Troponin T3 regulates nuclear localization of the calcium channel Cavβ1a subunit in skeletal muscle

The voltage-gated calcium channel (Ca-v) beta(1a) subunit (Ca-v beta(1a)) plays an important role in excitation-contraction coupling (ECC), a process in the myoplasm that leads to muscle-force generation. Recently, we discovered that the Ca-v beta(1a) subunit travels to the nucleus of skeletal muscle cells where it helps to regulate gene transcription. To determine how it travels to the nucleus, we performed a yeast two-hybrid screening of the mouse fast skeletal muscle cDNA library and identified an interaction with troponin T3 (TnT3), which we subsequently confirmed by co-immunoprecipitation and co-localization assays in mouse skeletal muscle in vivo and in cultured C2C12 muscle cells. Interacting domains were mapped to the leucine zipper domain in TnT3 COOH-terminus (160-244 aa) and Ca-v beta(1a) NH2-terminus (1-99 aa), respectively. The double fluorescence assay in C2C12 cells co-expressing TnT3/DsRed and Ca-v beta(1a)/YFP shows that TnT3 facilitates Ca-v beta(1a) a nuclear recruitment, suggesting that the two proteins play a heretofore unknown role during early muscle differentiation in addition to their classical role in FCC regulation. (C) 2015 Elsevier Inc. All rights reserved.