The Tyrosine Kinase Pyk2 Contributes to Complement-Mediated Phagocytosis in Murine Macrophages.

Proline-rich tyrosine kinase 2 (Pyk2) is a member of the focal adhesion kinase (FAK) family and is mainly expressed in neuronal and hematopoietic cells. As FAK family members are involved in signaling connections downstream of integrins, we studied the role of Pyk2 in complement-receptor 3 (CR3, also known as Mac-1, integrin αMβ2, CD11b/CD18)-mediated phagocytosis, a key process in innate immunity. Using 3 independent approaches, we observed that Pyk2 contributes to CR3-dependent phagocytosis by RAW 264.7 macrophages, but is dispensable for Fcγ receptor (FcγR)-mediated uptake. Reduction of Pyk2 expression levels via siRNA, the pharmacological inhibition of Pyk2 kinase activity as well as macrophage treatment with a cell permeable TAT fusion protein containing the C-terminus of Pyk2 (TAT-PRNK) significantly impaired CR3-mediated phagocytosis without affecting FcγR-mediated uptake. In addition, Pyk2 was strongly recruited to complement opsonized Escherichia coli and the pharmacological inhibition of Pyk2 significantly decreased uptake of the bacteria. Finally, CRISPR/Cas-mediated disruption of the pyk2 gene in RAW 264.7 macrophages confirmed the role of this protein tyrosine kinase in CR3-mediated phagocytosis. Together, our data demonstrate that Pyk2 selectively contributes to the coordination of phagocytosis-promoting signals downstream of CR3, but is dispensable for FcγR-mediated phagocytosis.