The tra2 gene encoding an alternative splicing regulator, transformer 2- (Tra2), generates five alternative splice variant transcripts (tra21-5). Functionally active, full-length Tra2 is encoded by tra21 isoform. Expression and physiological significance of the other isoforms, particularly tra24, are not fully understood. Rat gastric mucosa constitutively expressed tra21 isoform and specifically generated tra24 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 tra24 isoform and caused translocation of Tra2 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 up-regulated tra21 mRNA expression, and higher amounts of Tra2 were re-accumulated in their nuclei. Treatment with small interference RNAs targeting up-frameshift-1 or transfection of a plasmid containing tra21 cDNA did not induce tra24 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 participated in the tra24 isoform generation. Knockdown of Tra2 facilitated skipping of the central variable region of the CD44 gene and suppressed cell growth. In contrast, overexpression of Tra2 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 may regulate cellular oxidative response by changing alternative splicing of distinct genes including CD44.