Identification of inflammatory mediators by screening for glucocorticoid-attenuated response genes.

We describe an approach for identifying novel inflammatory mediators, based on screening for immediate early/primary response genes whose induction by an inflammatory stimulus is attenuated by glucocorticoids. This procedure can be applied to a wide range of cell types and tissues, using a variety of inducers. In an initial test of this idea, we identified cDNAs for 12 LPS-induced, glucocorticoid-attenuated response genes (GARGs) by differential hybridization screening of a lambda phage cDNA library from murine 3T3 fibroblasts. Seven of the GARGs were known genes, including the chemokines JE/MCP-1, fic/MARC/MCP-3, and crg2/IP-10. One of the novel cDNAs was a new C-X-C chemokine that we designated LIX, for LPS-induced C-X-C chemokine. Because the 12 GARG cDNAs were identified in a single screening of only 15,000 phage, and four were found as single isolates, these results suggest that there are many GARGs not yet described. Furthermore, six of the seven known GARGs encode proteins that modulate intercellular communication. These results support our hypothesis that GARGs predominantly encode products that function in paracrine cell communication. Here we provide an overview of the GARG strategy and the differential hybridization procedures used in our initial screening. A variety of other methods for identifying differentially expressed genes may be used in future searches for novel GARGs.