Sequential breakdown of 3-phosphorylated phosphoinositides is essential for the completion of macropinocytosis
Masashi Maekawa, Shimpei Terasaka, Yasuhiro Mochizuki, Katsuhisa Kawai, Yuka Ikeda, Nobukazu Araki, Edward Y. Skolnik, Tomohiko Taguchi, and Hiroyuki Arai
Macropinocytosis is a form of endocytosis that is accompanied by ruffling of plasma membrane and participates in a diverse range of pathophysiological processes, such as antigen uptake by immune cells and tumor growth. However, the molecular mechanism underlying this process is poorly understood. By exploiting the studies of fluid-phase endocytosis in Caenorhabditis elegans, we found (pp. E978–E987) that dephosphorylation of phosphoinositide PI(3)P is essential for macropinocytosis in mammalian cells. We also found that the sequential dephosphorylation of PI(3,4,5)P3 → PI(3,4)P2 → PI(3)P → PI at membrane ruffles is required for macropinocytosis. Identification of phosphoinositide phosphatases in the dephosphorylation cascade and a PI(3)P-sensitive K+ channel as essential factors for macropinocytosis may provide the way to selectively control macropinocytosis among various endocytic pathways.
Activation induced deaminase C-terminal domain links DNA breaks to end protection and repair during class switch recombination
Astrid Zahn, Anil K. Eranki, Anne-Marie Patenaude, Stephen P. Methot, Heather Fifield, Elena M. Cortizas, Paul Foster, Kohsuke Imai, Anne Durandy, Mani Larijani, Ramiro E. Verdun, and Javier M. Di Noia
The enzyme activation-induced deaminase (AID) triggers antibody class switch recombination (CSR), a critical mechanism for immune response. CSR is an intrachromosomal rearrangement requiring DNA double strand breaks that are initiated by AID and must be repaired by specific DNA repair pathways. We identify (pp. E988–E997) a domain of AID that is required to link the DNA damage step with the subsequent repair during CSR as well as for chromosomal translocations, a collateral effect of CSR. AID influences the recruitment of appropriate end-joining pathways for CSR, preventing aberrant DNA processing that leads to cell death or nonproductive repair and dominant-negative effects. Our results can also explain the basis of an autosomal dominant immunodeficiency caused by C-terminally truncated AID variants.
Dendritic cell fate is determined by BCL11A
Gregory C. Ippolito, Joseph D. Dekker, Yui-Hsi Wang, Bum-Kyu Lee, Arthur L. Shaffer, IIIJian Lin, Jason K. Wall, Baeck-Seung Lee, Louis M. Staudt, Yong-Jun Liu, Vishwanath R. Iyer, and Haley O. Tucker
This work demonstrates a key role of the B lymphocyte transcription factor BCL11A in dendritic cell (DC) development. Two major DC subsets—the plasmacytoid DC (pDC) and the conventional DC (cDC)—are believed to arise from a shared precursor called the common DC progenitor (CDP). Potential precursor differences between cDC and pDC generation might nevertheless remain to be elucidated. Here, we show that mutant mice can generate CDPs and cDCs in the absence of BCL11A, whereas pDCs (and also B cells) are abolished. This study (pp. E998–E1006) also identifies and validates BCL11A target genes using a variety of techniques, and provides a molecular model for BCL11A activity in the B lymphocyte and pDC lineages.
Duality of the murine CD8 compartment
Raphaël Genolet, Julie Leignadier, Magne Østerås, Laurent Farinelli, Brian J. Stevenson, and Immanuel F. Luescher
CD8αβ is expressed on CD8+ T cells and can govern their thymic selection, differentiation, and effector functions by inducing Ca2+ and nuclear factor of activated T cells (NFAT)-dependent signaling. Conversely, we showed that CD8-independent T cells are signaled in a Ca2+-independent, PI3K-dependent manner. By assessing the physical and functional affinities, signaling, and TCR repertoires of CD8-dependent and -independent T cells, we uncovered (pp. E1007–E1015) correlates between effector functions, their triggering, and the TCR repertoires. We suggest that the docking orientations of TCR–MHC complexes may influence CD8+ T-cell signaling and hence their functions. Together, these data argue that signaling events rather than affinity determine CD8 dependency and that the duality of the CD8 compartment may provide the organisms with broader protective immunity.
