CSF-1 activates MAPK-dependent and p53-independent pathways to induce growth arrest of hormone-dependent human breast cancer cells

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.

Stromal and therapy-induced macrophage proliferation promotes PDAC progression and susceptibility to innate immunotherapy

Tumor-associated macrophages (TAMs) are abundant in pancreatic ductal adenocarcinomas (PDACs). While TAMs are known to proliferate in cancer tissues, the impact of this on macrophage phenotype and disease progression is poorly understood. We showed that in PDAC, proliferation of TAMs could be driven by colony stimulating factor-1 (CSF1) produced by cancer-associated fibroblasts. CSF1 induced high levels of p21 in macrophages, which regulated both TAM proliferation and phenotype. TAMs in human and mouse PDACs with high levels of p21 had more inflammatory and immunosuppressive phenotypes. p21 expression in TAMs was induced by both stromal interaction and/or chemotherapy treatment. Finally, by modeling p21 expression levels in TAMs, we found that p21-driven macrophage immunosuppression in vivo drove tumor progression. Serendipitously, the same p21-driven pathways that drive tumor progression also drove response to CD40 agonist. These data suggest that stromal or therapy-induced regulation of cell cycle machinery can regulate both macrophage-mediated immune suppression and susceptibility to innate immunotherapy.

MEK1/2 overactivation can promote growth arrest by mediating ERK1/2-dependent phosphorylation of p70S6K

The extracellular signal-regulated kinase (ERK)1/2 mitogen-activated protein (MAP) kinase pathway has been involved in the positive and negative regulation of cell proliferation. Upon mitogen stimulation, ERK1/ERK2 activation is necessary for G1- to S-phase progression whereas when hyperactived, this pathway could elicit cell cycle arrest. The mechanisms involved are not fully elucidated but a kinase-independent function of ERK1/2 has been evidenced in the MAPK-induced growth arrest. Here, we show that p70S6K, a central regulator of protein biosynthesis, is essential for the cell cycle arrest induced by overactivation of ERK1/2. Indeed, whereas MEK1 silencing inhibits cell cycle progression, we demonstrate that active mutant form of MEK1 or MEK2 triggers a G1 phase arrest by stimulating an activation of p70S6K by ERK1/2 kinases. Silencing of ERK1/2 activity by shRNA efficiently suppresses p70S6K phosphorylation on Thr421/Ser424 and S6 phosphorylation on Ser240/244 as well as p21 expression, but these effects can be partially reversed by the expression of kinase-dead mutant form of ERK1 or ERK2. In addition, we demonstrate that the kinase p70S6K modulates neither the p21 gene transcription nor the stability of the protein but enhances the translation of the p21 mRNA. In conclusion, our data emphasizes the importance of the translational regulation of p21 by the MEK1/2-ERK1/2-p70S6K pathway to negatively control the cell cycle progression.

CSF-1R as an inhibitor of apoptosis and promoter of proliferation, migration and invasion of canine mammary cancer cells

Background

Tumor-associated macrophages (TAMs) have high impact on the cancer development because they can facilitate matrix invasion, angiogenesis, and tumor cell motility. It gives cancer cells the capacity to invade normal tissues and metastasize. The signaling of colony-stimulating factor-1 receptor (CSF-1R) which is an important regulator of proliferation and differentiation of monocytes and macrophages regulates most of the tissue macrophages. However, CSF-1R is expressed also in breast epithelial tissue during some physiological stages i.g.: pregnancy and lactation. Its expression has been also detected in various cancers. Our previous study has showed the expression of CSF-1R in all examined canine mammary tumors. Moreover, it strongly correlated with grade of malignancy and ability to metastasis. This study was therefore designed to characterize the role of CSF-1R in canine mammary cancer cells proliferation, apoptosis, migration, and invasion. As far as we know, the study presented hereby is a pioneering experiment in this field of veterinary medicine.

Results

We showed that csf-1r silencing significantly increased apoptosis (Annexin V test), decreased proliferation (measured as Ki67 expression) and decreased migration (“wound healing” assay) of canine mammary cancer cells. Treatment of these cells with CSF-1 caused opposite effect. Moreover, csf-1r knock-down changed growth characteristics of highly invasive cell lines on Matrigel matrix, and significantly decreased the ability of these cells to invade matrix. CSF-1 treatment increased invasion of cancer cells.

Conclusion

The evidence of the expression and functional role of the CSF-1R in canine mammary cancer cells indicate that CSF-1R targeting may be a good therapeutic approach.

