Janus family kinases and identification of immune modulators

Abstract

An isolated polynucleotide encodes JAK-3 protein. JAK-3 protein is a protein tyrosine kinase having a molecular weight of approximately 125 kDa which has tandem non-identical catalytic domains, lacks SH2 or SH3 domains, and is expressed in NK cells and stimulated or transformed T cells, but not in resting T cells. The protein itself and antibodies to this protein are also presented. Further, methods of identifying therapeutic agents for modulating the immune system make use of the foregoing.

1 . A method of identifying an agent having immunomodulating activity, comprising:
 determining the ability of the IL-2 receptor β or γ c  chain to physically associate with a Janus family kinase selected from the group consisting of JAK-1 and JAK-3 in the absence of a candidate agent; and   determining the ability of said chain of IL-2 receptor to physically associate with said Janus family kinase in the presence of said candidate agent;   wherein a lesser or greater ability to associate in the presence of said agent indicates immunomodulating activity.   
     
     
         2 . The method of  claim 1 , wherein each of the determining steps is performed in the presence of a cytokine compound. 
     
     
         3 . The method of  claim 2 , wherein said cytokine compound is a cytokine compound that binds to a receptor including γ chain. 
     
     
         4 . The method of  claim 3 , wherein said cytokine compound is selected from the group consisting of IL-2, IL-4, IL-7, IL-9 and IL-15. 
     
     
         5 . The method of  claim 1 , wherein each of the determining steps comprises immunoprecipitating said chain of IL-2 receptor with an antibody specific to said chain and determining if said Janus family kinase coprecipitates with said chain. 
     
     
         6 . The method of  claim 1 , wherein said candidate agent is a peptide fragment of said γ c  chain of IL-2. 
     
     
         7 . A method of identifying a therapeutic agent for modulating the immune system, comprising:
 isolating a Janus family kinase selected from the group consisting of JAK-1 and JAK-3;   determining the ability of said kinase to phosphorylate a substrate therefor in the absence of a candidate agent; and   determining the ability of said kinase to phosphorylate said substrate in the presence of said candidate agent;   wherein a decrease in the ability of said kinase to phosphorylate said substrate in the presence of said candidate agent indicates that said candidate agent is an immunosuppressive agent, and wherein a greater ability of said kinase to phosphorylate said substrate in the presence of said candidate agent indicates that said candidate agent is an immuno-enhancing agent.   
     
     
         8 . The method of  claim 7 , wherein the isolating step comprises immunoprecipitating said Janus family kinase with an antibody specific to said Janus family kinase. 
     
     
         9 . The method of  claim 7 , wherein each of the determining steps comprises:
 reacting said Janus family kinase with γ-labeled ATP to produce reaction products;   separating said reaction products by electrophoresis; and   identifying labeled products.   
     
     
         10 . The method of  claim 7 , wherein each of the determining steps comprises:
 reacting said Janus family kinase with ATP to produce reaction products;   separating said reaction products by electrophoresis;   exposing the separated reaction products to an antibody specific to phosphotyrosine; and   identifying reaction products that exhibit binding to said antibody.