Protein Phosphatase 2a Inhibits Gastric Cancer Cell Glycolysis by Reducing MYC Signaling.

Abstract

Aerobic glycolysis, also known as the Warburg effect, has emerged as a hallmark of cancer and is associated with tumor progression and unfavorable clinical outcomes in cancer patients. PP2A is a highly conserved eukaryotic serine/threonine protein phosphatase that functions as a tumor suppressor in a variety of human cancers. However, the relationship between PP2A and the Warburg effect in gastric cancer has yet to be fully understood. In this study, the expression profile of two endogenous inhibitors of PP2A, SET and CIP2A, in gastric cancer, were analyzed by real-time quantitative polymerase chain reaction. Loss-of-function and gain-of-function studies were performed to investigate the roles of PP2A in gastric cancer cell proliferation and glycolysis. Cell biological, molecular, and biochemical approaches were employed to uncover the underlying mechanisms. The results showed that SET and CIP2A were overexpressed in gastric cancer and associated with a decreased PP2A activity. Pharmacological activation of PP2A with FTY-720 and DT-061 in two gastric cancer cell lines significantly reduced gastric cancer cell proliferation and glycolytic ability. Importantly, inhibition of PP2A activity by genetic silencing of PPP2R5A resulted in a growth advantage, which can be largely compromised by the addition of the glycolysis inhibitor 2-Deoxy-D-glucose, suggesting a glycolysis-dependent effect of PP2A in gastric cancer. Mechanistically, the well-known transcription factor and glycolysis regulator c-Myc was discovered as the functional mediator of PP2A in regulating cell glycolysis. Ectopic expression of a phosphorylation-mutant c-Myc resistant to PP2A (MycT58A) restored the inhibitory effect of FTY-720 and DT-061 on lactate production and glucose uptake. Furthermore, there was a close association between SET and CIP2A expression and c-Myc gene signatures in gastric cancer samples. Collectively, this study provides strong evidence of the involvement of PP2A in the Warburg effect and indicates that it could be a novel antitumor strategy to target tumor metabolism in gastric cancer.