The caveolae membrane system

Regulation of bifunctional proteins in cells: Lessons from the phospholipase Cβ/G protein pathway

Some proteins can serve multiple functions depending on different cellular conditions. An example of a bifunctional protein is inositide-specific mammalian phospholipase Cβ (PLCβ). PLCβ is activated by G proteins in response to hormones and neurotransmitters to increase intracellular calcium. Recently, alternate cellular function(s) of PLCβ have become uncovered. However, the conditions that allow these different functions to be operative are unclear. Like many mammalian proteins, PLCβ has a conserved catalytic core along with several regulatory domains. These domains modulate the intensity and duration of calcium signals in response to external sensory information, and allow this enzyme to inhibit protein translation in a noncatalytic manner. In this review, we first describe PLCβ's cellular functions and regulation of the switching between these functions, and then discuss the thermodynamic considerations that offer insight into how cells manage multiple and competitive associations allowing them to rapidly shift between functional states.

Leishmania donovani Internalizes into Host Cells via Caveolin-mediated Endocytosis

Leishmania donovani is an intracellular protozoan parasite that causes visceral leishmaniasis, a major cause of mortality and morbidity worldwide. The host plasma membrane serves as the portal of entry for Leishmania to gain access to the cellular interior. Although several host cell membrane receptors have been shown to be involved in the entry of Leishmania donovani into host cells, the endocytic pathway involved in the internalization of the parasite is not known. In this work, we explored the endocytic pathway involved in the entry of Leishmania donovani into host macrophages, utilizing specific inhibitors against two major pathways of internalization, i.e., clathrin- and caveolin-mediated endocytosis. We show that pitstop 2, an inhibitor for clathrin-mediated endocytosis, does not affect the entry of Leishmania donovani promastigotes into host macrophages. Interestingly, a significant reduction in internalization was observed upon treatment with genistein, an inhibitor for caveolin-mediated endocytosis. These results are supported by a similar trend in intracellular amastigote load within host macrophages. These results suggest that Leishmania donovani utilizes caveolin-mediated endocytosis to internalize into host cells. Our results provide novel insight into the mechanism of phagocytosis of Leishmania donovani into host cells and assume relevance in the development of novel therapeutics against leishmanial infection.

Receptor tyrosine kinase inhibitor Sunitinib and integrin antagonist peptide HM-3 show similar lipid raft dependent biphasic regulation of tumor angiogenesis and metastasis

BACKGROUND

Anti-angiogenesis remains an attractive strategy for cancer therapy. Some anti-angiogenic reagents have bell-shape dose-response curves with higher than the effective doses yielding lower anti-angiogenic effects. In this study, two different types of anti-angiogenic reagents, a receptor tyrosine kinase inhibitor Sunitinib and an integrin antagonist peptide HM-3, were selected and their effects on tumor angiogenesis and metastasis were compared. The involved molecular mechanisms were investigated.

METHODS

The effect of high dose Sunitinib and HM-3 on tumor angiogenesis and metastasis was investigated with two animal models: metastasis of B16F10 cells in syngeneic mice and metastasis of human MDA-MB-231 cells in nude mice. Furthermore, mechanistic studies were performed with cell migration and invasion assays and with biochemical pull-down assays of intracellular RhoGTPases. Distribution of integrin αvβ3, α5β1, VEGFR2 and the complex of integrin αvβ3 and VEGFR2 inside or outside of lipid rafts was detected with lipid raft isolation and Western-blot analysis.

RESULTS

Both Sunitinib and HM-3 showed a bell-shape dose-response curve on tumor angiogenesis and metastasis in both animal models. The effects of Sunitinib and HM-3 on endothelial cell and tumor cell proliferation and migration were characterized. Activation of intracellular RhoGTPases and actin stress fiber formation in endothelial and cancer cells following Sunitinib and HM-3 treatment correlated with cell migration analysis. Mechanistic studies confirmed that HM-3 and Sunitinib regulated distribution of integrin αvβ3, α5β1, VEGFR2 and αvβ3-VEGFR2 complexes, both inside and outside of the lipid raft regions to regulate endothelial cell migration and intracellular RhoGTPase activities.

CONCLUSIONS

These data confirmed that a general non-linear dose-effect relationship for these anti-angiogenic drugs exists and their mechanisms are correlative. It also suggests that the effective dose of an anti-angiogenic drug may have to be strictly defined to achieve its optimal clinical effects.

The alpha-1 subunit of the Na+,K+-ATPase (ATP1A1) is required for macropinocytic entry of respiratory syncytial virus (RSV) in human respiratory epithelial cells

Human respiratory syncytial virus (RSV) is the leading viral cause of acute pediatric lower respiratory tract infections worldwide, with no available vaccine or effective antiviral drug. To gain insight into virus-host interactions, we performed a genome-wide siRNA screen. The expression of over 20,000 cellular genes was individually knocked down in human airway epithelial A549 cells, followed by infection with RSV expressing green fluorescent protein (GFP). Knockdown of expression of the cellular ATP1A1 protein, which is the major subunit of the Na⁺,K⁺-ATPase of the plasma membrane, had one of the strongest inhibitory effects on GFP expression and viral titer. Inhibition was not observed for vesicular stomatitis virus, indicating that it was RSV-specific rather than a general effect. ATP1A1 formed clusters in the plasma membrane very early following RSV infection, which was independent of replication but dependent on the attachment glycoprotein G. RSV also triggered activation of ATP1A1, resulting in signaling by c-Src-kinase activity that transactivated epidermal growth factor receptor (EGFR) by Tyr845 phosphorylation. ATP1A1 signaling and activation of both c-Src and EGFR were found to be required for efficient RSV uptake. Signaling events downstream of EGFR culminated in the formation of macropinosomes. There was extensive uptake of RSV virions into macropinosomes at the beginning of infection, suggesting that this is a major route of RSV uptake, with fusion presumably occurring in the macropinosomes rather than at the plasma membrane. Important findings were validated in primary human small airway epithelial cells (HSAEC). In A549 cells and HSAEC, RSV uptake could be inhibited by the cardiotonic steroid ouabain and the digitoxigenin derivative PST2238 (rostafuroxin) that bind specifically to the ATP1A1 extracellular domain and block RSV-triggered EGFR Tyr845 phosphorylation. In conclusion, we identified ATP1A1 as a host protein essential for macropinocytic entry of RSV into respiratory epithelial cells, and identified PST2238 as a potential anti-RSV drug.

RSV continues to be the most important viral cause of severe bronchiolitis and pneumonia in infants and young children, and also has a substantial impact in the elderly. It is estimated to claim the lives of ~118,000 children under five years of age annually. No vaccine or antiviral drug suitable for general use is available. The involvement of host factors in RSV infection and replication is not well understood, but this knowledge might lead to intervention strategies to prevent infection. Using a genome-wide siRNA screen to knock down the expression of over 20,000 individual cellular genes, we identified ATP1A1, the major subunit of the Na⁺,K⁺-ATPase, as an important host protein for RSV entry. We showed that ATP1A1 activation by RSV resulted in transactivation of EGFR by Src-kinase activity, resulting in the uptake of RSV particles into the host cell through macropinocytosis. We also showed that the cardiotonic steroid ouabain and the synthetic digitoxigenin derivative PST2238, which bind specifically to the extracellular domain of ATP1A1, significantly reduced RSV entry. Taken together, we describe a novel ATP1A1-enabled mechanism used by RSV to enter the host cell, and describe candidate antiviral drugs that block this entry.

Pathophysiological Role of Caveolae in Hypertension

Caveolae, flask-shaped cholesterol-, and glycosphingolipid-rich membrane microdomains, contain caveolin 1, 2, 3 and several structural proteins, in particular Cavin 1-4, EHD2, pacsin2, and dynamin 2. Caveolae participate in several physiological processes like lipid uptake, mechanosensitivity, or signaling events and are involved in pathophysiological changes in the cardiovascular system. They serve as a specific membrane platform for a diverse set of signaling molecules like endothelial nitric oxide synthase (eNOS), and further maintain vascular homeostasis. Lack of caveolins causes the complete loss of caveolae; induces vascular disorders, endothelial dysfunction, and impaired myogenic tone; and alters numerous cellular processes, which all contribute to an increased risk for hypertension. This brief review describes our current knowledge on caveolae in vasculature, with special focus on their pathophysiological role in hypertension.

