Modulation of CaV1.2 Channel Function by Interacting Proteins and Post-Translational Modifications: Implications in Cardiovascular Diseases and COVID-19.

CaV1.2 calcium channel is the primary conduit for Ca2+ influx into cardiac and smooth muscles that underscores its importance in the pathogenesis of hypertension, atherosclerosis, myocardial infarction, and heart failure. But, a few controversies still remain. Therefore, exploring new ways to modulate CaV1.2 channel activity will augment the arsenal of CaV1.2 channel-based therapeutics for treatment of cardiovascular diseases. Here, we will mainly introduce a couple of emerging CaV1.2 channel interacting proteins, such as Galectin-1 and Cereblon, and discuss their roles in hypertension and heart failure through fine-tuning CaV1.2 channel activity. Of current interest, we will also evaluate the implication of the role of CaV1.2 channel in SARS-CoV-2 infection and the potential treatments of COVID-19-related cardiovascular symptoms.

Calcium Channel Splice Variants and Their Effects in Brain and Cardiovascular Function.

Calcium ions serve as an important intracellular messenger in many diverse pathways, ranging from excitation coupling in muscles to neurotransmitter release in neurons. Physiologically, the concentration of free intracellular Ca2+ is up to 10,000 times less than that of the extracellular concentration, and increases of 10- to 100-fold in intracellular Ca2+ are observed during signaling events. Voltage-gated calcium channels (VGCCs) located on the plasma membrane serve as one of the main ways in which Ca2+ is able to enter the cell. Given that Ca2+ functions as a ubiquitous intracellular messenger, it is imperative that VGCCs are under tight regulation to ensure that intracellular Ca2+ concentration remains within the physiological range. In this chapter, we explore VGCCs' inherent control of Ca2+ entry as well as the effects of alternative splicing in CaV2.1 and posttranslational modifications of CaV1.2/CaV1.3 such as phosphorylation and ubiquitination. Deviation from this physiological range will result in deleterious effects known as calcium channelopathies, some of which will be explored in this chapter.

Regulation of cardiovascular calcium channel activity by post-translational modifications or interacting proteins.

Voltage-gated calcium channels are the major pathway for Ca2+ influx to initiate the contraction of smooth and cardiac muscles. Alterations of calcium channel function have been implicated in multiple cardiovascular diseases, such as hypertension, atrial fibrillation, and long QT syndrome. Post-translational modifications do expand cardiovascular calcium channel structure and function to affect processes such as channel trafficking or polyubiquitination by two E3 ubiquitin ligases, Ret finger protein 2 (Rfp2) or murine double minute 2 protein (Mdm2). Additionally, biophysical property such as Ca2+-dependent inactivation (CDI) could be altered through binding of calmodulin, or channel activity could be modulated via S-nitrosylation by nitric oxide and phosphorylation by protein kinases or by interacting protein partners, such as galectin-1 and Rem. Understanding how cardiovascular calcium channel function is post-translationally remodeled under distinctive disease conditions will provide better information about calcium channel-related disease mechanisms and improve the development of more selective therapeutic agents for cardiovascular diseases.

ß subunits of voltage-gated calcium channels in cardiovascular diseases.

Calcium signaling is required in bodily functions essential for survival, such as muscle contractions and neuronal communications. Of note, the voltage-gated calcium channels (VGCCs) expressed on muscle and neuronal cells, as well as some endocrine cells, are transmembrane protein complexes that allow for the selective entry of calcium ions into the cells. The α1 subunit constitutes the main pore-forming subunit that opens in response to membrane depolarization, and its biophysical functions are regulated by various auxiliary subunits-ß, α2δ, and γ subunits. Within the cardiovascular system, the γ-subunit is not expressed and is therefore not discussed in this review. Because the α1 subunit is the pore-forming subunit, it is a prominent druggable target and the focus of many studies investigating potential therapeutic interventions for cardiovascular diseases. While this may be true, it should be noted that the direct inhibition of the α1 subunit may result in limited long-term cardiovascular benefits coupled with undesirable side effects, and that its expression and biophysical properties may depend largely on its auxiliary subunits. Indeed, the α2δ subunit has been reported to be essential for the membrane trafficking and expression of the α1 subunit. Furthermore, the ß subunit not only prevents proteasomal degradation of the α1 subunit, but also directly modulates the biophysical properties of the α1 subunit, such as its voltage-dependent activities and open probabilities. More importantly, various isoforms of the ß subunit have been found to differentially modulate the α1 subunit, and post-translational modifications of the ß subunits further add to this complexity. These data suggest the possibility of the ß subunit as a therapeutic target in cardiovascular diseases. However, emerging studies have reported the presence of cardiomyocyte membrane α1 subunit trafficking and expression in a ß subunit-independent manner, which would undermine the efficacy of ß subunit-targeting drugs. Nevertheless, a better understanding of the auxiliary ß subunit would provide a more holistic approach when targeting the calcium channel complexes in treating cardiovascular diseases. Therefore, this review focuses on the post-translational modifications of the ß subunit, as well as its role as an auxiliary subunit in modulating the calcium channel complexes.