Functional MR imaging with venography for neurosurgical identification of the central sulcus

We evaluated the applicability of functional MR imaging overlaid onto brain images superimposed venography for neurosurgical identification of the central sulcus. In 20 volunteers and 12 patients with brain tumors located around the sensorimotor cortex, gradient echo and large flip angle functional MR image was performed to allow visualization of flow effect and susceptibility related changes in relative large vein by motor hand task. Functional MR image acquired was overlaid on 3D anatomical image with 3D venography. Based on the 3D mapping, intra-operative cortical somatosensory evoked potentials (SEPs) were recorded. The significant activation area obtained from functional MR imaging was projected on an ascending cortical vein in 16 volunteers (80%) and 10 patients (83%). Comparing the anatomical activation map with visual inspection of the exposed cortical surface made it easy to identify the activation area during surgery. The cortical veins in 9 of 10 were validated as a central vein by intra-operative cortical recording of SEPs. Combination of functional MR imaging overlaid onto 3D anatomical image with venography and intra-operative SEPs permitted rapid and accurate localization of the central sulcus during surgery.

The significance of the expression of tumor suppressor gene DCC in human gliomas

Deleted in colorectal carcinoma (DCC) gene has been as a candidate of tumor suppressor genes, has been identified recently and is thought to relate to the metastatic potential in some cancers. We examined the gene in 60 human gliomas (26 glioblastomas multiforme (GBMs), 16 anaplastic astrocytomas (AAs), 6 low grade astrocytomas (LGAs) of WHO Grade II, and 11 recurrent gliomas) and A172 human GBM cell line by reverse transcription polymerase chain reaction (RT-PCR). Twenty (77%) GBMs, 11 (69%) AAs, and 1 (17%) LGA revealed the reduced or absent DCC expression. Reduced DCC expression was also shown in 10 (91%) recurrent gliomas. Furthermore, in 5 cases with both primary and recurrent GBM, the DCC expressions of all recurrent tumors were lower than those of primary tumors. No significant correlation between DCC expression and Mib-1 labeling index was confirmed. The survival rate of patients without reduced DCC expression was significantly superior to that of patients with reduced DCC expression in overall malignant astrocytic tumors. In GBM and AA separately, DCC expression also tended to correlate with patient's prognosis. These results suggest that reduced DCC expression is an important marker in tumor malignancy and recurrence in astrocytic tumors and that may be a useful prognostic factor in patients with malignant astrocytic tumors.

Increased levels of CSF soluble CD27 in patients with primary central nervous system lymphoma

The aim of this study is to determine the diagnostic value of cerebrospinal fluid (CSF) soluble CD27 (sCD27) as a tumor marker for primary central nervous system lymphoma (PCNSL). We examined sCD27 levels in CSF obtained from various types of brain tumor patients. Forty-two patients were studied (including 12 PCNSL patients) who had not received any therapy for their tumors. In all PCNSL cases, CSF sCD27 levels were more than 15 U/ml (median 84.5 U/ml, range 17-484 U/ml) and in other brain tumor cases, CSF sCD27 levels were all less than 15 U/ml. Our data suggest that CSF sCD27 levels are useful to distinguish PCNSL from other brain tumors.

Choroid plexus carcinoma in infants: report of two cases and review of the literature

Choroid plexus carcinoma (CPC) is a rare malignant brain tumour which occurs predominantly in childhood. We present the cases of two infants with CPC. One, a 6-month-old boy with the tumour in the right lateral ventricle, who died of a postoperative intracranial haemorrhage and severe gastrointestinal bleeding, and the other, a 9-month-old boy with the tumour in the fourth ventricle, who has been well without recurrence for 12 months after total removal in combination with chemotherapy using cisplatin and VP-16 and local radiotherapy. In the 54 CPC cases in children under 2 years of age including our 2 cases in which the clinical results were described in the literature since 1983, tumour location (lateral ventricle, p = 0.0225), surgery (gross total resection, p = 0.0447), and chemotherapy (yes, p = 0.0010) were revealed to be significant positive prognostic factors by the univariate analysis using the log rank test, and surgery (gross total removal, p = 0.0259) and chemotherapy (yes, p = 0.0016) were independent, significant positive prognostic factors in the multivariate analysis using the Cox proportional hazard regression model. Although there is a risk in doing a statistical analysis of other people's reports, these results suggest that, at present, the gross total removal of the tumour with intensive chemotherapy is the best choice of initial treatment for young children with CPC, and that radiotherapy should be considered for patients after 24 months of age and/or should be performed locally.

