EFFECTS OF HIV-1 TAT ON EXPRESSION OF HLA CLASS-I MOLECULES

Tat protein of HIV-1 is a potent transactivator of transcription and e ssential for HIV-1 replication. In addition, Tat has been proposed to possess immunosuppressive functions, suggesting that Tat may play a di rect role in the immune dysfunction associated with AIDS. Recently, it has been reported that Tat represses activity of a major histocompati bility complex (MHC) class I gene promoter. Because HIV infection down modulates expression of class I molecules, this data strongly suggests that Tat downregulates class I expression and leads to loss of CTL ac tivity. Here, we report effects of Tat on class I expression using a h uman cell line, T0, expressing Tat (T0-Tat). Northern blot analysis sh ows that levels of MHC class I transcripts are normal in TO-Tat. Flow cytometry analyses indicate that expression of HLA class I molecules i s not substantially downregulated to any great extent by Tat in T0-Tat . Further, pulse-chase experiments followed by Endoglycosidase-H treat ment show that the rate of maturation and processing of class I molecu les in T0-Tat is indistinguishable from that in the original cell line , T0. Taken together, these data suggest that Tat expression does not necessarily result in downregulation of class I expression.