Hydrogen peroxide triggers a novel alternative splicing of arsenic (+3 oxidation state) methyltransferase gene

Abstract

We previously reported that two splicing variants of human AS3MT mRNA, exon-3 skipping form (Δ3) and exons-4 and -5 skipping form (Δ4,5), were detected in HepG2 cells and that both variants lacked arsenic methylation activity (Sumi et al., 2011). Here we studied whether hydrogen peroxide (H₂O₂) triggers alternative splicing of AS3MT mRNA. The results showed that exposure of HepG2 cells to H₂O₂ resulted in increased levels of a novel spliced form skipping exon-3 to exon-10 (Δ3-10) in an H₂O₂-concentration-dependent manner, although no change was detected in the mRNA levels of Δ3 AS3MT. We found decreased protein levels of serine/arginine-rich 40 (SRp40), which we determined to be a candidate splice factor for controlling the splicing of AS3MT mRNA. We next compared the amounts of methylated arsenic metabolites between control and H₂O₂-exposed HepG2 cells after the addition of arsenite as a substance. The results showed lower levels of methylated arsenic metabolites in HepG2 cells exposed to H₂O₂. These data suggest that the splicing of AS3MT pre-mRNA was disconcerted by oxidative stress and that abnormal alternative splicing of AS3MT mRNA may affect arsenic methylation ability.

Keywords: Alternative splicing; Arsenic (+3 oxidation state) methyltransferase; Methyltransferase activity.