AKT1 Is Required for a Complete Palbociclib-Induced Senescence Phenotype in BRAF-V600E-Driven Human Melanoma

Cellular senescence is a carefully regulated process of proliferative arrest accompanied by numerous functional and morphologic changes. Senescence allows damaged cells to avoid neoplastic proliferation, however induction of the senescence-associated secretory phenotype (SASP) can promote tumor growth. The complexity of the senescence response may limit the efficacy of anti-neoplastic agents, such as CDK4/6 inhibitors (Cdk4/6i), that induce a senescence-like, non-proliferative state in tumor cells. The AKT kinase family plays an important role in cellular growth and division, and is commonly hyperactive in many cancers including melanoma. AKT activity has also been implicated in regulation of senescence. The three AKT isoforms play both redundant and unique roles in tumorigenesis and cancer progression. To interrogate the role of AKT isoforms in the induction of cellular senescence by Cdk4/6i, we generated isoform specific AKT knockout human BRAF-V600E mutated melanoma cell lines. We found that the CDK4/6i Palbociclib induced a form of senescence in these cells that was dependent on AKT1. As a potential mechanism, we evaluated the activity of the cGAS-STING pathway, recently implicated in cellular senescence. While we showed cGAS-STING function to be dependent on AKT1, pharmacologic inhibition of either cGAS or STING had little effect on senescence. However, we found SASP factors to require NF-kB function, in part dependent on a stimulatory phosphorylation of IKKα by AKT1 previously reported in other models. In summary, we provide the first evidence of a novel, isoform specific role for AKT1 in therapy-induced senescence in human melanoma cells acting through NF-kB but independent of cGAS-STING.