Insulin modulates leptin-induced STAT3 activation in rat hypothalamus

Insulin and leptin have overlapping effects in the control of energy homeos tasis, but the molecular basis of this synergism is unknown, Insulin signal s through a receptor tyrosine kinase that phosphorylates and activates the docking proteins IRSs (insulin receptor substrates), whereas the leptin rec eptor and its associated protein tyrosine kinase JAK2 (Janus kinase 2) medi ate phosphorylation and activation of the transcription factor STAT3 (signa l transducer and activator of transcription). Here, we present evidence for the integration of leptin and insulin signals in the hypothalamus. Insulin induced JAK2 tyrosine phosphorylation, leptin receptor phosphorylation whi ch, in the presence of leptin, augmented the interaction between STAT3 and this receptor. Insulin also increased the leptin-induced phosphorylation of STAT3 and its activation. These results indicate that insulin modulates th e leptin signal transduction pathway, and may provide a molecular basis for the coordinated effects of insulin and leptin in feeding behavior and weig ht control. (C) 2001 Published by Elsevier Science B.V. on behalf of the Fe deration of European Biochemical Societies.