Postproliferative transcription of the rat osteocalcin gene is reflected by vitamin D-responsive developmental modifications in protein-DNA interactions at basal and enhancer promoter elements.
In the osteocalcin (OC) gene promoter, both independent positive and negative regulatory elements, as well as others with contiguous [TATA/glucocorticoid-responsive elements (GRE)] or overlapping [TATA/GRE, vitamin D-responsive enhancer elements (VDRE)/AP-1, and OC box/AP-1] domains, are sites for modifications in protein-DNA interactions. In the present studies, we have examined nuclear protein extracts from fetal rat calvarial cells that undergo a developmental sequence of bone cell differentiation. Our results demonstrate modifications in protein-DNA interactions that relate to the developmental stages of the osteoblast and support developmental regulation of OC gene transcription. Basal expression of the OC gene is associated with sequence-specific protein-DNA interactions at the OC box, VDRE, and TATA/GRE box. Distinct differences are observed in proliferating osteoblasts, where the OC gene is not transcribed compared to postproliferative, differentiated osteoblasts that transcribe the OC gene. Furthermore, the protein-DNA complexes that reflect hormonal control are also developmentally regulated, mediating both the transcriptionally active and repressed states of the OC gene. For example, in proliferating osteoblasts, a vitamin D receptor-antibody-sensitive complex is formed that is different from the DNA binding complex induced by vitamin D postproliferatively when the OC gene is transcribed. Mutational analysis of the steroid hormone binding domain and the overlapping AP-1 site at the VDRE supports mutually exclusive occupancy by Fos-Jun heterodimers and vitamin D receptor. Such protein-DNA interactions at the VDRE are consistent with repression of competency for vitamin D-mediated transcriptional enhancement in proliferating osteoblasts expressing high levels of Fos and Jun.
Department of Cell Biology, University of Massachusetts Medical Center, Worcester 01655.
T A
TA
Owen
R
R
Bortell
V
V
Shalhoub
A
A
Heinrichs
J L
JL
Stein
G S
GS
Stein
J B
JB
Lian
D000818:Animals; D001483:Base Sequence; D002455:Cell Division / Q000187:drug effects*; D002478:Cells, Cultured; D004247:DNA / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology; D004742:Enhancer Elements, Genetic; D006801:Humans; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D009838:Oligodeoxyribonucleotides; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015675:Osteocalcin / Q000235:genetics*; D010641:Phenotype; D011401:Promoter Regions, Genetic; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000378:metabolism; D051381:Rats; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid / Q000502:physiology; D016385:TATA Box; D014158:Transcription, Genetic / Q000187:drug effects; D014807:Vitamin D / Q000494:pharmacology*
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D009838:Oligodeoxyribonucleotides; D016755:Proto-Oncogene Proteins c-jun; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid; D015675:Osteocalcin; D014807:Vitamin D; D003907:Dexamethasone; D004247:DNA