Autocrine CSF-1R activation promotes Src-dependent disruption of mammary epithelial architecture

Colony-stimulating factor-1 receptor inhibition combined with paclitaxel exerts effective antitumor effects in the treatment of ovarian cancer

Ovarian cancer is the tumor with the highest mortality among gynecological malignancies. Studies have confirmed that paclitaxel chemoresistance is associated with increased infiltration of tumor-associated macrophages (TAMs) in the microenvironment. Colony-stimulating factor 1 (CSF-1) receptor (CSF-1R) plays a key role in regulating the number and differentiation of macrophages in certain solid tumors. There are few reports on the effects of targeted inhibition of CSF-1R in combination with chemotherapy on ovarian cancer and the tumor microenvironment. Here, we explored the antitumor efficacy and possible mechanisms of the CSF - 1R inhibitor pexidartinib (PLX3397) when combined with the first-line chemotherapeutic agent paclitaxel in the treatment of ovarian cancer. We found that CSF-1R is highly expressed in ovarian cancer cells and correlates with poor prognosis. Treatment by PLX3397 in combination with paclitaxel significantly inhibited the growth of ovarian cancer both in vitro and in vivo. Blockade of CSF-1R altered the macrophage phenotype and reprogrammed the immunosuppressive cell population in the tumor microenvironment.

CSF-1R in Cancer: More than a Myeloid Cell Receptor

Colony-stimulating factor 1 receptor (CFS-1R) is a myeloid receptor with a crucial role in monocyte survival and differentiation. Its overexpression is associated with aggressive tumors characterized by an immunosuppressive microenvironment and poor prognosis. CSF-1R ligands, IL-34 and M-CSF, are produced by many cells in the tumor microenvironment (TME), suggesting a key role for the receptor in the crosstalk between tumor, immune and stromal cells in the TME. Recently, CSF-1R expression was reported in the cell membrane of the cancer cells of different solid tumors, capturing the interest of various research groups interested in investigating the role of this receptor in non-myeloid cells. This review summarizes the current data available on the expression and activity of CSF-1R in different tumor types. Notably, CSF-1R+ cancer cells have been shown to produce CSF-1R ligands, indicating that CSF-1R signaling is positively regulated in an autocrine manner in cancer cells. Recent research demonstrated that CSF-1R signaling enhances cell transformation by supporting tumor cell proliferation, invasion, stemness and drug resistance. In addition, this review covers recent therapeutic strategies, including monoclonal antibodies and small-molecule inhibitors, targeting the CSF-1R and designed to block the pro-oncogenic role of CSF-1R in cancer cells.

In silico targeting of colony-stimulating factor-1 receptor: delineating immunotherapy in cancer

Aim

Delineate structure-based inhibition of colony-stimulating factor-1 receptor (CSF1R) by small molecule CSF1R inhibitors in clinical development for target identification and potential lead optimization in cancer therapeutics since CSF1R is a novel predictive biomarker for immunotherapy in cancer.

Methods

Compounds were in silico modelled by induced fit docking protocol in a molecular operating environment (MOE, MOE.v.2015). The 3-dimensional (3D) X-ray crystallized structure of CSF1R kinase (Protein Databank, ID 4R7H) was obtained from Research Collaboratory for Structural Bioinformatics (RSCB) Protein Databank. The 3D conformers of edicotinib, DCC-3014, ARRY-382, BLZ-945, chiauranib, dovitinib, and sorafenib were obtained from PubChem Database. These structures were modelled in Amber10:EHT molecular force field, and quick prep application was used to correct and optimize the structures for missing residues, H-counts, termini capping, and alternates. The binding site was defined within the vicinity of the co-crystallized ligand of CSF1R kinase. The compounds were docked by the triangular matcher placement method and ranked by the London dG scoring function. The docked poses were further refined by the induced fit method. The pose with the lowest binding score (ΔG) was used to model the ligand interaction profile in Discovery Studio Visualizer v17.2. The co-crystallized ligand was docked in its apo conformation, and root-mean-square deviation was computed to validate the docking protocol.

Results

All 7 CSF1R inhibitors interact with residue Met637 exhibiting selectivity except for edicotinib. The inhibitors maintain CSF1R in an auto-inhibitory conformation by interacting with Asp797 of the Asp-Phe-Gly (DFG) motif and/or hindering the conserved salt bridge formed between Glu633 and Lys616 thus stabilizing the activation loop, or interacting with tryptophan residue (Trp550) in the juxtamembrane domain. DCC-3014, ARRY-382, BLZ-945, and sorafenib bind with the lowest binding energy with CSF1R kinase.

Conclusions

Pyrimidines are potent inhibitors that interact with CSF1R residues. DCC-3014 and ARRY-382 exhibit exceptional pharmaceutical potential exhibiting great structural stability and affinity.

A DNA-PK phosphorylation site on MET regulates its signaling interface with the DNA damage response

The DNA damage response (DDR) is intertwined with signaling pathways downstream of oncogenic receptor tyrosine kinases (RTKs). To drive research into the application of targeted therapies as radiosensitizers, a better understanding of this molecular crosstalk is necessary. We present here the characterization of a previously unreported MET RTK phosphosite, Serine 1016 (S1016) that represents a potential DDR-MET interface. MET S1016 phosphorylation increases in response to irradiation and is mainly targeted by DNA-dependent protein kinase (DNA-PK). Phosphoproteomics unveils an impact of the S1016A substitution on the overall long-term cell cycle regulation following DNA damage. Accordingly, the abrogation of this phosphosite strongly perturbs the phosphorylation of proteins involved in the cell cycle and formation of the mitotic spindle, enabling cells to bypass a G2 arrest upon irradiation and leading to the entry into mitosis despite compromised genome integrity. This results in the formation of abnormal mitotic spindles and a lower proliferation rate. Altogether, the current data uncover a novel signaling mechanism through which the DDR uses a growth factor receptor system for regulating and maintaining genome stability.

A novel plasma proteomic-based model for predicting liver fibrosis in HIV/HBV co-infected adults

To establish a plasma model to predict the risk of liver fibrosis in HIV/HBV co-infected individuals. Quantitative liquid chromatography-tandem mass spectrometry(LC-MS/MS) was used to identify differentially expressed proteins (DEPs) in plasma collected from HIV/HBV co-infected individuals with and without liver fibrosis. In total, 97 DEPs were identified, among which 11 were further validated as potential biomarkers, with immunoglobulin and complement components being the most common proteins. These markedly altered proteins were found to mediate pathophysiological pathways, including humoral immune response, complement and coagulation cascades, and complement activation. A visual logistic model, in which immunoglobulin heavy variable 3-20 (IGHV3-20), immunoglobulin heavy variable 1-24 (IGHV1-24), and macrophage colony-stimulating factor 1 receptor (CSF1R) proteins were included, has been established to predict liver fibrosis in HIV/HBV co-infected individuals. The preliminary conclusion showed that the combination of IGHV3-20, IGFHV1-24, and CSF1R is expected to become a predictive model for liver fibrosis in the context of HIV/HBV co-infection and a further validation should be performed.

Macrophage-Colony-Stimulating Factor Receptor Enhances Prostate Cancer Cell Growth and Aggressiveness In Vitro and In Vivo and Increases Osteopontin Expression

Prostate cancer is a major public health concern and one of the most prevalent forms of cancer worldwide. The definition of altered signaling pathways implicated in this complex disease is thus essential. In this context, abnormal expression of the receptor of Macrophage Colony-Stimulating Factor-1 (M-CSF or CSF-1) has been described in prostate cancer cells. Yet, outcomes of this expression remain unknown. Using mouse and human prostate cancer cell lines, this study has investigated the functionality of the wild-type CSF-1 receptor in prostate tumor cells and identified molecular mechanisms underlying its ligand-induced activation. Here, we showed that upon CSF-1 binding, the receptor autophosphorylates and activates multiple signaling pathways in prostate tumor cells. Biological experiments demonstrated that the CSF-1R/CSF-1 axis conferred significant advantages in cell growth and cell invasion in vitro. Mouse xenograft experiments showed that CSF-1R expression promoted the aggressiveness of prostate tumor cells. In particular, we demonstrated that the ligand-activated CSF-1R increased the expression of spp1 transcript encoding for osteopontin, a key player in cancer development and metastasis. Therefore, this study highlights that the CSF-1 receptor is fully functional in a prostate cancer cell and may be a potential therapeutic target for the treatment of prostate cancer.

