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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.


SGK-1::GFP did not colocalize with RFP::RAB-5, mCHERRY::MANS or mCHERRY::TRAM.Confocal images of the intestine in transgenic worms expressing SGK-1::GFP together with RFP::RAB-5 (A-A”), mCHERRY::MANS (B-B”) or mCHERRY::TRAM (C-C”). Insets show magnified areas (× 2). Scale bars: 5 μm.
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pone.0130778.g009: SGK-1::GFP did not colocalize with RFP::RAB-5, mCHERRY::MANS or mCHERRY::TRAM.Confocal images of the intestine in transgenic worms expressing SGK-1::GFP together with RFP::RAB-5 (A-A”), mCHERRY::MANS (B-B”) or mCHERRY::TRAM (C-C”). Insets show magnified areas (× 2). Scale bars: 5 μm.

Mentions: To find out where SGK-1 may physically interact with the membrane trafficking system, we examined the distribution of SGK-1::GFP driven by its own promoter. SGK-1::GFP was expressed at a high level in the intestine, as well as the head and tail neurons (S13 Fig). In the intestinal cells, SGK-1::GFP was seen at the cortex of the plasma membrane (most prominently the apical membrane) (Fig 9A’ and S13 Fig) and throughout the cytoplasm in a diffuse pattern (Fig 9, panels B’ and C’, and S13B Fig), occasionally in punctate structures over a diffuse background (not shown). The cortical SGK-1::GFP pool did not colocalize with RFP::RAB-5 (Fig 9, panels A, A’ and A”). The diffused appearance of SGK-1::GFP in the cytoplasm precludes the conclusion of co-localization of SGK-1::GFP and mCHERRY::MANS or mCHERRY::TRAM, an ER marker (Fig 9). However, it is possible that SGK-1 may interact with membrane proteins or membrane-associated proteins and is transiently recruited to organelles.


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)

SGK-1::GFP did not colocalize with RFP::RAB-5, mCHERRY::MANS or mCHERRY::TRAM.Confocal images of the intestine in transgenic worms expressing SGK-1::GFP together with RFP::RAB-5 (A-A”), mCHERRY::MANS (B-B”) or mCHERRY::TRAM (C-C”). Insets show magnified areas (× 2). Scale bars: 5 μm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0130778.g009: SGK-1::GFP did not colocalize with RFP::RAB-5, mCHERRY::MANS or mCHERRY::TRAM.Confocal images of the intestine in transgenic worms expressing SGK-1::GFP together with RFP::RAB-5 (A-A”), mCHERRY::MANS (B-B”) or mCHERRY::TRAM (C-C”). Insets show magnified areas (× 2). Scale bars: 5 μm.
Mentions: To find out where SGK-1 may physically interact with the membrane trafficking system, we examined the distribution of SGK-1::GFP driven by its own promoter. SGK-1::GFP was expressed at a high level in the intestine, as well as the head and tail neurons (S13 Fig). In the intestinal cells, SGK-1::GFP was seen at the cortex of the plasma membrane (most prominently the apical membrane) (Fig 9A’ and S13 Fig) and throughout the cytoplasm in a diffuse pattern (Fig 9, panels B’ and C’, and S13B Fig), occasionally in punctate structures over a diffuse background (not shown). The cortical SGK-1::GFP pool did not colocalize with RFP::RAB-5 (Fig 9, panels A, A’ and A”). The diffused appearance of SGK-1::GFP in the cytoplasm precludes the conclusion of co-localization of SGK-1::GFP and mCHERRY::MANS or mCHERRY::TRAM, an ER marker (Fig 9). However, it is possible that SGK-1 may interact with membrane proteins or membrane-associated proteins and is transiently recruited to organelles.

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.