LEUKEMIA INHIBITORY FACTOR (LIF) MODULATES PROOPIOMELANOCORTIN (POMC)GENE-REGULATION IN STABLY TRANSFECTED ATT-20 CELLS OVEREXPRESSING LIF

Leukemia inhibitory factor (LIF) levels are elevated in sepsis and cor relate with shock and poor prognosis. We have previously shown that li popolysaccharide (LPS) administration induces hypothalamic and pituita ry LIF expression in vivo, which is associated with the acute rise in circulating adrenocorticotrophic hormone (ACTH) levels. As AtT-20 cell s respond to LIF, we established murine LIF (mLIF) stably transfected AtT-20 cell lines to study LIF regulation of pro-opiomelano-cortin (PO MC) expression and ACTH secretion. Our results show that mLIF transfec tants accumulated mLIF (up to 15.6 +/- 3.2 ng/mL after 24 h) as well a s increased ACTH secretion (up to 2.4-fold above control cells) in con ditioned medium. The magnitude of ACTH induction correlated with mLIF concentrations in different transfectants (r = 0.75-0.88, p < 0.05), M oreover, mLIF transfectants showed a higher sensitivity to CRH stimula tion with an increased ACTH production within 8 h (p < 0.05), whereas control cells were responsive to CRH at 24 h. Additionally, mLIF trans fectants exhibited a maximum threefold ACTH induction, compared to 1.7 -fold in control cells. Furthermore, mLIF transfectants have a blunted dexamethasone-mediated inhibition of ACTH (35% inhibition in control cells vs no inhibition in mLIf-transfected cells at 24 h). These findi ngs support and extend the previous observations of LIF acting at the pituitary level, and indicate that mLIF stably-transfected AtT-20 cell s are a useful model for studying mLIf-mediated gene regulation in pit uicytes.