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Infect Immun, June 1998, p. 2905-2913, Vol. 66, No. 6
Department of Microbiology and
Immunology1 and
Division of Infectious
Diseases, Department of Medicine,2 University of
Louisville, Louisville, Kentucky 40292
Received 21 January 1998/Returned for modification 6 March
1998/Accepted 26 March 1998
Legionella pneumophila causes Legionnaires' disease by
replication in alveolar macrophages and monocytes. The bacteria are internalized most efficiently by opsonin-dependent, CR3-mediated phagocytosis. This investigation focused on determining the role of
actin polymerization and phosphorylation signals in this uptake mechanism. Uptake inhibition assays and confocal microscopic analysis indicated that entry of L. pneumophila activated tyrosine
kinase (TK) and protein kinase C (PKC) and induced actin polymerization at the site of bacterial entry. Upon L. pneumophila entry,
six major cellular proteins (75, 71, 59, 56, 53, and 52 kDa) were TK
phosphorylated in soluble fractions of monocytes, and three of these
proteins (52, 53, and 56 kDa) were consistently found in insoluble
(i.e., cytoskeletal) fractions of monocytes as well. Tyrosine
phosphorylation was suppressed when cells were pretreated with the
kinase inhibitor genistein, tyrphostin, or staurosporine. A similar
tyrosine-phosphorylated protein pattern was observed with CR3-mediated
entry of avirulent L. pneumophila, Escherichia coli, or zymosan into monocytes. This study has shown that PKC and TK signals which activate actin polymerization during the process
of phagocytosis are induced upon L. pneumophila entry. In
addition, CR3 receptor-mediated phagocytosis into monocytes may involve
tyrosine phosphorylation of similar proteins, regardless of the
particle being phagocytosed. Therefore, the tyrosine-induced phosphorylation observed during opsonized L. pneumophila
entry is not a virulence-associated event.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Signal Transduction during Legionella
pneumophila Entry into Human Monocytes
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, School of Medicine, University of
Louisville, Louisville, KY 40292. Phone: (502) 852-4120. Fax: (502)
852-7531. E-mail: pycoxo01{at}ulkyvm.louisville.edu.
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