Prognostic factors in supratentorial WHO grade II astrocytoma in adults

The records of 33 adult patients with supratentorial World Health Organization grade II astrocytoma (A-II) treated between January 1980 and April 1997 at our hospitals were retrospectively reviewed. All tumours were surgically resected or biopsied and their MIB-1 labelling indices (LIs) were less than 1.5%. The median time to tumour progression after the initial surgery was 60 months, and the 5- and 10-year tumour progression-free rates were 53 and 39%, respectively. The median survival time was 107 months, and the 5- and 10-year survival rates were 66 and 43%, respectively. The major cause of death was tumour recurrence with malignant transformation, comprising 93% of all deaths due to unrestrained tumour growth. In a univariate analysis for survival rate by log-rank test, age (< 60 years), Karnofsky Performance Scale score (90-100%), tumour location (except for the basal ganglia), and extent of surgery (more than biopsy) were revealed to be significant positive prognostic factors. A Cox proportional hazard multivariate regression analysis confirmed that the age was the only independent, significant positive prognostic factor in this series. The survival time after the initial surgery in patients without radiotherapy tended to be prolonged compared with those of the patients with radiotherapy. Of the 26 patients who received radiotherapy, however, the survival time after the initial surgery in the nine patients with intraoperative radiotherapy was significantly prolonged compared with the 17 patients who received sole external beam radiotherapy. Gender, symptoms, histology, p53 LI, enhancement on CT/MRI, cyst, calcification and chemotherapy were not shown to be significant prognostic factors. The optimal management strategy for A-II is expected to be established by clarification of the natural history with cytological and molecular biological analyses of the biological features of this disease.

Primary pleomorphic adenoma in posterior cranial fossa

A 35-year-old woman had an intradural tumor in the posterior fossa adjacent to the posterior wall of the left pyramidal bone, which was totally removed and histologically diagnosed as a pleomorphic adenoma. Follow-up examination for 2 years showed no recurrence of the tumor. There was no primary lesion in any other gland of the body, and therefore there is no alternative but to conclude a "migration" of some gland cells. The pathogenesis of this tumor remains unclassified.

Multiple isoforms of neuregulin are expressed in developing rat dorsal root ganglia

Accumulating evidence suggests that neuregulin (NRG) plays special roles in the development of the mammalian nervous system. We have already identified NRG as a survival factor for Schwann cells during development. In this report, we have studied all possible NRG isoforms and expression of NRG in the developing rat dorsal root ganglia (DRG) and compared them with those of brain and spinal cord. Neural NRG isoforms comprise common immunoglobulin and epidermal growth factor domains. Various different transcripts were characterized, which arose by alternative splicing in several regions: N-terminal (exon 1 or 2), spacer (exon 5), juxtamembrane (exon 9 or 10), and cytoplasmic (exon 12, 13, or 14) domains. At least 13 novel isoforms among 16 splice variants were identified. The transmembrane isoforms of NRG are dominant forms in developing rat DRG. The mRNA expression of NRG isoforms in DRG is similar to that in spinal cord, while in brain the expression is much less. The mRNA in DRG was found at similar levels from birth to postnatal day 7 of the premyelinating stage, and it decreased afterward. Our results suggest that several NRGs, including isoforms not reported before, play a role as survival factors for Schwann cells in the premyelinating stage.

