that activation of GCGR by glucagon also induced the b-catenin signaling pathway. Importantly, we found that Lrp5/6 is required for glucagon-induced b-catenin signaling. These results may help to explain the pleiotropic phenotypes of Lrp5 and 6 mutations and have important implications in understanding the role of Lrp5/6 in metabolic syndrome. Results Glucagon agonist induced the cAMP/PKA pathway in GCGR-expressing cells As a classical GPCR, activation of the glucagon receptor causes an increase of intracellular cAMP level, which in turn activates the PKA signaling pathway to activate cAMP-response element -mediated gene expression. Using the CRE-Luc reporter construct, we found that HEK293 without GCGR transfection did not respond to GCG1-29 stimulation. After transfecting with GCGR, HEK293 cells became responsive to GCG1-29, but not to Oleandrin GCG9-29 . As a control, forskolin, a direct PKA activator, activated CRE luciferase activity independent of GCGR expression. Using western blot, we confirmed that HEK293 cells have no detectable expression of GCGR until after transfection with a GCGR expression plasmid. These experiments suggest that HEK293 cells can be used to model GCGR signaling after ectopic expression of the receptor. We 22314911 also asked if we could detect CRE luciferase activity in cells with endogenous GCGR expression. Primary liver hepatocytes are known to have endogenous GCGR expression. We found that the GCG1-29 could directly activate CRE luciferase activity in primary liver cells without the need to transfect with 9336340 a GCGR plasmid. catenin protein levels relative to a control, non-treated sample or that treated with the antagonist GCG9-29. As a positive control, treatment with lithium chloride also caused an increase in b-catenin levels, an indication of activation of the Wnt/b-catenin signaling pathway. To confirm this result, we also examined cells with endogenous GCGR expression, including the hepatocarcinoma cell line Hep3B and primary liver cells. Treatment of Hep3B cells with GCG1-29 caused a rapid increase of b-catenin protein levels within 15 minutes. Treatment of primary hepatocytes also caused an increase in b-catenin protein. These experiments demonstrate that activation of the GCGR receptor in cell lines and primary cells leads to bcatenin stabilization. Activation of the b-catenin pathway leads to stabilization of bcatenin in the cytosol, which can translocate into the nucleus and associate with TCF transcription factors to activate TCF promotermediated gene expression. Because we observed the stabilization of b-catenin protein upon activation of GCGR receptor, we next examined whether activation of GCGR stimulated TCF promotermediated luciferase activity, an indicator for an active b-catenin signaling pathway. 293STF cells were transfected with the GCGR receptor and then treated with GCG1-29 or GCG9-29 peptides. We observed a small but statistically significant increase in TCF-mediated luciferase activity upon treatment with GCG1-29, but not with GCG9-29. Treatment with LiCl also caused an increase in TCF luciferase activity. Similarly, we observed a dose-dependent increase in TCF luciferase activity in primary hepatocytes treated with GCG1-29, but not with GCG9-29 or PTH1-34 peptides. These experiments demonstrate that activation of the GCGR receptor increases TCF promoter activity. Together with the western results, they demonstrated that activation of GCGR receptor leads to active b-catenin signaling. Coexpression o