Structural and functional evolution of human immunodeficiency virus type 1 long terminal repeat CCAAT/enhancer...

The appearance and progression of human immunodeficiency virus type 1 (HIV-1)-associated pathogenesis in the immune and central nervous systems is dependent on the ability of the virus to replicate in these compartments, which is, in turn, controlled by numerous factors, including viral binding and entry, receptor and coreceptor usage, and regulation of viral expression by the long terminal repeat (LTR). The LTR promotes viral expression in conjunction with viral and cellular regulatory proteins, including members of the CCAAT/enhancer binding protein (C/EBP) family, which modulate LTR activity through at least two cis-acting binding sites. Previous studies have shown that these sites are necessary for HIV-1 replication in cells of the monocyte/macrophage lineage, but dispensable in T lymphocytes. To establish potential links between this important family of transcription factors and HIV-1-associated pathogenesis, C/EBP site I and II sequence variation in peripheral blood mononuclear cell (PBMC)-derived LTRs from HIV-1-infected patients with varying degrees of disease severity was examined. A high prevalence of C/EBP site variants 3T (site I) and consensus B (site II) within PBMC-derived HIV-1 LTRs was shown to correlate with late stage disease in HIV-1-infected patients. These results suggest that the increased prevalence in the PBMCs of HIV-1 LTRs containing the 3T C/EBP site I variant and the consensus B site II variant may serve as a molecular marker for disease progression within the immune system. The relative low or high binding affinity of C/EBP beta to sites I and II in electrophoretic mobility shift (EMS) analyses correlated with low or high LTR activity, respectively, in transient expression analyses during both early and late disease stages. The 3T C/EBP site I was the only variant examined that was not found in LTRs derived from PBMCs of patients at early stages of HIV-1 disease, but was found at increasing frequencies in patients with late stage disease. Furthermore, the 3T C/EBP site I was not found in brain-derived LTRs of patients without HIV-1-associated dementia (HIVD), but was found in increasing numbers in brain-derived LTRs from patients diagnosed with HIVD. The C/EBP site I 3T variant appears to be exclusive to patients progressing to increasingly severe HIV-1-associated immunologic and neurologic disease.