Prognostic Significance of CSF-1R Expression in Early Invasive Breast Cancer

Colony-stimulating factor-1 receptor (CSF-1R) signaling promotes an immune suppressive microenvironment enriched in M2 macrophages. Given that CSF-1R inhibitors are under investigation in clinical trials, including in breast cancer, CSF-1R expression and association with immune biomarkers could identify patients who derive greater benefit from combination with immunotherapies. TIMER2.0 and bc-GenExMiner v4.7 were used to assess the correlation of CSF1R mRNA with immune infiltrates and prognosis. Following a prespecified training-validation approach, an optimized immunohistochemistry assay was applied to assess CSF-1R on carcinoma cells and macrophages on breast cancer tissue microarray series representing 2384 patients, coupled to comprehensive clinicopathological, biomarker, and outcome data. Significant positive correlations were observed between CSF1R mRNA and immune infiltrates. High carcinoma CSF-1R correlated with grade 3 tumors >2 cm, hormone receptor negativity, high Ki67, immune checkpoint biomarkers, and macrophages expressing CSF-1R and CD163. High carcinoma CSF-1R was significantly associated with poor survival in univariate and multivariate analyses. Adverse prognostic associations were retained in ER+ cases regardless of the presence of CD8+ T cells. CSF-1R+ macrophages were not prognostic. High carcinoma CSF-1R is associated with aggressive breast cancer biology and poor prognosis, particularly in ER+ cases, and identifies patients in whom biomarker-directed CSF-1R therapies may yield superior therapeutic responses.

Triggering Receptor Expressed on Myeloid Cells-2 (TREM2) Interacts With Colony-Stimulating Factor 1 Receptor (CSF1R) but Is Not Necessary for CSF1/CSF1R-Mediated Microglial Survival

Triggering receptor expressed on myeloid cells-2 (TREM2) and colony-stimulating factor 1 receptor (CSF1R) are crucial molecules for microgliopathy, which is characterized by microglia dysfunction and has recently been proposed as the neuropathological hallmark of neurological disorders. TREM2 and CSF1R are receptors expressed primarily in microglia in the brain and modulate microglial activation and survival. They are thought to be in close physical proximity. However, whether there is a direct interaction between these receptors remains elusive. Moreover, the physiological role and mechanism of the interaction of TREM2 and CSF1R remain to be determined. Here, we found that TREM2 interacted with CSF1R based on a co-immunoprecipitation assay. Additionally, we found that CSF1R knockdown significantly reduced the survival of primary microglia and increased the Trem2 mRNA level. In contrast, CSF1R expression was increased in Trem2-deficient microglia. Interestingly, administration of CSF1, the ligand of CSF1R, partially restored the survival of Trem2-deficient microglia in vitro and in vivo. Furthermore, CSF1 ameliorated Aβ plaques deposition in Trem2 ^-/-; 5XFAD mouse brain. These findings provide solid evidence that TREM2 and CSF1R have intrinsic abilities to form complexes and mutually modulate their expression. These findings also indicate the potential role of CSF1 in therapeutic intervention in TREM2 variant-bearing patients with a high risk of Alzheimer's disease (AD).

PLX3397 treatment inhibits constitutive CSF1R-induced oncogenic ERK signaling, reduces tumor growth, and metastatic burden in osteosarcoma

Osteosarcoma (OSA) is a heterogeneous and aggressive solid tumor of the bone. We recently identified the colony stimulating factor 1 receptor (Csf1r) gene as a novel driver of osteosarcomagenesis in mice using the Sleeping Beauty (SB) transposon mutagenesis system. Here, we report that a CSF1R-CSF1 autocrine/paracrine signaling mechanism is constitutively activated in a subset of human OSA cases and is critical for promoting tumor growth and contributes to metastasis. We examined CSF1R and CSF1 expression in OSAs. We utilized gain-of-function and loss-of-function studies (GOF/LOF) to evaluate properties of cellular transformation, downstream signaling, and mechanisms of CSF1R-CSF1 action. Genetic perturbation of CSF1R in immortalized osteoblasts and human OSA cell lines significantly altered oncogenic properties, which were dependent on the CSF1R-CSF1 autocrine/paracrine signaling. These functional alterations were associated with changes in the known CSF1R downstream ERK effector pathway and mitotic cell cycle arrest. We evaluated the recently FDA-approved CSF1R inhibitor Pexidartinib (PLX3397) in OSA cell lines in vitro and in vivo in cell line and patient-derived xenografts. Pharmacological inhibition of CSF1R signaling recapitulated the in vitro genetic alterations. Moreover, in orthotopic OSA cell line and subcutaneous patient-derived xenograft (PDX)-injected mouse models, PLX3397 treatment significantly inhibited local OSA tumor growth and lessened metastatic burden. In summary, CSF1R is utilized by OSA cells to promote tumorigenesis and may represent a new molecular target for therapy.

High-grade mesenchymal pancreatic ductal adenocarcinoma drives stromal deactivation through CSF-1

Pancreatic ductal adenocarcinoma (PDAC) is characterized by an abundance of stroma. Multiple molecular classification efforts have identified a mesenchymal tumor subtype that is consistently characterized by high-grade growth and poor clinical outcome. The relation between PDAC stroma and tumor subtypes is still unclear. Here, we aimed to identify how PDAC cells instruct the main cellular component of stroma, the pancreatic stellate cells (PSCs). We found in primary tissue that high-grade PDAC had reduced collagen deposition compared to low-grade PDAC. Xenografts and organotypic co-cultures established from mesenchymal-like PDAC cells featured reduced collagen and activated PSC content. Medium transfer experiments using a large set of PDAC cell lines revealed that mesenchymal-like PDAC cells consistently downregulated ACTA2 and COL1A1 expression in PSCs and reduced proliferation. We identified colony-stimulating factor 1 as the mesenchymal PDAC-derived ligand that deactivates PSCs, and inhibition of its receptor CSF1R was able to counteract this effect. In conclusion, high-grade PDAC features stroma that is low in collagen and activated PSC content, and targeting CSF1R offers direct options to maintain a tumor-restricting microenvironment.

ProtRank: bypassing the imputation of missing values in differential expression analysis of proteomic data

Background

Data from discovery proteomic and phosphoproteomic experiments typically include missing values that correspond to proteins that have not been identified in the analyzed sample. Replacing the missing values with random numbers, a process known as “imputation”, avoids apparent infinite fold-change values. However, the procedure comes at a cost: Imputing a large number of missing values has the potential to significantly impact the results of the subsequent differential expression analysis.

Results

We propose a method that identifies differentially expressed proteins by ranking their observed changes with respect to the changes observed for other proteins. Missing values are taken into account by this method directly, without the need to impute them. We illustrate the performance of the new method on two distinct datasets and show that it is robust to missing values and, at the same time, provides results that are otherwise similar to those obtained with edgeR which is a state-of-art differential expression analysis method.

Conclusions

The new method for the differential expression analysis of proteomic data is available as an easy to use Python package.

