Proteomic Analysis of Vascular Endothelial Growth Factor-induced Endothelial Cell Differentiation Reveals a Role for Chloride Intracellular Channel 4 (CLIC4) in Tubular Morphogenesis

Department of Genetics and Pathology, Uppsala University, Dag Hammarskjölds väg 20, S-751 85 Uppsala, Sweden.
Journal of Biological Chemistry (Impact Factor: 4.57). 01/2006; 280(51):42397-404. DOI: 10.1074/jbc.M506724200
Source: PubMed


Formation of new vessels from pre-existing capillaries demands extensive reprogramming of endothelial cells through transcriptional
and post-transcriptional events. We show that 120 protein spots in a two-dimensional isoelectric focusing/electrophoretic
analysis were affected during vascular endothelial growth factor-A-induced endothelial cell tubular morphogenesis in vitro, as a result of changes in charge or expression level of the corresponding proteins. For about 22% of the spots, the protein
products could be identified, of which several previously have been implicated in cytoskeletal reorganization and angiogenesis.
One such protein was heat shock protein 27, a chaperone involved in β-actin rearrangement that was identified as regulated
in degree of serine phosphorylation. We also identified regulation of chloride intracellular channel 4 (CLIC4), the expression
of which decreased during tubular morphogenesis. CLIC4 was expressed at high levels in resting vessels, whereas expression
was modulated during pathological angiogenesis such as in tumor vessels. The subcellular localization of CLIC4 in endothelial
cells was dependent on whether cells were engaged in proliferation or tube formation. Antisense- and small interfering RNA-mediated
suppression of CLIC4 expression led to arrest in tubular morphogenesis. Our data implicate CLIC4 in formation of a vessel

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    • "This duality of structure has made it difficult to assign a single function that encompasses all the experimental observations involving CLIC proteins. The most experimentally supported direct result of a CLIC protein action is in the formation of the gut lumen in C. elegans (the CLIC homologue exc-4 gene product) and tube formation in mouse blood vessels (CLIC4); while the loss of exc-4 in C. elegans causes expansion of the gut lumen into a large cyst, deficiency of CLIC4 in mice and vascular endothelial cells prevents normal vascular tubulogenesis [17,18,30,31] Mice devoid of CLIC4 also have skin and cornea wound healing defects. It has been suggested that the vascular abnormalities result from a defect in acidification of vacuoles possibly dependent on ion transport functions of CLIC4 while the wound healing defects likely result from the involvement of soluble CLIC4 in TGF-β signaling [18,26]. "
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    ABSTRACT: Background Chloride Intracellular Channel 4 (CLIC4) is one of seven members in the closely related CLIC protein family. CLIC4 is involved in multiple cellular processes including apoptosis, cellular differentiation, inflammation and endothelial tubulogenesis. Despite over a decade of research, no comprehensive in situ expression analysis of CLIC4 in a living organism has been reported. In order to fulfill this goal, we generated a knock-in mouse to express Green Fluorescent Protein (GFP) from the CLIC4 locus, thus substituting the GFP coding region for CLIC4. We used GFP protein expression to eliminate cross reaction with other CLIC family members. Results We analyzed CLIC4 expression during embryonic development and adult organs. During mid and late gestation, CLIC4 expression is modulated particularly in fetal brain, heart, thymus, liver and kidney as well as in developing brown adipose tissue and stratifying epidermis. In the adult mouse, CLIC4 is highly expressed globally in vascular endothelial cells as well as in liver, lung alveolar septae, pancreatic acini, spermatogonia, renal proximal tubules, cardiomyocytes and thymic epithelial cells. Neural expression included axonal tracks, olfactory bulb, Purkinje cell layer and dentate gyrus. Renal CLIC4 expression was most pronounced in proximal tubules, although altered renal function was not detected in the absence of CLIC4. Myeloid cells and B cells of the spleen are rich in CLIC4 expression as are CD4 and CD8 positive T cells. Conclusions In a comprehensive study detailing CLIC4 expression in situ in a mouse model that excludes cross reaction with other family members, we were able to document previously unreported expression for CLIC4 in developing fetus, particularly the brain. In addition, compartmentalized expression of CLIC4 in specific adult tissues and cells provides a focus to explore potential functions of this protein not addressed previously.
    Full-text · Article · May 2014 · BMC Developmental Biology
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    • "It is closely related to adipocyte and keratinocyte differentiation [29], [31]. In addition, recent studies also provide evidence that the down-regulation of CLIC4 impairs angiogenesis and tubular morphogenesis [32]. CLIC4 is also shown to play a role in immune response of macrophages to LPS and in the host defense against bacterial infection [33]. "
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    ABSTRACT: Dental pulp stem cells (DPSCs), precursor cells of odontoblasts, are ideal seed cells for tooth tissue engineering and regeneration. Our previous study has demonstrated that stem cells exist in dental pulp with deep caries and are called carious dental pulp stem cells (CDPSCs). The results indicated that CDPSCs had a higher proliferative and stronger osteogenic differentiation potential than DPSCs. However, the molecular mechanisms responsible for the biological differences between DPSCs and CDPSCs are poorly understood. The aim of this study was to define the molecular features of DPSCs and CDPSCs by comparing the proteomic profiles using two-dimensional fluorescence difference gel electrophoresis (2-D DIGE) in combination with matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Our results revealed that there were 18 protein spots differentially expressed between DPSCs and CDPSCs in a narrow pH range of 4 to 7. These differently expressed proteins are mostly involved in the regulation of cell proliferation, differentiation, cell cytoskeleton and motility. In addition, our results suggested that CDPSCs had a higher expression of antioxidative proteins that might protect CDPSCs from oxidative stress. This study explores some potential proteins responsible for the biological differences between DPSCs and CDPSCs and expands our understanding on the molecular mechanisms of mineralization of DPSCs in the formation of the dentin-pulp complex.
    Full-text · Article · May 2014 · PLoS ONE
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    • "These findings suggest CLIC4 to be a potential responder or indirect regulator of autophagy. CLIC4 is susceptible to regulation; for example, CLIC4 was upregulated in the light-damaged retina and in endothelial cells treated with vascular endothelial growth factor [36], [37]. Thus, despite the name, CLIC4 may have a variety of discrete cellular functions in various physiological contexts. "
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    ABSTRACT: CLIC4/mtCLIC, a chloride intracellular channel protein, localizes to mitochondria, endoplasmic reticulum (ER), nucleus and cytoplasm, and participates in the apoptotic response to stress. Apoptosis and autophagy, the main types of the programmed cell death, seem interconnected under certain stress conditions. However, the role of CLIC4 in autophagy regulation has yet to be determined. In this study, we demonstrate upregulation and nuclear translocation of the CLIC4 protein following starvation in U251 cells. CLIC4 siRNA transfection enhanced autophagy with increased LC3-II protein and puncta accumulation in U251 cells under starvation conditions. In that condition, the interaction of the 14-3-3 epsilon isoform with CLIC4 was abolished and resulted in Beclin 1 overactivation, which further activated autophagy. Moreover, inhibiting the expression of CLIC4 triggered both mitochondrial apoptosis involved in Bax/Bcl-2 and cytochrome c release under starvation and endoplasmic reticulum stress-induced apoptosis with CHOP and caspase-4 upregulation. These results demonstrate that CLIC4 nuclear translocation is an integral part of the cellular response to starvation. Inhibiting the expression of CLIC4 enhances autophagy and contributes to mitochondrial and ER stress-induced apoptosis under starvation.
    Full-text · Article · Jun 2012 · PLoS ONE
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