Philpott S M, Buehring G C
Program in Infectious Diseases, School of Public Health, University of California, Berkeley 94720, USA.
J Natl Cancer Inst. 1999 Jun 2;91(11):933-42. doi: 10.1093/jnci/91.11.933.
Human T-cell leukemia virus (HTLV)/bovine leukemia virus (BLV) group retroviruses, which cause hematopoietic cancers, encode a unique protein, Tax, involved in the transformation of infected cells. Our purpose was to determine whether the mechanism by which Tax protein induces transformation in HTLV- or BLV-infected cells involves DNA damage.
We used a micronucleus assay to measure chromosomal damage and alkali denaturation analysis to test host-cell DNA integrity in cells infected with HTLV, BLV, or simian T-lymphotropic virus or in cells transfected with the tax gene of HTLV or BLV. Controls included uninfected cells and cells infected with other oncogenic retroviruses or oncogenic DNA viruses. We used a plasmid reactivation assay to examine whether the damage might be due to the inhibition of DNA repair. To ascertain which of several repair pathways might be inhibited, chemical methods were used to selectively introduce lesions repaired by specific pathways into the reporter plasmid.
The presence of Tax was associated with DNA damage. HTLV- or BLV-infected or tax-transfected cells showed normal ability to repair damage induced by deoxyribonuclease I or psoralen but markedly decreased ability to repair damage induced by UV light, quercetin, or hydrogen peroxide.
These data suggest that the DNA repair pathway most inhibited by Tax is base-excision repair of oxidative damage. To our knowledge, this is the first report demonstrating inhibition of DNA repair by any retrovirus and suggests that this inhibition of DNA repair may contribute to the mechanism of cell transformation by the HTLV/BLV group of viruses.
导致造血系统癌症的人类T细胞白血病病毒（HTLV）/牛白血病病毒（BLV）属逆转录病毒编码一种独特的蛋白质Tax，它参与受感染细胞的转化过程。我们的目的是确定Tax蛋白在HTLV或BLV感染细胞中诱导转化的机制是否涉及DNA损伤。
我们使用微核试验来测量染色体损伤，并通过碱变性分析来检测感染HTLV、BLV或猿猴T淋巴细胞白血病病毒的细胞或转染了HTLV或BLV的tax基因的细胞中宿主细胞DNA的完整性。对照组包括未感染的细胞以及感染其他致癌逆转录病毒或致癌DNA病毒的细胞。我们使用质粒再激活试验来检查损伤是否可能是由于DNA修复的抑制。为了确定几种修复途径中的哪一种可能受到抑制，我们采用化学方法将由特定途径修复的损伤选择性地引入报告质粒中。
Tax的存在与DNA损伤有关。HTLV或BLV感染的细胞或转染tax基因的细胞对脱氧核糖核酸酶I或补骨脂素诱导的损伤具有正常的修复能力，但对紫外线、槲皮素或过氧化氢诱导的损伤的修复能力明显下降。
这些数据表明，Tax最抑制的DNA修复途径是氧化损伤的碱基切除修复。据我们所知，这是第一份证明任何逆转录病毒可抑制DNA修复的报告，并表明这种对DNA修复的抑制可能有助于HTLV/BLV属病毒的细胞转化机制。