Colony-stimulating factor-1 receptor provides a growth advantage in epithelial cancer cell line A431 in the presence of epidermal growth factor receptor inhibitor gefitinib

Although epidermal growth factor receptor (EGFR) has been identified as a potent "oncogenic driver" in various tumors of epithelial origin, EGFR-targeted therapies are often of limited success. One of the challenges of improving targeted therapies is to overcome bypassing signaling pathways. Analysis of RNA-seq data of 1006 cell lines from the Cancer Cell Line Encyclopedia (CCLE) revealed that more than 12% of carcinoma cell lines expressed markedly elevated mRNA levels of colony-stimulating factor (CSF)-1 receptor (CSF-1R). Since epithelial cells also express CSF-1, elevated levels of CSF-1R may participate in providing alternative growth and survival signals under targeted therapies. To address this question, we ectopically expressed CSF-1R in A431 cells that express EGFR at high levels, but no biologically relevant level of CSF-1R. In the presence of EGFR inhibitor gefitinib, CSF-1R provided a significant growth advantage in A431 cells. As expected, activation of both receptors, EGFR or CSF-1R, induced phosphorylation of extracellular signal-regulated kinase (Erk)1/2, Akt, protein kinase C (PKC) and signal transducer and activator of transcription (STAT)3. However, EGFR, but not CSF-1R, also induced STAT5 phosphorylation. Inhibitor of phosphatidylinositol 3-kinase (PI3K) (AZD8186), MAPK/ERK kinase (MEK)1/2 (U0126), PKCs (Bisindolylmaleimide I or Gö6976) or STAT3 (Stattic) partially reduced proliferation of CSF-1R expressing A431 cells in the presence of gefitinib. Moreover, multi-kinase inhibitor, cabozantinib, suppressed CSF-1R activation and drastically reduced cell growth when combined with gefitinib. These data suggest that CSF-1R has the potential to reduce sensitivity to gefitinib and may be involved in resistance development.

AZ304, a novel dual BRAF inhibitor, exerts anti-tumour effects in colorectal cancer independently of BRAF genetic status

Background

BRAF mutation is associated with poor clinical outcome of patients with malignant tumours, and mediates resistance to chemotherapy and targeted therapy. This study aimed to determine whether V600E mutant and wild type BRAF colorectal cancers exhibit distinct sensitivities to the dual BRAF inhibitor AZ304.

Methods

Kinase activity was assessed by the AlphaScreen assay. Then, MTT assay, EdU assay, colony-formation assay and Western blot were performed to evaluate the anti-tumour effects of AZ304 in vitro. In vivo efficacy was investigated by xenograft analysis and immunohistochemistry.

Results

AZ304 exerted potent inhibitory effects on both wild type and V600E mutant forms of the serine/threonine-protein kinase BRAF, with IC₅₀ values of 79 nM and 38 nM, respectively. By suppressing ERK phosphorylation, AZ304 effectively inhibited a panel of human cancer cell lines with different BRAF and RAS genetic statuses. In selected colorectal cancer cell lines, AZ304 significantly inhibited cell growth in vitro and in vivo, regardless of BRAF genetic status. In addition, the EGFR inhibitor Cetuximab enhanced the potency of AZ304 independently of BRAF mutational status.

Conclusions

The BRAF inhibitor AZ304 has broad spectrum antitumour activity, which is significantly enhanced by combination with Cetuximab in colorectal cancers in vitro and in vivo.

Src activation decouples cell division orientation from cell geometry in mammalian cells

Orientation of cell division plane plays a crucial role in morphogenesis and regeneration. Misoriented cell division underlies many important diseases, such as cancer. Studies with Drosophila and C. elegance models show that Src, a proto-oncogene tyrosine-protein kinase, is a critical regulator of this aspect of mitosis. However, the role for Src in controlling cell division orientation in mammalian cells is not well understood. Using genetic and pharmacological approaches and two extracellular signals to orient cell division, we demonstrated a critical role for Src. Either knockout or pharmacological inhibition of Src would retain the fidelity of cell division orientation with the long-axis orientation of mother cells. Conversely, re-expression of Src would decouple cell division orientation from the pre-division orientation of the long axis of mother cells. Cell division orientation in human breast and gastric cancer tissues showed that the Src activation level correlated with the degree of mitotic spindle misorientation relative to the apical surface. Examination of proteins associated with cortical actin revealed that Src activation regulated the accumulation and local density of adhesion proteins on the sites of cell-matrix attachment. By analyzing division patterns in the cells with or without Src activation and through use of a mathematical model, we further support our findings and provide evidence for a previously unknown role for Src in regulating cell division orientation in relation to the pre-division geometry of mother cells, which may contribute to the misoriented cell division.

Inhibition of the colony-stimulating-factor-1 receptor affects the resistance of lung cancer cells to cisplatin

In the present work we show that multiple lung cancer cell lines contain cisplatin resistant cell subpopulations expressing the Colony-Stimulating-Factor-Receptor-1 (CSF-1R) and surviving chemotherapy-induced stress. By exploiting siRNA-mediated knock down in vitro and the use of an investigational CSF-1R TKI (JNJ-40346527) in vitro and in vivo, we show that expression and function of the receptor are required for the clonogenicity and chemoresistance of the cell lines. Thus, inhibition of the kinase activity of the receptor reduced the levels of EMT-associated genes, stem cell markers and chemoresistance genes. Additionally, the number of high aldehyde dehydrogenase (ALDH) expressing cells was reduced, consequent to the lack of cisplatin-induced increase of ALDH isoforms. This affected the collective chemoresistance of the treated cultures. Treatment of tumor bearing mice with JNJ-40346527, at pharmacologically relevant doses, produced strong chemo-sensitizing effects in vivo. These anticancer effects correlated with a reduced number of CSF-1Rpos cells, in tumors excised from the treated mice. Depletion of the CD45pos cells within the treated tumors did not, apparently, play a major role in mediating the therapeutic response to the TKI. Thus, lung cancer cells express a functional CSF-1 and CSF-1R duo which mediates pro-tumorigenic effects in vivo and in vitro and can be targeted in a therapeutically relevant way. These observations complement the already known role for the CSF-1R at mediating the pro-tumorigenic properties of tumor-infiltrating immune components.

Multiplexed Exchange-PAINT imaging reveals ligand-dependent EGFR and Met interactions in the plasma membrane

Signal transduction by receptor tyrosine kinases (RTKs) involves complex ligand- and time-dependent changes in conformation and modification state. High resolution structures are available for individual receptors dimers, but less is known about receptor clusters that form in plasma membranes composed of many different RTKs with the potential to interact. We report the use of multiplexed super-resolution imaging (Exchange-PAINT) followed by mean-shift clustering and random forest analysis to measure the precise distributions of five receptor tyrosine kinases (RTKs) from the ErbB, IGF-1R and Met families in breast cancer cells. We find that these receptors are intermixed nonhomogenously on the plasma membrane. Stimulation by EGF does not appear to induce a change in the density of EGFR in local clusters but instead results in formation of EGFR-Met and EGFR-ErbB3 associations; non-canonical EGFR-Met interactions are implicated in resistance to anti-cancer drugs but have not been previously detected in drug-naïve cells.

Identifying three-dimensional structures of autophosphorylation complexes in crystals of protein kinases

Protein kinase autophosphorylation is a common regulatory mechanism in cell signaling pathways. Crystal structures of several homomeric protein kinase complexes have a serine, threonine, or tyrosine autophosphorylation site of one kinase monomer located in the active site of another monomer, a structural complex that we call an "autophosphorylation complex." We developed and applied a structural bioinformatics method to identify all such autophosphorylation complexes in x-ray crystallographic structures in the Protein Data Bank (PDB). We identified 15 autophosphorylation complexes in the PDB, of which five complexes had not previously been described in the publications describing the crystal structures. These five complexes consist of tyrosine residues in the N-terminal juxtamembrane regions of colony-stimulating factor 1 receptor (CSF1R, Tyr(561)) and ephrin receptor A2 (EPHA2, Tyr(594)), tyrosine residues in the activation loops of the SRC kinase family member LCK (Tyr(394)) and insulin-like growth factor 1 receptor (IGF1R, Tyr(1166)), and a serine in a nuclear localization signal region of CDC-like kinase 2 (CLK2, Ser(142)). Mutations in the complex interface may alter autophosphorylation activity and contribute to disease; therefore, we mutated residues in the autophosphorylation complex interface of LCK and found that two mutations impaired autophosphorylation (T445V and N446A) and mutation of Pro(447) to Ala, Gly, or Leu increased autophosphorylation. The identified autophosphorylation sites are conserved in many kinases, suggesting that, by homology, these complexes may provide insight into autophosphorylation complex interfaces of kinases that are relevant drug targets.