Clinical trial of external beam-radiotherapy combined with daily administration of low-dose cisplatin for supratentorial glioblastoma multiforme--a pilot study

This trial tested the assumed efficacy and safety of external beam-radiotherapy combined with daily administration of low dose cisplatin (CDDP) (ERCLC therapy) for patients with glioblastoma multiforme (GBM). Thirty adult patients with supratentorial GBM received daily postoperative treatment with low dose intravenous CDDP (4-6 mg/m2) administered 30 minutes before external irradiation. In 10 patients, intraoperative radiotherapy (IORT) following surgery was given prior to ERCLC therapy. Tumor response on MRI, interval to tumor progression, survival, and toxicities were analyzed. None of the patients showed a tumor response to ERCIC therapy. Overall, the median time to tumor progression was 6 months with a 1-year tumor progression-free rate of 26.7% and a 2-year rate of 0%. The median survival time was 15 months with a 1-year survival rate of 69.9% and a 2-year rate of 31.5%. The survival rate of patients with IORT was better than that of those without IORT, however, there was no significant difference. Anorexia associated with nausea occurred in 70% and general fatigue in 10.0%. Leukopenia and thrombocytopenia occurred in 26.7% and 33.3%, respectively. However, none of the patients had to be withdrawn from therapy due to these toxicities. Other toxicities were not observed. This clinical study showed that daily administration of low dose CDDP did not enhance tumor response to irradiation for GBM on MRI. Regarding toxicity, however, ERCLC therapy was well tolerated. Although this trial did not provide sufficient data to determine whether ERCLC therapy was effective for GBM due to the small number of patients, additional clinical trials of this therapy may be warranted because that the survival rate in this study was equal to the better results recently reported for newly diagnosed GBM.

The relationship between moyamoya disease and bacterial infection

To examine the relationship between Moyamoya disease and bacterial infections, authors studied the serum of 85 cases of Moyamoya disease and the influence of Propionibacterium acnes (P. acnes) infection on intracranial arteries in rats. The serum levels of P. acnes antibody, IgM, transferrin (Tf), alpha 2-macroglobulin (alpha 2M) were significantly higher in Moyamoya disease than in normal volunteers. Moyamoya-like changes of the intracranial internal carotid arteries were histopathologically demonstrated in P. acnes infectious rats. These findings suggest that P. acnes and immunological factors might play a role in the pathogenesis of Moyamoya disease.

Arachidonic acid release induced by extracellular ATP in osteoblasts: role of phospholipase D

In a previous study, we have shown that extracellular ATP stimulates Ca2+ influx resulting in the release of arachidonic acid (AA) and prostaglandin E2 (PGE2) synthesis in osteoblast-like MC3T3-E1 cells. In addition, we have recently reported that extracellular ATP stimulates phosphatidylcholine hydrolysis by phospholipase D (PLD) independently from the activation of protein kinase C in these cells. It is well recognized that phosphatidylcholine is hydrolysed by PLD, generating phosphatidic acid, which can be further degraded by phosphatidic acid phosphohydrolase to diacylglycerol (DG). In the present study, we investigated the role of PLD activation in the extracellular ATP-induced AA release and PGE2 synthesis in osteoblast-like MC3T3-E1 cells. Extracellular ATP stimulated AA release dose-dependently in the range between 0.1 and 1 mM. Propranolol, which is known to inhibit phosphatidic acid phosphohydrolase, significantly inhibited the AA release induced by extracellular ATP in a dose-dependent manner in the range between 100 and 300 microM. 1,6-Bis-(cyclohexyloximinocarbonylamino)-hexane (RHC-80267), a selective inhibitor of DG lipase, significantly suppressed the AA release induced by extracellular ATP. Both the pretreatment of propranolol and RHC-80267 also inhibited the extracellular ATP-induced PGE2 synthesis. These results strongly suggest that the AA release induced by extracellular ATP is mediated at least in part by phosphatidylcholine hydrolysis by PLD in osteoblast-like cells.

The significant role of telomerase activity in human brain tumors

BACKGROUND

In this study, telomerase activity in human brain tumors was analyzed.

