Functional analysis of the chemokine and chemokine receptors encoded by human herpesvirus 6.

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Human henpesvirus 6(HHV-6), which belongs to the betaherpesvirus subfamily and infects mainly T cells and mononuclear cells in vitro, causes acute and latent infections. Two variants of HHV-6 have been distinguished on the basis of differences in several properties. We have determined the complete DNA sequence of HHV-6 variant B(HHV-6B)strain HST, the causative agent of exanthem subitum, and compared the sequence with that of variant A strain U1102. A total of 115 potential open reading frames(ORFs)were identified within the 161,573-bp contiguous sequence of the entire HHV-6 genome, including some genes with remarkable differences in amino acid identity. U83 of strain HST encodes a chemokine, which functions as a chemoattractant for monocytes. Similarly, U83 of strain U1102 encodes a chemokine homolog, but it does not contain a signal peptide sequence. Thus, U83 of strain U1102 may not be secreted and thus cnnot exert its chemotactic activity. If U83 functions as a chemoattractant in v … More ivo, it is possible that HHV-6 can easily spread through cell-to-cell infection, even in the presence of neutral antibodies. U12 of strain Z29 is truncated and dose not encode a calcium-mobilizing receptor for CC-chemokines which is encoded by that of strain HST.Nobody know the pathogenesis of strain Z29. These findigns suggested that the product of U12 may play an important role in the pathogenesis of HHV-6 through transmembrane signaling by binding with CC-chemokines.We have cloned the U83 gene and analyzed the biological function of this gene. The U83 gene contained an ORF encoding a 113-amino-acid peptide, starting at the first methionine and containing a possible signal peptide and the typical cysteine residues chanacteristic of the chemokines. Reverse transcription-PCR analysis of mRNA and immunofluorescent-antibody testing of infected cells both indicated that the encoded protein was a late protein. The ORF U83 gene fused to the FC gene was expressed as a fusion protcin in COS-7 cells by tnansfection, and the fusion protein was purified from the supernatant of transfected cells to test its biological function. The purified protein was capable of inducing transient calcium mobilization in THP-1 cells and of chemotactically activating THP-1 cells. These findings suggested that the U83 protein might play an important role in HHV-6 propagation in vivo by activating and trafficking mononuclear cells to sites of vira replication, thus aiding the development of superbly efficient virus production mechanisms. Less