Resistance to premature senescence in the Epithelioma papulosum cyprini fish cell line is associated with the absence of PML nuclear bodies

Cell lines derived from fish tissues are resistant to premature senescence under typical culture conditions. Previously, we demonstrated that fish genomes do not have a p16^INK4a/Arf locus and that the absence of this locus underlies the lack of senescence in cultured fish cells. However, other factors may also contribute to this resistance. In amniotes, promyelocytic leukemia (PML)-IV proteins are involved in the generation of PML nuclear bodies (PML NBs), which are connected with premature senescence. The lack of a pml gene in fish genomes may be involved in the mechanism of resistance to cellular senescence. Heterologous expression of human PML-IV in an Epithelioma papulosum cyprini cell line induced the formation of PML NB-like speckled structures. The cells displayed characteristic features of cellular senescence, namely, growth suppression, a large, flattened morphology, and increased SA-β-gal activity. Additionally, the levels of proinflammatory senescence-associated secretory phenotype (SASP) factors increased in the cells, suggesting a link between the absence of PML NBs and cellular resistance to senescence. Expression of the CCAT enhancer binding protein beta gene, which encodes a transcription factor of proinflammatory SASPs, was not increased, nor was there any elevation in the activity of NF-κB, a transcription factor for proinflammatory SASP factors and C/EBPβ. Epigenetic regulatory mechanisms may contribute to the induction of proinflammatory SASP factors by PML NBs.