Pdcd4–Rictor interaction suppresses mTORC2-PFKFB3 axis and tumorigenesis in NSCLC

Abstract

Programmed cell death 4 (Pdcd4) is a well-established tumor suppressor as well as an inhibitor of protein translation. Although Pdcd4-mediated translational repression contributes to tumor suppression, emerging evidence suggests that Pdcd4 also exerts translation-independent functions. In this study, we found that Pdcd4 suppresses tumorigenesis through disrupting mTORC2 complex formation by binding with the rapamycin-insensitive companion of mTOR (Rictor), a core component of the mTORC2 complex. Using deletion mapping and site-directed mutagenesis, we defined the Rictor-binding domain of Pdcd4 and identified three critical residues, R105, K108, and R110, for this interaction. Co-immunoprecipitation and in vitro kinase assays demonstrated that Pdcd4 binding to Rictor disrupted mTORC2 complex assembly and inhibited its kinase activity. Reverse phase protein array analysis revealed that 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3), a key regulator of glycolysis, was markedly upregulated in Pdcd4-knockdown cells. Restoration of wild-type Pdcd4, but not a Rictor-binding–deficient mutant, reduced PFKFB3 protein abundance by promoting ubiquitin–proteasome–mediated degradation. Functionally, Pdcd4–Rictor interaction suppressed glycolytic activity and inhibited tumor cell proliferation in cultured cells and xenograft models. Consistent with these findings, non–small cell lung cancer (NSCLC) tissues exhibited significantly elevated protein levels of Rictor and PFKFB3 compared with adjacent normal tissues, with a positive correlation between their expression. Collectively, these results demonstrate that Pdcd4-Rictor interaction disrupts mTORC2 signaling and downregulates PFKFB3, which plays a critical role in suppressing NSCLC growth and glycolysis.