FUNCTIONAL ANALYSIS OF A PDGF-INDUCIBLE CYTOKINE

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Growth factors exert their effects on target cells, in part, by inducing the expression of specific genes. For example, in 3T3 cells, platelet-derived growth factor (PDGF) induces the expression of proliferation-related proto-oncogenes as well as an additional 50-100 genes, the majority of which have no known function. The long-term goal of this proposal is to learn more about growth factor-mediated mitogenic processes by understanding the structure and function of some of the the latter group of PDGF-inducible genes, in particular the JE gene, the first PDGF-indudble gene to have been isolated. In preliminary studies, the JE gene has been shown to encode a low molecular weight secreted glycoprotein that is identical to a recently purified monocyte chemotactic factor. This factor also activates monocytes, enhancing their ability to engage in antibodyindependent tumor cell lysis. Thus the studies in this application will also have relevance to anti-tumor therapy. There are three hypotheses the specific aims of this proposal will test: First, because the JE protein exerts its effects at nanomolar concentrations, it is likely to act through a high affinity receptor. The first specific aim is to identify, clone, and test the activity of these receptors. These experiments will provide insight into the mechanisms of monocyte chemotaxis and activation, as well as providing tools for the examination of other cell types for the presence of the JE receptor. Second, because the sequence of the JE protein is highly similar to those of other cytokines with different activities, it is likely that its monocyte-specific effects are mediated through specific amino acids. The second specific aim is to perform a structure/function analysis of the JE protein by site-directed mutagenesis. The results of such a study could provide information for the development of specific agonists or antagonists of JE action. Finally, because there are cell types capable of expressing JE that play no role in the inflammatory response, it is likely that JE may have functions other than monocute chemotaxis. The third specific aim is the construction of transgenic mice expressing JE in a deregulated fashion. In addition to the potential for revealing new activities for JE, this model will also provide in vivo confirmation of JE's effects on monocute physiology.