JAK2 and neoplasm: To determine the functional activity of IL-4R on tumour cells, we and others have shown that IL-4 can cause phosphorylation of JAK1, JAK2 and STAT6 proteins in human colon carcinoma and ovarian carcinoma cell lines even though IL-4 does not mediate autocrine or paracrine growth of these tumour cell lines (Murata et al, 1995, 1997b).