Effects of notch signaling on regulation of myeloid cell differentiation in cancer

γ-Secretase inhibitor reduces immunosuppressive cells and enhances tumour immunity in head and neck squamous cell carcinoma

Immune evasion is a hallmark feature of cancer, and it plays an important role in tumour initiation and progression. In addition, tumour immune evasion severely hampers the desired antitumour effect in multiple cancers. In this study, we aimed to investigate the role of the Notch pathway in immune evasion in the head and neck squamous cell carcinoma (HNSCC) microenvironment. We first demonstrated that Notch1 signaling was activated in a Tgfbr1/Pten-knockout HNSCC mouse model. Notch signaling inhibition using a γ-secretase inhibitor (GSI-IX, DAPT) decreased tumour burden in the mouse model after prophylactic treatment. In addition, flow cytometry analysis indicated that Notch signaling inhibition reduced the sub-population of myeloid-derived suppressor cells (MDSCs), tumour-associated macrophages (TAMs) and regulatory T cells (Tregs), as well as immune checkpoint molecules (PD1, CTLA4, TIM3 and LAG3), in the circulation and in the tumour. Immunohistochemistry (IHC) of human HNSCC tissues demonstrated that elevation of the Notch1 downstream target HES1 was correlated with MDSC, TAM and Treg markers and with immune checkpoint molecules. These results suggest that modulating the Notch signaling pathway may decrease MDSCs, TAMs, Tregs and immune checkpoint molecules in HNSCC.

Conditioned media from the renal cell carcinoma cell line 786.O drives human blood monocytes to a monocytic myeloid-derived suppressor cell phenotype

Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells critical in mediating immune suppression in cancer patients. To develop an in vitro assay system that functionally mimics the tumor microenvironment, we cultured human monocytes with conditioned media from several cancer cell lines. Conditioned media from five tumor cell lines induced survival and differentiation of monocytes into cells characteristically similar to macrophages and MDSCs. Notably, media from the 786.O renal cell carcinoma line induced monocytes to acquire a monocytic MDSC phenotype characterized by decreased HLA-DR expression, increased nitric oxide production, enhanced proliferation, and ability to suppress autologous CD3⁺ T cell proliferation. We further demonstrated that these in vitro MDSCs are phenotypically and functionally similar to patient-derived MDSCs. Inhibitors of STAT3, CK2, and GM-CSF resulted in partial reversal of the MDSC phenotype. MDSCs generated in vitro from 786.O tumor conditioned media represent a platform to identify potential therapeutics that inhibit MDSC activities.

Inhibition of Protein Kinase CK2 Prevents Adipogenic Differentiation of Mesenchymal Stem Cells Like C3H/10T1/2 Cells

Protein kinase CK2 as a holoenzyme is composed of two catalytic α- or α'-subunits and two non-catalytic β-subunits. Knock-out experiments revealed that CK2α and CK2β are required for embryonic development. Little is known about the role of CK2 during differentiation of stem cells. Mesenchymal stem cells (MSCs) are multipotent cells which can be differentiated into adipocytes in vitro. Thus, MSCs and in particular C3H/10T1/2 cells are excellent tools to study a possible role of CK2 in adipogenesis. We found downregulation of the CK2 catalytic subunits as well as a decrease in CK2 kinase activity with progression of differentiation. Inhibition of CK2 using the potent inhibitor CX-4945 impeded differentiation of C3H/10T1/2 cells into adipocytes. The inhibited cells lacked the observed decrease in CK2 expression, but showed a constant expression of all three CK2 subunits. Furthermore, inhibition of CK2 resulted in decreased cell proliferation in the early differentiation phase. Analysis of the main signaling cascade revealed an elevated expression of C/EBPβ and C/EBPδ and reduced expression of the adipogenic master regulators C/EBPα and PPARγ2. Thus, CK2 seems to be implicated in the regulation of different steps early in the adipogenic differentiation of MSC.

