Genes involved in DNA repair and nitrosamine metabolism and those located on chromosome 14q32 are dysregulated in nasopharyngeal carcinoma.

Polymorphisms in nitrosamine metabolism, DNA repair, and immune response genes have been associated with nasopharyngeal carcinoma (NPC). Studies have suggested chromosomal regions involved in NPC. To shed light on NPC etiology, we evaluated host gene expression patterns in 31 NPC and 10 normal nasopharyngeal tissue specimens using the Affymetrix Human Genome U133 Plus 2.0 Array. We focused on genes in five a priori biological pathways and chromosomal locations. Rates of differential expression within these prespecified lists and overall were tested using a bootstrap method. Differential expression was observed for 7.6% of probe sets overall. Elevations in rate of differential expression were observed within the DNA repair (13.7%; P = 0.01) and nitrosamine metabolism (17.5%; P = 0.04) pathways. Differentially expressed probe sets within the DNA repair pathway were consistently overexpressed (93%), with strong effects observed for PRKDC, PCNA, and CHEK1. Differentially expressed probe sets within the nitrosamine metabolism pathway were consistently underexpressed (100%), with strong effects observed for NQ01, CYP2B6, and CYP2E1. No significant evidence of increases in rate of differential expression was seen within the immune/inflammatory pathway. A significant elevation in rate of differential expression was noted for chromosome 4p15.1-4q12 (13.0%; P = 0.04); both overexpression and underexpression were evident (38% and 62%, respectively). An elevation in the rate of differential expression on chromosome 14q32 was observed (11.3%; P = 0.06) with a consistent pattern of gene underexpression (100%; P < 0.0001). These effects were similar when excluding late-stage tumors. Our results suggest that nitrosamine activation and DNA repair are important in NPC. The consistent down-regulation of expression on chromosome 14q32 suggests loss of heterozygosity in this region.

Nasopharyngeal carcinoma and genetic polymorphisms of DNA repair enzymes XRCC1 and hOGG1.

Nitrosamine consumption and polymorphisms in CYP2E1, the product of which is involved in the activation of nitrosamines into reactive intermediates, have been shown to be associated with nasopharyngeal carcinoma (NPC) risk. Given that reactive intermediates created during nitrosamine metabolism are capable of DNA damage, we further hypothesized that differences between individuals in their ability to repair DNA damage might be important in NPC pathogenesis. To evaluate this hypothesis, this study focused on effects of genetic polymorphisms of DNA repair genes hOGG1 and XRCC1 on the development of NPC. We conducted a case-control study to investigate the genotypes of 334 patients with NPC and 283 healthy community controls matched by sex, age, and residence. The PCR-based RFLP assay was used to identify genetic polymorphisms. After adjustment for sex, age, and ethnicity, the odds ratio (OR) of developing NPC for hOGG1 codon 326 genotypes of Ser/Cys and Cys/Cys compared with the Ser/Ser genotype was 1.6 (95% CI, 1.0-2.6). For XRCC1 codon 280 genotypes of Arg/His and His/His compared with the Arg/Arg genotype, the OR was 0.64 (95% CI, 0.43-0.96). Among subjects with putative high-risk genotypes for both hOGG1 and XRCC1, the OR was 3.0 (95% CI, 1.0-8.8). Furthermore, subjects with putative high-risk genotypes for hOGG1, XRCC1, and CYP2E1 had an OR of disease of 25 (95% CI, 3.5-177). Polymorphisms of the DNA repair genes hOGG1 (codon 326) and XRCC1 (codon 280) are associated with an altered risk of NPC. Carriers of multiple putative high-risk genotypes have the highest risk of developing NPC.