Interleukin-4 mediates STAT6 activation in 3T3-L1 preadipocytes but not adipocytes

STAT6 is abundantly expressed in 3T3-L1 preadipocytes and adipocytes but ac tivating ligands are not well defined. In this report, we provide evidence that interleukin 4 (IL-4) induced JAK2-mediated STAT6 tyrosine phosphorylat ion and DNA binding in 3T3-L1 preadipocytes but not in 3T3-L1 adipocytes. L oss of IL-4-mediated STAT6 tyrosine phosphorylation occurred 2 days after p readipocytes were induced to differentiate into adipocytes but when cells r emained phenotypically preadipocytes. 3T3-L1 adipocytes were still responsi ve to IL-4 through tyrosine phosphorylation of other cellular proteins. We conclude that IL-4 signals through STAT6 in 3T3-L1 preadipocytes but not in 3T3-L1 adipocytes. This differentiation-dependent loss of STAT6 activation may be critical for distinct biological effects of IL-4 in 3T3-L1 preadipo cytes and adipocytes. (C) 2000 Academic Press.