Tyrosine phosphorylation of Wiskott-Aldrich syndrome protein (WASP) by Hck regulates macrophage function

Recent advances in hematopoietic cell kinase in cancer progression: Mechanisms and inhibitors

Hematopoietic cell kinase (Hck), a non-receptor tyrosine kinase belonging to the Src kinase family, is intricately linked to the pathogenesis of numerous human diseases, with a particularly pronounced association with cancer. Hck not only directly impacts the proliferation, migration, and apoptosis of cancer cells but also interacts with JAK/STAT, MEK/ERK, PI3K/AKT, CXCL12/CXCR4, and other pathways. Hck also influences the tumor microenvironment to facilitate the onset and progression of cancer. This paper delves into the functional role and regulatory mechanisms of Hck in various solid tumors. Additionally, it explores the implications of Hck in hematological malignancies. The review culminates with a summary of the current research status of Hck inhibitors, the majority of which are in the pre-clinical phase of investigation. Notably, these inhibitors are predominantly utilized in the therapeutic management of leukemia, with their combinatorial potential indicating promising avenues for future research. In conclusion, this review underscores the significance of the mechanism of Hck in solid tumors. This insight is crucial for comprehending the current research trends regarding Hck: targeted therapy against Hck shows great promise in both diagnosis and treatment of malignant tumors. Further investigation into the role of Hck in cancer, coupled with the development of specific inhibitors, has the potential to revolutionize approaches to cancer treatment.

HCK Promotes High-Grade Serous Ovarian Cancer Tumorigenesis through CD44 and NOTCH3 Signaling

High-grade serous ovarian cancer (HGSOC) is a highly aggressive and lethal subtype of ovarian cancer. While most patients initially respond to standard-of-care treatment, the majority will eventually relapse and succumb to their disease. Despite significant advances in our understanding of this disease, the mechanisms that govern the distinctions between HGSOC with good and poor prognosis remain unclear. In this study, we implemented a proteogenomic approach to analyze gene expression, proteomic and phosphoproteomic profiles of HGSOC tumor samples to identify molecular pathways that distinguish HGSOC tumors relative to clinical outcome. Our analyses identify significant upregulation of hematopoietic cell kinase (HCK) expression and signaling in poor prognostic HGSOC patient samples. Analyses of independent gene expression datasets and IHC of patient samples confirmed increased HCK signaling in tumors relative to normal fallopian or ovarian samples and demonstrated aberrant expression in tumor epithelial cells. Consistent with the association between HCK expression and tumor aggressiveness in patient samples, in vitro phenotypic studies showed that HCK can, in part, promote cell proliferation, colony formation, and invasive capacity of cell lines. Mechanistically, HCK mediates these phenotypes, partly through CD44 and NOTCH3-dependent signaling, and inhibiting CD44 or NOTCH3 activity, either genetically or through gamma-secretase inhibitors, can revert HCK-driven phenotypes.

IMPLICATIONS

Collectively, these studies establish that HCK acts as an oncogenic driver of HGSOC through aberrant activation of CD44 and NOTCH3 signaling and identifies this network as a potential therapeutic opportunity in a subset of patients with aggressive and recurrent HGSOC.

SKAP2 is downregulated in the villous tissues of patients with missed abortion and regulates growth and migration in trophoblasts through the WAVE2-ARP2/3 signaling pathway

INTRODUCTION

Abnormal placental trophoblast function is the main cause of missed abortion (MA). Src kinase-associated phosphoprotein 2 (SKAP2) indirectly affects actin reunion, which is significantly associated with cell migration.

METHODS

Twenty women with MA and 20 healthy women who underwent voluntarily induced abortion were included in this study. Immunohistochemistry, qRT-PCR, and western blotting were used to determine SKAP2, WAVE2, and ARP2 expression in the villous tissues. We investigated the effects of SKAP2 and the W336K mutant (blocked SKAP2 Src homology 3 function) on growth and migration in HTR8/SVneo cells using the CCK8 assay, flow cytometry, and transwell assay. The effects of SKAP2 on the WAVE2-ARP2/3 signaling pathway in HTR8/SVneo cells were evaluated by western blotting and immunofluorescence.