The pathogenesis of lysosomal storage disorders: beyond the engorgement of lysosomes to abnormal development and neuroinflammation

There is growing evidence that the complex clinical manifestations of lysosomal storage diseases (LSDs) are not fully explained by the engorgement of the endosomal-autophagic-lysosomal system. In this review, we explore current knowledge of common pathogenetic mechanisms responsible for the early onset of tissue abnormalities of two LSDs, Mucopolysaccharidosis type II (MPSII) and Niemann-Pick type C (NPC) diseases. In particular, perturbations of the homeostasis of glycosaminoglycans (GAGs) and cholesterol (Chol) in MPSII and NPC diseases, respectively, affect key biological processes, including morphogen signaling. Both GAGs and Chol finely regulate the release, reception and tissue distribution of Shh. Hence, not surprisingly, developmental processes depending on correct Shh signaling have been found altered in both diseases. Besides abnormal signaling, exaggerated activation of microglia and impairment of autophagy and mitophagy occur in both diseases, largely before the appearance of typical pathological signs.

Caveolin-1 and dynamin-2 overexpression is associated with the progression of bladder cancer

Caveolae-mediated endocytosis regulates cell adhesion and growth in an anchorage-dependent manner. Studies of the endocytic function of caveolae have suggested a wide-ranging list of cargoes, including a number of receptors and extracellular proteins, ligands and nutrients from the extracellular matrix. Disruption of the processes of caveolae-mediated endocytosis mediated by signaling proteins is critical to cellular integrity. Caveolin-1 and dynamin-2 are the 2 major proteins associated with endocytotic function. Mechanistically, dynamin-2 has a co-equal role with caveolin-1 in terms of caveolae-derived endosome formation. Recent studies have revealed the pathological outcomes associated with the dysregulation of caveolin-1 and dynamin-2 expression. Increased expression levels of the gene for caveolin, Cav-1, resulting in augmented cellular metastasis and invasion, have been demonstrated in various types of cancer, and overexpression of the gene for dynamin-2, DNM2, has been associated with tumorigenesis in cervical, pancreatic and lung cancer. An increased expression of Cav-1 and DNM2 is known to be associated with the invasive behavior of cancer cells, and with cancer progression. Furthermore, it has been previously demonstrated that, in caveolar assembly and caveolae mediated endocytosis, Cav-1 interacts directly with DNM2 during the processes. Altered expression of the 2 genes is critical for the normal function of the cell. The expression patterns of Cav-1 and DNM2 have been previously examined in bladder cancer cell lines, and were each demonstrated to be overexpressed. In the present study, the expression levels of these 2 genes in bladder cancer samples were quantified. The gene expression levels of Cav-1 and DNM2 were identified to be increased 8.88- and 8.62-fold, respectively, in tumors compared with the normal controls. Furthermore, high-grade tumors exhibited significantly increased expression levels of Cav-1 and DNM2 (both P<0.0001) compared with the low-grade tumors. In addition, compared with normal control samples, the expression of the 2 genes in tumor samples was observed to be highly significant (P<0.0001), with a marked positive correlation identified for the tumors (Pearson's correlation coefficient, r=0.80 for the tumor samples vs. r=0.32 in the normal control samples). Taken together, the results of the present study demonstrated that the overexpression of Cav-1 and DNM2 genes, and a determination of their correlation coefficients, may be a potential risk factor for bladder cancer, in addition to other clinical factors.

Utility of cytokeratin 7, S100A1 and caveolin-1 as immunohistochemical biomarkers to differentiate chromophobe renal cell carcinoma from renal oncocytoma

Background

Differentiation of chromophobe renal cell carcinoma (chRCC) from benign renal oncocytoma (RO) can be challenging especially when there are overlapping histological and morphological features. In this study we have investigated immunohistochemical biomarkers (cytokeratin 7/CK7, Caveolin-1/Cav-1 and S100 calcium-binding protein A1/S100A1) to aid in this difficult differentiation and attempted to validate their use in human renal tumour tissue to assess their discriminatory ability, particularly for chRCC and RO, in an Australian cohort of patients.

Methods

Retrospective study was carried out of archived formalin-fixed paraffin-embedded renal tumours from tumour nephrectomy specimens of 75 patients: 30 chRCC, 15 RO and 30 clear cell RCC (ccRCC). Sections were cut and immunostained with specific polyclonal antibodies of CK7, Cav-1 and S100A1. Morphometry was used to determine expression patterns of the biomarkers using Aperio ImageScope. Results were assessed with student t-test and ANOVA with significance at P<0.05.

Results

From this cohort, male-to-female ratio was 1.9:1. Median age was 64 (45-88 years) and median tumour size was 3.8 cm (range, 1.2-18 cm). There were 47 (62.7%) T1, 7 T2, 20 T3 and one T4 stage of RCC; with 2 patients presenting with M1 stage. There was significantly higher CK7 expression in chRCC compared to RO (P=0.03), and chRCC also had a different staining pattern and higher expression of Cav-1 compared to RO. There was higher expression of S100A1 in RO compared to chRCC.

Conclusions

Immunohistochemical staining and standard morphometry of CK7, Cav-1 and S100A1 can aid in the differentiation of chRCC and RO. This may guide clinicians in management of patients when faced with difficult diagnostic histological distinction between the two tumour subtypes.

Mechanical Stretch Redefines Membrane Gαq-Calcium Signaling Complexes

Muscle cells are routinely subjected to mechanical stretch but the impact of stretch on the organization of membrane domains is unknown. In this study, we characterize the effect of stretch on GPCR-Gαq protein signaling. Activation of this pathway leads to an increase in intracellular calcium. In muscle cells, GPCR-Gαq signals are enhanced when these proteins are localized in caveolae membrane domains whose curved structure can flatten with stretch. When we statically stretch rat aortic smooth muscle A10 cells by 1-5%, cellular calcium appears unperturbed as indicated by a calcium indicator. However, when we activate the bradykinin type 2 receptor (B2R)/Gαq pathway, we observe a loss in calcium that appears to be mediated through perturbations in calcium-activated stretch receptors. In contrast, if we apply oscillating stretch, calcium levels are enhanced. We tested whether the observed changes in B2R-Gαq calcium signals were caused by stretch-induced disruption of caveolae using a combination of silencing RNA technology and growth conditions. We find that stretch changes the ability of monoclonal caveolin antibodies to bind caveolae indicating a change in configuration of the domains. This change is seen by the inability of cells to survive stretch cycles when the level of caveolae is significantly reduced. Our studies show that the effect of calcium signals by mechanical stretch is mediated by the type of stretch and the amount of caveolae.

Serum deprivation-response protein regulates aldehyde dehydrogenase 1 through integrin-linked kinase signaling in endometrioid carcinoma cells

Endometrioid carcinoma (EC) is one of the most common malignancies of the female genital system. We reported previously that aldehyde dehydrogenase 1 (ALDH1), a predominant isoform of the ALDH family in mammals and a potential marker of normal and malignant stem cells, is related to the tumorigenic potential of EC. We compared the levels of various proteins in human EC cells with high and low ALDH1 expression using shotgun proteomics and found that serum deprivation‐response protein (SDPR) was preferentially expressed in cells with high ALDH1 expression. Also known as cavin‐2, SDPR is a member of the cavin protein family, which is required for the formation of caveolae. Using SDPR‐knockout EC cells generated using the CRISPR/Cas9 system, we revealed that SDPR was correlated with invasion, migration, epithelial‐mesenchymal transition, and colony formation, as well as the expression of ALDH1. RNA sequencing showed that integrin‐linked kinase (ILK) signaling is involved in the effect of SDPR on ALDH1. Immunohistochemical analysis revealed that the localization of ILK at the cell cortex was disrupted by SDPR knockout, potentially interfering with ILK signaling. Moreover, immunohistochemical analysis of clinical samples showed that SDPR is related to histological characteristics associated with invasiveness, such as poor differentiation, lymphatic invasion, and the microcystic, elongated, and fragmented histopathological pattern. This is, to our knowledge, the first report that SDPR is related to tumor progression.

Concepts of nanoparticle cellular uptake, intracellular trafficking, and kinetics in nanomedicine

Nanoparticle-based therapeutics and diagnostics are commonly referred to as nanomedicine and may significantly impact the future of healthcare. However, the clinical translation of these technologies is challenging. One of these challenges is the efficient delivery of nanoparticles to specific cell populations and subcellular targets in the body to elicit desired biological and therapeutic responses. It is critical for researchers to understand the fundamental concepts of how nanoparticles interact with biological systems to predict and control in vivo nanoparticle transport for improved clinical benefit. In this overview article, we review and discuss cellular internalization pathways, summarize the field`s understanding of how nanoparticle physicochemical properties affect cellular interactions, and explore and discuss intracellular nanoparticle trafficking and kinetics. Our overview may provide a valuable resource for researchers and may inspire new studies to expand our current understanding of nanotechnology-biology interactions at cellular and subcellular levels with the goal to improve clinical translation of nanomedicines.

