Role of SHPS-1 in the Regulation of Insulin-like Growth Factor I–stimulated Shc and Mitogen-activated Protein Kinase Activation in Vascular Smooth Muscle Cells

Abstract

Insulin-like growth factor I (IGF-I) stimulates smooth muscle cell (SMC) proliferation, and the mitogen-activated protein kinase (MAPK) pathway plays an important role in mediating IGF-I-induced mitogenic signaling. Our prior studies have shown that recruitment of Src homology 2 domain tyrosine phosphatase (SHP-2) to the membrane scaffolding protein Src homology 2 domain-containing protein tyrosine phosphatase substrate-1 (SHPS-1) is required for IGF-I-dependent MAPK activation. The current studies were undertaken to define the upstream signaling components that are required for IGF-I-stimulated MAPK activation and the role of SHPS-1 in regulating this process. The results show that IGF-I-induced Shc phosphorylation and its subsequent binding to Grb2 is required for sustained phosphorylation of MAPK and increased cell proliferation in SMCs. Furthermore, for Shc to be phosphorylated in response to IGF-I requires that Shc must associate with SHPS-1 and this association is mediated in part by SHP-2. Preincubation of cells with a peptide that contains a phospho-tyrosine binding motif sequence derived from SHPS-1 inhibited IGF-I-stimulated SHP-2 transfer to SHPS-1, the association of Shc with SHPS-1, and IGF-I-dependent Shc phosphorylation. Expression of an SHPS-1 mutant that did not bind to Shc or SHP-2 resulted in decreased Shc and MAPK phosphorylation in response to IGF-I. In addition, SMCs expressing a mutant form of the ␤3 subunit of the ␣V␤3, which results in impairment of SHP-2 transfer to SHPS-1, also showed attenuated IGF-I-dependent Shc and MAPK phosphorylation. Further analysis showed that Shc and SHP-2 can be coimmunoprecipitated after IGF-I stimulation. A cell-permeable peptide that contained a polyproline sequence from Shc selectively inhibited Shc/SHP-2 association and impaired Shc but not SHP-2 binding to SHPS-1. Exposure to this peptide also inhibited IGF-I-stimulated Shc and MAPK phosphorylation. Cells expressing a mutant form of Shc with the four prolines substituted with alanines showed no Shc/SHPS-1 association in response to IGF-I. We conclude that SHPS-1 functions as an anchor protein that recruits both Shc and SHP-2 and that their recruitment is necessary for IGF-Idependent Shc phosphorylation, which is required for an optimal mitogenic response in SMCs. INTRODUCTIONBoth vascular smooth muscle cell proliferation and migration in response to growth factor stimulation play important roles in the formation of atherosclerotic plaques, and insulin-like growth factor I (IGF-I) is a potent stimulator of smooth muscle cell proliferation and migration (Jones et al., 1996). In primary cultured smooth muscle cells (pSMCs), IGF-I induces activation of both the phosphatidylinositol (PI)-3 kinase and the mitogen-activated protein (MAP) kinase (MAPK) pathways. Both pathways have been shown to play roles in mediating IGF-I-dependent cell migration and cell proliferation responses (Imai and Clemmons, 1999;Maile et al., 2003).Previous studies have shown that the protein tyrosine phosphatase SHP-2 plays an impor...

Insulin-like Growth Factor-I-stimulated Insulin Receptor Substrate-1 Negatively Regulates Src Homology 2 Domain-containing Protein-tyrosine Phosphatase Substrate-1 Function in Vascular Smooth Muscle Cells

“…Our studies have shown that SHPS-1 phosphorylation and the subsequent assembly of a signaling complex that includes SHP-2, Src, Shc (Src homology 2 domain-containing protein), and Grb2 (growth factor receptor-bound protein 2) is essential for these cells to respond to hyperglycemic stress and that it enhances the ability of IGF-I to activate both MAPK and phosphatidylinositol 3-kinase pathways, leading to increased proliferation and migration (2,3,20). Following their tyrosine phosphorylation, IRS-1 and Shc bind independently to Grb2, which increases activation of MAPK/ extracellular signal-regulated kinase (ERK) (2,21,22). However, the relative contribution of Shc and IRS-1 in regulating this cascade has not been clearly delineated for many different cell types (12,23).…”

“…Insulin-like growth factor-I (IGF-I) 2 binds selectively to the type I IGF receptor, which results in stimulation of several biological functions. IGF-I is a known stimulant of vascular smooth muscle cell (VSMC) proliferation and migration, and these effects are mediated through the phosphatidylinositol 3-kinase and MAPK pathways (1)(2)(3).…”

“…IGF-I is a known stimulant of vascular smooth muscle cell (VSMC) proliferation and migration, and these effects are mediated through the phosphatidylinositol 3-kinase and MAPK pathways (1)(2)(3). Upon ligand occupancy, the receptor undergoes a conformational change that activates its tyrosine kinase, which phosphorylates downstream signaling molecules.…”

IGF-1 regulation of key signaling pathways in bone

“…3,4 In case of IGF-1 induction, IRS1 activates phosphatidylinositol 3 kinase (PI3K), 5 and the extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) network by binding to Shc and Grb2 ( Figure 1). [6][7][8] Activated PI3K phosphorylates phosphatidylinositol 4,5 bisphosphate converting it to phosphatidylinositol 3,4,5, trisphosphate. Phosphatidylinositol 3,4,5, trisphosphate recruits PDK1 (a Ser/Thr kinase), which can phosphorylate protein kinase B (AKT) at Thr 308 and then leads to partial activation of AKT (a AGC kinase).…”

The role of Src homology 2 containing protein tyrosine phosphatase 2 in vascular smooth muscle cell migration and proliferation

“…IGF-1-dependent Shc phosphorylation is required for MAPK activation and cell proliferation. Recruitment of SHP2 and Shc to SHPS-1 in response to IGF-1 are both required for Shc phosphorylation and therefore necessary for mediating IGF-1 dependent mitogenic signaling in SMCs [50] . On a separate note, unsaturated lysophosphatidic acid (LPA) is capable of transforming the primary differentiated VSMCs into dedifferentiated VSMCs via ERK and p38 MAPKs [51] .…”