Melatonin Induces PERK-ATF4 Unfolded Protein Response and Apoptosis in Human Choriocarcinoma Cells

Melatonin, an indolamine primarily recognized for regulating circadian rhythms, has also demonstrated notable antitumoral properties. Melatonin induces endoplasmic reticulum (ER) stress, modulates autophagy, and promotes apoptosis in various tumors, including gastric, ovarian, cervical, oral tongue, colorectal, renal, hepatic, and bladder cancer. In placental choriocarcinoma, melatonin reduces cell viability and induces apoptosis by inhibiting autophagy and disrupting the mitochondrial membrane potential. However, its effects on ER stress and the unfolded protein response (UPR) pathway remain unexplored. It is hypothesized here that the proapoptotic effects of melatonin in choriocarcinoma cells occur through the activation of the UPR pathway. The factors implicated in the UPR (PERK, IRE1ɑ, ATF6, GRP78, ATF4, CHOP, P-eIF2α) pathways were evaluated by Western blot, RT-qPCR, and flow cytometry in BeWo (human choriocarcinoma) cells treated with or without melatonin (1 mM). Melatonin significantly increased protein levels of GRP78 (p = 0.0329), IRE1α (p = 0.0394), p-eIF2α (p = 0.0439), ATF4 (p = 0.0267), CHOP (p = 0.0379), Bax and cleaved PARP but did not affect TRAF2 and NFkB protein levels nor XBP1 mRNA splicing. PERK knockdown, via siRNA, prevented the rise in GRP78, p-eIF2α/eIF2α, and ATF4 levels by melatonin. Additionally, melatonin increased early apoptosis in BeWo cells (p = 0.0371) and PERK knockdown increased the susceptibility of BeWo cells to apoptosis when treated with tunicamycin (p = 0.0359), suggesting that ER stress plays a role in BeWo cell survival. This study demonstrates that melatonin activates the PERK-ATF4-P-eIF2α-CHOP pathway and induces early apoptosis in BeWo cells, while PERK deficiency compromises cell survival under ER stress. Our findings suggest that modulating PERK-UPR signaling with melatonin could present a promising therapeutic strategy for cancer, including placental choriocarcinoma.