A Novel Role for SUMO-specific Proteases in Senescence of Human Cells

Senescence can be induced prematurely in normal human cells by stress, DNA damage, inappropriate mitogenic stimuli, or the overexpression of tumor suppressors, such as p53. In a genetic screen to isolate mediators of induced senescence, we isolated SENP6, a SUMO-specific protease. Sumoylation, specifically factors that increase sumoylation such as PIASy and SUMO-2/3, have been suggested to play a role in senescence. To study the role of desumoylating factors in senescence we used shRNA targeting to stably repress expression of the dominant SUMO-specific protease in humans, SENP1. We demonstrated that repression of SENP1 in early passage human fibroblasts (HFFs) resulted in a rapid, p53-dependent senescence response. Repression of SENP1 resulted in enhanced transcriptional activity of p53, indicating activation of the p53 pathway, but did not trigger a DNA damage response that is normally associated with p53-mediated senescence. In addition, we showed that repression of SENP1 resulted in a global accumulation of sumoylated proteins as well as localized accumulation of SUMO-1 and SUMO-2 at nuclear PML bodies. The SUMO/PML bodies also contained p53 and CBP, which are components of a prosenescence complex observed in other induced and replicative senescence systems. Senescence induced by repression of SENP1 closely resembled replicative senescence, suggesting that induced senescence systems, such as senescence induced by SENP1 repression, may permit the study or identification of genes that mediate the senescence process.