A quantitative assay for trans-activation by HIV-1 Tat, using liposome-mediated DNA uptake and a parallel ELISA system

Expression of human immunodeficiency virus type 1 tat from a replication-deficient herpes simplex type 1 vector induces antigen-specific T cell responses

Herpes simplex type-1 virus (HSV-1) based vectors have been widely used in different gene therapy approaches and also as experimental vaccines against HSV-1 infection. Recent advances in the HSV-1 technology do support the use of replication defective HSV-1 as vaccine vectors for delivery of foreign antigens. We have examined the ability of a recombinant replication-defective HSV-1 vector expressing the HIV-1 Tat protein to induce long-term Tat-specific immune responses in the Balb/c murine model. The results showed that vector administration by the subcutaneous route elicits anti-Tat specific T-cell mediated immune responses in mice characterized by the presence of the Tat-specific cytotoxic activity and production of high levels of IFN-gamma.

The human immunodeficiency virus Tat proteins specifically associate with TAK in vivo and require the carboxyl-terminal domain of RNA polymerase II for function

Human immunodeficiency virus types 1 and 2 encode closely related proteins, Tat-1 and Tat-2, that stimulate viral transcription. Previously, we showed that the activation domains of these proteins specifically interact in vitro with a cellular protein kinase named TAK. In vitro, TAK phosphorylates the Tat-2 but not the Tat-1 protein, a 42-kDa polypeptide of unknown identity, and the carboxyl-terminal domain (CTD) of RNA polymerase II (RNAP II). We now show that the 42-kDa substrate of TAK cochromatographs with TAK activity, suggesting that this 42-kDa polypeptide is a subunit of TAK. We also show that the Tat proteins specifically associate with TAK in vivo, since wild-type Tat-1 and Tat-2 proteins expressed in mammalian cells, but not mutant Tat proteins containing a nonfunctional activation domain, can be coimmunoprecipitated with TAK. We also mapped the in vivo phosphorylation sites of Tat-2 to the carboxyl terminus of the protein, but analysis of proteins with mutations at these sites suggests that phosphorylation is not essential for Tat-2 transactivation function. We further investigated whether the CTD of RNAP II is required for Tat function in vivo. Using plasmid constructs that express an alpha-amanitin-resistant RNAP II subunit with a truncated or full-length CTD, we found that an intact CTD is required for Tat function. These observations strengthen the proposal that the mechanism of action of Tat involves the recruitment or activation of TAK, resulting in activated transcription through phosphorylation of the CTD.

Lentivirus Tat proteins specifically associate with a cellular protein kinase, TAK, that hyperphosphorylates the carboxyl-terminal domain of the large subunit of RNA polymerase II: candidate for a Tat cofactor

Efficient replication of human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2) requires the virus transactivator proteins known as Tat. In order to understand the molecular mechanisms involved in Tat transactivation, it is essential to identify the cellular target(s) of the Tat activation domain. Using an in vitro kinase assay, we previously identified a cellular protein kinase activity, Tat-associated kinase (TAK), that specifically binds to the activation domains of Tat proteins. Here it is demonstrated that TAK fulfills the genetic criteria established for a Tat cofactor. TAK binds in vitro to the activation domains of the Tat proteins of HIV-1 and HIV-2 and the distantly related lentivirus equine infectious anemia virus but not to mutant Tat proteins that contain nonfunctional activation domains. In addition, it is shown that TAK is sensitive to dichloro-1-beta-D-ribofuranosylbenzimidazole, a nucleoside analog that inhibits a limited number of kinases and is known to inhibit Tat transactivation in vivo and in vitro. We have further identified an in vitro substrate of TAK, the carboxyl-terminal domain of the large subunit of RNA polymerase II. Phosphorylation of the carboxyl-terminal domain has been proposed to trigger the transition from initiation to active elongation and also to influence later stages during elongation. Taken together, these results imply that TAK is a very promising candidate for a cellular factor that mediates Tat transactivation.