Pdcd4-Rictor Interaction Suppresses PFKFB3 to inhibit Tumorigenesis

Programmed cell death 4 (Pdcd4) is a well-established tumor suppressor and 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 direct interaction 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 the translation-independent mechanism by which Pdcd4 disrupts mTORC2 signaling and downregulates PFKFB3 plays a critical role in suppressing NSCLC growth and glycolysis.