DNA Methylation-Derived Neutrophil-to-Lymphocyte Ratio: An Epigenetic Tool to Explore Cancer Inflammation and Outcomes

Background: The peripheral blood neutrophil-to-lymphocyte ratio (NLR) is a cytologic marker of both inflammation and poor outcomes in patients with cancer. DNA methylation is a key element of the epigenetic program defining different leukocyte subtypes and may provide an alternative to cytology in assessing leukocyte profiles. Our aim was to create a bioinformatic tool to estimate NLR using DNA methylation, and to assess its diagnostic and prognostic performance in human populations.Methods: We developed a DNA methylation-derived NLR (mdNLR) index based on normal isolated leukocyte methylation libraries and established cell-mixture deconvolution algorithms. The method was applied to cancer case-control studies of the bladder, head and neck, ovary, and breast, as well as publicly available data on cancer-free subjects.Results: Across cancer studies, mdNLR scores were either elevated in cases relative to controls, or associated with increased hazard of death. High mdNLR values (>5) were strong indicators of poor survival. In addition, mdNLR scores were elevated in males, in nonHispanic white versus Hispanic ethnicity, and increased with age. We also observed a significant interaction between cigarette smoking history and mdNLR on cancer survival.Conclusions: These results mean that our current understanding of mature leukocyte methylomes is sufficient to allow researchers and clinicians to apply epigenetically based analyses of NLR in clinical and epidemiologic studies of cancer risk and survival.Impact: As cytologic measurements of NLR are not always possible (i.e., archival blood), mdNLR, which is computed from DNA methylation signatures alone, has the potential to expand the scope of epigenome-wide association studies. Cancer Epidemiol Biomarkers Prev; 26(3); 328-38. ©2016 AACR.

Upregulation of T-cell Immunoglobulin and Mucin-Domain Containing-3 (Tim-3) in Monocytes/Macrophages Associates with Gastric Cancer Progression

T-cell immunoglobulin and mucin-domain containing-3 (Tim-3) is an important immune regulatory molecule in cancer immune system. However, expression and function of Tim-3 in monocytes/macrophages in cancer progression mainly remain unclear. In this study, we analyzed Tim-3 levels in peripheral blood mononuclear cells (PBMCs) from 62 gastric cancer patients and 45 healthy controls using flow cytometry and then associated Tim-3 levels with clinical pathological data from patients. We found Tim-3 level was significantly upregulated in monocytes from gastric cancer patients compared with those from healthy controls, and that upregulated Tim-3 levels associated with depth of tumor invasion and tumor lymph node metastasis and advanced clinical stages of gastric cancer patients. Furthermore, tumor-bearing mouse experiments revealed that Tim-3 level on monocytes/macrophages associated with xenograft formation and growth. In addition, culture of monocytes from healthy controls with gastric cancer cell-conditioned medium upregulated Tim-3 expression, but IL-10, TNF-α, IFN-γ, or GM-CSF treatment or T-bet, Eomes, and T-bet/Eomes double gene knockout did not affect Tim-3 levels in blood monocytes/macrophages from human or mouse, respectively. Gal-9/Tim-3 signal was able to significantly stimulate monocyte to secrete IL-6, IL-8, and IL-10, but not IL-1β, IL-12p70, or TNF-α in presence of LPS. In conclusion, our study demonstrated that Tim-3 expressed by monocyte/macrophages might be an important mechanism in gastric cancer progression.

