Caveolin proteins: a molecular insight into disease

Small-conductance calcium-activated potassium channels in the heart: expression, regulation and pathological implications

Ca2+-activated K+ channels are critical to cellular Ca2+ homeostasis and excitability; they couple intracellular Ca2+ and membrane voltage change. Of these, the small, 4-14 pS, conductance SK channels include three, KCNN1-3 encoded, SK1/KCa2.1, SK2/KCa2.2 and SK3/KCa2.3, channel subtypes with characteristic, EC50 ∼ 10 nM, 40 pM, 1 nM, apamin sensitivities. All SK channels, particularly SK2 channels, are expressed in atrial, ventricular and conducting system cardiomyocytes. Pharmacological and genetic modification results have suggested that SK channel block or knockout prolonged action potential durations (APDs) and effective refractory periods (ERPs) particularly in atrial, but also in ventricular, and sinoatrial, atrioventricular node and Purkinje myocytes, correspondingly affect arrhythmic tendency. Additionally, mitochondrial SK channels may decrease mitochondrial Ca2+ overload and reactive oxygen species generation. SK channels show low voltage but marked Ca2+ dependences (EC50 ∼ 300-500 nM) reflecting their α-subunit calmodulin (CaM) binding domains, through which they may be activated by voltage-gated or ryanodine-receptor Ca2+ channel activity. SK function also depends upon complex trafficking and expression processes and associations with other ion channels or subunits from different SK subtypes. Atrial and ventricular clinical arrhythmogenesis may follow both increased or decreased SK expression through decreased or increased APD correspondingly accelerating and stabilizing re-entrant rotors or increasing incidences of triggered activity. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

Structural analysis of the P132L disease mutation in caveolin-1 reveals its role in the assembly of oligomeric complexes

Caveolin-1 (CAV1) is a membrane-sculpting protein that oligomerizes to generate flask-shaped invaginations of the plasma membrane known as caveolae. Mutations in CAV1 have been linked to multiple diseases in humans. Such mutations often interfere with oligomerization and the intracellular trafficking processes required for successful caveolae assembly, but the molecular mechanisms underlying these defects have not been structurally explained. Here, we investigate how a disease-associated mutation in one of the most highly conserved residues in CAV1, P132L, affects CAV1 structure and oligomerization. We show that P132 is positioned at a major site of protomer-protomer interactions within the CAV1 complex, providing a structural explanation for why the mutant protein fails to homo-oligomerize correctly. Using a combination of computational, structural, biochemical, and cell biological approaches, we find that despite its homo-oligomerization defects P132L is capable of forming mixed hetero-oligomeric complexes with WT CAV1 and that these complexes can be incorporated into caveolae. These findings provide insights into the fundamental mechanisms that control the formation of homo- and hetero-oligomers of caveolins that are essential for caveolae biogenesis, as well as how these processes are disrupted in human disease.

Extracellular vesicles in heart failure – A study in patients with heart failure with preserved ejection fraction or heart failure with reduced ejection fraction characteristics undergoing elective coronary artery bypass grafting

Aims

Extracellular vesicles (EVs) were investigated as potential biomarkers associated with heart failure (HF) pathophysiology in patients undergoing elective coronary artery bypass surgery characterized by HF phenotype.

Materials and methods

Patients with preoperative proxy-diagnoses of HF types i.e., preserved (HFpEF; n = 19) or reduced ejection fraction (HFrEF; n = 20) were studied and compared to patients with normal left ventricular function (n = 42). EVs in plasma samples collected from the coronary sinus, an arterial line, and from the right atrium were analyzed by flow cytometry. We studied EVs of presumed cardiomyocyte origin [EVs exposing Connexin-43 + Caveolin-3 (Con43 + Cav3) and Connexin-43 + Troponin T (Con43 + TnT)], of endothelial origin [EVs exposing VE-Cadherin (VE-Cad)] and EVs exposing inflammatory markers [myeloperoxidase (MPO) or pentraxin3 (PTX3)].

Results

Median concentrations of EVs exposing Con43 + TnT and Con43 + Cav3 were approximately five to six times higher in coronary sinus compared to radial artery indicative of cardiac release. Patients with HFrEF had high trans-coronary gradients of both Con43 + TnT and Con43 + Cav3 EVs, whereas HFpEF had elevated gradients of Con43 + Cav3 EVs but lower gradients of Con43 + TnT. Coronary sinus concentrations of both Con43 + TnT and Con43 + Cav3 correlated significantly with echocardiographic and laboratory measures of HF. MPO-EV concentrations were around two times higher in the right atrium compared to the coronary sinus, and slightly higher in HFpEF than in HFrEF. EV concentrations of endothelial origin (VE-Cad) were similar in all three patient groups.

