In transient gene expression assays we observed an increase in expression of the bacterial chloramphenicol acetyl-transferase (CAT) gene, under the transcriptional control of the HIVA LTR (pLTR-CAT), when this plasmid was cotransfected into Vero or MRC-5 cells with a plasmid containing either the HCMV immediate early 1 and 2 (E1, IE2) genes (pRL43a) or just the IEZ gene (pMP18). When the HCMV IE, gene (pMP12) was cotransfected with pLTR-CAT into Vero cells the level of measurable CAT gene activity was below the level observed when pLTR-CAT was cotransfected with a nonspecific carrier plasmid (pGEM3). The negative influence of the HCMV IE1, gene product on the HIVA LTR in Vero cells was also observed when the HIVA tat gene (pLTR-TAT) was cotransfected into Vero cells with pLTR-CAT and pMP12. However, when the HCMV IE1 gene was cotransfected into rhabdomyosarcoma (RD) cells with proviral HIV-1 DNA, an increase in viral production, as monitored by measurement of HIV-1 reverse transcriptase activity, was observed. In electrophoretic mobility shift assays, nuclear extracts obtained 15 hr post-HCMV infection (hpi) were found to contain a lower level of interaction with an oligonucleotide which corresponded to the HIVA LTR Sp-1 binding motif. Nuclear extracts obtained 40 hpi of MRC-5 cells had a greater level of interaction with, and changed the mobility of, the Sp-1 oligonucleotide relative to the uninfected nuclear extracts. HCMV-infected MRC-5 cell nuclear extracts also contain a factor(s) which interacted with the HIV-1 LTR between nucleotide positions -15 to -2 relative to the HIV-1 mRNA Start Site.
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