Interleukin 4 Activates a Signal Transducer and Activator of Transcription ( Stat ) Protein which Interacts with an Interferon - y Activation Site - like Sequence Upstream of the 1 Exon in a Human B Cell Line

Germ line CQ transcripts can be induced by 1L-4 in the human B cell line, BL-2. Utilizing a IFN-y activation sitelike DNA sequence element located upstream of the L 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 1L4 NAF (IL-4-induced nuclear-activating factors) and was identified as a tyrosine phosphoprotein, which translocates from the cytosol to the nucleus upon 11-4 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 11-4 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, 1L-4 induced robust Janus kinase 3 (JAK3) activity in BL-2 cells. Cotransfection ofJAK3 with 11-4 Stat into COS-7 cells produced an intracellular activity which bound the same IFN-y activation site-like sequence and comigrated with 1L-4 NAF in electrophoretic mobility shift assay. These results show that 1L-4 NAF is 11-4 Stat, which is activated by JAK3 in response to 1L-4 receptor engagement. (J. Clin. Invest. 1995. 96:907-914.)