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Stress-mediated activation of the hypothalamic-pituitary axis (HPA) enables adaptation to immune-mediated inflammation. A candidate central mediator of this effect is the growth and differentiation factor LIF, which we have previously shown to be expressed in pituitary tissue in-vivo and to induce ACTH in-vitro. As both hypothalamic and pituitary LIF and LIF-receptor are expressed in-vivo, we determined LIF action on POMC transcription with a POMC-luc construct (-706/+64). 1 nM LIF induced POMC transcription by 200%, compared to 540% for 10 nM CRH, while the combination of LIF and CRH strikingly enhanced POMC induction -20-fold. The LIF-related cytokine oncostatin M (l nM) was also a weak agonist of POMC transcription (160% induction), and also potently synergised witb CRH (10-fold induction). CRH acts through adcnylate cyclase, and both forskolin and 8bromo cAMP also stimulated POMC transcription (270%), while addition of 1 nM LIF was again synergistic (740% induction). Transaction of 3' POMC deletion mutants revealed a critical LIF/CRH response region between -323 and -166. However, the combination of LIF and CRH still stimulated expression of a -323/-166 deleted POMC construct to 270% of control, possibly through the recently defined AP-1 site within the non-coding exon 1. Sitedirected mutagenesis of this AP-1 site, while reducing basal activity of the promoter to 60% of wild-type, did not alter LIF, CRH or UF/CRH responses, suggesting that the 5' flanking region of POMC between -323 and -166 was solely responsible for conferring POMC transcriptional responsiveness to LIF as POMC contains no typical cytokine response element. These results demonstrate a direct effect of LIF on the POMC gene in marked synergy with CRH, indicating the presence of a potent central cytokine-mediated response at the level of the pituitary corticotroph.


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