MYO5B levels are linked to microRNAs and UNC45A in colorectal cancer
Authors: Dooley Sarah , Stubler Rachel , DiGrazia Jessica , Engevik Amy 
Published: May 2024

Background: Colorectal cancer (CRC) is currently the third most prevalent cancer worldwide and ranks as the second deadliest. Colon cancer is characterized by disruption in cellular structure and polarity, processes that are commonly regulated by cell traffcking. The molecular motor Myosin 5b (Myo5b) is a key component of intracellular traffcking in the intestinal epithelium. Myo5b moves along F-actin tracks to transport cargo to and from the apical membrane. When Myo5b function is impaired, it leads to significant changes in gastrointestinal epithelial cells, including hyper-proliferation, alterations in tight junction proteins, and reduced differentiation. For Myo5b to function properly it must be properly folded; a process regulated by the myosin chaperone Unc45a. Recent work demonstrates that Myo5b levels are decreased in gastric cancer and during the progression of colorectal tumors. However, the mechanism driving this altered Myo5b expression in colorectal cancer remains unknown. We hypothesize that microRNAs regulate the expression of Unc45a, which subsequently impacts Myo5b function, promoting colorectal cancer. Methods and Results: Analysis of high-throughput RNA-sequencing data from the Cancer Genome Atlas (TCGA) revealed hyper-methylation of the Myo5b gene in CRC tumors (n=286) compared to controls (n=41). Findings in gastric cancer have shown that hyper-methylation leads to the silencing of Myo5b gene expression. Consistent with these findings, we observe a significant reduction in Myo5b gene expression in CRC tumors. Immunostaining of CRC tumor arrays and analysis from the Clinical Proteomic Tumor Analysis Consortium (CPTAC) demonstrated a corresponding decrease in Myo5b protein levels. For comparison, we examined Myo5b levels in normal human colonic organoids and the colon cancer cell lines T84,HT-29, HT29-MTX, HCT-8 and HCT-116. Using qPCR, we confirmed a significant reduction in Myo5b gene expression in cancer cells compared to human colonic organoids. We postulated that even if Myo5b was expressed in CRC, it might not function properly if Unc45a function was perturbed. Using the same databases, we found that while Unc45a gene expression levels remain unchanged, its protein levels were significantly reduced. Analysis of the miRMap data reveled multiple microRNAs that could target Unc45a. The top 10 Unc45a-targeting microRNAs were all found to be elevated in CRC compared to normal control tissue, suggesting that microRNAs may lead to reduced Unc45a protein levels. The functional importance of decreased Myo5b in CRC was underscored by the observation that CRC patients with lower levels of Myo5b had reduced survival compared to those CRC patients with higher levels of Myo5b. Additionally, the loss of Myo5b correlated with increased ribosome biogenesis, a key driver of tumor proliferation. Conclusions: These findings indicate that reduced Myo5b in CRC may be attributed to gene methylation and impaired protein folding by Unc45a. The loss of Myo5b holds significance, as it is associated with poorer prognosis and linked with cancer progression. National Diabetes and Digestive and Kidney Diseases Grant R43 DK109820, RO1 DK048370, KO1 DK121869, MUSC start up funds, Histochemical 2022 Cornerstone Grant, and NIDDK T32. This is the full abstract presented at the American Physiology Summit 2024 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.