TAPI polymorphisms in several human ethnic groups: characteristics, evolution, and genotyping strategies

The antigen processing-associated transporter gene polymorphism: Role on gene and protein expression in HPV-infected pre-cancerous cervical lesion

Human papillomavirus (HPV) is the major pathogen for cervical lesions. The evasion mechanism of the immune response and persistence of HPV infection can be influenced by polymorphisms (SNPs) in genes associated with transporter associated with antigen processing (TAP), which may change the peptide binding affinity or the TAP expression impacting the efficiency of peptide transport in the secretory pathway, and the presentation of peptides to cytotoxic T lymphocytes. This study aimed to evaluate the role of the TAP1 and TAP2 polymorphisms, TAP1, and TAP2 genes expressions, and protein levels in cervical cells presenting different degrees of pre-cancerous lesions in 296 immunocompetent women infected or not by HPV. TAP SNPs were genotyped by Sanger sequencing, and gene expression by real-time PCR. Aneuploidy was determined by DNA index using flow cytometry. TAP-1 and TAP-2 tissue expressions were evaluated by immunohistochemistry. The Asp697Gly SNP of TAP1 presented a risk for cellular aneuploidy (P=0.0244). HPV+ women had higher TAP-2 mRNA (P=0.0212) and protein (P<0.0001) levels. The TAP2D and TAP2E haplotypes were associated with the risk for aneuploidy and pre-cancerous lesions. In conclusion, nucleotide variability at the peptide binding region of peptide transporter genes, particularly of the TAP2 gene, may influence the HPV-peptide transportation from the cytosol to the endoplasmic reticulum, increasing the susceptibility to the development of high-grade cervical lesions.

Association between TAP gene polymorphisms and tuberculosis susceptibility in a Han Chinese population in Guangdong

Tuberculosis (TB) is an important public health problem. Studies indicated that TAP plays a key role in the presentation and transport of antigenic peptides during anti-M.tb infection. Given the important biological role of the TAP gene involved in anti-M.tb infection, a family-based case–control study including 133 tuberculosis patients, 107 healthy household contacts, and 173 healthy controls was conducted to assess the association between TAP gene polymorphisms and TB susceptibility. The basic information of subjects and their blood samples were collected. Four SNPs including rs1135216, rs1057141, rs241447, and rs3819721 were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR–RFLP). Our results suggested that BMI, residence, bedroom crowding, indoor humidity, fitness activities, history of smoking, and TB exposure history were associated with the occurrence of tuberculosis (P < 0.05). A significant association was observed between the TAP1 rs1135216 CT/CC genotype and increased TB risk, and the ORs were 2.56 (95% CI 1.31–4.99) and 6.73 (95% CI 1.33–34.02), respectively. TAP2 rs3819721 GG genotype carriers also showed an increased risk of TB when compared TB patients to healthy household contacts. Haplotype analysis revealed that the haplotype CT at rs1057141 and rs1135216 (OR = 11.34, 95% CI 1.49–86.56; OR = 7.45, 95% CI 1.43–38.76), as well as TA at rs241447 and rs3819721 (OR = 2.20, 95% CI 1.07–4.56) had a significantly increased risk of TB. The genetic risk scores (GRS) analysis of the four loci indicated that the risk of tuberculosis increased with increasing GRS scores in TB vs HHC (P_trend = 0.010) and in TB vs HC (P_trend = 0.001). In conclusion, our findings suggested that the SNPs of rs1135216 and rs3819721 were associated with TB susceptibility among the tuberculosis-prone families in the Chinese Han population and the risk of developing tuberculosis increases with the number of risk alleles, which could help identify high-risk groups in time and take scientific preventive measures. Further cohort studies with large samples are needed to validate the role of TAP gene variants on TB susceptibility.

