Recruitment of Pyk2 to SHPS-1 signaling complex is required for IGF-I-dependent mitogenic signaling in vascular smooth muscle cells

In vascular smooth muscle cells, IGF-I stimulates SHPS-1/SHP2/Src complex formation which is required for IGF-I-stimulated cell proliferation. Using SHP2/Src silencing and a Pyk2/Y402F mutant, we showed that Pyk2 was also recruited to the SHPS-1 complex. Pyk2 recruitment to SHPS-1 is mediated via the interaction of Pyk2 Tyr402 and the Src in response to IGF-I. Following Src/Pyk2 association, Src phosphorylates Pyk2 on Tyr881 providing a binding site for Grb2. Cells expressing Pyk2/Y881F showed decreased Grb2 recruitment to SHPS-1 and impaired Shc/Grb2 association. This change led to reduced Erk1/2 (MAP kinase) activation and cell proliferation in response to IGF-I. Our results show that, following its recruitment to the SHPS-1 signaling complex, Pyk2 localizes Grb2 in close proximity to Shc thereby facilitating Shc/Grb2 association which leads to Erk1/2 activation in response to IGF-I. Thus, Pyk2 recruitment to SHPS-1 plays an important role in regulating the IGF-I-stimulated mitogenic response.

PDK1 recruitment to the SHPS-1 signaling complex enhances insulin-like growth factor-i-stimulated AKT activation and vascular smooth muscle cell survival

In vascular smooth muscle cells, exposed to hyperglycemia and insulin-like growth factor-I (IGF-I), SHPS-1 functions as a scaffold protein, and a signaling complex is assembled that leads to AKT activation. However, the underlying mechanism by which formation of this complex activates the kinase that phosphorylates AKT (Thr(308)) is unknown. Therefore, we investigated the mechanism of PDK1 recruitment to the SHPS-1 signaling complex and the consequences of disrupting PDK1 recruitment for downstream signaling. Our results show that following IGF-I stimulation, PDK1 is recruited to SHPS-1, and its recruitment is mediated by Grb2, which associates with SHPS-1 via its interaction with Pyk2, a component of the SHPS-1-associated complex. A proline-rich sequence in PDK1 bound to an Src homology 3 domain in Grb2 in response to IGF-I. Disruption of Grb2-PDK1 by expression of either a Grb2 Src homology 3 domain or a PDK1 proline to alanine mutant inhibited PDK1 recruitment to SHPS-1, leading to impaired IGF-I-stimulated AKT Thr(308) phosphorylation. Following its recruitment to SHPS-1, PDK1 was further activated via Tyr(373/376) phosphorylation, and this was required for a maximal increase in PDK1 kinase activity and AKT-mediated FOXO3a Thr(32) phosphorylation. PDK1 recruitment was also required for IGF-I to prevent apoptosis that occurred in response to hyperglycemia. Assembly of the Grb2-PDK1 complex on SHPS-1 was specific for IGF-I signaling because inhibiting PDK1 recruitment to SHPS-1 had no effect on EGF-stimulated AKT Thr(308) phosphorylation. These findings reveal a novel mechanism for recruitment of PDK1 to the SHPS-1 signaling complex, which is required for IGF-I-stimulated AKT Thr(308) phosphorylation and inhibition of apoptosis.

Crystallization and preliminary X-ray analysis of rat SHPS-1

SHPS-1, a receptor-type transmembrane protein, is abundantly expressed in neural and myeloid tissues. The most amino-terminal immunoglobulin-like domain of SHPS-1 plays an important role in a variety of cell functions by binding its ligand CD47. Interaction between SHPS-1 and CD47 is thought to be involved in negative regulation of phagocytosis. The ligand-binding domain of rat SHPS-1 was purified and crystallized using the vapour-diffusion method with the solution-stirring technique. Preliminary X-ray diffraction data were collected from SHPS-1 crystals to 2.8 A resolution and reduced to primitive hexagonal space group P622. Unit-cell parameters are a = b = 100.5, c = 101.3 A.

The murine P84 neural adhesion molecule is SHPS-1, a member of the phosphatase-binding protein family

P84 is a neuronal membrane glycoprotein that promotes the attachment and neurite outgrowth of cultured murine cerebellar cells. The heterophilic adhesive properties of P84 and its localization at sites of synaptogenesis suggest that it may be involved in regulation of synapse formation or maintenance. P84 is expressed in subsets of neurons throughout the CNS. By cloning the cDNA encoding murine P84, we have discovered that this molecule is a member of a family of phosphatase-binding proteins and is identical to the murine SHPS-1 cDNA. Here we report the cloning of two alternatively spliced forms of P84 and describe its localization within the CNS by in situ hybridization.