Altered Expression of Shorter p53 Family Isoforms Can Impact Melanoma Aggressiveness

SIMPLE SUMMARY: TP53 is one of the most important tumor suppressor genes, which has been found to be mutated in more than half of human cancers and is considered the “Guardian of the genome”. However, it is rarely mutated in melanoma (less than 20% of cases). Although several cancer-oriented studies focus on p53 biology, only recently have researchers started to appreciate the importance of shorter p53 isoforms as potential modifiers of p53-dependent responses. In this study, we showed that melanoma-derived cell lines express a wide array of p53 and p73 isoforms, with Δ160p53α as the most variable. For the first time, we reported that Δ160p53α, and to a lesser extent Δ160p53β, can be recruited on chromatin, and Δ160p53γ can localize in perinuclear foci; moreover, all Δ160p53 isoforms can stimulate proliferation and, potentially, migration. Lastly, we showed an increased expression of the potentially pro-oncogenic Δ40p53β isoform and a decrease in the tumor-suppressive TAp73β isoform in melanoma cells resistant to vemurafenib (BRAF inhibitor). With this study, we suggest that p53 family isoforms play a significant role in melanoma cells’ aggressiveness. ABSTRACT: Cutaneous melanoma is the most aggressive form of skin cancer. Despite the significant advances in the management of melanoma in recent decades, it still represents a challenge for clinicians. The TP53 gene, the guardian of the genome, which is altered in more than 50% of human cancers, is rarely mutated in melanoma. More recently, researchers started to appreciate the importance of shorter p53 isoforms as potential modifiers of the p53-dependent responses. We analyzed the expression of p53 and p73 isoforms both at the RNA and protein level in a panel of melanoma-derived cell lines with different TP53 and BRAF status, in normal conditions or upon treatment with common anti-cancer DNA damaging agents or targeted therapy. Using lentiviral vectors, we also generated stable clones of H1299 p53 null cells over-expressing the less characterized isoforms Δ160p53α, Δ160p53β, and Δ160p53γ. Further, we obtained two melanoma-derived cell lines resistant to BRAF inhibitor vemurafenib. We observed that melanoma cell lines expressed a wide array of p53 and p73 isoforms, with Δ160p53α as the most variable one. We demonstrated for the first time that Δ160p53α, and to a lesser extent Δ160p53β, can be recruited on chromatin, and that Δ160p53γ can localize in perinuclear foci; moreover, all Δ160p53 isoforms can stimulate proliferation and in vitro migration. Lastly, vemurafenib-resistant melanoma cells showed an altered expression of p53 and p73 isoforms, namely an increased expression of potentially pro-oncogenic Δ40p53β and a decrease in tumor-suppressive TAp73β. We therefore propose that p53 family isoforms can play a role in melanoma cells’ aggressiveness.