Calcium sensing receptor forms complex with and is up-regulated by caveolin-1 in cultured human osteosarcoma (Saos-2) cells.
The calcium sensing receptor (CaSR) plays an important role for sensing local changes in the extracellular calcium concentration ([Ca(2+)](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 ([Ca(2+)](i)) was increased by an increment of [Ca(2+)](o). This [Ca(2+)](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 [Ca(2+)](o)-induced [Ca(2+)](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.
Jung
Sang Yong
SY
Department of Physiology and Biophysics, College of Medicine Inha University, Incheon, Korea.
Kwak
Jin-Oh
JO
Kim
Hyun-Woo
HW
Kim
Dong Su
DS
Ryu
Seung-Duk
SD
Ko
Chang-Bo
CB
Cha
Seok Ho
SH
D001859:Bone Neoplasms; D002118:Calcium / Q000378:metabolism*; D022461:Caveolins / Q000378:metabolism*; D002458:Cell Fractionation; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism*; D006801:Humans; D018613:Microscopy, Confocal; D020320:Oligoribonucleotides, Antisense / Q000494:pharmacology; D012516:Osteosarcoma; D044169:Receptors, Calcium-Sensing / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015854:Up-Regulation
D022461:Caveolins; D020320:Oligoribonucleotides, Antisense; D044169:Receptors, Calcium-Sensing; D002118:Calcium