Our objective was to identify the signaling pathway activated by thyroid stimulating hormone (TSH) that induces interleukin (IL)-6 secretion from human abdominal subcutaneous differentiated adipocytes. Human abdominal subcutaneous preadipocytes in culture were differentiated into adipocytes. IL-6 release stimulated by TSH was inhibited by 35% (P<0.05) with SN50, an inhibitor of nuclear factor B (NF-B) nuclear translocation, and by 60% (P<0.01) with sc-514, an inhibitor of inhibitory B kinase (IKK) . Phosphorylation of IKK increased upon TSH treatment (10.3-fold, P<0.01), and IB levels were reduced by 78% (P<0.01). TSH activated NF-B (23-fold, P<0.001), a process that was inhibited (60%, P<0.01) by SN50. Inhibition of protein kinase A by H89 did not affect TSH-stimulated IKK phosphorylation or IB degradation. TSH-mediated NF-B activation and IL-6 induction also specifically occurred in Chinese hamster ovarian cells expressing the human TSH receptor, resulting in a 5.9-fold (P<0.001) increase in IKK phosphorylation and a 9.5-fold increase in IL-6 mRNA expression. Our data demonstrate that the IKK/NF-B pathway is a novel TSH target that is required for TSH-induced IL-6 release from human adipocytes.