Ultrastructural analysis of submacular choriocapillaris and its transport systems in AMD and aged control eyes

The choriocapillaris is the source of nutrients and oxygen for photoreceptors, which consume more oxygen per gram of tissue than any other cell in the body. The purpose of this study was to evaluate and compare the ultrastructure of the choriocapillaris and its transport systems in patients with and without age-related macular degeneration (AMD). Ultrastructural changes were also evaluated in subjects that were homozygous for polymorphisms in high risk CFH alleles (Pure 1) only or homozygous only for high risk ARMS2/HTRA1 (Pure 10) alleles. Tissue samples were obtained from the macular region of forty male (n = 24) and female (n = 16) donor eyes and prepared for ultrastructural studies with transmission electron microscopy (TEM). The average age of the aged donors was 74 ± 7.2 (n = 30) and the young donors 31.7 ± 11.25 (n = 10). There was no significant difference in average ages between the adult groups. TEM images of the capillaries in the choriocapillaris (CC) were taken at 4,000X and 25,000X and used to measure the area of endothelial cell somas, the number of fenestrations, and area of caveolae within the endothelial cells per length of Bruchs membrane (BrMb). The Student t-test and Wilcoxon sum rank test were used to determine significant differences. There was no significant difference between young subjects and aged controls in any of the morphological criteria assessed. There was a significant decrease in the number of fenestrations/mm of BrMb in atrophic areas of GA eyes (p = 0.007) when compared with aged control eyes. A significant increase was found in the caveolae area as a percent of the endothelial cell soma of capillaries from GA subjects as compared with the controls (p = 0.03). Loss of capillary segments in choriocapillaris was also evident, especially in areas of geographic atrophy and CNV. In eyes from patients with sequence variations, the capillary endothelial cells often appeared degenerative and exhibited atypical fenestrations and pericytes covering the blood vessels. Subjects that were homozygous for polymorphisms in high risk CFH alleles only had more fenestrations/mm of BrMb than subjects that were homozygous only for high risk ARMS2/HTRA1 alleles (p = 0.04), while the latter had greater caveolae area/endothelial cell area than the former (p = 0.007). This study demonstrated an attenuation of CC and a significant decline in the two major transport systems in CC endothelial cells in AMD. This may contribute to drusen deposition, nutrient transport, and vision loss in AMD subjects.

Role of the Endocytosis of Caveolae in Intracellular Signaling and Metabolism

Caveolae are 60-80 nm invaginated plasma membrane (PM) nanodomains, with a specific lipid and protein composition, which assist and regulate multiple processes in the plasma membrane-ranging from the organization of signalling complexes to the mechanical adaptation to changes in PM tension. However, since their initial descriptions, these structures have additionally been found tightly linked to internalization processes, mechanoadaptation, to the regulation of signalling events and of endosomal trafficking. Here, we review caveolae biology from this perspective, and its implications for cell physiology and disease.

Design, mechanism, delivery and therapeutics of canonical and Dicer-substrate siRNA

Upon the discovery of RNA interference (RNAi), canonical small interfering RNA (siRNA) has been recognized to trigger sequence-specific gene silencing. Despite the benefits of siRNAs as potential new drugs, there are obstacles still to be overcome, including off-target effects and immune stimulation. More recently, Dicer substrate siRNA (DsiRNA) has been introduced as an alternative to siRNA. Similarly, it also is proving to be potent and target-specific, while rendering less immune stimulation. DsiRNA is 25–30 nucleotides in length, and is further cleaved and processed by the Dicer enzyme. As with siRNA, it is crucial to design and develop a stable, safe, and efficient system for the delivery of DsiRNA into the cytoplasm of targeted cells. Several polymeric nanoparticle systems have been well established to load DsiRNA for in vitro and in vivo delivery, thereby overcoming a major hurdle in the therapeutic uses of DsiRNA. The present review focuses on a comparison of siRNA and DsiRNA on the basis of their design, mechanism, in vitro and in vivo delivery, and therapeutics.

Cholesterol-Dependent Gating Effects on Ion Channels

Biomembranes separate a live cell from its environment and keep it in an off-equilibrium, steady state. They contain both phospholipids and nonphospholipids, depending on whether there are phosphate groups in the headgroup regions. Cholesterol (CHOL) is one type of nonphospholipids, and one of the most abundant lipid molecules in humans. Its content in plasma membranes and intracellular membranes varies and is tightly regulated. Voltage-gated ion channels are universally present in every cell and are fairly diversified in the eukaryotic domain of life. Our lipid-dependent gating hypothesis postulates that the controlled switch of the voltage-sensor domains (VSDs) in a voltage-gated potassium (Kv) channel between the "down" and the "up" state (gating) is sensitive to the ratio of phospholipids:nonphospholipids in the annular layer around the channel. High CHOL content is found to exert strong inhibitory effects on Kv channels. Such effects have been observed in in vitro membranes, cultured cells, and animal models for cholesterol metabolic defects. Thermodynamic analysis of the CHOL-dependent gating suggests that the inhibitory effects of CHOL result from collective interactions between annular CHOL molecules and the channel, which appear to be a more generic principle behind the CHOL effects on other ion channels and transporters. We will review the recent progress in the CHOL-dependent gating of voltage-gated ion channels, discuss the current technical limitations, and then expand briefly the learned principles to other ion channels that are known to be sensitive to the CHOL-channel interactions.

A review of the role of cav-1 in neuropathology and neural recovery after ischemic stroke

Ischemic stroke starts a series of pathophysiological processes that cause brain injury. Caveolin-1 (cav-1) is an integrated protein and locates at the caveolar membrane. It has been demonstrated that cav-1 can protect blood–brain barrier (BBB) integrity by inhibiting matrix metalloproteases (MMPs) which degrade tight junction proteins. This article reviews recent developments in understanding the mechanisms underlying BBB dysfunction, neuroinflammation, and oxidative stress after ischemic stroke, and focuses on how cav-1 modulates a series of activities after ischemic stroke. In general, cav-1 reduces BBB permeability mainly by downregulating MMP9, reduces neuroinflammation through influencing cytokines and inflammatory cells, promotes nerve regeneration and angiogenesis via cav-1/VEGF pathway, reduces apoptosis, and reduces the damage mediated by oxidative stress. In addition, we also summarize some experimental results that are contrary to the above and explore possible reasons for these differences.

Perturbing the Dynamics and Organization of Cell Membrane Components: A New Paradigm for Cancer-Targeted Therapies

Cancer is a multi-process disease where different mechanisms exist in parallel to ensure cell survival and constant adaptation to the extracellular environment. To adapt rapidly, cancer cells re-arrange their plasma membranes to sustain proliferation, avoid apoptosis and resist anticancer drugs. In this review, we discuss novel approaches based on the modifications and manipulations that new classes of molecules can exert in the plasma membrane lateral organization and order of cancer cells, affecting growth factor signaling, invasiveness, and drug resistance. Furthermore, we present azurin, an anticancer protein from bacterial origin, as a new approach in the development of therapeutic strategies that target the cell membrane to improve the existing standard therapies.

Differential targeting and signalling of voltage-gated T-type Cav 3.2 and L-type Cav 1.2 channels to ryanodine receptors in mesenteric arteries

KEY POINTS

In arterial smooth muscle, Ca2+ sparks are elementary Ca2+ -release events generated by ryanodine receptors (RyRs) to cause vasodilatation by opening maxi Ca2+ -sensitive K+ (BKCa ) channels. This study elucidated the contribution of T-type Cav 3.2 channels in caveolae and their functional interaction with L-type Cav 1.2 channels to trigger Ca2+ sparks in vascular smooth muscle cells (VSMCs). Our data demonstrate that L-type Cav 1.2 channels provide the predominant Ca2+ pathway for the generation of Ca2+ sparks in murine arterial VSMCs. T-type Cav 3.2 channels represent an additional source for generation of VSMC Ca2+ sparks. They are located in pit structures of caveolae to provide locally restricted, tight coupling between T-type Cav 3.2 channels and RyRs to ignite Ca2+ sparks.