Analysis of transporter associated with antigen presentation (TAP) genes polymorphisms with HIV-1 infection

Human leukocyte antigen (HLA) class I molecules of the human major histocompatibility complex (MHC) play an important role in modulating immune response. HLA class I molecules present antigenic peptides to CD8⁺ T cells and thereby play a role in the immune surveillance of cells infected with viruses. TAP1 and TAP2 are MHC-II-encoded genes necessary for the generation of a cellular immune response and polymorphism of these genes can influence the specificity of peptides preferentially presented by the MHC class I molecules and the outcome of the immune response. Several studies implicated genetic variation in TAP genes to various immune-mediated and infectious diseases. To determine the correlation between HIV-1 infection and the TAP1 and TAP2 genes polymorphisms, we performed PCR–RFLP assay of these genes in 500 HIV-1 seropositives and the matched seronegative individuals. Statistical analysis of the data disclosed no correlation between TAP1 (C/T intron 7) gene polymorphism and HIV-1/AIDS disease. However, the current results demonstrated that the heterozygous A/G [OR (95% CI) 1.39 (1.06–1.83), P = 0.0171] and homozygous G/G [OR (95% CI) 3.38(1.56–7.46), P = 0.0010] variants of TAP2 (A/G exon 11) (T665A) gene are positively associated with an increased risk of HIV-1/AIDS infection. This case–control analysis might suggest a possible role of TAP2 (A/G exon 11) (T665A) gene in the susceptibility to HIV-1 infection and disease outcome among North Indian patients.

Improved Transgenic Mouse Model for Studying HLA Class I Antigen Presentation

HLA class I (HLA-I) transgenic mice have proven to be useful models for studying human MHC-related immune responses over the last two decades. However, differences in the processing and presentation machinery between humans and mice may have profound effects on HLA-I restricted antigen presentation. In this study, we generated a novel human TAP-LMP (hTAP-LMP) gene cluster transgenic mouse model carrying an intact human TAP complex and two human immunoproteasome LMP subunits, PSMB8/PSMB9. By crossing the hTAP-LMP strain with different HLA-I transgenic mice, we found that the expression levels of human HLA-I molecules, especially the A3 supertype members (e.g., A11 and A33), were remarkably enhanced in corresponding HLA-I/hTAP-LMP transgenic mice. Moreover, we found that humanized processing and presentation machinery increased antigen presentation of HLA-A11-restricted epitopes and promoted the rapid reduction of hepatitis B virus (HBV) infection in HLA-A11/hTAP-LMP mice. Together, our study highlights that HLA-I/hTAP-LMP mice are an improved model for studying antigen presentation of HLA-I molecules and their related CTL responses.

Dimorphism of TAP-1 gene in Caucasian with juvenile myoclonic epilepsy and in Tunisian with idiopathic generalized epilepsies

Juvenile myoclonic epilepsy (JME) is the most common form of idiopathic generalized epilepsies (IGE) that account for about 5-10% of all types of epilepsies. The first putative locus termed EJM1 is on the human leucocyte antigen (HLA-II) region of chromosome 6p21.3. Interestingly, the EJM1 region includes the Transporter associated with antigen processing 1 (TAP-1) gene encoding the TAP-1, and previous studies have reported associations between HLA-II polymorphisms and different types of epilepsy. In this study, we report an association between two TAP-1 functional polymorphisms the I333V and the D637G and most common IGE in Tunisian population, but we fail to find significant results in Caucasian with JME.

BRD2 and TAP-1 genes and juvenile myoclonic epilepsy

Juvenile myoclonic epilepsy (JME) is a genetically determined common subtype of idiopathic generalized epilepsy. Linkage of JME to the chromosomal region 6p21.3 has been reported. An association has been previously observed between JME and the positional candidate, 6p21.3 linked, BRD2. Another candidate in this region is the TAP-1 gene encoding the Transporter Associated with Antigen Processing. The aim of the present study is to determine whether these two genes modulate the vulnerability to JME. While no difference was observed in the allele and genotype frequencies of BRD2 between JME and controls, an association was found between a TAP-1 haplotype and JME, suggesting that this gene may be another 6p21.3 linked vulnerability factor to JME.

