Initially described as a potent cyclin-dependent kinase inhibitor and thus a negative regulator of cell cycle, p21waf1/cip1 is a protein whose expression is often altered in cancer. Paradoxically, its upregulation has been correlated with aggressiveness and poor prognosis. p21waf1/cip1 fits the definition of antagonistic duality, since its cytoplasmic functions differ from its nuclear tasks. Our group had previously developed a murine melanoma progression model, which culminated in the establishment of cell lines representing different stages in melanoma genesis. Surprisingly, we detected overexpression of p21waf1/cip1 protein in a metastatic melanoma cell line (4C11+), which exhibits highly aggressive behavior. Despite its aberrant overexpression has already been described in melanoma, including metastases, little is known about the impact of its ectopic overexpression in melanoma aggressiveness. We performed viral-mediated overexpression and downregulation of p21waf1/cip1 in the non-metastatic melanoma lineage (4C11-) which does not express this protein and in the metastatic melanoma cell line (4C11+), respectively, and assessed for its impact on melanoma survival upon Dacarbazine treatment. Flow cytometry analyses were conducted to investigate p21waf1/cip1 cell cycle control in these lineages. Through Western blot analysis, we also evaluated the expression of phospho-Akt and phospho-p21 as well as p21waf1/cip1 subcellular localization, in an attempt to investigate the mechanisms underlying ectopic location of p21waf1/cip1 and thus its oncogenic activities. Our research shows that upregulated cytoplasmic p21waf1/cip1 increases metastatic melanoma survival upon Dacarbazine treatment, which can be reverted by p21waf1/cip1 silencing. We also detected high levels of phospho-Akt(Ser473) and phospho-p21(Thr145), which are determinant in promoting p21waf1/cip1 cytoplasmic retention. Using Wortmannin, a PI3K inhibitor that prevents Akt activation, cytoplasmic p21waf1/cip1 level was substantially diminished. Importantly, we identified high levels of p21waf1/cip1 and phospho-p21waf1/cip1 in patients-derived metastatic melanoma cells. We provided new insights about molecular pathways involved in Dacarbazine-associated resistance in melanomas, pointing p21waf1/cip1 and PI3K/Akt as key contributors in this process. Altogether, our findings contribute to not only design new therapeutic approaches against metastatic melanoma, but also help to elucidate the contradictory and complex role exerted by p21waf1/cip1 in cancer.

Supported by FAPESP and CNPq

Citation Format: Gabriela Nana Colaneri, Adriana Taveira Cruz, Débora CP Silva, Roberta Sessa Stilhano, Sang Won Han, Miriam G. Jasiulionis. Cytoplasmic p21WAF1/CIP1 increases metastatic melanoma survival upon chemotherapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1167.