Biological and functional consequences of polymorphisms in the XPD gene

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Title: Biological and functional consequences of polymorphisms in the XPD gene
Author: Kevin James Wolfe
Abstract: Epidemiological studies have documented many associations between single nucleotide polymorphisms (SNPs ) in the nucleotide excision repair gene XPD (ERCC2 ) and cancer risk . Little is known , however , about the underlying mechanisms for these associations . I used lymphocytes from healthy subjects to explore novel mechanisms which could explain the reported risk -modifying effects on disease susceptibility of three SNPs in the XPD gene , the synonymous C156A SNP in exon 6 and the nonsynonymous SNPs Asp312Asn in exon 10 and Lys751Gln in exon 23 . Baseline and NNK -induced chromosomal aberrations (Ca ) were assessed by cytogenetic analysis and then P values were calculated as estimates of sub -population differences for increased frequencies of CAs associated with the three XPD polymorphisms . I found significant elevation in baseline frequencies of CAs among smokers with the variant 312Asn polymorphism (P=0 .028 ) . Elevations in NNK -induced aberrations were found among younger subjects (age <39 years ) with the 156A or the 751Gln polymorphism , (P=0 .025 and P=0 .037 , respectively ) and in females compared to males with a combination of the 312Asn and the 751Gln polymorphisms (P=0 .045 ) . Application of real time PCR showed that each SNP , alone and in combination , significantly decreased constitutive XPD mRNA levels (P <0 .003 ) in lymphocytes . Decreases in XPD mRNA levels were significantly higher in older subjects and in smokers . Localized Mfold structure analysis of the mRNA sequence surrounding the studied SNPs were predicted to alter mRNA secondary structure , which indicated that these SNPs potentially affect local folding and mRNA stability . UVC treatment of cells with wild type XPD produced a significant increase (P=0 .03 ) in XPD protein levels by 30 min , which surprisingly coincided with a decrease in XPD mRNA transcript copy number (P=0 .0002 ) . Fluorescent confocal microscopy demonstrated that this increase in XPD protein appeared largely due to an increase in nuclear localization of XPD , which was evident at 30 min and persistent at 6 hrs . New observations from this project provide possible mechanistic explanations for the association of polymorphisms in XPD with increased genetic damage (CAs ) and cancer risk .
URI: http : / /hdl .handle .net /2152 .3 /248
Date: 2006-10-23


Biological and functional consequences of polymorphisms in the XPD gene. Doctoral dissertation, The University of Texas Medical Branch. Available electronically from http : / /hdl .handle .net /2152 .3 /248 .

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