Impaired inhibition of NF-κB activity by melanoma-associated p16INK4a mutations

The cyclin-dependent kinase inhibitor p16INK4a has been identified as tumor suppressor and melanoma predisposition gene. While its cell cycle inhibitory ability is important in protecting cells from uncontrolled growth and possible tumor formation, other functions of p16INK4a are likely to contribute to its nature as a tumor suppressor. p16INK4a binding and inhibition of the transcription factor NF-κB has been shown and is consistent with the reports of abnormally increased NF-κB activity in various cancers including melanoma. Here, we present evidence that wild type p16INK4a binds to the NF-κB subunit RelA more efficiently than melanoma-associated p16INK4a mutations. Furthermore, whereas wild type p16INK4a strongly inhibits NF-κB transcriptional activity, a subset of melanoma-associated p16INK4a mutants show reduced NF-κB inhibitory function. p16INK4a does not affect NF-κB nuclear translocation or DNA binding, suggesting a mechanism that reduces NF-κB transactivation activity.