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Molecular Biology of the Cell

Cary R Boyd-Shiwarski, Daniel J Shiwarski, Ankita Roy, Lubika J Nkashama, Hima N Namboodiri, Jian Xie, Kara L McClain, Allison Marciszyn, Thomas R Kleyman, Roderick J Tan, Donna B Stolz, Manojkumar A Puthenveedu, Chou-Long Huang, Arohan R Subramanya
With-No-Lysine (WNK) kinases coordinate volume and potassium homeostasis by regulating renal tubular electrolyte transport. In the distal convoluted tubule (DCT), potassium imbalance causes WNK signaling complexes to concentrate into large discrete foci, which we call "WNK bodies." Though these structures have been reported previously, the mechanisms that drive their assembly remain obscure. Here, we show that kidney-specific WNK1 (KS-WNK1), a truncated kinase-defective WNK1 isoform that is highly expressed in the DCT, is critical for WNK body formation...
December 13, 2017: Molecular Biology of the Cell
Andreas Jeschke, Albert Haas
Phagosomes mature into phagolysosomes by sequential fusion with early endosomes, late endosomes, and lysosomes. Phagosome-with-lysosome fusion (PLF) results in the delivery of lysosomal hydrolases into phagosomes and in digestion of the cargo. The machinery that drives PLF has been little investigated. Using a cell-free system, we recently identified the phosphoinositide lipids (PIPs) phosphatidylinositol 3-phosphate [PI(3)P] and phosphatidylinositol 4-phosphate [PI(4)P] as regulators of PLF. We now report the identification and the PIP requirements of four distinct sub-reactions of PLF...
December 13, 2017: Molecular Biology of the Cell
Eigo Takeda, Natsuko Jin, Eisuke Itakura, Shintaro Kira, Yoshiaki Kamada, Lois S Weisman, Takeshi Noda, Akira Matsuura
Target of rapamycin complex 1 (TORC1) is a central cellular signaling coordinator that allows eukaryotic cells to adapt to the environment. In the budding yeast, Saccharomyces cerevisiae, TORC1 senses nitrogen and various stressors, and modulates proteosynthesis, nitrogen uptake and metabolism, stress responses, and autophagy. There is some indication that TORC1 may regulate these downstream pathways individually. However, the potential mechanisms for such differential regulation are unknown. Here we show that the serine/threonine protein kinase Sch9 branch of TORC1 signaling depends specifically on the integrity of the vacuolar membrane, and this dependency originates in changes in Sch9 localization reflected by phosphatidylinositol 3,5-bisphosphate...
December 13, 2017: Molecular Biology of the Cell
Rachel Howard-Till, Josef Loidl
Condensin is a protein complex with diverse functions in chromatin packaging and chromosome condensation and segregation. We studied condensin in the evolutionarily distant protist model Tetrahymena, which features non-canonical nuclear organization and divisions. In Tetrahymena, the germline and soma are partitioned into two different nuclei within a single cell. Consistent with their functional specializations in sexual reproduction and gene expression, condensins of the germline nucleus and the polyploid somatic nucleus are composed of different subunits...
December 13, 2017: Molecular Biology of the Cell
Régis E Meyer, Jamin Brown, Lindsay Beck, Dean S Dawson
In budding yeast meiosis, homologous chromosomes become linked by chiasmata and then move back and forth on the spindle until they are bi-oriented - with the kinetochores of the partners attached to microtubules from opposite spindle poles. Certain mutations in the conserved kinase, Mps1, result in catastrophic meiotic segregation errors but mild mitotic defects. We tested whether Dam1, a known substrate of Mps1 was necessary for its critical meiotic role. We found that kinetochore-microtubule attachments are established even when Dam1 is not phosphorylated by Mps1, but that Mps1 phosphorylation of Dam1 sustains those connections...
December 13, 2017: Molecular Biology of the Cell
Naël Osmani, Julien Pontabry, Jordi Comelles, Nina Fekonja, Jacky G Goetz, Daniel Riveline, Elisabeth Georges-Labouesse, Michel Labouesse
Hemidesmosomes (HDs) are epithelial-specific cell-matrix adhesions, which stably anchor the intracellular keratin network to the extracellular matrix. Although their main role is to protect the epithelial sheet from external mechanical strain, how HDs respond to mechanical stress remains poorly understood. Here we identify a pathway essential for HD remodeling, and outline its role with respect to α6β4 integrin recycling. We find that α6β4 integrin chains localize to the plasma membrane, caveolae and Arf6+ endocytic compartments...
December 13, 2017: Molecular Biology of the Cell
Li Zheng, Sean D Conner
The Notch signaling pathway is essential throughout development and continues into adulthood where it performs a critical role in tissue homeostasis. The fact that defects in signaling can lead to malignancy illustrate the need to tightly control Notch activity. GSK3β is an established regulator of the Notch signaling pathway, although its mechanism of action remains unclear. Given the emerging role for GSK3β in receptor trafficking, we tested the idea that GSK3β controls signaling by regulating Notch transport...
