CD4 PROMOTER TRANSACTIVATION BY HUMAN-HERPESVIRUS-6

The observation that human herpesvirus 6 (HHV-6) can induce CD4 gene t ranscription and expression in CD4(-) cells was reported several years ago (P. Lusso, A. De Maria, M. Malnati, F. Lori, S. E. DeRocco, M. Ba seler, and R. C. Gallo, Nature 349:533-535, 1991) and subsequently con firmed (P. Lusso, M. S. Malnati, A. Garzino-Demo, R. W. Crowley, E. O. Long, and R. C. Gallo, Nature 362:458-462, 1993; G. Furlini, M. Vigno li, E. Ramazzotti, M. C. Re, G. Visani, and M. LaPlaca, Blood 87:4737- 4745, 1996). Our objective was to identify the mechanisms underlying s uch phenomena. Using reporter gene constructs driven by the CD4 promot er, we report that HHV-6 can efficiently transactivate such genetic el ements. Activation of the CD? promoter occurs in the presence of the v iral DNA polymerase inhibitor phosphonoformic acid, which limits expre ssion to the immediate-early and early classes of viral genes. Using d eletion mutants and specific CD I promoter mutants, we identified an A TF/CRE binding site located at nucleotides -67 to -60 upstream of the CD4 gene transcription start site that is important for HHV-6 transact ivation. The ATF/CRE site is also essential for CD4 promoter activatio n by forskolin, an activator of adenylate cyclase. Using electrophoret ic mobility shift assays and specific antibodies, we showed that CREB- 1 binds specifically to the -79 to -52 region of the CD4 promoter. Las t, we have identified two open reading frames (ORFs) of HHV-6, U86 and U89 from the immediate-early locus A, that can transactivate the CD4 promoter in HeLa cells. However, transactivation of the CD4 promoter b y ORFs U86 and U89 is independent of the CRE element, suggesting that additional HHV-6 ORFs are likely to contribute to CD4 gene activation. Taken together, our results will help to understand the complex inter actions occurring between HHV-6 and the CD4 promoter and provide addit ional information regarding the class of transcription factors involve d in the control of CD4 gene expression.