GABARAPL2 and Alix mediate reciprocal regulation of autophagy and exosome pathways to facilitate cellular homeostasis

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 pathways 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 the 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. The two pathways, when independently inhibited, did not present any significant effect on restricting cancer cell growth. However, a combined inhibition of both pathways led to substantial reduction in cancer cell proliferation. To evaluate the reciprocal regulation of two pathways, we blocked the autophagy pathway and observed an increase in the release of exosomes from MDA-MB-231 cells, along with decreased expression of Alix and CD63 genes. In contrast, inhibition of exosome biogenesis led to an increase in the expression of ATG5 and ATG16L1, and a significant decrease in expression of GABARAPL2. Interestingly, the knockdown of GABARAPL2 abrogated the decrease in Alix expression upon autophagy inhibition, 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.