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Fig. 7. Involvement of c-src and downstream effector, cortactin, in Rickettsia conorii invasion of mammalian cells. (A) Immunofluorescence microscopy reveals that R. conorii colocalizes with endogenous c-src within 15 minutes of infection (arrow). Colocalization is not caused by antibody crossreactivity as not all adherent bacteria recruit c-src (arrowheads). (B) Pharmacological inhibition of Src-family PTKs with protein phosphatase 1 (PP1), diminishes bacterial entry but has no effect on bacterial adherence or cellular viability (data not shown). (C) R. conorii infection induces the co-immunoprecipitation of c-Src with phosphotyrosine proteins, suggesting that this may be a mechanism for activating c-src during the invasion process. Densitometric analysis of scanned immunoblots indicates the relative amount of c-src that co-immunoprecipitates with pTyr proteins in response to bacterial infection. Immunoblot analysis of pre-immune precipitated cellular lysates serves as a loading control. (D) The c-src kinase substrate, cortactin, colocalizes with some (arrows), but not all (arrowheads) extracellular R. conorii within 15 minutes of infection, suggesting that specific cortactin recruitment plays a role in the uptake process. (E) The boxed area in (D) has been enlarged to show detail. Bars in (A,E), 6 µm; (D), 3 µm.
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