Mitochondrial dysfunction matures Ras-induced early senescence to full senescence with a proinflammatory senescence-associated secretory phenotype in the fish cell line, EPC.

Fish cell lines differ from most mammalian diploid cell lines by the fact that cellular senescence is not readily induced. Previously, we demonstrated that the absence of the p16 gene in the fish genome prevents cells from reaching full senescence even when Ras is activated. Drosophila also lacks p16; however, early senescence triggered by Ras activation progresses to full senescence and is accompanied by a proinflammatory senescence-associated secretory phenotype (SASP), due to mitochondrial deficiency. It is unclear whether mitochondrial deficiency can also induce the maturation of Ras-induced early senescence (RIS) to full senescence along with a proinflammatory SASP in fish cell lines. Here, we investigated whether mitochondrial dysfunction induced by carbonyl cyanide 3-chlorophenylhydrazone (CCCP) in concert with activated Ras results in full senescence and whether this is accompanied by a proinflammatory SASPs in the EPC fish cell line. We found that although EPC cells with mitochondrial dysfunction exhibited a proinflammatory SASP, this did not result in permanent cell proliferation arrest or the upregulation of endogenous Ras expression. These findings suggest that other factors must act in concert with mitochondrial dysfunction to induce full senescence. The proliferation of EPC cells overexpressing a constitutively active mutant of H-Ras (H-Ras) was markedly reduced, irrespective of CCCP treatment. These findings suggest that there are similarities between the cellular senescence observed in fish and Drosophila cells lacking the p16 gene. However, it should be noted that fish cells differ from Drosophila cells in that mitochondrial dysfunction alone can induce proinflammatory SASP factors.