The mechanism by which the human T-cell leukemia viruses types I and II (HTLV-I and -II) transform T cells is unknown, but the nonstructural Tax protein that these viruses produce is known to be essential for viral replication and to have the capacity to trans-activate cellular gene expression. The HTLV-I and -II Tax proteins have been shown to activate the promoter of both the human and mouse granulocyte-macrophage colony-stimulating factor (GM-CSF) genes in mature T-cell lines. T-cell-specific Tax-responsive sequences were previously localized to the 90-bp region extending from base pairs -53 to +37 in the human GM-CSF promoter. In this study, a series of site-directed and deletion mutations were created in the human GM-CSF promoter, which was linked to the chloramphenicol acetyltransferase (CAT) gene, and the constructs were assayed for their response to Tax by using a Tax-expressing plasmid in transient cotransfection assays. The results demonstrated that both copies of the repeated sequence CATTA(A/T), located between base pairs -48 and -36, are required for Tax responsiveness in T cells and that these sequences bind nuclear factors present in T cells. The Tax-responsiveness of other sequences located 5' of base pair -53 was also examined, including an NF-κB consensus sequence and the CK1, CK2, and GC-rich regions identified in both the mouse and human GM-CSF promoters. These sequences did not have Tax-responsive regulatory activity when they were examined in the context of the intact human GM-CSF promoter in T cells. The sequence requirements for Tax responsiveness were the same as those required for mitogen-inducible GM-CSF promoter function, suggesting that the mechanism of Tax activation of the GM-CSF gene is similar to that utilized by mitogen. Additional studies with multiple T-cell activation signals suggested that the trans-activating effect of Tax on the GM-CSF promoter, like its effects on the long terminal repeats of HTLV-I and -II, are not mediated via the activation of protein kinase C.
|Original language||English (US)|
|Number of pages||8|
|State||Published - Dec 3 1991|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)