Toxoplasma gondii disrupts $\beta1$-integrin signaling and focal adhesion formation during monocyte hypermotility

Abstract

The motility of blood monocytes is orchestrated by the activity of cell-surface integrins, which translate extracellular signals into cytoskeletal changes to mediate adhesion and migration. Toxoplasma gondii is an intracellular parasite that infects migratory cells and enhances their motility, but the mechanisms underlying T. gondii –induced hypermotility are incompletely understood. We investigated the molecular basis for the hypermotility of primary human peripheral blood monocytes and THP-1 cells infected with T. gondii. Compared with uninfected monocytes, T. gondii infection of monocytes reduced cell spreading and the number of activated $\beta1$ integrin clusters in contact with fibronectin during settling, an effect not observed in monocytes treated with lipopolysaccharide (LPS) or Escherichia coli. Furthermore, T. gondii infection disrupted the phosphorylation of focal adhesion kinase (FAK) at tyrosine 397 (Tyr- 397) and Tyr-925 and of the related protein proline-rich tyrosine kinase (Pyk2) at Tyr-402. The localization of paxillin, FAK, and vinculin to focal adhesions and the colocalization of these proteins with activated $\beta1$ integrins were also impaired in T. gondii –infected monocytes. Using time-lapse confocal microscopy of THP-1 cells expressing enhanced GFP (eGFP)-FAK during settling on fibronectin, we found that T. gondii -induced monocyte hypermotility was characterized by a reduced number of enhanced GFP-FAK–containing clusters over time compared with uninfected cells. This study demonstrates an integrin conformation–independent regulation of the $\beta1$ integrin adhesion pathway, providing further insight into the molecular mechanism of T. gondii–induced monocyte hypermotility.