RESULTS

Compared to the women in the voluntary abortion group, SKAP2 and WAVE2 expression levels were downregulated in the villous of patients with MA. In HTR8/SVneo cells, SKAP2 siRNA silencing regulated the growth and migration, while SKAP2 overexpression promoted growth and migration, and inhibited apoptosis. Additionally, SKAP2 regulated the expression of WAVE2 and ARP2, as well as the colocalization of actin with WAVE2. The SKAP2 W336K mutant could not alter WAVE2 and ARP2 expression, nor HTR8/SVneo cell growth and migration, with or without SKAP2 siRNA transfection.

DISCUSSION

SKAP2 could activate the WAVE2-ARP2/3 pathway resulting in an increase of growth and migration in trophoblasts. SKAP2 probably played an important role in MA by affecting the growth and migration of trophoblasts.

Identification of hub genes and regulatory networks in histologically unstable carotid atherosclerotic plaque by bioinformatics analysis

Objective

This study identified underlying genetic molecules associated with histologically unstable carotid atherosclerotic plaques through bioinformatics analysis that may be potential biomarkers and therapeutic targets.

Methods

Three transcriptome datasets (GSE41571, GSE120521 and E-MTAB-2055) and one non-coding RNA dataset (GSE111794) that met histological grouping criteria of unstable plaque were downloaded. The common differentially expressed genes (co-DEGs) of unstable plaques identified from three mRNA datasets were annotated by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomics (KEGG). A protein–protein interaction (PPI) network was constructed to present the interaction between co-DEGs and screen out hub genes. MiRNet database and GSE111794 dataset were used to identify the miRNAs targeting hub genes. Associated transcription factors (TFs) and drugs were also predicted. These predicted results were used to construct miRNA/TFs-hub gene and drug-hub gene regulatory networks.

Results

A total of 105 co-DEGs were identified, including 42 up-regulated genes and 63 down-regulated genes, which were mainly enriched in collagen-containing extracellular matrix, focal adhesion, actin filament bundle, chemokine signaling pathway and regulates of actin cytoskeleton. Ten hub genes (up-regulated: HCK, C1QC, CD14, FCER1G, LCP1 and RAC2; down-regulated: TPM1, MYH10, PLS3 and FMOD) were screened. HCK and RAC2 were involved in chemokine signaling pathway, MYH10 and RAC2 were involved in regulation of actin cytoskeleton. We also predicted 12 miRNAs, top5 TFs and 25 drugs targeting hub genes. In the miRNA/TF-hub gene regulatory network, PLS3 was the most connected hub genes and was targeted by six miRNAs and all five screened TFs. In the drug-hub gene regulatory network, HCK was targeted by 20 drugs including 10 inhibitors.

Conclusions

We screened 10 hub genes and predicted miRNAs and TFs targeting them. These molecules may play a crucial role in the progression of histologically unstable carotid plaques and serve as potential biomarkers and therapeutic targets.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01257-1.

Macrophage 3D migration: A potential therapeutic target for inflammation and deleterious progression in diseases

Macrophages are heterogeneous cells that have different physiological functions, such as chemotaxis, phagocytosis, endocytosis, and secretion of various factors. All physiological functions of macrophages are integral to homeostasis, immune defense and tissue repair. However, in several diseases, macrophages are recruited from the blood towards inflammatory sites. This process is called macrophage migration, which promotes deleterious disease progression. Macrophage migration is a key player in many inflammatory diseases, autoimmune diseases and cancers because it contributes to the accumulation of proinflammatory factors, the destruction of tissues and the development of tumors. Therefore, macrophage migration is proposed to be a potential therapeutic target. Macrophages migrate between two-dimensional (2D) and three-dimensional (3D) environments, implying that distinct migratory features and mechanisms are involved. Compared with the 2D migration of macrophages, 3D migration involves more complex variations in cellular morphology and dynamics. The structure of the extracellular matrix, a key factor, is modified in diseases that influence macrophage 3D migration. Macrophage 3D migration relates to disease pathology. Research that focuses on macrophage 3D migration is an emerging field and was reviewed in this article to indicate the molecular and cellular mechanisms of macrophage migration in 3D environments and to provide potential targets for controlling disease progression associated with this migration.