A core of kinase-regulated interactomes defines the neoplastic MDSC lineage

Myeloid-derived suppressor cells (MDSCs) differentiate from bone marrow precursors, expand in cancer-bearing hosts and accelerate tumor progression. MDSCs have become attractive therapeutic targets, as their elimination strongly enhances anti-neoplastic treatments. Here, immature myeloid dendritic cells (DCs), MDSCs modeling tumor-infiltrating subsets or modeling non-cancerous (NC)-MDSCs were compared by in-depth quantitative proteomics. We found that neoplastic MDSCs differentially expressed a core of kinases which controlled lineage-specific (PI3K-AKT and SRC kinases) and cancer-induced (ERK and PKC kinases) protein interaction networks (interactomes). These kinases contributed to some extent to myeloid differentiation. However, only AKT and ERK specifically drove MDSC differentiation from myeloid precursors. Interfering with AKT and ERK with selective small molecule inhibitors or shRNAs selectively hampered MDSC differentiation and viability. Thus, we provide compelling evidence that MDSCs constitute a distinct myeloid lineage distinguished by a “kinase signature” and well-defined interactomes. Our results define new opportunities for the development of anti-cancer treatments targeting these tumor-promoting immune cells.

Signal transducer and activator of transcription 3 in myeloid-derived suppressor cells: an opportunity for cancer therapy

Cancer progression is in part determined by interactions between cancer cells and stromal cells in the tumor microenvironment (TME). The identification of cytotoxic tumor-infiltrating lymphocytes has instigated research into immune stimulating cancer therapies. Although a promising direction, immunosuppressive mechanisms exerted at the TME hamper its success. Myeloid-derived suppressor cells (MDSCs) have come to the forefront as stromal cells that orchestrate the immunosuppressive TME. Consequently, this heterogeneous cell population has been the object of investigation. Studies revealed that the transcription factor signal transducer and activator of transcription 3 (STAT3) largely dictates the recruitment, activation and function of MDSCs in the TME. Therefore, this review will focus on the role of this key transcription factor during the MDSC's life cycle and on the therapeutic opportunities it offers.

Downregulation of leptin inhibits growth and induces apoptosis of lung cancer cells via the Notch and JAK/STAT3 signaling pathways

Previous studies have documented that leptin is involved in the pathogenesis of many human cancer types by regulation of numerous signal transduction pathways. The aim of this study was to investigate the biological roles of leptin and the mechanisms attributed to its action in non-small cell lung cancer (NSCLC) cell lines. The expression of leptin was measured by quantitative real-time PCR and western blot in seven NSCLC cell lines. Proliferation and apoptosis of NSCLC cells in response to leptin knockdown were determined by MTT assay and flow cytometry, respectively. The effect of leptin knockdown on the Notch and JAK/STAT3 signaling pathways was further examined by western blot. Leptin expression was significantly increased in NSCLC cell lines compared with normal human bronchial epithelial cell HBE. Leptin knockdown inhibited cell proliferation and induced apoptosis in NSCLC cell lines through inactivation of the Notch and JAK/STAT3 signaling pathways. Furthermore, gene silencing of Notch signaling with Notch-1 siRNA or inhibition of JAK/STAT3 signaling by JSI-124, an inhibitor of STAT3, resulted in proliferation inhibition and apoptosis induction in NSCLC A549 cells. Our findings suggested that leptin knockdown could become a new approach for the prevention of lung cancer progression, which is likely to be mediated at least partially by inactivation of the Notch and JAK/STAT3 signaling pathways.

Summary: Leptin knockdown could become a new approach for the prevention of lung cancer progression, which we have shown is likely to be mediated by inactivation of the Notch and JAK/STAT3 signaling pathways.

Myeloid-Derived Suppressor Cell Survival and Function Are Regulated by the Transcription Factor Nrf2

