Ras family proteins: New players involved in the diplotene arrest of <i>Xenopus</i> oocytes

Jessus, Catherine; Rime, Hélène; Ozon, René

doi:10.1111/j.1768-322x.1998.tb01066.x

Cited by 8 publications

(3 citation statements)

References 70 publications

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“…1) as well as the conferred water permeability could neither be increased nor decreased with cAMP or H89, respectively. It is well known that Xenopus oocytes are blocked in the prophase I stage of development by high intracellular cAMP levels and active PKA, whereas a progesterone-induced reduction of cAMP levels initiates meiotic divisions (Jessus et al, 1998). Therefore, the absence of an 8-Br-cAMP effect in our study is presumably caused by high levels of endogenous cAMP in oocytes, which might also explain the absence of an inhibitory effect of H89 on PKA (Fig.…”

Section: Table I Fractions Of Aqp2 Expected In the Plasma Membrane At Variable Aqp2-s256d-f/aqp2-s256a Ratiosmentioning

confidence: 54%

The Subcellular Localization of an Aquaporin-2 Tetramer Depends on the Stoichiometry of Phosphorylated and Nonphosphorylated Monomers

Kamsteeg

Heijnen

et al. 2000

The Journal of Cell Biology

166

130

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In renal principal cells, vasopressin regulates the shuttling of the aquaporin (AQP)2 water channel between intracellular vesicles and the apical plasma membrane. Vasopressin-induced phosphorylation of AQP2 at serine 256 (S256) by protein kinase A (PKA) is essential for its localization in the membrane. However, phosphorylated AQP2 (p-AQP2) has also been detected in intracellular vesicles of noninduced principal cells. As AQP2 is expressed as homotetramers, we hypothesized that the number of p-AQP2 monomers in a tetramer might be critical for the its steady state distribution. Expressed in oocytes, AQP2-S256D and AQP2-S256A mimicked p-AQP2 and non–p-AQP2, respectively, as routing and function of AQP2-S256D and wild-type AQP2 (wt-AQP2) were identical, whereas AQP2-S256A was retained intracellularly. In coinjection experiments, AQP2-S256A and AQP2-S256D formed heterotetramers. Coinjection of different ratios of AQP2-S256A and AQP2-S256D cRNAs revealed that minimally three AQP2-S256D monomers in an AQP2 tetramer were essential for its plasma membrane localization. Therefore, our results suggest that in principal cells, minimally three monomers per AQP2 tetramer have to be phosphorylated for its steady state localization in the apical membrane. As other multisubunit channels are also regulated by phosphorylation, it is anticipated that the stoichiometry of their phosphorylated and nonphosphorylated subunits may fine-tune the activity or subcellular localization of these complexes.

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Section: Table I Fractions Of Aqp2 Expected In the Plasma Membrane At Variable Aqp2-s256d-f/aqp2-s256a Ratiosmentioning

confidence: 54%

The Subcellular Localization of an Aquaporin-2 Tetramer Depends on the Stoichiometry of Phosphorylated and Nonphosphorylated Monomers

Kamsteeg

Heijnen

et al. 2000

The Journal of Cell Biology

166

130

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“…Depending on the cell type and on the extracellular signal, Ras proteins interact with various effectors, including Raf kinase, phosphatidylinositol 3 (PI3) kinase and Ral-GDS (Burgering and Bos, 1995). In the Xenopus oocyte, injection of human H-RasV12 protein induces activation of cdc2, p42 MAPK and meiotic maturation (for review, see Jessus et al, 1998). However, there are contradictory data in the abundant literature concerning the pathway induced by human H-RasV12 in the oocyte.…”

Section: Discussionmentioning

confidence: 98%

Xenopus H-RasV12 promotes entry into meiotic M phase and cdc2 activation independently of Mos and p42MAPK

et al. 2002

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In the Xenopus oocyte, progesterone triggers M phase Promoting Factor (MPF) activation in a protein synthesis dependent manner. Although the synthesis of the p42 MAPK activator Mos appears to be required for MPF activation, p42 MAPK activity has been shown to be dispensable. To clarify this paradox, we attempted to activate the p42 MAPK pathway independently of Mos synthesis by cloning and using Xenopus H-Ras in the oocyte. We demonstrate that the injection of the constitutively active Xe H-RasV12 mutant induces p42 MAPK and MPF activation through two independent pathways. Xe H-RasV12 induces only a partial activation of p42 MAPK when protein synthesis and MPF activation are prevented. A full level of p42 MAPK activation is reached when MPF is activated and Mos is present. In contrast, MPF activation induced by Xe HRasV12 is achieved independently of Mos synthesis and p42 MAPK activation but still depends on protein synthesis. Therefore, the amphibian oocyte represents a new model system to analyse an original H-Ras pathway ending to MPF activation and distinct from the p42 MAPK pathway. The identification of the proteins synthesized in response to Xe H-RasV12 and required for MPF activation, represents an important clue in understanding the mechanism of progesterone action.