ABSTRACT

Recent data suggest that T-type Cav 3.2 channels in arterial vascular smooth muscle cells (VSMCs) and pits structure of caveolae could contribute to elementary Ca2+ signalling (Ca2+ sparks) via ryanodine receptors (RyRs) to cause vasodilatation. While plausible, their precise involvement in igniting Ca2+ sparks remains largely unexplored. The goal of this study was to elucidate the contribution of caveolar Cav 3.2 channels and their functional interaction with Cav 1.2 channels to trigger Ca2+ sparks in VSMCs from mesenteric, tibial and cerebral arteries. We used tamoxifen-inducible smooth muscle-specific Cav 1.2-/- (SMAKO) mice and laser scanning confocal microscopy to assess Ca2+ spark generation in VSMCs. Ni2+ , Cd2+ and methyl-β-cyclodextrin were used to inhibit Cav 3.2 channels, Cav 1.2 channels and caveolae, respectively. Ni2+ (50 μmol L-1 ) and methyl-β-cyclodextrin (10 mmol L-1 ) decreased Ca2+ spark frequency by ∼20-30% in mesenteric VSMCs in a non-additive manner, but failed to inhibit Ca2+ sparks in tibial and cerebral artery VSMCs. Cd2+ (200 μmol L-1 ) suppressed Ca2+ sparks in mesenteric arteries by ∼70-80%. A similar suppression of Ca2+ sparks was seen in mesenteric artery VSMCs of SMAKO mice. The remaining Ca2+ sparks were fully abolished by Ni2+ or methyl-β-cyclodextrin. Our data demonstrate that Ca2+ influx through CaV 1.2 channels is the primary means of triggering Ca2+ sparks in murine arterial VSMCs. CaV 3.2 channels, localized to caveolae and tightly coupled to RyR, provide an additional Ca2+ source for Ca2+ spark generation in mesenteric, but not tibial and cerebral, arteries.

Caveolin-1 facilitated KCNA5 expression, promoting breast cancer viability

Potassium voltage-gated channel subfamily A member 5 (KCNA5) is a voltage-gated potassium channel protein encoded by the KCNA5 gene. A large number of studies have shown that KCNA5 is associated with the survival of malignant tumors, including breast cancer, but the detailed mechanism remains inconclusive. Our previous study found that KCNA5 is co-expressed with a scaffolding protein, caveolin-1 in MCF-10A-neoT non-tumorigenic epithelial cell. In the present study, KCNA5 and caveolin-1 were expressed in breast cancer tissues and cell lines. Exposing MCF-10A-neoT to 2 mM of methyl-β-cyclodextrin, an agent to disrupt caveolae and lipid rafts led to a downregulation of caveolin-1 that reduced the expression of KCNA5. Furthermore, following caveolin-1 knockdown, the expression of KCNA5 was decreased in MDA-MB-231 human breast cancer and MCF-10A-neoT non-tumorigenic epithelial cell lines. In subsequent experiments, the MTT assay showed that increased caveolin-1 and KCNA5 expression promoted the survival of MCF-7 human breast cancer cells, but cell survival was not affected following KCNA5 overexpression alone. Using small interfering RNA technology, KCNA5-silenced MCF-10A-neoT cells were established and a decreased level of phosphorylated-AKT serine/threonine kinase (AKT) was observed in the cells compared with the parental cells. Overall, these results suggested that caveolin-1 facilitated KCNA5 expression and may be associated with AKT activation.

Cellular Uptake of Nanoparticles versus Small Molecules: A Matter of Size

The primary function of the cell membrane is to protect cells from their surroundings. This entails a strict regulation on controlling the exchange of matter between the cell and its environment. A key factor when considering potential biological applications of a particular chemical structure has to do with its ability to internalize into cells. Molecules that can readily cross cell membranes are frequently needed in biological research and medicine, since most therapeutic entities are designed to modulate intracellular components. However, the design of molecules that do not penetrate cells is also relevant toward, for example, extracellular contrast agents, which are most widely used in clinical diagnosis. Small molecules have occupied the forefront of biomedical research until recently, but the past few decades have seen an increasing use of larger chemical structures, such as proteins or nanoparticles, leading to unprecedented and often unexpectedly novel research. Great achievements have been made toward understanding the rules that govern cellular uptake, which show that cell internalization of molecules is largely affected by their size. For example, macromolecules such as proteins and nucleic acids are usually unable to internalize cells. Intriguingly, in the case of nanoparticles, larger sizes seem to facilitate internalization via endocytic pathways, through which the particles remain trapped in lysosomes and endosomes. In this Account, we aimed at presenting our personal view of how different chemical structures behave in terms of cell internalization due to their size, ranging from small drugs to large nanoparticles. We first introduce the properties of cell membranes and the main mechanisms involved in cellular uptake. We then discuss the cellular internalization of molecules, distinguishing between those with molecular weights below 1 kDa and biological macromolecules such as proteins and nucleic acids. In the last section, we review the biological behavior of nanoparticles, with a special emphasis on plasmonic nanoparticles, which feature a high potential in the biomedical field. For each group of chemical structures, we discuss the parameters affecting their cellular internalization but also strategies that can be applied to achieve the desired intracellular delivery. Particular attention is paid to approaches that allow conditional regulation of the cell internalization process using external triggers, such as activable cell penetrating peptides, due to the impact that these systems may have in drug delivery and sensing applications. The Account ends with a "Conclusions and Outlook" section, where general lessons and future directions toward further advancements are briefly presented.

Neospora caninum Dense Granule Protein 7 Regulates the Pathogenesis of Neosporosis by Modulating Host Immune Response

Neospora caninum is a protozoan parasite closely related to Toxoplasma gondii Neosporosis caused by N. caninum is considered one of the main causes of abortion in cattle and nervous-system dysfunction in dogs, and identification of the virulence factors of this parasite is important for the development of control measures. Here, we used a luciferase reporter assay to screen the dense granule proteins genes of N. caninum, and we found that NcGRA6, NcGRA7, and NcGRA14 are involved in the activation of the NF-κB, calcium/calcineurin, and cAMP/PKA signals. To analyze the functions of these proteins and Neospora cyclophilin, we successfully knocked out their genes in the Nc1 strain using plasmids containing the CRISPR/Cas9 components. Among the deficient lines, the NcGRA7-deficient parasites showed reduced virulence in mice. An RNA sequencing analysis of infected macrophage cultures showed that NcGRA7 mainly regulates the host cytokine and chemokine production. The levels of gamma interferon in the ascites fluid, CXCL10 expression in the peritoneal cells, and CCL2 expression in the spleen were lower 5 days after infection with the NcGRA7-deficient parasite than after infection with the parental strain. The parasite burden and the degree of necrosis in the brains of mice infected with the NcGRA7-deficient parasite were also lower than in those of the parental strain. Collectively, our data suggest that both the NcGRA7-dependent activation of the inflammatory response and the parasite burden are important in Neospora virulence.IMPORTANCENeospora caninum invades and replicates in a broad range of host species and cells within those hosts. The effector proteins exported by Neospora induce its pathogenesis by modulating the host immunity. We show that most of the transcriptomic effects in N. caninum-infected cells depend upon the activity of NcGRA7. A deficiency in NcGRA7 reduced the virulence of the parasite in mice. This study demonstrates the importance of NcGRA7 in the pathogenesis of neosporosis.

Caveolin-1 Scaffolding Domain Peptides Alleviate Liver Fibrosis by Inhibiting TGF-β1/Smad Signaling in Mice

Liver fibrosis is the common pathological process characterized by activation of hepatic stellate cells (HSCs) and overproduction of extracellular matrix (ECM). Caveolin-1 (Cav1), the principal component of caveolae, is regarded as an important inhibitor of multiple signaling molecules including transforming growth factor β1(TGF-β1) signaling. To evaluate the role of Cav1 in liver fibrosis, Cav1 deficient (Cav1^−/−) and wild type (WT) mice were subjected to liver fibrosis induced by carbon tetrachloride (CCl₄). Results indicated no significant difference between Cav1^−/− and WT mice in inflammation or collagen content before CCl₄ treatment. After CCl₄ administration, Cav1^−/− mice showed enhanced TGF-β1 signaling, as reflected by a significantly greater amount of phosphorylation of Smad2 and collagen deposition in livers over WT animals. Qualitative and quantitative analysis indicated that inflammatory injury to the liver was markedly aggravated, accompanied by increased degeneration and necrosis of hepatocytes, higher alanine aminotransferase (ALT)/aspartate aminotransferase (AST), TGF-α and IL-1β levels in Cav1^−/− animals. The mRNA and protein levels of α-smooth muscle actin (α-SMA), Collagen α1(I), and Collagen α1(III) were further enhanced in Cav1^−/− animals. We also observed a significant decrease in collagen content in Cav1^−/− and WT animals administrated with Cav1 scaffolding domain peptides (CSD). In vitro study indicated that phosphorylation of Smad2 was inhibited after CSD treatment, accompanied by decreased protein levels of α-SMA, Collagen α1(I), and Collagen α1(III) in HSCs. We conclude that Cav1 is an important inhibitor of TGF-β1/Smad signaling in HSCs activation and collagen production, which might make it a promising target for therapy of liver fibrosis.

