The Molecular Motor Myosin 5B and Its Folding Chaperone UNC45A Are Decreased in Colorectal Cancer.

Background & Aims: Colorectal cancer (CRC) ranks among the most common and deadliest cancers worldwide. Previous studies have found that the molecular motor Mysoin 5b (MYO5B) is decreased at the level of mRNA in CRC, but the mechanism behind this reduction remains unknown. In normal cells, MYO5B function is contingent on proper folding by the chaperone protein unc-45 myosin chaperone A (UNC45A). However, little is known about the role of UNC45A in CRC.

Methods: We examined RNA, methylation, and protein levels of MYO5B and UNC45A and identified microRNAs (miRNAs) targeting UNC45A in normal colon, colon adenocarcinoma (COAD) samples, cancer cell lines, and human colonic organoids. Cells were treated with the DNA-demethylating agent 5-aza-2'-deoxycytidine to examine the role of methylation in regulating MYO5B levels. Additionally, the UNC45A targeting miR-296-3p was inhibited in cells, and UNC45A levels were examined.

Results: Consistent with previous reports, we found that MYO5B mRNA was reduced in COAD compared with controls. We observed that the MYO5B gene was hyper-methylated in COAD and treatment of cancer cells with a demethylating compound increased MYO5B expression, suggesting that methylation silences MYO5B in COAD. The MYO5B folding chaperone UNC45A was not changed at the mRNA level but was decreased at the protein level. We identified several UNC45A targeting miRNAs that were elevated in COAD patients. We confirmed that these miRNAs were elevated in colon cancer cell lines compared with normal colonic organoids and found that inhibition of one of these miRNAs increased UNC45A protein.

Conclusions: These findings suggest that decreased levels of MYO5B in COAD may result from gene methylation and improper folding by UNC45A.