CpG DNA enhances macrophage cell spreading by promoting the Src-family kinase-mediated phosphorylation of paxillin

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Macrophages are key innate immune cells activated by pathogens via Toll-like receptors (TLRs).
• Bacterial DNA with unmethylated CpG motifs is recognized by TLR9, initiating intracellular signaling and inflammatory responses.
• TLR9 activation orchestrates macrophage responses to microbial pathogens.

Purpose of the Study:

• To investigate the effects of CpG DNA on macrophage morphology and cytoskeletal organization.
• To elucidate the signaling pathways involved in CpG DNA-mediated macrophage activation.
• To determine the role of Src-family kinases and paxillin in CpG DNA-induced cellular changes.

Main Methods:

• Primary mouse bone marrow macrophages were stimulated with CpG DNA.
• Cell size and spreading were measured.
• Protein tyrosine phosphorylation and protein-protein interactions were analyzed using techniques like Western blotting and co-immunoprecipitation.
• In vitro kinase assays were performed.

Main Results:

• CpG DNA stimulation significantly increased macrophage cell size by approximately 70% and promoted actin cytoskeleton reorganisation and cell spreading.
• CpG DNA-induced cell spreading was dependent on Src-family kinase activity.
• Tyrosine phosphorylation of proteins, including paxillin, increased upon CpG DNA stimulation in a Src-family kinase-dependent manner.
• The Src-family kinase Hck phosphorylated paxillin, enhancing its binding capacity to the adapter protein Crk.

Conclusions:

• CpG DNA activates macrophages, inducing significant cell spreading and cytoskeletal remodeling.
• Src-family kinases, particularly Hck, play a crucial role in mediating these changes.
• Phosphorylation of paxillin by Hck creates a binding site for Crk, suggesting a mechanism for cytoskeletal reorganization and enhanced cell spreading in activated macrophages.