The CSF-1 receptor ligands IL-34 and CSF-1 exhibit distinct developmental brain expression patterns and regulate neural progenitor cell maintenance and maturation

The CSF-1 receptor (CSF-1R) regulates CNS microglial development. However, the localization and developmental roles of this receptor and its ligands, IL-34 and CSF-1, in the brain are poorly understood. Here we show that compared to wild type mice, CSF-1R-deficient (Csf1r-/-) mice have smaller brains of greater mass. They further exhibit an expansion of lateral ventricle size, an atrophy of the olfactory bulb and a failure of midline crossing of callosal axons. In brain, IL-34 exhibited a broader regional expression than CSF-1, mostly without overlap. Expression of IL-34, CSF-1 and the CSF-1R were maximal during early postnatal development. However, in contrast to the expression of its ligands, CSF-1R expression was very low in adult brain. Postnatal neocortical expression showed that CSF-1 was expressed in layer VI, whereas IL-34 was expressed in the meninges and layers II-V. The broader expression of IL-34 is consistent with its previously implicated role in microglial development. The differential expression of CSF-1R ligands, with respect to CSF-1R expression, could reflect their CSF-1R-independent signaling. Csf1r-/- mice displayed increased proliferation and apoptosis of neocortical progenitors and reduced differentiation of specific excitatory neuronal subtypes. Indeed, addition of CSF-1 or IL-34 to microglia-free, CSF-1R-expressing dorsal forebrain clonal cultures, suppressed progenitor self-renewal and enhanced neuronal differentiation. Consistent with a neural developmental role for the CSF-1R, ablation of the Csf1r gene in Nestin-positive neural progenitors led to a smaller brain size, an expanded neural progenitor pool and elevated cellular apoptosis in cortical forebrain. Thus our results also indicate novel roles for the CSF-1R in the regulation of corticogenesis.

The colony-stimulating factor-1 (CSF-1) receptor sustains ERK1/2 activation and proliferation in breast cancer cell lines

Breast cancer is the second leading cause of cancer-related deaths in western countries. Colony-Stimulating Factor-1 (CSF-1) and its receptor (CSF-1R) regulate macrophage and osteoclast production, trophoblast implantation and mammary gland development. The expression of CSF-1R and/or CSF-1 strongly correlates with poor prognosis in several human epithelial tumors, including breast carcinomas. We demonstrate that CSF-1 and CSF-1R are expressed, although at different levels, in 16/17 breast cancer cell lines tested with no differences among molecular subtypes. The role of CSF-1/CSF-1R in the proliferation of breast cancer cells was then studied in MDAMB468 and SKBR3 cells belonging to different subtypes. CSF-1 administration induced ERK1/2 phosphorylation and enhanced cell proliferation in both cell lines. Furthermore, the inhibition of CSF-1/CSF-1R signaling, by CSF-1R siRNA or imatinib treatment, impaired CSF-1 induced ERK1/2 activation and cell proliferation. We also demonstrate that c-Jun, cyclin D1 and c-Myc, known for their involvement in cell proliferation, are downstream CSF-1R in breast cancer cells. The presence of a proliferative CSF-1/CSF-1R autocrine loop involving ERK1/2 was also found. The wide expression of the CSF-1/CSF-1R pair across breast cancer cell subtypes supports CSF-1/CSF-1R targeting in breast cancer therapy.

Gab2 promotes colony-stimulating factor 1-regulated macrophage expansion via alternate effectors at different stages of development

Colony-stimulating factor 1 (CSF-1) receptor (CSF-1R, or macrophage CSF receptor [M-CSFR]) is the primary regulator of the proliferation, survival, and differentiation of mononuclear phagocytes (MNPs), but the critical CSF-1 signals for these functions are unclear. The scaffold protein Gab2 is a major tyrosyl phosphoprotein in the CSF-1R signaling network. Here we demonstrate that Gab2 deficiency results in profoundly defective expansion of CSF-1R-dependent MNP progenitors in the bone marrow, through decreased proliferation and survival. Reconstitution and phospho-flow studies show that downstream of CSF-1R, Gab2 uses phosphatidylinositol 3-kinase (PI3K)-Akt and extracellular signal-regulated kinase (Erk) to regulate MNP progenitor expansion. Unexpectedly, Gab2 ablation enhances Jun N-terminal protein kinase 1 (JNK1) phosphorylation in differentiated MNPs but reduces their proliferation; inhibition of JNK signaling or reduction of JNK1 levels restores proliferation. MNP recruitment to inflammatory sites and the corresponding bone marrow response is strongly impaired in Gab2-deficient mice. Our data provide genetic and biochemical evidence that CSF-1R, through Gab2, utilizes different effectors at different stages of MNP development to promote their expansion.

