Cell Cycle and Senescence Mutual Exclusivity Analysis of Genetic and Epigenetic Drivers in Melanoma Identifies a Link Between p14 and RARb Signaling

Melanoma genomes contain thousands of alterations including: mutations, copy number alterations, structural aberrations, and methylation changes. The bulk of this variation is stochastic and functionally neutral, with only a small minority representing "drivers" that contribute to the genesis and maintenance of tumors. Drivers are often directly or inversely correlated across tumors, reflecting the molecular and regulatory signaling pathways in which they operate. Here, a profile of genetic and epigenetic drivers in 110 human melanoma cell lines was generated and searched for non-random distribution patterns. Statistically significant mutual exclusivity was revealed among components of each of the p16-CDK4-RB, RAS-RAF-MEK-ERK and PI3K-AKT signaling pathways. In addition, an inverse correlation was observed between promoter hypermethylation of retinoic acid receptor b (RARB) and CDKN2A alterations affecting p14 (P < 0.0001), suggesting a functional link between RARb signaling and the melanoma-suppressive activities of p14. Mechanistically, all-trans retinoic acid (ATRA) treatment increased the expression of p14 in primary human melanocytes and the steady-state levels of p14 in these cells were shown to be regulated via RARb. Furthermore, the ability of ATRA to induce senescence is reduced in p14-depleted melanocytes, and we provide proof-of-concept that ATRA can induce irreversible growth arrest in melanoma cells with an intact RARb-p14 signaling axis, independent of p16 and p53