The Bax inhibitor-1 gene is differentially regulated in adult testis and developing lung by two alternative TATA-less promoters.
We identified Bax inhibitor-1, BI-1, as a developmentally regulated gene product in perinatal lung using suppressive subtractive hybridization. BI-1 is a novel suppressor of apoptosis that was previously cloned as testis-enhanced gene transcript (TEGT). However, sequence analysis of lung BI-1 revealed unique nucleotides starting 29 bases upstream of the ATG initiation codon and extending to the 5' end of lung-derived BI-1 cDNA compared to the original transcript from the testis. Cloning and sequencing of the upstream region of the BI-1 gene revealed that these unique sequences originated from two alternative first exons, located in tandem and separated by approximately 600 bases. Neither was preceded by a TATA box in the usual position, and S1 nuclease mapping at each exon 1 revealed multiple transcription start points with a major site being overlapped by a consensus initiator element. Promoter activity from each region was documented by transient transfection analysis in vitro using DNA sequences ligated to a reporter gene. The proximal promoter, P1, may exhibit cell type-specific differences in fibroblasts versus epithelia, whereas the distal promoter, P2, may exhibit species-specific differences in rat versus human cells. RT-PCR analysis for expression in adult tissues using exon 1-specific 5' primers and common 3' primers revealed that P1 is tissue-specific; P2 is ubiquitously active. The developmental regulation of BI-1 in the late fetal and early postnatal lung is specific for P2, indicating that these two TATA-less promoters are differentially regulated in adult testis and developing lung. Since Bax inhibitor-1 functions as a suppressor of apoptosis, its expression could provide a survival advantage for select cell populations during the peak period of apoptosis that occurs at birth.
Jean
J C
JC
The Pulmonary Center, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
Oakes
S M
SM
Joyce-Brady
M
M
D000818:Animals; D051017:Apoptosis Regulatory Proteins; D015152:Blotting, Northern; D002460:Cell Line; D004247:DNA / Q000737:chemistry / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D005333:Fetus / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D006367:HeLa Cells; D006801:Humans; D008168:Lung / Q000196:embryology / Q000254:growth & development / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011506:Proteins; D012313:RNA / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016385:TATA Box; D013737:Testis / Q000378:metabolism*; D014018:Tissue Distribution; D014158:Transcription, Genetic
D051017:Apoptosis Regulatory Proteins; D018076:DNA, Complementary; D008565:Membrane Proteins; D011506:Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; C484209:TMBIM6 protein, human; C088008:Tmbim6 protein, rat; D012313:RNA; D004247:DNA