Inhibition of macroautophagy by bafilomycin A1 lowers proliferation and induces apoptosis in colon cancer cells

Macroautophagy is a process by which cytoplasmic content and organelles are sequestered by double-membrane bound vesicles and subsequently delivered to lysosomes for degradation. Macroautophagy serves as a major intracellular pathway for protein degradation and as a pro-survival mechanism in time of stress by generating nutrients. In the present study, bafilomycin A1, a vacuolar type H+-ATPase inhibitor, suppresses macroautophagy by preventing acidification of lysosomes in colon cancer cells. Diminished macroautophagy was evidenced by the accumulation of undegraded LC3 protein. Suppression of macroautophagy by bafilomycin A1 induced G0/G1 cell cycle arrest and apoptosis which were accompanied by the down-regulation of cyclin D1 and cyclin E, the up-regulation of p21Cip1 as well as cleavages of caspases-3, -7, -8, and -9 and PARP. Further investigation revealed that bafilomycin A1 increased the phosphorylation of ERK, JNK, and p38. In this regard, p38 inhibitor partially reversed the anti-proliferative effect of bafilomycin A1. To conclude, inhibition of macroautophagy by bafilomycin A1 lowers G1-S transition and induces apoptosis in colon cancer cells. Our results not only indicate that inhibitors of macroautophagy may be used therapeutically to inhibit cancer growth, but also delineate the relationship between macroautophagy and apoptosis.