14-3-3 protein regulation of excitation-contraction coupling

The dispensability of 14-3-3 proteins for the regulation of human cardiac sodium channel Nav1.5

BACKGROUND

14-3-3 proteins are ubiquitous proteins that play a role in cardiac physiology (e.g., metabolism, development, and cell cycle). Furthermore, 14-3-3 proteins were proposed to regulate the electrical function of the heart by interacting with several cardiac ion channels, including the voltage-gated sodium channel Nav1.5. Given the many cardiac arrhythmias associated with Nav1.5 dysfunction, understanding its regulation by the protein partners is crucial.

AIMS

In this study, we aimed to investigate the role of 14-3-3 proteins in the regulation of the human cardiac sodium channel Nav1.5.

METHODS AND RESULTS

Amongst the seven 14-3-3 isoforms, only 14-3-3η (encoded by YWHAH gene) weakly co-immunoprecipitated with Nav1.5 when heterologously co-expressed in tsA201 cells. Total and cell surface expression of Nav1.5 was however not modified by 14-3-3η overexpression or inhibition with difopein, and 14-3-3η did not affect physical interaction between Nav1.5 α-α subunits. The current-voltage relationship and the amplitude of Nav1.5-mediated sodium peak current density were also not changed.

CONCLUSIONS

Our findings illustrate that the direct implication of 14-3-3 proteins in regulating Nav1.5 is not evident in a transformed human kidney cell line tsA201.

14-3-3-η interacts with BCL-2 to protect human endothelial progenitor cells from ox-LDL-triggered damage

Oxidized low-density lipoprotein (ox-LDL) causes dysfunction of endothelial progenitor cells (EPCs), and we recently reported that 14-3-3-η can attenuate the damage triggered by ox-LDL in EPCs. However, the molecular mechanisms by which 14-3-3-η protects EPCs from the damage caused by ox-LDL are not fully understood. In this study, we observed that the expression of 14-3-3-η and BCL-2 were downregulated in ox-LDL-treated EPCs. Overexpression of 14-3-3-η in ox-LDL-treated EPC significantly increased BCL-2 level, while knockdown of BCL-2 reduced 14-3-3-η expression and mitigated the protective effect of 14-3-3-η on EPCs. In addition, we discovered that 14-3-3-η colocalizes and interacts with BCL-2 in EPCs. Taken together, these data suggest that 14-3-3-η protects EPCs from ox-LDL-induced damage by its interaction with BCL-2.

Peroxisomal hydrogen peroxide signaling: A new chapter in intracellular communication research

Hydrogen peroxide (H2O2), a natural metabolite commonly found in aerobic organisms, plays a crucial role in numerous cellular signaling processes. One of the key organelles involved in the cell's metabolism of H2O2 is the peroxisome. In this review, we first provide a concise overview of the current understanding of H2O2 as a molecular messenger in thiol redox signaling, along with the role of peroxisomes as guardians and modulators of cellular H2O2 balance. Next, we direct our focus toward the recently identified primary protein targets of H2O2 originating from peroxisomes, emphasizing their importance in unraveling the complex interplay between peroxisomal H2O2 and cell signaling. We specifically focus on three areas: signaling through peroxiredoxin redox relay complexes, calcium signaling, and phospho-signaling. Finally, we highlight key research directions that warrant further investigation to enhance our comprehension of the molecular and biochemical mechanisms linking alterations in peroxisomal H2O2 metabolism with disease.

Arsenic disrupts extracellular vesicle-mediated signaling in regenerating myofibers

Chronic exposure to environmental arsenic is a public health crisis affecting hundreds of millions of individuals worldwide. Though arsenic is known to contribute to many pathologies and diseases, including cancers, cardiovascular and pulmonary diseases, and neurological impairment, the mechanisms for arsenic-promoted disease remain unresolved. This is especially true for arsenic impacts on skeletal muscle function and metabolism, despite the crucial role that skeletal muscle health plays in maintaining cardiovascular health, systemic homeostasis, and cognition. A barrier to researching this area is the challenge of interrogating muscle cell-specific effects in biologically relevant models. Ex vivo studies investigating mechanisms for muscle-specific responses to arsenic or other environmental contaminants primarily utilize traditional 2-dimensional culture models that cannot elucidate effects on muscle physiology or function. Therefore, we developed a contractile 3-dimensional muscle construct model-composed of primary mouse muscle progenitor cells differentiated in a hydrogel matrix-to study arsenic exposure impacts on skeletal muscle regeneration. Muscle constructs exposed to low-dose (50 nM) arsenic exhibited reduced strength and myofiber diameter following recovery from muscle injury. These effects were attributable to dysfunctional paracrine signaling mediated by extracellular vesicles (EVs) released from muscle cells. Specifically, we found that EVs collected from arsenic-exposed muscle constructs recapitulated the inhibitory effects of direct arsenic exposure on myofiber regeneration. In addition, muscle constructs treated with EVs isolated from muscles of arsenic-exposed mice displayed significantly decreased strength. Our findings highlight a novel model for muscle toxicity research and uncover a mechanism of arsenic-induced muscle dysfunction by the disruption of EV-mediated intercellular communication.

