Sulfur Dioxide Activates Cl-/HCO3- Exchanger via Sulphenylating AE2 to Reduce Intracellular pH in Vascular Smooth Muscle Cells

Sulfur dioxide (SO2) is a colorless and irritating gas. Recent studies indicate that SO2 acts as the gas signal molecule and inhibits vascular smooth muscle cell (VSMC) proliferation. Cell proliferation depends on intracellular pH (pH(i)). Transmembrane cystein mutation of Na+-independent Cl-/HCO3- exchanger (anion exchanger, AE) affects pH(i). However, whether SO2 inhibits VSMC proliferation by reducing pH(i) is still unknown. Here, we investigated whether SO2 reduced pH(i) to inhibit the proliferation of VSMCs and explore its molecular mechanisms. Within a range of 50-200 mu M, SO2 was found to lower the pH(i) in VSMCs. Concurrently, NH4Cl pre-perfusion showed that SO2 significantly activated AE, whereas the AE inhibitor 4,4'-diisothiocyanatostilbene-2,20-disulfonic acid (DIDS) significantly attenuated the effect of SO2 on pH(i) in VSMCs. While 200 mu M SO2 sulphenylated AE2, while dithiothreitol (DTT) blocked the sulphenylation of AE2 and subsequent AE activation by SO2, thereby restoring the pH(i) in VSMCs. Furthermore, DIDS pretreatment eliminated SO2-induced inhibition of PDGF-BB-stimulated VSMC proliferation. We report for the first time that SO2 inhibits VSMC proliferation in part by direct activation of the AE via posttranslational sulphenylation and induction of intracellular acidification.