This pattern of TC changes was very similar to that of the change in HMGCR in response to TSH stimulation. We performed a series of experiments to investigate whether TSH induced HMGCR expression in liver cells via TSHR as TSH acts in thyroid selleck chemicals llc gland. To block TSHR, we used a monoclonal antibody (CS-17) with competitive antagonist properties against human TSHR.19, 20 The results showed that TSH-stimulated production of cAMP in L-02 cells and human primary hepatocytes cultured in the presence of CS-17 was significantly lower than that in cells cultured without CS-17 (P < 0.001) (Fig. 3A, upper). Moreover,

both basal and TSH-stimulated HMGCR protein levels in L-02 cells were substantially reduced by CS-17 (Fig. 3A, lower). We also used a lentivirus-based RNA interfere (RNAi) delivery system to knock down the expression of TSHR in L-02 cells. Fluorescent microscopic examination revealed that the efficiency of lentiviral infection was higher than 90% at 72 hours (Supporting Fig. 2). As shown in Fig. 3B, the expression of TSHR was significantly and specifically knocked down by RNAi. Correspondingly, TSH-stimulated

cAMP levels, HMGCR protein and TC production were greatly diminished in cells infected with RNAi lentivirus. In selleck contrast, in cells infected with negative control lentivirus (NS lentivirus), TSH could still increase cAMP levels, up-regulate HMGCR protein and enhance TC production. Treatment of cells with NS lentivirus or RNAi lentivirus alone had no effect on HMGCR protein expression. In separate experiments, we used siRNA to knock down TSHR expression in BNL cells and

achieved similar results to those in the L-02 cells with RNAi approach (Supporting Fig. 3). TSH-stimulated cAMP production in L-02 cells and human primary hepatocytes was significantly inhibited by treatment with AC inhibitor (SQ22536) (P < 0.001) (Fig. 4A). Similarly, the protein expression of HMGCR in L-02 cells stimulated by TSH was dramatically reduced by SQ22536 (Fig. 4A). These suggested that TSH increased HMGCR levels in liver cells through a cAMP-dependent pathway. It was reported that the HMGCR promoter contained a cAMP-responsive element CRE.21, 22 We constructed a recombined luciferase reporter plasmid pGL4-CRE and transfected into L-02 cells. The significant increase in luciferase activity was detected upon TSH or forskolin Janus kinase (JAK) treatment. After we mutated the CRE binding site of HMGCR promoter (pGL4-muCRE), we found neither forskolin nor TSH could up-regulate its luciferase activity, which strongly indicated that the CRE site was essential for TSH in regulation of HMGCR (Fig. 4B). To assess whether TSH has any effect on DNA-binding activity of CREB with CRE locating HMGCR promoter, EMSA was performed. Results showed that CREB-DNA binding activity was specific because the band disappeared with an excess of unlabeled CRE, whereas the mutant failed to influence the bound.