GABAC-receptor stimulation activates cAMP-dependent protein kinase via A-kinase anchoring protein 220.

In our previous study, anti-apoptotic effects of GABA(C)-receptor stimulation was suppressed by inhibitors of cAMP-dependent protein kinase (PKA), implying GABA(C) receptor-mediated PKA activation. The present study showed that GABA(C)-receptor stimulation with its agonist, cis-4-aminocrotonic acid (CACA), protected cultured hippocampal neurons from amyloid beta 25 - 35 (Abeta25 - 35) peptide-enhanced glutamate neurotoxicity. This protective effect of CACA was blocked by PKA inhibitors, KT 5720 and H-89, as well as a specific GABA(C)-receptor antagonist, (1,2,5,6-tetrahydropyridine-4-yl) methylphosphinic acid (TPMPA). To test the possibility of GABA(C) receptor-mediated PKA activation, association of GABA(C) receptor with A-kinase anchoring proteins (AKAPs) and effect of an AKAP antisense oligonucleotide on the PKA activation were examined in primary cultured rat hippocampal neurons. Stimulation of the cells with CACA-activated PKA was assessed by the phosphorylated PKA substrate (135 kDa) level. Specific antibodies raised against GABA(C)-receptor rho subunits precipitated each rho subunit, AKAP220, and PKA regulatory and catalytic subunits from rat brain lysates, suggesting that rho is associated with the AKAP220/PKA complex. Furthermore, antisense oligonucleotide of AKAP220 suppressed such GABA(C) stimulation-induced PKA activation, suggesting that GABA(C)-receptor stimulation activates PKA via AKAP220.

Anti-prolactin (PRL) autoantibodies suppress PRL bioactivity in patients with macroprolactinaemia.

OBJECTIVE: Macroprolactinaemia, mainly caused by anti-prolactin (PRL) autoantibodies, is frequently found in patients with hyperprolactinaemia. Characteristically, these patients lack clinical symptoms of hyperprolactinaemia, but the serum bioactive PRL concentrations in vitro measured by the Nb2 bioassay are usually high. In this study, we investigated the causes of the discrepancy and the true biological features of macroprolactin. SUBJECTS AND METHODS: Sixteen patients with macroprolactinaemia due to anti-PRL autoantibodies were studied. PRL bioactivity was determined by the phosphorylation of signal transducer and activator of transcription (Stat)5 in T47D human breast cancer cells and the proliferation of Nb2 rat lymphoma cells. RESULTS: PRL bioactivity by the T47D bioassay, expressed as the density of the band of phosphorylated Stat5/immunoreactive PRL, was significantly lower in sera containing anti-PRL autoantibodies (2.4 +/- 1.1) than in control sera (7.2 +/- 3.1). Dissociation of PRL from the autoantibodies by acidification resulted in an increase in phosphorylated Stat5. PRL bioactivity by the Nb2 bioassay was not significantly different between sera with and without anti-PRL autoantibodies, and free PRL in the medium gradually increased during the incubation in a time-dependent manner in sera containing anti-PRL autoantibodies. CONCLUSIONS: We conclude that the level of bioactivity of macroprolactin in the Nb2 bioassay is normal due to dissociation of PRL from the autoantibodies as a result of the longer incubation and more dilute assay conditions than in the T47D bioassay. The bioactivity of macroprolactin is low in vivo due to anti-PRL autoantibodies, but monomeric PRL dissociated from the autoantibodies retains full biological activity in patients with macroprolactinaemia.

Amplification of MDS1/EVI1 and EVI1, located in the 3q26.2 amplicon, is associated with favorable patient prognosis in ovarian cancer.

Increased copy number involving chromosome 3q26 is a frequent and early event in cancers of the ovary, lung, head and neck, cervix, and BRCA1 positive and basal breast cancers. The p110alpha catalytic subunit of phosphoinositide-3-kinase (PI3KCA) and protein kinase Ciota (PKCiota) have previously been shown as functionally deregulated by 3q copy number increase. High-resolution array comparative genomic hybridization of 235 high-grade serous epithelial ovarian cancers using contiguous bacterial artificial chromosomes across 3q26 delineated an approximately 2 Mb-wide region at 3q26.2 encompassing PDCD10 to MYNN (chr3:168722613-170908630). Ecotropic viral integration site-1 (EVI1) and myelodysplastic syndrome 1 (MDS1) are located at the center of this region, and their DNA copy number increases are associated with at least 5-fold increased RNA transcript levels in 83% and 98% of advanced ovarian cancers, respectively. Moreover, MDS1/EVI1 and EVI1 protein levels are increased in ovarian cancers and cancer cell lines. EVI1 and MDS1/EVI1 gene products increased cell proliferation, migration, and decreased transforming growth factor-beta-mediated plasminogen activator inhibitor-1 promoter activity in ovarian epithelial cells. Intriguingly, the increases in EVI1 DNA copy number and MDS1/EVI1 transcripts are associated with improved patient outcomes, whereas EVI1 transcript levels are associated with a poor patient survival. Thus, the favorable patient prognosis associated with increased DNA copy number seems to be as a result of high-level expression of the fusion transcript MDS1/EVI1. Collectively, these studies suggest that MDS1/EVI1 and EVI1, previously implicated in acute myelogenous leukemia, contribute to the pathophysiology of epithelial ovarian cancer.