Tumor-induced myeloid-derived suppressor cells (MDSC) contribute to immune suppression in tumor-bearing individuals and are a major obstacle to effective immunotherapy. Reactive oxygen species (ROS) are one of the mechanisms used by MDSC to suppress T cell activation. Although ROS are toxic to most cells, MDSC survive despite their elevated content and release of ROS. NF erythroid 2-related factor 2 (Nrf2) is a transcription factor that regulates a battery of genes that attenuate oxidative stress. Therefore, we hypothesized that MDSC resistance to ROS may be regulated by Nrf2. To test this hypothesis, we used Nrf2(+/+)and Nrf2(-/-)BALB/c and C57BL/6 mice bearing 4T1 mammary carcinoma and MC38 colon carcinoma, respectively. Nrf2 enhanced MDSC suppressive activity by increasing MDSC production of H2O2, and it increased the quantity of tumor-infiltrating MDSC by reducing their oxidative stress and rate of apoptosis. Nrf2 did not affect circulating levels of MDSC in tumor-bearing mice because the decreased apoptotic rate of tumor-infiltrating MDSC was balanced by a decreased rate of differentiation from bone marrow progenitor cells. These results demonstrate that Nrf2 regulates the generation, survival, and suppressive potency of MDSC, and that a feedback homeostatic mechanism maintains a steady-state level of circulating MDSC in tumor-bearing individuals.

Significance and therapeutic implications of endothelial progenitor cells in angiogenic-mediated tumour metastasis

Cancer conveys profound social and economic consequences throughout the world. Metastasis is responsible for approximately 90% of cancer-associated mortality and, when it occurs, cancer becomes almost incurable. During metastatic dissemination, cancer cells pass through a series of complex steps including the establishment of tumour-associated angiogenesis. The human endothelial progenitor cells (hEPCs) are a cell population derived from the bone marrow which are required for endothelial tubulogenesis and neovascularization. They also express abundant inflammatory cytokines and paracrine angiogenic factors. Clinically hEPCs are highly correlated with relapse, disease progression, metastasis and treatment response in malignancies such as breast cancer, ovarian cancer and non-small-cell lung carcinoma. It has become evident that the hEPCs are involved in the angiogenesis-required progression and metastasis of tumours. However, it is not clear in what way the signalling pathways, controlling the normal cellular function of human BM-derived EPCs, are hijacked by aggressive tumour cells to facilitate tumour metastasis. In addition, the actual roles of hEPCs in tumour angiogenesis-mediated metastasis are not well characterised. In this paper we reviewed the clinical relevance of the hEPCs with cancer diagnosis, progression and prognosis. We further summarised the effects of tumour microenvironment on the hEPCs and underlying mechanisms. We also hypothesized the roles of altered hEPCs in tumour angiogenesis and metastasis. We hope this review may enhance our understanding of the interaction between hEPCs and tumour cells thus aiding the development of cellular-targeted anti-tumour therapies.

The Notch intracellular domain integrates signals from Wnt, Hedgehog, TGFβ/BMP and hypoxia pathways

Notch signaling is a highly conserved signal transduction pathway that regulates stem cell maintenance and differentiation in several organ systems. Upon activation, the Notch receptor is proteolytically processed, its intracellular domain (NICD) translocates into the nucleus and activates expression of target genes. Output, strength and duration of the signal are tightly regulated by post-translational modifications. Here we review the intracellular post-translational regulation of Notch that fine-tunes the outcome of the Notch response. We also describe how crosstalk with other conserved signaling pathways like the Wnt, Hedgehog, hypoxia and TGFβ/BMP pathways can affect Notch signaling output. This regulation can happen by regulation of ligand, receptor or transcription factor expression, regulation of protein stability of intracellular key components, usage of the same cofactors or coregulation of the same key target genes. Since carcinogenesis is often dependent on at least two of these pathways, a better understanding of their molecular crosstalk is pivotal.

Phenotype, development, and biological function of myeloid-derived suppressor cells