The caveolar membrane system in endothelium: From cell signaling to vascular pathology

Caveolae are 50- to 100-nm cholesterol and glycosphingolipid-rich flask-shaped invaginations commonly observed in many terminally differentiated cells. These organelles have been described in many cell types and are particularly abundant in endothelial cells, where they have been involved in the regulation of certain signaling pathways. Specific scaffolding proteins termed caveolins, along with the more recently discovered members of the cavin family, represent the major protein components during caveolae biogenesis. In addition, multiple studies aimed to investigate the expression and the regulation of these proteins significantly contributed to elucidate the role of caveolae and caveolins in endothelial cell physiology and disease. The aim of this review is to survey recent evidence of the involvement of the caveolar network in endothelial cell biology and endothelial cell dysfunction.

Model of OSBP-Mediated Cholesterol Supply to Aichi Virus RNA Replication Sites Involving Protein-Protein Interactions among Viral Proteins, ACBD3, OSBP, VAP-A/B, and SAC1

Positive-strand RNA viruses, including picornaviruses, utilize cellular machinery for genome replication. Previously, we reported that each of the 2B, 2BC, 2C, 3A, and 3AB proteins of Aichi virus (AiV), a picornavirus, forms a complex with the Golgi apparatus protein ACBD3 and phosphatidylinositol 4-kinase IIIβ (PI4KB) at viral RNA replication sites (replication organelles [ROs]), enhancing PI4KB-dependent phosphatidylinositol 4-phosphate (PI4P) production. Here, we demonstrate AiV hijacking of the cellular cholesterol transport system involving oxysterol-binding protein (OSBP), a PI4P-binding cholesterol transfer protein. AiV RNA replication was inhibited by silencing cellular proteins known to be components of this pathway, OSBP, the ER membrane proteins VAPA and VAPB (VAP-A/B), the PI4P-phosphatase SAC1, and PI-transfer protein β. OSBP, VAP-A/B, and SAC1 were present at RNA replication sites. We also found various previously unknown interactions among the AiV proteins (2B, 2BC, 2C, 3A, and 3AB), ACBD3, OSBP, VAP-A/B, and SAC1, and the interactions were suggested to be involved in recruiting the component proteins to AiV ROs. Importantly, the OSBP-2B interaction enabled PI4P-independent recruitment of OSBP to AiV ROs, indicating preferential recruitment of OSBP among PI4P-binding proteins. Protein-protein interaction-based OSBP recruitment has not been reported for other picornaviruses. Cholesterol was accumulated at AiV ROs, and inhibition of OSBP-mediated cholesterol transfer impaired cholesterol accumulation and AiV RNA replication. Electron microscopy showed that AiV-induced vesicle-like structures were close to ER membranes. Altogether, we conclude that AiV directly recruits the cholesterol transport machinery through protein-protein interactions, resulting in formation of membrane contact sites between the ER and AiV ROs and cholesterol supply to the ROs.IMPORTANCE Positive-strand RNA viruses utilize host pathways to modulate the lipid composition of viral RNA replication sites for replication. Previously, we demonstrated that Aichi virus (AiV), a picornavirus, forms a complex comprising certain proteins of AiV, the Golgi apparatus protein ACBD3, and the lipid kinase PI4KB to synthesize PI4P lipid at the sites for AiV RNA replication. Here, we confirmed cholesterol accumulation at the AiV RNA replication sites, which are established by hijacking the host cholesterol transfer machinery mediated by a PI4P-binding cholesterol transfer protein, OSBP. We showed that the component proteins of the machinery, OSBP, VAP, SAC1, and PITPNB, are all essential host factors for AiV replication. Importantly, the machinery is directly recruited to the RNA replication sites through previously unknown interactions of VAP/OSBP/SAC1 with the AiV proteins and with ACBD3. Consequently, we propose a specific strategy employed by AiV to efficiently accumulate cholesterol at the RNA replication sites via protein-protein interactions.

Receptor-mediated endocytosis generates nanomechanical force reflective of ligand identity and cellular property

Whether environmental (thermal, chemical, and nutrient) signals generate quantifiable, nanoscale, mechanophysical changes in the cellular plasma membrane has not been well elucidated. Assessment of such mechanophysical properties of plasma membrane may shed lights on fundamental cellular process. Atomic force microscopic (AFM) measurement of the mechanical properties of live cells was hampered by the difficulty in accounting for the effects of the cantilever motion and the associated hydrodynamic force on the mechanical measurement. These challenges have been addressed in our recently developed control-based AFM nanomechanical measurement protocol, which enables a fast, noninvasive, broadband measurement of the real-time changes in plasma membrane elasticity in live cells. Here we show using this newly developed AFM platform that the plasma membrane of live mammalian cells exhibits a constant and quantifiable nanomechanical property, the membrane elasticity. This mechanical property sensitively changes in response to environmental factors, such as the thermal, chemical, and growth factor stimuli. We demonstrate that different chemical inhibitors of endocytosis elicit distinct changes in plasma membrane elastic modulus reflecting their specific molecular actions on the lipid configuration or the endocytic machinery. Interestingly, two different growth factors, EGF and Wnt3a, elicited distinct elastic force profiles revealed by AFM at the plasma membrane during receptor-mediated endocytosis. By applying this platform to genetically modified cells, we uncovered a previously unknown contribution of Cdc42, a key component of the cellular trafficking network, to EGF-stimulated endocytosis at plasma membrane. Together, this nanomechanical AFM study establishes an important foundation that is expandable and adaptable for investigation of cellular membrane evolution in response to various key extracellular signals.

Oral delivery of anti-diabetes therapeutics using cell penetrating and transcytosing peptide strategies

Oral delivery of insulin and other anti-diabetic peptides is inhibited by low intestinal absorption caused by the poor permeability across cellular membranes and the susceptibility to enzymatic degradation in the gastrointestinal tract. Cell-penetrating peptides (CPPs) have been investigated for a number of years as oral absorption enhancers for hydrophilic macromolecules by electrostatic or covalent conjugation on in conjunction with nanotechnology. Endogenous cellular uptake mechanisms present in the intestine can be exploited by engineering peptide conjugates that transcytose; entering cells by endocytosis and leaving by exocytosis. Efficiently delivering hydrophilic and sensitive peptide drugs to safely transverse the digestive barrier with no effect on gut physiology using remains a key driver for formulation research. Here we review the use of CPP and transcytosis peptide approaches, their modification and use in delivering anti-diabetic peptides (with the primary example of Insulin and engineered homologues) by direct oral administration to treat diabetes and associated metabolic disorders.

Hormone induced differential transcriptome analysis of Sertoli cells during postnatal maturation of rat testes

Sertoli cells (Sc) are unique somatic cells of testis that are the target of both FSH and testosterone (T) and regulate spermatogenesis. Although Sc of neonatal rat testes are exposed to high levels of FSH and T, robust differentiation of spermatogonial cells becomes conspicuous only after 11-days of postnatal age. We have demonstrated earlier that a developmental switch in terms of hormonal responsiveness occurs in rat Sc at around 12 days of postnatal age during the rapid transition of spermatogonia A to B. Therefore, such “functional maturation” of Sc, during pubertal development becomes prerequisite for the onset of spermatogenesis. However, a conspicuous difference in robust hormone (both T and FSH) induced gene expression during the different phases of Sc maturation restricts our understanding about molecular events necessary for the spermatogenic onset and maintenance. Here, using microarray technology, we for the first time have compared the differential transcriptional profile of Sc isolated and cultured from immature (5 days old), maturing (12 days old) and mature (60 days old) rat testes. Our data revealed that immature Sc express genes involved in cellular growth, metabolism, chemokines, cell division, MAPK and Wnt pathways, while mature Sc are more specialized expressing genes involved in glucose metabolism, phagocytosis, insulin signaling and cytoskeleton structuring. Taken together, this differential transcriptome data provide an important resource to reveal the molecular network of Sc maturation which is necessary to govern male germ cell differentiation, hence, will improve our current understanding of the etiology of some forms of idiopathic male infertility.