December 13, 2017: Molecular Biology of the Cell
Francesca Burgos-Bravo, Nataniel L Figueroa, Nathalie Casanova-Morales, Andrew F G Quest, Christian A M Wilson, Lisette Leyton
Thy-1 and αvβ3 integrin mediate bidirectional cell-to-cell communication between neurons and astrocytes. Thy-1/αvβ3 interactions stimulate astrocyte migration and the retraction of neuronal prolongations, both processes in which internal forces are generated affecting the bimolecular interactions that maintain cell-cell adhesion. Nonetheless, how the Thy-1/αvβ3 interactions respond to mechanical cues is an unresolved issue. In this study, optical tweezers were used as a single-molecule force transducer, and the Dudko-Hummer-Szabo Model was applied to calculate the kinetic parameters of Thy-1/αvβ3 dissociation...
December 6, 2017: Molecular Biology of the Cell
David C Stieg, Stephen D Willis, Vidyaramanan Ganesan, Kai Li Ong, Joseph Scurozo, Mia Song, Julianne Grose, Randy Strich, Katrina F Cooper
In response to oxidative stress, cells decide whether to mount a survival or cell death response. The conserved cyclin C and its kinase partner Cdk8 play a key role in this decision. Both are members of the Cdk8 kinase module that, with Med12 and Med13, associate with the core mediator complex of RNA polymerase II. In S. cerevisiae, oxidative stress triggers Med13 destruction, which thereafter releases cyclin C into the cytoplasm. Cytoplasmic cyclin C associates with mitochondria where it induces hyper-fragmentation and regulated cell death...
December 6, 2017: Molecular Biology of the Cell
Rajesh Arasada, Wasim A Sayyad, Julien Berro, Thomas D Pollard
To internalize nutrients and cell surface receptors via clathrin mediated endocytosis cells assemble at least 50 proteins including clathrin, clathrin-interacting proteins, actin filaments and actin binding proteins in a highly ordered and regulated fashion. The molecular mechanism by which actin filament polymerization deforms the cell membrane is unknown, largely due to lack of knowledge about the organization of the regulatory proteins and actin filaments. We used high-speed super-resolution localization microscopy (FPALM) of live fission yeast cells to improve the spatial resolution to ∼35 nm with 1 s temporal resolution...
December 6, 2017: Molecular Biology of the Cell
Xinming Xie, Shaojun Li, Yanting Zhu, Lu Liu, Rui Ke, Jian Wang, Xin Yan, Lan Yang, Li Gao, Weijin Zang, Manxiang Li
Loss of peroxisome proliferator-activated receptor γ (PPARγ) has been found to contribute to pulmonary artery smooth muscle cell (PASMC) proliferation and pulmonary arterial remodeling therefore the development of pulmonary hypertension (PH). Yet, the molecular mechanisms underlying PPARγ reduction in PASMC remain poorly understood. Here, we demonstrated that leptin dose- and time-dependently inducued PPARγ down-regulation and proliferation of primary cultured rat PASMC, this was accompanied with the activation of extracellular regulated kinase1/2 (ERK1/2) signaling pathway and subsequent induction of early growth response-1 (Egr-1) expression...
December 6, 2017: Molecular Biology of the Cell
Michael Bruderek, Witold Jaworek, Anne Wilkening, Cornelia Rüb, Giovanna Cenini, Arion Förtsch, Marc Sylvester, Wolfgang Voos
Aggregation processes can cause severe perturbations of cellular homeostasis and are frequently associated with diseases. We performed a comprehensive analysis of mitochondrial quality and function in presence of aggregation-prone polypeptides. Despite a significant aggregate formation inside mitochondria, we observed only a minor impairment of mitochondrial function. Detoxification of aggregated reporter polypeptides as well as endogenous proteins inside mitochondria takes place via their sequestration into a specific organellar deposit site we termed intra-mitochondrial protein quality control compartment (IMiQ)...
December 6, 2017: Molecular Biology of the Cell
Mahmoud Abdul Karim, Christopher Leonard Brett
Loss-of-function mutations in human endosomal Na+(K+)/H+ Exchangers (NHEs) NHE6 and NHE9 are implicated in neurological disorders including Christianson Syndrome, autism and attention deficit and hyperactivity disorder (ADHD). These mutations disrupt retention of surface receptors within neurons and glial cells by affecting their delivery to lysosomes for degradation. However, the molecular basis of how these endosomal NHEs control endocytic trafficking is unclear. Using Saccharomyces cerevisiae as a model, we conducted cell-free organelle fusion assays to show that transport activity of the orthologous endosomal NHE Nhx1 is important for multivesicular body (MVB)-vacuolar lysosome fusion, the last step of endocytosis required for surface protein degradation...
