Tumor suppressor p16^INK4A inhibits cancer cell growth by downregulating eEF1A2 through a direct interaction

The tumor suppressor protein p^16INK4a is a member of the INK4 family of cyclin-dependent kinase (Cdk) inhibitors, which are involved in the regulation of the eukaryotic cell cycle. However, the mechanisms underlying the anti-proliferative effects of p16INK4a have not been fully elucidated. Using yeast two-hybrid screening, we identified the eukaryotic elongation factor (eEF)1A2 as a novel interacting partner of p16INK4a. eEF1A2 is thought to function as an oncogene in cancers. The p^16INK4a protein interacted with all but the D2 (250-327 aa) domain of eEF1A2. Ectopic expression of pp16^INK4a decreased the expression of eEF1A2 and inhibited cancer cell growth. Furthermore, suppression of protein synthesis by expression of pp16^INK4a ex vivo was verified by luciferase reporter activity. Microinjection of pp16^INK4a mRNA into the cytoplasm of Xenopus embryos suppressed the luciferase mRNA translation, whereas the combination of pp16^INK4a and morpholino-eEF1A2 resulted in a further reduction in translational activity. We conclude that the interaction of pp16^INK4a with eEF1A2, and subsequent downregulation of the expression and function of eEF1A2 is a novel mechanism explaining the anti-proliferative effects of p16^INK4a.