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2. EP08.02-171 PRO-CTCAE Analysis of Mobocertinib in EGFR Exon 20 Insertion‒Positive Metastatic Non‒Small Cell Lung Cancer (NSCLC)

Author

García Campelo, M.R., primary, Zhou, C., additional, Ramalingam, S.S., additional, Lin, H.M., additional, Kim, T.M., additional, Riely, G.J., additional, Mekhail, T., additional, Nguyen, D., additional, Biber, J., additional, Romero, H., additional, Goodman, E., additional, Popat, S., additional, and Jänne, P.A., additional

Published
2022
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18. Regulation of intestinal phosphate cotransporter NaPi IIb by ubiquitin ligase Nedd4--2 and by serum- and glucocorticoid-dependent kinase 1

Author

Palmada, M., Dieter, M., Speil, A., Bohmer, C., Mack, A.F., Wagner, H.J., Klingel, K., Kandolf, R., Murer, H., Biber, J., Closs, E.I., and Lang, F.

Subjects
Transforming growth factors -- Research, Protein kinases -- Research, Biological sciences
Abstract

Serum and glucocorticoid-inducible kinase 1 (SGK1) is highly expressed in enterocytes. The significance of the kinase in regulation of intestinal function has, however, remained elusive. In Xenopus laevis oocytes, SGK1 stimulates the epithelial [Na.sup.+] channel by phosphorylating the ubiquitin ligase Nedd4-2, which regulates channels by ubiquitination leading to subsequent degradation of the channel protein. Thus the present study has been performed to explore whether SGK1 regulates transport systems expressed in intestinal epithelial cells, specifically type lib sodium-phosphate ([Na.sup.+]-[P.sub.i]) cotransporter (NaPi IIb). Immunohistochemistry in human small intestine revealed SGK1 colocalization with Nedd4-2 in villus enterocytes. For functional analysis cRNA encoding NaPi IIb, the SGK isoforms and/or the Nedd4-2 were injected into X. laevis oocytes, and transport activity was quantified as the substrate-induced current (Ip). Exposure to 3 mM phosphate induces an [I.sub.P] in NaPi IIb-expressing oocytes. Coinjection of Nedd4-2, but not the catalytically inactive mutant [sup.c938S]Nedd4-2, significantly downregulates [I.sub.P], whereas the coinjection of [sup.S422D]SGK1 markedly stimulates [I.sub.P] and even fully reverses the effect of Nedd4-2 on [I.sub.P]. The effect of [sup.S422D]SGK1 on NaPi IIb is mimicked by wild-type SGK3 but not by wild-type SGK2, constitutively active [sup.T308D,S473D]PKB, or inactive [sup.K127N]SGK1. Moreover, [sup.S422D]SGK1 and SGK3 phosphorylate Nedd4-2. In conclusion, SGK1 stimulates the NaPi IIb, at least in part, by phosphorylating and thereby inhibiting Nedd4-2 binding to its target. Thus the present study reveals a novel signaling pathway in the regulation of intestinal phosphate transport, which may be important for regulation of phosphate balance. transforming growth factor-[beta]; phosphatidylinositol 3-kinase; transporter; protein kinase B; protein kinases

Published
2004

43. NaPi-IIa and interacting partners

Author

Hernando, N., Gisler, S. M., Pribanic, S., Déliot, N., Capuano, P., Wagner, C. A., Moe, O. W., Biber, J., and Murer, H.

Published
2005

44. Expression of proximal tubular Na-Pi and Na-SO4 cotransporters in MDCK and LLC-PK1 cells by transfection

Author

Quabius, E.S., Murer, H., and Biber, J.

Subjects
Proteins -- Research, Transfection -- Research, Genetic regulation -- Research, Biological sciences
Abstract

Reverse transcription-polymerase chain reaction with dexamethasone induces the expression of proximal tubular Na-Pi and Na-SO4 cotransporters in Madin-Darby canine kidney (MDCK) and transfected LLC-PKi. The expression is high in MDCK cells and minimal in LLC-PKi. NaPi-2 and NaSi-1 related mRNAs are expressed in proximal tubules, whereas NaPi-2 proteins are present in the apical membranes of proximal tubular cells. The Na-SO4 cotransporter NaPi-2 has an apical sorting behavior, and the Na-Pi cotransporter NaPi-2's behavior is dual.

Published
1996

46. The renal type IIa Na/Pi cotransporter: Structure-function relationships

Author

Murer, H, Köhler, K, Lambert, G, Stange, G, Biber, J, Forster, I C, University of Zurich, and Murer, H

Subjects
1307 Cell Biology, 1303 Biochemistry, 570 Life sciences, biology, 10052 Institute of Physiology, 1304 Biophysics
Abstract

The type IIa Na/Pi cotransporter mediates proximal tubular brush-border membrane secondary active phosphate (Pi) flux. It is rate limiting in tubular Pi reabsorption and, thus, a final target in many physiological and pathophysiological situations of altered renal Pi handling (1-4). In the present short review, we will briefly summarize our current knowledge about the transport mechanism (cycle) as well as particular regions of the transporter protein ("molecular domains”) that potentially determine transport characteristics

Published
2018

49. Functionally Important Residues in the Predicted 3rd Transmembrane Domain of the Type IIa Sodium-phosphate Cotransporter (NaPi-IIa)

Author

Virkki, L.V., Forster, I.C., Bacconi, A., Biber, J., Murer, H., Virkki, L.V., Forster, I.C., Bacconi, A., Biber, J., and Murer, H.

Abstract

The type IIa Na+/Pi, cotransporter (NaPi-IIa) mediates electrogenic transport of three Na+ and one divalent Pi ion (and one net positive charge) across the cell membrane. Sequence comparison of electrogenic NaPi-IIa and IIb isoforms with the electroneutral NaPi-IIc isoform pointed to the third transmembrane domain (TMD-3) as a possibly significant determinant of substrate binding. To elucidate the role of TMD-3 in the topology and mechanism underlying NaPi-IIa function we subjected it to cysteine scanning mutagenesis. The constructs were expressed in Xenopus oocytes and Pi transport kinetics were assayed by electrophysiology and radiotracer uptake. Cys substitution resulted in only marginally altered kinetics of Pi transport in those mutants providing sufficient current for analysis. Only one site, at the extracellular end of TMD-3, appeared to be accessible to methanethiosulfonate reagents. However, additional mutations carried out at D224 (replaced by E, G or N) and N227 (replaced by D or Q) resulted in markedly altered voltage and substrate dependencies of the Pi-dependent currents. Replacing Asp-224 (highly conserved in electrogenic a and b isoforms) with Gly (the residue found in the electroneutral c isoform) resulted in a mutant that mediated electroneutral Na+-dependent Pi transport. Since electrogenic NaPi-II transports 3 Na+/transport cycle, whereas electroneutral NaPi-IIc only transports 2, we speculate that this loss of electrogenicity might result from the loss of one of the three Na+ binding sites in NaPi-IIa

Published
2018

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