Abstract
Targeting of Toxoplasma gondii by autophagy is an effective mechanism by which host cells kill the protozoan. Thus, the parasite must avoid autophagic targeting to survive. Here we show that the mammalian cytoplasmic molecule Focal Adhesion Kinase (FAK) becomes activated during invasion of host cells. Activated FAK appears to accompany the formation of the moving junction (as assessed by expression the parasite protein RON4). FAK activation was inhibited by approaches that impaired β1 and β3 integrin signaling. FAK caused activation of Src that in turn mediated Epidermal Growth Factor Receptor (EGFR) phosphorylation at the unique Y845 residue. Expression of Src-resistant Y845F EGFR mutant markedly inhibited ROP16-independent activation of STAT3 in host cells. Activation of FAK, Y845 EGFR or STAT3 prevented activation of PKR and eIF2α, key stimulators of autophagy. Genetic or pharmacologic inhibition of FAK, Src, EGFR phosphorylation at Y845, or STAT3 caused accumulation of the autophagy protein LC3 and LAMP-1 around the parasite and parasite killing dependent on autophagy proteins (ULK1 and Beclin 1) and lysosomal enzymes. Parasite killing was inhibited by expression of dominant negative PKR. Thus, T. gondii activates a FAK→Src→Y845-EGFR→STAT3 signaling axis within mammalian cells, thereby enabling the parasite to survive by avoiding autophagic targeting through a mechanism likely dependent on preventing activation of PKR and eIF2α.
Highlights
Toxoplasma gondii is an obligate intracellular protozoan that can cause disease in humans, including retinochoroiditis and encephalitis
Avoiding lysosomal degradation including that mediated by autophagy is central to the ability of T. gondii to survive within these cells
We uncovered that during the process of active invasion of host cells, T. gondii activates in a broad range of mammalian cells a signaling cascade downstream of Focal Adhesion Kinase (FAK)-Src that prevents targeting of the intracellular parasite by autophagy enabling its survival
Summary
Toxoplasma gondii is an obligate intracellular protozoan that can cause disease in humans, including retinochoroiditis and encephalitis. T. gondii actively invades host cells, a process powered by the parasite’s own motility that is dependent on the sequential secretion of proteins present in the apical organelles called micronemes and rhoptries [1,2,3]. Micronemal proteins (MIC) act as adhesins that interact with the host cell membrane and function through their association with the parasite glideosome that powers motility [2]. A complex of rhoptry neck proteins (RON) are secreted into the host cell membrane anchoring the parasite to the cell being invaded [1,2,3]. T. gondii dissociates from the host cell membrane and resides within a specialized niche called parasitophorous vacuole (PV)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.