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Intracellular Bacteria Find the Right Motion

2015; Cell Press; Volume: 161; Issue: 2 Linguagem: Inglês

10.1016/j.cell.2015.03.035

1097-4172

Edith Gouin, Juan J. Quereda, Pascale Cossart,

Coagulation, Bradykinin, Polyphosphates, and Angioedema

Benanti et al. report that Burkholderia pseudomallei and Burkholderia mallei bacteria express proteins that mimic Ena/Vasp family proteins to polymerize actin, thereby inducing actin-based motility. Thus, bacteria can use the various cellular actin polymerization mechanisms for intra- and inter-cellular dissemination. Benanti et al. report that Burkholderia pseudomallei and Burkholderia mallei bacteria express proteins that mimic Ena/Vasp family proteins to polymerize actin, thereby inducing actin-based motility. Thus, bacteria can use the various cellular actin polymerization mechanisms for intra- and inter-cellular dissemination. Intracellular bacterial pathogens such as Listeria monocytogenes and Shigella flexneri received a lot of attention in the early 1990s, when it was discovered that, after internalization by mammalian cells and escape from the endocytic vacuole, they actively recruit monomeric actin and polymerize it into filaments. This actin assembly process creates a force that then propels the bacteria through the cytosol. In this issue of Cell, Benanti et al., 2015Benanti E.L. Nguyen C.M. Welch M.D. Cell. 2015; 161 (this issue): 348-360Abstract Full Text Full Text PDF PubMed Scopus (73) Google Scholar reveal that bacterial pathogens Burkholderia pseudomallei and Burkholderia mallei move inside of cells by mimicking one of the several cellular mechanisms that control actin polymerization. The study of bacterial motility led to the discovery of the role of Arp2/3 in actin polymerization (Welch et al., 1998Welch M.D. Rosenblatt J. Skoble J. Portnoy D.A. Mitchison T.J. Science. 1998; 281: 105-108Crossref PubMed Scopus (412) Google Scholar). This seven-protein complex needs to be activated by WASP family proteins to generate a dense array of actin filaments. Polymerization of actin filaments takes place on preformed filaments at an angle of 70°, a characteristic feature that can be visualized in cells by electron microscopy or in vitro using fluorescent actin and Arp2/3. Other nucleators, such as formins or Ena/VASP proteins, as recently shown (Winkelman et al., 2014Winkelman J.D. Bilancia C.G. Peifer M. Kovar D.R. Proc. Natl. Acad. Sci. USA. 2014; 111: 4121-4126Crossref PubMed Scopus (99) Google Scholar), generate linear long filaments. These proteins act processively on barbed ends in which they sit during the entire polymerization process. Interestingly, while Listeria and Shigella use Arp2/3, the intracellular pathogens Rickettsia early in infection use Arp2/3 and later on switch to a different mechanism, expressing proteins that mimic formins to promote actin-based motility (Welch et al., 1998Welch M.D. Rosenblatt J. Skoble J. Portnoy D.A. Mitchison T.J. Science. 1998; 281: 105-108Crossref PubMed Scopus (412) Google Scholar, Suzuki et al., 1998Suzuki T. Miki H. Takenawa T. Sasakawa C. EMBO J. 1998; 17: 2767-2776Crossref PubMed Scopus (198) Google Scholar, Gouin et al., 2004Gouin E. Egile C. Dehoux P. Villiers V. Adams J. Gertler F. Li R. Cossart P. Nature. 2004; 427: 457-461Crossref PubMed Scopus (212) Google Scholar, Reed et al., 2014Reed S.C. Lamason R.L. Risca V.I. Abernathy E. Welch M.D. Curr. Biol. 2014; 24: 98-103Abstract Full Text Full Text PDF PubMed Scopus (73) Google Scholar) (see below and Figure 1). It is, however, the first time that bacterial mimics of Ena/VASP proteins are characterized (Benanti et al., 2015Benanti E.L. Nguyen C.M. Welch M.D. Cell. 2015; 161 (this issue): 348-360Abstract Full Text Full Text PDF PubMed Scopus (73) Google Scholar). The proteins encoded by the two Burkholderia species are called BpBimA and BmBimA and display three or one WH2 domains, respectively. WH2 domains bind to actin and are present in a number of actin-binding proteins, including Ena/VASP proteins. Two hallmarks of Ena/VASP proteins are their properties to oligomerize and to uncap actin filament barbed ends capped by capping proteins. Ena/VASP proteins can thus nucleate actin, elongate filaments at their barbed ends, and bundle them. Previously, it was known that the non-pathogenic species Burkholderia thailandensis expressed a BimA protein called BtBimA and that Arp2/3 was necessary to induce actin-based motility. Here, the authors demonstrate that BtBimA has a VCA domain, known to bind and activate Arp2/3. In contrast, this domain is absent in BpBimA or BmBimA of the pathogenic species. A VCA domain is also present in WASP family proteins and in ActA of Listeria (Kocks et al., 1992Kocks C. Gouin E. Tabouret M. Berche P. Ohayon H. Cossart P. Cell. 1992; 68: 521-531Abstract Full Text PDF PubMed Scopus (654) Google Scholar). ActA is a bona fide mimic of WASP family proteins (Welch et al., 1998Welch M.D. Rosenblatt J. Skoble J. Portnoy D.A. Mitchison T.J. Science. 