Conclusion

Con43 + TnT and Con43 + Cav3 EVs are released over the heart indicating cardiomyocyte origin. In HFrEF the EV release profile is indicative of myocardial injury and myocardial stress with elevated trans-coronary gradients of both Con43 + TnT and Con43 + Cav3 EVs, whereas in HFpEF the profile indicates myocardial stress with less myocardial injury.

Upregulation of OGT by Caveolin-1 promotes hepatocellular carcinoma cell migration and invasion

Caveolin-1 (CAV1), a major structural protein of caveolae, is reported to exert a positive regulatory effect on tumor growth and to play a crucial role in hepatocellular carcinoma (HCC) cell metastasis by regulating glycosyltransferase expression and cellular glycosylation. However, the role of CAV1 in modulating protein glycosylation and tumor metastasis remains to be further elucidated. In the present study, we showed that CAV1 promoted the expression of O-GlcNAc transferase (OGT), which catalyzed the addition of O-GlcNAc residues to a variety of nuclear and cytoplasmic proteins. In human HCC cell lines with different metastatic potentials, high levels of OGT and cellular O-GlcNAcylation were associated with CAV1 expression and cell metastasis. Overexpression of CAV1 increased the levels of OGT and O-GlcNAcylation, and cell migration was also increased. Furthermore, CAV1 was found to reduce the expression of Runt-related transcription factor 2 (RUNX2) in HCC cells. Subsequently, this effect resulted in the attenuation of the RUNX2-induced transcription of microRNA24 (miR24), a microRNA previously shown to suppress OGT mRNA expression by targeting its 3' untranslated regions (UTR). Finally, we demonstrated that CAV1 induced cellular O-GlcNAcylation and HCC cell invasion. This study provides evidence of CAV1-mediated increases in OGT expression and O-GlcNAcylation. These data provide insight into a novel mechanism underlying HCC metastasis and suggest a novel strategy for the treatment of HCC.

Multifaceted Roles of Caveolin-1 in Lung Cancer: A New Investigation Focused on Tumor Occurrence, Development and Therapy

Lung cancer is one of the most common and malignant cancers with extremely high morbidity and mortality in both males and females. Although traditional lung cancer treatments are fast progressing, there are still limitations. Caveolin-1 (Cav-1), a main component of caveolae, participates in multiple cellular events such as immune responses, endocytosis, membrane trafficking, cellular signaling and cancer progression. It has been found tightly associated with lung cancer cell proliferation, migration, apoptosis resistance and drug resistance. In addition to this, multiple bioactive molecules have been confirmed to target Cav-1 to carry on their anti-tumor functions in lung cancers. Cav-1 can also be a predictor for lung cancer patients’ prognosis. In this review, we have summarized the valuable research on Cav-1 and lung cancer in recent years and discussed the multifaceted roles of Cav-1 on lung cancer occurrence, development and therapy, hoping to provide new insights into lung cancer treatment.

Ten years of research on the role of BVES/ POPDC1 in human disease: a review

Since the blood vessel epicardial substance or Popeye domain-containing protein 1 (BVES/POPDC1) was first identified in the developing heart by two independent laboratories in 1999, an increasing number of studies have investigated the structure, function, and related diseases of BVES/POPDC1. During the first 10 years following the discovery of BVES/POPDC1, studies focused mainly on its structure, expression patterns, and functions. Based on these studies, further investigations conducted over the previous decade examined the role of BVES/POPDC1 in human diseases, such as colitis, heart diseases, and human cancers. This review provides an overview of the structure and expression of BVES/POPDC1, mainly focusing on its potential role and mechanism through which it is involved in human cancers.

Caveolin-1 and MLRs: A potential target for neuronal growth and neuroplasticity after ischemic stroke

Ischemic stroke is a leading cause of morbidity and mortality worldwide. Thrombolytic therapy, the only established treatment to reduce the neurological deficits caused by ischemic stroke, is limited by time window and potential complications. Therefore, it is necessary to develop new therapeutic strategies to improve neuronal growth and neurological function following ischemic stroke. Membrane lipid rafts (MLRs) are crucial structures for neuron survival and growth signaling pathways. Caveolin-1 (Cav-1), the main scaffold protein present in MLRs, targets many neural growth proteins and promotes growth of neurons and dendrites. Targeting Cav-1 may be a promising therapeutic strategy to enhance neuroplasticity after cerebral ischemia. This review addresses the role of Cav-1 and MLRs in neuronal growth after ischemic stroke, with an emphasis on the mechanisms by which Cav-1/MLRs modulate neuroplasticity via related receptors, signaling pathways, and gene expression. We further discuss how Cav-1/MLRs may be exploited as a potential therapeutic target to restore neuroplasticity after ischemic stroke. Finally, several representative pharmacological agents known to enhance neuroplasticity are discussed in this review.

