Coordinate occupancy of AP-1 sites in the vitamin D-responsive and CCAAT box elements by Fos-Jun in the osteocalcin gene: model for phenotype suppression of transcription
Department of Cell Biology; Department of Medicine, Division of Endocrinology and Metabolism; Department of Medicine, Division of Diabetes
Animals; Base Sequence; Calcitriol; Cell Differentiation; Cell Division; Cell Line; Cells, Cultured; DNA; DNA-Binding Proteins; *Genes; *Genes, Regulator; Hela Cells; Humans; Molecular Sequence Data; Osteoblasts; Osteocalcin; Osteosarcoma; Phenotype; Protein-Tyrosine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-fos; Proto-Oncogene Proteins c-jun; *Proto-Oncogenes; Rats; *Regulatory Sequences, Nucleic Acid; *Suppression, Genetic; Transcription Factors; *Transcription, Genetic
Life Sciences | Medicine and Health Sciences
Osteocalcin, a bone-specific protein and marker of the mature osteoblast, is expressed only in nonproliferating osteoblasts in a mineralizing extracellular matrix, while type I collagen is expressed in proliferating cells. The nuclear proteins encoded by the c-fos and c-jun protooncogenes are expressed during the proliferation period of osteoblast phenotype development. We present evidence that AP-1 (HeLa cell-activating protein 1) sites residing within two promoter elements of the osteocalcin gene bind the Fos-Jun protein complex: the osteocalcin box (OC box; nucleotides -99 to -76), which contains a CCAAT motif as a central element and influences tissue-specific basal levels of osteocalcin gene transcription, and the vitamin D-responsive element (VDRE; nucleotides -462 to -440), which mediates enhancement of osteocalcin gene transcription. Gel electrophoretic mobility-shift analysis demonstrated high AP-1 binding activity in proliferating osteoblasts and dramatic changes in this activity after the down-regulation of proliferation and the initiation of extracellular-matrix mineralization in primary cultures of normal diploid osteoblasts. Methylation interference analysis established at single nucleotide resolution that purified recombinant Fos and Jun proteins bind in a sequence-specific manner to the AP-1 sites within the VDRE and OC box. Similarly, an AP-1 motif within a putative VDRE of the alkaline phosphatase gene, which is also expressed after the completion of proliferation, binds the Fos-Jun complex. These results support a model in which coordinate occupancy of the AP-1 sites in the VDRE and OC box in proliferating osteoblasts may suppress both basal level and vitamin D-enhanced osteocalcin gene transcription as well as transcription of other genes associated with osteoblast differentiation--a phenomenon we describe as phenotype suppression. This model is further supported by binding of the Fos-Jun complex at an AP-1 site in the type alpha I collagen promoter that is contiguous with, but not overlapping, the VDRE. Such a sequence organization in the collagen VDRE motif is compatible with vitamin D modulation of collagen but not with osteocalcin and alkaline phosphatase expression in proliferating osteoblasts.
Proc Natl Acad Sci U S A. 1990 Dec;87(24):9990-4.
Proceedings of the National Academy of Sciences of the United States of America
Owen TA, Bortell R, Yocum SA, Smock SL, Zhang M, Abate C, Shalhoub V, Aronin N, Wright KL, Van Wijnen AJ. (1990). Coordinate occupancy of AP-1 sites in the vitamin D-responsive and CCAAT box elements by Fos-Jun in the osteocalcin gene: model for phenotype suppression of transcription. Open Access Publications by UMMS Authors. Retrieved from https://escholarship.umassmed.edu/oapubs/1827