Elucidation of the Roles and Functional Implications of the RET Receptor Tyrosine Kinase in Cancer

Abstract

RET is a receptor tyrosine kinase that plays important roles in normal development of the kidney, spermatogonia, and neuroendocrine tissues. RET is also implicated in various diseases, including tumors of the breast, prostate and thyroid. Normally, RET is activated through the formation of a tri-molecular complex involving its co-receptor, GFRα1, and its ligand, GDNF. The formation of this tri-molecular complex leads to the activation of many signaling pathways that induce cellular processes such as cell survival, differentiation and proliferation. RET is expressed in approximately 30-70% breast cancer cases. While initial work suggested that RET was associated with luminal forms of breast cancer, more recent data suggest that this receptor tyrosine kinase may be more broadly implicated with multiple subtypes of breast cancer. Here, we used in vitro cell-based models to further investigate the role of RET in breast cancer. Through our analysis, we found five RET-positive breast cancer cell lines, and confirmed the suitability of these models to explore the role of RET in breast cancer. Further, our data suggest that RET activation through GDNF treatment increases proliferation of most of these breast cancer cells. In a high throughput screen using a protein domain microarray dataset, a potential interaction between RET and the BCAR3 adaptor protein was previously identified. To gain a more mechanistic understanding of RET’s contribution to cancer, we characterized and explored the functional implications of RET’s interaction with the adaptor protein, BCAR3. Here, we confirm that RET and BCAR3 interact, and that it is a direct interaction between the SH2 domain of BCAR3 and RET. As we were not able to identify in our studies a suitable breast cancer cell model in which RET and BCAR3 were co-expressed, we used SH-SY5Y neuroblastoma cells, a cell line that co-expresses RET and BCAR3, for our functional analyses. Our data suggest that BCAR3 knockdown in SH-SY5Y neuroblastoma cells has a broad role in proliferation and adhesion, independent of RET. Further research is required to fully elucidate the functional relevance of the RET-BCAR3 association.