title: Hypoxia-inducible factor-1 (HIF-1) but not HIF-2 is essential for hypoxic induction of collagen prolyl 4-hydroxylases in primary newborn mouse epiphyseal growth plate chondrocytes.
abstract: Hypoxia-inducible factors (HIFs) are the master regulators of hypoxia-responsive genes. They play a critical role in the survival, development, and differentiation of chondrocytes in the avascular hypoxic fetal growth plate, which is rich in extracellular matrix (ECM) and in its main component, collagens. Several genes involved in the synthesis, maintenance, and degradation of ECM are regulated by HIFs. Collagen prolyl 4-hydroxylases (C-P4Hs) are key enzymes in collagen synthesis because the resulting 4-hydroxyprolines are necessary for the stability of all collagen molecules. The vertebrate C-P4Hs are α(2)β(2) tetramers with three isoforms of the catalytic α subunit, yielding C-P4Hs of types I-III. C-P4H-I is the main form in most cells, but C-P4H-II is the major form in chondrocytes. We postulated here that post-translational modification of collagens, particularly 4-hydroxylation of proline residues, could be one of the modalities by which HIF regulates the adaptive responses of chondrocytes in fetal growth plates. To address this hypothesis, we used primary epiphyseal growth plate chondrocytes isolated from newborn mice with conditionally inactivated genes for HIF-1α, HIF-2α, or the von Hippel-Lindau protein. The data obtained showed that C-P4H α(I) and α(II) mRNA levels were increased in hypoxic chondrocytes in a manner dependent on HIF-1 but not on HIF-2. Furthermore, the increases in the C-P4H mRNA levels were associated with both increased amounts of the C-P4H tetramers and augmented C-P4H activity in hypoxia. The hypoxia inducibility of the C-P4H isoenzymes is thus likely to ensure sufficient C-P4H activity for collagen synthesis occurring in chondrocytes in a hypoxic environment.
authors.affiliation: Oulu Center for Cell-Matrix Research, Biocenter Oulu and Department of Medical Biochemistry and Molecular Biology, University of Oulu, FIN-90014 Oulu, Finland.
authors.forename: Ellinoora
authors.initials: E
authors.lastname: Aro
authors.forename: Richa
authors.initials: R
authors.lastname: Khatri
authors.forename: Rita
authors.initials: R
authors.lastname: Gerard-O'Riley
authors.forename: Laura
authors.initials: L
authors.lastname: Mangiavini
authors.forename: Johanna
authors.initials: J
authors.lastname: Myllyharju
authors.forename: Ernestina
authors.initials: E
authors.lastname: Schipani
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D015687:Cell Hypoxia / Q000235:genetics; D002478:Cells, Cultured; D019902:Chondrocytes / Q000201:enzymology* / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D055785:Gene Knockdown Techniques; D006132:Growth Plate / Q000166:cytology*; D006801:Humans; D006909:Hydroxyproline / Q000096:biosynthesis; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D061251:Primary Cell Culture; D011393:Procollagen-Proline Dioxygenase / Q000235:genetics* / Q000378:metabolism; D055503:Protein Multimerization; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D051794:Von Hippel-Lindau Tumor Suppressor Protein / Q000235:genetics / Q000378:metabolism; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D006909:Hydroxyproline; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011393:Procollagen-Proline Dioxygenase; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D000099162:Endothelial PAS Domain-Containing Protein 1; C497443:Hif1a protein, mouse; C494469:VHL protein, mouse