METHODS

Telomerase activity was examined in 41 brain tumor cases (20 of glioblastoma multiformes [GBMs] [14 primary tumors and 6 recurrent tumors], 3 anaplastic astrocytomas [AAs], 4 low grade astrocytomas [LGAs] [World Health Organization Grade 2], 2 oligodendrogliomas [OGs], 9 meningiomas [MNs], and 3 metastatic brain tumors [MBTs]) by means of telomeric repeat amplification protocol assay. The activity of telomerase was compared with histologic diagnosis, the MIB-1 proliferative cell index (PCI), and the patient's prognosis.

RESULTS

Twelve of 20 GBMs, 2 of 2 OGs, and 3 of 3 MBTs demonstrated telomerase activity. AAs, LGAs, and MNs exhibited no activity. No clear correlations were confirmed in GBMs between telomerase activity and the MIB-1 PCI data. However, the telomerase activity tended to correlate with the patient's prognosis.

CONCLUSIONS

These results suggest that telomerase activity may be an important marker of brain tumor malignancy. Furthermore, the change from negative activity to positive activity in the recurrent tumors appeared to be a useful prognosticator for malignant astrocytic tumor.

ETA receptor mediates the signaling of endothelin-1 in osteoblast-like cells

We previously reported that endothelin-1 (ET-1) stimulates phosphatidylcholine-hydrolyzing phospholipase D independently of phosphoinositide hydrolysis in osteoblast-like MC3T3-E1 cells. In the present study, we investigated the characteristics of the receptors mediating ET-1-induced intracellular signaling pathway in MC3T3-E1 cells. Cyclo-D-Trp-D-Asp-Pro-D-Val-Leu (BQ123), a selective ETA receptor antagonist, significantly inhibited the ET-1-induced formation of inositol phosphates in a dose-dependent manner in the range between 22 nmol/L (IC50) and 2.2 mumol/L (IC50 x 100). On the contrary, N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma MeLeu-D-Trp(COOMe)-D-Nle-ONa (BQ788), a selective ETB receptor antagonist, had no effect on the ET-1-induced formation of inositol phosphates in the range between 1.2 nmol/L (IC50) and 120 nmol/L (IC50 x 100). BQ123 significantly suppressed the ET-1-induced formation of choline dose-dependently, however, BQ788 did not affect the choline formation. BQ123 also inhibited the ET-1-induced release of arachidonic acid, but BQ788 had little effect. The results strongly suggest that ETA receptor mediates the three intracellular signaling pathways of ET-1: (1) phosphoinositide hydrolysis by phospholipase C; (2) phosphatidylcholine hydrolysis by phospholipase D; (3) arachidonic acid release in osteoblast-like cells.

Mechanism of thrombin-induced arachidonic acid release in osteoblast-like cells

In a previous study, we have reported that thrombin stimulates phosphatidylcholine hydrolysis by phospholipase (PL) D, but has little effect on phosphoinositide hydrolysis by PLC in osteoblast-like MC3T3-E1 cells. In the present study, we investigated the mechanism of the thrombin-induced arachidonic acid (AA) release in MC3T3-E1 cells. Thrombin stimulated AA release dose dependently in the range between 0.1 and 1 U/ml. Quinacrine, a PLA2 inhibitor, suppressed the thrombin-induced AA release. In addition, quinacrine also suppressed the thrombin-induced prostaglandin E2 synthesis in these cells. On the other hand, propranolol, which is known to inhibit phosphatidic acid phosphohydrolase, did not affect the thrombin-induced AA release. 1(6-((17beta-3-Methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H- pyrrole-2,5-dione (U-73122), a PLC inhibitor, had no effect on the AA release by thrombin. In addition, 1,6-bis-(cyclohexyloximinocarbonylamino)-hexane (RHC-80267), a selective inhibitor of diacylglycerol lipase, had little effect on the thrombin-induced AA release. Neither propranolol, U-73122 nor RHC-80267 affect the thrombin-induced prostaglandin E2 synthesis. These results strongly suggest that thrombin induces AA release not by phosphatidylcholine hydrolysis by PLD nor phosphoinositide hydrolysis by PLC but mainly by PLA2 in osteoblast-like cells.

