Hydrogen Sulfide Lowers Proliferation and Induces Protective Autophagy in Colon Epithelial Cells

Hydrogen sulfide (H2S) is a gaseous bacterial metabolite that reaches high levels in the large intestine. In the present study, the effect of H2S on the proliferation of normal and cancerous colon epithelial cells was investigated. An immortalized colon epithelial cell line (YAMC) and a panel of colon cancer cell lines (HT-29, SW1116, HCT116) were exposed to H2S at concentrations similar to those found in the human colon. H2S inhibited normal and cancerous colon epithelial cell proliferation as measured by MTT assay. The anti-mitogenic effect of H2S was accompanied by G(1)-phase cell cycle arrest and the induction of the cyclin-dependent kinase inhibitor p21(Cip). Moreover, exposure to H2S led to features characteristic of autophagy, including increased formation of LC3B(+) autophagic vacuoles and acidic vesicular organelles as determined by immunofluorescence and acridine orange staining, respectively. Abolition of autophagy by RNA interference targeting Vps34 or Atg7 enhanced the anti-proliferative effect of H2S. Further mechanistic investigation revealed that H2S stimulated the phosphorylation of AMP-activated protein kinase (AMPK) and inhibited the phosphorylation of mammalian target of rapamycin (mTOR) and S6 kinase. Inhibition of AMPK significantly reversed H2S-induced autophagy and inhibition of cell proliferation. Collectively, we demonstrate that H2S inhibits colon epithelial cell proliferation and induces protective autophagy via the AMPK pathway.