Abstract
Cardiac transient receptor potential canonical (TRPC) channels are crucial upstream components of Ca(2+)/calcineurin/nuclear factor of activated T cells (NFAT) signaling, thereby controlling cardiac transcriptional programs. The linkage between TRPC-mediated Ca(2+) signals and NFAT activity is still incompletely understood. TRPC conductances may govern calcineurin activity and NFAT translocation by supplying Ca(2+) either directly through the TRPC pore into a regulatory microdomain or indirectly via promotion of voltage-dependent Ca(2+) entry. Here, we show that a point mutation in the TRPC3 selectivity filter (E630Q), which disrupts Ca(2+) permeability but preserves monovalent permeation, abrogates agonist-induced NFAT signaling in HEK293 cells as well as in murine HL-1 atrial myocytes. The E630Q mutation fully retains the ability to convert phospholipase C-linked stimuli into L-type (Ca(V)1.2) channel-mediated Ca(2+) entry in HL-1 cells, thereby generating a dihydropyridine-sensitive Ca(2+) signal that is isolated from the NFAT pathway. Prevention of PKC-dependent modulation of TRPC3 by either inhibition of cellular kinase activity or mutation of a critical phosphorylation site in TRPC3 (T573A), which disrupts targeting of calcineurin into the channel complex, converts cardiac TRPC3-mediated Ca(2+) signaling into a transcriptionally silent mode. Thus, we demonstrate a dichotomy of TRPC-mediated Ca(2+) signaling in the heart constituting two distinct pathways that are differentially linked to gene transcription. Coupling of TRPC3 activity to NFAT translocation requires microdomain Ca(2+) signaling by PKC-modified TRPC3 complexes. Our results identify TRPC3 as a pivotal signaling gateway in Ca(2+)-dependent control of cardiac gene expression.