Endoplasmic reticulum stress induces autophagy and apoptosis while inhibiting proliferation and drug resistance in multiple myeloma through the PI3K/Akt/mTOR signaling pathway

We investigated the effects of endoplasmic reticulum stress (ERS) on autophagy, proliferation, apoptosis, and drug resistance in multiple myeloma (MM). MM patients enrolled in our study (n = 268) were classified into sensitive and resistant groups based on chemotherapy efficacy, and their serum levels of β2-MG, albumin (ALB), lactic dehydrogenase (LDH), Ca2+ and hemoglobin were determined. In addition, human MM U266 and MOLP-2/R cells were divided into blank, tunicamycin (TM), TM + insulin-like growth factor-1 (IGF-1), and TM + rapamycin groups, and measured expression of ERS-related, PI3K/Akt/mTOR pathway-related, and autophagy-related mRNA and proteins. Serum levels of β2-MG, LDH and Ca2+, and expression of PI3K, Akt, and mTOR were higher in the resistant than sensitive group. Serum levels of ALB and hemoglobin, and expression of glucose-regulated protein 78 (GRP78), GRP94, microtubule associated protein 1 light chain 3 (LC3), and Beclin1, were lower in the resistant than sensitive group. In U266 cells treated with TM and IGF-1 or rapamycin, ERS promoted autophagy and apoptosis while inhibiting proliferation through inhibition of PI3K/Akt/mTOR signaling. ERS also reversed drug resistance in MOLP-2/R cells via the PI3K/Akt/mTOR signaling pathway. These data suggest that ERS activation could be exploited for therapeutic benefits in the treatment of MM.