Expression of Apoptosis-Associated Proteins in Tumor Cells under Autophagy and Endoplasmic Reticulum Stress...

The autophagy-related structures, the size of the rough endoplasmic reticulum (ER) cisterns, and the expression of apoptosis-related proteins were assessed by transmission electron microscopy and immunohistochemistry in tumor samples from mice with B16 skin melanoma after administration of autophagy inducer (rapamycin) or ER stress inducer (brefeldin A). Brefeldin A stimulated significant ER stress in mouse skin melanoma cells, but rapamycin contributed to the maintenance of cell homeostasis by inducing autophagy, which was confirmed by the presence of autophagy-related structures and significantly smaller sizes of the rough ER cisterns in the group of mice receiving both rapamycin and brefeldin A. Brefeldin A-induced ER stress triggered apoptosis of tumor cells. Moreover, simultaneous stimulation of autophagy and ER stress in tumor cells promoted cytoprotective selective autophagy (reticulophagy) aimed at resolving ER stress, which may be a mechanism underlying the development of chemoresistance in skin melanoma.