Wang, Xuan

Abstract Purpose: Various studies have shown the importance of the GAIP interacting protein, COOH-terminus (GIPC, also known as Synectin) as a central adaptor molecule in different signaling pathways and as an important mediator of receptor stability. GIPC/Synectin is associated with different growth-promoting receptors such as insulin-like growth factor receptor I (IGF-IR) and integrins. These interactions were mediated through its PDZ domain. GIPC/Synectin has been shown to be overexpressed in pancreatic and breast cancer. The goal of this study was to show the importance of GIPC/Synectin in pancreatic cancer growth and to evaluate a possible therapeutic strategy by using a GIPC-PDZ domain inhibitor. Furthermore, the effect of targeting GIPC on the IGF-I receptor as one of its associated receptors was tested. Experimental Design: The in vivo effects of GIPC/Synectin knockdown were studied after lentiviral transduction of luciferase-expressing pancreatic cancer cells with short hairpin RNA against GIPC/Synectin. Additionally, a GIPC-PDZ–targeting peptide was designed. This peptide was tested for its influence on pancreatic cancer growth in vitro and in vivo. Results: Knockdown of GIPC/Synectin led to a significant inhibition of pancreatic adenocarcinoma growth in an orthotopic mouse model. Additionally, a cell-permeable GIPC-PDZ inhibitor was able to block tumor growth significantly without showing toxicity in a mouse model. Targeting GIPC was accompanied by a significant reduction in IGF-IR expression in pancreatic cancer cells. Conclusions: Our findings show that targeting GIPC/Synectin and its PDZ domain inhibits pancreatic carcinoma growth and is a potential strategy for therapeutic intervention of pancreatic cancer.

Vascular endothelial growth factor-A (VEGF) is critical for angiogenesis but fails to induce neovascularization in ischemic tissue lesions in mice lacking endothelial nitric oxide synthase (eNOS). VEGF receptor-2 (VEGFR-2) is critical for angiogenesis, although little is known about the precise role of endothelial VEGFR-1 and its downstream effectors in this process. Here we have used a chimeric receptor approach in which the extracellular domain of the epidermal growth factor receptor was substituted for that of VEGFR-1 (EGLT) or VEGFR-2 (EGDR) and transduced into primary cultures of human umbilical vein endothelial cells (HUVECs) using a retroviral system. Activation of HUVECs expressing EGLT or EGDR induced rapid phosphorylation of eNOS at Ser1177, release of NO, and formation of capillary networks, similar to VEGF. Activation of eNOS by VEGFR-1 was dependent on Tyr794 and was mediated via phosphatidylinositol 3-kinase, whereas VEGFR-2 Tyr951 was involved in eNOS activation via phospholipase Cγ1. Consistent with these findings, the VEGFR-1–specific ligand placenta growth factor-1 activated phosphatidylinositol 3-kinase and VEGF-E, which is selective for VEGFR-2–activated phospholipase Cγ1. Both VEGFR-1 and VEGFR-2 signal pathways converged on Akt, as dominant-negative Akt inhibited the NO release and in vitro tube formation induced following activation of EGLT and EGDR. The identification Tyr794 of VEGFR-1 as a key residue in this process provides direct evidence of endothelial VEGFR-1 in NO-driven in vitro angiogenesis. These studies provide new sites of modulation in VEGF-mediated vascular morphogenesis and highlight new therapeutic targets for management of vascular diseases.

ABSTRACT Initially, it was thought that there was no intracellular signaling mediated by NRP‐1 alone in response to its ligands. However, the emerging data from our group as well as others suggest that the signaling through NRP‐1 actually promotes angiogenesis and is mediated through its C‐terminal domain and downstream molecules such as phosphoinositide 3‐kinase. Hence, understanding the signal transduction pathways mediated by NRP‐1 and identification of its downstream molecules are of importance. By using both in vivo zebrafish model and in vitro tissue culture system, we have shown that the C‐terminal three amino acids of NRP‐1 (SEA‐COOH) are required for NRP‐1‐mediated angiogenesis. Furthermore, knocking down of RGS‐GAIP‐interacting protein C terminus (GIPC) in zebrafish, which is associated with C‐terminal domain of NRP‐1, exhibits similar vasculature phenotypes to those from NRP‐1 null. Specific and effective silencing of GIPC in vascular endothelium results in inhibition of NRP‐1‐mediated migration. In both cases as described, PDZ domain of GIPC is responsible for its function. Taken together, our data suggest a novel role of GIPC in angiogenesis and vessel formation and also support our hypothesis that NRP‐1 can facilitate downstream signaling to promote angiogenesis through GIPC.—Wang, L., Mukhopadhyay, D., Xu, X. C terminus of RGS‐GAIP‐interacting protein conveys neuropilin‐1‐mediated signaling during angiogenesis. FASEB J. 20, E732–E741 (2006)