title: 1,25-Dihydroxy vitamin D3 and tri-iodothyronine stimulate the expression of a protein immunologically related to osteocalcin.
abstract: Osteocalcin (OC), a bone-specific protein, is a marker of late osteoblastic differentiation. Its expression is influenced by various growth factors and hormones. We investigated the effect of 1, 25-dihydroxy vitamin D3 (D3) and tri-iodothyronine (T3) on OC expression in osteoblast-like MC3T3-E1 cells. A heterologous OC green fluorescence protein (GFP) fusion vector was established and expressed to study possible effects on protein transport. Immunostaining of endogenous OC revealed a significant increase in the percentage of positive cells after D3 and T3 treatment. This was consistent for MC3T3-E1 cells as well as nonosteogenic NIH-3T3 and mammary carcinoma cells, but not for neuroblastoma cells. The perinuclear immunostaining corresponded to the NBD C6 ceramide Golgi staining. Conversely, we found a strong induction of OC in MC3T3-E1 cells at the mRNA and protein levels only with T3 and not with D3. OC mRNA and protein expression was not detected in NIH fibroblasts. OC GFP transfection experiments indicate rapid transport and secretion of OC, because OC GFP was not found to be accumulated at intracellular compartments after hormone treatment. We conclude that the strong perinuclear immunostaining does not represent OC but a protein immunologically related to OC, as indicated by preabsorption experiments. The expression of this OC epitope-sharing protein is regulated by both D3 and T3 in the osteoblastic MC3T3-E1 and in nonosteogenic cells.
authors.affiliation: Ludwig Boltzmann Institute of Osteology, Fourth Medical Department, Hanusch-Hospital, Vienna, Austria.
authors.forename: E
authors.initials: E
authors.lastname: Luegmayr
authors.forename: F
authors.initials: F
authors.lastname: Varga
authors.forename: H
authors.initials: H
authors.lastname: Glantschnig
authors.forename: N
authors.initials: N
authors.lastname: Fratzl-Zelman
authors.forename: M
authors.initials: M
authors.lastname: Rumpler
authors.forename: A
authors.initials: A
authors.lastname: Ellinger
authors.forename: K
authors.initials: K
authors.lastname: Klaushofer
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D002117:Calcitriol / Q000494:pharmacology*; D002478:Cells, Cultured; D019084:Fluorescent Antibody Technique, Indirect; D006056:Golgi Apparatus / Q000378:metabolism; D049452:Green Fluorescent Proteins; D007202:Indicators and Reagents / Q000378:metabolism; D008164:Luminescent Proteins / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D015675:Osteocalcin / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D011863:Radioimmunoassay; D014162:Transfection; D014284:Triiodothyronine / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D007202:Indicators and Reagents; D008164:Luminescent Proteins; D012333:RNA, Messenger; D014284:Triiodothyronine; D015675:Osteocalcin; D049452:Green Fluorescent Proteins; D002117:Calcitriol