1998; 281: 105-108Crossref PubMed Scopus (412) Google Scholar) (Figure 1). In the case of Shigella, the outer-membrane protein IcsA/VirG (Bernardini et al., 1989Bernardini M.L. Mounier J. d'Hauteville H. Coquis-Rondon M. Sansonetti P.J. Proc. Natl. Acad. Sci. USA. 1989; 86: 3867-3871Crossref PubMed Scopus (539) Google Scholar) recruits N-WASP (Suzuki et al., 1998Suzuki T. Miki H. Takenawa T. Sasakawa C. EMBO J. 1998; 17: 2767-2776Crossref PubMed Scopus (198) Google Scholar), which in turn recruits and activates Arp2/3 (Figure 1). In Rickettsia, early during infection, the protein RickA, which displays a VCA domain, mimics WASP family proteins and recruits Arp2/3 (Gouin et al., 2004Gouin E. Egile C. Dehoux P. Villiers V. Adams J. Gertler F. Li R. Cossart P. Nature. 2004; 427: 457-461Crossref PubMed Scopus (212) Google Scholar, Reed et al., 2014Reed S.C. Lamason R.L. Risca V.I. Abernathy E. Welch M.D. Curr. Biol. 2014; 24: 98-103Abstract Full Text Full Text PDF PubMed Scopus (73) Google Scholar). Later, the surface protein Sca2 acts as a formin (Reed et al., 2014Reed S.C. Lamason R.L. Risca V.I. Abernathy E. Welch M.D. Curr. Biol. 2014; 24: 98-103Abstract Full Text Full Text PDF PubMed Scopus (73) Google Scholar). As Sca2, BimA proteins belong to a family of bacterial proteins called "autotransporters" because they have the capacity to insert themselves in the outer membrane and then display their N-terminal parts on the outside of the bacterium. To this end, they trimerize via a coiled-coil domain that generates a pore through which transport does occur. In the case of BimA proteins, trimerization results in the exposure on the surface of nine WH2 domains for B. pseudomallei and three WH2 for B. mallei. In their study, Benanti et al. perform a series of in vitro assays with purified proteins, mutants analysis, observations of comet tails, and plaque assays to analyze the dissemination of the bacteria from one infected cell to its neighbors. They find that BtBimA polymerizes actin if Arp2/3 is present but does not in its absence. In contrast, the two other BimAs are able to polymerize actin in the absence of Arp2/3. They also demonstrate that the two proteins remain associated with the barbed ends as the filaments grow. The affinities of BpBimA and BmBimA for the barbed ends are in a similar range to those of formin and Ena/VASP for barbed ends, supporting the idea that they are functionally related. In addition, the two BimAs can gather two filaments and elongate them as VASP does, as well as displace CapZ from the barbed ends. By creating mutations in the coiled-coil domain, the authors establish that trimerization is critical for actin nucleation, barbed end elongation, and anti-capping activity. They then compare the tails produced by B. thailandensis, B. pseudomallei, and B. mallei and find that they are curved for B. thailandensis and straight for the two other species. Importantly, the efficiency of movement (length of displacement) is higher in the case of B. pseudomallei and B. mallei, as these bacteria moved in a linear path in contrast to B.thailandensis, which moved in a curved path, with potential implications for the pathogenicity of these species. In summary, this study unveils how bacteria can exploit different mechanisms offered by the host cell to polymerize actin. In fact, the results raise the possibility that other bacteria such as Rickettsia, although belonging to the same genus, may also use different mechanisms to move inside of cells. Finally, it remains possible that BimA proteins play other roles in infection, as is the case of ActA, which covers the bacterial surface and as a Trojan horse protects Listeria from autophagy (Yoshikawa et al., 2009Yoshikawa Y. Ogawa M. Hain T. Yoshida M. Fukumatsu M. Kim M. Mimuro H. Nakagawa I. Yanagawa T. Ishii T. et al.Nat. Cell Biol. 2009; 11: 1233-1240Crossref PubMed Scopus (345) Google Scholar), Virulent Burkholderia Species Mimic Host Actin Polymerases to Drive Actin-Based MotilityBenanti et al.CellApril 09, 2015In BriefPathogenic and non-pathogenic Burkholderia species use distinct strategies to drive actin-based motility in host cells, suggesting that mimicry of different polymerization mechanisms influences bacterial spread from cell to cell and the outcome of infection. Full-Text PDF Open ArchiveIntracellular Bacteria Find the Right MotionGouin et al.CellAugust 13, 2015In Brief(Cell 161, 199–200; April 9, 2015) Full-Text PDF Open Archive