Publications

2018

• Role of aIF1 in Pyrococcus abyssi translation initiation
  
  • Monestier Auriane
  • Lazennec-Schurdevin Christine
  • Coureux Pierre-Damien
  • Mechulam Yves
  • Schmitt Emmanuelle
  Nucleic Acids Research, Oxford University Press, 2018, 46 (20), pp.11061-11074. In archaeal translation initiation, a preinitiation complex (PIC) made up of aIF1, aIF1A, the ternary complex (TC, e/aIF2-GTP-Met-tRNA i Met) and mRNA bound to the small ribosomal subunit is responsible for start codon selection. Many archaeal mRNAs contain a Shine-Dalgarno (SD) sequence allowing the PIC to be prepositioned in the vicinity of the start codon. Nevertheless, cryo-EM studies have suggested local scanning to definitely establish base pairing of the start codon with the tRNA anticodon. Here, using flu-orescence anisotropy, we show that aIF1 and mRNA have synergistic binding to the Pyrococcus abyssi 30S. Stability of 30S:mRNA:aIF1 strongly depends on the SD sequence. Further, toeprinting experiments show that aIF1-containing PICs display a dynamic conformation with the tRNA not firmly accommodated in the P site. AIF1-induced destabilization of the PIC is favorable for proofreading erroneous initiation complexes. After aIF1 departure, the stability of the PIC increases reflecting initiator tRNA fully base-paired to the start codon. Altogether, our data support the idea that some of the main events governing start codon selection in eukaryotes and archaea occur within a common structural and functional core. However, idiosyncratic features in loop 1 sequence involved in 30S:mRNA binding suggest adjustments of e/aIF1 functioning in the two domains. (10.1093/nar/gky850)
  DOI : 10.1093/nar/gky850
• GBF1 and Arf1 interact with Miro and regulate mitochondrial positioning within cells
  
  • Walch Laurence
  • Pellier Emilie
  • Leng Weihua
  • Lakisic Goran
  • Gautreau Alexis
  • Contremoulins Vincent
  • Verbavatz Jean-Marc
  • Jackson Catherine
  Scientific Reports, Nature Publishing Group, 2018, 8, pp.17121. The spatial organization of cells depends on coordination between cytoskeletal systems and intracellular organelles. The Arf1 small G protein and its activator GBF1 are important regulators of Golgi organization, maintaining its morphology and function. Here we show that GBF1 and its substrate Arf1 regulate the spatial organization of mitochondria in a microtubule-dependent manner. Miro is a mitochondrial membrane protein that interacts through adaptors with microtubule motor proteins such as cytoplasmic dynein, the major microtubule minus end directed motor. We demonstrate a physical interaction between GBF1 and Miro, and also between the active GTP-bound form of Arf1 and Miro. Inhibition of GBF1, inhibition of Arf1 activation, or overexpression of Miro, caused a collapse of the mitochondrial network towards the centrosome. The change in mitochondrial morphology upon GBF1 inhibition was due to a twofold increase in the time engaged in retrograde movement compared to control conditions. Electron tomography revealed that GBF1 inhibition also resulted in larger mitochondria with more complex morphology. Miro silencing or drug inhibition of cytoplasmic dynein activity blocked the GBF1-dependent repositioning of mitochondria. Our results show that blocking GBF1 function promotes dynein-and Miro-dependent retrograde mitochondrial transport along microtubules towards the microtubule-organizing center, where they form an interconnected network. (10.1038/s41598-018-35190-0)
  DOI : 10.1038/s41598-018-35190-0
• The trimeric coiled‐coil HSBP 1 protein promotes WASH complex assembly at centrosomes
  
  • Visweshwaran Sai
  • Thomason Peter
  • Guérois Raphaël
  • Vacher Sophie
  • Denisov Evgeny V
  • Tashireva Lubov
  • Lomakina Maria
  • Lazennec‐schurdevin Christine
  • Lakisic Goran
  • Lilla Sergio
  • Molinie Nicolas
  • Henriot Veronique
  • Mechulam Yves
  • Alexandrova Antonina
  • Cherdyntseva Nadezhda
  • Bièche Ivan
  • Schmitt Emmanuelle
  • Insall Robert
  • Gautreau Alexis
  EMBO Journal, EMBO Press, 2018, 37 (13), pp.e97706. The Arp2/3 complex generates branched actin networks that exert pushing forces onto different cellular membranes. WASH complexes activate Arp2/3 complexes at the surface of endosomes and thereby fission transport intermediates containing endocy-tosed receptors, such as a5b1 integrins. How WASH complexes are assembled in the cell is unknown. Here, we identify the small coiled-coil protein HSBP1 as a factor that specifically promotes the assembly of a ternary complex composed of CCDC53, WASH, and FAM21 by dissociating the CCDC53 homotrimeric precursor. HSBP1 operates at the centrosome, which concentrates the building blocks. HSBP1 depletion in human cancer cell lines and in Dictyos-telium amoebae phenocopies WASH depletion, suggesting a critical role of the ternary WASH complex for WASH functions. HSBP1 is required for the development of focal adhesions and of cell polarity. These defects impair the migration and invasion of tumor cells. Overexpression of HSBP1 in breast tumors is associated with increased levels of WASH complexes and with poor prognosis for patients. (10.15252/embj.201797706)
  DOI : 10.15252/embj.201797706
• The Arp2/3 Regulatory System and Its Deregulation in Cancer
  
  • Molinie Nicolas
  • Gautreau Alexis
  Physiological Reviews, American Physiological Society, 2018, 98 (1), pp.215-238. (10.1152/physrev.00006.2017)
  DOI : 10.1152/physrev.00006.2017