Molecular mechanism of Abl-mediated PI3K activation in macrophage podosome assembly

Abstract

Macrophages are motile immune cells which intrinsically assemble podosomes as the primary adhesion devices. Podosome is an integrin-mediated cell-matrix adhesion and plays pivotal roles in macrophage extracellular matrix degradation and migration towards the chemoattractant. A chorus of molecules has been identified and functionally implicated in podosome formation. Centrally enriched actin core is one of the characteristic components of the podosome. Assembly of polymerized actin at the core is regulated by nucleation promoting factors such as WASP and subsequently nucleated by Arp2/3 complex. Here, I elaborate that phosphatidylinositol (3,4,5)-trisphosphate lipids are selectively present at macrophage podosome core. Importantly, PIK3CB catalytic subunit is distinctly recruited to podosome core. Knockdown of PIK3CB further disrupts podosome assembly and attenuates macrophage extracellular matrix degradation. Besides, PIK3R1 regulatory subunit is recruited to podosome core by Abl kinase. Inhibition of Abl activity results in the disassociation of PIK3R1 from podosome core, impedes PI3K activation, and triggers podosome dissolution. Abl is natively present at an autoinhibitory conformation based on intramolecular interactions. Phosphorylation of particular tyrosine residues by Src kinase can release the autoinhibition and activate Abl. Moreover, I demonstrate that inhibition of Src activity suppresses Abl activation, results in the disassociation of Abl and PIK3R1 from podosome core, and attenuates podosome assembly. Inhibition of Src, Abl, and PIK3CB activity further impairs macrophage podosome formation, extracellular matrix degradation, and cell migration towards the chemoattractant. Collectively, the present study denotes that Src-mediated Abl activation is essential for PIK3CB-dependent local phosphatidylinositol (3,4,5)-trisphosphate lipids enrichment, WASP activation, and Arp2/3-mediated actin polymerization at macrophage podosomes.