DOC PREVIEW
CALTECH APH 161 - Actin Filaments and the Growth, Movement

This preview shows page 1-2-3-4 out of 12 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 12 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 12 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 12 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 12 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 12 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

Actin Filaments and the Growth, Movement, and Spread of the Intracellular Bacterial Parasite, Listeria monocytogenes Lewis G. T'dney* and Daniel A. Portnoy* * Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6018; and * Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6076 Abstract. Listeria monocytogenes was used as a model intracellular parasite to study stages in the en- try, growth, movement, and spread of bacteria in a macrophage cell line. The first step in infection is phagocytosis of the Listeria, followed by the dissolu- tion of the membrane surrounding the phagosome pre- sumably mediated by hemolysin secreted by Listeria as nonhemolytic mutants remain in intact vacuoles. Within 2 h after infection, each now cytoplasmic Listeria becomes encapsulated by actin filaments, identified as such by decoration of the actin filaments with subfragment 1 of myosin. These filaments are very short. The Listeria grow and divide and the actin filaments rearrange to form a long tail (often 5/~m in length) extending from only one end of the bacterium, a "comet's tail," in which the actin filaments appear randomly oriented. The ~'steria "comet" moves to the cell surface with its tail oriented towards the cell center and becomes encorporated into a cell extension with the Listeria at the tip of the process and its tail trailing into the cytoplasm behind it. This extension contacts a neighboring macrophage that phagocytoses the exten- sion of the first macrophage. Thus, within the cyto- plasm of the second macrophage is a Listeria with its actin tail surrounded by a membrane that in turn is surrounded by the phagosome membrane of the new host. Both these membranes are then solubilized by the Listeria and the cycle is repeated. Thus, once in- side a host cell, the infecting Listeria and their prog- eny can spread from cell to cell by remaining intracel- lular and thus bypass the humoral immune system of the organism. To establish if actin filaments are essen- tial for the spread of Listeria from cell to cell, we treated infected macrophages with cytochalasin D. The Listeria not only failed to spread, but most were found deep within the cytoplasm, rather than near the pe- riphery of the cell. Thin sections revealed that the net of actin filaments is not formed nor is a "comet" tail produced. T HERE is an enormous biological range of organisms that function as intracellular parasites from protozoa to tiny RNA viruses. Some of these organisms are quite intimidating and cause serious human illnesses; they include viruses (rabies, yellow fever, smallpox, influenza, AIDS, to name a few), bacteria (acute diarrhea, Shigellaflex- neri; scrub typhus, Rickettsiae tsutsugamushi; Rocky Moun- tain spotted fever, Rickettsiae rickettsiae; tuberculosis, My- cobacterium tuberculosis; leprosy, Mycobacterium leprae; Legionnaires disease, Legionella pneumophila), and pro- tozoa (Chagas disease, Trypanosoma cruzi; Kala azar, Leish- mania donovani; and malaria, Plasmodium falciparum). Other parasites are much less dangerous and in fact can benefit the host; e.g., the symbiotic relationship between Chlorella (a green algae) and an epidermal cell of the fresh- water hydra, Hydra viridis. The study of intracellular para- sites illustrates the fascinating diversity of mechanisms that have evolved to allow this interaction to occur and accord- ingly helps us to learn more about the physiology of the host ceils. Furthermore, by discovering how the parasite evades the immune system of the host, we may be able to devise suit- able therapeutic protocols to control infection and/or prolif- eration of life threatening parasites. It is useful at the outset to separate intracellular parasites into two groups (Moulder, 1985). One group is comprised of parasites which throughout their lives are enclosed by a membrane of the host, an endosome; e.g., Mycobacterium, LegioneUa, Chlorella, and Plasmodium. The second group consists of parasites that grow, feed, and replicate within the cytoplasm proper, not confined by a vacuolar membrane of the host. These include T. cruzi, S. flexneri, R. tsutsuga- mushi, and L. monocytogenes. These are particularly insidi- ous as not only are they protected from the immune system of the host, being intracellular, but, as will be shown below, at least for one organism (L. monocytogenes), are also trans- mitted from cell to cell without ever leaving the host's cytoplasm. In the past 10 years, there have been two new approaches to the study of how intracellular parasites adapt to the cytoplasm of the host (Edelson, 1982; Moulder, 1985). The © The Rockefeller University Press, 0021-9525/g9/10/1597/12 $2.00 The Journal of Cell Biology, Volume 109, October 1989 1597-1608 1597 on January 17, 2005 www.jcb.orgDownloaded fromThe Journal of Cell Biology, Volume 109, 1989 1598 on January 17, 2005 www.jcb.orgDownloaded fromfirst is the use of macrophage cell lines rather than parts of infected organisms which greatly simplifies investigations into the cell biology of the parasites. The second is the use of transposon mutagenesis and techniques of molecular biol- ogy to study infection, multiplication, and spread of mutant parasites in these cell lines. Listeria monocytogenes is an intracellular parasite that penetrates, multiplies, and is transmitted from cell to cell in macrophage, fibroblast, and enterocyte cell lines. It is a model for understanding other cytoplasmic parasites (Gail- lard et al., 1986, 1987; Havell, 1986, Kuhn et al., 1988; Port- noy et al., 1988). The parasite is a pathogen that is transmit- ted in the human population by contaminated milk products, but is not extremely toxic to humans although it can be seri- ous and cause death in pregnant women and neonates and in individuals whose immune systems are compromised (Lin- nen et al., 1988) and, very rarely, in apparently healthy indi- viduals. Although it has been studied by a number of investi- gators over the past 25 years as a model for cell-mediated immunity (Hahn and Kaufman, 1981; Mackaness, 1962), so that there is a wealth of information on the immune response to Listeria, the cell biology of infection has been virtually ignored. Some .information is available on the entry of Listeria into the cytoplasm of a human carcinoma cell


View Full Document

CALTECH APH 161 - Actin Filaments and the Growth, Movement

Documents in this Course
Lecture 2

Lecture 2

12 pages

Lecture 3

Lecture 3

18 pages

Load more
Download Actin Filaments and the Growth, Movement
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Actin Filaments and the Growth, Movement and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Actin Filaments and the Growth, Movement 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?