Caveolin 1 Promotes Renal Water and Salt Reabsorption

Caveolin-1 (Cav1) is essential for the formation of caveolae. Little is known about their functional role in the kidney. We tested the hypothesis that caveolae modulate renal salt and water reabsorption. Wild-type (WT) and Cav1-deficient (Cav1−/−) mice were studied. Cav1 expression and caveolae formation were present in vascular cells, late distal convoluted tubule and principal connecting tubule and collecting duct cells of WT but not Cav1−/− kidneys. Urinary sodium excretion was increased by 94% and urine flow by 126% in Cav1−/− mice (p < 0.05). A decrease in activating phosphorylation of the Na-Cl cotransporter (NCC) of the distal convoluted tubule was recorded in Cav1−/− compared to WT kidneys (−40%; p < 0.05). Isolated intrarenal arteries from Cav1−/− mice revealed a fourfold reduction in sensitivity to phenylephrine (p < 0.05). A significantly diminished maximal contractile response (−13%; p < 0.05) was suggestive of enhanced nitric oxide (NO) availability. In line with this, the abundance of endothelial NO synthase (eNOS) was increased in Cav1−/− kidneys +213%; p < 0.05) and cultured caveolae-deprived cells showed intracellular accumulation of eNOS, compared to caveolae-intact controls. Our results suggest that renal caveolae help to conserve water and electrolytes via modulation of NCC function and regulation of vascular eNOS.

The Molecular Basis for Specificity at the Level of the Protein Kinase a Catalytic Subunit

Assembly of multi enzyme complexes at subcellular localizations by anchoring- and scaffolding proteins represents a pivotal mechanism for achieving spatiotemporal regulation of cellular signaling after hormone receptor targeting [for review, see (1)]. In the 3' 5'-cyclic adenosine monophosphate (cAMP) dependent protein kinase (PKA) signaling pathway it is generally accepted that specificity is secured at several levels. This includes at the first level stimulation of receptors coupled to heterotrimeric G proteins which through stimulation of adenylyl cyclase (AC) forms the second messenger cAMP. Cyclic AMP has several receptors including PKA. PKA is a tetrameric holoenzyme consisting of a regulatory (R) subunit dimer and two catalytic (C) subunits. The R subunit is the receptor for cAMP and compartmentalizes cAMP signals through binding to cell and tissue-specifically expressed A kinase anchoring proteins (AKAPs). The current dogma tells that in the presence of cAMP, PKA dissociates into an R subunit dimer and two C subunits which are free to phosphorylate relevant substrates in the cytosol and nucleus. The release of the C subunit has raised the question how specificity of the cAMP and PKA signaling pathway is maintained when the C subunit no longer is attached to the R subunit-AKAP complex. An increasing body of evidence points toward a regulatory role of the cAMP and PKA signaling pathway by targeting the C subunits to various C subunit binding proteins in the cytosol and nucleus. Moreover, recent identification of isoform specific amino acid sequences, motifs and three dimensional structures have together provided new insight into how PKA at the level of the C subunit may act in a highly isoform-specific fashion. Here we discuss recent understanding of specificity of the cAMP and PKA signaling pathway based on C subunit subcellular targeting as well as evolution of the C subunit structure that may contribute to the dynamic regulation of C subunit activity.

Genetics and Therapies for GM2 Gangliosidosis

Tay-Sachs disease, caused by impaired β-N-acetylhexosaminidase activity, was the first GM2 gangliosidosis to be studied and one of the most severe and earliest lysosomal diseases to be described. The condition, associated with the pathological build-up of GM2 ganglioside, has acquired almost iconic status and serves as a paradigm in the study of lysosomal storage diseases. Inherited as a classical autosomal recessive disorder, this global disease of the nervous system induces developmental arrest with regression of attained milestones; neurodegeneration progresses rapidly to cause premature death in young children. There is no effective treatment beyond palliative care, and while the genetic basis of GM2 gangliosidosis is well established, the molecular and cellular events, from diseasecausing mutations and glycosphingolipid storage to disease manifestations, remain to be fully delineated. Several therapeutic approaches have been attempted in patients, including enzymatic augmentation, bone marrow transplantation, enzyme enhancement, and substrate reduction therapy. Hitherto, none of these stratagems has materially altered the course of the disease. Authentic animal models of GM2 gangliodidosis have facilitated in-depth evaluation of innovative applications such as gene transfer, which in contrast to other interventions, shows great promise. This review outlines current knowledge pertaining the pathobiology as well as potential innovative treatments for the GM2 gangliosidoses.

Triglyceride Metabolism in the Liver

Triglyceride molecules represent the major form of storage and transport of fatty acids within cells and in the plasma. The liver is the central organ for fatty acid metabolism. Fatty acids accrue in liver by hepatocellular uptake from the plasma and by de novo biosynthesis. Fatty acids are eliminated by oxidation within the cell or by secretion into the plasma within triglyceride-rich very low-density lipoproteins. Notwithstanding high fluxes through these pathways, under normal circumstances the liver stores only small amounts of fatty acids as triglycerides. In the setting of overnutrition and obesity, hepatic fatty acid metabolism is altered, commonly leading to the accumulation of triglycerides within hepatocytes, and to a clinical condition known as nonalcoholic fatty liver disease (NAFLD). In this review, we describe the current understanding of fatty acid and triglyceride metabolism in the liver and its regulation in health and disease, identifying potential directions for future research. Advances in understanding the molecular mechanisms underlying the hepatic fat accumulation are critical to the development of targeted therapies for NAFLD. © 2018 American Physiological Society. Compr Physiol 8:1-22, 2018.

Cytoplasmic cleavage of DPPA3 is required for intracellular trafficking and cleavage-stage development in mice

Degradation of maternal proteins by the ubiquitin-proteasome system (UPS) accompanies the maternal-to-zygotic transition. DPPA3/Stella/PGC7, encoded by a maternal effect gene, is present in the nucleus and cytoplasm of zygotes and has been associated with protecting the female pronucleus from TET3-mediated demethylation. We now report that cytoplasmic DPPA3 is partially cleaved by the ubiquitin-proteasome system and an N-terminus fragment remains in the cytoplasm where it associates with early and re-cycling endosomes. If DPPA3 is absent or if cleavage is prevented, multiple vesicles coalesce/aggregate and markers of lysosomes are decreased. Fertilized eggs develop poorly into blastocysts, which results in significantly decreased fecundity of Dppa3 R60A transgenic mice. This phenocopies aspects of Lamp1/2 knockdowns and Dppa3 KO embryos can be partially rescued in vitro by DPPA31-60 and to a lesser extent by LAMP1/2. Thus, the N-terminus of DPPA3 has a significant role in cytoplasmic vesicular trafficking in addition to its previously reported nuclear function.

Identification and characterization of molluscan caveolin-1 ortholog from Haliotis discus discus: Possible involvement in embryogenesis and host defense mechanism against pathogenic stress

Caveolins are principal membrane proteins of caveolae that play a central role in signal transduction, substrate transport, and membrane trafficking in various cell types. Numerous studies have reported the crucial role of caveolin-1 (CAV1) in response to invading microbes; yet, very little is known about molluscan CAV1. In this study, we identified and characterized CAV1 ortholog from the disk abalone, Haliotis discus discus (HdCAV1). The cDNA sequence of HdCAV1 is 826 bp long and encodes a 127-amino acid polypeptide. Characteristic caveolin superfamily domain (Glu³ - Lys¹²⁶) and two possible transmembrane domains (Cys⁴⁸ - Tyr⁶⁷ and Ile¹⁰³ - Phe¹²⁰) were identified in the HdCAV1 protein. Homology analysis revealed that HdCAV1 shared higher identity (>47%) with molluscans, but lower identity with other species. Phylogenetic tree constructed by the neighbor-joining (NJ) method revealed a distinct evolutionary pathway for molluscans. Transcriptional analysis by SYBR Green qPCR showed the highest expression of HdCAV1 mRNA in late veliger stage, as compared to that in other embryonic developmental stages of disk abalone. In adult animals, gill tissue showed highest HdCAV1 transcript levels under normal physiological condition. Stimulations with two bacteria (Vibrio parahaemolyticus and Listeria monocytogenes), viral hemorrhagic septicemia virus, and two pathogen-associated molecular patterns (LPS and poly I:C) significantly modulated the expression of HdCAV1 transcripts. Collectively, these data suggest that CAV1 plays an important role in embryogenesis and host immune defense in disk abalone.