A novel glycobiomarker, Wisteria floribunda agglutinin macrophage colony-stimulating factor receptor, for predicting carcinogenesis of liver cirrhosis

Recently, we identified a novel liver fibrosis glycobiomarker, Wisteria floribunda agglutinin (WFA)-reactive colony stimulating factor 1 receptor (WFA(+) -CSF1R), using a glycoproteomics-based strategy. The aim of this study was to assess the value of measuring WFA(+) -CSF1R levels for the prognosis of carcinogenesis and outcome in liver cirrhosis (LC) patients with hepatitis C virus (HCV). WFA(+) -CSF1R and Total-CSF1R levels were measured in serum samples from 214 consecutive HCV-infected patients to evaluate their impact on carcinogenesis and the survival of LC patients. Serum WFA(+) -CSF1R levels were significantly higher in LC patients than chronic hepatitis (CH) patients (p < 0.001). The AUC of WFA(+) -CSF1R for predicting overall survival, calculated by time-dependent ROC analysis, was 0.691 and the HR (per 1-SD increase) was 1.80 (95% CI, 1.23-2.62, p < 0.001). Furthermore, the survival rate of LC patients with high WFA(+) -CSF1R levels (≥ 310 ng/ml) was significantly worse than those with lower levels (p < 0.01). The AUC of WFA(+) /total-CSF1R percentage (WFA(+) -CSF1R%) for predicting the cumulative carcinogenesis rate was 0.760, with an HR of 1.66 (95% CI 1.26-2.20, p < 0.001). In fact, the carcinogenesis rate was significantly higher in LC patients with a high WFA(+) -CSF1R% (≥ 35%, p = 0.006). Assessing serum levels of WFA(+) -CSF1R has diagnostic value for predicting carcinogenesis and the survival of LC patients.

Activation of MET via diverse exon 14 splicing alterations occurs in multiple tumor types and confers clinical sensitivity to MET inhibitors

Focal amplification and activating point mutation of the MET gene are well-characterized oncogenic drivers that confer susceptibility to targeted MET inhibitors. Recurrent somatic splice site alterations at MET exon 14 (METex14) that result in exon skipping and MET activation have been characterized, but their full diversity and prevalence across tumor types are unknown. Here, we report analysis of tumor genomic profiles from 38,028 patients to identify 221 cases with METex14 mutations (0.6%), including 126 distinct sequence variants. METex14 mutations are detected most frequently in lung adenocarcinoma (3%), but also frequently in other lung neoplasms (2.3%), brain glioma (0.4%), and tumors of unknown primary origin (0.4%). Further in vitro studies demonstrate sensitivity to MET inhibitors in cells harboring METex14 alterations. We also report three new patient cases with METex14 alterations in lung or histiocytic sarcoma tumors that showed durable response to two different MET-targeted therapies. The diversity of METex14 mutations indicates that diagnostic testing via comprehensive genomic profiling is necessary for detection in a clinical setting.

SIGNIFICANCE

Here we report the identification of diverse exon 14 splice site alterations in MET that result in constitutive activity of this receptor and oncogenic transformation in vitro. Patients whose tumors harbored these alterations derived meaningful clinical benefit from MET inhibitors. Collectively, these data support the role of METex14 alterations as drivers of tumorigenesis, and identify a unique subset of patients likely to derive benefit from MET inhibitors.

Soluble endoglin antagonizes Met signaling in spindle carcinoma cells

Increased levels of soluble endoglin (Sol-Eng) correlate with poor outcome in human cancer. We have previously shown that shedding of membrane endoglin, and concomitant release of Sol-Eng is a late event in chemical mouse skin carcinogenesis associated with the development of undifferentiated spindle cell carcinomas (SpCCs). In this report, we show that mouse skin SpCCs exhibit a high expression of hepatocyte growth factor (HGF) and an elevated ratio of its active tyrosine kinase receptor Met versus total Met levels. We have evaluated the effect of Sol-Eng in spindle carcinoma cells by transfection of a cDNA encoding most of the endoglin ectodomain or by using purified recombinant Sol-Eng. We found that Sol-Eng inhibited both mitogen-activated protein kinase (MAPK) activity and cell growth in vitro and in vivo. Sol-Eng also blocked MAPK activation by transforming growth factor-β1 (TGF-β1) and impaired both basal and HGF-induced activation of Met and downstream MAPK. Moreover, Sol-Eng strongly reduced basal and HGF-stimulated spindle cell migration and invasion. Both Sol-Eng and full-length endoglin were shown to interact with Met by coimmunoprecipitation experiments. However, full-length endoglin expressed at the plasma membrane of spindle carcinoma cells had no effect on Met signaling activity, and was unable to inhibit HGF-induced cell migration/invasion. These results point to a paradoxical suppressor role for Sol-Eng in carcinogenesis.

Autocrine CSF1R signaling mediates switching between invasion and proliferation downstream of TGFβ in claudin-low breast tumor cells

Patient data suggest that colony stimulating factor-1 (CSF1) and its receptor (CSF1R) play critical roles during breast cancer progression. We have previously shown that in human breast tumors expressing both CSF1 and CSF1R, invasion in vivo is dependent both on a paracrine interaction with tumor-associated macrophages and an autocrine regulation of CSF1R in the tumor cells themselves. Although the role of the paracrine interaction between tumor cells and macrophages has been extensively studied, very little is known about the mechanism by which the autocrine CSF1R signaling contributes to tumor progression. We show here that breast cancer patients of the claudin-low subtype have significantly increased expression of CSF1R. Using a panel of breast cancer cells lines, we confirm that CSF1R expression is elevated and regulated by TGFβ specifically in claudin-low cell lines. Abrogation of autocrine CSF1R signaling in MDA-MB-231 xenografts (a claudin-low cell line) leads to increased tumor size by enhanced proliferation, but significantly reduced invasion, dissemination and metastasis. Indeed, we show that proliferation and invasion are oppositely regulated by CSF1R downstream of TGFβ only in claudin-low cells lines. Intravital multiphoton imaging revealed that inhibition of CSF1R in the tumor cells leads to decreased in vivo motility and a more cohesive morphology. We show that, both in vitro and in vivo, CSF1R inhibition results in a reversal of claudin-low marker expression by significant upregulation of luminal keratins and tight junction proteins such as claudins. Finally, we show that artificial overexpression of claudins in MDA-MB-231 cells is sufficient to tip the cells from an invasive state to a proliferative state. Our results suggest that autocrine CSF1R signaling is essential in maintaining low claudin expression and that it mediates a switch between the proliferative and the invasive state in claudin-low tumor cells downstream of TGFβ.

Autocrine CSF-1R signaling drives mesothelioma chemoresistance via AKT activation

Clinical management of malignant pleural mesothelioma (MPM) is very challenging because of the uncommon resistance of this tumor to chemotherapy. We report here increased expression of macrophage colony-stimulating-factor-1-receptor (M-CSF/CSF-1R) mRNA in mesothelioma versus normal tissue specimens and demonstrate that CSF-1R expression identifies chemoresistant cells of mesothelial nature in both primary cultures and mesothelioma cell lines. By using RNAi or ligand trapping, we demonstrate that the chemoresistance properties of those cells depend on autocrine CSF-1R signaling. At the single-cell level, the isolated CSF-1R^pos cells exhibit a complex repertoire of pluripotency, epithelial–mesenchymal transition and detoxifying factors, which define a clonogenic, chemoresistant, precursor-like cell sub-population. The simple activation of CSF-1R in untransformed mesothelial cells is sufficient to confer clonogenicity and resistance to pemetrexed, hallmarks of mesothelioma. In addition, this induced a gene expression profile highly mimicking that observed in the MPM cells endogenously expressing the receptor and the ligands, suggesting that CSF-1R expression is mainly responsible for the phenotype of the identified cell sub-populations. The survival of CSF1R^pos cells requires active AKT (v-akt murine thymoma viral oncogene homolog 1) signaling, which contributed to increased levels of nuclear, transcriptionally competent β-catenin. Inhibition of AKT reduced the transcriptional activity of β-catenin-dependent reporters and sensitized the cells to senescence-induced clonogenic death after pemetrexed treatment. This work expands what is known on the non-macrophage functions of CSF-1R and its role in solid tumors, and suggests that CSF-1R signaling may have a critical pathogenic role in a prototypical, inflammation-related cancer such as MPM and therefore may represent a promising target for therapeutic intervention.

