Up-regulation of sodium pump activity in <i>Xenopus laevis</i> oocytes by expression of heterologous <i>β</i>1 subunits of the sodium pump

Schmalzing, Günther; Gloor, Sergio M.; Omay, Halit; Kröner, Silke; Appelhans, Heribert; Schwarz, Wolfgang

doi:10.1042/bj2790329

Cited by 72 publications

(64 citation statements)

References 45 publications

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“…However, given that all combinations of Na + /K + ATPase α and β subunits form functional ion pumps (Lemas et al, 1994;Schmalzing et al, 1991;Schmalzing et al, 1997), these results also raise the possibility that neither nrv2 isoform has specific functions and that any β subunit could substitute for Nrv2. We therefore tested whether either of the two other Drosophila Na + /K + ATPase β subunits, nrv1 (Sun and Salvaterra, 1995b) or nrv3 (CG8663), had tube-size or barrier activities.…”

Section: Nrv21 and Nrv22 Both Have Tracheal Tube-size Control And Jmentioning

confidence: 85%

The Na+/K+ ATPase is required for septate junction function and epithelial tube-size control in theDrosophilatracheal system

et al. 2003

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Although the correct architecture of epithelial tubes is crucial for the function of organs such as the lung, kidney and vascular system, little is known about the molecular mechanisms that control tube size. We show that mutations in the ATPα α and nrv2 β subunits of the Na+/K+ ATPase cause Drosophila tracheal tubes to have increased lengths and expanded diameters. ATPαand nrv2 mutations also disrupt stable formation of septate junctions, structures with some functional and molecular similarities to vertebrate tight junctions. The Nrv2 β subunit isoforms have unique tube size and junctional functions because Nrv2, but not other DrosophilaNa+/K+ ATPase β subunits, can rescue nrv2mutant phenotypes. Mutations in known septate junctions genes cause the same tracheal tube-size defects as ATPα and nrv2 mutations,indicating that septate junctions have a previously unidentified role in epithelial tube-size control. Double mutant analyses suggest that tube-size control by septate junctions is mediated by at least two discernable pathways,although the paracellular diffusion barrier function does not appear to involved because tube-size control and diffusion barrier function are genetically separable. Together, our results demonstrate that specific isoforms of the Na+/K+ ATPase play a crucial role in septate junction function and that septate junctions have multiple distinct functions that regulate paracellular transport and epithelial tube size.

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Section: Nrv21 and Nrv22 Both Have Tracheal Tube-size Control And Jmentioning

confidence: 85%

The Na+/K+ ATPase is required for septate junction function and epithelial tube-size control in theDrosophilatracheal system

et al. 2003

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“…(Paul et al, 2003)]. This finding was surprising because in vitro studies concluded that virtually any Na,K-ATPase ␤-subunit can associate with an ␣-subunit to generate a functional ion pump (reviewed by Blanco and Mercer, 1998;Schmalzing et al, 1991). To begin to understand the molecular basis of these Nrv2-specific activities, we created isoform-specific reagents to determine the endogenous subcellular localizations of these proteins (Figs 1, 2 and see Materials and methods).…”

Section: Assays Of Sj Functionmentioning

confidence: 99%

“…Given the high degree of conservation between ␣-subunits in eukaryotes (>70% identity between flies and vertebrates), and the fact that multiple combinations of ␣-and ␤-subunits of the different species can form functional complexes (Schmalzing et al, 1991), we investigated whether a vertebrate ␣-subunit could function in the fly context. We selected rat ␣1 because, of the four vertebrate ␣-subunit isoforms, ␣1 is the only one expressed in all epithelial tissues and therefore seemed the most likely to have a junctional function (Blanco, 2005).…”

Section: Ion-pump-independence Of the Nak-atpase Tube Size And Barrimentioning

confidence: 99%

A pump-independent function of the Na,K-ATPase is required for epithelial junction function and tracheal tube-size control

