Reconstitution of the functional granulocyte macrophage colony stimulating factor promoter: evidence for distinct activation mechanisms that mediate the response to phorbol ester/calcium and human T cell leukemia virus type I Tax signals

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Abstract
Functional elements in the promoter region of the mouse granulocyte-macrophage colony stimulating factor (GM-CSF) gene were assessed by constructing chimeric promoters linked to the bacterial chloramphenicol acetyitransferase (CAT) gene and by employing a transient transfection assay of human T cell leukemia Jurkat cells. We previously reported that CLE2/GC-box (at positions −95 to −73, which is homologous to the NF-xB binding site) and CLE0 (at positions −54 to −40) of the mouse GM-CSF promoter are essential for transcriptional activation in response to phorbol-12-myristate-13-acetate (PMA)/calcium ionophore (A23187). Here we show that CLE2/GC-box and the NF-xB binding motif are functionally interchangeable and that CLE2/GC-box and CLE0 as a unit activate the basic GM-CSF promoter in response to PMA/calcium signals. This unit is also capable of activating heterologous promoters in response to PMA/calcium signals. In addition, we show that Tax, the trans-activator encoded by human T cell leukemia virus type I (HTLV-I), activates the GM-CSF promoter via CLE2/GC-box without the involvement of CLE0. These results indicate that PMA/A23187-dependent and Tax-dependent activation of the GM-CSF gene proceeds through distinct mechanisms.

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