Apoptosis regulates the number of Schwann cells at the premyelinating stage

At the premyelinating stage, the Schwann cells of peripheral nerves are able to recognize the axon, to arrange themselves along it in a nonoverlapping manner, and finally to establish a one-to-one cell-axon relationship. The mechanism that regulates these processes is not known in detail. We found the existence of a significant Schwann cell apoptosis in vivo of rat postnatal sciatic nerve, peaking around postnatal day 3. More than 50% of the neonatal Schwann cells cultured in axon-free medium undergo a rapid apoptosis. The apoptosis can be suppressed by addition of survival factors such as Neu differentiation factors or by increasing the adhesion of Schwann cells to substratum. We suggest that in neonatal nerves in vivo, Schwann cells are highly susceptible to apoptosis, but they are saved from death by contact with axons. The dramatic increase in number of Schwann cells between postnatal day 0 and 3 overcomes the number of axons available for them. Consequently the Schwann cells that fail to contact an axon undergo apoptosis. In conclusion, the number of Schwann cells in the developing nerves is regulated by the apoptosis and clearly depends on the survival signals from axons.

Differential expression of Rho family GTP-binding proteins and protein kinase C isozymes during C6 glial cell differentiation

The differential expression of Rho family of low molecular weight GTP-binding proteins and protein kinase C (PKC) isozymes were examined during differentiation of rat C6 glial cells to astrocytic phenotypes induced by dibutyryl cAMP (dbcAMP)/theophylline. The cells showed rapid and distinct morphological changes, resembling stellate astrocytes at 12 h after the treatment. The treated cells had a round cell body that extended several long processes each with a beaded appearance. In addition to morphological changes, Western blot analysis revealed that S-100 protein, known as a glial cell differentiation marker, increased and reached the maximal level (approximately 6-fold increase) at 24 h following the addition of dbcAMP. In the control experiments with cells cultured in the absence of serum but also without dbcAMP/theophylline, morphological changes were marginal and apparent increases of S-100 protein were not observed by Western blotting. In response to dbcAMP/theophylline treatment, RhoA showed increases in the mRNA level followed by the protein level, as inferred by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting, respectively. Rac1 and Cdc42 proteins were undetectable by Western blot analyses. In PKC isozymes, increases were observed in PKC beta 1, epsilon, and zeta by RT-PCR, and in beta 1 and epsilon by Western blotting. Among them, PKC epsilon showed the most distinct changes. Its mRNA level transiently increased from 3 to 6 h and then decreased even below the basal level at 18 h after the treatment. In contrast, Western blot analysis revealed that PKC epsilon gradually increased time-dependently to 24 h (approximately 6-fold increase), and remained elevated until 48 h. These results suggested that RhoA and PKC epsilon, and probably also PKC beta 1 and PKC zeta, were closely implicated in C6 cell differentiation.

Involvement of phospholipase D activation in endothelin-1-induced release of arachidonic acid in osteoblast-like cells

In a previous study, we have that endothelin-1 (ET-1) activates phospholipase D independently from protein kinase C in osteoblast-like MC3T3-E1 cells. It is well recognized that phosphatidylycholine hydrolysis by phospholipase D generates phosphatidic acid, which can be further degraded by phosphatidic acid phosphohydrolase to diacylglycerol. In the present study, we investigated the role of phospholipase D activation in ET-1 stimulated arachidonic acid release and prostaglandin E2 (PGE2) synthesis in osteoblast-like MC3T3-E1 cells. ET-1 stimulated arachidonic acid dose-dependently in the range between 0.1 nM and 0.1 microM. Propranolol, an inhibitor of phosphatidic acid phosphohydrolase, significantly inhibited the ET-1-induced arachidonic acid release in a dose-dependent manner as well as the ET-1-induced diacylglycerol formation. 1,6-bis-(cyclohexyloxyminocarbonylamino)-hexane (RHC-80267), an inhibitor of diacylglycerol lipase, significantly suppressed the ET-1-induced arachidonic acid release. The pretreatment with propranolol and RHC-80267 also inhibited the ET-1-induced PGE2 synthesis. These results strongly suggest that phosphatidylcholine hydrolysis by phospholipase D is involved in the arachidonic acid release induced by ET-1 in osteoblast-like cells.

