Title

The role of Crk SH3 binding proteins in Crk transformation

Date of Completion

January 2009

Keywords

Biology, Genetics

Degree

Ph.D.

Abstract

v-Crk is an oncogene product of avian sarcoma virus CT10, and is composed mostly of Src homology 2 (SH2) and SH3 domains. Overexpression of c-CrkI, the cellular homolog of v-Crk, can induce cellular transformation of mouse fibroblasts, and both the SH2 and SH3 domains are required for Crk transformation. Increased levels of c-CrkI are observed in several human cancers. The SH3 domain of Crk can bind to multiple target molecules including the nonreceptor tyrosine kinase c-Abl, and three guanine-nucleotide exchange proteins, C3G, SOS and DOCK 180. ^ My study is based on the hypothesis that CrkI binds to its partners, such as C3G, SOS, Abl and DOCK 180 via SH3 domain to cause cell transformation. The aim of my study is to determine which Crk SH3-binding proteins are involved in transformation by CrkI. We found that siRNA-mediated knockdown of C3G and SOS suppresses the anchorage-independent growth of NIH-3T3 cells overexpressing c-CrkI; by contrast, knockdown of c-Abl or inhibition of Abl with the small-molecule inhibitor STI571 (Imatinib) enhances CrkI transformation. Subcutaneous injection of CrkI-transformed NIH-3T3 cells leads to tumor formation in nude mice. We found that knockdown of SOS efficiently suppresses the tumor growth in nude mice, whereas knockdown of Abl accelerates it. These results strongly suggest that SOS plays an essential role in CrkI induced transformation of mouse fibroblasts, and also suggest a surprising negative role for Abl kinase activity. CrkI-induced cell transformation activates downstream JNK pathway. We found that knockdown of C3G suppresses JNK activation, whereas knockdown of c-Abl or inhibition of Abl with STI571 enhances it. My study will not only help us get better understanding of those signaling pathways involved in Crk transformation, but also provide useful information for finding suitable therapeutic targets in cancer treatment. ^