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Biomedical subjects

Y Oiso

Publications and source records attributed to Y Oiso.

At least 109 records · Page 6Linked to original sources
PubMed1994

Prostaglandin F2 alpha activates phospholipase D independently from activation of protein kinase C in osteoblast-like cells.

We previously reported that prostaglandin F2 alpha (PGF2 alpha) receptor is coupled to pertussis toxin (PTX)-sensitive GTP-binding protein (G protein) in osteoblast-like MC3T3-E1 cells [Miwa et al. (1990): Biochem Biophys Res Commun 171:1229-1235]. In the present study, we examined the effect of PGF2 alpha on the activation of phosphatidylcholine-hydrolyzing phospholipase D in MC3T3-E1 cells. PGF2 alpha stimulated the formation of choline in a dose-dependent manner in the range between 10 nM and 10 microM. The formation of choline was stimulated by 12-O-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C (PKC)-activating phorbol ester. 4 alpha-Phorbol 12, 13-didecanoate, a PKC-nonactivating phorbol ester, had little effect on choline formation. The formation of choline stimulated by a combination of PGF2 alpha and TPA was additive. Staurosporine, an inhibitor for protein kinases, which inhibited the effect of TPA on choline formation, dose-dependently enhanced the formation of choline induced by PGF2 alpha. NaF, an activator of G protein, stimulated the formation of choline. The formation of choline stimulated by a combination of PGF2 alpha and NaF was not additive. NaF-induced formation of choline was dose-dependently enhanced by staurosporine. PTX dose-dependently inhibited the PGF2 alpha-induced formation of choline. These results strongly suggest that PGF 2 alpha activates phospholipase D independently from the activation of PKC in osteoblast-like cells and PTX-sensitive G protein is involved in the PGF2 alpha-induced phospholipase D activation.

Alkaloids↗
PubMed1994

Okadaic acid reverses the inhibitory effect of protein kinase C on alkaline phosphatase activity in osteoblast-like cells.

We previously reported that fetal calf serum-induced alkaline phosphatase activity is suppressed due to the activation of protein kinase C in osteoblast-like MC3T3-E1 cells (Miwa et al. (1991) Bone Miner. 14, 15-25; Kotoyori et al. (1994) Horm. Metab. Res. 26, 116-118). In the present study, we examined the effect of okadaic acid, a potent and specific inhibitor of protein phosphatase type 1 and 2A, on fetal calf serum-induced alkaline phosphatase activity in MC3T3-E1 cells. The pretreatment with okadaic acid enhanced the fetal calf serum-induced alkaline phosphatase activity in a dose-dependent manner in the range between 0.1 and 5 nM. 1-Norokadaone, a less potent analogue of okadaic acid, had little effect on the fetal calf serum-induced alkaline phosphatase activity. Okadaic acid partially reversed the suppression of fetal calf serum-induced alkaline phosphatase activity by 12-O-tetradecanoylphorbol-13-acetate, a protein kinase C activator. The effect of okadaic acid was dose-dependent in the range between 0.1 and 5 nM. The patterns of the dose-dependency of both okadaic acid effects on fetal calf serum-induced alkaline phosphatase activity and on the suppression by 12-O-tetradecanoylphorbol-13-acetate were similar. These results strongly suggest that protein phosphatase type 1 and/or 2A act as a regulator of alkaline phosphatase activity at a point downstream from protein kinase C in osteoblast-like cells.

Alkaline Phosphatase↗
PubMed1994

Effect of endothelin-1 on phospholipase D activity in osteoblast-like cells.

We examined the effect of endothelin-1 (ET-1) on phosphatidylcholine-hydrolyzing phospholipase D activity in osteoblast-like MC3T3-E1 cells. ET-1 stimulated the formation of choline (EC50 10 nM) as well as that of inositol phosphates (EC50 1.2 nM). The effects of ET-1 and 12-O-tetradecanoylphorbol-13-acetate, a protein kinase C-activating phorbol ester, were additive. Staurosporine enhanced the ET-1-induced formation of choline. NaF or pertussis toxin were ineffective. The results indicate that ET-1 activates phospholipase D independent of protein kinase C in osteoblast-like cells.

Alkaloids↗
PubMed1994

Pituitary adenylate cyclase-activating polypeptide induces cAMP production independently from vasoactive intestinal polypeptide in osteoblast-like cells.