Genetic engineering of Hoxb8-immortalized hematopoietic progenitors - a potent tool to study macrophage tissue migration

Tumor-associated macrophages (TAMs) are detrimental in most cancers. Controlling their recruitment is thus potentially therapeutic. We previously found that TAMs perform protease-dependent mesenchymal migration in cancer, while macrophages perform amoeboid migration in other tissues. Inhibition of mesenchymal migration correlates with decreased TAM infiltration and tumor growth, providing rationale for a new cancer immunotherapy specifically targeting TAM motility. To identify new effectors of mesenchymal migration, we produced ER-Hoxb8-immortalized hematopoietic progenitors (cells with estrogen receptor-regulated Hoxb8 expression), which show unlimited proliferative ability in the presence of estrogen. The functionality of macrophages differentiated from ER-Hoxb8 progenitors was compared to bone marrow-derived macrophages (BMDMs). They polarized into M1- and M2-orientated macrophages, generated reactive oxygen species (ROS), ingested particles, formed podosomes, degraded the extracellular matrix, adopted amoeboid and mesenchymal migration in 3D, and infiltrated tumor explants ex vivo using mesenchymal migration. We also used the CRISPR/Cas9 system to disrupt gene expression of a known effector of mesenchymal migration, WASP (also known as WAS), to provide a proof of concept. We observed impaired podosome formation and mesenchymal migration capacity, thus recapitulating the phenotype of BMDM isolated from Wasp-knockout mice. Thus, we validate the use of ER-Hoxb8-immortalized macrophages as a potent tool to investigate macrophage functionalities.

Inhibition of the SRC Kinase HCK Impairs STAT3-Dependent Gastric Tumor Growth in Mice

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.

Tunneling nanotubes, a novel mode of tumor cell-macrophage communication in tumor cell invasion

The interaction between tumor cells and macrophages is crucial in promoting tumor invasion and metastasis. In this study, we examined a novel mechanism of intercellular communication, namely membranous actin-based tunneling nanotubes (TNTs), that occurs between macrophages and tumor cells in the promotion of macrophage-dependent tumor cell invasion. The presence of heterotypic TNTs between macrophages and tumor cells induced invasive tumor cell morphology, which was dependent on EGF-EGFR signaling. Furthermore, reduction of a protein involved in TNT formation, M-Sec (TNFAIP2), in macrophages inhibited tumor cell elongation, blocked the ability of tumor cells to invade in 3D and reduced macrophage-dependent long-distance tumor cell streaming in vitro Using an in vivo zebrafish model that recreates macrophage-mediated tumor cell invasion, we observed TNT-mediated macrophage-dependent tumor cell invasion, distant metastatic foci and areas of metastatic spread. Overall, our studies support a role for TNTs as a novel means of interaction between tumor cells and macrophages that leads to tumor progression and metastasis.

Protrusion Force Microscopy: A Method to Quantify Forces Developed by Cell Protrusions

In numerous biological contexts, animal cells need to interact physically with their environment by developing mechanical forces. Among these, traction forces have been well-characterized, but there is a lack of techniques allowing the measurement of the protrusion forces exerted by cells orthogonally to their substrate. We designed an experimental setup to measure the protrusion forces exerted by adherent cells on their substrate. Cells plated on a compliant Formvar sheet deform this substrate and the resulting topography is mapped by atomic force microscopy (AFM) at the nanometer scale. Force values are then extracted from an analysis of the deformation profile based on the geometry of the protrusive cellular structures. Hence, the forces exerted by the individual protruding units of a living cell can be measured over time. This technique will enable the study of force generation and its regulation in the many cellular processes involving protrusion. Here, we describe its application to measure the protrusive forces generated by podosomes formed by human macrophages.

