MYO5B levels are linked to microRNAs and UNC45A in colorectal cancer
Authors: Dooley Sarah , Digrazia Jessica , Engevik Amy 
Published: May 2023

Background: Colorectal cancer (CRC) is currently the third most common cancer worldwide and the second most deadly cancer. CRC is characterized by the loss of cellular architecture and altered polarity; features which can be controlled by cell-trafficking. In the intestine key cell trafficking pathways are controlled by Myosin 5b (MYO5B). Loss of functional MYO5B leads to profound changes in gastrointestinal epithelial cells including increased proliferation, alterations in tight junction proteins, and decreased differentiation. For MYO5B to be functional, it must be folded into the correct structure. This folding is accomplished by the chaperone UNC45A. Recent work indicates that MYO5B is decreased in gastric cancer and during colorectal tumor progression. However, the mechanism resulting in altered MYO5B expression in colorectal cancer is currently unknown. Hypothesis: We hypothesize that microRNAs regulate the expression of UNC45A which in turn can impact MYO5B function to promote colorectal cancer. Methods & Results: Analysis of high-throughput RNA-sequencing data in the Cancer Genome Atlas revealed that the MYO5B gene was hyper-methylated in CRC tumors (n=286) compared to controls (n=41). In gastric cancer, hyper-methylation leads to silencing of MYO5B gene expression. Consistent with findings in gastric cancer, we found that MYO5B gene expression was significantly reduced in CRC tumors. Immunostaining of CRC tumor arrays and analysis of the Clinical Proteomic Tumor Analysis Consortium demonstrated that MYO5B was also reduced at the protein level. For comparison, we examined MYO5B levels in normal human colonic organoid monolayers, immortalized human colon NCM-460 cells, and colon cancer cell lines T84 and HT29-MTX cells. By qPCR, we found that MYO5B gene expression was significantly reduced in the cancer cells compared to the human colonic organoids, confirming our database analysis. We reasoned that even if MYO5B was generated in CRC, it might not be functional if UNC45A was not present. Using the same databases, we found that UNC45A levels were unchanged at the level of gene expression, but significantly reduced at the level of protein. Analysis of miRMap data revealed that multiple microRNAs can target UNC45A. The top 10 UN45A-targeting microRNAs were all found to be increased in CRC compared to normal control tissue; suggesting that UNC45A protein may be diminished due to microRNA mediated cleavage. The functional significance of decreased MYO5B in CRC was highlighted by the fact that patients with lower levels of MYO5B had decreased survival compared to those with higher levels of MYO5B. Additionally, loss of MYO5B correlated with increased ribosome biogenesis; a key driver of tumor proliferation. Conclusions: These data indicate the MYO5B is likely decreased in CRC due to gene methylation and improper protein folding by UNC45A. Loss of MYO5B is significant since it is associated with a worse prognosis and c This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.