The need for complex 3D culture models to unravel novel pathways and identify accurate biomarkers in breast cancer

The recent cataloging of the genomic aberrations in breast cancer has revealed the diversity and complexity of the disease at the genetic level. To unravel the functional consequences of specific repertoires of mutations and copy number changes on signaling pathways in breast cancer, it is crucial to develop model systems that truly recapitulate the disease. Here we discuss the three-dimensional culture models currently being used or recently developed for the study of normal mammary epithelial cells and breast cancer, including primary tumors and dormancy. We discuss the insights gained from these models in regards to cell signaling and potential therapeutic strategies, and the challenges that need to be met for the generation of heterotypic breast cancer model systems that are amenable for high-throughput approaches.

Autocrine inhibition of the c-fms proto-oncogene reduces breast cancer bone metastasis assessed with in vivo dual-modality imaging

Breast cancer cells preferentially home to the bone microenvironment, which provides a unique niche with a network of multiple bidirectional communications between host and tumor, promoting survival and growth of bone metastases. In the bone microenvironment, the c-fms proto-oncogene that encodes for the CSF-1 receptor, along with CSF-1, serves as one critical cytokine/receptor pair, functioning in paracrine and autocrine fashion. Previous studies concentrated on the effect of inhibition of host (mouse) c-fms on bone metastasis, with resulting decrease in osteolysis and bone metastases as a paracrine effect. In this report, we assessed the role of c-fms inhibition within the tumor cells (autocrine effect) in the early establishment of breast cancer cells in bone and the effects of this early c-fms inhibition on subsequent bone metastases and destruction. This study exploited a multidisciplinary approach by employing two non-invasive, in vivo imaging methods to assess the progression of bone metastases and bone destruction, in addition to ex vivo analyses using RT-PCR and histopathology. Using a mouse model of bone homing human breast cancer cells, we showed that an early one-time application of anti-human c-fms antibody delayed growth of bone metastases and bone destruction for at least 31 days as quantitatively measured by bioluminescence imaging and computed tomography, compared to controls. Thus, neutralizing human c-fms in the breast cancer cell alone decreases extent of subsequent bone metastasis formation and osteolysis. Furthermore, we are the first to show that anti-c-fms antibodies can impact early establishment of breast cancer cells in bone.

Building bridges toward invasion: tumor promoter treatment induces a novel protein kinase C-dependent phenotype in MCF10A mammary cell acini

The potent tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) alters many cellular processes through activation of its receptor protein kinase C (PKC), including gene expression, cell cycle, and the regulation of cell morphology, raising an important question for developing targeted methods to prevent cancer: which effects of TPA are crucial for carcinogenesis? To address this question, we studied TPA action in the 3-dimensional (3D) MCF10A human breast epithelial cell system, which models important features of in vivo epithelial tissue including growth constraints, structural organization of cells, and establishment of a basement membrane. MCF10A cells, which are immortalized but nontumorigenic, form hollow, spheroid structures in 3D culture referred to as acini. The development of normal acini requires the tight spatiotemporal regulation of cellular proliferation, polarization, apoptosis, and growth arrest. Treatment of MCF10A acini with TPA caused the appearance of multi-acinar structures. Surprisingly, this phenotype did not involve an increase in cell number or major changes in cell death, and polarization. Instead, live cell and confocal microscopy revealed that TPA stimulates MCF10A acini to aggregate. TPA induces the PKC-dependent production of actin-based protrusions, which leads to the formation of cellular bridges between acini, the clustering of acini, and allows cells to move into adjacent acini. During this process, the integrity of the laminin V basement membrane is disrupted, while E-cadherin-based cell-cell contacts remain intact. Altogether, our results show that under the biochemical and structural constraints of epithelial tissue, as modeled by the 3D MCF10A system, TPA induces a novel PKC-dependent phenotype that resembles local invasion. Of the many effects caused by TPA, these studies highlight the aggressive production of actin-based cellular protrusions as a potentially important event along the pathway to carcinogenesis.

Cullin 5 destabilizes Cas to inhibit Src-dependent cell transformation

Phosphorylation-dependent protein ubiquitylation and degradation provides an irreversible mechanism to terminate protein kinase signaling. Here, we report that mammary epithelial cells require cullin-5-RING-E3-ubiquitin-ligase complexes (Cul5-CRLs) to prevent transformation by a Src-Cas signaling pathway. Removal of Cul5 stimulates growth-factor-independent growth and migration, membrane dynamics and colony dysmorphogenesis, which are all dependent on the endogenous tyrosine kinase Src. Src is activated in Cul5-deficient cells, but Src activation alone is not sufficient to cause transformation. We found that Cul5 and Src together stimulate degradation of the Src substrate p130Cas (Crk-associated substrate). Phosphorylation stimulates Cas binding to the Cul5-CRL adaptor protein SOCS6 and consequent proteasome-dependent degradation. Cas is necessary for the transformation of Cul5-deficient cells. Either knockdown of SOCS6 or use of a degradation-resistant Cas mutant stimulates membrane ruffling, but not other aspects of transformation. Our results show that endogenous Cul5 suppresses epithelial cell transformation by several pathways, including inhibition of Src-Cas-induced ruffling through SOCS6.

Specific fate decisions in adult hepatic progenitor cells driven by MET and EGFR signaling

The relative contribution of hepatocyte growth factor (HGF)/MET and epidermal growth factor (EGF)/EGF receptor (EGFR), two key signal transduction systems in the normal and diseased liver, to fate decisions of adult hepatic progenitor cells (HPCs) has not been resolved. Here, we developed a robust culture system that permitted expansion and genetic manipulation of cells capable of multilineage differentiation in vitro and in vivo to examine the individual roles of HGF/MET and EGF/EGFR in HPC self-renewal and binary cell fate decision. By employing loss-of-function and rescue experiments in vitro, we showed that both receptors collaborate to increase the self-renewal of HPCs through activation of the extracellular signal-regulated kinase (ERK) pathway. MET was a strong inducer of hepatocyte differentiation by activating AKT and signal transducer and activator of transcription (STAT3). Conversely, EGFR selectively induced NOTCH1 to promote cholangiocyte specification and branching morphogenesis while concomitantly suppressing hepatocyte commitment. Furthermore, unlike the deleterious effects of MET deletion, the liver-specific conditional loss of Egfr facilitated rather than suppressed progenitor-mediated liver regeneration by switching progenitor cell differentiation toward hepatocyte lineage. These data provide new insight into the mechanisms regulating the stemness properties of adult HPCs and reveal a previously unrecognized link between EGFR and NOTCH1 in directing cholangiocyte differentiation.

Dynamics and regulation of epithelial adherens junctions: recent discoveries and controversies

Adherens junctions (AJs) are evolutionarily conserved plasma-membrane structures that mediate cell-cell adhesions in multicellular organisms. They are organized by several types of adhesive integral membrane proteins, most notably cadherins and nectins that are clustered and stabilized by a number of cytoplasmic scaffolds. AJs are key regulators of tissue architecture and dynamics via control of cell proliferation, polarity, shape, motility, and survival. They are absolutely critical for normal tissue morphogenesis and their disruption results in pathological abnormalities in different tissues. Although the field of adherens-junction research dramatically progressed in recent years, a number of important questions remain controversial and poorly understood. This review outlines basic principles that regulate organization of AJs in mammalian epithelia and discusses recent advances and standing controversies in the field. A special attention is paid to the regulation of AJs by vesicle trafficking and the intracellular cytoskeleton as well as roles and mechanisms of adherens-junction disruption during tumor progression and tissue inflammation.

