Abstract
Therapy-induced senescence in cancer cells is an irreversible antiproliferative state, which inhibits tumor growth and is therefore a potent anti-neoplastic mechanism. In this study, low doses of Abrus agglutinin (AGG)-induced senescence through autophagy in prostate carcinoma cells (PC3) and inhibited proliferation. The inhibition of autophagy with 3-methyl adenine reversed AGG-induced senescence, thus confirming that AGG-triggered senescence required autophagy. AGG treatment also led to lipophagy-mediated accumulation of free fatty acids (FFAs), with a concomitant decrease in the number of lipid droplets. Lalistat, a lysosomal acid lipase inhibitor, abrogated AGG-induced lipophagy and senescence in PC3 cells, indicating that lipophagy is essential for AGG-induced senescence. The accumulation of FFAs increased reactive oxygen species generation, a known facilitator of senescence, which was also reduced in the presence of lalistat. Furthermore, AGG upregulated silent mating type information regulator 2 homolog 1 (SIRT1), while the presence of sirtinol reduced autophagy flux and the senescent phenotype in the AGG-treated cells. Mechanistically, AGG-induced cytoplasmic SIRT1 deacetylated a Lys residue on the cytoplasmic domain of lysosome-associated membrane protein 1 (LAMP1), an autolysosomal protein, resulting in lipophagy and senescence. Taken together, our findings demonstrate a novel SIRT1/LAMP1/lipophagy axis mediating AGG-induced senescence in prostate cancer cells.