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Serum- and Glucocorticoid-Inducible Kinase-1 (SGK-1) Plays a Role in Membrane Trafficking in Caenorhabditis elegans.

Zhu M, Wu G, Li YX, Stevens JK, Fan CX, Spang A, Dong MQ - PLoS ONE (2015)

Bottom Line: This effect can be explained in part by altered sphingolipid levels, because reducing glucosylceramide biosynthesis restored the localization of MIG-14::GFP.The recycling of MIG-14/Wntless through the Golgi might be partially responsible for the observed phenotype because the subcellular distribution of two plasma membrane cargoes that do not recycle through the trans-Golgi network (TGN) was affected to a lesser degree.In addition, we found that sgk-1(RNAi) induced unfolded protein response in the ER, suggesting at least an indirect role of SGK-1 early in the secretory pathway.

View Article: PubMed Central - PubMed

Affiliation: College of Life Sciences, Beijing Normal University, Beijing, China; National Institute of Biological Sciences, Beijing, Beijing, China.

ABSTRACT
The mammalian serum- and glucocorticoid-inducible kinase SGK1 regulates the endocytosis of ion channels. Here we report that in C. elegans sgk-1 mutants, GFP-tagged MIG-14/Wntless, the sorting receptor of Wnt, failed to localize to the basolateral membrane of intestinal cells; instead, it was mis-sorted to lysosomes. This effect can be explained in part by altered sphingolipid levels, because reducing glucosylceramide biosynthesis restored the localization of MIG-14::GFP. Membrane traffic was not perturbed in general, as no obvious morphological defects were detected for early endosomes, the Golgi apparatus, and the endoplasmic reticulum (ER) in sgk-1 animals. The recycling of MIG-14/Wntless through the Golgi might be partially responsible for the observed phenotype because the subcellular distribution of two plasma membrane cargoes that do not recycle through the trans-Golgi network (TGN) was affected to a lesser degree. Consistently, knockdown of the ArfGEF gbf-1 altered the distribution of SGK-1 at the basolateral membrane of intestinal cells. In addition, we found that sgk-1(RNAi) induced unfolded protein response in the ER, suggesting at least an indirect role of SGK-1 early in the secretory pathway. We propose that SGK-1 function is required for lipid homeostasis and that it acts at different intracellular trafficking steps.

No MeSH data available.


Both putative sgk-1() alleles abolished the plasma membrane localization of MIG-14::GFP in intestinal cells.Confocal images of the intestine of wild type (A, A’), sgk-1(ok538) (B, B’) and sgk-1(mg455) (C, C’) animals expressing MIG-14::GFP. In wild type intestinal cells, MIG-14::GFP is seen on the basolateral membrane (arrows, best viewed on a focal plane near the top of the cell) but not on the apical membrane (arrowheads, best viewed on a focal plane in the middle of the cell). Scale bars: 5 μm. (D) Quantitation of average pixel intensity of MIG-14::GFP localized in the cytoplasm. The average intensity is denoted with a red line. *** P value <0.001, ** P value <0.01 (Wilcoxon rank sum test).
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pone.0130778.g001: Both putative sgk-1() alleles abolished the plasma membrane localization of MIG-14::GFP in intestinal cells.Confocal images of the intestine of wild type (A, A’), sgk-1(ok538) (B, B’) and sgk-1(mg455) (C, C’) animals expressing MIG-14::GFP. In wild type intestinal cells, MIG-14::GFP is seen on the basolateral membrane (arrows, best viewed on a focal plane near the top of the cell) but not on the apical membrane (arrowheads, best viewed on a focal plane in the middle of the cell). Scale bars: 5 μm. (D) Quantitation of average pixel intensity of MIG-14::GFP localized in the cytoplasm. The average intensity is denoted with a red line. *** P value <0.001, ** P value <0.01 (Wilcoxon rank sum test).

Mentions: The distribution of MIG-14/Wntless clearly changed in sgk-1 mutants. In wild-type animals, MIG-14::GFP is located on the basolateral membrane (Fig 1A) and also on dispersed punctate structures in the cytoplasm (Fig 1A’). In two putative mutants of sgk-1, ok538 and mg455, the basolateral membrane localization of MIG-14::GFP was hardly detectable, and most of MIG-14::GFP punctate structures localized near the apical membrane and the averaged fluorescence intensity of the cytoplasmic MIG-14::GFP decreased slightly (Fig 1B–1D and S1–S5 Figs). Thus the subcellular localization of MIG-14 is dependent on SGK-1.


