Infection of lymphoid cells by integration-defective human immunodeficiency virus type 1 increases de novo methylation

DNA methylation, by regulating the transcription of genes, is a major modif ier of the eukaryotic genome. DNA methyltransferases (DNMTs) are responsibl e for both maintenance and de novo methylation. We have reported that human immunodeficiency virus type 1 (HIV-1) infection increases DNMT1 expression and de novo methylation of genes such as the gamma interferon gene in CD4( +) cells. Here, we examined the mechanisms) by which HIV-1 infection increa ses the cellular capacity to methylate genes. While the RNAs and proteins o f all three DNMTs (1, 3a, and 3b) were detected in Hut 78 lymphoid cells, o nly the expression of DNMT1 was significantly increased 3 to 5 days postinf ection. This increase was observed with either wild-type HIV-1 or an integr ase (IN) mutant, which renders HIV replication defective, due to the inabil ity of the provirus to integrate into the host genome. Unintegrated viral D NA is a common feature of many retroviral infections and is thought to play a role in pathogenesis. These results indicate another mechanism by which unintegrated viral DNA affects the host. In addition to the increase in ove rall genomic methylation, hypermethylation and reduced expression of the p1 6(INK4A) gene, one of the most commonly altered genes in human cancer, were seen in cells infected with both wild-type and IN-defective HIV-1. Thus, i nfection of lymphoid cells with integration-defective HIV-1 can increase th e methylation of CpG islands in the promoters of genes such as the p16(INK4 A) gene, silencing their expression.