Transforming growth factor-beta 1 regulation of bone sialoprotein gene transcription: identification of a TGF-beta activation element in the rat BSP gene promoter.
Transforming growth factor-beta (TGF-beta) increases steady-state mRNA levels of several extracellular matrix proteins in mineralized connective tissues. Bone sialoprotein (BSP) is a major constituent of the bone matrix, thought to initiate and regulate the formation of mineral crystals. To determine the molecular pathways of TGF-beta 1 regulation of bone proteins, we have analyzed the effects of the TGF-beta 1 on the expression of the BSP in the rat osteosarcoma cell line (ROS 17/2.8). TGF-beta 1 at 1 ng/ml, increased BSP mRNA levels in ROS 17/2.8 cells approximately 8-fold: the stimulation was first evident at 3 hr, reached maximal levels at 12 hr and slowly declined thereafter. Since the stability of the BSP mRNA was not significantly affected by TGF-beta 1, and nuclear "run-on" transcription analyses revealed only a approximately 2-fold increase in the transcription of the BSP gene, most of the increase in BSP mRNA appeared to involve a nuclear post-transcriptional mechanism. Moreover, the effects of TGF-beta 1 were indirect, since the increase in BSP mRNA was abrogated by cycloheximide (28 micrograms/ml). To identify the site of transcriptional regulation by TGF-beta 1, transient transfection analyses were performed using BSP gene promoter constructs linked to a luciferase reporter gene. Constructs that included nt -801 to -426 of the promoter sequence were found to enhance transcriptional activity approximately 1.8-fold in cells treated with TGF-beta 1. Within this sequence, approximately 500 nt upstream of the transcription start site, a putative TGF-beta activation element (TAE) was identified that contained the 5'-portion of the nuclear factor-1 (NF-1) canonical sequence (TTGGC) overlapping a consensus sequence for activator protein-2 (AP-2). The functionality of the TAE was shown by an increased binding of a nuclear protein from TGF-beta 1 stimulated cells in gel mobility shift assays and from the attenuation of TGF-beta 1-induced luciferase activity when cells were co-transfected with a double-stranded TAE oligonucleotide. Competition gel mobility shift analyses revealed that the nuclear protein that binds to the TAE has similar properties to, but is distinct from, NF-1 nuclear protein. These studies have therefore identified a TGF-beta activation element (TAE) in the rat BSP gene promoter that mediates the stimulatory effects of TGF-beta 1 on BSP gene transcription.
Ogata
Y
Y
Department of Periodontology, Nihon University School of Dentistry at Matsudo, Chiba, Japan.
Niisato
N
N
Furuyama
S
S
Cheifetz
S
S
Kim
R H
RH
Sugiya
H
H
Sodek
J
J
D000818:Animals; D058574:Integrin-Binding Sialoprotein; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017422:Sequence Analysis, DNA; D012795:Sialoglycoproteins / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
C546873:Ibsp protein, rat; D058574:Integrin-Binding Sialoprotein; D012333:RNA, Messenger; D012795:Sialoglycoproteins; D016212:Transforming Growth Factor beta