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G/C element contributes to the cell line–specific expression of the proximal osteocalcin promoter
Author(s) -
Goldberg Daniella,
Gardiner Edith,
Morrison Nigel A.,
Eisman John A.
Publication year - 1995
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.240580413
Subject(s) - repressor , promoter , osteocalcin , osteoblast , microbiology and biotechnology , transcription (linguistics) , transcription factor , gene , transfection , chemistry , reporter gene , biology , gene expression , biochemistry , alkaline phosphatase , in vitro , enzyme , linguistics , philosophy
Sequential activation of cell type–specific genes occurs during osteoblast development. The promoter of one such gene, osteocalcin, has been widely studied, but the DNA sequences that govern osteoblast‐specific expression have not been defined. The proximal osteocalcin promoter linked to pTKCAT directs strong promoter activity in osteoblast‐like ROS17/2.8 cells and comparatively weak promoter activity in nonosteoblastic NIH3T3 cells. To identify sequences important in conferring cell‐specific expression of the osteocalcin gene, a deletion series of the human proximal promoter was constructed and the activities assessed in ROS17/2.8 and NIH3T3 cells. These studies identified a 30 bp sequence within the proximal promoter (osteocalcin repressor element‐1 [ORE‐1]) which is responsible for repressing the transcriptional activity in NIH3T3 cells. In electrophoretic mobility shift assays from both NIH3T3 and ROS17/2.8 cells, a protein complex bound to the ORE‐1 that was related to a complex which binds the G/C‐rich repressor element in the collagen type I (α1) promoter. In addition, there was a second complex from NIH3T3 cells but not ROS17/2.8 cells that bound the ORE‐1 fragment. The presence of this additional factor in NIH3T3 cells parallels the observation that constructs carrying the ORE‐1 sequence have repressed promoter activity relative to the analogous constructs lacking the ORE‐1 when transfected into NIH3T3 and suggests that the NIH3T3‐specific factor is a repressor. These data indicate that the G/C element in the ORE‐1 contributes to the repression of osteocalcin gene transcription in a nonosteoblast cell line. The high homology between the ORE‐1 sequence and a related sequence and a related sequence in the collagen type I (α2) proximal promoter suggests that homologous regions in other osteoblast‐expressed genes may function similarly.