Reduced membrane cholesterol after chronic hypoxia limits Orai1-mediated pulmonary endothelial Ca2+ entry

Endothelial dysfunction in chronic hypoxia (CH)-induced pulmonary hypertension is characterized by reduced store-operated Ca²⁺ entry (SOCE) and diminished Ca²⁺-dependent production of endothelium-derived vasodilators. We recently reported that SOCE in pulmonary arterial endothelial cells (PAECs) is tightly regulated by membrane cholesterol and that decreased membrane cholesterol is responsible for impaired SOCE after CH. However, the ion channels involved in cholesterol-sensitive SOCE are unknown. We hypothesized that cholesterol facilitates SOCE in PAECs through the interaction of Orai1 and stromal interaction molecule 1 (STIM1). The role of cholesterol in Orai1-mediated SOCE was initially assessed using CH exposure in rats (4 wk, 380 mmHg) as a physiological stimulus to decrease PAEC cholesterol. The effects of Orai1 inhibition with AnCoA4 on SOCE were examined in isolated PAEC sheets from control and CH rats after cholesterol supplementation, substitution of endogenous cholesterol with epicholesterol (Epichol), or vehicle treatment. Whereas cholesterol restored endothelial SOCE in CH rats, both Epichol and AnCoA4 attenuated SOCE only in normoxic controls. The Orai1 inhibitor had no further effect in cells pretreated with Epichol. Using cultured pulmonary endothelial cells to allow better mechanistic analysis of the molecular components of cholesterol-regulated SOCE, we found that Epichol, AnCoA4, and Orai1 siRNA each inhibited SOCE compared with their respective controls. Epichol had no additional effect after knockdown of Orai1. Furthermore, Epichol substitution significantly reduced STIM1-Orai1 interactions as assessed by a proximity ligation assay. We conclude that membrane cholesterol is required for the STIM1-Orai1 interaction necessary to elicit endothelial SOCE. Furthermore, reduced PAEC membrane cholesterol after CH limits Orai1-mediated SOCE. NEW & NOTEWORTHY This research demonstrates a novel contribution of cholesterol to regulate the interaction of Orai1 and stromal interaction molecule 1 required for pulmonary endothelial store-operated Ca²⁺ entry. The results provide a mechanistic basis for impaired pulmonary endothelial Ca²⁺ influx after chronic hypoxia that may contribute to pulmonary hypertension.

Quantitative proteomic Analysis Reveals up-regulation of caveolin-1 in FOXP3-overexpressed human gastric cancer cells

Forkhead box protein 3 (FOXP3) is implicated in tumor progression and prognosis in various types of tumor cells. We have recently reported that FOXP3 inhibited proliferation of gastric cancer (GC) cells through activating the apoptotic signaling pathway. In this study, we found that over-expression of FOXP3 inhibited GC cell migration, invasion and proliferation. Then, the label-free quantitative proteomic approach was employed to further investigating the down-stream proteins regulated by FOXP3, resulting in a total of 3,978 proteins quantified, including 186 significantly changed proteins. Caveolin-1 (CAV1), as a main constituent protein of caveolae, was one of those changed proteins up-regulated in FOXP3-overexpressed GC cells, moreover, it was assigned as one of the node proteins in the protein-protein interaction network and the key protein involved in focal adhesion pathway by bioinformatics analysis. Further biological experiments confirmed that FOXP3 directly bound to the promoter regions of CAV1 to positively regulate CAV1 transcription in GC cells. In summary, our study suggested that FOXP3 can be considered as a tumor suppressor in GC via positively regulating CAV1 through transcriptional activation, and this FOXP3-CAV1 transcriptional regulation axis may play an important role in inhibiting invasion and metastasis of GC cells. Data are available via ProteomeXchange under identifier PXD007725.

Genetic polymorphisms in caveolin-1 associate with breast cancer risk in Chinese Han population

Caveolin-1(CAV-1) was demonstrated to be a tumor suppressor gene and be implicated in the development of breast cancer (BC). Numerous potentially functional polymorphisms in CAV-1 have been identified, but their effects on BC were not clear. This case-control study aims to evaluate the relationship between CAV-1 polymorphisms and BC risk. 560 BC patients and 583 healthy controls were enrolled in the present study, all from Chinese Han population. We detected 3 single nucleotide polymorphisms (rs3807987, rs1997623, and rs7804372) in CAV-1 using the Sequenom MassARRAY method. The association between CAV-1genotypes and BC risk was assessed in six genetic models by calculating the odds ratio (OR) and 95% confidence intervals (95% CIs) with χ2-test. The CAV-1 rs3807987 polymorphism was observed to increase the risk of BC And the A allele of rs3807987 relates to a larger tumor size (≥2cm) and lower incidence of PR-positive BC while the AA genotype of rs7804372 associates with a higher ER and Her-2 positive rate among BC patients. In addition, Ars1997623Grs3807987Trs7804372 haplotype was linked to a decreased risk of BC (OR =0.64, 95%CI=0.44-0.93), whereas Crs1997623Ars3807987Trs7804372 haplotype was related to an increased BC risk (OR =1.74, 95%CI=1.04-2.92). Our study suggests that CAV-1 rs3807987 can increase the BC risk among Chinese Han women. And the rs3807987 and rs7804372 in CAV-1 may serve as predictors for prognosis of BC.

Determination of μ-, δ- and κ-opioid receptors in forebrain cortex of rats exposed to morphine for 10 days: Comparison with animals after 20 days of morphine withdrawal

BACKGROUND

Chronic exposure of mammalian organism to morphine results in adaption to persistent high opioid tone through homeostatic adjustments. Our previous results indicated that in the frontal brain cortex (FBC) of rats exposed to morphine for 10 days, such a compensatory adjustment was detected as large up-regulation of adenylylcyclases I (8-fold) and II (2.5-fold). The other isoforms of AC (III-IX) were unchanged. Importantly, the increase of ACI and ACII was reversible as it disappeared after 20 days of morphine withdrawal. Changes of down-stream signaling molecules such as G proteins and adenylylcyclases should respond to and be preceded by primary changes proceeding at receptor level. Therefore in our present work, we addressed the problem of reversibility of the long-term morphine effects on μ-, δ- and κ-OR protein levels in FBC.

METHODS

Rats were exposed to increasing doses of morphine (10-40 mg/kg) for 10 days and sacrificed either 24 h (group +M10) or 20 days (group +M10/-M20) after the last dose of morphine in parallel with control animals (groups -M10 and -M10/-M20). Post-nuclear supernatant (PNS) fraction was prepared from forebrain cortex, resolved by 1D-SDS-PAGE under non-dissociated (-DTT) and dissociated (+DTT) conditions, and analyzed for the content of μ-, δ- and κ-OR by immunoblotting with C- and N-terminus oriented antibodies.

RESULTS

Significant down-regulation of δ-OR form exhibiting Mw ≈ 60 kDa was detected in PNS prepared from both (+M10) and (+M10/-M20) rats. However, the total immunoblot signals of μ-, δ- and κ-OR, respectively, were unchanged. Plasma membrane marker Na, K-ATPase, actin and GAPDH were unaffected by morphine in both types of PNS. Membrane-domain marker caveolin-1 and cholesterol level increased in (+M10) rats and this increase was reversed back to control level in (+M10/-M20) rats.

CONCLUSIONS

In FBC, prolonged exposure of rats to morphine results in minor (δ-OR) or no change (μ- and κ-OR) of opioid receptor content. The reversible increases of caveolin-1 and cholesterol levels suggest participation of membrane domains in compensatory responses during opioid withdrawal.

GENERAL SIGNIFICANCE

Analysis of reversibility of morphine effect on mammalian brain.

Unraveling the role of membrane microdomains during microbial infections

Infectious diseases pose major socioeconomic and health-related threats to millions of people across the globe. Strategies to combat infectious diseases derive from our understanding of the complex interactions between the host and specific bacterial, viral, and fungal pathogens. Lipid rafts are membrane microdomains that play important role in life cycle of microbes. Interaction of microbial pathogens with host membrane rafts influences not only their initial colonization but also their spread and the induction of inflammation. Therefore, intervention strategies aimed at modulating the assembly of membrane rafts and/or regulating raft-directed signaling pathways are attractive approaches for the. management of infectious diseases. The current review discusses the latest advances in terms of techniques used to study the role of membrane microdomains in various pathological conditions and provides updated information regarding the role of membrane rafts during bacterial, viral and fungal infections.

Sterol transporters at membrane contact sites regulate TORC1 and TORC2 signaling

Membrane contact sites (MCSs) function to facilitate the formation of membrane domains composed of specialized lipids, proteins, and nucleic acids. In cells, membrane domains regulate membrane dynamics and biochemical and signaling pathways. We and others identified a highly conserved family of sterol transport proteins (Ltc/Lam) localized at diverse MCSs. In this study, we describe data indicating that the yeast family members Ltc1 and Ltc3/4 function at the vacuole and plasma membrane, respectively, to create membrane domains that partition upstream regulators of the TORC1 and TORC2 signaling pathways to coordinate cellular stress responses with sterol homeostasis.