Differential regulation of S-region hypermutation and class-switch recombination by noncanonical functions of uracil DNA glycosylase
Ashraf S. Yousif, Andre Stanlie, Samiran Mondal, Tasuku Honjo, and Nasim A. Begum
Uracil DNA glycosylase (UNG) has been known as a critical base excision repair protein required for class switch recombination (CSR) and somatic hypermutation (SHM). On the other hand, its precise function in both CSR and SHM is extremely debatable and elusive. Here (pp. E1016–E1024), we showed that UNG suppresses S region SHM (s-SHM) by recruiting the faithful DNA repair complex and, in the absence of UNG, the error-prone repair complex that induces s-SHM overrides. Moreover, UNG promotes activation-induced cytidine deaminase-induced CSR by regulating S-S synapse and DNA end repair. Interestingly, the enzymatic activity of UNG is dispensable for s-SHM suppression and CSR promotion.
Rod-like bacterial shape is maintained by feedback between cell curvature and cytoskeletal localization
Tristan S. Ursell, Jeffrey Nguyen, Russell D. Monds, Alexandre Colavin, Gabriel Billings, Nikolay Ouzounov, Zemer Gitai, Joshua W. Shaevitz, and Kerwyn Casey Huang
Across all kingdoms of life, maintaining the correct cell shape is critical for behaviors such as sensing, motility, surface attachment, and nutrient acquisition. Maintaining proper shape requires cellular-scale coordination of proteins and feedback systems that enable responses that correct local morphological perturbations. Here (pp. E1025–E1034), we demonstrate that the MreB cytoskeleton in Escherichia coli preferentially localizes to regions of negative curvature, directing growth away from the poles and actively straightening locally curved regions of the cell. Moreover, our biophysical simulations of curvature-biased growth suggest that cell wall insertion causes surface deformations that could be responsible for the circumferential motion of MreB. Taken together, our work demonstrates that MreB’s local orchestration of persistent, bursty growth enables robust, uniform growth at the cellular scale.
Blood–spinal cord barrier disruption contributes to early motor-neuron degeneration in ALS-model mice
Ethan A. Winkler, Jesse D. Sengillo, Abhay P. Sagare, Zhen Zhao, Qingyi Ma, Edward Zuniga, Yaoming Wang, Zhihui Zhong, John S. Sullivan, John H. Griffin, Don W. Cleveland, and Berislav V. Zlokovic
The blood–spinal cord barrier (BSCB) is damaged in human ALS and rodents expressing ALS-associated superoxide dismutase mutations. The role of BSCB breakdown in disease pathogenesis remains, however, unclear. Early motor-neuron dysfunction and injury are now shown to be proportional to the degree of BSCB disruption, and early protection of the BSCB integrity with an activated protein C analog is found to delay onset of motor-neuron impairment and degeneration. Altogether, these findings (pp. E1035–E1042) in mice show that BSCB breakdown plays a role in early-stage disease pathogenesis and that restoring BSCB integrity retards the disease process. These findings are relevant to the corresponding disease mechanism in human ALS in which ALS-associated vascular pathology is associated.
Fatty acid-inducible ANGPTL4 governs lipid metabolic response to exercise
Milène Catoire, Sheril Alex, Nicolas Paraskevopulos, Frits Mattijssen, Inkie Evers-van Gogh, Gert Schaart, Jacob Jeppesen, Anita Kneppers, Marco Mensink, Peter J. Voshol, Gunilla Olivecrona, Nguan Soon Tan, Matthijs K. C. Hesselink, Jimmy F. Berbée, Patrick C. N. Rensen, Eric Kalkhoven, Patrick Schrauwen, and Sander Kersten
Physical exercise causes profound changes in energy metabolism in humans. In this study we show that resting skeletal muscle has a crucial role in the metabolic response to acute exercise. During endurance exercise, selective induction of the protein angiopoietin-like 4 (ANGPTL4) in nonexercising muscle reduces local fatty acid uptake, presumably to prevent fat overload, while directing fatty acids to the active skeletal muscle as fuel. Our data (pp. E1043–E1052) thus suggest that nonexercising muscle has a key role in governing lipid homeostasis during exercise.
Endogenous localizome identifies 43 mitotic kinesins in a plant cell
Tomohiro Miki, Haruko Naito, Momoko Nishina, and Gohta Goshima
It has been a mystery as to why plants have many more kinesins than do animals (e.g., 45 in humans, >60 in land plants). To address this issue, the experimental analysis of each kinesin is critical. However, it has not been trivial to analyze >60 kinesins in a comprehensive manner in plants. Here (pp. E1053–E1061), by using endogenous YFP tagging, we found that as many as 43 kinesins are localized to the mitotic apparatus in the moss Physcomitrella patens. All but one kinesin showed a localization pattern distinct from the animal homologues, indicating the necessity of studying individual kinesin functions in plants.