WASP-mediated regulation of anti-inflammatory macrophages is IL-10 dependent and is critical for intestinal homeostasis

Mutations in Wiskott–Aldrich syndrome protein (WASP) cause autoimmune sequelae including colitis. Yet, how WASP mediates mucosal homeostasis is not fully understood. Here we show that WASP-mediated regulation of anti-inflammatory macrophages is critical for mucosal homeostasis and immune tolerance. The generation and function of anti-inflammatory macrophages are defective in both human and mice in the absence of WASP. Expression of WASP specifically in macrophages, but not in dendritic cells, is critical for regulation of colitis development. Importantly, transfer of WT anti-inflammatory macrophages prevents the development of colitis. DOCK8-deficient macrophages phenocopy the altered macrophage properties associated with WASP deficiency. Mechanistically, we show that both WASP and DOCK8 regulates macrophage function by modulating IL-10-dependent STAT3 phosphorylation. Overall, our study indicates that anti-inflammatory macrophage function and mucosal immune tolerance require both WASP and DOCK8, and that IL-10 signalling modulates a WASP-DOCK8 complex.

Deficiency in Wiskott-Aldrich syndrome protein (WASP) has been associated with autoimmune colitis, but the underlying mechanism is still unclear. Here the authors show that WASP deficiency is associated with defective WASP/DOCK8 complex formation, altered IL-10 signalling, and impaired anti-inflammatory macrophage functions.

Podosomes, But Not the Maturation Status, Determine the Protease-Dependent 3D Migration in Human Dendritic Cells

Dendritic cells (DC) are professional Antigen-Presenting Cells scattered throughout antigen-exposed tissues and draining lymph nodes, and survey the body for pathogens. Their ability to migrate through tissues, a 3D environment, is essential for an effective immune response. Upon infection, recognition of Pathogen-Associated Molecular Patterns (PAMP) by Toll-like receptors (TLR) triggers DC maturation. Mature DC (mDC) essentially use the protease-independent, ROCK-dependent amoeboid mode in vivo, or in collagen matrices in vitro. However, the mechanisms of 3D migration used by human immature DC (iDC) are still poorly characterized. Here, we reveal that human monocyte-derived DC are able to use two migration modes in 3D. In porous matrices of fibrillar collagen I, iDC adopted the amoeboid migration mode. In dense matrices of gelled collagen I or Matrigel, iDC used the protease-dependent, ROCK-independent mesenchymal migration mode. Upon TLR4 activation by LPS, mDC-LPS lose the capacity to form podosomes and degrade the matrix along with impaired mesenchymal migration. TLR2 activation by Pam₃CSK₄ resulted in DC maturation, podosome maintenance, and efficient mesenchymal migration. Under all these conditions, when DC used the mesenchymal mode in dense matrices, they formed 3D podosomes at the tip of cell protrusions. Using PGE₂, known to disrupt podosomes in DC, we observed that the cells remained in an immature status and the mesenchymal migration mode was abolished. We also observed that, while CCL5 (attractant of iDC) enhanced both amoeboid and mesenchymal migration of iDC, CCL19 and CCL21 (attractants of mDC) only enhanced mDC-LPS amoeboid migration without triggering mesenchymal migration. Finally, we examined the migration of iDC in tumor cell spheroids, a tissue-like 3D environment. We observed that iDC infiltrated spheroids of tumor cells using both migration modes. Altogether, these results demonstrate that human DC adopt the mesenchymal mode to migrate in 3D dense environments, which relies on their capacity to form podosomes independent of their maturation status, paving the way of further investigations on in vivo DC migration in dense tissues and its regulation during infections.

