Patra, Sujata

Endothelial cell proliferation and migration is essential to angiogenesis. Typically, proliferation and chemotaxis of endothelial cells is driven by growth factors such as vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF). VEGF activates phospholipases (PLCs) – specifically PLCγ1 – that are important for tubulogenesis, differentiation and DNA synthesis. However, we show here that VEGF, specifically through VEGFR2, induces phosphorylation of two serine residues on PLCβ3, and this was confirmed in an ex vivo embryoid body model. Knockdown of PLCβ3 in HUVEC cells affects IP3 production, actin reorganization, migration and proliferation; whereas migration is inhibited, proliferation is enhanced. Our data suggest that enhanced proliferation is precipitated by an accelerated cell cycle, and decreased migration by an inability to activate CDC42. Given that PLCβ3 is typically known as an effector of heterotrimeric G-proteins, our data demonstrate a unique crosstalk between the G-protein and receptor tyrosine kinase (RTK) axes and reveal a novel molecular mechanism of VEGF signaling and, thus, angiogenesis.

Abstract Purpose: In humans, several distinctive cancers result from mutations that aberrantly activate hedgehog (HH) signal transduction. Here, we investigate the role of HH signaling in ovarian cancer. Experimental Design: We assessed the expression of different components of hedghehog pathway in primary tumor samples and cell lines. We used specific hedghehog pathway blocker to study the effect on clonal growth and proliferation of ovarian cancer cell both in vitro and in vivo. Results: We show that the up-regulation of several HH pathway components is a common feature of primary ovarian tumors and cell lines. However, expression of PATCHED1 (PTCH1), a direct transcriptional target of the HH pathway, is down-regulated in ovarian cancer in direct contrast to the expression observed in other adult solid tumors. Cyclopamine, a specific HH pathway inhibitor, inhibits the proliferation and clonal growth of ovarian tumor cells in vitro and arrests ovarian tumor growth in vivo. Expression of BMI-1, a polycomb gene, is down-regulated in ovarian cancer cells following cyclopamine treatment. Overexpression of PTCH1 phenocopied the effects of cyclopamine; it down-regulated BMI-1 and reduced clonal growth in ovarian cancer cell lines. Furthermore, knocking down BMI-1 using small interfering RNA also inhibited the clonal growth of all the ovarian cancer cell lines tested. Conclusions: In brief, the constitutive low-level expression of PTCH1 contributes to proliferation and clonal growth of ovarian cancer cells by an aberrant HH signal. Because the HH pathway can be inhibited by specific inhibitors, these findings point toward possible new treatments to inhibit ovarian cancer growth.