Cytoglobin is a respiratory protein in connective tissue and neurons, which is up-regulated by hypoxia.
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.
Schmidt
Marc
M
Institute of Zoology, Johannes Gutenberg-University, D-55099 Mainz, Germany.
Gerlach
Frank
F
Avivi
Aaron
A
Laufs
Tilmann
T
Wystub
Sylvia
S
Simpson
Jeremy C
JC
Nevo
Eviatar
E
Saaler-Reinhardt
Sigrid
S
Reuss
Stefan
S
Hankeln
Thomas
T
Burmester
Thorsten
T
D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000276:immunology; D000918:Antibody Specificity; D001842:Bone and Bones / Q000737:chemistry; D002467:Cell Nucleus / Q000737:chemistry; D002522:Chlorocebus aethiops; D003238:Connective Tissue / Q000737:chemistry*; D000078842:Cytoglobin; D003593:Cytoplasm / Q000737:chemistry; D005347:Fibroblasts / Q000737:chemistry; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation; D005914:Globins / Q000032:analysis / Q000737:chemistry / Q000235:genetics*; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D007150:Immunohistochemistry; D008099:Liver / Q000737:chemistry / Q000648:ultrastructure; D008164:Luminescent Proteins / Q000235:genetics; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009206:Myocardium / Q000737:chemistry; D009474:Neurons / Q000737:chemistry*; D009687:Nuclear Proteins / Q000032:analysis / Q000737:chemistry / Q000235:genetics*; D010100:Oxygen / Q000008:administration & dosage; D010446:Peptide Fragments / Q000737:chemistry / Q000276:immunology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D011993:Recombinant Fusion Proteins; D012137:Respiratory System / Q000737:chemistry*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014132:Trachea / Q000737:chemistry; D014162:Transfection; D014709:Vero Cells
D000906:Antibodies; C000627265:CYGB protein, human; C000627267:Cygb protein, mouse; C000627268:Cygb protein, rat; D000078842:Cytoglobin; D008164:Luminescent Proteins; D009687:Nuclear Proteins; D010446:Peptide Fragments; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D005914:Globins; D010100:Oxygen