2007

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The heterodimeric Na,K-ATPase has been implicated in vertebrate and invertebrate epithelial cell junctions, morphogenesis and oncogenesis, but the mechanisms involved are unclear. We previously showed that the Drosophila Na,K-ATPase is required for septate junction (SJ)formation and that of the three β-subunit loci, only Nrv2 isoforms support epithelial SJ barrier function and tracheal tube-size control. Here we show that Nrv1 is endogenously co-expressed with Nrv2 in the epidermis and tracheal system, but Nrv1 has a basolateral localization and appears to be excluded from the Nrv2-containing SJs. When the normally neuronal Nrv3 is expressed in epithelial cells, it does not associate with SJs. Thus, theβ-subunit is a key determinant of Na,K-ATPase subcellular localization as well as function. However, localization of the Na,K-ATPase to SJs is not sufficient for junctional activity because although several Nrv2/Nrv3 chimericβ-subunits localize to SJs, only those containing the extracellular domain of Nrv2 have junctional activity. Junctional activity is also specific to different α-subunit isoforms, with only some isoforms from the majorα-subunit locus being able to provide full barrier function and produce normal tracheal tubes. Importantly, mutations predicted to inactivate ATPα catalytic function do not compromise junctional activity,demonstrating that the Drosophila Na,K-ATPase has an ion-pump-independent role in junction formation and tracheal morphogenesis. These results define new functions for the intensively studied Na,K-ATPase. Strikingly, the rat α1 isoform has full junctional activity and can rescue Atpα-null mutants to viability, suggesting that the Na,K-ATPase has an evolutionarily conserved role in junction formation and function.

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“…cRNA Synthesis and Oocyte Expression-Capped cRNAs were synthesized from linearized templates with SP6 RNA polymerase (Amersham Pharmacia Biotech) and purified as described (26). For oocyte injection, the cRNAs were dissolved in 5 mM Tris/HCl, pH 7.5, at 0.5 g/l, using the absorbance reading at 260 nm for quantitation (A 1.0 ϭ 40 g/l).…”

Section: Materials and Antibodies-sulfosuccinimidyl-3-(4-hydroxyphenyl)mentioning

confidence: 99%

Ubiquitination Precedes Internalization and Proteolytic Cleavage of Plasma Membrane-bound Glycine Receptors

Büttner¹,

Sadtler²,

Leyendecker³

et al. 2001

Journal of Biological Chemistry

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The inhibitory glycine receptor (GlyR) in developing spinal neurones is internalized efficiently upon antagonist inhibition. Here we used surface labeling combined with affinity purification to show that homopentameric ␣1 GlyRs generated in Xenopus oocytes are proteolytically nicked into fragments of 35 and 13 kDa upon prolonged incubation. Nicked GlyRs do not exist at the cell surface, indicating that proteolysis occurs exclusively in the endocytotic pathway. Consistent with this interpretation, elevation of the lysosomal pH, but not the proteasome inhibitor lactacystin, prevents GlyR cleavage. Prior to internalization, ␣1 GlyRs are conjugated extensively with ubiquitin in the plasma membrane. Our results are consistent with ubiquitination regulating the endocytosis and subsequent proteolysis of GlyRs residing in the plasma membrane. Ubiquitin-conjugating enzymes thus may have a crucial role in synaptic plasticity by determining postsynaptic receptor numbers.The efficiency of synaptic transmission depends critically on a dense packing of neurotransmitter receptors in the postsynaptic membrane. At fast synapses, ligand-gated ion channels (LGICs) 1 mediate the postsynaptic response. Different lines of evidence indicate that the distribution and density of LGICs in the plasma membrane are regulated tightly. In differentiating muscle fibers, the formation of a densely packed postsynaptic matrix of nicotinic acetylcholine receptors (nAChRs) at the developing motor endplate requires restriction of gene expression to subsynaptic nuclei, efficient internalization and degradation of extrasynaptic receptors, synaptic clustering by rapsyn, and slowing of the turnover of synaptically accumulated nAChRs (1, 2). Inversely, muscle denervation (2) or blockade of neurotransmission by ␣-bungarotoxin (3) causes a loss of nAChRs from the postsynaptic membrane because of an increased rate of protein turnover (4). Because nAChR degradation occurs only after internalization and lysosomal targeting of the receptor protein (4, 5

show abstract

Up-regulation of sodium pump activity in Xenopus laevis oocytes by expression of heterologous β1 subunits of the sodium pump

Cited by 72 publications

References 45 publications

The Na+/K+ ATPase is required for septate junction function and epithelial tube-size control in theDrosophilatracheal system

The Na+/K+ ATPase is required for septate junction function and epithelial tube-size control in theDrosophilatracheal system

A pump-independent function of the Na,K-ATPase is required for epithelial junction function and tracheal tube-size control

Ubiquitination Precedes Internalization and Proteolytic Cleavage of Plasma Membrane-bound Glycine Receptors

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