Exp Mol Med.
2005 Apr;37(2):91-100.
Calcium sensing receptor forms complex with and is up-regulated by caveolin-1 in cultured human osteosarcoma (Saos-2) cells
- Affiliations
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- 1Department of Physiology and Biophysics, College of Medicine Inha University, Incheon, Korea.
- 2Department of Pharmacology and Toxicology, College of Medicine Inha University, Incheon, Korea. shcha@inha.ac.kr
- 3Department of Dentistry, College of Medicine Inha University, Incheon, Korea.
- 4Hormone Research Center, School of Biological Sciences and Technology, Chonnam National University, 300 Yongbong-dong, Buk-gu, Gwangju, Korea.
- 5Kidney Disease Research Group in Inha, Research Institute for Medical Sciences, Korea.
Abstract
- The calcium sensing receptor (CaSR) plays an important role for sensing local changes in the extracellular calcium concentration ([Ca2+]o) in bone remodeling. Although the function of CaSR is known, the regulatory mechanism of CaSR remains controversial. We report here the regulatory effect of caveolin on CaSR function as a process of CaSR regulation by using the human osteosarcoma cell line (Saos-2). The intracellular calcium concentration ([Ca2+]i) was increased by an increment of [Ca2+]o. This [Ca2+]i increment was inhibited by the pretreatment with NPS 2390, an antagonist of CaSR. RT-PCR and Western blot analysis of Saos-2 cells revealed the presence of CaSR, caveolin (Cav)-1 and -2 in both mRNA and protein expressions, but there was no expression of Cav-3 mRNA and protein in the cells. In the isolated caveolae-rich membrane fraction from Saos-2 cells, the CaSR, Cav-1 and Cav-2 proteins were localized in same fractions (fraction number 4 and 5). The immuno-precipitation experiment using the respective antibodies showed complex formation between the CaSR and Cav-1, but no complex formation of CaSR and Cav-2. Confocal microscopy also supported the co-localization of CaSR and Cav-1 at the plasma membrane. Functionally, the [Ca2+]o- induced [Ca2+]i increment was attenuated by the introduction of Cav-1 antisense oligodeoxynucleotide (ODN). From these results, in Saos-2 cells, the function of CaSR might be regulated by binding with Cav-1. Considering the decrement of CaSR activity by antisense ODN, Cav-1 up-regulates the function of CaSR under normal physiological conditions, and it may play an important role in the diverse pathophysiological processes of bone remodeling or in the CaSR- related disorders in the body.
Keyword
MeSH Terms
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Bone Neoplasms
Calcium/*metabolism
Caveolins/*metabolism
Cell Fractionation
Cell Line, Tumor
Cell Membrane/*metabolism
Humans
Microscopy, Confocal
Oligoribonucleotides, Antisense/pharmacology
Osteosarcoma
Receptors, Calcium-Sensing/antagonists & inhibitors/*metabolism
Research Support, Non-U.S. Gov't
Up-Regulation
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