Arrest of Mycobacterial Phagosome Maturation Is Caused by a Block in Vesicle Fusion between Stages Controlled by rab5 and rab7*
- Laura E. Via‡,
- Dusanka Deretic§,
- Roseann J. Ulmer¶,
- Nina S. Hibler¶,
- Lukas A. Huber‖ and
- V. Deretic‡**
- From the Departments of ‡Microbiology and Immunology,§Ophthalmology and Anatomy and Cell Biology, University of Michigan Medical School, Ann Arbor, Michigan 48109, the¶Department of Microbiology, University of Texas Health Science Center, San Antonio, Texas 78284, and the ‖Research Institute of Molecular Pathology, A-1030 Vienna, Austria
Abstract
Mycobacterium tuberculosis and the closely related organism Mycobacterium bovis can survive and replicate inside macrophages. Intracellular survival is at least in part attributed to the failure of mycobacterial phagosomes to undergo fusion with lysosomes. The transformation of phagosomes into phagolysosomes involves gradual acquisition of markers from the endosomal compartment. Members of the rab family of small GTPases which confer fusion competence in the endocytic pathway are exchanged sequentially onto the phagosomal membranes in the course of their maturation. To identify the step at which the fusion capability of phagosomes containing mycobacteria is compromised, we purified green fluorescent protein-labeled M. bovis BCG phagosomal compartments (MPC) and compared GTP-binding protein profiles of these vesicles with latex bead phagosomal compartments (LBC). We report that the MPC do not acquire rab7, specific for late endosomes, even 7 days postinfection, whereas this GTP-binding protein is present on the LBC within hours after phagocytosis. By contrast, rab5 is retained and enriched with time on the MPC, suggesting fusion competence with an early endosomal compartment. Prior infection of macrophages withM. bovis BCG also affected the dynamics of rab5 and rab7 acquisition by subsequently formed LBC. Selective exclusion of rab7, coupled with the retention of rab5 on the mycobacterial phagosome, may allow organisms from the M. tuberculosis complex to avert the usual physiological destination of phagocytosed material.
Footnotes
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↵* This work was supported by National Institutes of Health Grant AI35217.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵** To whom correspondence should be addressed: Dept. of Microbiology and Immunology, University of Michigan Medical School, 5641 Medical Science Bldg. II, Ann Arbor, MI 48109-0620. Tel.: 313-763-1580; Fax: 313-647-6243; E-mail: deretic{at}umich.edu.
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↵1 The abbreviations used are: LBC, latex bead compartment(s); BCG, Bacillus Calmette-Guérin; MPC, mycobacterial phagosomal compartment(s); PAGE, polyacrylamide gel electrophoresis; GFP, green fluorescent protein.
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- Received October 31, 1996.
- Revision received February 6, 1997.
