The NPC collaborative study has as its primary objective the discovery of genes and characterization of variant alleles associated with the development of NPC in a Chinese population. NPC is a leading cause of cancer deaths in the Cantonese population in China. Case-control studies have indicated a strong role for environmental factors, including food preservatives (carcinogenic nitrosamines), salt-preserved fish, and phorbol esters in herbs and plants that are commonly consumed among ethnic populations with the highest NPC rates. Familial aggregation of NPC and evidence of linkage have been observed in China and in other countries. Since chronic EBV replication, as evidenced by detection of immunoglobulin A (IgA) antibody against EBV viral capsid, and exposure to dietary factors are predictive of NPC but do not explain all of the disease, we have hypothesized that there may also be genetic factors contributing to the development of NPC. We have therefore developed a case-control study to investigate the genetic correlates of NPC in a highly impacted region of southern China. HCC is one of the most common cancers worldwide and a leading cause of death in many countries, especially in East Asia and sub-Saharan African. HCC is also increasing in developed countries. In the United States the incidence of HCC increased from 1.4 per 100,000 population for the period from 1976 to 1980 to 2.4 per 100,000 for the period from 1991 to 1995. Both aflatoxin B1 (AFB1) contamination and HBV infection are well-recognized risk factors for HCC. AFB1 is one of the most potent carcinogens to which humans are exposed. AFB1 has a wide distribution and high concentration in human and animal foods particularly in HCC endemic regions along the southeast seacoast. Among them Guangxi is a HCC high-risk region where both AFB1 contamination and HBV infection are common. In Southeast Asia and certain regions of Africa, aflatoxin consumption and infection by HBV are important factors giving rise to the extraordinarily high incidence rates (24.235.5/100 000) of HCC in these areas. HBV-induced chronic active hepatitis and cirrhosis constitute major factors in liver carcinogenesis. HBV is associated with 70-75% of all HCC cases in Asia, the continent with the highest prevalence of HBV. A synergistic effect of AFB1 and HBV in increasing risk for HCC has been reported in many studies. We hypothesize that if there is a host genetic effect on oxidative stress leading to the development of HCC, it would be most evident in a population exposed to environmental hepatocarcinogens where exposure and dosage is strong enough to manifest the genetic effects. Both animal and in vitro studies indicate that oxidative stress might contribute to the key pathways in either virus or chemical induced hepatocarcinogenesis. There is evidence for strong correlations between environmental carcinogens and oxidative stress in study participants with both HBV infection and exposures to environmental carcinogens, providing an opportunity to screen candidate genotypes/haplotypes for HCC risk in this unique population. We will be using a candidate gene approach selecting genes involved in oxidative repair pathways. For targeted genes, all SNPs within regulatory, splice sites or coding regions (both synonymous and nonsynonymous) will be selected and htSNPs added to capture more than 95% of the variation. Gene-gene and gene-environment interactions will be fully analyzed in this model. The findings will be further compared with a HBV outcome case-control study of subjects from northern China. Accomplishments: Completion of enrollment and data collection for the NPC study: Enrollment, data collection, and DNA extractions for the NPC study Phase I and Phase II of the NPC study have been completed. Family triads were enrolled for haplotype inference and for quality control assessment of the pilot. No Mendelian errors were observed within any of the family triads attesting to the fidelity of sample handling and genotyping. Phase II is a cross-sectional case-control study and included a questionnaire to capture environmental factors, including occupational, dietary and tobacco exposures. The completion of enrollment of Phase I and II participants (n=4000) and the addition of environmental exposure data provides adequate power to discover main effect genes and to test gene-environment interactions. To investigate the roles of genetic variations of carcinogen metabolic genes in NPC susceptibility in Han Chinese population, polymorphisms CYP2E1, GSTP1, MPO, NQO1 and deletion alleles that knockout GSTM1 and GSTT1 expression were genotyped in NPC cases and controls. We found male individuals who carried GSTM1/GSTT1 double null genotype had a higher risk for NPC (OR = 1.76, 95% CI = 1.04-2.97, p = 0.03); this association was not observed for females. We are now looking for interactions with smoking since more than 75% of men report tobacco smoking but less than 10% of women. Our results suggest that the GSTM1/GSTT1 double null genotype may be a risk factor for NPC in southern China, but this result requires replication. We have also completed analysis of environmental risk factors. Domestic exposures to wood fires, occupational exposures to solvents, and a family history of NPC were all significantly associated with increased risk for the development of NPC. Sample collection and biomarker status for the HCC study: DNA from HCC liver tissues from HBV-infected persons and peripheral leukocytes of HBV-infected controls, together with plasma and urinary biomarkers of HIV infection, aflatoxin exposure and oxidative stress have been completed. Candidate genes and SNPs have been selected for genotyping using the Illumina Goldengate platform. These include genes involved in carcinogenesis, biotransformation and oxidative damage repair pathways. SNPs were selected based on their putative or known function or because they were haplotype tagging All samples are from HCC patients and local controls from Guangxi Province, a HCC endemic area in China where both AFB1 contamination and HBV infection are well-recognized risk factors. A database of all laboratory and clinical records, including carcinogen (aflatoxin) and oxidative stress biomarkers, has been established. We have also completed sequencing of p53 in patients with HCC and domestic exposures to aflatoxin and alcohol.
| An, Ping; Johnson, Randall; Phair, John et al. (2009) APOBEC3B deletion and risk of HIV-1 acquisition. J Infect Dis 200:1054-8 |
| Guo, Xiuchan; Johnson, Randall C; Deng, Hong et al. (2009) Evaluation of nonviral risk factors for nasopharyngeal carcinoma in a high-risk population of Southern China. Int J Cancer 124:2942-7 |
