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

Abstract

The voltage-gated calcium channel (Cav) β1a subunit (Cavβ1a) 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 Cavβ1a 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 Cavβ1a NH2-terminus (1-99 aa), respectively. The double fluorescence assay in C2C12 cells co-expressing TnT3/DsRed and Cavβ1a/YFP shows that TnT3 facilitates Cavβ1a nuclear recruitment, suggesting that the two proteins play a heretofore unknown role during early muscle differentiation in addition to their classical role in ECC regulation.

Troponin through the looking-glass: emerging roles beyond regulation of striated muscle contraction

“…In addition to the classical role of Ca v β 1a as part of the dihydropyridine receptor that is the voltage sensor in the transverse-tubule membrane for Ca 2+ release from the sarcoplasmic reticulum, it has also been shown to localize to the nucleus of muscle progenitor cells and regulate gene expression [ 119 ]. In an effort to understand the molecular mechanisms governing the translocation, the same group subsequently demonstrated that TnT3 facilitates the nuclear recruitment of Ca v β 1a [ 40 ]. These results are consistent with a previous report demonstrating nuclear-localized troponin early in muscle cell differentiation [ 35 ].…”

Cardiac troponin T and fast skeletal muscle denervation in ageing

“…For instance, Tn and Tm are found in the nucleus in various tissues 2, 3. We recently found that fast skeletal muscle TnT3 can function as a transcription regulator that modulates muscle contraction‐related gene expression, including calcium channel beta1a and alpha1s subunits, by nuclear translocation 4, 5…”

“…2,3 We recently found that fast skeletal muscle TnT3 can function as a transcription regulator that modulates muscle contraction-related gene expression, including calcium channel beta1a and alpha1s subunits, by nuclear translocation. 4,5 Unlike cardiac TnI, which is highly specific for cardiac muscle, TnT2, the cardiac isoform of troponin T (cTnT), is also expressed in developing skeletal muscles, after sciatic nerve denervation, and in various neuromuscular diseases. [6][7][8] Whereas injury to myocardium causes the simultaneous release of both cTnI and cTnT into the circulation, denervation and chronic injury of skeletal muscle may induce expression and release of cTnT, but not cTnI, from the skeletal muscle.…”

The loss of slow skeletal muscle isoform of troponin T in spindle intrafusal fibres explains the pathophysiology of Amish nemaline myopathy

“…The ssTnT mutation‐originated pathogenesis and pathophysiology of ANM may also be complicated by other non‐canonical effects involving proteolytic fragmentation of TnT and TnT translocation into the nuclei, as reported in previous studies (Zhang et al. ; Zhang et al. ; Johnston et al.…”