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First published online 22 July 2003
doi: 10.1242/jcs.00666

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Novel PI 3-kinase-dependent mechanisms of trypanosome invasion and vacuole maturation

¹ Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, MA 02115, USA
² Division of Signal Transduction, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA 02115, USA
³ Institut fuer Biochemie, Freie Universitaet Berlin, Berlin, Germany

^* Author for correspondence (e-mail: bburleig{at}hsph.harvard.edu)

Accepted 12 May 2003

Mammalian cell invasion by the protozoan parasite, Trypanosoma cruzi, is facilitated by the activation of host cell phosphatidylinositol 3 (PI 3)-kinases. We demonstrate that the well-characterized Ca²⁺-regulated lysosome-mediated parasite entry pathway is abolished by wortmannin pretreatment. In addition, we have characterized a novel route of T. cruzi invasion unexpectedly revealed in the course of this study. For over a decade, targeted exocytosis of lysosomes at the host cell plasma membrane was considered as the primary mechanism for T. cruzi entry into non-professional phagocytic cells. We now provide evidence that a significant fraction (50% or greater) of invading T. cruzi trypomastigotes exploit an alternate actin-independent entry pathway that involves formation of a tightly associated host cell plasma membrane-derived vacuole enriched in the lipid products of class I PI 3-kinases, PtdInsP₃/PtdIns(3,4)P₂. Initially devoid of lysosomal markers, the resultant parasite-containing vacuoles gradually acquire lysosome associated membrane protein 1 (lamp-1) and fluid phase endocytic tracer from the lysosomal compartment. In striking contrast to latex bead phagosomes, few T. cruzi vacuoles associate with the early endosomal marker, EEA1 and the 'maturation' process becomes refractory to PI 3-kinase inhibition immediately following parasite internalization. Jointly, these data provide a new paradigm for T. cruzi invasion of non-professional phagocytic cells and reveal a novel vacuole maturation process that appears to bypass the requirement for EEA1.

Key words: Phosphatidylinositol, Phagocytosis, Invasion, Trypanosoma cruzi, Maturation

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