Discovery of 14-3-3 zeta as a potential biomarker for cardiac hypertrophy

Acute myocardial infarction (AMI) is a multifaceted syndrome influenced by the functions of various extrinsic and intrinsic pathways and pathological processes, which can be detected in circulation using biomarkers. In this study, we investigated the secretome protein profile of induced-hypertrophy cardiomyocytes to identify next-generation biomarkers for AMI diagnosis and management. Hypertrophy was successfully induced in immortalized human cardiomyocytes (T0445) by 200 nM ET-1 and 1 μM Ang II. The protein profiles of hypertrophied cardiomyocyte secretomes were analyzed by nano-liquid chromatography with tandem mass spectrometry and differentially expressed proteins that have been identified by Ingenuity Pathway Analysis. The levels of 32 proteins increased significantly (＞1.4 fold), whereas 17 proteins (＜0.5 fold) showed a rapid decrease in expression. Proteomic analysis showed significant upregulation of six 14-3-3 protein isoforms in hypertrophied cardiomyocytes compared to those in control cells. Multi-reaction monitoring results of human plasma samples showed that 14-3-3 protein-zeta levels were significantly elevated in patients with AMI compared to those of healthy controls. These findings elucidated the role of 14-3-3 protein-zeta in cardiac hypertrophy and cardiovascular disorders and demonstrated its potential as a novel biomarker and therapeutic strategy. [BMB Reports 2023; 56(6): 341-346].

Mechano-growth factor E-domain modulates cardiac contractile function through 14-3-3 protein interactomes

In the heart, alternative splicing of the igf-I gene produces two isoforms: IGF-IEa and IGF-IEc, (Mechano-growth factor, MGF). The sequence divergence between their E-domain regions suggests differential isoform function. To define the biological actions of MGF's E-domain, we performed in silico analysis of the unique C-terminal sequence and identified a phosphorylation consensus site residing within a putative 14-3-3 binding motif. To test the functional significance of Ser 18 phosphorylation, phospho-mimetic (S/E¹⁸) and phospho-null (S/A¹⁸) peptides were delivered to mice at different doses for 2 weeks. Cardiovascular function was measured using echocardiography and a pressure-volume catheter. At the lowest (2.25 mg/kg/day) and highest (9 mg/kg/day) doses, the peptides produced a depression in systolic and diastolic parameters. However, at 4.5 mg/kg/day the peptides produced opposing effects on cardiac function. Fractional shortening analysis also showed a similar trend, but with no significant change in cardiac geometry. Microarray analysis discovered 21 genes (FDR p < 0.01), that were expressed accordant with the opposing effects on contractile function at 4.5 mg/kg/day, with the nuclear receptor subfamily 4 group A member 2 (Nr4a2) identified as a potential target of peptide regulation. Testing the regulation of the Nr4a family, showed the E-domain peptides modulate Nr4a gene expression following membrane depolarization with KCl in vitro. To determine the potential role of 14-3-3 proteins, we examined 14-3-3 isoform expression and distribution. 14-3-3γ localized to the myofilaments in neonatal cardiac myocytes, the cardiac myocytes and myofilament extracts from the adult heart. Thermal shift analysis of recombinant 14-3-3γ protein showed the S/A¹⁸ peptide destabilized 14-3-3γ folding. Also, the S/A¹⁸ peptide significantly inhibited 14-3-3γ's ability to interact with myosin binding protein C (MYPC3) and phospholamban (PLN) in heart lysates from dobutamine injected mice. Conversely, the S/E¹⁸ peptide showed no effect on 14-3-3γ stability, did not inhibit 14-3-3γ's interaction with PLN but did inhibit the interaction with MYPC3. Replacing the glutamic acid with a phosphate group on Ser 18 (pSer¹⁸), significantly increased 14-3-3γ protein stability. We conclude that the state of Ser 18 phosphorylation within the 14-3-3 binding motif of MGF's E-domain, modulates protein-protein interactions within the 14-3-3γ interactome, which includes proteins involved in the regulation of contractile function.

Phosphoregulation of Kinesins Involved in Long-Range Intracellular Transport

Kinesins, the microtubule-dependent mechanochemical enzymes, power a variety of intracellular movements. Regulation of Kinesin activity and Kinesin-Cargo interactions determine the direction, timing and flux of various intracellular transports. This review examines how phosphorylation of Kinesin subunits and adaptors influence the traffic driven by Kinesin-1, -2, and -3 family motors. Each family of Kinesins are phosphorylated by a partially overlapping set of serine/threonine kinases, and each event produces a unique outcome. For example, phosphorylation of the motor domain inhibits motility, and that of the stalk and tail domains induces cargo loading and unloading effects according to the residue and context. Also, the association of accessory subunits with cargo and adaptor proteins with the motor, respectively, is disrupted by phosphorylation. In some instances, phosphorylation by the same kinase on different Kinesins elicited opposite outcomes. We discuss how this diverse range of effects could manage the logistics of Kinesin-dependent, long-range intracellular transport.