Pituitary adenylate cyclase-activating polypeptide (PACAP) isolated from ovine hypothalamic tissue is a novel neuropeptide which stimulates adenylate cyclase in rat anterior pituitary cell cultures. In osteoblasts, the detail of intracellular signalling systems of PACAP has not yet been clarified. In this study, we investigated the effects of PACAP on cAMP accumulation, phosphoinositide hydrolysis and Ca2+ influx in osteoblast-like MC3T3-E1 cells, compared with those of vasoactive intestinal polypeptide (VIP), which shows a considerable homology with PACAP in the N-terminal sequence. PACAP stimulated cAMP accumulation in a dose-dependent manner in the range between 0.1 nM and 0.1 microM in these cells. VIP also stimulated cAMP accumulation dose-dependently between 1 nM and 0.1 microM. The effect of PACAP on cAMP accumulation (EC50 = 3 nM) was more potent than that of VIP (EC50 = 30 nM). The cAMP accumulation stimulated by a combination of PACAP (3 nM) and VIP (30 nM) was additive. [Lys1, Pro2,5, Arg3,4, Tyr6]-VIP, and antagonist for the VIP receptor which markedly inhibited the VIP-induced cAMP accumulation, had little effect on the PACAP-induced cAMP accumulation. Either PACAP or VIP had little effect on the formation of inositol phosphates and Ca2+ influx in these cells. These results strongly suggest that PACAP stimulates cAMP production via an independent binding site from VIP in osteoblast-like MC3T3-E1 cells and that PACAP has no effect on the activation of protein kinase C nor the intracellular Ca2+ mobilization in these cells.

Animals↗
PubMed1994

Effect of vitamin D3 on prostaglandin E2 synthesis in osteoblast-like cells.

We previously showed that prostaglandin (PG) F2 alpha stimulates PGE2 synthesis in osteoblast-like MC3T3-E1 cells, and that the activation of protein kinase C (PKC) amplifies the effect of PGF2 alpha through the potentiation of phospholipase A2 activity (H. Tokuda, Y. Oiso and O. Kozawa, J Cell Biochem. 48: 262-268, 1992). In the present study, we investigated the effects of vitamin D3 on PGF2 alpha-induced PGE2 synthesis in MC3T3-E1 cells. The pretreatment with 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3], an active form of vitamin D3, significantly inhibited the PGF2 alpha-induced PGE2 synthesis in a dose-dependent manner in the range between 1 pM and 1 nM. This inhibitory effect of 1,25-(OH)2D3 was dependent on the time of pretreatment up to 8 h. On the contrary, the pretreatment with 24,25-dihydroxyvitamin D3, an inactive form of vitamin D3, had little effect on the PGF2 alpha-induced PGE2 synthesis in these cells. However, the pretreatment with 1,25-(OH)2D3 no longer affected the amplification of PGF2 alpha-induced PGE2 synthesis by 12-O-tetradecanoylphorbol-13-acetate, a PKC activator. These results strongly suggest that 1,25-(OH)2D3 inhibits PGF2 alpha-induced PGE2 synthesis in osteoblast-like cells, however, the activation of PKC reverses this inhibitory effect of 1,25-(OH)2D3.

24,25-Dihydroxyvitamin D 3↗
PubMed1994

Effect of retinoic acid on prostaglandin F2 alpha-induced prostaglandin E2 synthesis in osteoblast-like cells.

We previously reported that prostaglandin F2 alpha (PGF2 alpha) stimulates phosphoinositide hydrolysis via pertussis toxin-sensitive GTP-binding protein in osteoblast-like MC3T3-E1 cells (Miwa, Tokuda, Tsushita, Kotoyori, Takahashi, Ozaki, Kozawa and Oiso 1990) and that PGF2 alpha stimulates arachidonic acid release and prostaglandin E2 (PGE2) synthesis, and the activation of protein kinase C (PKC) amplifies the effect of PGF2 alpha in MC3T3-E1 cells (Tokuda, Oiso and Kozawa 1992). In the present study, we investigated the effect of retinoic acid (RA), a vitamin A (retinol) metabolite, on PGF2 alpha-induced PGE2 synthesis in MC3T3-E1 cells. The pretreatment with RA, which by itself had little effect on synthesis, significantly inhibited PGE2 synthesis induced by PGF2 alpha in a dose-dependent manner in the range between 1 nM and 0.1 microM. This effect of RA was dependent on the time of pretreatment up to 8 h. In addition, RA inhibited the amplification of PGF2 alpha-induced PGE2 synthesis by 12-O-tetradecanoylphorbol-13-acetate, known to be a PKC activator. However, RA had little effect on PGE2 synthesis induced by melittin, known as a phospholipase A2 activator. Moreover, pertussis toxin had little effect on arachidonic acid release induced by PGF2 alpha. These results strongly suggest that RA inhibits PGE2 synthesis induced by PGF2 alpha in osteoblast-like cells and the inhibitory effect is exerted at the point prior to the activation of phospholipase A2.

