MOLECULAR-CLONING OF A NOVEL HUMAN CDNA-ENCODING A ZINC-FINGER PROTEIN THAT BINDS TO THE INTERLEUKIN-3 PROMOTER

The CT/GC-rich region (-76 to -47) is one transcriptional regulatory r egion of the interleukin-3 (IL-3) gene which confers basic transcripti onal activity and responds to trans-activation by human T-cell leukemi a virus type I-encoded Tax. We isolated three types of cDNAs encoding Cys(2)/His(2)-type zinc finger proteins that bind to this region. Two were identical to known transcription factors, EGR1 and EGR2, and the other clone, named DB1, encoded a novel protein of 516 amino acids wit h six zinc finger motifs. DB1 mRNA was present in human tissues, ubiqu itously. Two constitutive transcripts of 4.0 and 4.8 kb in length were present in Jurkat cells. Electrophoretic mobility shift assay, with s pecific antibodies, showed that DB1 constitutively binds to this regio n whereas EGR1 binds in a T-cell activation-dependent manner. Overexpr ession of DB1 in Jurkat cells had no detectable effect on the transcri ption activity of the IL-3 promoter, in a transient-transfection assay , EGR1 and EGR2 increased IL-3 promoter activity when the transfected cells were stimulated,vith phorbol-12-myristate-13-acetate and A23187. When DBI was cotransfected with a Tax expression vector, transcriptio n activity of the IL-3 promoter induced by Tax was significantly incre ased, while EGR1 and EGR2 were without effect. These results suggest t hat EGR1 has a role in inducible transcription of the IL-3 gene, while DB1 sustains basal transcriptional activity and also cooperates with Tax to activate the IL-3 promoter.