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

The tra2[beta] gene encoding an alternative splicing regulator, transformer 2-[beta] (Tra2[beta]), generates five alternative splice variant transcripts (tra2[beta]1-5). Functionally active, full-length Tra2[beta] is encoded by tra2[beta]1 isoform. Expression and physiological significance of the other isoforms, particularly tra2[beta]4, are not fully understood. Rat gastric mucosa constitutively expressed tra2[beta]1 isoform and specifically generated tra2[beta]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 [micro]M) preferentially generated tra2[beta]4 isoform and caused translocation of Tra2[beta] 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 tra2[beta]1 mRNA expression, and higher amounts of Tra2[beta] were reaccumulated in their nuclei. Treatment with small interference RNAs targeting up-frameshift-1 or transfection of a plasmid containing tra2[beta]1 cDNA did not induce tra2[beta]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 Tra2[beta] participated in the tra2[beta]4 isoform generation. Knockdown of Tra2[beta] facilitated skipping of the central variable region of the CD44 gene and suppressed cell growth. In contrast, overexpression of Tra2[beta] 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 Tra2[beta] may regulate cellular oxidative response by changing alternative splicing of distinct genes including CD44. arsenite; splicing regulator; tra2[beta]4 isoform; premature termination codon; cell growth