Cells, Cultured↗
PubMed1994

Molecular cloning of the rat thyroxine-binding globulin gene and analysis of its promoter activity.

We cloned the rat T4-binding globulin (rTBG) gene, characterized its organization, and studied its promoter activity and regulation. A genomic DNA library was constructed and screened using an rTBG complementary DNA (cDNA) as a probe. An 8.6-kilobase pair (kbp) clone was partially sequenced and compared with the sequence of the previously cloned cDNA. It helped complete the cDNA sequence and identify the first noncoding exon (exon 0). The transcription start site was identified using an RNase protection assay. The rTBG genomic clone contained 1.2 kbp 5'-flanking and 1.7 kbp 3'-flanking regions. The sizes of exons and introns of the rTBG gene are similar to those of the human TBG gene, belonging to the serine protease inhibitor family. The 5'-flanking region contains a TATA box, a CAAT box, and a consensus sequence for the hepatocyte nuclear factor 1-binding site. We tested the promoter activity of the 1.2-kbp 5'-flanking region using a luciferase reporter plasmid. When transfected into a hepatocyte-derived cell line (HepG2), the plasmid construct containing the fragment -1227 to +11 (transcription start site, +1) showed a 9-fold increase in luciferase activity compared with that of a promoterless luciferase vector. No promoter activity was detected in a nonhepatocyte-derived cell line (COS1). Serial 5'-deletion revealed that the construct containing the fragment -180 to +11 had 40% of the maximal promoter-induced luciferase activity. And that containing the fragment -53 to +11 showed no significant increase of luciferase activity. These results suggest that the region -180 to -53, containing hepatocyte nuclear factor 1-binding site, is essential to the liver-specific expression. We previously reported down-regulation of rTBG messenger RNA by T3 in vivo. The present study failed to show T3's effect on the promoter activity of the 1.2-kbp 5'-flanking region of the rTBG gene.

Animals↗
PubMed1994

A truncated thyroxine-binding globulin due to a frameshift mutation is retained within the rough endoplasmic reticulum: a possible mechanism of complete thyroxine-binding globulin deficiency in Japanese.

We have previously reported six unrelated Japanese families having the same mutation in the TBG gene and manifesting complete TBG deficiency (TBG-CDJ). The deficiency consists of a single nucleotide deletion resulting in the production of C-terminal truncation due to a frameshift and premature termination. However, the reason for the failure to detect TBG in the serum of subjects harboring this mutation remains unknown. In this communication we investigated the mechanism of the TBG deficiency associated with TBG-CDJ. The complementary DNAs of TBG-CDJ and normal TBG (TBG-N) were expressed in COS-1 cells. Pulse-chase experiments revealed a complete absence of secretion of TBG-CDJ, whereas TBG-N was already present in the medium at time 0 and was almost entirely secreted by 3 h. In cell lysates, TBG-CDJ had a smaller molecular mass [52 kilodalton (kDa)] than TBG-N (54 kDa) and gradually decreased during the chase. Thus, failure of TBG-CDJ secretion accounts for the complete TBG deficiency. The molecular mass of TBG-CDJ (42 kDa) was also smaller than that of TBG-N (44 kDa) when synthesized in the presence of tunicamycin. These findings are consistent with the premature termination of the TBG-CDJ molecule deduced from the nucleotide sequence analysis. Intracellular TBG-N was resistant to endoglycosidase H but not TBG-CDJ, suggesting the retention of TBG-CDJ within the rough endoplasmic reticulum. Indeed, subcellular fractionation revealed that most of TBG-CDJ was located in the rough endoplasmic reticulum compartment, and TBG-N was distributed in the Golgi fractions. Our results suggested that the lack of intracellular transport of the truncated TBG molecule is the cause for the absence of immunoreactive TBG in the serum of subjects harboring the TBG-CDJ variant.

Animals↗
PubMed1994

Novel mutations in the V2 vasopressin receptor gene in two pedigrees with congenital nephrogenic diabetes insipidus.

