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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.


Related in: MedlinePlus

MIG-14::GFP was delivered to early lysosomes marked by RAB-7.Confocal images of the wild type (A, A’, A”) and sgk-1() (B, B’, B”) intestinal cells expressing MIG-14::GFP (A, B) or mCHERRY::RAB-7 (A’, B’). Insets show magnified areas (× 2.5). Scale bars: 5 μm. Quantitation of RAB-7-positive ring-like vesicles with or without MIG-14::GFP puncta inside (C). *** P value <0.001, ** P value <0.01 (Student’s t-test).
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pone.0130778.g002: MIG-14::GFP was delivered to early lysosomes marked by RAB-7.Confocal images of the wild type (A, A’, A”) and sgk-1() (B, B’, B”) intestinal cells expressing MIG-14::GFP (A, B) or mCHERRY::RAB-7 (A’, B’). Insets show magnified areas (× 2.5). Scale bars: 5 μm. Quantitation of RAB-7-positive ring-like vesicles with or without MIG-14::GFP puncta inside (C). *** P value <0.001, ** P value <0.01 (Student’s t-test).

Mentions: Cargo that cannot be retrieved to the TGN remains mostly in endosomes and hence should be transported to lysosomes [42]. To test this notion, we determined the subcellular localization of MIG-14::GFP in sgk-1 mutants. In wild-type animals, late endosomes and early lysosomes are both marked by mCHERRY::RAB-7 but can be distinguished morphologically: the former are punctate structures and the latter ring-like vesicles [33, 43]. We found that mCHERRY::RAB-7 labeled ring-like vesicles contained no or only a single MIG-14::GFP punctum in the wild type (Fig 2, panels A, A’, A” and C), while most of the them contained two or more MIG-14::GFP puncta in the sgk-1 mutant, indicating that MIG-14::GFP is mis-sorted to lysosomes (Fig 2, panels B, B’, B” and C). A similar phenotype of MIG-14::GFP was reported in a mutant lacking rme-8 [42], which encodes a retromer-associated protein.


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)

MIG-14::GFP was delivered to early lysosomes marked by RAB-7.Confocal images of the wild type (A, A’, A”) and sgk-1() (B, B’, B”) intestinal cells expressing MIG-14::GFP (A, B) or mCHERRY::RAB-7 (A’, B’). Insets show magnified areas (× 2.5). Scale bars: 5 μm. Quantitation of RAB-7-positive ring-like vesicles with or without MIG-14::GFP puncta inside (C). *** P value <0.001, ** P value <0.01 (Student’s t-test).
© Copyright Policy
Related In: Results  -  Collection

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

pone.0130778.g002: MIG-14::GFP was delivered to early lysosomes marked by RAB-7.Confocal images of the wild type (A, A’, A”) and sgk-1() (B, B’, B”) intestinal cells expressing MIG-14::GFP (A, B) or mCHERRY::RAB-7 (A’, B’). Insets show magnified areas (× 2.5). Scale bars: 5 μm. Quantitation of RAB-7-positive ring-like vesicles with or without MIG-14::GFP puncta inside (C). *** P value <0.001, ** P value <0.01 (Student’s t-test).
Mentions: Cargo that cannot be retrieved to the TGN remains mostly in endosomes and hence should be transported to lysosomes [42]. To test this notion, we determined the subcellular localization of MIG-14::GFP in sgk-1 mutants. In wild-type animals, late endosomes and early lysosomes are both marked by mCHERRY::RAB-7 but can be distinguished morphologically: the former are punctate structures and the latter ring-like vesicles [33, 43]. We found that mCHERRY::RAB-7 labeled ring-like vesicles contained no or only a single MIG-14::GFP punctum in the wild type (Fig 2, panels A, A’, A” and C), while most of the them contained two or more MIG-14::GFP puncta in the sgk-1 mutant, indicating that MIG-14::GFP is mis-sorted to lysosomes (Fig 2, panels B, B’, B” and C). A similar phenotype of MIG-14::GFP was reported in a mutant lacking rme-8 [42], which encodes a retromer-associated protein.

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.


Related in: MedlinePlus