CSF1R signaling blockade stanches tumor-infiltrating myeloid cells and improves the efficacy of radiotherapy in prostate cancer

Radiotherapy is used to treat many types of cancer, but many treated patients relapse with local tumor recurrence. Tumor-infiltrating myeloid cells (TIM), including CD11b (ITGAM)(+)F4/80 (EMR1)+ tumor-associated macrophages (TAM), and CD11b(+)Gr-1 (LY6G)+ myeloid-derived suppressor cells (MDSC), respond to cancer-related stresses and play critical roles in promoting tumor angiogenesis, tissue remodeling, and immunosuppression. In this report, we used a prostate cancer model to investigate the effects of irradiation on TAMs and MDSCs in tumor-bearing animals. Unexpectedly, when primary tumor sites were irradiated, we observed a systemic increase of MDSCs in spleen, lung, lymph nodes, and peripheral blood. Cytokine analysis showed that the macrophage colony-stimulating factor CSF1 increased by two-fold in irradiated tumors. Enhanced macrophage migration induced by conditioned media from irradiated tumor cells was completely blocked by a selective inhibitor of CSF1R. These findings were confirmed in patients with prostate cancer, where serum levels of CSF1 increased after radiotherapy. Mechanistic investigations revealed the recruitment of the DNA damage-induced kinase ABL1 into cell nuclei where it bound the CSF1 gene promoter and enhanced CSF1 gene transcription. When added to radiotherapy, a selective inhibitor of CSF1R suppressed tumor growth more effectively than irradiation alone. Our results highlight the importance of CSF1/CSF1R signaling in the recruitment of TIMs that can limit the efficacy of radiotherapy. Furthermore, they suggest that CSF1 inhibitors should be evaluated in clinical trials in combination with radiotherapy as a strategy to improve outcomes.

Substrate stiffness regulates cadherin-dependent collective migration through myosin-II contractility

The mechanical microenvironment is known to influence single-cell migration; however, the extent to which mechanical cues affect collective migration of adherent cells is not well understood. We measured the effects of varying substrate compliance on individual cell migratory properties in an epithelial wound-healing assay. Increasing substrate stiffness increased collective cell migration speed, persistence, and directionality as well as the coordination of cell movements. Dynamic analysis revealed that wounding initiated a wave of motion coordination from the wound edge into the sheet. This was accompanied by a front-to-back gradient of myosin-II activation and establishment of cell polarity. The propagation was faster and farther reaching on stiff substrates, indicating that substrate stiffness affects the transmission of directional cues. Manipulation of myosin-II activity and cadherin-catenin complexes revealed that this transmission is mediated by coupling of contractile forces between neighboring cells. Thus, our findings suggest that the mechanical environment integrates in a feedback with cell contractility and cell-cell adhesion to regulate collective migration.

Biologic characteristics of premalignant breast disease

Breast cancer is the second leading cause of cancer death in women in the United States. While mammography and breast magnetic resonance imaging (MRI) improve detection of early disease, there remains an unmet need for biomarkers for risk stratification, early detection, prediction, and disease prognosis. A number of early breast lesions, from atypical hyperplasias to carcinomas in situ, are associated with an increased risk of developing subsequent invasive breast carcinoma. The recent development of genomic, epigenomic, and proteomic tools for tissue biomarker detection, including array CGH, RNA expression microarrays, and proteomic arrays have identified a number of potential biomarkers that both identify patients at increased risk, as well as provided insights into the pathology of early breast cancer development. This chapter focuses on the detection and application of tissue and serum biomarkers for the identification and risk stratification of early breast cancer lesions.

Functional characterization of cancer-associated Gab1 mutations

Grb2-associated binder 1 (Gab1) is a docking protein that transduces signals from a variety of tyrosine kinases, including Met and the epidermal growth factor receptor (EGFR). Although the related protein Gab2 is strongly implicated in human cancer, a role for Gab1 has been less clear. However, a screen for gene mutations in breast cancer identified two somatic mutations in Gab1, Y83C and T387N. In this paper we describe the functional characterization of these Gab1 mutants. MCF-10A immortalized mammary epithelial cells overexpressing Gab1 Y83C and T387N exhibited a more elongated, fibroblastic phenotype compared with wild-type Gab1 controls. Expression of Gab1 or the mutants promoted epidermal growth factor (EGF)-independent proliferation in monolayer culture to a similar degree. However, in Matrigel culture, both mutants enhanced the formation of acini exhibiting an aberrant, branched morphology. In addition, expression of the mutants modestly increased Erk activation. The two mutants also enhanced branching morphogenesis in a different mammary epithelial cell line, HC11. To gain further insights into the mechanism of action of these mutations, we mapped Gab1 phosphorylation sites by mass spectrometry. This detected phosphorylation of T387 but ;not Y83. Cellular stimulation with EGF or hepatocyte growth factor (HGF) led to a transient, or sustained, induction of T387 phosphorylation, respectively. As T387 corresponds in position to Gab2 T391, which suppresses Gab2 signaling in a phosphorylation-dependent manner, these data support a model in which the T387N mutation abrogates negative-feedback regulation of Gab1. Interrogation of publically-available databases revealed additional cancer-associated mutations at, or in close proximity to, identified serine/threonine phosphorylation sites in other docking proteins. These data indicate that aberrant Gab1 signaling can directly contribute to breast cancer progression, and that negative feedback sites in docking proteins can be targeted by oncogenic mutations.

Global gene expression profiles of canine macrophages and canine mammary cancer cells grown as a co-culture in vitro

Background

Solid tumours comprise various cells, including cancer cells, resident stromal cells, migratory haemopoietic cells and other. These cells regulate tumour growth and metastasis. Macrophages constitute probably the most important element of all interactions within the tumour microenvironment. However, the molecular mechanism, that guides tumour environment, still remains unknown. Exploring the underlying molecular mechanisms that orchestrate these phenomena has been the aim of our study.

A co-culture of canine mammary cancer cells and macrophages was established and maintained for 72 hrs. Having sorted the cells, gene expression in cancer cells and macrophages, using DNA microarrays, was examined. The results were confirmed using real-time qPCR and confocal microscopy. Moreover, their ability for migration and invasion has been assessed.

Results

Microarray analysis showed that the up-regulated genes in the cancer cell lines are involved in 15 highly over-manifested pathways. The pathways that drew our diligent attention included: the inflammation pathway mediated by chemokine and cytokine, the Toll receptor signalling pathway and the B cell activation. The up-regulated genes in the macrophages were involved in only 18 significantly over-manifested pathways: the angiogenesis, the p53 pathway feedback loops2 and the Wnt signalling pathway. The microarray analysis revealed that co-culturing of cancer cells with macrophages initiated the myeloid-specific antigen expression in cancer cells, as well as cytokine/chemokine genes expression. This finding was confirmed at mRNA and protein level. Moreover, we showed that macrophages increase cancer migration and invasion.

Conclusions

The presence of macrophages in the cancer environment induces acquisition of the macrophage phenotype (specific antigens and chemokines/cytokines expression) in cancer cells. We presumed that cancer cells also acquire other myeloid features, such as: capabilities of cell rolling, spreading, migration and matrix invasion (what has also been confirmed by our results). It may, perhaps, be the result of myeloid-cancer cell hybrid formation, or cancer cells mimicking macrophages phenotype, owing to various proteins secreted by macrophages.