Novel finding of caveolin-2 in apical membranes of proximal tubule and first detection of caveolin-2 in urine: A promising biomarker of renal disease

Caveolin-2 (Cav-2) is expressed in a variety of cell tissue, and it has also been found in renal tissue. The expression of Cav-2 in proximal tubules is still unclear. The aim of this study was to carry out a complete evaluation of the expression pattern of Cav-2 in rat renal cortex to clarify and deepen the knowledge about the localization of Cav-2 in the proximal tubules and also to evaluate its presence in urine. Male Wistar rats were used to assess Cav-2 expression by Western blot analysis in homogenates, apical, and basolateral membranes from kidney cortex, in lysates and total plasma membranes from renal cortical cell suspensions, in urine, and in urinary exosomes. Cav-2 was clearly expressed in renal cortex homogenates and in both apical and basolateral membranes isolated from kidney cortex, with a greater expression on the former membranes. It was also observed in lysates and in plasma membranes from cortical cell suspensions. Moreover, Cav-2 was found in urine and in its exosomal fraction. These results confirmed the presence of Cav-2 in proximal tubule cells in the kidney of healthy rats, and showed for the first time its expression at the apical membrane of these cells and in urine. Besides, urinary exosomal pathway could be involved in Cav-2 urinary excretion under normal conditions. We observed an increase in the urinary abundance of Cav-2 in two models of acute kidney injury, and thus we proposed the urinary excretion of Cav-2 as a potential biomarker of kidney injury.

Trichostatin A alters cytoskeleton and energy metabolism of pancreatic adenocarcinoma cells: An in depth proteomic study

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal of all human cancers with a high mortality rate. Resistance to conventional treatments and chemotherapeutics is a typical feature of PDAC. To investigate the causes of drug resistance it is essential to deeply investigate the mechanism of action of chemotherapeutics. In this study, we performed an in depth shotgun proteomic approach using the label-free proteomic SWATH-MS analysis to investigate novel insights of the mechanism of action of the histone deacetylase (HDAC) inhibitor trichostatin A (TSA) in PDAC cells. This proteomic analysis in PaCa44 cells and data elaboration of TSA-regulated proteins by bioinformatics showed an overall up-regulation of cytokeratins and other proteins related to the cytoskeleton organization, keratinization, and apoptotic cell death. On the contrary, a large amount of the down-regulated proteins by TSA treatment belongs to the cellular energetic metabolism and to the machinery of protein synthesis, such as ribosomal proteins, determining synergistic cell growth inhibition by the combined treatment of TSA and the glycolytic inhibitor 2-deoxy-d-glucose in a panel of PDAC cell lines. Data are available via ProteomeXchange with identifier PXD007801.

The influence of caveolin-1 gene polymorphisms on hepatitis B virus-related hepatocellular carcinoma susceptibility in Chinese Han population: A case-control study

This study aimed to explore the genetic association of polymorphisms in caveolin-1 gene (CAV1) with hepatitis B virus-related hepatocellular carcinoma (HBV-related HCC) susceptibility in a Chinese Han population.The genotyping of polymorphism was conducted using polymerase chain reaction-restriction fragment length polymorphism method. Whether the genotype distribution of polymorphisms in the healthy controls was consistent with Hardy-Weinberg equilibrium (HWE) was detected. The genotype and allele frequency difference between the 2 groups was compared by chi-square test. Odds ratio (OR) and 95% confidence interval (95% CI) were calculated to show the relative risk of HCC which resulted from genetic variants in CAV1. Moreover, the linkage disequilibrium of CAV1 polymorphisms was analyzed by Haploview.The AG genotype and A allele of rs1049334 showed significantly higher frequency in HCC patients than that of chronic HBV patients and the healthy controls (P < .05); so their carriage obviously increased the susceptibility to HBV-related HCC, irrespective of the fact whether individuals were infected with hepatitis B virus or not (AG vs GG: OR 1.958, 95% CI 1.050-3.650, OR 1.899, 95% CI 1.034-3.487; A vs G: OR 1.667, 95% CI 1.033-2.689, OR 1.777, 95% CI 1.103-2.863). Additionally, A-G haplotype of rs3807989-rs1049334 showed the protective role for HBV-related HCC (OR 0.102, 95% CI 0.035-0.293; OR 0.135, 95% CI 0.046-0.395).CAV1 rs1049334 polymorphism is significantly associated with the occurrence risk of HBV-related HCC, and the interaction of polymorphisms should not be neglected.