Caveolin proteins and estrogen signaling in the brain

Best described outside the nervous system, caveolins are structural proteins that form caveolae, functional microdomains at the plasma membrane that cluster related signaling molecules. Caveolin-associated proteins include G protein-coupled receptors and G proteins, receptor tyrosine kinases, as well as protein kinases, ion channels and various other signaling enzymes. Not surprisingly, a wide array of biological disorders are thought to be rooted in caveolin dysfunction. In addition, caveolins traffic and cluster estrogen receptors to caveolae. Interactions between the estrogen receptors ERalpha and ERbeta with caveolins appear critical in many non-neuronal cell types, e.g., disruption of normal function may underlie many forms of breast cancer. Recent findings suggest caveolins may also play an essential role in membrane estrogen receptor function in the nervous system. Not only are they expressed in neurons and glia, but different caveolin isoforms also appear necessary to generate distinct functional signaling complexes. With membrane estrogen receptors responsible for the efficient activation of a multitude of intracellular signaling pathways, which in turn influence a wide variety of nervous system functions, caveolin proteins are poised to act as the central coordinators of these processes.     

囊泡—囊泡素1在清道夫受体AⅠ转基因小鼠动脉粥样硬化发生中的作用

研究囊泡／囊泡素1与清道夫受体A的相互作用及在动脉粥样硬化发生发展中的作用。将16只正常小鼠随机分为正常对照组和高脂组，16只清道夫受体I转基因小鼠随机分为转基因组和转基因高脂组。正常对照组和转基因组用基础饲料喂养，高脂组和转基因高脂组用高脂饲料喂养。24周后用免疫组织化学法检测小鼠主动脉血管上囊泡素1的表达，计算机图像分析观察主动脉斑块面积及内膜／中膜厚度，电镜观察囊泡在主动脉内皮细胞膜上的表达。结果发现，高脂组、转基因组、转基因高脂组小鼠的内膜厚度和中膜厚度明显增加，是正常对照组的2－4倍，3组均可见明显动脉粥样硬化斑块形成。正常小鼠主动脉血管表达高水平的囊泡及囊泡素1，而转基因鼠囊泡及囊泡素1表达明显减少。转基因鼠经高脂喂养后，上述表现更加明显。以上结果提示转基因清道夫受体AI小鼠动脉粥样硬化的发生可能与其动脉内皮细胞上囊泡／囊泡素1下调有关。     

Caveolin-1 promotes gastric cancer progression by up-regulating epithelial to mesenchymal transition by crosstalk of signalling mechanisms under hypoxic condition

Gastric cancer is the second most fatal common form of cancer. The crosstalk among signalling pathways that results in the acceleration of epithelial to mesenchymal transition (EMT) plays a pivotal role in the molecular mechanism of gastric carcinogenesis. To understand the role of caveolin-1 (Cav-1), the expression pattern was studied in human gastric adenocarcinoma tissues and also in AGS and KATO III cell lines. Here, we show that during hypoxic condition, the increase in the levels of hypoxia-inducible factor-1α (HIF-1α) results in a significant decrease in the expression of caveolin-1 which is regulated by heat shock protein 90 (HSP90). The reduced levels of Cav-1 correlated with the increased epidermal growth factor receptor (EGFR) activation resulting in the significant activation of its downstream target STAT3. Accumulation of pSTAT3 in the nucleus results in the decreased expression of E-cadherin and increased expression of mesenchymal markers (Slug, α-SMA, N-cadherin and vimentin). Crosstalk of EGFR and transforming growth factor β (TGF-β) signalling with Wnt signalling enhances cell proliferation, cell survival and upregulates EMT. There was no significant alteration in the expression of epithelial and mesenchymal molecules in both the cell lines studied. Thus, we provide evidence that Cav-1 was modulated by HSP90 and functions as a crucial regulator of EMT in gastric cancer.     

Caveolin-1在支气管哮喘中的研究进展

微囊（caveolae）是存在于细胞膜上烧瓶样的内陷微结构，它参与细胞的众多生命活动，如细胞的内吞作用、胆固醇代谢、肿瘤的发生以及信号转导过程。微囊蛋白-1（caveolin-1）是caveolae最重要的结构蛋白，研究表明许多呼吸系统疾病与caveolin-1的表达异常密切相关，本文就其在支气管哮喘中的研究进展作一综述。     

Mesothelial cells can detach from the mesentery and differentiate into macrophage-like cells

Peritoneal cell suspension is composed of heterogeneous cell population. Macrophages are the most numerous cells among them. They can originate from different sources and can be resident, exudate and elicited. When we used Freund's adjuvant to elicit peritoneal macrophages, cells having large amount of caveolae on their plasma membrane appeared in the peritoneal wash. The number of these caveolae-rich cells increased by the time of the Freund's adjuvant treatment. Although their morphology was different form from the common macrophages, they were labelled with pan-macrophage antibodies. As the origin of these cells is unknown in this work, we tried to find out where they can originate from. Our interest turned towards the mesothelial cells. We found that the adjuvant treatment resulted in significant morphological changes in these cells and stimulate them to leave the surface of the mesentery. By the time of the adjuvant treatment, the macrophage markers expression increased in the mesothelial cells and more cells were found to detach from the mesentery. These results strongly suggest that under special stimuli mesothelial cells can leave the mesentery and differentiate into phagocytotic (macrophage-like) cells. These data raises the idea that mesothelial cells might not entirely differentiated and represent a multipotential cell lineage. To study whether this is the case we used anti-nestin antibody, which is a specific marker for multifunctional, multi-lineage progenitor cells. Mesothelial cells showed strong labelling with this antibody indicating that these cells really represent a 'young', not entirely differentiated cell population.     

