PKCη promotes senescence induced by oxidative stress and chemotherapy

Senescence is characterized by permanent cell-cycle arrest despite continued viability and metabolic activity, in conjunction with the secretion of a complex mixture of extracellular proteins and soluble factors known as the senescence-associated secretory phenotype (SASP). Cellular senescence has been shown to prevent the proliferation of potentially tumorigenic cells, and is thus generally considered a tumor suppressive process. However, some SASP components may act as pro-tumorigenic mediators on premalignant cells in the microenvironment. A limited number of studies indicated that protein kinase C (PKC) has a role in senescence, with different isoforms having opposing effects. It is therefore important to elucidate the functional role of specific PKCs in senescence. Here we show that PKC η , an epithelial specific and anti-apoptotic kinase, promotes senescence induced by oxidative stress and DNA damage. We further demonstrate that PKC η promotes senescence through its ability to upregulate the expression of the cell cycle inhibitors p21 Cip1 and p27 Kip1 and enhance transcription and secretion of interleukin-6 (IL-6). Moreover, we demonstrate that PKC η creates a positive loop for reinforcing senescence by increasing the transcription of both IL-6 and IL-6 receptor, whereas the expression of IL-8 is specifically suppressed by PKC η . Thus, the presence/absence of PKC η modulates major components of SASP. Furthermore, we show that the human polymorphic variant of PKC η , 374I, that exhibits higher kinase activity in comparison to WT-374V, is also more effective in IL-6 secretion, p21 Cip1 expression and the promotion of senescence, further supporting a role for PKC η in senescence. As there is now considerable interest in senescence activation/elimination to control tumor progression, it is first crucial to reveal the molecular regulators of senescence. This will improve our ability to develop new strategies to harness senescence as a potential cancer therapy in the future.