Human BAG-1/RAP46 protein is generated as four isoforms by alternative translation initiation and overexpressed in cancer cells.
Previously, a Bcl-2-interacting protein, BAG-1, was cloned from mouse cells and was shown to interact with several other proteins and to be important for inhibition of apoptosis. Human BAG-1 (hBAG-1) cDNA, recently isolated by us and two other groups, has been shown to be identical to a hormone receptor-binding protein, RAP46. However, different molecular masses of hBAG-1 protein products were noted by these three groups. Here we demonstrated that hBAG-1 protein was expressed as four isoforms, designated p50, p46, p33 and p29, with apparent molecular masses of 50 kDa, 46 kDa, 33 kDa and 29 kDa, respectively. Deletion, site-directed mutagenesis and in vitro transcription/translation analysis showed that the four protein products of hBAG-1 were expressed by alternative initiation from four different start codons through a leaky scanning mechanism. Furthermore, we demonstrated that the distinct forms of hBAG-1 have different subcellular localizations, suggesting that they may have distinct functions in the cells. Characterization of hBAG-1 RNA and protein also showed that hBAG-1 was overexpressed in human cervical, breast and lung cancer cell lines. Taken together, these data clarify the conflicting observations reported in the literature and suggest that hBAG-1 is expressed as four forms of protein products, which may play a differential role in apoptosis and oncogenesis of human cells.
Yang
X
X
Basic Medical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St John's, Canada.
Chernenko
G
G
Hao
Y
Y
Ding
Z
Z
Pater
M M
MM
Pater
A
A
Tang
S C
SC
D017398:Alternative Splicing / Q000235:genetics; D001483:Base Sequence; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D002460:Cell Line; D004268:DNA-Binding Proteins; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D006801:Humans; D007536:Isomerism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009928:Organ Specificity / Q000235:genetics; D010442:Peptide Chain Initiation, Translational / Q000235:genetics*; D013347:Subcellular Fractions / Q000378:metabolism; D014157:Transcription Factors; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
C091732:BCL2-associated athanogene 1 protein; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D014157:Transcription Factors