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Parathyroid hormone regulates the expression of rat osteoblast and osteosarcoma nuclear matrix proteins
J Bidwell1, H Feister, D Swartz
1Departments of Periodontics, Indiana University School of Dentistry, Indianapolis 46202, USA.
Abstract:
Parathyroid hormone (PTH) alters osteoblast morphology. How these changes in cell shape modify nuclear structure and ultimately gene expression is not known. Chronic exposure to rat PTH (1-34) [10 nM] attenuated the expression of 200, 190, and 160 kD proteins in the nuclear matrix-intermediate filament subfraction of the rat osteosarcoma cells, ROS 17/2.8 [Bidwell et al. (1994b): Endocrinology 134:1738-1744]. Here, we determined that these same PTH-responsive proteins were expressed in rat metaphyseal osteoblasts. We identified the 200 kD protein as a non-muscle myosin. Although the molecular weights, subcellular distribution, and half-lives of the 190 and 160 kD proteins were similar to topoisomerase II-alpha and -beta, nuclear matrix enzymes that mediate DNA topology, the 190 and 160 kD proteins did not interact with topoisomerase antibodies. Nevertheless, the expression of topoisomerase II-alpha, and NuMA, a component of the nuclear core filaments, was also regulated by PTH in the osteosarcoma cells. The 190 kD protein was selectively expressed in bone cells as it was not observed in OK opossum kidney cells, H4 hepatoma cells, or NIH3T3 cells. PTH attenuated mRNA expression of the PTH receptor in our cell preparations. These results demonstrate that PTH selectively alters the expression of osteoblast membrane, cytoskeletal, and nucleoskeletal proteins. Topoisomerase II-alpha, NuMA, and the 190 and 160 kD proteins may direct the nuclear PTH signalling pathways to the target genes and play a structural role in osteoblast gene expression.
Insights
Parathyroid hormone (PTH) changes osteoblast shape and regulates key nuclear proteins, including non-muscle myosin and topoisomerase II-alpha. These PTH-induced alterations in cytoskeletal and nucleoskeletal proteins likely influence gene expression in bone cells.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Parathyroid hormone (PTH) is known to affect osteoblast morphology.
- The precise mechanisms by which PTH-induced changes in cell shape influence nuclear structure and gene expression remain unclear.
Purpose of the Study:
- To investigate the effects of PTH on nuclear matrix-intermediate filament proteins in osteoblasts.
- To identify specific PTH-responsive proteins and elucidate their role in nuclear structure and gene regulation.
Main Methods:
- Utilized rat osteosarcoma cells (ROS 17/2.8) and primary rat metaphyseal osteoblasts.
- Employed Western blotting and antibody interaction assays to identify and characterize proteins.
- Investigated mRNA expression of PTH receptor.
Main Results:
- PTH (1-34) attenuated the expression of 200, 190, and 160 kD proteins in the nuclear matrix-intermediate filament subfraction.
- The 200 kD protein was identified as non-muscle myosin.
- Expression of topoisomerase II-alpha and NuMA was also regulated by PTH; the 190 kD protein showed selective expression in bone cells.
Conclusions:
- PTH selectively alters the expression of osteoblast membrane, cytoskeletal, and nucleoskeletal proteins.
- Topoisomerase II-alpha, NuMA, and identified 190/160 kD proteins may mediate nuclear PTH signaling pathways.
- These proteins likely play a structural role in regulating osteoblast gene expression.