The circMYBL2-encoded p185 protein suppresses colorectal cancer progression by inhibiting serine biosynthesis.

Circular RNAs (circRNAs) are a class of covalently closed single-stranded loop RNAs that have been implicated to play a functional role in almost all types of cancers. Previous studies have revealed that circMYBL2 acts as a tumor-promoting circRNA. Here, we found that circMYBL2 in colorectal cancer (CRC) encodes a 185-amino acid protein, p185. Functionally, circMYBL2-encoded p185 suppressed the growth and aggressiveness of CRC cells in vitro and in vivo. Mechanistically, p185 counteracted UCHL3-mediated deubiquitination of phosphoglycerate dehydrogenase (PHGDH) by competitively binding to the C1 domain of UCHL3, resulting in PHGDH degradation and a subsequent reduction in serine and glycine biosynthesis. These data revealed that the circMYBL2-encoded p185 isoform serves as a tumor suppressor to inhibit the progression of CRC by reducing serine biosynthesis.