The product of the Interferon gamma (IFN-gamma) gene is a potent modulator of the immune response. Induction of both IFN-gamma and IL2 mRNA transcription is concurrently stimulated by T-cell activation agents. Molecular analysis of the human IFN-gamma promoter has revealed separate sequence elements which either respond to T-cell activation signals, or to an alternate activator encoded by the human retroviruses, HTLV-I and II. Using a combination of gel retardation analysis, methylation protection, and UV cross-linking we will identify the molecular components in the nucleus which bind to the previously identified functionally important sequences within the IFN-gamma promoter. Since human retroviruses are capable of being transcriptionally activated by T-cell inducing agents, it is likely that the nuclear products identified by the above techniques which bind to sequences in the IFN-gamma promoter would also interact with the products of the viral transactivator genes (tax I or tax II) similar to the protein:promoter binding of the AP-1 and Fos gene products. Some of these proteins (such as Nuclear Factor-kB) may also be utilized by the HIV promoter within the long terminal repeat, as a T-cell activation-specific transcription factor. We will isolate the genes which encode the nuclear factors important in IFN-gamma regulation, by screening an expression library with either an oligonucleotide specific to a nuclear factor binding site, or an oligonucleotide derived from the isolated and sequenced nuclear factors. These studies are aimed at an understanding of how the viral activation of the IFN-gamma gene is related to the concurrent oncogenic transformation of cells harboring the HTLV type of retrovirus. Use of Jurkat cells as a model system is one approach through the introduction of vectors expressing tax and studying their effects on endogenous genes such as IFN-gamma. Introduction of tax expression vectors and/or IFN-gamma promoter deletion plasmids into peripheral blood lymphocytes by electroporation would be an additional physiological approach to characterize sequences important in promoter activation, as compared to the Jurkat T-cell tumor model. Additional studies have revealed that the immunosuppressive agent cyclosporine A (Cs A) can overcome the activation of the IFN-gamma promoter by T-cell activating agents. It is an important goal to determine at which level of regulation does Cs A inhibit IFN-gamma transcription. Since tax gene products are able to relieve the inhibitory effects of Cs A on IFN-gamma induction, it will be equally important to discover how those two pathways interact to modify IFN-gamma gene regulation. The discovery that HTLV gene products modify the action of Cs A on the immune system has potential implication for patients in need of immunosuppressive therapy (transplantation) who have attendant retroviral- associated (HTLV) disease.
| Brown, D A; Kondo, K L; Wong, S W et al. (1992) Characterization of nuclear protein binding to the interferon-gamma promoter in quiescent and activated human T cells. Eur J Immunol 22:2419-28 |