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“…This concept has precedence with the AQP2 water channel in which high, but variable, levels of channel phosphorylation in Xenopus oocytes can yield contrasting effects of exogenous cAMP on the PKA-dependent surface expression response (52,53). It is well known that Xenopus oocytes are developmentally arrested at the first meiotic prophase by high intracellular cAMP and active PKA levels and that meiotic maturation depends on a progesteroneinduced reduction in cAMP (54). The high levels of active PKA, in turn, generally drive a high basal activity of ROMK in this expression system (12,15).…”

Section: Discussionmentioning

confidence: 99%

Cell Surface Expression of the ROMK (Kir 1.1) Channel Is Regulated by the Aldosterone-induced Kinase, SGK-1, and Protein Kinase A

Yoo¹,

Kim

Campo

et al. 2003

Journal of Biological Chemistry

159

146

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The Kir1.1 (ROMK) subtypes of inward rectifier K ؉ channels mediate potassium secretion and regulate sodium chloride reabsorption in the kidney. The density of ROMK channels on the cortical collecting duct apical membrane is exquisitely regulated in concert with physiological demands. Although protein kinase A-dependent phosphorylation of one of the three phospho-acceptors in Kir1.1, Ser-44, also a canonical serum-glucocorticoid-regulated kinase (SGK-1) phosphorylation site, controls the number of active channels, it is unknown whether this involves activating dormant channels already residing on the plasma membrane or recruiting new channels to the cell surface. Here we explore the mechanism and test whether SGK-1 phosphorylation of ROMK regulates cell surface expression. Removal of the phosphorylation site by point mutation (Kir1.1, S44A) dramatically attenuated the macroscopic current density in Xenopus oocytes. As measured by antibody binding of external epitope-tagged forms of Kir1.1, surface expression of Kir1.1 S44A was inhibited, paralleling the reduction in macroscopic current. In contrast, surface expression and macroscopic current density was augmented by a phosphorylation mimic mutation, Kir1.1 S44D. In vitro phosphorylation assays revealed that Ser-44 is a substrate of SGK-1 phosphorylation, and expression of SGK-1 with the wild type channel increased channel density to the same level as the phosphorylation mimic mutation. Moreover, the stimulatory effect of SGK-1 was completely abrogated by mutation of the phosphorylation site. In conclusion, SGK-1 phosphorylation of Kir1.1 drives expression on the plasmalemma. Because SGK-1 is an early aldosterone-induced gene, our results suggest a possible molecular mechanism for aldosterone-dependent regulation of the secretory potassium channel in the kidney.Extracellular potassium homeostasis, maintained by the regulation of renal potassium excretion, is dependent on the activity of weakly inward rectifying ''small conductance'' potassium channels (SK) 1 that are expressed on the apical membrane of epithelial cells in the distal nephron (1, 2). Encoded by the ROMK (Kir 1.1 or KCNJ1) gene (3, 4), these Kir channels are thought to be the major, but not exclusive (5, 6), route for potassium transport into the tubule lumen and constitute a final regulated component of the potassium secretory machinery of the kidney (7,8). Indeed, aldosterone, vasopressin, and other factors precisely regulate SK activity, controlling potassium excretion in accord with the demands of potassium balance. Because ROMK channels normally exhibit a very high open probability, near unity, physiologic augmentation of channel activity, as controlled by hormones and dietary potassium (9), is achieved largely by regulated changes in the number of active channels on the plasmalemma.Although the precise molecular mechanisms responsible for physiological augmentation of ROMK channel surface density have remained unclear, a growing body of evidence has pointed to an important role of protein kina...

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Ras family proteins: New players involved in the diplotene arrest of Xenopus oocytes

Cited by 8 publications

References 70 publications

The Subcellular Localization of an Aquaporin-2 Tetramer Depends on the Stoichiometry of Phosphorylated and Nonphosphorylated Monomers

The Subcellular Localization of an Aquaporin-2 Tetramer Depends on the Stoichiometry of Phosphorylated and Nonphosphorylated Monomers

Xenopus H-RasV12 promotes entry into meiotic M phase and cdc2 activation independently of Mos and p42MAPK

Cell Surface Expression of the ROMK (Kir 1.1) Channel Is Regulated by the Aldosterone-induced Kinase, SGK-1, and Protein Kinase A

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