Transporter associated with antigen processing (TAP) 1 gene polymorphisms in patients with hypersensitivity pneumonitis

Hypersensitivity pneumonitis (HP) is a lung inflammatory disease caused by the inhalation of a variety of antigens. Previous studies support the role of the major histocompatibility complex (MHC) class II genes in the susceptibility to develop HP. However, the putative role of other MHC loci has not been elucidated. Transporters associated with antigen processing (TAP) genes are located within the MHC class II region and play an important role transporting peptides across the endoplasmic reticulum membrane for MHC class I molecules assembly. The distribution of single nucleotide polymorphisms (SNPs) in TAP1 genes was analyzed in 73 hypersensitivity pneumonitis (HP) patients and 58 normal subjects. We found a significant association of the allele Gly-637 (GGC) (p=0.00004, OR=27.30, CI=3.87-548.04) and the genotypes Asp-637/Gly-637 (p=0.01, OR=16.0, CI=2.19-631.21), Pro-661/Pro-661 (p=0.006, OR=11.30, CI=2.28-75.77) with HP. A significant decrease in the frequency of the allele Pro-661 (CCA) (p=0.008, OR=0.06, CI=0-0.45), the genotype Asp-637/Asp-637 (p=0.01, OR=0.17, 95% CI=0.05-0.58) and the haplotype [Val-333 (GTC), Val-458 (GTG), Gly-637 (GGC), Pro-661 (CCA)] was detected in HP patients compared with controls (p=0.002, OR=0.07, CI=0.0-0.57). These findings suggest that TAP1 gene polymorphisms are related to HP risk, and highlight the importance of the MHC in the development of this disease.

A Rare Transporter Associated with Antigen Processing Polymorphism Overpresented in HLAlow Colon Cancer Reveals the Functional Significance of the Signature Domain in Antigen Processing

Transporter associated with antigen processing (TAP), a member of the ATP-binding cassette transporter superfamily, is composed of two integral membrane proteins, TAP-1 and TAP-2. Each subunit has a C-terminal nucleotide-binding domain that binds and hydrolyzes ATP to energize peptide translocation across the endoplasmic reticulum membrane. A motif comprising the sequence LSGGQ (called the signature motif) and the amino acid that is immediately C-terminal to this motif are highly conserved in the nucleotide-binding domains of ATP-binding cassette transporters. To search for natural variants of TAP-1 with alterations in or near the signature motif, we sequenced the TAP-1 exon 10 amplified from 103 human colon cancer samples. We found a rare TAP-1 allele with an R>Q alteration at a residue immediately C-terminal to the signature motif (R648) that occurred 17.5 times more frequently in colon cancers with down-regulated surface class I MHC than those with normal MHC levels (P = 0.01). Functional analysis revealed that the Q648 variant had significantly reduced peptide translocation activity compared with TAP-1 (R648). In addition, we found that mutations S644R, G645R, G646S, and G646D interfered with TAP-1 activity. TAP-1 G646D, which showed the most severe defect, resided normally in the endoplasmic reticulum and associated with the peptide loading complex, but failed to transport peptide across the endoplasmic reticulum membrane. Thus, a TAP-1 polymorphism adjacent to the signature motif may be a contributing factor for MHC class I down-regulation in colon cancer. Given the widespread defects in DNA mismatch repair in colon cancer, mutations at or near the signature domain can potentially modulate antigen processing.

Molecular typing of human leukocyte antigen and related polymorphisms following whole genome amplification

Reliable, high-resolution genotyping of human leukocyte antigen (HLA) polymorphisms is often compromised by DNA samples of suboptimal quality or limited quantity. We tested the feasibility of molecular typing for variants at HLA and neighboring loci using whole genome amplification (WGA) strategy facilitated by the Phi29 DNA polymerase. With little (5-100 ng) starting genomic DNA of varying quality and source materials, WGA was deemed successful in 167 of 169 DNA from 47 cell lines, 100 European Americans, and 22 native Africans. The Phi29-processed DNA provided adequate templates for polymerase chain reaction (PCR)-based analyses of several HLA (A, B, C, DRB1, and DQB1) and related loci (HFE, MICA, and 10 microsatellites) in the 6p24.3-6p21.3 region, with PCR amplicons ranging from 92 to 2200 bp. Five different genotyping techniques resolved and confirmed 364 genotypes when both original and Phi29-processed DNA worked in PCRs. General population genetic analyses provided additional evidence that WGA may represent a reliable and simple approach to securing ample genomic DNA for typing HLA, MICA, and related variants.

