Sam68 promotes aerobic glycolysis in colorectal cancer by regulating PKM2 alternative splicing.

BACKGROUND

Sam68, an RNA-binding protein, exerts oncogenic functions in several types of cancer. However, the specific functions and mechanisms of Sam68 in colorectal cancer (CRC) had not been previously clarified. Pyruvate kinase muscle (PKM)2 is the key rate-limiting enzyme in glycolysis, and PKM2 maintains the glycolysis-dominant energy metabolism in most cancer cells.

METHODS

CCK8 assay was performed to show the effect of Sam68 on cell growth. Pyruvate kinase activity and lactate detection assays were performed to analyze the effects of Sam68 on aerobic glycolysis. RNA immunoprecipitation (RIP) was used to detect the binding of Sam68 to the sequence. Western blot and real-time PCR were executed to analyze the regulation of by Sam68.

RESULTS

Gain-of-function and loss-of-function studies showed that ectopic expression of Sam68 promoted glycolysis and cell proliferation in CRC cells, whereas Sam68 knockdown inhibited glycolysis and cell proliferation. Mechanically, Sam68 modulated the expression profile of pyruvate kinase (PKM2 or PKM1) by regulating its alternative splicing. Overexpression of Sam68 was associated with decreased / ratio, which positively contributed to the glycolysis procedure. Sam68 significantly promoted cell proliferation and caused a decrease of / ratio, resulting in the metabolism of glucose switched from oxidative phosphorylation to glycolysis in CRC cells. Besides, Sam68 enhanced mRNA transport from the nucleus to cytoplasm and increased the expression of PKM2 protein, resulting in elevated pyruvate kinase activity and lactate production.

CONCLUSIONS

These findings suggested that Sam68 affected cell growth and glycolysis pathway by regulating the alternative splicing and expression of PKM2 in CRC.