Inhibition of the c-fms proto-oncogene autocrine loop and tumor phenotype in glucocorticoid stimulated human breast carcinoma cells

The c-fms proto-oncogene encoded CSF-1 receptor and its ligand represent a feedback loop, which in a paracrine manner, is well known to promote spread of breast cancers. The role of the autocrine feedback loop in promotion of breast tumor behavior, in particular in vitro, is less well understood. The physiologic stimulation of c-fms expression by glucocorticoids (GCs) in vitro and in vivo magnifies the tumor promoting effect seen in these cells from activated c-fms signaling by CSF-1. Targeted molecular therapy against c-fms could therefore abrogate both complementary feedback loops. Using breast cancer cells endogenously co-expressing receptor and ligand, we used complementary approaches to inhibit c-fms expression and function within this autocrine pathway in the context of GC stimulation. Silencing RNA (shRNA), antisense oligonucleotide therapy (AON), and inhibition of c-fms signaling, were all used to quantitate inhibition of GC-stimulated adhesion, motility, and invasion of human breast cancer cells in vitro. shRNA to c-fms downregulated GC-stimulated c-fms mRNA by fourfold over controls, correlating with over twofold reduction in cellular invasiveness. AON therapy was also able to inhibit GC stimulation of c-fms mRNA, and resulted in threefold less invasiveness and 1.5 to 2-fold reductions in adhesion and motility. Finally, the small-molecule c-fms inhibitor Ki20227 was able to decrease in a dose-response manner, breast cancer cell invasion by up to fourfold. Inhibition of this receptor/ligand pair may have clinical utility in inhibition of the autocrine as well as the known paracrine interactions in breast cancer, thus further supporting use of targeted therapies in this disease.

Profiling Y561-dependent and -independent substrates of CSF-1R in epithelial cells

Receptor tyrosine kinases (RTKs) activate multiple downstream cytosolic tyrosine kinases following ligand stimulation. SRC family kinases (SFKs), which are recruited to activated RTKs through SH2 domain interactions with RTK autophosphorylation sites, are targets of many subfamilies of RTKs. To date, there has not been a systematic analysis of the downstream substrates of such receptor-activated SFKs. Here, we conducted quantitative mass spectrometry utilizing stable isotope labeling (SILAC) analysis to profile candidate SRC-substrates induced by the CSF-1R tyrosine kinase by comparing the phosphotyrosine-containing peptides from cells expressing either CSF-1R or a mutant form of this RTK that is unable to bind to SFKs. This analysis identified previously uncharacterized changes in tyrosine phosphorylation induced by CSF-1R in mammary epithelial cells as well as a set of candidate substrates dependent on SRC recruitment to CSF-1R. Many of these candidates may be direct SRC targets as the amino acids flanking the phosphorylation sites in these proteins are similar to known SRC kinase phosphorylation motifs. The putative SRC-dependent proteins include known SRC substrates as well as previously unrecognized SRC targets. The collection of substrates includes proteins involved in multiple cellular processes including cell-cell adhesion, endocytosis, and signal transduction. Analyses of phosphoproteomic data from breast and lung cancer patient samples identified a subset of the SRC-dependent phosphorylation sites as being strongly correlated with SRC activation, which represent candidate markers of SRC activation downstream of receptor tyrosine kinases in human tumors. In summary, our data reveal quantitative site-specific changes in tyrosine phosphorylation induced by CSF-1R activation in epithelial cells and identify many candidate SRC-dependent substrates phosphorylated downstream of an RTK.

The microenvironment determines the breast cancer cells' phenotype: organization of MCF7 cells in 3D cultures

Background

Stromal-epithelial interactions mediate breast development, and the initiation and progression of breast cancer. In the present study, we developed 3-dimensional (3D) in vitro models to study breast cancer tissue organization and the role of the microenvironment in phenotypic determination.

Methods

The human breast cancer MCF7 cells were grown alone or co-cultured with primary human breast fibroblasts. Cells were embedded in matrices containing either type I collagen or a combination of reconstituted basement membrane proteins and type I collagen. The cultures were carried out for up to 6 weeks. For every time point (1-6 weeks), the gels were fixed and processed for histology, and whole-mounted for confocal microscopy evaluation. The epithelial structures were characterized utilizing immunohistochemical techniques; their area and proliferation index were measured using computerized morphometric analysis. Statistical differences between groups were analyzed by ANOVA, Dunnett's T3 post-hoc test and chi-square.

Results

Most of the MCF7 cells grown alone within a collagen matrix died during the first two weeks; those that survived organized into large, round and solid clusters. The presence of fibroblasts in collagen gels reduced MCF7 cell death, induced cell polarity, and the formation of round and elongated epithelial structures containing a lumen. The addition of reconstituted basement membrane to collagen gels by itself had also survival and organizational effects on the MCF7 cells. Regardless of the presence of fibroblasts, the MCF7 cells both polarized and formed a lumen. The addition of fibroblasts to the gel containing reconstituted basement membrane and collagen induced the formation of elongated structures.

Conclusions

Our results indicate that a matrix containing both type I collagen and reconstituted basement membrane, and the presence of normal breast fibroblasts constitute the minimal permissive microenvironment to induce near-complete tumor phenotype reversion. These human breast 3D tissue morphogenesis models promise to become reliable tools for studying tissue interactions, therapeutic screening and drug target validation.

Unregulated ARF6 activation in epithelial cysts generates hyperactive signaling endosomes and disrupts morphogenesis

This study shows that constitutive ARF6 activation during epithelial cyst morphogenesis promotes the formation of signaling endosomes that serve as platforms for hyperactive receptor signaling and leads to the generation of tumorigenic glandular phenotypes.

Tumor development in glandular tissues is associated with structural alterations in the hollow ducts and spherical structures that comprise such tissues. We describe a signaling axis involving sustained activation of the GTP-binding protein, ARF6, that provokes dramatic changes in the organization of epithelial cysts, reminiscent of tumorigenic glandular phenotypes. In reconstituted basement membrane cultures of renal epithelial cysts, enhanced ARF6 activation induces the formation of cell-filled glandular structures with multiple lumens and disassembled cadherin-based cell–cell contacts. All of these alterations are accompanied by growth factor receptor internalization into signaling endosomes and reversed by blocking ARF6 activation or receptor endocytosis. Receptor localization in signaling endosomes results in hyperactive extracellular signal-regulated kinase signaling leading to Bcl-2 stabilization and aberrant cysts. Similarly, formation of hyperproliferative and disorganized mammary acini induced by chronic stimulation of colony-stimulating factor 1 receptor is coupled to endogenous ARF6 activation and constitutive receptor internalization and is reversed by ARF6 inhibition. These findings identify a previously unrecognized link between ARF6-regulated receptor internalization and events that drive dramatic alterations in cyst morphogenesis providing new mechanistic insight into the molecular processes that can promote epithelial glandular disruption.

Endocytosis and recycling of tight junction proteins in inflammation

A critical function of the epithelial lining is to form a barrier that separates luminal contents from the underlying interstitium. This barrier function is primarily regulated by the apical junctional complex (AJC) consisting of tight junctions (TJs) and adherens junctions (AJs) and is compromised under inflammatory conditions. In intestinal epithelial cells, proinflammatory cytokines, for example, interferon-gamma (IFN-gamma), induce internalization of TJ proteins by endocytosis. Endocytosed TJ proteins are passed into early and recycling endosomes, suggesting the involvement of recycling of internalized TJ proteins. This review summarizes mechanisms by which TJ proteins under inflammatory conditions are internalized in intestinal epithelial cells and point out comparable mechanism in nonintestinal epithelial cells.

Renal cell carcinoma bone metastases: clinical advances

Bone is a common site of metastatic spread in patients with advanced renal cell carcinoma (RCC) occurring in around one-third of patients enrolled in clinical trials evaluating modern systemic therapies for this disease. Until recently, limited systemic therapeutic options were available for advanced RCC. Nowadays, a quiver of agents have demonstrated activity, including compounds targeting the vascular endothelial growth factor (VEGF) axis and those targeting the mammalian target of rapamycin (mTOR). Despite a detailed biological understanding of how these drugs work, their effect on bony metastases is less clear. Data suggesting that bisphosphonates (namely zoledronic acid) benefit patients with bone metastases from advanced RCC was gathered prior to the targeted therapy era; therefore, there is some uncertainty about their role in patients on modern RCC therapies. This review summarizes the current targeted therapies registered for use in advanced RCC and postulates how some of them might affect the behavior of bone metastases. It also explores the data available on the role of bisphosphonates for bone metastases from RCC, describes methods of assessing response to therapy for bone metastases and delineates future expectations for the treatment of bone metastases from advanced RCC.

