, PKC inhibitors and PKC depletion increased extracellular signal-regulated kinase (ERK) activity and phosphorylation, but not calcium/calmodulin-dependent protein kinase II (CaMK II) activity, in response to H. pylori infection. PKC activated by H. pylori inhibited activation of ERK induced by H. pylori without affecting the CaMK II activity and negatively regulated IL-8 production in human gastric epithelial cells.
Collapse
Affiliation(s)
- Yoshihisa Nozawa
- Pharmacobioregulation Research Laboratory, Taiho Pharmaceutical Co, Ltd, Saitama, Japan.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
23
|
MacGillivray M, Herrera-Abreu MT, Chow CW, Shek C, Wang Q, Vachon E, Feng GS, Siminovitch KA, McCulloch CAG, Downey GP. The protein tyrosine phosphatase SHP-2 regulates interleukin-1-induced ERK activation in fibroblasts. J Biol Chem 2003; 278:27190-8. [PMID: 12721296 DOI: 10.1074/jbc.m213083200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Focal adhesion complexes are actin-rich, cytoskeletal structures that mediate cell adhesion to the substratum and also selectively regulate signal transduction pathways required for interleukin (IL)-1beta signaling to the MAP kinase, ERK. IL-1-induced ERK activation is markedly diminished in fibroblasts deprived of focal adhesions whereas activation of p38 and JNK is unaffected. While IL-1 signaling is known to involve the activity of protein and lipid kinases including MAP kinases, FAK, and PI3K, little is known about the role of phosphatases in the regulation of IL-1 signal generation and attenuation. Here we demonstrate that SHP-2, a protein tyrosine phosphatase present in focal adhesions, modulates IL-1-induced ERK activation and the transient actin stress fiber disorganization that occurs following IL-1 treatment in human gingival fibroblasts. Using a combination of immunoblotting, immunoprecipitation, and immunostaining we show that SHP-2 is present in nascent focal adhesions and undergoes phosphorylation on tyrosine 542 in response to IL-1 stimulation. Blocking anti-SHP-2 antibodies, electoporated into the cytosol of fibroblasts, inhibited IL-1-induced ERK activation, actin filament assembly, and cell contraction, indicating a role for SHP-2 in these processes. In summary, our data indicate that SHP-2, a focal adhesion-associated protein, participates in IL-1-induced ERK activation likely via an adaptor function.
Collapse
Affiliation(s)
- Mairi MacGillivray
- Division of Respirology, the Department of Medicine, The Toronto General Hospital Research Institute of the University Health Network, Toronto, Ontario M5S 1A8, Canada
| | | | | | | | | | | | | | | | | | | |
Collapse
|
24
|
Eitel K, Staiger H, Brendel MD, Brandhorst D, Bretzel RG, Häring HU, Kellerer M. Different role of saturated and unsaturated fatty acids in beta-cell apoptosis. Biochem Biophys Res Commun 2002; 299:853-6. [PMID: 12470657 DOI: 10.1016/s0006-291x(02)02752-3] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
It is believed that free fatty acids contribute to the pathogenesis of type 2 diabetes in humans. We have recently shown that lipoapoptosis of human beta-cells is specifically induced by saturated fatty acids while unsaturated had no effect. In the present study we tested the effect of co-incubation of different saturated and unsaturated free fatty acids on lipoapoptosis in beta-cells. RIN1046-38 cells and isolated human beta-cells were incubated with combinations of saturated fatty acids (palmitate, stearate) and mono- or polyunsaturated fatty acids (palmitoleate, oleate, and linoleate). Cells were incubated for 24-72 h with 1mM fatty acids. All unsaturated fatty acids tested completely prevented palmitate- or stearate-induced apoptosis of rat and human beta-cells as assessed by flow cytometric cell cycle analysis and TUNEL assay. This might suggest that apoptosis in vivo is predominantly determined by the content of unsaturated fatty acids in a mixed fatty acid pool.
Collapse
Affiliation(s)
- Katrin Eitel
- Internal Medicine IV, University of Tübingen, Otfried-Müller-Str. 10, D-72076 Tübingen, Germany
| | | | | | | | | | | | | |
Collapse
|
25
|
Hers I, Bell CJ, Poole AW, Jiang D, Denton RM, Schaefer E, Tavaré JM. Reciprocal feedback regulation of insulin receptor and insulin receptor substrate tyrosine phosphorylation by phosphoinositide 3-kinase in primary adipocytes. Biochem J 2002; 368:875-84. [PMID: 12220227 PMCID: PMC1223033 DOI: 10.1042/bj20020903] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2002] [Revised: 08/16/2002] [Accepted: 09/09/2002] [Indexed: 11/17/2022]
Abstract
Signalling by the insulin receptor substrate (IRS) proteins is critically dependent on the tyrosine phosphorylation of specific binding sites that recruit Src homology 2 (SH2)-domain-containing proteins, such as the p85 subunit of phosphoinositide 3-kinase (PI 3-kinase), the tyrosine phosphatase SHP-2 and the adapter protein Grb2. Here we show that stimulation by insulin of freshly isolated primary adipocytes resulted in the expected rapid tyrosine phosphorylation of the insulin receptor, IRS-1 and IRS-3. Inhibition of PI 3-kinase enhanced the insulin-stimulated phosphorylation of IRS-1 on (i) Tyr(612) and Tyr(941) (p85 binding sites), concomitant with an increased association of the p85 subunit of PI 3-kinase; (ii) Tyr(896) (a Grb2 binding site); and (iii) Tyr(1229) (an SHP-2 binding site), although little or no binding of SHP-2 to IRS-1 was detectable under any conditions. In contrast, inhibition of PI 3-kinase led to a decrease in insulin-stimulated p85 binding to IRS-3, but had no effect on SHP-2 binding. Furthermore, insulin-induced insulin receptor tyrosine phosphorylation, phosphorylation of Tyr(1158) and insulin receptor tyrosine kinase activity were all reduced by inhibition of PI 3-kinase at later time points (>or=20 min). The results demonstrate that, in primary adipocytes, PI 3-kinase feedback control of signalling by the insulin receptor and IRS proteins is multifaceted and reciprocal, illustrating the complexity of predicting the net flux of the insulin signal(s) through the IRS proteins.
Collapse
Affiliation(s)
- Ingeborg Hers
- Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.
| | | | | | | | | | | | | |
Collapse
|