Tumor suppressor p16INK4a inhibits cancer cell growth by down-regulating eEF1A2 through a direct interaction

The tumor suppressor p16INK4a protein 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 known to function as a putative oncogene in cancers. The p16INK4a protein interacted with all but the D2 (250–327 aa) domain of eEF1A2. Ectopic expression of p16INK4a decreased the expression of eEF1A2 and inhibited cancer cell growth. Furthermore, suppression of protein synthesis by expression of p16INK4a ex vivo was verified by luciferase reporter activity. Microinjection of p16INK4a mRNA into the cytoplasm of Xenopus embryos suppressed the luciferase mRNA translation, whereas the combination of p16INK4a and morpholino-eEF1A2 showed a further reduction in translational activity. We conclude that the interaction of p16INK4a with eEF1A2 and subsequent down-regulation of the expression and function of eEF1A2 is a novel mechanism explaining the anti-proliferative effects of p16INK4a.