Colony stimulating factor-1 (CSF-1) stimulates mononuclear phagocytic cell survival, growth and differentiation into macrophages through activation and autophosphorylation of the CSF-1 receptor (CSF-1R). We have previously demonstrated that CSF-1-induced phosphorylation of Y721 in the receptor kinase insert triggers its association with the p85 regulatory subunit of phosphoinositide 3′-kinase (PI3K). Binding of p85 PI3K to the CSF-1R pY721 motif activates the associated p110 PI3K catalytic subunit and stimulates spreading and motility in macrophages and their enhancement of tumor cell invasion. Here we show that pY721-based signaling is necessary for CSF-1-stimulated PtdIns(3,4,5)P (PIP3) production. While primary bone marrow-derived macrophages (BMM) and the immortalized bone marrow-derived macrophage cell line, M−/−.WT, express all three Class IA PI3K isoforms, p110δ predominates in the cell line. Treatment with p110δ specific inhibitors demonstrates that the hematopoietically enriched isoform, p110δ, mediates CSF-1 regulated spreading and invasion in macrophages. Thus GS-1101, a potent and selective p110δ inhibitor, may have therapeutic potential by targeting the infiltrative capacity of tumor-associated macrophages that is critical for their enhancement of tumor invasion and metastasis.

Persistent activation of the latent transcription factor STAT3 is observed in gastric tumor epithelial and immune cells and is associated with a poor patient prognosis. Although targeting STAT3-activating upstream kinases offers therapeutically viable targets with limited specificity, direct inhibition of STAT3 remains challenging. Here we provide functional evidence that myeloid-specific hematopoietic cell kinase (HCK) activity can drive STAT3-dependent epithelial tumor growth in mice and is associated with alternative macrophage activation alongside matrix remodeling and tumor cell invasion. Accordingly, genetic reduction of HCK expression in bone marrow-derived cells or systemic pharmacologic inhibition of HCK activity suppresses alternative macrophage polarization and epithelial STAT3 activation, and impairs tumor growth. These data validate HCK as a molecular target for the treatment of human solid tumors harboring excessive STAT3 activity.

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Migratory macrophages play critical roles in tissue development, homeostasis and disease so it is important to understand how their migration machinery is regulated. Whole transcriptome sequencing revealed that CSF-1-stimulated differentiation of bone marrow-derived precursors into mature macrophages is accompanied by widespread, profound changes in expression of genes regulating adhesion, actin cytoskeletal remodeling and extracellular matrix degradation. Significantly altered expression of almost 40% of adhesion genes, 60 to 86% of Rho family GTPases, their regulators and effectors and over 70% of extracellular proteases occurred. The gene expression changes were mirrored by changes in macrophage adhesion associated with increases in motility and matrix degrading capacity. IL-4 further increased motility and matrix degrading capacity in mature macrophages with additional changes in migration machinery gene expression. Finally, siRNA-induced reductions in the expression of core adhesion proteins, paxillin and leupaxin, decreased macrophage spreading and adhesion numbers with distinct effects on adhesion numbers and their distribution and on matrix degradation. Together, the datasets provide an important resource for our understanding of the regulation of migration in macrophages and to develop therapies targeting disease-enhancing macrophages.