Abstract 13278: β-Catenin Inhibition of NaV1.5 Requires both TCF4 and FoxO1 in Cardiomyocytes
Background: Wnt/β-catenin/TCF4 signaling plays many roles in cardiac diseases, but its function in the regulation of cardiac ion channels is largely unknown. Our previous study revealed that oxidative stress (OS) inhibited NaV1.5 expression through FoxO1. It has been shown that OS promotes β-catenin to interact with FoxO1 and affect the gene expression. It is not defined if β-catenin can associate with FoxO1 to control cardiac NaV1.5 expression. Therefore, we explored if β-catenin inhibits NaV1.5 expression and if this inhibition requires both TCF4 and FoxO1.
Methods: Western blot and RT-PCR were performed to determine the NaV1.5 expression. Whole-cell Na+ current was recorded in HL-1 cardiomyocytes. Cardiac-specific APC deletion was performed by Cre expression driven by the α-MHC promoter to determine if β-catenin affects the NaV1.5 expression. Luciferase assays were used to examine the effects of β-catenin and TCF4 on the SCN5a promoter activity. Chromatin immunoprecipitation (ChIP) was performed to investigate the recruitment of β-catenin and TCF4 within the SCN5a promoter.
Results: NaV1.5 expression was significantly decreased in HL-1 cells treated with the GSK-3β inhibitors LiCl or BIO, or expressing a stabilized form of β-catenin. β-catenin was significantly increased and Na+ current was significantly decreased by LiCl. In contrast, expression of constitutively active GSK-3βS9A significantly reduced β-catenin and increased the NaV1.5 protein levels. Cardiac APC deletion in mice increased β-catenin protein levels and decreased NaV1.5 expression. In silico analysis revealed that mouse, rat, and human SCN5a promoters all harbor a TCF4-conservative DNA binding sequence, near the FoxO1 binding site. ChIP assays indicated that β-catenin and TCF4 were recruited to the region of the SCN5a promoter containing FoxO1 binding sites in human hearts. Luciferase assays showed that β-catenin significantly decreased both the mutated FoxO1 binding site and the SCN5a wild type promoter activity. The former, however, is less affected. Knockdown of TCF4 or FoxO1 by siRNA reversed the suppression of SCN5a promoter activity by β-catenin.
Conclusion: Both FoxO1 and TCF4 are required for β-catenin to transcriptionally suppress cardiac NaV1.5 expression.
- © 2013 by American Heart Association, Inc.