The β2-Subunit of Voltage-Gated Calcium Channels Regulates Cardiomyocyte Hypertrophy

Abstract

L-type voltage-gated calcium channels (LTCCs) regulate crucial physiological processes in the heart. They are composed of the Cavα1 pore-forming subunit and the accessory subunits Cavβ, Cavα2δ, and Cavγ. Cavβ is a cytosolic protein that regulates channel trafficking and activity, but it also exerts other LTCC-independent functions. Cardiac hypertrophy, a relevant risk factor for the development of congestive heart failure, depends on the activation of calcium-dependent pro-hypertrophic signaling cascades. Here, by using shRNA-mediated Cavβ silencing, we demonstrate that Cavβ2 downregulation enhances α1-adrenergic receptor agonist-induced cardiomyocyte hypertrophy. We report that a pool of Cavβ2 is targeted to the nucleus in cardiomyocytes and that the expression of this nuclear fraction decreases during in vitro and in vivo induction of cardiac hypertrophy. Moreover, the overexpression of nucleus-targeted Cavβ2 in cardiomyocytes inhibits in vitro-induced hypertrophy. Quantitative proteomic analyses showed that Cavβ2 knockdown leads to changes in the expression of diverse myocyte proteins, including reduction of calpastatin, an endogenous inhibitor of the calcium-dependent protease calpain. Accordingly, Cavβ2-downregulated cardiomyocytes had a 2-fold increase in calpain activity as compared to control cells. Furthermore, inhibition of calpain activity in Cavβ2-downregulated cells abolished the enhanced α1-adrenergic receptor agonist-induced hypertrophy observed in these cells. Our findings indicate that in cardiomyocytes, a nuclear pool of Cavβ2 participates in cellular functions that are independent of LTCC activity. They also indicate that a downregulation of nuclear Cavβ2 during cardiomyocyte hypertrophy promotes the activation of calpain-dependent hypertrophic pathways.

Nanoenviroments of the β-Subunit of L-Type Voltage-Gated Calcium Channels in Adult Cardiomyocytes

“…In this study, we first corroborated the expression pattern of the five Ca v β 2 splice variants (Ca v β 2a -Ca v β 2e ) in cultured ARCs. RT-PCR analyses confirmed that Ca v β 2b is the predominant splice variant and that the other ones are detected at very low levels (Figure 1B) as also ocurrs in neonatal rat cardiomyocytes (Pickel et al, 2021). In order to detect the expression of protein Ca v β 2b in cardiomyocytes, we produced an antibody that specifically recognizes and targets the N-terminus of this Ca v β 2 splice variant.…”

New Insights in CaVβ Subunits: Role in the Regulation of Gene Expression and Cellular Homeostasis

“…An instance supporting this hypothesis is CaVβ4C, which interaction with HP1γ has been shown as mandatory to localize to the nucleus in mammalian cells ( Hibino et al, 2003 ), while the truncation of a large part of its GK domain cut off the exclusive requirement of SH3/GK interaction for nuclear docking of CaVβs proteins. The molecular aspects of nuclear targeting were less studied for CaVβ2 and CaVβ3, for which some studies mentioning their binding with chaperone proteins may be relevant in supporting their tackling to the nuclei ( Zhang et al, 2010 ; Pickel et al, 2021 ).…”

“…The authors hypothesized that the potential mechanism modifying disease phenotype was based on the attenuation of CaV-dependent Ca 2+ current associated with CACNB2 mutations. However, an additional possibility came out a few years later with a study that correlated the reduced cardiomyocyte hypertrophy to a CaV-independent CaVβ2 function ( Pickel et al, 2021 ). CaVβ2 localization and activity in cardiomyocyte nuclei were shown to significantly regulate Calpain activity and Calpastatin expression ( Pickel et al, 2021 ), a pro-hypertrophic protease and its inhibitor, respectively.…”

“…However, an additional possibility came out a few years later with a study that correlated the reduced cardiomyocyte hypertrophy to a CaV-independent CaVβ2 function ( Pickel et al, 2021 ). CaVβ2 localization and activity in cardiomyocyte nuclei were shown to significantly regulate Calpain activity and Calpastatin expression ( Pickel et al, 2021 ), a pro-hypertrophic protease and its inhibitor, respectively. Even though these events have not been explicitly linked to the reduction of cardiomyocyte hypertrophy, a correlation between the two might be hypothesized and would need to be further studied ( Table 1 ).…”

Natural L-type calcium channels antagonists from Chinese medicine

“…The auxiliary subunits β belongs to the MAGUK-scaffolding protein family, a cytosolic soluble protein with high affinity binding to channel, including four subtypes of β 1 - β 4 [ 16 ]. The mutation of β subunit is associated with arrhythmia and stroke [ 16 ].…”