Novel mutations in the V2 vasopressin receptor gene were identified in two Japanese pedigrees with X-linked congenital nephrogenic diabetes insipidus. The V2 receptor belongs to the family of G-protein-coupled receptors that contain seven distinct transmembrane domains, and the V2 receptor gene is encoded by three exons. The coding regions amplified by polymerase chain reaction were directly sequenced. In a pedigree, one of four consecutive guanine sequences (nucleotides 528-531) in the second exon was deleted (528delG). This deletion mutation results in a frame shift beginning at codon 154 in the second intracellular domain and a premature termination at codon 161. In another pedigree, a missense mutation (A-->G) was identified at nucleotide position 310 in the second exon. This point mutation, H80R, changes a histidine at codon 80 in the second transmembrane domain to an arginine that is more positively charged than histidine under the neutral environment. Each mutation cosegregated with the phenotype of diabetes insipidus and supposed to be a cause for resistance to arginine vasopressin.

Adolescent↗
PubMed1994

Impaired intracellular transport contributes to partial thyroxine-binding globulin deficiency in a Japanese family.

We have previously reported a Japanese family manifesting partial TBG deficiency (TBG-PDJ). This variant was characterized by a decreased level of serum TBG concentration, heat lability, and normal isoelectric focussing pattern, but the affinity to iodothyronine is unknown. The TBG-PDJ gene possesses a single nucleotide substitution replacing the normal Pro363(CCT) with Leu(CTT); however, the precise mechanism that results in the reduction of the TBG concentration in the serum of the subjects harboring this mutation remains unknown. This was investigated in the current communication by expressing the complementary DNAs of TBG-PDJ and the common type TBG (TBG-C) in COS-1 cells. Pulse-chase experiments revealed impaired secretion of TBG-PDJ. TBG-C secretion into the medium was evident during 60 min of the pulse period and was almost completed by 12 h. On the other hand, TBG-PDJ was secreted slowly and continued to accumulate between 12-24 h of the chase period. The molecular mass of TBG-PDJ in the cell lysate was identical to that of TBG-C when estimated by gel electrophoresis (54 kilodaltons). The content of TBG-PDJ in the cell lysate decreased less rapidly than that of TBG-C, indicating that impaired TBG-PDJ secretion accounts for the partial TBG deficiency. Oligosaccharide units of intracellular TBG-C were resistant to endoglycosidase-H, but half of those of TBG-PDJ were sensitive to the enzyme digestion, suggesting partial retention of TBG-PDJ within the rough endoplasmic reticulum. Northern blot analysis revealed abundant messenger ribonucleic acid for the glucose-regulated protein-78, the level of which was 3.54-fold greater in the cells transfected with TBG-PDJ than in nontransfected COS-1 cells, whereas that in TBG-C-transfected cells was same as that in the nontransfected cells. Increased expression of glucose-regulated protein-78 together with the sensitivity to endoglycosidase-H suggests impairment of intracellular processing of TBG-PDJ. Our results indicate that the impaired intracellular transport of the TBG-PDJ molecule is the main cause of the reduced concentration of immunoreactive TBG in the serum of subjects harboring this TBG variant.

Base Sequence↗
PubMed1994

Intracellular signaling mechanism of bradykinin in osteoblast-like cells: comparison with prostaglandin E2.

Bradykinin is recognized to be involved in the process of bone resorption in chronic inflammatory diseases. We previously reported that prostaglandin E2 (PGE2), known as a potent bone resorbing agent, induces phosphoinositide hydrolysis, cAMP production and Ca2+ influx in osteoblast-like MC3T3-E1 cells, and these dose-dependencies are different to one another. To clarify the signaling mechanism of bradykinin, we compared the intracellular signaling system of bradykinin with that of PGE2 in these cells. Bradykinin stimulated Ca2+ influx dose-dependently in the range between 0.1 nM and 0.1 microM even in the presence of nifedipine, a Ca2+ antagonist that inhibits the voltage-dependent L-type Ca2+ channel. The maximum effect of bradykinin (0.1 microM) on Ca2+ influx was almost as great as that of PGE2 (0.5 microM). Bradykinin had little effect on cAMP accumulation, while PGE2 significantly stimulated it. Bradykinin stimulated the formation of inositol phosphates much less strongly than PGE2. Bradykinin stimulated inositol 1, 4, 5-trisphosphate [Ins(1, 4, 5)P3] formation dose-dependently between 0.1 nM and 0.1 microM, and the dose-dependent curves of bradykinin-induced Ca2+ influx and Ins(1, 4, 5)P3 were similar. However, the maximum effect of PGE2 (10 microM) on Ins (1, 4, 5) P3 formation was about 2-fold higher than that of bradykinin (0.1 microM). These results suggest that bradykinin induces Ca2+ influx independent of the voltage-dependent L-type Ca2+ channel and phosphoinositide hydrolysis in a similar dose-dependent manner in osteoblast-like cells.

