The pathogenesis of choroid plexus papillomas, intraventricular papillary neoplasms most often occurring sporadically in children and young adults, remains poorly understood. To identify pathways operative in the development of choroid plexus papillomas, gene expression profiles obtained from laser-microdissected human choroid plexus papilloma cells (n = 7) were compared with that of normal choroid plexus epithelial cells laser microdissected from autopsy tissue (n = 8). On DNA microarray data analysis, 53 probe sets were differentially expressed in choroid plexus papilloma tumor cells (>7-fold). Up-regulation of TWIST1, WIF1, TRPM3, BCLAF1, and AJAP1, as well as down-regulation of IL6ST was confirmed using quantitative reverse transcription-PCR. Knockdown of Twist1 gene expression in the rat choroid plexus epithelial cell line Z310 significantly reduced proliferation as assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and cell invasion in a Matrigel assay, whereas cell migration was not affected. Screening for expressional changes of cancer-related genes upon Twist1 knockdown revealed up-regulation of Cdkn1a, Cflar, and Serpinb2 and down-regulation of Figf. To conclude, using gene expression profiling, several genes differentially expressed in human choroid plexus papillomas could be identified. Among those, TWIST1 is highly expressed in choroid plexus papillomas and promotes proliferation and invasion.

Abstract. Kidney transplantation often leads to disturbances of solute and volume maintenance in humans. To investigate underlying mechanisms, expression and function of renal transporters and receptors of the proximal tubule (PT) were analyzed in an acute rejection model of rat kidney transplantation. Semiquantitative RT-PCR and Western blot, histology, immunohistochemistry, and microfluorometry were performed on whole kidneys and isolated PT. With acute rejection, Na ϩ / H ϩ -exchanger type-3 (NHE-3) was markedly downregulated. Na ϩ -HCO 3 Ϫ -cotransporter (NBC-1) and Na ϩ -glucose transporter type-2 (SGLT2) were upregulated after transplantation. Expressions of Na ϩ /H ϩ -exchanger type-1 (NHE-1), Na ϩ /K ϩ -ATPase (NKA), angiotensin II (AngII) receptor (AT-1), or natriuretic peptide receptor (GC-A) were unaltered. Microfluorometric analyses of intracellular pH, Na ϩ , and Ca 2ϩ demonstrated a decrease in NHE-3 function and AngII-mediated stimulation of NHE-3. AngII-mediated inhibition of NHE-1 and function of all other transporters tested remained unaltered. Function of AT-1 and GC-A were unaffected. Reduced expression of NHE-3 was also confirmed by semiquantitative immunohistochemistry. These findings suggest that expression and function of transmembrane proteins involved in Na ϩ -transport after transplantation and rejection is specifically modulated. The local renin-angiotensin-system is apparently not altered.

Modulation of cell proliferation has often been thought to be connected to changes in the activity of pH-regulatory transporters and consequently intracellular pH (pH_i). The influence of natriuretic peptides, diadenosine polyphosphates, adenosine and ATP as well as platelet-derived growth factor (PDGF) on pH_i regulation of cultured rat mesangial cells was examined with the pH-sensitive dye 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. The inhibitors of Na⁺/H⁺ exchange, amiloride and HOE694, blocked pH_i recovery completely in the absence of and by approximately 50% in the presence of HCO₃^–/CO₂. Natriuretic peptides (ANP, BNP, CNP, urodilatin) completely inhibited pH_i recovery in the absence of and by approximately 40% in the presence of HCO₃^–/CO₂. These effects were abolished by the cGMP-dependent protein kinase inhibitor KT5823. Diadenosine polyphosphates (Ap3A-Ap6A), ATP and adenosine also inhibited pH_i recovery completely in the absence of and partially (30–40%) in the presence of HCO₃^–/ CO₂. The effect of adenosine was abolished in the presence of the cAMP-dependent protein kinase inhibitor KT5720, and that of Ap5A by the protein kinase C inhibitor calphostin C. PDGF activated acid extrusion in these cells by approximately 40%. From the four cloned isoforms of the Na⁺/H⁺ exchanger in the rat, only transcripts of NHE-1 were found in these mesangial cell cultures using RT-PCR analysis. These data suggest that in these rat mesangial cells the Na⁺/H⁺ exchanger, specifically the NHE-1 isoform, accounts for around 50% of pH_i recovery from an acid load under physiological conditions, and that Na⁺/H⁺ exchange stimulated by acidification can be inhibited by activation of PKG, PKA, and PKC and stimulated by PDGF after acute exposition to these agonists.

