Over-expression of Bim α3, a novel isoform of human Bim, result in cell apoptosis1

Bim proteins are essential factors of apoptosis. Nine isoforms of Bim have been submitted to GenBank database. In order to improve the understanding of the regulation of Bims’ proapoptotic activity, we screened a multiple tissue cDNA panels for Bim isoforms and tested their proapoptotic activity by over-expression. Two novel cDNA isoforms of Bim family are generated by alternative splicing. One isoform encodes a 79 residue putative protein with a BH3 domain, named Bim α3. There is not any significant ORF found in another isoform, named Bim β5. Subcellular localized analysis of EGFP-Bim fusion protein suggests Bim α3 distributed to both plasma and nucleus of HEK 293 cell. HEK 293 cells transfected with pcDNA-Bim α3 presented a similar proapoptotic activity (32.05±6.42%) with Bim α2 (30.14±2.66%). The proapoptotic activity of Bim α3 was obviously weaker than that of Bim S (46.52±5.07%) and Bim L (55.53±1.99%). Anti-sense over-expression of Bim in HEK 293 cells results in a weak down-regulated proapoptotic level. Expression pattern analysis reveals that both the novel cDNAs are expressed widely in normal tissue just like the other reported isoforms. The expression pattern of Bim isoforms shows tissue specific obviously. The results suggest that BH3 domain is sufficiency for proapoptotic activity of Bim proteins. The functional state of Bims might be regulated both in the transcript and post transcript process.