Soybean-derived phosphatidylinositol inhibits in vivo low concentrations of amyloid beta protein-induced degeneration of hippocampal neurons in V337M human tau-expressing mice.

In our previous reports using primary cultured rat hippocampal neurons, pathophysiological concentrations (< or =10 nM) of amyloid beta proteins (Abetas) showed neurotoxicity via a phosphatidylinositol metabolism disorder, and soybean-derived phosphatidylinositol protected the neurons against the Abeta's neurotoxicity. In the present study, such a neurotoxic effect of Abeta and a neuroprotective effect of phosphatidylinositol were examined in vivo using transgenic mice expressing V337 M human tau. Intrahippocampal CA1 injection of 1.5 mul of 100 nM or 1 microM Abeta25-35 increased the number of degenerating neurons with an apoptotic feature in bilateral hippocampal CA1, CA2, CA3 and dentate gyrus regions in 1 month, demonstrating an in vivo neurotoxic effect of Abeta at lower concentrations after diffusion. Intrahippocampal co-injection or intracerebroventricular administration of 1.5 microl of 500 nM phosphatidylinositol prevented the Abeta25-35-induced neuronal degeneration in all the hippocampal regions, while co-injection of another acidic phospholipid, phosphatidylserine (1.5 microl, 500 nM) with Abeta25-35 showed no protective effects. Thus, exogenously applied phosphatidylinositol appeared to minimize the toxic effects of Abeta in vivo. These results suggest that soybean-derived phosphatidylinositol may be effective in the treatment of Alzheimer's disease.

Development of anti-PRL (prolactin) autoantibodies by homologous PRL in rats: a model for macroprolactinemia.

Macroprolactinemia is hyperprolactinemia in humans mainly due to anti-PRL (prolactin) autoantibodies and is a pitfall for the differential diagnosis of hyperprolactinemia. Despite its high prevalence, the pathogenesis remains unclear. In this study, we examined whether anti-PRL autoantibodies develop via immunization with homologous rat pituitary PRL in rats to elucidate what mechanisms are involved and whether they cause hyperprolactinemia with low PRL bioactivity, as seen in human macroprolactinemia. Anti-PRL antibodies were developed in 19 of 20 rats immunized with homologous rat pituitary PRL and 29 of 30 rats with heterogeneous bovine or porcine pituitary PRL but did not develop in 25 control rats. In rats with anti-PRL antibodies, the basal serum PRL levels were elevated, and a provocative test for PRL secretion using dopamine D2 receptor antagonist (metoclopramide) showed a normal rising response with a slower clearance of PRL because of the accumulation of macroprolactin in blood. Antibodies developed by porcine or rat pituitary PRL reduced the bioactivity of rat serum PRL, and gonadal functions in these rats were normal despite hyperprolactinemia. Anti-PRL antibodies were stable and persisted for at least 5 wk after the final injection of PRL. These findings suggest that pituitary PRL, even if homologous, has antigenicity, leading to the development of anti-PRL autoantibodies. We successfully produced an animal model of human macroprolactinemia, with which we can explain the mechanisms of its clinical characteristics, i.e. asymptomatic hyperprolactinemia.

Down-regulation of Cl- pump ClP55 subunit induced enhancement of glutamate neurotoxicity in cultured rat hippocampal neurons.

To test whether the increased intracellular Cl- concentration ([Cl-]i) is responsible for the enhanced glutamate toxicity, antisense oligonucleotide of ClP55, a Cl- -ATPase/pump associated protein, was transfected in cultured rat hippocampal neurons. Neuronal [Cl-]i in the antisense oligonucleotide-transfected culture increased to a level 3- to 4-fold higher than that in control. Glutamate exposure (10 microM, 10 min) increased neuronal apoptosis and decreased Akt-pS473 level in the antisense oligonucleotide-transfected neurons, but not in control or sense oligonucleotide-transfected ones, suggesting the responsibility of elevated [Cl-]i in the enhancement of glutamate neurotoxicity.