Bradykinin↗
PubMed1994

Pamidronate treatment in patients with tumor-associated hypercalcemia: pharmacological effects and pharmacokinetics.

The purpose of this study was to investigate the effects of pamidronate, a second generation bisphosphonate, on the change in calcium homeostasis in patients with tumor-associated hypercalcemia. Eight patients with tumor-associated hypercalcemia received intravenous infusion of pamidronate (45 mg) and their high mean serum calcium concentration significantly decreased from 3.56 mmol/L to 2.62 mmol/L7 days after treatment. Serum intact PTH before treatment had been suppressed to below normal in all patients but returned to normal range in six patients within 7 days after treatment. Urinary PTH related peptide (PTHrP) excretion before treatment had been elevated in seven patients and then significantly increased further after pamidronate therapy. The serum bone Gla protein concentration was not apparently changed by the treatment. Pamidronate in serum was rapidly eliminated after the treatment and urinary excretion reached a plateau on the second day (13.8% of the administered dose), suggesting that the major portion of the infused dose had been distributed to the bone and other tissues. These findings suggest that pamidronate has a potent hypocalcemic effect and that PTHrP production in malignant tumors could be affected by pamidronate therapy.

Aged↗
PubMed1994

Effect of glucocorticoid on prostaglandin F2 alpha-induced prostaglandin E2 synthesis in osteoblast-like cells: inhibition of phosphoinositide hydrolysis by phospholipase C as well as phospholipase A2.

It is well known that osteoporosis is a common complication of patients with glucocorticoid excess. We showed previously that prostaglandin (PG) F2 alpha stimulates the synthesis of PGE2, a potent bone resorbing agent, and that the activation of protein kinase C amplifies the PGF2 alpha-induced PGE2 synthesis through the potentiation of phospholipase A2 activity in osteoblast-like MC3T3-E1 cells. In the present study, we examined the effect of dexamethasone on PGE2 synthesis induced by PGF2 alpha in MC3T3-E1 cells. The pretreatment with dexamethasone significantly inhibited the PGE2 synthesis in a dose-dependent manner in the range between 0.1 and 10 nmol/l in these cells. This effect of dexamethasone was dependent on the time of pretreatment up to 8 h. Dexamethasone also inhibited PGE2 synthesis induced by melittin, known as a phospholipase A2 activator. Furthermore, dexamethasone significantly inhibited the enhancement of PGF2 alpha- or melittin-induced PGE2 synthesis by 12-O-tetradecanoylphorbol-13-acetate, known as a protein kinase C activator. In addition, dexamethasone significantly inhibited PGF2 alpha-induced formation of inositol phosphates in a dose-dependent manner between 0.1 and 10 nmol/l in MC3T3-E1 cells. These results strongly suggest that glucocorticoid inhibits PGF2 alpha-induced PGE2 synthesis through the inhibition of phosphoinositide hydrolysis by phospholipase C as well as phospholipase A2 in osteoblast-like cells.

Animals↗
PubMed1994

Humoral hypercalcemia of malignancy associated with parathyroid hormone-related protein producing transitional cell carcinoma of the ureter.

A 78-year old male with ureteral carcinoma manifesting hypercalcemia is reported. He was diagnosed as having ureteral carcinoma of the left side 2 years previously and was treated by nephrectomy with ureterovesicostomy. In October 1991, he was admitted for anorexia. A clinical examination revealed recurrence of the ureteral carcinoma with metastasis to the rectum and liver. His serum calcium level was elevated (13.9 mg/dl). In addition to rehydration and furosemide, treatment with eel-calcitonin and prednisolone failed to decrease his serum calcium level. Finally, he was administered mithramycin but he died 13 days later. He had no evidence of bone metastasis or hyperparathyroidism. Nephrogenic cAMP and urinary parathyroid hormone-related protein (PTHrP) were markedly elevated. Immunohistochemical study demonstrated expression of PTHrP in the tumor cells. Thus, the hypercalcemia was thought to be mediated by PTHrP secreted from the neoplastic tumor. Although there have been several reports of ureteral carcinoma associated with humoral hypercalcemia of malignancy, this is considered to be the first case associated with elevation of PTHrP.

