Oxidative stress-induced alternative splicing of transformer 2 β ( SFRS10 ) and CD44 pre-mRNAs in gastric epithelial cells

The tra2β gene encoding an alternative splicing regulator, transformer 2-β (Tra2β), generates five alternative splice variant transcripts ( tra2β 1– 5). Functionally active, full-length Tra2β is encoded by tra2β 1 isoform. Expression and physiological significance of the other isoforms, particularly tra2β 4, are not fully understood. Rat gastric mucosa constitutively expressed tra2β 1 isoform and specifically generated tra2β 4 isoform that includes premature termination codon-containing exon 2, when exposed to restraint and water immersion stress. Treatment of a gastric cancer cell line (AGS) with arsenite (100 μM) preferentially generated tra2β 4 isoform and caused translocation of Tra2β from the nucleus to the cytoplasm in association with enhanced phosphorylation during the initial 4–6 h (acute phase). Following the acute phase, AGS cells continued upregulated tra2β 1 mRNA expression, and higher amounts of Tra2β were reaccumulated in their nuclei. Treatment with small interference RNAs targeting up-frameshift-1 or transfection of a plasmid containing tra2β 1 cDNA did not induce tra2β 4 isoform expression and did not modify the arsenite-induced expression of this isoform, suggesting that neither the nonsense-mediated mRNA decay nor the autoregulatory control by excess amounts of Tra2β participated in the tra2β 4 isoform generation. Knockdown of Tra2β facilitated skipping of the central variable region of the CD44 gene and suppressed cell growth. In contrast, overexpression of Tra2β stimulated combinatorial inclusion of multiple variable exons in the region and cell growth. The similar skipping and inclusion of the variable region were observed in arsenite-treated cells. Our results suggest that Tra2β may regulate cellular oxidative response by changing alternative splicing of distinct genes including CD44.