Gamma-aminobutyric acid (GABA)-C receptor stimulation increases prolactin (PRL) secretion in cultured rat anterior pituitary cells.

Gamma-aminobutyric acid (GABA) reportedly inhibits secretion of anterior pituitary hormones by directly acting on GABA-A and GABA-B receptors on anterior pituitary cells, but the roles of GABA-C receptors are little known. In this study, involvement of GABA-C receptors in the secretion of prolactin (PRL) was examined using cultured rat anterior pituitary cells. GABA-C receptor agonist, cis-4-aminocrotonic acid (CACA, 0.1-1 mM) increased PRL secretion dose-dependently, while GABA-A receptor agonist, 100 microM muscimol, but not GABA-B receptor agonist, 100 microM baclofen, decreased the secretion. GABA-C receptor antagonist, 15 microM (1,2,5,6-tetrahydropyridin-4-yl) methylphosphinic acid (TPMPA), and GABA-A receptor antagonist, 100 microM bicuculline, not only reversed such an agonist-induced increase or decrease in PRL secretion, but also suppressed or enhanced spontaneous PRL secretion, raising a possibility of GABA-C or GABA-A receptor stimulation by intrinsic pituitary-derived GABA. GABA-C receptor subunits (rho1, rho2, rho3) and GABA synthesizing enzymes (GAD 65 and GAD 67) were shown to be expressed as assayed by RT-PCR, and GABA-C receptor stimulation by CACA obviously increased intracellular Ca2+ concentration in the anterior pituitary cells. Thus, PRL secretion from anterior pituitary cells appears to be enhanced via direct GABA-C receptor stimulation by GABA originating from the anterior pituitary cells besides well-known hypothalamic GABA.

Suppression of cell proliferation with induction of p21 by Cl(-) channel blockers in human leukemic cells.

The existence of Cl(-) channels in lymphocytes and neutrophils has been increasingly recognized, but the biological functions are not yet clear. We examined the effects of Cl(-) channel blockers on the cell proliferation and the cell cycle of human leukemic cell lines. The growth of leukemic cells was suppressed most efficiently by NPPB (5-nitro-2-(3-phenylpropylamino) benzoic acid), partially by 9-AC (9-anthracenecarboxylic acid) and tamoxifen, but not by stilbene compounds. NPPB increased the G0/G1 population and induced the expression of p21, one of the critical molecules for G1/S checkpoint. Antisense oligonucleotide for a NPPB-sensitive and stilbene-insensitive Cl(-) channel, ClC-2, sufficiently suppressed the ClC-2 protein synthesis, but did not affect the growth of leukemic cells. These findings suggest that NPPB-sensitive and stilbene-insensitive Cl(-) channels other than ClC-2 play important roles in cell cycles and cell proliferation of human leukemic cells.

Single cell RT-PCR demonstrates differential expression of GABAC receptor rho subunits in rat hippocampal pyramidal and granule cells.

Although gamma-aminobutyric acid (GABA)C receptor rho1, rho2 and rho3 subunits are reportedly expressed in pyramidal and granule cells in the hippocampus at various developmental stages, it is not clear whether these three rho subunits are coexpressed in a single neuron. To attempt to answer this question, we performed single-cell RT-PCR for rho subunits from neurons of rat brain hippocampus. In hippocampal cultures, pyramidal cells were positive for rho1 mRNA expression in 89%, rho2 in 94% and rho3 in 94%, while granule cells were positive for rho1 mRNA in only 6%, rho2 in 36% and rho3 in 91%. Intensive amplification of the RT-PCR products by the second PCR revealed that all the three rho subunits were coexpressed in a single pyramidal and granule cells from both of the cultures and the slices. These results suggest that all the three GABAC receptor rho1, rho2 and rho3 subunits are present probably in different compositions in pyramidal and granule cells in the rat hippocampus.

Expression and roles of Cl- channel ClC-5 in cell cycles of myeloid cells.

ClC-5 is a chloride channel known to be expressed in the kidney. We previously reported that ClC-5 mRNA was also strongly expressed in immature human myeloid cell line (HL-60), but weakly expressed in mature neutrophils. To clarify the underlying mechanisms, we examined the relationship between ClC-5 expression and cell cycle. Dimethyl sulfoxide treatment of HL-60 that causes differentiation with G0/G1 cell cycle arrest decreased the expression of ClC-5 mRNA. Cell sorting and synchronization experiments revealed that ClC-5 mRNA expression was high in S and G2/M phases and low in G0/G1 phase. ClC-5 antisense oligonucleotide suppressed proliferation of HL-60 cells with a decrease in ClC-5 protein expression, probably due to G2 arrest. These results suggest that cell cycle-dependent expression of ClC-5 has a role in cell cycle progression in myeloid cells.