RESUMO
The incidence of carcinomas highly increases with age. However, the initial steps of the age-related molecular carcinogenic processes remain poorly characterized. We previously showed that normal human epidermal keratinocytes spontaneously and systematically escape from senescence to give rise to preneoplastic emerging cells through a process called post-senescence neoplastic emergence (PSNE). To identify molecular pathways involved in the switch from senescence to pre-transformation, we performed Connectivity Map analyses and DAVID functional annotations followed by hierarchical clustering and multidimensional scaling of the gene expression signature of PSNE cells. We identified endoplasmic reticulum stress related pathways as key regulators of PSNE. Invalidation by RNA interference of the UPR sensors PERK, ATF6α, but not IRE1α, delayed the occurrence of senescence when performed in pre-senescent cells, and increased the PSNE frequency when performed in already senescent cells. Conversely, endoplasmic reticulum stress inducers applied to already senescent cells decreased the frequency of PSNE. In conclusion, these results indicate that the activation of the UPR could protect from the early carcinogenic steps by senescence evasion. This opens new avenues to explore therapeutics that could be useful in decreasing the age-associated tumor incidence.
Assuntos
Fator 6 Ativador da Transcrição/genética , Transformação Celular Neoplásica/genética , Transcriptoma , Resposta a Proteínas não Dobradas/genética , eIF-2 Quinase/genética , Fator 6 Ativador da Transcrição/metabolismo , Envelhecimento/genética , Envelhecimento/patologia , Linhagem Celular , Transformação Celular Neoplásica/metabolismo , Transformação Celular Neoplásica/patologia , Senescência Celular/efeitos dos fármacos , Senescência Celular/genética , Estresse do Retículo Endoplasmático/efeitos dos fármacos , Estresse do Retículo Endoplasmático/genética , Humanos , Queratinócitos/efeitos dos fármacos , Queratinócitos/metabolismo , Preparações Farmacêuticas/administração & dosagem , Preparações Farmacêuticas/classificação , Lesões Pré-Cancerosas/genética , Lesões Pré-Cancerosas/metabolismo , Lesões Pré-Cancerosas/patologia , Interferência de RNA , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/genética , Resposta a Proteínas não Dobradas/efeitos dos fármacos , eIF-2 Quinase/metabolismoRESUMO
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.
Assuntos
Fator 6 Ativador da Transcrição/metabolismo , Senescência Celular , Ciclo-Oxigenase 2/metabolismo , Dinoprostona/metabolismo , Fibroblastos/metabolismo , Transdução de Sinais , Resposta a Proteínas não Dobradas , Ciclo-Oxigenase 2/genética , Dinoprostona/genética , Fibroblastos/patologia , HumanosRESUMO
Cellular senescence is known as an anti-tumor barrier and is characterized by a number of determinants including cell cycle arrest, senescence associated ß-galactosidase activity and secretion of pro-inflammatory mediators. Senescent cells are also subjected to enlargement, cytoskeleton-mediated shape changes and organelle alterations. However, the underlying molecular mechanisms responsible for these last changes remain still uncharacterized. Herein, we have identified the Unfolded Protein Response (UPR) as a player controlling some morphological aspects of the senescent phenotype. We show that senescent fibroblasts exhibit ER expansion and mild UPR activation, but conserve an ER stress adaptive capacity similar to that of exponentially growing cells. By genetically invalidating the three UPR sensors in senescent fibroblasts, we demonstrated that ATF6α signaling dictates senescence-associated cell shape modifications. We also show that ER expansion and increased secretion of the pro-inflammatory mediator IL6 were partly reversed by silencing ATF6α in senescent cells. Moreover, ATF6α drives the increase of senescence associated-ß-galactosidase activity. Collectively, these findings unveil a novel and central role for ATF6α in the establishment of morphological features of senescence in normal human primary fibroblasts.
