IDENTIFICATION OF IFN-GAMMA RECEPTOR-BINDING SITES FOR JAK2 AND ENHANCEMENT OF BINDING BY IFN-GAMMA AND ITS C-TERMINAL PEPTIDE IFN-GAMMA(95-133)

The tyrosine kinase jAK2 is an integral part of the signal transduction pathways of a number of cytokines and growth factors, including IFN-gamma. previously, we identified a species-nonspecific binding site for the C terminus of IFN-gamma, encompassed by lFN-gamma peptide IFN-gamma(95-133), on the membrane proximal region of the cytoplasmic domain of the lFN-gamma R alpha-chain. Using both a radioligand binding assay and coimmunoprecipitation with antireceptor antiserum, we were able to demonstrate specific interaction of JAK2 with the murine IFN-gamma R (MIR) cu-chain. Furthermore, this interaction is increased by the addition of murine IFN-gamma or its C-terminal peptide, mulFN-gamma(95-133). We also identified two regions of the cytoplasmic domain of the receptor that interact with JAK2 using synthetic peptides of the MIR alpha-chain in receptor competition studies. These regions are encompassed by receptor peptide MIR(283-309), which is adjacent to the membrane proximal region at which the C terminus of IFN-gamma binds, and receptor peptide MIR(404-432), which lies near the C terminus of the receptor, encompassing a potentially important phosphorylation site. These data show site-specific interaction between JAK2 and IFN-gamma with the IFN-gamma R and have broader implications for the role of the IFN-gamma ligand in the IFN-gamma signal transduction pathway. Furthermore, the data support previous studies that demonstrated that intracellular lFN-gamma plays a role in cell activation.