Cloning and characterization of the human BAG-1 gene promoter: upregulation by tumor-derived p53 mutants

BAG-1 is an anti-apoptotic protein that interacts with Bcl-2, BcL-X-L, Hsp7 0/Hsc70, Raf-1 and numerous hormone or growth factor receptors, Recently, B AG-1 has been found to be overexpressed in a variety of human cancer cell l ines and some tumors. However, the molecular mechanism of BAG-1 upregulatio n is still unclear. In this study, me cloned 0.9 kb of human genomic DNA, B GEV, 5' flanking the BAG-1 open reading frame. BGEV subcloned into a promot erless luciferase reporter vector conferred high promoter activity in vario us human cancer cell lines. Deletion analysis of this sequence localized th e region of maximal BAG-1 promoter activity from nucleotide positions -353 to -54, upstream of the first start codon CTG. Sequence analysis of the BAG -1 promoter region showed the absence of a TATA box but identified a CCAAT box, several GC boxes, a CpG island and several transcriptional factor bind ing sites, which may be important in the regulation of BAG-1 transcription. Most importantly, functional characterization of the BAG-1 promoter in viv o demonstrated that gain-of-function p53 mutants derived from human tumors upregulated the transcription of BAG-1 RNA and the expression of a reporter gene from the BAG-1 promoter. These results indicated that me have isolate d the functional constitutive BAG-1 promoter. Furthermore, the data suggest ed that overexpression of BAG-1 in some tumors may be due to upregulation o f the human BAG-1 promoter by mutant p53.