Mechanism of angiotensin II-induced arachidonic acid metabolite release in aortic smooth muscle cells: involvement of phospholipase D

In a previous study, we have shown that angiotensin II (Ang II) activates phosphatidylcholine-hydrolyzing phospholipase D due to Ang II-induced Ca2+ influx from extracellular space in subcultured rat aortic smooth muscle cells. In the present study, we have investigated the role of phospholipase D in Ang II-induced arachidonic acid (AA) metabolite release and prostacyclin synthesis in subcultured rat aortic smooth muscle cells. Ang II significantly stimulated AA metabolite release in a concentration-dependent manner in the range between 1 nmol/I and 0.1 mumol/I. D.L.-Propranolol hydrochloride (propranolol), an inhibitor of phosphatidic acid phosphohydrolase, significantly inhibited the Ang II-induced release of AA metabolites. The Ang II-induced AA metabolite release was reduced by chelating extracellular Ca2+ with EGTA. Genistein, an inhibitor of protein tyrosine kinases, significantly suppressed the Ang II-induced AA metabolite release. 1,6-Bis-(cyclohexyloximinocarbonylamino)-hexane (RHC-80267), a potent and selective inhibitor of diacylglycerol lipase, significantly inhibited the Ang II-induced AA metabolite release. Both propranolol and RHC-80267 inhibited the Ang II-induced synthesis of 6-keto-prostaglandin F1 alpha, a stable metabolite of prostacyclin. The synthesis was suppressed by genistein. These results strongly suggest that the AA metabolite release induced by Ang II is mediated, at least in part, through phosphatidylcholine hydrolysis by phospholipase D activation in aortic smooth muscle cells.

Involvement of phosphatidylcholine hydrolysis by phospholipase D in extracellular ATP-induced arachidonic acid release in aortic smooth muscle cells

We investigated the effect of extracellular ATP on phosphatidylcholine-hydrolyzing phospholipase D activity and the role of phospholipase D activation in extracellular ATP-induced arachidonic acid release in cultured rat aortic smooth muscle cells. ATP significantly stimulated the formation of choline in a dose-dependent manner in the range between 0.01 and 0.5 mmol/L. However, ATP had no effect on the formation of phosphocholine. Staurosporine, an inhibitor of protein kinases, did not affect the ATP-induced formation of choline. ATP significantly stimulated arachidonic acid release in a dose-dependent manner in the range between 0.01 and 0.5 mmol/L. DL-Propranolol hydrochloride (propranolol), an inhibitor of phosphatidic acid phosphohydrolase, significantly inhibited the ATP-induced release of arachidonic acid. 1,6-Bis(cyclohexyloximinocarbonylamino)-hexane (RHC-80267), a potent and selective inhibitor of diacylglycerol lipase, reduced ATP-induced arachidonic acid release. Quinacrine, a phospholipase A2 inhibitor, suppressed ATP-induced arachidonic acid release. Both propranolol and RHC-80267 markedly inhibited the ATP-induced synthesis of 6-ketoprostaglandin F1 alpha, a stable metabolite of prostacyclin. These results strongly suggest that extracellular ATP activates phosphatidylcholine-hydrolyzing phospholipase D independently of protein kinase C in aortic smooth muscle cells and that the arachidonic acid release induced by extracellular ATP is mediated, at least in part, through phosphatidylcholine hydrolysis by phospholipase D activation.

