A small-molecule LF3 abrogates β-catenin/TCF4-mediated suppression of Na1.5 expression in HL-1 cardiomyocytes.

Increased nuclear β-catenin interacting with T-cell factor 4 (TCF4) affects the expression of target genes including SCN5A in ischemic heart disease, which is characterized by frequent ventricular tachycardia/fibrillation. A complex of β-catenin and TCF4 inhibits cardiac Na channel activity by reducing Na1.5 expression through suppressing SCN5A promoter activity in HL-1 cardiomyocytes. LF3, a 4-thioureido-benzenesulfonamide derivative and an inhibitor of β-catenin/TCF4 interaction, has been shown to block the self-renewal capacity of cancer stem cells. We performed studies to determine if LF3 can reverse suppressive effects of β-catenin/TCF4 signaling on the expression of Na1.5 in HL-1 cardiomyocytes. Western blotting and real-time qRT-PCR analyses showed that 10 μM LF3 significantly increased the expression of Na1.5 but it did not alter β-catenin and TCF4 expression. Subcellular fractionation analysis demonstrated that LF3 significantly increased the levels of Na1.5 in both membrane and cytoplasm. Whole-cell patch-clamp recordings revealed that Na currents were significantly increased with no changes in the steady-state parameters, activation and inactivation time constants and recovery from inactivation of Na channel in HL-1 cells treated with LF3. Immunoprecipitation exhibited that LF3 blocked the interaction of β-catenin and TCF4. Luciferase reporter assays performed in HEK 293 cells and HL-1 revealed that LF3 increased the SCN5A promoter activity in HL-1 cells and prevented β-catenin suppressive effect on SCN5A promoter activity in HEK 293 cells. Taken together, we conclude that LF3, an inhibitor of β-catenin/TCF4 interaction, elevates Na1.5 expression, leading to increase Na channel activity in HL-1 cardiomyocytes.