Dr. Rishi Gara Thesis Paper

Abstract:

Over 80% of colon cancer development and progression is a result of the deregulation of the β-catenin signaling pathway. Therefore, it is imperative to understand the expression, subcellular localization, and regulation of β-catenin, in order to develop effective colon cancer treatment modalities. Herein, for the first time, we demonstrate that a novel serine-threonine kinase, Protein Kinase D1 (PKD1), modulates the functions of β-catenin to suppress colon cancer growth. Analysis of normal and colon cancer tissues reveals co-localization of PKD1 with β-catenin in the colon crypts and shows severe downregulation of PKD1 expression in advanced stages of colon cancer. This PKD1 downregulation corresponds with the aberrant expression and nuclear localization of β-catenin. In-vitro investigation of the PKD1-β-catenin interaction in SW480 and SW48 colon cancer cell lines reveals that PKD1 overexpression suppresses cell proliferation and clonogenic potential and enhances cell-cell aggregation. We also revealed that PKD1 directly interacts with β-catenin and attenuates β-catenin transcriptional activity by decreasing the levels of nuclear β-catenin, a process that requires an enzymatically active catalytic domain in PKD1. Additionally, we show that inhibition of nuclear β-catenin transcriptional activity is primarily influenced by nuclear PKD1. This subcellular modulation of β-catenin results in an enhanced membrane localization of β-catenin, and thereby, increases cell-cell adhesion. We further extend these studies to investigate in vivo functions of PKD1 in a xenograft mouse model. Our results indicate that PKD1 overexpression delayed tumor appearance, enhanced necrosis, and lowered tumor hypoxia compared to control tumors. Overall, our results demonstrate a putative tumor-suppressor function of PKD1 in colon tumorigenesis, via modulation of β-catenin functions in cells.

Introduction:

Colorectal cancer is the third most commonly diagnosed cancer and the...