Basic fibroblast growth factor stimulates phosphatidylcholine-hydrolyzing phospholipase D in osteoblast-like cells

We examined the effect of basic fibroblast growth factor (bFGF) on the activation of phosphatidylcholine-hydrolyzing phospholipase D in osteoblast-like MC3T3-E1 cells. bFGF stimulated both the formations of choline (EC50 was 30 ng/ml) and inositol phosphates (EC50 was 10 ng/ml). Calphostin C, an inhibitor of protein kinase C (PKC), had little effect on the bFGF-induced formation of choline. bFGF stimulated the formation of choline also in PKC down regulated cells. Genistein and methyl 2,5-dihydroxycinnamate, inhibitors of protein tyrosine kinases, significantly suppressed the bFGF-induced formation of choline. Sodium orthovanadate, an inhibitor of protein tyrosine phosphatases, enhanced the bFGF-induced formation of choline. In vitro kinase assay for FGF receptors revealed that FGF receptor 1 and 2 were autophosphorylated after FGF stimulation. bFGF dose-dependently stimulated DNA synthesis of these cells. These results strongly suggest that bFGF activates phosphatidylcholine-hydrolyzing phospholipase D through the activation of tyrosine kinase, but independently of PKC activated by phosphoinositide hydrolysis in osteoblast-like cells.

Function of Ca2+ in phosphatidylcholine-hydrolyzing phospholipase D activation in osteoblast-like cells

We investigated the function of Ca2+ in the activation of phosphatidylcholine (PC)-hydrolyzing phospholipase D (PLD) in osteoblast-like MC3T3-E1 cells. Fetal calf serum (FCS) stimulated the formation of choline in a dose-dependent manner in the range between 0.6% and 10%. The effect of a combination of FCS and 12-O-tetradecanoylphorbol-13-acetate, a protein kinase C (PKC) activator, on the formation of choline was additive. Staurosporine, an inhibitor of protein kinases, enhanced the formation of choline induced by FCS. BAPTA/AM, a chelator of intracellular Ca2+, inhibited the formation of choline induced by FCS. The depletion of extracellular Ca2+ by EGTA markedly reduced the FCS-induced formation of choline. SK&F 96365, an inhibitor of receptor-operated Ca2+ entry, significantly inhibited the choline formation induced by FCS. On the other hand, nifedipine, an inhibitor of L-type voltage-dependent Ca2+ channels, had little effect on the choline formation. TMB-8, an inhibitor of Ca2+ mobilization from intracellular Ca2+ store, significantly inhibited FCS-induced choline formation. These results strongly suggest that Ca2+ mobilization, through both the influx via receptor-operated Ca2+ channel and the release from intracellular Ca2+ store, plays an important role in the activation of PLD in osteoblast-like cells.

Effect of retinoic acid on prostaglandin F2 alpha-induced phospholipase D activity in osteoblast-like cells

We previously reported that prostaglandin F2 alpha (PGF2 alpha) activates phosphatidylcholine-hydrolyzing phospholipase D independently from the activation of protein kinase C (PKC) in osteoblast-like MC3T3-E1 cells, and reported that pertussis toxin-sensitive GTP-binding protein (G-protein) is involved in the PGF2 alpha-induced phospholipase D activation. In this study, we examined the effect of retinoic acid (RA) on the phospholipase D activity stimulated by PGF2 alpha in these cells. The pretreatment of RA markedly inhibited the formation of choline induced by PGF2 alpha (10 microM) in a dose-dependent manner in the range between 1 nM and 0.1 microM. This inhibitory effect of RA was dependent on the time of pretreatment up to 8 h. However, RA had little effect on the choline formation induced by NaF, a G-protein activator, or 12-O-tetradecanoylphorbol-13-acetate, an activator of PKC. These results strongly suggest that RA suppresses the phospholipase D activated by PGF2 alpha in osteoblast-like cells and that the effect of RA is exerted at the point between PGF2 alpha receptor and G-protein.

Differential mRNA expression of phospholipase D (PLD) isozymes during cAMP-induced differentiation in C6 glioma cells

GTP gamma S-dependent phospholipase D (PLD) activity time-dependently increased during differentiation of rat C6 glioma cells to astrocytic phenotypes induced by dibutyryl cyclic AMP (dbcAMP)/theophylline. The changes in PLD mRNA level were examined by reverse transcriptase-polymerase chain reaction (RT-PCR) method using the degenerate primers designed based on two conserved amino acid sequences in PLDs of human and yeast. The amplified three DNA fragments (tentatively termed as rPLDa, b, and c) contained the conserved regions present in PLDs of various organisms. RT-PCR using non-degenerate primers showed that rPLDa mRNA increased within 12h following treatment with dbcAMP, reaching a broad plateau and then returned to the initial level at 48h. In contrast, the level of rPLDb mRNA showed a concurrent decrease. rPLDc decreased in a time-dependent manner. These results suggest that the expression of PLD mRNAs are differentially regulated during differentiation in C6 glioma cells.

