Transcriptional Regulation of Antioxidant and DNA Repair Transcript Abundance in Human Bronchial Epithelial Cells
Cigarette smoking is the primary cause of bronchogenic carcinoma (BC), yet only 10-15% of heavy smokers develop BC, indicating a genetically determined variation in risk. In previous studies, transcript abundance values for several antioxidant and DNA repair genes were correlated in normal bronchial epithelial cells (NBEC) from non-BC individuals but correlation was reduced in NBEC from BC individuals. From these data we hypothesized that in NBEC, these genes are co-regulated by one or more transcription factors. Of the 14 transcription factors that have recognition sites in the regulatory regions of each of the target genes, only CEBPG was significantly (p < 0.0001) correlated with four of the genes (XRCC1, ERCC5, GSTP1, and SOD1) in non-BC individuals and significantly less correlated (p < 0.01) with these four genes in BC individuals. We concluded that CEBPG is the transcription factor primarily responsible for regulating the transcription of key antioxidant and DNA repair genes in non-BC individuals. In order to experimentally confirm the regulatory role of CEBPG, CEBPG or CEBPB expression vector was co-transfected into the H23 lung cell line with an ERCC5 promoter-luciferase construct containing two CEBP recognition sites. Transfection of 7, 10, 14 or 21 µg of CEBPG reproducibly activated the exogenous ERCC5 promoter-luciferase construct versus the empty vector control, while transfection of CEBPB caused less activation of the luciferase construct. Transfection of exogenous CEBPG did not alter expression of the endogenous ERCC5 gene. Additionally, two polymorphisms were identified from sequence analysis of 22 patient samples and the H23 and BEP2D cell lines. Homozygosity of the G-221A MF allele (GG) or heterozygosity of the T-227G polymorphism was associated with samples more than two standard deviations removed from the linear equation for the regression line defining the relationship between CEBPG and ERCC5 transcript abundance in non-BC individuals. These studies identify CEBPG as the potential source of co-regulation of key protective genes in NBEC, and demonstrate that it can, either directly or indirectly, regulate expression of ERCC5. This study brings the field nearer to a mechanistic understanding of correlated expression of key genes in non-BC individuals, potentially leading to early identification high-risk individuals.
School:University of Toledo Health Science Campus
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:cebpg transcriptional regulation human bronchial epithelial cells antioxidant genes dna repair
Date of Publication:01/01/2006