INTERLEUKIN-4 ACTIVATES A SIGNAL TRANSDUCER AND ACTIVATOR OF TRANSCRIPTION (STAT) PROTEIN WHICH INTERACTS WITH AN INTERFERON-GAMMA ACTIVATION SITE-LIKE SEQUENCE UPSTREAM OF THE I-EPSILON EXON IN A HUMAN B-CELL LINE - EVIDENCE FOR THE INVOLVEMENT OF JANUS-KINASE-3 AND INTERLEUKIN-4 STAT

Germ line C-epsilon transcripts can be induced by IL-4 in the human B cell line, BL-2. Utilizing a IFN-gamma activation site-like DNA sequence element located upstream of the I-epsilon exon, we demonstrated by gel mobility shift assays that IL-4 induced a binding activity in the cytosol and nucleus of BL-2 cells, This factor was designated IL-4 NAF (IL-4-induced nuclear-activating factors) and was identified as a tyrosine phosphoprotein, which translocates from the cytosol to the nucleus upon IL-4 treatment, Because these are the characteristics of a signal transducer and activator of transcription (Stat) protein, we determined whether antibodies to Stat proteins will interfere with gel mobility shift and found that antibodies to IL-4 Stat, also known as Stat6, but not antibodies to other Stat proteins, interfere with the formation of the IL-4 NAF complex, Congruous with the involvement of a Stat protein, IL-4 induced robust Janus kinase 3 (JAK3) activity in BL-2 cells, Cotransfection of JAK3 with IL-4 Stat into COS-7 cells produced an intracellular activity which bound the same IFN-gamma activation site-like sequence and comigrated with IL-4 NAP in electrophoretic mobility shift assay. These results show that IL-4 NAF is IL-4 Stat, which is activated by JAK3 in response to IL-4 receptor engagement.