Expression of CD44H in the cells of neural crest origin in peripheral nervous system

We investigated the expression of the adhesion molecule CD44 in rat peripheral nervous system (PNS) at the protein and mRNA levels. Most migrating neural crest cells strongly expressed CD44, in contrast to the lack of expression in the neural tube. In dorsal root ganglion (DRG) and sciatic nerve, the distribution of CD44, neurofilament (NF) and S100 suggested the localization of CD44 on the membrane of Schwann cell and neurones and in extracellular matrix (ECM). The expression of CD44 was also confirmed on the membrane of cultured neurones and Schwann cells from DRG. mRNA coding for the haematopoietic form of CD44, CD44H, was detected in neural crest cells, DRG neurones and Schwann cells. These results show that CD44 may play some role in migration of neural crest cells and myelination in terms of adhesion between Schwann cells, axons and ECM.

Thrombin induces proliferation of osteoblast-like cells through phosphatidylcholine hydrolysis

We examined the effect of thrombin on phosphatidylcholine-hydrolyzing phospholipase D activity in osteoblast-like MC3T3-E1 cells. Thrombin stimulated the formation of choline dose dependently in the range between 0.01 and 1 U/ml, but not the phosphocholine formation. Diisopropylfluorophosphate (DFP)- inactivated thrombin had little effect on the choline formation. The combined effects of thrombin and 12-O-tetradecanoylphorbol-13-acetate, a protein kinase C-activating phorbol ester, on the choline formation were additive. Staurosporine, an inhibitor of protein kinases, had little effect on the thrombin-induced formation of choline. Combined addition of thrombin and NaF, an activator of heterotrimeric GTP-binding protein, did not stimulate the formation of choline further. Pertussis toxin had little effect on the thrombin-induced formation of choline. Thrombin stimulated Ca2+ influx from extracellular space time and dose dependently. The depletion of extracellular Ca2+ by EGTA exclusively reduced the thrombin-induced choline formation. Thrombin had only a slight effect on phosphoinositide-hydrolyzing phospholipase C activity. Thrombin induced diacylglycerol formation and DNA synthesis, and increased the number of MC3T3-E1 cells, but DFP-inactivated thrombin did not. Thrombin suppressed both basal and fetal calf serum-induced alkaline phosphatase activity in these cells. Propranolol, an inhibitor of phosphatidic acid phosphohydrolase, inhibited both the thrombin-induced diacylglycerol formation and DNA synthesis. These results suggest that thrombin stimulates phosphatidylcholine-hydrolyzing phospholipase D due to self-induced Ca2+ influx independently of protein kinase C activation in osteoblast-like cells and that its proliferative effect depends on phospholipase D activation.

Suppressed expression of CD44 variant isoforms during human glioma A172 cell differentiation induced by cyclic AMP

CD44 is a major receptor for hyaluronic acid, which is the most frequent route of malignant glioma invasion. Multiple isoforms of CD44 are generated by alternative mRNA splicing. We have examined differential expression of CD44 variant isoforms (CD44vs) during dibutyryl cyclic AMP (dbcAMP)/theophylline-induced differentiation of human glioma A172 cells using reverse transcriptase-polymerase chain reaction (RT-PCR). Treatment of cells with dbcAMP and theophylline caused decreased expression of all CD44 isoforms after 24 h. The CD44 standard form was observed to return to the unstimulated level after 72 h, whereas the variant isoforms, CD44 8v-10v and 10v, remained at the low level after 24-72 h. Changes of CD44vs were correlated with the level of expression of c-jun. These results suggested that the expression patterns of CD44vs might correlate with cellular differentiation in human glioma cells.).