title: PDGF-induced vascular smooth muscle cell proliferation is associated with dysregulation of insulin receptor substrates.
abstract: In vascular smooth muscle cells (VSMCs), platelet-derived growth factor (PDGF) plays a major role in inducing phenotypic switching from contractile to proliferative state. Importantly, VSMC phenotypic switching is also determined by the phosphorylation state/expression levels of insulin receptor substrate (IRS), an intermediary signaling component that is shared by insulin and IGF-I. To date, the roles of PDGF-induced key proliferative signaling components including Akt, p70S6kinase, and ERK1/2 on the serine phosphorylation/expression of IRS-1 and IRS-2 isoforms remain unclear in VSMCs. We hypothesize that PDGF-induced VSMC proliferation is associated with dysregulation of insulin receptor substrates. Using human aortic VSMCs, we demonstrate that prolonged PDGF treatment led to sustained increases in the phosphorylation of protein kinases such as Akt, p70S6kinase, and ERK1/2, which mediate VSMC proliferation. In addition, PDGF enhanced IRS-1/IRS-2 serine phosphorylation and downregulated IRS-2 expression in a time- and concentration-dependent manner. Notably, phosphoinositide 3-kinase (PI 3-kinase) inhibitor (PI-103) and mammalian target of rapamycin inhibitor (rapamycin), which abolished PDGF-induced Akt and p70S6kinase phosphorylation, respectively, blocked PDGF-induced IRS-1 serine phosphorylation and IRS-2 downregulation. In contrast, MEK1/ERK inhibitor (U0126) failed to block PDGF-induced IRS-1 serine phosphorylation and IRS-2 downregulation. PDGF-induced IRS-2 downregulation was prevented by lactacystin, an inhibitor of proteasomal degradation. Functionally, PDGF-mediated IRS-1/IRS-2 dysregulation resulted in the attenuation of insulin-induced IRS-1/IRS-2-associated PI 3-kinase activity. Pharmacological inhibition of PDGF receptor tyrosine kinase with imatinib prevented IRS-1/IRS-2 dysregulation and restored insulin receptor signaling. In conclusion, strategies to inhibit PDGF receptors would not only inhibit neointimal growth but may provide new therapeutic options to prevent dysregulated insulin receptor signaling in VSMCs in nondiabetic and diabetic states.
authors.affiliation: Departments of Medicine and Pharmacology, Heart & Vascular Institute, Penn State College of Medicine, 500 University Drive, Hershey, PA 17033, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhao
authors.forename: Swarajit K
authors.initials: SK
authors.lastname: Biswas
authors.forename: Patrick H
authors.initials: PH
authors.lastname: McNulty
authors.forename: Mark
authors.initials: M
authors.lastname: Kozak
authors.forename: John Y
authors.initials: JY
authors.lastname: Jun
authors.forename: Lakshman
authors.initials: L
authors.lastname: Segar
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000077214:Becaplermin; D001549:Benzamides; D002070:Butadienes / Q000494:pharmacology; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D005663:Furans / Q000494:pharmacology; D006801:Humans; D000068877:Imatinib Mesylate; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism*; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000166:cytology*; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D009570:Nitriles / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010879:Piperazines / Q000494:pharmacology; D010982:Platelet-Derived Growth Factor / Q000235:genetics / Q000494:pharmacology*; D020574:Proto-Oncogene Proteins c-sis; D011725:Pyridines / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology
chemical_list: D000903:Antibiotics, Antineoplastic; D000077214:Becaplermin; D001549:Benzamides; D002070:Butadienes; D004791:Enzyme Inhibitors; D048049:Extracellular Signal-Regulated MAP Kinases; D005663:Furans; D000068877:Imatinib Mesylate; D055504:Insulin Receptor Substrate Proteins; D048369:MAP Kinase Kinase 1; D009570:Nitriles; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010879:Piperazines; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D011725:Pyridines; D011743:Pyrimidines; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D020123:Sirolimus; C522973:PI103; C113580:U 0126