We have recently reported that IL-13R may share a component with IL-4R. Here we report that both IL-4 and IL-13 share signaling events in human colon carcinoma cell lines (HT-29 and WiDr). IL-13 caused rapid phosphorylation of the three out of four members of the known Janus family of kinases (JAKs). We show that JAK2 kinase is rapidly phosphorylated and activated in response to IL-13. Within 1 min of activation, JAK2 was phosphorylated, and peaked in 10 min. In addition, IL-13 phosphorylated insulin response substrate-1, IL-4R p140, JAK1, and Tyk2, but not JAK3 kinase. IL-4 also stimulated all three kinases and substrates, but unlike in immune cells, IL-4 did not involve JAK3 activation for its signaling in colon cancer cell lines. Furthermore, JAK2 associated with the IL-4R p140 before and after stimulation with IL-13. Both IL-13 and IL-4 induced phosphorylation of IL-4 STAT (STAT6) but not STAT1, STAT3, or STAT5. 125I-IL-13 did not bind to colon cancer cell lines, but unlabeled IL-13 competed for the binding of 125I-IL-4. Our data suggest that IL-13 utilizes IL-4R and its signaling pathway, and JAK2 may play an important role in the function of IL-4R and IL-13R in colon cancer cells.

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