HCPTPA, a protein tyrosine phosphatase that regulates vascular endothelialgrowth factor receptor-mediated signal transduction and biological activity

Angiogenesis is a tightly controlled process in which signaling by the rece ptors for vascular endothelial growth factor (VEGF) plays a key role. In or der to define signaling pathways downstream of VEGF receptors (VEGFR), the kinase domain of VEGFRS (Flk-1) was used as a bait to screen a human fetal heart library in the yeast two-hybrid system. One of the signaling molecule s identified in this effort was HCPTPA, a low molecular weight, cytoplasmic protein tyrosine phosphatase. Although HCPTPA possesses no identifiable ph osphotyrosine binding domains (i.e. SH2 or phosphotyrosine binding domains) , it bound specifically to active, autophosphorylated VEGFR2 but not to a m utated, kinase-inactive VEGFR2. Recombinant VEGFR2 and endogenous VEGFR2 we re substrates for recombinant HCPTPA, and HCPTPA was co-expressed with VEGF R2 in endothelial cell. Lines, suggesting that HCPTPA may be It negative re gulator of VEGFR2 signal transduction. To pursue this possibility, an adeno virus directing the expression of HCPTPA was constructed. When used to infe ct cultured endothelial cells, this adenovirus directed high level expressi on of HCPTPA that resulted in impairment of VEGF-mediated VEGFR2 autophosph orylation and mitogen-activated protein kinase activation. Adenovirus-media ted overexpression of HCPTPA also inhibited VEGF-induced cellular responses (endothelial cell migration and proliferation) and inhibited angiogenesis in the rat aortic ring assay. Taken together, these findings indicate that HCPTPA may be an important regulator of VEGF mediated signaling and biologi cal activity. Potential interactions with other signaling pathways and poss ible therapeutic implications are discussed.