An autophagy inhibitor enhances the inhibition of cell proliferation induced by a proteasome inhibitor in MCF-7 cells

Abstract

Abstract. The ubiquitin-proteasome system and the autophagy-lysosome pathway are the two main routes for eukaryotic intracellular protein clearance. Inhibition of proteasome activity leads to cell death. Due to the dual roles of autophagy in tumor cell survival and death, the effect of suppression of autophagy on breast cancer cells remains to be elucidated. We investigated whether inhibition of the proteasome is capable of inducing autophagy, and we assessed the effect of combined inhibition of the proteasome and autophagy on human breast cancer MCF-7 cells. The proteasome inhibitor bortezomib was used to induce autophagy in MCF-7 cells, and the effect of autophagy on the proliferation of MCF-7 cells was investigated using the autophagy inhibitor 3-MA. Cell viability was measured by MTT assay. The expression of autophagy-related proteins was determined by Western blot analysis and the GFP-LC3 redistribution was detected using a fluorescence microscope after MCF-7 cells were infected with a GFP-LC3-expressing adenovirus. MCF-7 cell proliferation was inhibited and autophagy was activated in the same dose-dependent manner. Bortezomib induced a dose-dependent increase in LC3-II. However, when MCF-7 cells were co-treated with bortezomib and 3-MA, 3-MA blocked the increase in LC3-II protein expression and led to a significant inhibition of cell proliferation. Inhibition of the proteasome may induce autophagy in human breast cancer MCF-7 cells and 3-MA could inhibit autophagy induced by the proteasome inhibitor. A combination of 3-MA and bortezomib increases cell death. These findings indicate that suppression of the two intracellular degradation systems may shed new light on breast cancer control.

Proteasome inhibitors in glioblastoma

“…Proteasome inhibitors have been found to induce autophagy in a variety of cell types including prostate cancer (35) and melanoma (36). Induction of autophagy is generally thought to be a protective mechanism in cancer cells treated with proteasome inhibitors, and dual inhibition of the proteasome and autophagy has been shown to increase cell death (37). Increased death after dual inhibition of the proteasome and autophagy appears to be specific to transformed cells, possibly indicating an increased reliance of cancer cells on these cellular processes (38).…”

Autophagy in Thyroid Cancer: Present Knowledge and Future Perspectives

“…Proteasome inhibitors, including the multipathway inhibitor bortezomib, are promising agents for treatment of highly aggressive cancer ( 118 ). Studies performed on several cancer cell lines demonstrated that autophagy inhibitors can synergize with the cytotoxic effects of the proteasome inhibitors ( 119 – 121 ). Based on these preclinical data, a number of trials investigating autophagy inhibition in combination with proteasome inhibitors have been initiated.…”

Bortezomib Treatment Modulates Autophagy in Multiple Myeloma

“…Previous studies demonstrated that simultaneous proteasome and autophagy inhibition results in the accumulation of ubiquitinated proteins and thus in cytotoxicity [20,22,23]. Moreover, autophagy inhibition enhances the efficacy of many anticancer drugs, both in cell lines and in animal models [24][25][26][27][28], and synergistically increases bortezomib cytotoxicity in in vitro models of myeloma [29,30], colon carcinoma [31], and hepatocarcinoma [25]. Hydroxychloroquine (HCQ) is a well-known inhibitor of autophagy [32][33][34] and is commonly used to treat autoimmune diseases [35][36][37].…”