Macrophage-Dependent Cytoplasmic Transfer during Melanoma Invasion In Vivo

Interactions between tumor cells and tumor-associated macrophages play critical roles in the initiation of tumor cell motility. To capture the cellular interactions of the tumor microenvironment with high-resolution imaging, we directly visualized tumor cells and their interactions with macrophages in zebrafish. Live imaging in zebrafish revealed that macrophages are dynamic, yet maintain sustained contact with tumor cells. In addition, the recruitment of macrophages to tumor cells promotes tumor cell dissemination. Using a Cre/LoxP strategy, we found that macrophages transfer cytoplasm to tumor cells in zebrafish and mouse models. Remarkably, macrophage cytoplasmic transfer correlated with melanoma cell dissemination. We further found that macrophages transfer cytoplasm to tumor cells upon cell contact in vitro. Thus, we present a model in which macrophage/tumor cell contact allows for the transfer of cytoplasmic molecules from macrophages to tumor cells corresponding to increased tumor cell motility and dissemination.

The Role of Rho-GTPases and actin polymerization during Macrophage Tunneling Nanotube Biogenesis

Macrophage interactions with other cells, either locally or at distances, are imperative in both normal and pathological conditions. While soluble means of communication can transmit signals between different cells, it does not account for all long distance macrophage interactions. Recently described tunneling nanotubes (TNTs) are membranous channels that connect cells together and allow for transfer of signals, vesicles, and organelles. However, very little is known about the mechanism by which these structures are formed. Here we investigated the signaling pathways involved in TNT formation by macrophages using multiple imaging techniques including super-resolution microscopy (3D-SIM) and live-cell imaging including the use of FRET-based Rho GTPase biosensors. We found that formation of TNTs required the activity and differential localization of Cdc42 and Rac1. The downstream Rho GTPase effectors mediating actin polymerization through Arp2/3 nucleation, Wiskott-Aldrich syndrome protein (WASP) and WASP family verprolin-homologous 2 (WAVE2) proteins are also important, and both pathways act together during TNT biogenesis. Finally, TNT function as measured by transfer of cellular material between cells was reduced following depletion of a single factor demonstrating the importance of these factors in TNTs. Given that the characterization of TNT formation is still unclear in the field; this study provides new insights and would enhance the understanding of TNT formation towards investigating new markers.

A three-dimensional co-culture system to investigate macrophage-dependent tumor cell invasion

Macrophages infiltrate cancers and promote progression to invasion and metastasis. To directly examine tumor-associated macrophages (TAMs) and tumor cells interacting and co-migrating in a three-dimensional (3D) environment, we have developed a co-culture model that uses a PyVmT mouse mammary tumor-derived cell line and mouse bone marrow-derived macrophages (BMM). The Py8119 cell line was cloned from a spontaneous mammary tumor in a Tg(MMTV:LTR-PyVmT) C57Bl/6 mouse and these cells form 3-dimensional (3D) spheroids under conditions of low adhesion. Co-cultured BMM infiltrate the Py8119 mammospheres and embedding of the infiltrated mammospheres in Matrigel leads to subsequent invasion of both cell types into the surrounding matrix. This physiologically relevant co-culture model enables examination of two critical steps in the promotion of invasion and metastasis by BMM: 1) macrophage infiltration into the mammosphere and, 2) subsequent invasion of macrophages and tumor cells into the matrix. Our methodology allows for quantification of BMM infiltration rates into Py8119 mammospheres and demonstrates that subsequent tumor cell invasion is dependent upon the presence of infiltrated macrophages. This method is also effective for screening macrophage motility inhibitors. Thus, we have developed a robust 3D in vitro co-culture assay that demonstrates a central role for macrophage motility in the promotion of tumor cell invasion.

Src family kinase expression and subcellular localization in macrophages: implications for their role in CSF-1-induced macrophage migration