The macrophage colony-stimulating factor 1 response signature in breast carcinoma

PURPOSE

Macrophages play an important role in breast carcinogenesis. The pathways that mediate the macrophage contribution to breast cancer and the heterogeneity that exists within macrophages are incompletely understood. Macrophage colony-stimulating factor 1 (CSF1) is the primary regulator of tissue macrophages. The purpose of this study was to define a novel CSF1 response signature and to evaluate its clinical and biological significance in breast cancer.

EXPERIMENTAL DESIGN

We defined the CSF1 response signature by identifying genes overexpressed in tenosynovial giant cell tumor and pigmented villonodular synovitis (tumors composed predominantly of macrophages recruited in response to the overexpression of CSF1) compared with desmoid-type fibromatosis and solitary fibrous tumor. To characterize the CSF1 response signature in breast cancer, we analyzed the expression of CSF1 response signature genes in eight published breast cancer gene expression data sets (n = 982) and did immunohistochemistry and in situ hybridization for CSF1 response genes on a breast cancer tissue microarray (n = 283).

RESULTS

In both the gene microarray and tissue microarray analyses, a consistent subset (17-25%) of breast cancers shows the CSF1 response signature. The signature is associated with higher tumor grade, decreased expression of estrogen receptor, decreased expression of progesterone receptor, and increased TP53 mutations (P < 0.001).

CONCLUSIONS

Our data show that the CSF1 response signature is consistently seen in a subset of breast carcinomas and correlates with biological features of the tumor. Our findings provide insight into macrophage biology and may facilitate the development of personalized therapy for patients most likely to benefit from CSF1-targeted treatments.

Circulating colony stimulating factor-1 and breast cancer risk

Colony stimulating factor-1 (CSF1) and its receptor (CSF1-R) are important in mammary gland development and have been implicated in breast carcinogenesis. In a nested case-control study in the Nurses' Heath Study of 726 breast cancer cases diagnosed between June 1, 1992, and June 1, 1998, and 734 matched controls, we prospectively evaluated whether circulating levels of CSF1 (assessed in 1989-1990) are associated with breast cancer risk. The association varied by menopausal status (P(heterogeneity) = 0.009). CSF1 levels in the highest quartile (versus lowest) were associated with an 85% reduced risk of premenopausal breast cancer [relative risk (RR), 0.15; 95% confidence interval (95% CI), 0.03-0.85; P(trend) = 0.02]. In contrast, CSF1 levels in the highest quartile conferred a 33% increased risk of postmenopausal breast cancer (RR, 1.33; 95% CI, 0.96-1.86; P(trend) = 0.11), with greatest risk for invasive (RR, 1.45; 95% CI, 1.02-2.07; P(trend) = 0.06) and ER+/PR+ tumors (RR, 1.72; 95% CI, 1.11-2.66; P(trend) = 0.04). Thus, the association of circulating CSF1 levels and breast cancer varies by menopausal status.

Gender dimorphism in the myeloid differentiation of bone marrow precursor cells in a murine host bearing a T cell lymphoma

Little information is available regarding the existence of gender dimorphism of tumor growth for most types of tumors. In a previous report we have demonstrated the existence of gender dimorphism in the growth of a murine T cell lymphoma, designated as Dalton's lymphoma (DL); moreover, tumor-associated macrophages (TAM) were found to play a central role in the manifestation of gender dimorphism observed in the growth of this T cell lymphoma. In view of these observations, the present investigation was undertaken to study if gender dimorphism in the growth of a T cell tumor also could be associated with a gender-dependent differential myelopoiesis of bone marrow cells. We have demonstrated the existence of a gender dimorphism in the proliferation, apoptosis and myeloid differentiation of bone marrow cells obtained from male and female tumor-bearing hosts. Androgen and estrogen were found to alter directly the growth properties of bone marrow cells, as also determined by the use of receptor antagonists of these hormones, flutamide and tamoxifen. Bone marrow cells of male and female tumor-bearing hosts also showed a differential expression of the cell cycle and apoptosis regulatory protein p53 and macrophage-colony stimulating factor (M-CSF) genes. Bone marrow cells of male tumor-bearing hosts showed a predominant differentiation in the macrophage lineage whereas those of female tumor-bearing mice were in the granulocyte lineage. Bone marrow-derived macrophages (BMDM) from male and female tumor-bearing mice also showed the existence of gender dimorphism with respect to their differentiation and activation. These observations are of clinical significance with respect to understanding of the host-tumor relationship at the level of gender dimorphism of myelopoiesis.

