The sequential proliferation, lineage-specific differentiation, migration and death of the epithelial cells of the intestinal mucosa is a tightly regulated process modulated by a broad range of regulatory peptides, neurotransmitters, bioactive lipids and differentiation signals. Many of these stimuli act through heptahelical G protein-coupled receptors (GPCRs). Despite their fundamental importance, the intracellular signal transduction mechanisms involved remain incompletely understood. Protein kinase D (PKD) is emerging as a key node in GPCR signaling and consequently the understanding of PKD regulation and function in intestinal epithelial cells is of intense interest and potential impact. The highly conserved Hippo/YAP/TAZ pathway is also attracting strong attention as a key regulator of organ-size, tissue regeneration, carcinogenesis and GPCR signaling. Based on our preliminary results, we identified a novel crosstalk between PKD and YAP that plays a critical role in promoting intestinal epithelial cell proliferation. Further preliminary results demonstrate that FDA-approved statins act as potent inhibitors of GPCR/PKD-induced YAP-induced transcription and DNA synthesis in intestinal epithelial cells. Statins also abrogated enteroid formation in vitro and prevented regeneration of colon mucosa after injury. Consequently, our central hypotheses are: 1) PKD/YAP/TAZ signaling plays a vital role in promoting the proliferation of intestinal epithelial cells including progenitor/stem cells and 2) statins restrain intestinal epithelial cell proliferation by targeting the PKD/YAP/TAZ axis in these cells. An important translational corollary is that the widely used drugs of the statin family provide a novel strategy in the chemoprevention of colorectal (CRC) and IBD-related CRC through inhibition of the growth-promoting PKD/YAP/TAZ axis.
Three Specific Aims are proposed:
SPECIFIC AIM 1 : Identify the mechanism(s) by which the lipid- lowering drugs of the statin family target signaling through the PKD/YAP axis in intestinal epithelial cells;
SPECIFIC AIM 2 : Characterize the impact of statin-induced inhibition of the PKD/YAP/TEAD pathway on the proliferation of intestinal epithelial cells in vivo, including progenitor and Lgr5+ intestinal stem cells and enteroids in 3 D cultures in vitro;
SPECIFIC AIM 3 : Determine the role of the statin-sensitive PKD/YAP/TEAD axis in intestinal epithelial cell regeneration and carcinogenesis. We anticipate that the outcome of this proposal will provide a robust rationale for implementing innovative therapeutic interventions targeting the PKD/YAP signaling axis in proliferative diseases of the digestive system, including CRC and IBD- associated CRC in US veterans as well as in the US population at large.
The mechanistic studies proposed in this application on the impact of statins on the function of the PKD/YAP axis using genetically modified mice and intestinal epithelial cells in culture are of importance to define the role of this novel pathway in the regulation of intestinal epithelial stem cell multiplication. These studies are of high significance for Colorectal Cancer (CRC), Inflammatory Bowel Disease (IBD) and regenerative medicine. The completion of the proposed mechanistic studies using statins will provide a robust intellectual framework for targeting the PKD/YAP axis for therapy of CRC, I B D - r e l a t e d C R C and other intestinal diseases in US Veterans as well as in the US population at large.
