Rapid activation of protein tyrosine kinase and phospholipase C-gamma2 and increase in cytosolic free calcium are required by Ehrlichia chaffeensis for internalization and growth in THP-1 cells.
Ehrlichia chaffeensis, a bacterium that cannot survive outside the eukaryotic cell, proliferates exclusively in human monocytes and macrophages. In this study, signaling events required for ehrlichial infection of human monocytic cell line THP-1 were characterized. Entry and proliferation of E. chaffeensis in THP-1 cells were significantly blocked by various inhibitors that can regulate calcium signaling, including 8-(diethylamino)octyl-3,4,5-trimethoxybenzoate and 2-aminoethoxydiphenyl borate (intracellular calcium mobilization inhibitors), verapamil and 1-[beta-[3-(4-methoxyphenyl)propyl]-4-methoxyphenethyl]-1H-imidazole (SKF-96365) (calcium channel inhibitors), neomycin and 1-(6-[[17beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl)-1H-pyrrole-2,5-dione (U-73122) (phospholipase C [PLC] inhibitors), monodansylcadaverine (a transglutaminase [TGase] inhibitor), and genistein (a protein tyrosine kinase [PTK] inhibitor). Addition of E. chaffeensis resulted in rapid increases in the level of inositol 1,4,5-trisphosphate (IP(3)) and the level of cytosolic free calcium ([Ca(2+)](i)) in THP-1 cells, which were prevented by pretreatment of THP-1 cells with inhibitors of TGase, PTK, and PLC. E. chaffeensis induced rapid tyrosine phosphorylation of PLC-gamma2, and the presence of a PLC-gamma2 antisense oligonucleotide in THP-1 cells significantly blocked ehrlichial infection. Furthermore, tyrosine-phosphorylated proteins and PLC-gamma2 were colocalized with ehrlichial inclusions, as determined by double-immunofluorescence labeling. The heat-sensitive component of viable E. chaffeensis cells was essential for these signaling events. E. chaffeensis, therefore, can recruit interacting signal-transducing molecules and induce the following signaling events required for the establishment of infection in host cells: protein cross-linking by TGase, tyrosine phosphorylation, PLC-gamma2 activation, IP(3) production, and an increase in [Ca(2+)](i).
Lin
Mingqun
M
Department of Veterinary Biosciences. Neurobiotechnology Center, The Ohio State University, Columbus, Ohio 43210, USA.
Zhu
Michael X
MX
Rikihisa
Yasuko
Y
D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D018469:Ehrlichia chaffeensis / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D004705:Endocytosis; D004789:Enzyme Activation; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis; D007527:Isoenzymes / Q000378:metabolism*; D051966:Phospholipase C gamma; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D013997:Time Factors; D010738:Type C Phospholipases / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
D007527:Isoenzymes; D014443:Tyrosine; D015544:Inositol 1,4,5-Trisphosphate; D011505:Protein-Tyrosine Kinases; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D002118:Calcium