MNK1 and MNK2 regulation in HER2-overexpressing breast cancer lines

MAPK-interacting protein kinases 1 and 2 (MNK1 and MNK2) function downstream of p38 and ERK MAPK, but there are large gaps in our knowledge of how MNKs are regulated and function. As proteins activated in the HER2/Ras/Raf/ERK pathway, the MNKs are of potential interest in HER2-overexpressing cancers. We utilized a panel of breast cell lines (HCC1419, AU565, SKBR3, MCF7, and MCF10A), three of which overexpress HER2, to characterize the amounts and activation status of MNKs and other pathway enzymes (ERKs and RSKs) in these cells. We generated a phosphospecific antibody to Thr(P)-214 in the T-loop of MNKs and found that phosphorylations of both Thr-209 and Thr-214 in human MNK1 are required for activation. Increased phosphorylation and activity of the MNKs correlate with HER2 overexpression, and inhibition of the MNKs reduces colony formation in soft agar. Our work identifies the MNKs as potential therapeutic targets for breast cancer treatments.

All-trans retinoic acid induces p62DOK1 and p56DOK2 expression which enhances induced differentiation and G0 arrest of HL-60 leukemia cells

p62(DOK1) (DOK1) and p56(DOK2) (DOK2) are sequence homologs that act as docking proteins downstream of receptor or nonreceptor tyrosine kinases. Originally identified in chronic myelogenous leukemia cells as a highly phosphorylated substrate for the chimeric p210(bcr-abl) protein, DOK1 was suspected to play a role in leukemogenesis. However, p62(DOK1-/-) fibroblast knockout cells were found to have enhanced MAPK signaling and proliferation due to growth factors, suggesting negative regulatory capabilities for DOK1. The role of DOK1 and DOK2 in leukemogeneis thus is enigmatic. The data in this report show that both the DOK1 and the DOK2 adaptor proteins are constitutively expressed in the myelomonoblastic leukemia cell line, HL-60, and that expression of both proteins is induced by the chemotherapeutic differentiation causing agents, all-trans retinoic acid (atRA) and 1,25-dihydroxyvitamin D3 (VD3). Ectopic expression of either protein enhances atRA- or VD3-induced growth arrest, differentiation, and G(0)/G(1) cell cycle arrest and results in increased ERK1/2 phosphorylation. DOK1 and DOK2 are similarly effective in these capabilities. The data provide evidence that DOK1 and DOK2 proteins have a similar role in regulating cell proliferation and differentiation and are positive regulators of the MAPK signaling pathway in this context.

Model systems in drug discovery: chemical genetics meets genomics

Animal model systems are an intricate part of the discovery and development of new medicines. The sequencing of not only the human genome but also those of the various pathogenic bacteria, the nematode Caenorhabditis elegans, the fruitfly Drosophila, and the mouse has enabled the discovery of new drug targets to push forward at an unprecedented pace. The knowledge and tools in these "model" systems are allowing researchers to carry out experiments more efficiently and are uncovering previously hidden biological connections. While the history of bacteria, yeast, and mice in drug discovery are long, their roles are ever evolving. In contrast, the history of Drosophila and C. elegans at pharmaceutical companies is short. We will briefly review the historic role of each model organism in drug discovery and then update the readers as to the abilities and liabilities of each model within the context of drug development.

Differential modulation of signaling pathways and apoptosis of ras-transformed 10T1/2 cells by the depsipeptide FR901228

(E)-(1S,4S,10S,21R)-7-[(Z)-ethylidene]-4,21-diisopropyl-2-oxa-12,13-dithia-5,8,20,23-tetraazabicyclo[8,7,6]-tricos-16-ene-3,6,9,19,22-pentanone (FR901228), a natural anticancer depsipeptide, induces apoptosis of ras-transformed 10T1/2 cells whereas it induces growth arrest of nontransformed counterpart cells in G0/G1 phase of the cell cycle. Our study of the effect of FR901228 treatment on intracellular signaling pathways reveals a discriminating activity of FR901228 to regulate signaling cascades differently in ras-transformed 10T1/2 cells and nontransformed counterpart cells. Induction of apoptosis of ras-transformed cells by FR901228 correlates with suppression of the extracellular signal-regulated kinase (ERK) signaling pathway through reduction of Raf expression and deactivation of Mek and Erk, inhibition of the phosphoinositide-3 kinase (PI3-K) pathway indexed by suppression of Akt activity, suppression of p38 activity, and activation of caspase-3. Expression of p21(Cip1) is not induced in ras-transformed cultures undergoing apoptosis induced by FR901228. In contrast, FR901228 induces p21(Cip1) expression in nontransformed counterpart cultures growth-arrested in G0/G1 that is also accompanied by moderate induction of the kinase activities of Raf, Mek, Erk, and Akt, but not accompanied by activation of caspase-3 or changes in p38 activity. Our study indicates a potential value of FR901228 in the treatment of cancer cells involving aberrant regulation of Ras through preferential induction of the caspase cascade and suppression of the ERK, PI3-K, and p38 pathways.