Caveolae蛋白与胃癌发生发展的表观遗传学关系

胃癌是我国最常见的恶性肿瘤之一,其死亡率占我国恶性肿瘤死亡率之首。胃癌的病因复杂,虽经数十年的研究,至今仍无明确定论。目前普遍认为其发生是遗传和环境因素共同作用的结果。随着对表观遗传学认识的深入,遗传因子在疾病中的作用被不断发现,对疾病的诊断、治疗和预防起到了一定的作用。本文结合Caveolae蛋白的研究现状综述其与胃癌发生发展的表观遗传学关系,希望对胃癌发病机制的研究提供新的思路。     

Alterations of Na/K-ATPase function in caveolin-1 knockout cardiac fibroblasts

Recent studies have demonstrated that the Na⁺/K⁺-ATPase is not only an ion pump, but also a membrane receptor that confers the ligand-like effects of cardiotonic steroids (CTS) such as ouabain on protein kinases and cell growth. Because CTS have been implicated in cardiac fibrosis, this study examined the role of caveolae in the regulation of Na⁺/K⁺-ATPase function and CTS signaling in cardiac fibroblasts. In cardiac fibroblasts prepared from wild-type and caveolin-1 knockout [Cav-1(−/−)] mice, we found that the absence of caveolin-1 did not affect total cellular amount or surface expression of Na⁺/K⁺-ATPase α1 subunit. However, it did increase ouabain-sensitive ⁸⁶Rb⁺ uptake. While knockout of caveolin-1 increased basal activities of Src and ERK1/2, it abolished the activation of these kinases induced by ouabain but not angiotensin II. Finally, ouabain stimulated collagen synthesis and cell proliferation in wild type but not Cav-1(−/−) cardiac fibroblasts. Thus, we conclude that caveolae are important for regulating both pumping and signal transducing functions of Na⁺/K⁺-ATPase. While depletion of caveolae increases the pumping function of Na⁺/K⁺-ATPase, it suppresses CTS-induced signal transduction, growth, and collagen production in cardiac fibroblasts.     

[Na+] i /[K+] i -independent death of ouabain-treated renal epithelial cells is not mediated by Na+,K+-ATPase internalization and de novo gene expression

The cytotoxic effect of long-term exposure of renal epithelial cells to ouabain and other cardiotonic steroids (CTS) is mediated by the interaction of these compounds with Na⁺,K⁺-ATPase but is independent of the inhibition of Na⁺,K⁺-ATPase-mediated ion fluxes. Sustained application of CTS also leads to Na⁺,K⁺-ATPase endocytosis and its translocation into the nuclei that might trigger the cell death machinery via the regulation of gene expression. This study examines the role of Na⁺,K⁺-ATPase internalization and de novo gene expression in the death of ouabain-treated C7-Madin–Darby canine kidney (MDCK) cells derived from distal tubules of the MDCK. In these cells, 6-h exposure to 3 μM ouabain led to the internalization of ∼50% of plasmalemmal Na⁺,K⁺-ATPase. Prolonged incubation in a K⁺-free medium abolished ouabain-induced Na⁺,K⁺-ATPase internalization but did not affect the cytotoxic action of ouabain seen after 18-h incubation. Previously, it was shown that CTS-induced Na⁺,K⁺-ATPase internalization is mediated by its interaction with Src within caveolae. Neither caveolae damage by cholesterol depletion with methyl-β-cyclodextrin nor Src inhibition with 4-amino-5(4-chlorophenyl)-7-(t-butyl)pyrazol[3,4-d]pyridine affected the death of ouabain-treated C7-MDCK cells. Actinomycin D at the 0.1-μg/ml concentration almost completely abolished ribonucleic acid synthesis but did not protect C7-MDCK cells from the cytotoxic action of ouabain. Our results show that neither Na⁺,K⁺-ATPase endocytosis nor de novo gene expression contributes to -independent cell death signaling evoked by prolonged exposure to CTS.     

Association of a single nucleotide polymorphism in the ubxn6 gene with long-term non-progression phenotype in HIV-positive individuals

ObjectivesThe long-term non-progressors (LTNPs) are a heterogeneous group of HIV-positive individuals characterized by their ability to maintain high CD4⁺ T-cell counts and partially control viral replication for years in the absence of antiretroviral therapy. The present study aims to identify host single nucleotide polymorphisms (SNPs) associated with non-progression in a cohort of 352 individuals.MethodsDNA microarrays and exome sequencing were used for genotyping about 240 000 functional polymorphisms throughout more than 20 000 human genes. The allele frequencies of 85 LTNPs were compared with a control population. SNPs associated with LTNPs were confirmed in a population of typical progressors. Functional analyses in the affected gene were carried out through knockdown experiments in HeLa–P4, macrophages and dendritic cells.ResultsSeveral SNPs located within the major histocompatibility complex region previously related to LTNPs were confirmed in this new cohort. The SNP rs1127888 (UBXN6) surpassed the statistical significance of these markers after Bonferroni correction (q = 2.11 × 10⁻⁶). An uncommon allelic frequency of rs1127888 among LTNPs was confirmed by comparison with typical progressors and other publicly available populations. UBXN6 knockdown experiments caused an increase in CAV1 expression and its accumulation in the plasma membrane. In vitro infection of different cell types with HIV-1 replication-competent recombinant viruses caused a reduction of the viral replication capacity compared with their corresponding wild-type cells expressing UBXN6.ConclusionsA higher prevalence of Ala31Thr in UBXN6 was found among LTNPs within its N-terminal region, which is crucial for UBXN6/VCP protein complex formation. UBXN6 knockdown affected CAV1 turnover and HIV-1 replication capacity.