Role of CSF-1 in progression of epithelial ovarian cancer

Despite the dismal outcome seen in the majority of epithelial ovarian cancer patients, there is ongoing progress in understanding the disease at a molecular level. Elucidation of pathways underlying disease progression and metastasis of ovarian cancer is key to development of targeted therapeutics. It is only in this way that therapeutic potential can be translated to reality. Here, we describe the evidence to date for the role of CSF-1/c-fms signaling in ovarian cancer invasiveness and metastasis, including the recent understanding of how CSF-1/c-fms expression is regulated with identification of significant post-transcriptional regulators.

Invasion of human breast cancer cells in vivo requires both paracrine and autocrine loops involving the colony-stimulating factor-1 receptor

Colony-stimulating factor-1 (CSF-1) and its receptor (CSF-1R) have been implicated in the pathogenesis and progression of various types of cancer, including breast cancer. This is based on high levels of circulating CSF-1 in patient sera with aggressive disease and increased CSF-1R staining in the tumor tissues. However, there have been no direct in vivo studies to determine whether a CSF-1 autocrine signaling loop functions in human breast cancer cells in vivo and whether it contributes to invasion. Recently, in mouse and rat models, it has been shown that invasion and metastasis are driven by an epidermal growth factor (EGF)/CSF-1 paracrine loop between tumor cells and host macrophages. In this macrophage-dependent invasion, tumor cells secrete CSF-1 and sense EGF, whereas the macrophages secrete EGF and sense CSF-1. Here, we test the hypothesis that in human breast tumors, the expression of both the CSF-1 ligand and its receptor in tumor cells leads to a CSF-1/CSF-1R autocrine loop which contributes to the aggressive phenotype of human breast tumors. Using MDA-MB-231 cell-derived mammary tumors in severe combined immunodeficiency mice, we show here for the first time in vivo that invasion in a human mammary tumor model is dependent on both paracrine signaling with host macrophages as well as autocrine signaling involving the tumor cells themselves. In particular, we show that the autocrine contribution to invasion is specifically amplified in vivo through a tumor microenvironment-induced upregulation of CSF-1R expression via the transforming growth factor-beta1.

Quantitative analysis of three-dimensional human mammary epithelial tissue architecture reveals a role for tenascin-C in regulating c-met function

Remodeling of the stromal extracellular matrix and elevated expression of specific proto-oncogenes within the adjacent epithelium represent cardinal features of breast cancer, yet how these events become integrated is not fully understood. To address this question, we focused on tenascin-C (TN-C), a stromal extracellular matrix glycoprotein whose expression increases with disease severity. Initially, nonmalignant human mammary epithelial cells (MCF-10A) were cultured within a reconstituted basement membrane (BM) where they formed three-dimensional (3-D) polarized, growth-attenuated, multicellular acini, enveloped by a continuous endogenous BM. In the presence of TN-C, however, acini failed to generate a normal BM, and net epithelial cell proliferation increased. To quantify how TN-C alters 3-D tissue architecture and function, we developed a computational image analysis algorithm, which showed that although TN-C disrupted acinar surface structure, it had no effect on their volume. Thus, TN-C promoted epithelial cell proliferation leading to luminal filling, a process that we hypothesized involved c-met, a proto-oncogene amplified in breast tumors that promotes intraluminal filling. Indeed, TN-C increased epithelial c-met expression and promoted luminal filling, whereas blockade of c-met function reversed this phenotype, resulting in normal BM deposition, proper lumen formation, and decreased cell proliferation. Collectively, these studies, combining a novel quantitative image analysis tool with 3-D organotypic cultures, demonstrate that stromal changes associated with breast cancer can control proto-oncogene function.

Derepression of HMGA2 via removal of ZBRK1/BRCA1/CtIP complex enhances mammary tumorigenesis

The high mobility group AT-hook 2 (HMGA2), a DNA architectural protein, is highly regulated during development and plays an important role in tumorigenesis. Indeed, HMGA2 was overexpressed in many different kinds of tumors. However, the mechanisms regulating HMGA2 expression remain elusive. Using microarray analysis, we found that HMGA2, along with a dozen of other genes, was co-repressed by ZBRK1, BRCA1, and CtIP. BRCA1 exerts its transcriptional repression activity through interaction with the transcriptional repressor ZBRK1 in the central domain, and with CtIP in the C-terminal BRCT domain. Here, we show that ZBRK1, BRCA1, and CtIP form a repression complex that coordinately regulates HMGA2 expression via a ZBRK1 recognition site in the HMGA2 promoter. Depletion of any of the proteins in this complex via adenoviral RNA interference in MCF10A mammary epithelial cells activates HMGA2 expression, resulting in increased colony formation in soft agar. Similarly, depletion of ZBRK1, or ectopic overexpression of HMGA2, in MCF10A cells induces abnormal acinar size with increased cell number and inhibits normal acinar formation. Consistently, many BRCA1-deficient mouse breast tumors express higher levels of HMGA2 than BRCA1-proficient tumors. These results suggest that activation of HMGA2 gene expression through derepression of the ZBRK1/BRCA1/CtIP complex is a significant step in accelerating breast tumorigenesis.

Lobular neoplasia of the breast: an update

CONTEXT

Lobular neoplasias (LNs) of the breast include atypical lobular neoplasia and lobular carcinoma in situ. Recent evidence suggests that LN is not only a risk factor for invasive lobular carcinoma, but is also a nonobligate precursor. Pleomorphic lobular carcinoma in situ (PLCIS) is a subtype of LN that has high-grade nuclei and other features that may mimic high-grade ductal carcinoma in situ. The management and follow-up of patients diagnosed with LN on core biopsy is a current issue of debate. However, recent genomic and molecular studies have identified candidate genes that may be important in understanding the pathogenesis of atypical lobular neoplasia and lobular carcinoma in situ, and thus may lead to other therapeutic interventions.

OBJECTIVE

To review the literature on LN of the breast and discuss current issues in the diagnosis and management of this entity, with particular attention to the relatively newly recognized lesion PLCIS. Because the management of PLCIS varies from the other LN lesions, the recognition of PLCIS by the pathologist is necessary. Current issues in the molecular pathogenesis of LN are also presented.

DATA SOURCES

Extensive review of the literature. Hematoxylin-eosin-stained and immunohistochemical-stained tissue from the author's personal collection.

CONCLUSIONS

Although morphology and immunohistochemical stains, such as E-cadherin, are important in the diagnosis and understanding of LN, genomic and molecular studies may guide the way these lesions are handled in the future. Recognizing PLCIS is important both for patient management and for our future understanding of LN pathogenesis.

Model of autocrine/paracrine signaling in epithelial layer: geometrical regulation of intercellular communication

An autocrine/paracrine signaling model in epithelial layers is described. The axially symmetric model of the epithelial layer explicitly considers the microvilli of the epithelial cells and the gaps between nearest neighbor microvilli. Ligand trapping site distribution functions and probability of autocrine signaling are calculated for different epithelial geometries and ligand sources by numerically solving the inhomogeneous stationary diffusion equation, the Poisson equation. In general, the global characteristics of the trapping site distribution curves are similar to the ones obtained for a planar epithelial model, and the superimposed small periodical changes of the curves reflect the details of the epithelial geometry. However, when ligands are emitted into a narrow gap between nearest neighbor microvilli the probability of local trapping is particularly high, causing a locally large deviation from the overall behavior of the trapping site distribution curves. If the microvilli of the cell are closely packed, then the probability of paracrine signaling is about 0.2. However, this probability jumps to about 0.5 if the cell is able to slightly loosen the tight packing, for example, by decreasing the diameter of the microvilli by only 2%. On the basis of our calculations, alteration of microvillus geometry represents a mechanism by which epithelial cells can efficiently regulate intercellular signaling.