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 ([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.

Secondary Fish-Odor Syndrome Can be Acquired by Nitric Oxide-mediated Impairment of Flavin-containing Monooxygenase in Hepatitis B Virus-Infected Patients

Primary fish-odor syndrome (FOS) is a genetic disorder caused by defective flavin-containing monooxygenase 3 gene (FMO3) with deficient N-oxidation of trimethylamine (TMA), causing trimethylaminuria (TMAU). By contrast, secondary FOS can be acquired by decreased FMO activities in patients with chronic liver diseases, but the underlying mechanisms are unknown. In the present study, we examined plasma NOx concentrations and viral DNA contents as well as in vivo FMO activities and their correlations in chronic viral hepatitis (CVH) patients. Plasma concentration of NOx was significantly increased by 2.1 fold (56.2+/-26.5 vs. 26.6+/-5.4micrometer, p< 0.01), and it was positively correlated with plasma hepatitis B virus (HBV) DNA contents (r2=0.2838, p=0.0107). Furthermore, the elevated plasma NOx values were inversely and significantly correlated with in vivo FMO activities detected by ranitidine-challenged test (8.3% vs. 20.0%, r2=0.2109, p=0.0315). TMA N-oxidation activities determined in CVH patients without challenge test were also significantly low (73.6% vs. 95.7%, p< 0.05). In conclusion, these results suggested that secondary FOS could be acquired by the endogenously elevated NO in patients with CVH.