Aged↗
PubMed1994

Hypothalamic dysfunction in Parkinson's disease patients.

Ten patients with idiopathic Parkinson's disease (PD) (3 men and 7 women, group A) who had received no treatment for the disease; 102 patients with PD (36 men and 66 women, group B) who had undergone treatment and 45 healthy volunteers (15 men and 30 women, control group) were subject to thyrotropin-releasing hormone (TRH) tests and levodopa tests. In group A basal plasma prolactin (PRL) levels were significantly higher than in the controls both before and during treatment. Peak plasma PRL levels during TRH tests were significantly higher before treatment, but returned to the control levels during treatment. Nadir plasma PRL levels during levodopa tests were significantly increased before and during treatment. In group B basal plasma thyroid-stimulating hormone (TSH) and PRL levels were significantly higher than in the control group. Peak plasma PRL levels during TRH tests and nadir plasma PRL levels during levodopa tests were also significantly increased. The results strongly suggest a disturbance of pituitary hormone secretion due to hypothalamic dysfunction in PD patients.

Administration, Oral↗
PubMed1994

C-peptide response to glucagon in type 2 diabetes mellitus: a comparison with oral glucose tolerance test.

C-peptide immunoreactivity (CPR) response during glucagon test (intravenous injection of 1 mg glucagon) was compared with CPR response during 75 g oral glucose tolerance test (oGTT) in 58 patients with newly-diagnosed, untreated type 2 (non-insulin-dependent) diabetes mellitus. Both tests were also repeated after blood glucose was well controlled with sulfonylurea or insulin in 17 patients. CPR secretory response was estimated by delta CPR, i.e. the difference between maximal and basal levels of CPR during each test. In the 58 untreated patients, the mean fasting plasma glucose (FPG) level was 12.8 +/- 0.6 mmol/L (M +/- SE), and there was no significant correlation between delta CPR during glucagon test and delta CPR during oGTT. The therapy for diabetes mellitus in 17 patients resulted in a fall in FPG (from 15.1 +/- 0.5 to 6.7 +/- 0.3 mmol/L) and a marked increase in delta CPR during oGTT (from 0.28 +/- 0.06 to 1.18 +/- 0.17 nmol/L, P < 0.01), but did not influence delta CPR during glucagon test (from 0.39 +/- 0.06 to 0.42 +/- 0.06 nmol/L, N.S.). In these patients, delta CPR during glucagon test before therapy correlated significantly with delta CPR during oGTT after therapy. Of the 13 patients who showed impaired CPR response during oGTT (delta CPR < 0.5 nmol/L) but substantial response during glucagon test (delta CPR > or = 0.5 nmol/L), 12 were successfully controlled without insulin therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Effects of vitamin D3 on signaling by prostaglandin E2 in osteoblast-like cells.

We investigated the effects of vitamin D3 on the signaling pathways by prostaglandin E2 (PGE2) in osteoblast-like MC3T3-E1 cells. The pretreatment with 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3), an active form of vitamin D3, significantly inhibited cAMP accumulation induced by 10 microM PGE2 in a dose-dependent manner in the range between 1 pM and 1 nM. This effect of 1,25-(OH)2D3 was dependent on the time of pretreatment up to 8h. 1,25-(OH)2D3 also inhibited the cAMP accumulation induced by NaF, a GTP-binding protein activator, or forskolin which directly activates adenylate cyclase. On the other hand, 1,25-(OH)2D3 significantly inhibited PGE2-induced IP3 formation in a dose-dependent manner between 10 pM and 1 nM. However, 1,25-(OH)2D3 had little effect on NaF-induced IP3 formation. The pretreatment with 24,25-dihydroxyvitamin D3, an inactive form of vitamin D3, affected neither cAMP accumulation nor IP3 formation induced by PGE2. These results strongly suggest that 1,25-(OH)2D3 modulates the signaling by PGE2 in osteoblast-like cells as follows: the inhibitory effect on the cAMP production is exerted at a point downstream from adenylate cyclase and the inhibitory effect on the phosphoinositide hydrolysis is exerted at the point between the PGE2 receptor and GTP-binding protein, probably Gi2.

Animals↗