NOVEL INTERACTIONS BETWEEN HUMAN T-CELL LEUKEMIA-VIRUS TYPE-I TAX ANDACTIVATING TRANSCRIPTION FACTOR-3 AT A CYCLIC AMP-RESPONSIVE ELEMENT

Human proenkephalin gene transcription is transactivated by human T-ce ll leukemia virus type I (HTLV-I) Tax in human Jurkat T lymphocytes. T his transactivation was further enhanced in Jurkat cells treated with concanavalin A, cyclic AMP, or 12-O-tetradecanoylphorbol-13-acetate. D eletion and cis-element transfer analyses of the human proenkephalin p romoter identified a cyclic AMP-responsive AP-1 element (-92 to -86) a s both necessary and sufficient to confer Tax-dependent transactivatio n. Different AP-1 or cyclic AMP-responsive element-binding protein (CR EB)/activating transcription factor (ATF) proteins which bind this ele ment were expressed in murine teratocarcinoma F9 cells to identify tho se capable of mediating Tax-dependent transactivation of human proenke phalin gene transcription. Although CREB, c-Fos, c-Jun, and JunD did n ot have significant effects, JunB inhibited the Tax-dependent transact ivation. In contrast, ATF3 dramatically induced Tax-dependent transact ivation, which was further enhanced by protein kinase A. Electrophoret ic mobility shift assays with recombinant fusion proteins expressed an d purified from bacteria indicate that the DNA-binding activity of ATF 3 is also dramatically enhanced by Tax. Chimeric fusion proteins consi sting of the DNA-binding domain of the yeast transcription factor Gal4 and the amino-terminal domain (residues 1 to 66) of ATF3 were able to mediate Tax-dependent transactivation of a Gal4-responsive promoter, which suggests a direct involvement of this region of ATF3. Recombinan t fusion proteins of glutathione S-transferase with either the amino- or carboxy-terminal (residues 139 to 181) domain of ATF3 were able to specifically interact with Tax. Furthermore, specific antisera directe d against Tax coimmunoprecipitated ATF3 only in the presence of Tax.