Hydrogen sulfide (H2S) is an important endogenous gaseous transmitter mediator, which regulates a variety of cellular functions in autocrine and paracrine manner. The
enzymes responsible for the
biological generation of H2S include
cystathionine-β-synthase (CBS),
cystathionine-γ-
lyase (CSE) and
3-mercaptopyruvate sulfurtransferase (3-MST). Increased expression of these
enzymes and overproduction of H2S has been implicated in essential processes of various
cancer cells, including the stimulation of metabolism, maintenance of cell proliferation and cytoprotection.
Cancer cell identity is characterized by so-called "transition states". The progression from normal (epithelial) to transformed (mesenchymal) state is termed epithelial-to-mesenchymal transition (EMT) whereby epithelial cells lose their cell-to-cell adhesion capacity and gain mesenchymal characteristics. The transition process can also proceed in the opposite direction, and this process is termed mesenchymal-to-epithelial transition (MET). The current project was designed to determine whether inhibition of endogenous H2S production in
colon cancer cells affects the EMT/MET balance in vitro. Inhibition of H2S biosynthesis in HCT116 human
colon cancer cells was achieved either with
aminooxyacetic acid (AOAA) or 2-[(4-hydroxy-6-methylpyrimidin-2-yl)sulfanyl]-1-(naphthalen-1-yl)ethan-1-one (HMPSNE). These inhibitors induced an upregulation of
E-cadherin and Zonula occludens-1 (ZO-1) expression and downregulation of
fibronectin expression, demonstrating that H2S biosynthesis inhibitors can produce a pharmacological induction of MET in
colon cancer cells. These actions were functionally reflected in an inhibition of cell migration, as demonstrated in an in vitro "scratch
wound" assay. The mechanisms involved in the action of endogenously produced H2S in
cancer cells in promoting (or maintaining) EMT (or tonically inhibiting MET) relate, at least in part, in the induction of
ATP citrate lyase (ACLY)
protein expression, which occurs via upregulation of ACLY
mRNA (via activation of the ACLY promoter). ACLY in turn, regulates the Wnt-β-
catenin pathway, an essential regulator of the EMT/MET balance. Taken together, pharmacological inhibition of endogenous H2S biosynthesis in
cancer cells induces MET. We hypothesize that this may contribute to anti-
cancer / anti-metastatic effects of H2S biosynthesis inhibitors.