Tyrosine phosphorylation of proteins in primary human myeloid leukemic cells stimulated by macrophage colony-stimulating factor: analysis by disease type and comparison with normal human hematopoietic cells

We investigated tyrosine phosphorylation of proteins in primary human leukemic cells stimulated by macrophage colony-stimulating factor (M-CSF) in 60 patients with acute myeloid leukemia (AML) and 5 patients with chronic myelomonocytic leukemia and compared the findings for leukemic cells with those of normal human monocytes and bone marrow immature hematopoietic cells. M-CSF induced tyrosine phosphorylation of p140-200, p110, p60, p44, and p42 frequently, and that of p95 and p55 less frequently, in primary myeloid leukemic cells, whereas M-CSF-induced phosphorylation of proteins was not detected in the normal human hematopoietic cells tested. Of these phosphoproteins, p140-200 was phosphorylated in all patients who responded to M-CSF and was considered to be almost identical to Fms, a product of the c-fms proto-oncogene. M-CSF-induced tyrosine phosphorylation was observed frequently (89%) in AML of French-American-British class M4 and infrequently in all other subtypes of AML, including M5. In chronic myelomonocytic leukemia, M-CSF-induced protein phosphorylation was prominent in blast crisis but was not detected in the chronic phase. Both bone marrow immature cells and mature monocytes showed low responsiveness to M-CSF. These findings for responsiveness to M-CSF were correlated with the amount of Fms in each type of cell. We also identified tyrosine phosphorylation of Vav, Shc, and extracellular signal-regulated kinase by M-CSF in some cases. These findings clarified an M-CSF-specific pattern of protein tyrosine phosphorylation and the responsiveness to M-CSF of primary human myeloid cells. Particularly, enhanced phosphorylation responses to M-CSF and increased amounts of Fms protein were observed in restricted human hematopoietic cells with a premature myelomonocytic character.

Both src-dependent and -independent mechanisms mediate phosphatidylinositol 3-kinase regulation of colony-stimulating factor 1-activated mitogen-activated protein kinases in myeloid progenitors

Colony-stimulating factor 1 (CSF-1) supports the proliferation, survival, and differentiation of bone marrow-derived cells of the monocytic lineage. In the myeloid progenitor 32D cell line expressing CSF-1 receptor (CSF-1R), CSF-1 activation of the extracellular signal-regulated kinase (ERK) pathway is both Ras and phosphatidylinositol 3-kinase (PI3-kinase) dependent. PI3-kinase inhibition did not influence events leading to Ras activation. Using the activity of the PI3-kinase effector, Akt, as readout, studies with dominant-negative and oncogenic Ras failed to place PI3-kinase downstream of Ras. Thus, PI3-kinase appears to act in parallel to Ras. PI3-kinase inhibitors enhanced CSF-1-stimulated A-Raf and c-Raf-1 activities, and dominant-negative A-Raf but not dominant-negative c-Raf-1 reduced CSF-1-provoked ERK activation, suggesting that A-Raf mediates a part of the stimulatory signal from Ras to MEK/ERK, acting in parallel to PI3-kinase. Unexpectedly, a CSF-1R lacking the PI3-kinase binding site (DeltaKI) remained capable of activating MEK/ERK in a PI3-kinase-dependent manner. To determine if Src family kinases (SFKs) are involved, we demonstrated that CSF-1 activated Fyn and Lyn in cells expressing wild-type (WT) or DeltaKI receptors. Moreover, CSF-1-induced Akt activity in cells expressing DeltaKI is SFK dependent since Akt activation was prevented by pharmacological or genetic inhibition of SFK activity. The docking protein Gab2 may link SFK to PI3-kinase. CSF-1 induced Gab2 tyrosyl phosphorylation and association with PI3-kinase in cells expressing WT or DeltaKI receptors. However, only in DeltaKI cells are these events prevented by PP1. Thus in myeloid progenitors, CSF-1 can activate the PI3-kinase/Akt pathway by at least two mechanisms, one involving direct receptor binding and one involving SFKs.