Cytoglobin Is a Respiratory Protein in Connective Tissue and Neurons, Which Is Up-regulated by Hypoxia

Abstract

Cytoglobin is a recently discovered vertebrate globin distantly related to myoglobin, and its function is unknown. Here we present the first detailed analysis of the distribution and expression of cytoglobin. Northern and Western blotting experiments show the presence of cytoglobin mRNA and protein in a broad range of tissues. Quantitative PCR demonstrates an up-regulation of cytoglobin mRNA levels in rat heart and liver under hypoxic conditions (22 and 44 h of 9% oxygen). Immunofluorescence studies with three antibodies directed against different epitopes of the protein consistently show cytoglobin in connective tissue fibroblasts as well as in hepatic stellate cells. Cytoglobin is also present in chondroblasts and osteoblasts and shows a decreased level of expression upon differentiation to chondrocytes and osteocytes. Cytoglobin is located in the cytoplasm of these cell types. Evidence against an exclusively nuclear localization of cytoglobin, as recently proposed, is also provided by transfection assays with green fluorescent protein fusion constructs, which demonstrates the absence of an active nuclear import. The differential expression of cytoglobin argues against a general respiratory function of this molecule, but rather indicates a connective tissue-specific function. We hypothesize that cytoglobin may be involved in collagen synthesis. Cytoglobin expression was also observed in some neuronal subpopulations of the central and the peripheral nervous systems. Surprisingly, cytoglobin is localized in both the cytoplasm and nucleus of neurons, indicating a possible additional role of this protein in neuronal tissues.

Inhibition of fibroblast to myofibroblast transition by halofuginone contributes to the chemotherapy-mediated antitumoral effect

“…These results are consistent with our previous findings that halofuginone inhibited collagen type I synthesis in various preclinical studies in which excess of collagen was the hallmark of the disease (20,21), and halofuginone-dependent inhibition of collagen type I synthesis was correlated with reduction in tumor progression (26,27). In addition, only halofuginone inhibited the synthesis of Cygb/STAP, which is known to regulate collagen synthesis under the control of TGF-h (18,19), a finding that is consistent with the notion that halofuginone acts through the inhibition of Smad2/3 phosphorylation downstream of TGF-h (22 -24). The expression of Cygb/ STAP was up-regulated in fibrotic lesions of the pancreas and kidney in which activated fibroblast-like cells or myofibroblasts are known to proliferate (18).…”

“…Collagen type I has been hypothesized to be a signal for invasion, and its intratumoral expression level has been associated with increased tumor invasiveness (16,17). The association of collagen type I with stellate cell activation -associated protein, also known as cytoglobin (Cygb/STAP), which has been hypothesized to regulate collagen synthesis under the control of TGF-h, is characteristic of cells that exhibit an activated phenotype (18,19).…”

Cytoglobin, a Novel Member of the Globin Family, Protects Kidney Fibroblasts against Oxidative Stress under Ischemic Conditions

“…The localization of Cygb was consistent with previous reports that identified Cygb in splanchnic fibroblasts of various organs. 6,7 Given the status of fibroblasts as one of the most important and episodically active cell types in the kidney, providing delicate collagenous matrices and remodeling of the interstitium, this localization may suggest a crucial role for Cygb in the pathogenesis of kidney injury. 31,32 An antibody-dependent difference was observed in the Cygb staining pattern in the glomeruli; whereas one antibody demonstrated positive staining in the mesangial area, a second antibody demonstrated positive staining only after antigen retrieval in the mesangial area.…”

“…Cygb can be upregulated in other tissues and cells under hypoxic conditions. 6,33,34 Induction of Cygb via ischemia might be explained by a hypoxia-inducible factor-dependent mechanism. The promoter region of Cygb contains multiple conserved hypoxia-response elements.…”

“…4,5 Serial studies clarified that Cygb was localized in splanchnic fibroblasts of various organs. 3,6 In the normal rat, findings at immunohistochemical analysis suggested that Cygb-positive cells are positive for HSP47, a collagen-specific molecular chaperone of the kidney and intestine, and also for CD73, a marker of renal cortical fibroblast-like cells, in the normal rat kidney interstitium. 7 Whereas hemoglobin and myoglobin share the pentacoordinated heme, Cygb and neuroglobin are endowed with hexa-coordinated heme-iron atoms in their ferrous and ferric forms.…”