Effect of autophagy on stemness in ovarian clear cell carcinoma

Abstract

BACKGROUND: Macroautophagy, also known as autophagy, is a tightly regulated process with multiple steps. Autophagy mediates the degradation and recycling of long-live proteins and cytosolic organelles like mitochondrion. Evidence illustrated that autophagy is important for cell homeostasis and sustains tumor cell survival under stressful microenvironment by preventing accumulation of toxic aggregates and recycling metabolites to meet the high energy demands for continuous tumor growth. Moreover, the cytoprotective effect of autophagy may render tumor cells to become chemoresistant. Chemoresistance and relapse are the major hurdles when treating ovarian cancer. One reason may be attributed to the existence of cancer initiating cells (CIC) whose are of chemoresistant nature and incomplete eradication of them by conventional treatments may result in relapse. Thus, evaluating the role of autophagy in contributing stemness and chemosensitivity in CIC will be important. RESULTS: We found that the sphere forming subpopulation of ovarian clear cell carcinoma (OCCC) cells possess stem-cell like properties and are accompanied with upregulation of autophagy as illustrated by an increase in LC3BII. Besides stemness, these CIC-like spheroid cultures exhibited a more resistant response towards cisplatin. Knockdown of autophagy-related machineries such as Beclin 1 or Atg5 restored the tumor sensitivity towards cisplatin. Inhibition of autophagy with bafilomycin also showed similar sensitization. Moreover, OCCC cells with defective autophagy formed fewer spheres and expressed fewer stem-cell markers than their normal counterparts, indicating that autophagy is important for pluripotency. Furthermore, MEK/ERK pathway was upregulated in CIC-like spheroid culture than their differentiated counterparts, suggesting that MAPK activation may affect stemness through autophagy. SUMMARY: Our results suggested that including autophagy inhibitor in therapeutic regimen may improve the efficacy of conventional chemotherapy in treating OCCC.