Abstract:Pathogenic, motile, aerobic sporulating bacilli isolated from a contaminated blood culture and from air and soil were tentatively identified as Bacillus siamensis (Siribaed) the most common of the aerobic spore-formers in soil, it is probable that many of the "motile, anthrax-like" and "pathogenic subtilis" bacilli isolated by earlier workers were likewise Bacillus cereus.
“…GIV regulates epithelial cell polarity and morphogenesis (Bhandari et al, 2015; Houssin et al, 2015; Sasaki et al, 2015); it's role at cell-cell junctions has been attributed to its ability to bind PAR3 (Sasaki et al, 2015) and the cadherin-catenin complexes (Houssin et al, 2015), and accelerate nucleotide exchange on (i.e. activate) the trimeric G-protein α subunit, Gαi via its C-terminal GEF motif; Figure 1A (Sasaki et al, 2015).…”
Section: Resultsmentioning
confidence: 99%
“…Although further experiments will be needed to shed light on these mechanisms, the results presented in this work and the published literature to date support the following model (see legend Figure 7G): Energetic stress triggers AMPK signaling and phosphorylation of GIV at S245, pS245-GIV localizes to TJs, the N-terminus of GIV binds α-tubulin and junction-associated microtubule tracks. It is here that GIV may subsequently impact cell polarity and junctional integrity by assembling various functional complexes with its C-terminus, i.e., by (i) binding the Par3/Par6/aPKC polarity complex (Ohara et al, 2012; Sasaki et al, 2015); (ii) binding and modulating the endocytic trafficking of E-cadherin (Ichimiya et al, 2015); (iii) linking cadherin-catenin complexes to the actin cytoskeleton (Houssin et al, 2015); and finally, (iv) binding and activating G protein, Gαi via its GEF motif and maintaining epithelial polarity through the Par polarity complex (Sasaki et al, 2015). Each of these functional associations of GIV have been implicated in the generation of cell polarity.10.7554/eLife.20795.018Figure 7.Phosphorylation of GIV at S245 increases its ability to bind α-tubulin.( A ) Bacterially expressed and purified His-GIV-NT WT were phosphorylated (+) or not (-) with recombinant AMPK heterotrimers (α/β/γ) in vitro prior to their use in binding assays with GST-α-Tubulin-CT or GST-β-Tubulin-CT immobilized on glutathione-agarose beads.…”
Section: Resultsmentioning
confidence: 99%
“…Once activated, AMPK phosphorylates GIV at S245 (step 3) triggering its localization to the cell-cell junction (TJs) via increased ability to bind TJ-associated microtubules (Lee et al, 2007) (step 4). Once localized to the cell-cell junctions, GIV has been shown (Houssin et al, 2015) to bind AJ-localized protein complexes, e.g., α- and β-Catenins and E-cadherin and links the catenin-cadherin complexes to the actin cytoskeleton (steps 5 and 8). GIV has also been shown to bind TJ proteins, e.g., aPKC/Par3/Par6 complex (Ohara et al, 2012) (step 6), and link these proteins to G proteins and the actin cytoskeleton (Sasaki et al, 2015) (steps 7 and 8). DOI:
http://dx.doi.org/10.7554/eLife.20795.018…”
Loss of epithelial polarity impacts organ development and function; it is also oncogenic. AMPK, a key sensor of metabolic stress stabilizes cell-cell junctions and maintains epithelial polarity; its activation by Metformin protects the epithelial barrier against stress and suppresses tumorigenesis. How AMPK protects the epithelium remains unknown. Here, we identify GIV/Girdin as a novel effector of AMPK, whose phosphorylation at a single site is both necessary and sufficient for strengthening mammalian epithelial tight junctions and preserving cell polarity and barrier function in the face of energetic stress. Expression of an oncogenic mutant of GIV (cataloged in TCGA) that cannot be phosphorylated by AMPK increased anchorage-independent growth of tumor cells and helped these cells to evade the tumor-suppressive action of Metformin. This work defines a fundamental homeostatic mechanism by which the AMPK-GIV axis reinforces cell junctions against stress-induced collapse and also provides mechanistic insight into the tumor-suppressive action of Metformin.DOI:
http://dx.doi.org/10.7554/eLife.20795.001
“…GIV regulates epithelial cell polarity and morphogenesis (Bhandari et al, 2015; Houssin et al, 2015; Sasaki et al, 2015); it's role at cell-cell junctions has been attributed to its ability to bind PAR3 (Sasaki et al, 2015) and the cadherin-catenin complexes (Houssin et al, 2015), and accelerate nucleotide exchange on (i.e. activate) the trimeric G-protein α subunit, Gαi via its C-terminal GEF motif; Figure 1A (Sasaki et al, 2015).…”
Section: Resultsmentioning
confidence: 99%
“…Although further experiments will be needed to shed light on these mechanisms, the results presented in this work and the published literature to date support the following model (see legend Figure 7G): Energetic stress triggers AMPK signaling and phosphorylation of GIV at S245, pS245-GIV localizes to TJs, the N-terminus of GIV binds α-tubulin and junction-associated microtubule tracks. It is here that GIV may subsequently impact cell polarity and junctional integrity by assembling various functional complexes with its C-terminus, i.e., by (i) binding the Par3/Par6/aPKC polarity complex (Ohara et al, 2012; Sasaki et al, 2015); (ii) binding and modulating the endocytic trafficking of E-cadherin (Ichimiya et al, 2015); (iii) linking cadherin-catenin complexes to the actin cytoskeleton (Houssin et al, 2015); and finally, (iv) binding and activating G protein, Gαi via its GEF motif and maintaining epithelial polarity through the Par polarity complex (Sasaki et al, 2015). Each of these functional associations of GIV have been implicated in the generation of cell polarity.10.7554/eLife.20795.018Figure 7.Phosphorylation of GIV at S245 increases its ability to bind α-tubulin.( A ) Bacterially expressed and purified His-GIV-NT WT were phosphorylated (+) or not (-) with recombinant AMPK heterotrimers (α/β/γ) in vitro prior to their use in binding assays with GST-α-Tubulin-CT or GST-β-Tubulin-CT immobilized on glutathione-agarose beads.…”
Section: Resultsmentioning
confidence: 99%
“…Once activated, AMPK phosphorylates GIV at S245 (step 3) triggering its localization to the cell-cell junction (TJs) via increased ability to bind TJ-associated microtubules (Lee et al, 2007) (step 4). Once localized to the cell-cell junctions, GIV has been shown (Houssin et al, 2015) to bind AJ-localized protein complexes, e.g., α- and β-Catenins and E-cadherin and links the catenin-cadherin complexes to the actin cytoskeleton (steps 5 and 8). GIV has also been shown to bind TJ proteins, e.g., aPKC/Par3/Par6 complex (Ohara et al, 2012) (step 6), and link these proteins to G proteins and the actin cytoskeleton (Sasaki et al, 2015) (steps 7 and 8). DOI:
http://dx.doi.org/10.7554/eLife.20795.018…”
Loss of epithelial polarity impacts organ development and function; it is also oncogenic. AMPK, a key sensor of metabolic stress stabilizes cell-cell junctions and maintains epithelial polarity; its activation by Metformin protects the epithelial barrier against stress and suppresses tumorigenesis. How AMPK protects the epithelium remains unknown. Here, we identify GIV/Girdin as a novel effector of AMPK, whose phosphorylation at a single site is both necessary and sufficient for strengthening mammalian epithelial tight junctions and preserving cell polarity and barrier function in the face of energetic stress. Expression of an oncogenic mutant of GIV (cataloged in TCGA) that cannot be phosphorylated by AMPK increased anchorage-independent growth of tumor cells and helped these cells to evade the tumor-suppressive action of Metformin. This work defines a fundamental homeostatic mechanism by which the AMPK-GIV axis reinforces cell junctions against stress-induced collapse and also provides mechanistic insight into the tumor-suppressive action of Metformin.DOI:
http://dx.doi.org/10.7554/eLife.20795.001
“…Studies in Drosophila and mammalian cells have implicated Girdin in cadherin-mediated cell adhesion (Houssin et al, 2015; Ichimiya et al, 2015; Muramatsu et al, 2015). Analysis of cadherin/ hmr-1 or β-catenin/ hmp-2 hypomorphs showed no defects in AWB cilia and dendrite morphology or GRDN-1 localization (Figure S5A, S5B).…”
SUMMARY
Primary cilia are ubiquitous sensory organelles that mediate diverse signaling pathways. Cilia position on the cell surface is determined by the location of the basal body (BB) that templates the cilium. The mechanisms that regulate BB positioning in the context of ciliogenesis are largely unknown. Here we show that the conserved signaling and scaffolding protein Girdin localizes to the proximal regions of centrioles and regulates BB positioning and ciliogenesis in C. elegans sensory neurons and human RPE-1 cells. Girdin depletion alters localization of the intercentriolar linker and ciliary rootlet component rootletin, and rootletin knockdown in RPE-1 cells mimics Girdin-dependent phenotypes. C. elegans Girdin also regulates localization of the apical junction component AJM-1, suggesting that in nematodes, Girdin may position BBs via rootletin- and AJM-1-dependent anchoring to the cytoskeleton and plasma membrane, respectively. Together, our results describe a conserved role for Girdin in BB positioning and ciliogenesis.
“…Girdin), a multimodular polarity scaffold protein is a novel substrate of AMPK, and defined the molecular mechanisms by which the AMPK-GIV signaling axis protects the epithelium by stabilizing TJs and preserving cell polarity when challenged with energetic stress. GIV, a guanine nucleotide exchange factor (GEF) for trimeric G proteins, had previously been shown to serve as a polarity scaffold protein that regulates epithelial cell polarity and morphogenesis [35-37]. GIV's role at cell-cell junctions has been attributed to its ability to assemble various functional complexes with its C-terminus, e.g., (i) binding the Par3/Par6/ aPKC polarity complex [36, 38]; (ii) binding and modulating the endocytic trafficking of E-cadherin [39]; (iii) linking cadherin-catenin complexes to the actin cytoskeleton [37]; and finally, (iv) binding and activating G protein, Gαi via its GEF motif and maintaining epithelial polarity through the Par polarity complex [36].…”
Section: The Polarity Scaffold Giv Is a Novel Substrate And Effectomentioning
Loss of cell polarity impairs organ development and function; it can also serve as one of the first triggers for oncogenesis. In 2006-2007 two groups simultaneously reported the existence of a special pathway for maintaining epithelial polarity in the face of environmental stressors. In this pathway, AMPK, a key sensor of metabolic stress stabilizes tight junctions, preserves cell polarity, and thereby, maintains epithelial barrier functions. Accumulating evidence since has shown that pharmacologic activation of AMPK by Metformin protects the epithelial barrier against multiple environmental and pathological stressful states and suppresses tumorigenesis. How AMPK protects the epithelium remained unknown until recently Aznar et al. identified GIV/Girdin as a novel effector of AMPK at the cell-cell junctions; phosphorylation of GIV at a single site by AMPK appears to be both necessary and sufficient for strengthening tight junctions and preserving cell polarity and epithelial barrier function in the face of energetic stress. Here we review the fundamentals of this specialized signaling pathway that buttresses cell-cell junctions against stress-induced collapse and discuss its pathophysiologic relevance in the context of a variety of diseases, including cancers, diabetes, aging, and the growing list of beneficial effects of the AMPK-activator, Metformin.
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