Transforming growth factor beta-induced dissociation between vitamin D receptor level and 1,25-dihydroxyvitamin D3 action in osteoblast-like cells.
In the present study the interaction between a locally produced factor in bone, transforming growth factor beta (TGF beta) and a systemic regulator of bone metabolism, 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) was investigated. In rat (UMR 106, ROS 17/2.8) and human (MG-63) osteoblastic cell lines and in isolated fetal rat osteoblasts TGF beta caused a comparable increase in vitamin D receptor (VDR) level. A maximum was observed after 6 h at 1 ng/ml TGF beta. Scatchard analysis revealed that up-regulation of VDR is due to an increase in receptor number and not to a change in affinity. This was supported by Northern blot analysis which showed a dose- and time-dependent increase in VDR mRNA by TGF beta. To assess the significance of the TGF beta-induced increase in VDR level for 1,25-(OH)2D3 effects cells were preincubated with TGF for 4 h (causing a 2-3-fold increase of the VDR level) and subsequently incubated with 1,25-(OH)2D3 for 4 h and 24 h. TGF beta preincubation potently inhibited subsequent 1,25-(OH)2D3 stimulation of osteocalcin production in both ROS 17/2.8 and MG-63 cells on protein as well as mRNA level. A similar inhibition by TGF beta was observed on the 1,25-(OH)2D3-induced increase in osteopontin mRNA. The current study demonstrates dissociation between regulation of VDR level and modulation of two 1,25-(OH)2D3 biological responses by TGF beta in osteoblast-like cell lines of different origin. This dissociation shows that, besides interaction at VDR level also at other levels in the cell interaction(s) exist between TGF beta and 1,25-(OH)2D3. Besides, these data emphasize the potential importance of the interplay of locally produced factors and systemic calciotrophic hormones in the regulation of bone metabolism.
Staal
A
A
Department of Internal Medicine III, Erasmus University Medical School, Rotterdam, The Netherlands.
Birkenhäger
J C
JC
Pols
H A
HA
Buurman
C J
CJ
Vink-van Wijngaarden
T
T
Kleinekoort
W M
WM
van den Bemd
G J
GJ
van Leeuwen
J P
JP
D000818:Animals; D015152:Blotting, Northern; D001842:Bone and Bones / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D002117:Calcitriol / Q000494:pharmacology*; D002460:Cell Line; D004347:Drug Interactions; D006801:Humans; D010006:Osteoblasts / Q000737:chemistry* / Q000166:cytology* / Q000378:metabolism; D015675:Osteocalcin / Q000378:metabolism; D053495:Osteopontin; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D051381:Rats; D018167:Receptors, Calcitriol / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D012795:Sialoglycoproteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D015854:Up-Regulation
D012333:RNA, Messenger; D018167:Receptors, Calcitriol; C506895:SPP1 protein, human; D012795:Sialoglycoproteins; C506897:Spp1 protein, rat; D016212:Transforming Growth Factor beta; D015675:Osteocalcin; D053495:Osteopontin; D002117:Calcitriol