Reciprocal regulation of autophagy and exosome pathway is mediated by GABARAPL2 and Alix to facilitate cellular homeostasis

Abstract

The continuous reliance of cancer cells to acquire energy and communicate their nutrient needs makes them resilient and vulnerable. It provides an opportunity to stifle cancer cells by restricting their energy generation and communication ability. Autophagy and exosome biogenesis are two such pathways that are essential in maintaining the robust growth and survival of cancer cells. In this study we observed that inhibition of one pathway altered the expression of genes in other pathway. Exosome biogenesis, when blocked, led to an increase in breast cancer cell proliferation, while inhibition of autophagy did not significantly affect cancer cell proliferation. Therefore, the two pathways, when independently inhibited, did not present any significant effect on restricting cancer cell growth. However, we observed a substantial reduction in cancer cell proliferation upon combined inhibition of two pathways. To evaluate the reciprocal regulation of two pathways, we blocked the autophagy pathway and observed increase in the secretion of exosomes from MDA-MB-231 cells, along with decreased expression of Alix and CD63. On contrary, inhibition of exosome biogenesis led to an increase in the expression of ATG5 and ATG16L1, which caused a significant decrease in expression of GABARAPL2. Interestingly, the knockdown of GABARAPL2 abrogated the decrease in Alix expression upon autophagy inhibition, thus highlighting the essential role of GABARAPL2 in Alix secretion. Thus, our study highlights for the first time the synergistic effects of autophagy and exosome pathway inhibition in restricting cancer cell growth as well as the involvement of GABARAPL2 in the regulation of exosome secretion via modulating Alix expression.