A major role of colony-stimulating factor-1 is to stimulate the differentiation of mononuclear phagocytic lineage cells into adherent, motile, mature macrophages. The colony-stimulating factor-1 receptor transduces colony-stimulating factor-1 signaling, and we have shown previously that phosphatidylinositol 3-kinase p110δ is a critical mediator of colony-stimulating factor-1-stimulated motility through the colony-stimulating factor-1 receptor pY721 motif. Src family kinases are also implicated in the regulation of macrophage motility and in colony-stimulating factor-1 receptor signaling, although functional redundancy of the multiple SFKs expressed in macrophages makes it challenging to delineate their specific functions. We report a comprehensive analysis of individual Src family kinase expression in macrophage cell lines and primary macrophages and demonstrate colony-stimulating factor-1-induced changes in Src family kinase subcellular localization, which provides clues to their distinct and redundant functions in macrophages. Moreover, expression of individual Src family kinases is both species specific and dependent on colony-stimulating factor-1-induced macrophage differentiation. Hck associated with the activated colony-stimulating factor-1 receptor, whereas Lyn associated with the receptor in a constitutive manner. Consistent with this, inhibitor studies revealed that Src family kinases were important for both colony-stimulating factor-1 receptor activation and colony-stimulating factor-1-induced macrophage spreading, motility, and invasion. Distinct colony-stimulating factor-1-induced changes in the subcellular localization of individual SFKs suggest specific roles for these Src family kinases in the macrophage response to colony-stimulating factor-1.

Sos1 Regulates Macrophage Podosome Assembly and Macrophage Invasive Capacity

Podosomes are protrusive structures implicated in macrophage extracellular matrix degradation and three-dimensional migration through cell barriers and the interstitium. Podosome formation and assembly are regulated by cytoskeleton remodeling requiring cytoplasmic tyrosine kinases of the Src and the Abl families. Considering that Abl has been reported to phosphorylate the guanine nucleotide exchange factor Sos1, eliciting its Rac-guanine nucleotide exchange factor activity, and Rac regulates podosome formation in myeloid cells and invadopodia formation in cancer cells, we addressed whether Sos1 is implicated in podosome formation and function in macrophages. We found that ectopically expressed Abl or the Src kinase Fgr phosphorylate Sos1, and the Src kinases Hck and Fgr are required for Abl and Sos1 phosphorylation and Abl/Sos1 interaction in macrophages. Sos1 localizes to podosomes in both murine and human macrophages, and its silencing by small interfering RNA results in disassembly of murine macrophage podosomes and a marked reduction of GTP loading on Rac. Matrix degradative capacity, three-dimensional migration through Matrigel, and transmigration through an endothelial cell monolayer of Sos1-silenced macrophages were inhibited. In addition, Sos1- or Abl-silenced macrophages, or macrophages treated with the selective Abl inhibitor imatinib mesylate had a reduced capability to migrate into breast tumor spheroids, the majority of cells remaining at the margin and the outer layers of the spheroid itself. Because of the established role of Src and Abl kinases to regulate also invadopodia formation in cancer cells, our findings suggest that targeting the Src/Abl/Sos1/Rac pathway may represent a double-edged sword to control both cancer-invasive capacities and cancer-related inflammation.

HIV-1 Infection of T Lymphocytes and Macrophages Affects Their Migration via Nef

The human immunodeficiency virus (HIV-1) disseminates in the body and is found in several organs and tissues. Although HIV-1 mainly targets both CD4⁺ T lymphocytes and macrophages, it has contrasting effects between these cell populations. HIV-1 infection namely reduces the viability of CD4⁺ T cells, whereas infected macrophages are long-lived. In addition, the migration of T cells is reduced by the infection, whereas HIV-1 differentially modulates the migration modes of macrophages. In 2-dimensions (2D) assays, infected macrophages are less motile compared to the control counterparts. In 3D environments, macrophages use two migration modes that are dependent on the matrix architecture: amoeboid and mesenchymal migration. HIV-1-infected macrophages exhibit a reduced amoeboid migration but an enhanced mesenchymal migration, via the viral protein Nef. Indeed, the mesenchymal migration involves podosomes, and Nef stabilizes these cell structures through the activation of the tyrosine kinase Hck, which in turn phosphorylates the Wiskott–Aldrich syndrome protein (WASP). WASP is a key player in actin remodeling and cell migration. The reprogramed motility of infected macrophages observed in vitro correlates in vivo with enhanced macrophage infiltration in experimental tumors in Nef-transgenic mice compared to control mice. In conclusion, HIV infection of host target cells modifies their migration capacity; we infer that HIV-1 enhances virus spreading in confined environments by reducing T cells migration, and facilitates virus dissemination into different organs and tissues of the human body by enhancing macrophage mesenchymal migration.