Serum- and Glucocorticoid-Inducible Kinase-1 (SGK-1) Plays a Role in Membrane Trafficking in Caenorhabditis elegans.

Zhu M, Wu G, Li YX, Stevens JK, Fan CX, Spang A, Dong MQ - PLoS ONE (2015)

Both putative sgk-1() alleles abolished the plasma membrane localization of MIG-14::GFP in intestinal cells.Confocal images of the intestine of wild type (A, A’), sgk-1(ok538) (B, B’) and sgk-1(mg455) (C, C’) animals expressing MIG-14::GFP. In wild type intestinal cells, MIG-14::GFP is seen on the basolateral membrane (arrows, best viewed on a focal plane near the top of the cell) but not on the apical membrane (arrowheads, best viewed on a focal plane in the middle of the cell). Scale bars: 5 μm. (D) Quantitation of average pixel intensity of MIG-14::GFP localized in the cytoplasm. The average intensity is denoted with a red line. *** P value <0.001, ** P value <0.01 (Wilcoxon rank sum test).
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4482599&req=5

pone.0130778.g001: Both putative sgk-1() alleles abolished the plasma membrane localization of MIG-14::GFP in intestinal cells.Confocal images of the intestine of wild type (A, A’), sgk-1(ok538) (B, B’) and sgk-1(mg455) (C, C’) animals expressing MIG-14::GFP. In wild type intestinal cells, MIG-14::GFP is seen on the basolateral membrane (arrows, best viewed on a focal plane near the top of the cell) but not on the apical membrane (arrowheads, best viewed on a focal plane in the middle of the cell). Scale bars: 5 μm. (D) Quantitation of average pixel intensity of MIG-14::GFP localized in the cytoplasm. The average intensity is denoted with a red line. *** P value <0.001, ** P value <0.01 (Wilcoxon rank sum test).
Mentions: The distribution of MIG-14/Wntless clearly changed in sgk-1 mutants. In wild-type animals, MIG-14::GFP is located on the basolateral membrane (Fig 1A) and also on dispersed punctate structures in the cytoplasm (Fig 1A’). In two putative mutants of sgk-1, ok538 and mg455, the basolateral membrane localization of MIG-14::GFP was hardly detectable, and most of MIG-14::GFP punctate structures localized near the apical membrane and the averaged fluorescence intensity of the cytoplasmic MIG-14::GFP decreased slightly (Fig 1B–1D and S1–S5 Figs). Thus the subcellular localization of MIG-14 is dependent on SGK-1.

Bottom Line: This effect can be explained in part by altered sphingolipid levels, because reducing glucosylceramide biosynthesis restored the localization of MIG-14::GFP.The recycling of MIG-14/Wntless through the Golgi might be partially responsible for the observed phenotype because the subcellular distribution of two plasma membrane cargoes that do not recycle through the trans-Golgi network (TGN) was affected to a lesser degree.In addition, we found that sgk-1(RNAi) induced unfolded protein response in the ER, suggesting at least an indirect role of SGK-1 early in the secretory pathway.

View Article: PubMed Central - PubMed

Affiliation: College of Life Sciences, Beijing Normal University, Beijing, China; National Institute of Biological Sciences, Beijing, Beijing, China.

ABSTRACT
The mammalian serum- and glucocorticoid-inducible kinase SGK1 regulates the endocytosis of ion channels. Here we report that in C. elegans sgk-1 mutants, GFP-tagged MIG-14/Wntless, the sorting receptor of Wnt, failed to localize to the basolateral membrane of intestinal cells; instead, it was mis-sorted to lysosomes. This effect can be explained in part by altered sphingolipid levels, because reducing glucosylceramide biosynthesis restored the localization of MIG-14::GFP. Membrane traffic was not perturbed in general, as no obvious morphological defects were detected for early endosomes, the Golgi apparatus, and the endoplasmic reticulum (ER) in sgk-1 animals. The recycling of MIG-14/Wntless through the Golgi might be partially responsible for the observed phenotype because the subcellular distribution of two plasma membrane cargoes that do not recycle through the trans-Golgi network (TGN) was affected to a lesser degree. Consistently, knockdown of the ArfGEF gbf-1 altered the distribution of SGK-1 at the basolateral membrane of intestinal cells. In addition, we found that sgk-1(RNAi) induced unfolded protein response in the ER, suggesting at least an indirect role of SGK-1 early in the secretory pathway. We propose that SGK-1 function is required for lipid homeostasis and that it acts at different intracellular trafficking steps.

No MeSH data available.