In cytokine receptors, there is no consensus sequence motif for tyrosine and/or serine/threonine kinases in its intracellular domain (1 ). Cytokine receptors associate with and activate members of the Janus kinase family (JAK), which is phosphorylated following ligand binding (2 ). The JAK family consists of four kinase members, JAK1, JAK2, JAK3, and Tyk2. Recently, we have shown that in ovarian cancer cell lines, many IL-4 receptors were expressed and IL-4 inhibited the proliferation of ovarian carcinoma cell lines (3 ). Moreover, IL-4 induced the phosphorylation of JAK1, JAK2, Tyk2, STAT6, and IRS-1 proteins following ligand-receptor interaction (4 ).