Novel TAP1 polymorphisms in indigenous Zimbabweans: their potential implications on TAP function and in human diseases

Because of the essential role of transporter associated with antigen processing (TAP1 or TAP2) molecule in antigen processing, the implication of its polymorphism as a factor involved in human diseases and the possible genetic variation at this locus among ethnically diverse populations, we underwent a study to analyze the full extent of TAP1 polymorphism in an indigenous Zimbabwean population (Shona ethnic group). Using single-stranded conformation polymorphism and DNA direct sequencing procedures, we detected the presence of 11 nucleotide sequence variations in the entire coding region of TAP1. Of these variants, eight are nonconservative substitutions with respect to amino acid composition and are located in a critical part of the protein that could modulate its function. Five new polymorphic sites were identified in exon 1 (codons 7 Pro --> Ser, 17 Gly --> Arg, 141 Val --> Val), exon 6 (codon 419 Gly --> Cys), and exon 7 (codon 487 Arg --> Arg). Significant differences were seen in the distribution of TAP1*0201 and TAP1*0401 alleles, and codon 333 (Ile --> Val) polymorphism among African and non-African populations. Thus, TAP1 polymorphism has evolved differently among populations presumably because of the evolutionary pressures generated by prevalent pathogens in these geographically distinct regions.

Single nucleotide polymorphism identification in candidate gene systems of obesity

We have constructed a large panel of single nucleotide polymorphisms (SNP) identified in 68 candidate genes for obesity. Our panel combines novel SNP identification methods based on EST data, with public SNP data from largescale genomic sequencing, to produce a total of 218 SNPs in the coding regions of obesity candidate genes, 178 SNPs in untranslated regions, and over 1000 intronic SNPs. These include new non-conservative amino acid changes in thyroid receptor beta, esterase D, acid phosphatase 1. Our data show evidence of negative selection among these polymorphisms implying functional impacts of the non-conservative mutations. Comparison of overlap between SNPs identified independently from EST data vs genomic sequencing indicate that together they may constitute about one half of the actual total number of amino acid polymorphisms in these genes that are common in the human population (defined here as a population allele frequency above 5%). We have analyzed our polymorphism panel to construct a database of detailed information about their location in the gene structure and effect on protein coding, available on the web at http://www.bioinformat ics.ucla.edu/snp/obesity. We believe this panel can serve as a valuable new resource for genetic and pharmacogenomic studies of the causes of obesity.

Distribution of TAP gene polymorphisms and extended MHC haplotypes in Mexican Mestizos and in Seri Indians from northwest Mexico

The study of the genetic structure is very useful for investigating the biological significance of polymorphism and may provide clues to understand population origins. We present TAP1/TAP2 gene analysis in the Seri indians from Sonora, and in Mestizos from the highlands of Mexico. Thirty-two Seri and 89 Mestizos were studied. TAP genes were typed using the ARMS-PCR technique. The most frequent alleles in Seri were: TAP1*0101/02, (68.8%); TAP1*02011/02012, (31.2%); TAP2*0201, (38.7%) and TAP2*0101, (29.0%). TAP1*0301, TAP1*0401, TAP2*0102 TAP2*0103 and TAP2H were absent in them. For Mestizos, the prevalent alleles were: TAP1*0101/02 (75.8%); TAP1*02011/12 (20.3%); TAP2*0101 (45.4%) and TAP2*0201 (29.3%). These results are similar to those found in Kaingang and Caucasians from Brazil, four Mediterranean, other Caucasians, two Oriental and one African group. In Seri, the extended prevalent haplotypes are typically Amerindian, such as TAP1*0101/2-TAP2*0201-QBP3.21-DQB1*0302-QAP*3.1-DQA1*03011-DRB1*0407-B*3501-A*0201 (HF = 16.6%). Thirty-two extended haplotypes were found in Seri, although TAP contributed scarcely to diversity. Mestizos show Amerindian and Caucasian combinations. No difference was detected in the distribution of amino acids in the individual variable sites, between both groups. These findings are the basis for further anthropological studies and to explore the contribution of TAP genes to disease expression in Mexicans.