CELLULAR AND VIRAL SPECIFICITY OF EQUINE INFECTIOUS-ANEMIA VIRUS TAT TRANSACTIVATION

Lentiviruses vary in their dependence on a functional tat gene during their viral life cycle. To begin to understand the viral and cellular parameters controlling equine infectious anemia virus (EIAV) transacti vation, we investigated Tat function and Tat and LTR structural requir ements necessary for successful transactivation. EIAV Tat expression w as required for detection of viral antigens from a full-length proviru s. The level of transactivation by EIAV Tat as measured by LTR-CAT ass ays correlated well with viral antigen expression. Using horse/mouse s omatic cell hybrids (SCH), a single SCH line which supported EIAV tran sactivation was identified, indicating that the presence of specific h orse chromosomes provided cellular factors required for transactivatio n. Transformed cell lines from several different species were also tes ted and found to differ in their ability to support EIAV transactivati on. A canine cell line, Cf2Th, which was permissive for EIAV transacti vation, and a human cell line, HeLa, which was not permissive for EIAV transactivation, were used to map regions of the LTR and Tat that wer e important in cell-specific transactivation. As expected, the R regio n of EIAV LTR was required for transactivation by EIAV Tat in all cell lines studied. Similarly, the R region of HIV LTR was necessary for t ransactivation by HIV Tat. However, the composition of the Us region a lso influenced transactivation in a cell-specific manner. In Cf2Th cel ls, replacement of EIAV U3 sequences with HIV U3 sequences resulted in high basal (nontransactivated) expression, and as a result, only a tw ofold increase in expression was observed in the presence of EIAV Tat. Similar studies using HIV Tat demonstrated that transactivation occur red in Cf2Th cells when either EIAV or HIV U3 sequences were present i n the LTR. In contrast, transactivation by either HIV or EIAV Tat in H eLa cells required the presence of HIV enhancer sequences. These findi ngs suggested that the ability of transactivation to occur in some cel l lines may involve interactions between cell-specific transcription f actors and the activation domain of Tat. For transactivation in other cell lines, Tat appeared to require more ubiquitious factors that inte ract with both EIAV and HIV U3 sequences. (C) 1994 Academic Press, Inc .