A single nucleotide polymorphism in the Bax gene promoter affects transcription and influences retinal ganglion cell death.
Pro-apoptotic Bax is essential for RGC (retinal ganglion cell) death. Gene dosage experiments in mice, yielding a single wild-type Bax allele, indicated that genetic background was able to influence the cell death phenotype. DBA/2J(Bax+/-) mice exhibited complete resistance to nerve damage after 2 weeks (similar to Bax(-/-) mice), but 129B6(Bax+/-) mice exhibited significant cell loss (similar to wild-type mice). The different cell death phenotype was associated with the level of Bax expression, where 129B6 neurons had twice the level of endogenous Bax mRNA and protein as DBA/2J neurons. Sequence analysis of the Bax promoters between these strains revealed a single nucleotide polymorphism (T(129B6) to C(DBA/2J)) at position -515. A 1.5- to 2.5-fold increase in transcriptional activity was observed from the 129B6 promoter in transient transfection assays in a variety of cell types, including RGC5 cells derived from rat RGCs. Since this polymorphism occurred in a p53 half-site, we investigated the requirement of p53 for the differential transcriptional activity. Differential transcriptional activity from either 129B6 or DBA/2J Bax promoters were unaffected in p53(-/-) cells, and addition of exogenous p53 had no further effect on this difference, thus a role for p53 was excluded. Competitive electrophoretic mobility-shift assays identified two DNA-protein complexes that interacted with the polymorphic region. Those forming Complex 1 bound with higher affinity to the 129B6 polymorphic site, suggesting that these proteins probably comprised a transcriptional activator complex. These studies implicated quantitative expression of the Bax gene as playing a possible role in neuronal susceptibility to damaging stimuli.
Semaan
Sheila J
SJ
Department of Opthalmology and Visual Sciences, University of Wisconsin, School of Medicine and Public Health, 1300 University Avenue, Madison, WI 53706, U.S.A.
Li
Yan
Y
Nickells
Robert W
RW
D000818:Animals; D016923:Cell Death / Q000235:genetics; D002478:Cells, Cultured; D020022:Genetic Predisposition to Disease / Q000235:genetics; D051379:Mice; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D018345:Mice, Knockout; D041681:NIH 3T3 Cells; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding / Q000235:genetics; D012165:Retinal Ganglion Cells / Q000473:pathology / Q000502:physiology*; D014158:Transcription, Genetic / Q000235:genetics*; D051028:bcl-2-Associated X Protein / Q000096:biosynthesis / Q000235:genetics*
C494827:Bax protein, mouse; D051028:bcl-2-Associated X Protein