ABSTRACT
Cartilage oligomeric matrix protein (COMP) is a soluble pentameric protein expressed in cartilage and involved in collagen organization. Tissue microarrays derived from two cohorts of patients with breast cancer (n=122 and n=498) were immunostained, revealing varying expression of COMP, both in the tumor cells and surrounding stroma. High levels of COMP in tumor cells correlated, independently of other variables, with poor survival and decreased recurrence-free survival. Breast cancer cells, MDA-MB-231, stably expressing COMP were injected into the mammary fat pad of SCID (CB-17/Icr-Prkdcscid/Rj) mice. Tumors expressing COMP were significantly larger and were more prone to metastasize as compared with control, mock-transfected, tumors. In vitro experiments confirmed that COMP-expressing cells had a more invasive phenotype, which could in part be attributed to an upregulation of matrix metalloprotease-9. Furthermore, microarray analyses of gene expression in tumors formed in vivo showed that COMP expression induced higher expression of genes protecting against endoplasmic reticulum stress. This observation was confirmed in vitro as COMP-expressing cells showed better survival as well as a higher rate of protein synthesis when treated with brefeldin A, compared with control cells. Further, COMP-expressing cells appeared to undergo a metabolic switch, that is, a Warburg effect. Thus, in vitro measurement of cell respiration indicated decreased mitochondrial metabolism. In conclusion, COMP is a novel biomarker in breast cancer, which contributes to the severity of the disease by metabolic switching and increasing invasiveness and tumor cell viability, leading to reduced survival in animal models and human patients.
Subject(s)
Breast Neoplasms/etiology , Breast Neoplasms/metabolism , Cartilage Oligomeric Matrix Protein/metabolism , Cell Transformation, Neoplastic/metabolism , Animals , Apoptosis/genetics , Biomarkers, Tumor , Breast Neoplasms/mortality , Breast Neoplasms/pathology , Cartilage Oligomeric Matrix Protein/genetics , Cell Adhesion/genetics , Cell Line , Cell Membrane/metabolism , Cell Movement/genetics , Disease Models, Animal , Endoplasmic Reticulum/metabolism , Endoplasmic Reticulum Stress , Female , Gene Expression , Gene Expression Profiling , Heterografts , Humans , Immunohistochemistry , Matrix Metalloproteinase 9/genetics , Matrix Metalloproteinase 9/metabolism , Mice, SCID , Neoplasm Metastasis , Oxidative Phosphorylation , Prognosis , Proportional Hazards Models , RecurrenceABSTRACT
Complement convertases are enzymatic complexes that play a central role in sustaining and amplification of the complement cascade. Impairment of complement function leads directly or indirectly to pathological conditions, including higher infection rate, kidney diseases, autoimmune- or neurodegenerative diseases and ischaemia-reperfusion injury. An assay for direct measurement of activity of the convertases in patient sera is not available. Existing assays testing convertase function are based on purified complement components and, thus, convertase formation occurs under non-physiological conditions. We designed a new assay, in which C5 blocking compounds enabled separation of the complement cascade into two phases: the first ending at the stage of C5 convertases and the second ending with membrane attack complex formation. The use of rabbit erythrocytes or antibody-sensitized sheep erythrocytes as the platforms for convertase formation enabled easy readout based on measurement of haemolysis. Thus, properties of patient sera could be studied directly regarding convertase activity and membrane attack complex formation. Another advantage of this assay was the possibility to screen for host factors such as C3 nephritic factor and other anti-complement autoantibodies, or gain-of-function mutations, which prolong the half-life of complement convertases. Herein, we present proof of concept, detailed description and validation of this novel assay.
Subject(s)
Complement C3-C5 Convertases/analysis , Erythrocytes/enzymology , Immunoassay/methods , Animals , Autoantibodies/immunology , Complement C3 Nephritic Factor/immunology , Complement C3-C5 Convertases/immunology , Complement Pathway, Alternative/immunology , Complement System Proteins/immunology , Erythrocytes/immunology , Guinea Pigs , Half-Life , Humans , Rabbits , SheepABSTRACT
In previous work we have demonstrated increased expression of NOX2 in cardiomyocytes of infarcted human hearts. In the present manuscript we investigated the functional role of NOX2 in ischemically challenged H9c2 cells, a rat cardiomyoblast cell line, and adult rat cardiomyocytes. Expression of NOX2 in H9c2 cells was confirmed by RT-PCR. In Western-blot experiments, increased NOX2 expression was detected during ischemia, which was inhibited by transcription and translation inhibitors. Surprisingly, under ischemia, in addition to an increased cytosolic expression, NOX2 was localized mainly in the nucleus of apoptotic cardiomyocytes, where it colocalized with nitrotyrosine residues and activated caspase 3. Inhibition of reactive-oxygen-species generation with the flavoenzyme inhibitor diphenylene iodonium (DPI) and the NADPH-oxidase inhibitor apocynin led to a significantly decreased induction of apoptosis as assessed by quantification of caspase-3 activity and by TUNEL analysis. These results demonstrate that NOX2 is expressed in the nucleus of cardiomyocytes during apoptosis and that it likely participates in proapoptotic signaling. To the best of our knowledge, this is the first demonstration of nuclear NOX2 expression and its involvement in cardiomyocyte apoptosis.
