It is known that many viruses including HIV-1 induce cell cycle arrest in G2 phase via G2/M checkpoint activation through a variety of mechanisms.[18] HIV-1 is a subtype of HIV, that functions like retrovirus and the integration after reverse transcription is important for its proliferation.[19] The integration of HIV-1 can cause DSB of CD4+ T cell and activate G2/M checkpoint that leads to cell cycle arrest.[20, 21] This mechanism will also affect the proliferation of HIV-1.[22] Therefore, it is critical to investigate the association between G2/M checkpoint and HIV-1. In this study, 42 tSNPs in ATR, Chk1, Cdc25C and CDK1 gene were genotyped to analysis the association with susceptibility to HIV-1 infection and AIDS progress among MSM population in the northern China.
ATR, as a sensor of DNA damage, contributes to cell cycle arrest, DNA damage repair and stable replication of cells after being activated, which is an important kinase of avoiding apoptosis for cells.[23, 24] A study also found that Vpr-induced structural alteration of DNA can trigger ATR-mediated DNA damage response and contributed to HIV-1 infection.[13] Previous reports showed that rs13091637, which also located in the ATR intronic region and was in strong linkage disequilibrium with rs34660854 in Chinese population of and, was significantly associated with melanoma and breast cancer.[25–27] The results in our study showed that rs34660854-A and rs75368165-A in ATR gene were significantly associated with increased susceptibility to HIV-1 infection. These two SNPs also showed significant differences under codominant and dominant model. It indicated that the rs34660854-A and rs75368165-A in ATR gene were the pathogenic factors for HIV-1 infection. The genotypes carrying risk alleles of these tSNPs were more likely to infect HIV-1 among MSM population in the northern China. By analyzing the effect of the SNPs on AIDS progression, rs75069062 showed a difference between clinical phase I/II/III and clinical phase IV. Although rs34660854, rs75368165 and rs75069062 were all located in the intronic regions, they might be responsible for affecting gene function at transcription level, splicing enhancer or silencer and other mechanisms.
Chk1 was phosphorylated and activated by ATR after DNA damage had been sensed by ATR at G2/M checkpoint. The genetic mutations of Chk1 gene can cause many kinds of disease such as breast cancers, colorectal cancers, human lymphoid neoplasms and so on.[28–30] However, there are few reports which clearly explain the association between Chk1 and HIV-1 infection. Our results showed that rs12576279 and rs540436 in Chk1 gene were significantly associated with HIV-1 infection risk under codominant and dominant model. The results found that the individuals carrying rs12576279-T were at lower risk for HIV-1infection. It also indicated that the genotypes including rs540436-T were pathogenic factors for HIV-1 infection. In addition, rs10893405 also showed significant differences between clinical phase I/II/III and IV by analyzing the association between the polymorphisms of Chk1 gene and AIDS progression. It indicated that the rs10893405-G was the risk factor of AIDS progression. Furthermore, a haplotype (H7) and haploid allele of Chk1 gene was significantly associated with HIV-1 infection susceptibility. These three SNPs were all located in the intronic regions and we didn’t find any publications about them in NCBI database (https://www.ncbi.nlm.nih.gov). Moreover, the functional studies about these SNPs with HIV-1 infection needed to be carried out.
The protein Cdc25 is a key inducer for the entry of M phase and controls the timing of mitosis. It includes three homologues i.e. Cdc25A, Cdc5B and Cdc25C.[31] Cdc25C, which are phosphorylated and inactivated by Chk1, play important roles in the process of G2/M checkpoint.[32] Many reports showed that Cdc25A and Cdc25B were associated with breast cancers, colorectal cancers, non-small cell lung cancers and so on. But there were few reports about the association between Cdc25C and carcinogenesis.[33] Vpr, which is an important protein of HIV-1, can trigger G2 arrest by inhibiting the Cdc25C phosphatase activities. However, no study reported the association between the polymorphisms of Cdc25C and HIV-1 infection and AIDS progression.[12] Our results showed that rs3756766-A in Cdc25C gene was significantly associated with increased susceptibility to HIV-1 infection. Moreover, this SNP also showed a significant association under codominant and dominant model. It indicated that the rs3456766-A was the pathogenic factor of HIV-1 infection. Hence the genotypes including allele A could increase the cumulative risk of HIV-1 infection.
CDK1-Cyclin B1 complex plays an important role in the process of G2/M transition. The activation and nuclear accumulation of this complex are key events for G2/M transition.[34, 35] In the process of G2/M checkpoint, Cdc25C phosphatase activates CDK1 by removing two inhibitory phosphates from Thr14 and Tyr15.[36] A study showed that the Vif of HIV-1 could impair the mitotic entry by interfering with CDK1-Cyclin B1 complex activation causing cell cycle arrest.[10] However, the association of CDK1 polymorphisms and HIV-1infection and AIDS progression remains unclear. The results in our study showed that CDK1 rs139245206 was significantly associated with HIV-1 infection under codominant and recessive model. Although this SNP located in intron regions, it might regulate gene transcription level by binding with transcription factors.
Gene-gene interaction is extremely important, because many genes involve the complex process of G2/M checkpoint regulating cell cycle and the role of a single gene may be finite. Therefore, GMDR software was used to investigate the impact of interaction between ATR, Chk1, Cdc25C and CDK1 gene polymorphisms on HIV-1 infection susceptibility. Our results showed a three-locus model including ATR rs68065420, Chk1 rs1057733 and Cdc25C rs6861656, and participants with rs68065420-AA and rs1057733-TT and rs6861656-TT genotype had the highest HIV-1 infection risk. We also observed a drift of progressively increased risk of HIV-1 infection along with the high risk alleles observed in carrier participants.