REGULATION OF JAK3 EXPRESSION IN HUMAN MONOCYTES - PHOSPHORYLATION INRESPONSE TO INTERLEUKIN-2, INTERLEUKIN-4, AND INTERLEUKIN-7

The Janus family of kinases (JAKs) has been shown to be involved in th e signal transduction of a number of cytokine receptors. Recently, we have cloned a novel JAK family member, JAK3, that is expressed in natu ral killer and activated T cells and is coupled functionally and physi cally to the interleukin 2 (IL-2) receptor in these cells. Here we rep ort that JAK3 was expressed at low but detectable levels in human mono cytes. In contrast, JAK3 expression was strongly induced during activa tion by interferon gamma (IFN-gamma) or lipopolysaccharide. Moreover, JAK3 became tyrosine phosphorylated in response to IL-2, IL-4, and IL- 7 but not response to IFN-gamma or granulocyte/macrophage colony-stimu lating factor. Together, these findings suggest that JAK3 is functiona lly important in activated monocytes and cells of the myeloid lineage and is involved in signaling responses of cytokines that use the commo n gamma-chain of the IL-2 receptor.