Diadenosine polyphosphates have differential hemodynamic effects. The role of the endothelium in the vascular effects of these agonists is still unclear. Primary cultures of rat aortal endothelial cells and Ea.hy 926 cells (a continuous endothelial cell line) were used to investigate the effects of Ap3A–Ap6A, adenosine triphosphate (ATP), and for comparison, arginine vasopressin (AVP) and angiotensin II (A II) on the intracellular Ca²⁺ concentration, [Ca²⁺]_i. Fura-2 was used as Ca²⁺ indicator. In rat aortal endothelial cells, ATP and Ap4A concentration dependently increased [Ca²⁺]_i with an initial peak followed by an elevated plateau. The half-maximal effects were reached at approximately 7 µmol/l for ATP and at approximately 10 µmol/l for Ap4A. The maximal peak effects at 100 µmol/l were 1,035 ± 413 nmol/l (n = 3) and 437 ± 271 nmol/l (n = 8) for ATP and Ap4A, respectively. At 100 µmol/l Ap3A and Ap6A slightly increased [Ca²⁺]_i, while Ap5A had no significant effect. The known endothelial agonists AVP (100 nmol/l) and A II (10 nmol/l) increased [Ca²⁺]_i initially by 1,549 ± 913 nmol/l (n = 7) and 209 ± 45 nmol/l (n = 9), respectively. In Ea.hy 926 cells an increase in [Ca²⁺]_i was obtained only with ATP (10 µmol/l) and with Ap4A (100 µmol/l). Ap3A, Ap5A, and Ap6A (each 100 µmol/l) and also AVP (100 nmol/l) and A II (10 nmol/l) had no significant effects in these cells. These results show that a considerable increase in [Ca²⁺]_i in endothelial cells can only be induced by Ap4A among the diadenosine polyphosphates, indicating that the vasoactive effects of only this polyphosphate could at least partly be mediated via Ca²⁺-dependent mechanisms in endothelial cells, comparable to the known effects of AVP, A II, and ATP. The fact that A II and AVP did not influence [Ca²⁺]_i in Ea.hy 926 cells is probably due to the loss of the respective receptors in this cell line.

<div>Abstract<p>The pathogenesis of choroid plexus papillomas, intraventricular papillary neoplasms most often occurring sporadically in children and young adults, remains poorly understood. To identify pathways operative in the development of choroid plexus papillomas, gene expression profiles obtained from laser-microdissected human choroid plexus papilloma cells (<i>n</i> = 7) were compared with that of normal choroid plexus epithelial cells laser microdissected from autopsy tissue (<i>n</i> = 8). On DNA microarray data analysis, 53 probe sets were differentially expressed in choroid plexus papilloma tumor cells (>7-fold). Up-regulation of <i>TWIST1, WIF1, TRPM3, BCLAF1</i>, and <i>AJAP1,</i> as well as down-regulation of <i>IL6ST</i> was confirmed using quantitative reverse transcription-PCR. Knockdown of <i>Twist1</i> gene expression in the rat choroid plexus epithelial cell line Z310 significantly reduced proliferation as assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and cell invasion in a Matrigel assay, whereas cell migration was not affected. Screening for expressional changes of cancer-related genes upon <i>Twist1</i> knockdown revealed up-regulation of <i>Cdkn1a, Cflar</i>, and <i>Serpinb2</i> and down-regulation of <i>Figf</i>. To conclude, using gene expression profiling, several genes differentially expressed in human choroid plexus papillomas could be identified. Among those, <i>TWIST1</i> is highly expressed in choroid plexus papillomas and promotes proliferation and invasion. [Cancer Res 2009;69(6):2219–23]</p></div>