December 6, 2017: Molecular Biology of the Cell
Lauren Humphrey, Isabella Felzer-Kim, Ajit P Joglekar
The microtubule-associated protein Stu2 (XMAP215) has the remarkable ability to act as either a polymerase or a destabilizer of the microtubule plus-end. In budding yeast, it is required for the dynamicity of spindle microtubules and also for kinetochore force generation. To understand how Stu2 contributes to these distinct activities, we analyzed the contributions of its functional domains to its localization and function. We find that Stu2 colocalizes with kinetochores using its TOG domains, which bind GTP-tubulin, a coiled-coil homodimerization domain, and a domain that interacts with plus-end interacting proteins...
November 29, 2017: Molecular Biology of the Cell
P A Nguyen, C M Field, T J Mitchison
The cleavage furrow in Xenopus zygotes is positioned by two large microtubule asters that grow out from the poles of the 1st mitotic spindle. Where these asters meet at the midplane they assemble a disc-shaped interaction zone consisting of anti-parallel microtubule bundles coated with chromosome passenger complex (CPC) and centralspindlin which instructs the cleavage furrow. Here, we investigate the mechanism that keeps the two asters separate, and forms a distinct boundary between them, focusing on the conserved cytokinesis midzone proteins Prc1 and Kif4A...
November 29, 2017: Molecular Biology of the Cell
Jonathan Lam, Stephen Vadia, Sarika Pathak-Sharma, Eric McLaughlin, Xiaoli Zhang, Joel Swanson, Stephanie Seveau
Host cell invasion is an indispensable step for a successful infection by intracellular pathogens. Recent studies identified pathogen-induced host cell plasma membrane perforation as a novel mechanism used by diverse pathogens (Trypanosoma cruzi, Listeria monocytogenes, and adenovirus) to promote their internalization into target cells. It was concluded that T. cruzi and adenovirus damage the host cell plasma membrane to hijack the endocytic-dependent membrane resealing machinery, thereby invading the host cell...
November 29, 2017: Molecular Biology of the Cell
Brett Robison, Vincent Guacci, Douglas Koshland
Cohesin is a conserved protein complex required for sister chromatid cohesion, chromosome condensation, DNA damage repair, and regulation of transcription. Although cohesin functions to tether DNA duplexes, the contribution of its individual domains to this activity remains poorly understood. We interrogated the Smc3p subunit of cohesin by random insertion mutagenesis. Analysis of a mutant in the Smc3p hinge revealed an unexpected role for this domain in cohesion maintenance and condensation. Further investigation revealed that the Smc3p hinge functions at a step following cohesin's stable binding to chromosomes and independently of Smc3p's regulation by the Eco1p acetyltransferase...
November 29, 2017: Molecular Biology of the Cell
Karen P Haase, Jaime C Fox, Amy E Byrnes, Rebecca C Adikes, Sarah K Speed, Julian Haase, Brandon Friedman, Diana M Cook, Kerry Bloom, Nasser M Rusan, Kevin C Slep
XMAP215/Dis1 family proteins are potent microtubule polymerases, critical for mitotic spindle structure and dynamics. While microtubule polymerase activity is driven by an N-terminal TOG domain array, proper cellular localization is requisite for full activity and is mediated by a C-terminal domain. Structural insight into the C-terminal domain's architecture and localization mechanism remain outstanding. We present the crystal structure of the S. cerevisiae Stu2 C-terminal domain, revealing a 15 nm parallel homodimeric coiled coil...
November 29, 2017: Molecular Biology of the Cell
Raqual Bower, Douglas Tritschler, Kristyn VanderWaal Mills, Thomas Heuser, Daniela Nicastro, Mary E Porter
The nexin-dynein regulatory complex (N-DRC) plays a central role in the regulation of ciliary and flagellar motility. In most species, the N-DRC contains at least eleven subunits, but the specific function of each subunit is unknown. Mutations in three subunits (DRC1, DRC2/CCDC65, DRC4/GAS8) have been linked to defects in ciliary motility in humans and lead to a ciliopathy known as primary ciliary dyskinesia (PCD). Here we characterize the biochemical, structural, and motility phenotypes of two mutations in the DRC2 gene of Chlamydomonas Using high-resolution proteomic and structural approaches, we find that the C-terminal region of DRC2 is critical for the co-assembly of DRC2 and DRC1 to form the base plate of N-DRC and its attachment to the outer doublet microtubule...
November 22, 2017: Molecular Biology of the Cell
G D N Gayathri Samarasekera, Vanessa Jane Auld
Tricellular junctions (TCJs) are uniquely placed permeability barriers formed at the corners of polarized epithelia where tight junctions (TJ) in vertebrates or septate junctions (SJ) in invertebrates from three cells converge. Gliotactin is a Drosophila TCJ protein and loss of Gliotactin results in SJ and TCJ breakdown, and permeability barrier loss. When overexpressed, Gliotactin spreads away from the TCJs resulting in disrupted epithelial architecture including over-proliferation, cell delamination and migration...
November 22, 2017: Molecular Biology of the Cell
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