Endocytotic uptake of HPMA-based polymers by different cancer cells: impact of extracellular acidosis and hypoxia

Background

Polymeric nanoparticles allow to selectively transport chemotherapeutic drugs to the tumor tissue. These nanocarriers have to be taken up into the cells to release the drug. In addition, tumors often show pathological metabolic characteristics (hypoxia and acidosis) which might affect the polymer endocytosis.

Materials and methods

Six different N-(2-hydroxypropyl)methacrylamide (HPMA)-based polymer structures (homopolymer as well as random and block copolymers with lauryl methacrylate containing hydrophobic side chains) varying in molecular weight and size were analyzed in two different tumor models. The cellular uptake of fluorescence-labeled polymers was measured under hypoxic (pO₂ ≈1.5 mmHg) and acidic (pH 6.6) conditions. By using specific inhibitors, different endocytotic routes (macropinocytosis and clathrin-mediated, dynamin-dependent, cholesterol-dependent endocytosis) were analyzed separately.

Results

The current results revealed that the polymer uptake depends on the molecular structure, molecular weight and tumor line used. In AT1 cells, the uptake of random copolymer was five times stronger than the homopolymer, whereas in Walker-256 cells, the uptake of all polymers was much stronger, but this was independent of the molecular structure and size. Acidosis increased the uptake of random copolymer in AT1 cells but reduced the intracellular accumulation of homopolymer and block copolymer. Hypoxia reduced the uptake of all polymers in Walker-256 cells. Hydrophilic polymers (homopolymer and block copolymer) were taken up by all endocytotic routes studied, whereas the more lipophilic random copolymer seemed to be taken up preferentially by cholesterol- and dynamin-dependent endocytosis.

Conclusion

The study indicates that numerous parameters of the polymer (structure, size) and of the tumor (perfusion, vascular permeability, pH, pO₂) modulate drug delivery, which makes it difficult to select the appropriate polymer for the individual patient.

Characterization of physiochemical properties of caveolin-1 from normal and prion-infected human brains

Caveolin-1 is a major component protein of the caveolae—a type of flask shaped, 50-100 nm, nonclathrin-coated, microdomain present in the plasma membrane of most mammalian cells. Caveolin-1 functions as a scaffolding protein to organize and concentrate signaling molecules within the caveolae, which may be associated with its unique physicochemical properties including oligomerization, acquisition of detergent insolubility, and association with cholesterol. Here we demonstrate that caveolin-1 is detected in all brain areas examined and recovered in both detergent-soluble and -insoluble fractions. Surprisingly, the recovered molecules from the two different fractions share a similar molecular size ranging from 200 to 2,000 kDa, indicated by gel filtration. Furthermore, both soluble and insoluble caveolin-1 molecules generate a proteinase K (PK)-resistant C-terminal core fragment upon the PK-treatment, by removing ˜36 amino acids from the N-terminus of the protein. Although it recognizes caveolin-1 from A431 cell lysate, an antibody against the C-terminus of caveolin-1 fails to detect the brain protein by Western blotting, suggesting that the epitope in the brain caveolin-1 is concealed. No significant differences in the physicochemical properties of caveolin-1 between uninfected and prion-infected brains are observed.

Tenofovir disoproxil fumarate loaded PLGA nanoparticles for enhanced oral absorption: Effect of experimental variables and in vitro, ex vivo and in vivo evaluation

In this study, PLGA based nanoparticles of tenofovir disoproxil fumarate (TDF) were designed for enhancing its oral absorption. To develop PLGA based TDF nanoparticles with the goal of minimum particle size and maximum entrapment efficiency statistical optimization techniques (factorial design and response surface methodology) were employed. The optimized nanoparticles were characterized for size, shape, charge and physical state. Further, the stability, cytotoxicity and metabolic protective effect of the nanoparticles were evaluated. Single dose pharmacokinetic study in rats was conducted to evaluate the oral absorption of the designed nanoparticles. Ex vivo everted gut sac studies were performed to evaluate the role of active uptake mechanisms in the absorption of the designed nanoparticles. The results showed that the statistical models employed could determine the interaction effects of the critical factors which were used in the optimization of the nanoparticles. The optimized nanoparticles with a particle size of 218±3.85nm and an entrapment efficiency of 57.3±1.6%. The nanoparticles were able to increase the AUC of tenofovir by 5.8 fold. It was observed that active uptake mechanisms predominantly via clathrin-mediated uptake played a key role in increasing the oral absorption of TDF.

Cellular uptake of nanoparticles: journey inside the cell

Nanoscale materials are increasingly found in consumer goods, electronics, and pharmaceuticals. While these particles interact with the body in myriad ways, their beneficial and/or deleterious effects ultimately arise from interactions at the cellular and subcellular level. Nanoparticles (NPs) can modulate cell fate, induce or prevent mutations, initiate cell-cell communication, and modulate cell structure in a manner dictated largely by phenomena at the nano-bio interface. Recent advances in chemical synthesis have yielded new nanoscale materials with precisely defined biochemical features, and emerging analytical techniques have shed light on nuanced and context-dependent nano-bio interactions within cells. In this review, we provide an objective and comprehensive account of our current understanding of the cellular uptake of NPs and the underlying parameters controlling the nano-cellular interactions, along with the available analytical techniques to follow and track these processes.

Inhibitory effect of caveolin-1 in vascular endothelial cells, pericytes and smooth muscle cells

Caveolin-1 (Cav1) is the principle structural protein of caveolae. It plays important roles in the vascular system under both physiological and pathological conditions. Although Cav1 has been shown to inhibit microvascular permeability and has been considered as a tumor-suppressor for years, the underlying cellular mechanism has yet to be discovered. Here, we systematically investigated Cav1 functions in the main types of vascular cells, including endothelial cells (ECs), pericytes (PCs) and smooth muscle cells (SMCs). We synthesized a cell-permeable peptide called cavtratin that is derived from the Cav1 scaffolding domain. We found that cavtratin inhibited ECs in all assays, including survival, proliferation, migration and permeability assays. It also inhibited the proliferation of PCs and SMCs but had no effect on their survival or migration. The inhibitory effect of cavtratin on the proliferation of all vascular cells suggests that Cav1 plays important roles in vascular development and angiogenesis. Under physiological condition, the main function of Cav1 is to inhibit EC permeability.

Effect of Alkylation on the Cellular Uptake of Polyethylene Glycol-Coated Gold Nanoparticles

Alkyl groups (C_nH_2n+1) are prevalent in engineered bionanomaterials used for many intracellular applications, yet how alkyl groups dictate the interactions between nanoparticles and mammalian cells remains incomprehensively investigated. In this work, we report the effect of alkylation on the cellular uptake of densely polyethylene glycol-coated nanoparticles, which are characterized by their limited entry into mammalian cells. Specifically, we prepare densely PEGylated gold nanoparticles that bear alkyl chains of varying carbon chain lengths (n) and loading densities (termed "alkyl-PEG-AuNPs"), followed by investigating their uptake by Kera-308 keratinocytes. Strikingly, provided a modest alkyl mass percentage of 0.2% (2 orders of magnitude lower than that of conventional lipid-based NPs) in their PEG shells, dodecyl-PEG-AuNPs (n = 12) and octadecyl-PEG-AuNPs (n = 18) can enter Kera-308 cells 30-fold more than methoxy-PEG-AuNPs (no alkyl groups) and hexyl-PEG-AuNPs (n = 6) after 24 h of incubation. Such strong dependence on n is valid for all serum concentrations considered (even under serum-free conditions), although enhanced serum levels can trigger the agglomeration of alkyl-PEG-AuNPs (without permanent aggregation of the AuNP cores) and can attenuate their cellular uptake. Additionally, alkyl-PEG-AuNPs can rapidly enter Kera-308 cells via the filipodia-mediated pathway, engaging the tips of membrane protrusions and accumulating within interdigital folds. Most alkyl-PEG-AuNPs adopt the "endo-lysosomal" route of trafficking, but ∼15% of them accumulate in the cytosol. Regardless of intracellular location, alkyl-PEG-AuNPs predominantly appear as individual entities after 24 h of incubation. Our work offers insights into the incorporation of alkyl groups for designing bionanomaterials for cellular uptake and cytosolic accumulation with intracellular stability.