Hematopoietic cell kinase (HCK) as a therapeutic target in immune and cancer cells

The hematopoietic cell kinase (HCK) is a member of the SRC family of cytoplasmic tyrosine kinases (SFKs), and is expressed in cells of the myeloid and B-lymphocyte cell lineages. Excessive HCK activation is associated with several types of leukemia and enhances cell proliferation and survival by physical association with oncogenic fusion proteins, and with functional interactions with receptor tyrosine kinases. Elevated HCK activity is also observed in many solid malignancies, including breast and colon cancer, and correlates with decreased patient survival rates. HCK enhances the secretion of growth factors and pro-inflammatory cytokines from myeloid cells, and promotes macrophage polarization towards a wound healing and tumor-promoting alternatively activated phenotype. Within tumor associated macrophages, HCK stimulates the formation of podosomes that facilitate extracellular matrix degradation, which enhance immune and epithelial cell invasion. By virtue of functional cooperation between HCK and bona fide oncogenic tyrosine kinases, excessive HCK activation can also reduce drug efficacy and contribute to chemo-resistance, while genetic ablation of HCK results in minimal physiological consequences in healthy mice. Given its known crystal structure, HCK therefore provides an attractive therapeutic target to both, directly inhibit the growth of cancer cells, and indirectly curb the source of tumor-promoting changes in the tumor microenvironment.

Phagocytosis: receptors, signal integration, and the cytoskeleton

Phagocytosis is a remarkably complex and versatile process: it contributes to innate immunity through the ingestion and elimination of pathogens, while also being central to tissue homeostasis and remodeling by clearing effete cells. The ability of phagocytes to perform such diverse functions rests, in large part, on their vast repertoire of receptors. In this review, we address the various receptor types, their mobility in the plane of the membrane, and two modes of receptor crosstalk: priming and synergy. A major section is devoted to the actin cytoskeleton, which not only governs receptor mobility and clustering but also is instrumental in particle engulfment. Four stages of the actin remodeling process are identified and discussed: (i) the 'resting' stage that precedes receptor engagement, (ii) the disruption of the cortical actin prior to formation of the phagocytic cup, (iii) the actin polymerization that propels pseudopod extension, and (iv) the termination of polymerization and removal of preassembled actin that are required for focal delivery of endomembranes and phagosomal sealing. These topics are viewed in the larger context of the differentiation and polarization of the phagocytic cells.

HIV-1 reprograms the migration of macrophages

Macrophages are motile leukocytes, targeted by HIV-1, thought to play a critical role in host dissemination of the virus. However, whether infection impacts their migration capacity remains unknown. We show that 2-dimensional migration and the 3-dimensional (3D) amoeboid migration mode of HIV-1-infected human monocyte-derived macrophages were inhibited, whereas the 3D mesenchymal migration was enhanced. The viral protein Nef was necessary and sufficient for all HIV-1-mediated effects on migration. In Nef transgenic mice, tissue infiltration of macrophages was increased in a tumor model and in several tissues at steady state, suggesting a dominant role for mesenchymal migration in vivo. The mesenchymal motility involves matrix proteolysis and podosomes, cell structures constitutive of monocyte-derived cells. Focusing on the mechanisms used by HIV-1 Nef to control the mesenchymal migration, we show that the stability, size, and proteolytic function of podosomes are increased via the phagocyte-specific kinase Hck and Wiskott-Aldrich syndrome protein (WASP), 2 major regulators of podosomes. In conclusion, HIV-1 reprograms macrophage migration, which likely explains macrophage accumulation in several patient tissues, which is a key step for virus spreading and pathogenesis. Moreover, Nef points out podosomes and the Hck/WASP signaling pathway as good candidates to control tissue infiltration of macrophages, a detrimental phenomenon in several diseases.