The ATF6α arm of the Unfolded Protein Response mediates replicative senescence in human fibroblasts through a COX2/prostaglandin E2 intracrine pathway

Senescence is recognized as a cellular state acquired in response to various stresses. It occurs in correlation with the activation of the Unfolded Protein Response (UPR) pathway. However, the UPR targets which might relay the establishment of the senescent phenotype are not known. Herein, we investigated whether the up-regulation of the COX2 (PTGS2) limiting enzyme in the prostaglandin biosynthesis pathway, known to mediate cellular senescence in normal human fibroblasts, could be controlled by the UPR sensors ATF6α, IRE1α and PERK. We found that UPR inducers cause premature senescence through an increase in COX2 expression, and an overproduction of prostaglandin E2 (PGE2) in wild type fibroblasts but not in ATF6α invalidated ones. In replicative senescent fibroblasts, ATF6α and IRE1α silencing abrogated COX2 up-regulation and PGE2 production. The expanded ER and the large cell size characteristics of senescent fibroblasts were both reduced upon the invalidation of COX2 as well as ATF6α. These effects of the ATF6α invalidation were prevented by favoring the import of PGE2, but not just by supplying extracellular PGE2. Taken together, our results support a critical role of ATF6α in the establishment and maintenance of cellular senescence in normal human fibroblasts via the up-regulation of a COX2/PGE2 intracrine pathway.