RESUMO
Endoplasmic reticulum (ER) stress leads to activation of the unfolded protein response (UPR) that results in transient suppression of protein translation to allow recovery but leads to cell death when stress cannot be resolved. Central to initiation of the UPR is the activation of the ER transmembrane kinase protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK). Here we report that the thiol oxidoreductase ERp57 and protein disulfide isomerase-A1 (PDI), which belong to the same family of luminal ER oxidoreductases, have strikingly opposing roles in the regulation of PERK function. In HCT116 colon carcinoma cells, lentiviral depletion of ERp57 resulted in oxidation of PDI and activation of PERK, whereas depletion or chemical inhibition of PDI reduced PERK signaling and sensitized the cancer cells to hypoxia and ER stress. We conclude that oxidized PDI acts as a PERK activator, whereas ERp57 keeps PDI in a reduced state in the absence of ER stress. Thus, our study defines a new interface between metabolic redox signaling and PERK-dependent activation of the UPR and has the potential to influence future cancer therapies that target PERK signaling.
Assuntos
Pró-Colágeno-Prolina Dioxigenase/metabolismo , Isomerases de Dissulfetos de Proteínas/metabolismo , Resposta a Proteínas não Dobradas/fisiologia , eIF-2 Quinase/metabolismo , Fator 6 Ativador da Transcrição/genética , Fator 6 Ativador da Transcrição/metabolismo , Apoptose/genética , Apoptose/fisiologia , Linhagem Celular Tumoral , Sobrevivência Celular/genética , Sobrevivência Celular/fisiologia , Retículo Endoplasmático/genética , Retículo Endoplasmático/metabolismo , Estresse do Retículo Endoplasmático/genética , Estresse do Retículo Endoplasmático/fisiologia , Endorribonucleases/genética , Endorribonucleases/metabolismo , Células HCT116 , Humanos , Oxirredução , Pró-Colágeno-Prolina Dioxigenase/genética , Isomerases de Dissulfetos de Proteínas/genética , Proteínas Serina-Treonina Quinases/genética , Proteínas Serina-Treonina Quinases/metabolismo , Transdução de Sinais/genética , Transdução de Sinais/fisiologia , Resposta a Proteínas não Dobradas/genética , eIF-2 Quinase/genéticaRESUMO
Rapidly growing tumor cells must synthesize proteins at a high rate and therefore depend on an efficient folding and quality control system for nascent secretory proteins in the endoplasmic reticulum (ER). The ER resident thiol oxidoreductase ERp57 plays an important role in disulfide bond formation. Lentiviral, doxycycline-inducible ERp57 knockdown was combined with irradiation and treatment with chemotherapeutic agents. The knockdown of ERp57 significantly enhanced the apoptotic response to anticancer treatment in HCT116 colon cancer cells via a p53-dependent mechanism. Instead of a direct interaction with p53, depletion of ERp57 induced cell death via a selective activation of the PERK branch of the Unfolded Protein Response (UPR). In contrast, apoptosis was reduced in MDA-MB-231 breast cancer cells harboring mutant p53. Nevertheless, we observed a strong reduction of proliferation in response to ERp57 knockdown in both cell lines regardless of the p53 status. Depletion of ERp57 reduced the phosphorylation activity of the mTOR-complex1 (mTORC1) as demonstrated by reduction of p70S6K phosphorylation. Our data demonstrate that ERp57 is a promising target for anticancer therapy due to synergistic p53-dependent induction of apoptosis and p53-independent inhibition of proliferation.