CD11b⁺Gr-1⁺ myeloid-derived suppressor cells (MDSCs) are an important population of innate regulatory cells mainly comprising monocytic MDSCs (M-MDSCs) with a phenotype of CD11b⁺Ly6G^-Ly6C^high and granulocytic MDSCs (G-MDSCs) with a phenotype of CD11b⁺Ly6G⁺Ly6C^low in mice. They play crucial roles in the pathogenesis of cancers, chronic infections, autoimmune diseases, and transplantation. Various extracellular factors such as lipopolysaccharide (LPS), macrophage colony-stimulating factor (M-CSF), granulocyte macrophage colony-stimulating factor (GM-CSF), stem cell factor (SCF), interleukin (IL)-6, interferon gamma (IFNγ), IL-1β, vascular endothelial growth factor (VEGF), Hsp72, IL-13, C5a, and prostaglandin E2 (PGE2) can induce MDSC differentiation, whereas IL-4 and all-trans-retinoic acid can inhibit this process. For the intracellular signals, signal transducer and activator of transcription (STAT) family members, C/EBPβ and cyclooxigenase-2 (COX-2) promote MDSC function, whereas interferon regulatory factor-8 (IRF-8) and Smad3 downregulate MDSC activity. The immunosuppressive function of MDSCs is mediated through various effector molecules, primarily cellular metabolism-related molecules such as nitric oxide (NO), arginase, reactive oxygen species (ROS), transforming growth factor β (TGFβ), IL-10, indoleamine 2,3-dioxygenase (IDO), heme oxygenase-1 (HO-1), carbon monoxide (CO), and PGE2. In this article, we will summarize the molecules involved in the induction and function of MDSCs as well as the regulatory pathways of MDSCs.

Transcriptional regulation of myeloid-derived suppressor cells

Myeloid-derived suppressor cells are a heterogeneous group of pathologically activated immature cells that play a major role in the negative regulation of the immune response in cancer, autoimmunity, many chronic infections, and inflammatory conditions, as well as in the regulation of tumor angiogenesis, tumor cell invasion, and metastases. Accumulation of myeloid-derived suppressor cells is governed by a network of transcriptional regulators that could be combined into 2 partially overlapping groups: factors promoting myelopoiesis and preventing differentiation of mature myeloid cells and factors promoting pathologic activation of myeloid-derived suppressor cells. In this review, we discuss the specific nature of these factors and their impact on myeloid-derived suppressor cell development.

Protein kinase CK2 in breast cancer: the CK2β regulatory subunit takes center stage in epithelial plasticity

Structurally, protein kinase CK2 consists of two catalytic subunits (α and α') and two regulatory subunits (β), which play a critical role in targeting specific CK2 substrates. Compelling evidence shows the complexity of the CK2 cellular signaling network and supports the view that this enzyme is a key component of regulatory protein kinase networks that are involved in several aspects of cancer. CK2 both activates and suppresses the expression of a number of essential oncogenes and tumor suppressors, and its expression and activity are upregulated in blood tumors and virtually all solid tumors. The prognostic significance of CK2α expression in association with various clinicopathological parameters highlighted this kinase as an adverse prognostic marker in breast cancer. In addition, several recent studies reported its implication in the regulation of the epithelial-to-mesenchymal transition (EMT), an early step in cancer invasion and metastasis. In this review, we briefly overview the contribution of CK2 to several aspects of cancer and discuss how in mammary epithelial cells, the expression of its CK2β regulatory subunit plays a critical role in maintaining an epithelial phenotype through CK2-mediated control of key EMT-related transcription factors. Importantly, decreased CK2β expression in breast tumors is correlated with inefficient phosphorylation and nuclear translocation of Snail1 and Foxc2, ultimately leading to EMT induction. This review highlights the pivotal role played by CK2β in the mammary epithelial phenotype and discusses how a modest alteration in its expression may be sufficient to induce dramatic effects facilitating the early steps in tumor cell dissemination through the coordinated regulation of two key transcription factors.

Myeloid-Derived Suppressor Cells: Critical Cells Driving Immune Suppression in the Tumor Microenvironment

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells that suppress innate and adaptive immunity. MDSCs are present in many disease settings; however, in cancer, they are a major obstacle for both natural antitumor immunity and immunotherapy. Tumor and host cells in the tumor microenvironment (TME) produce a myriad of pro-inflammatory mediators that activate MDSCs and drive their accumulation and suppressive activity. MDSCs utilize a variety of mechanisms to suppress T cell activation, induce other immune-suppressive cell populations, regulate inflammation in the TME, and promote the switching of the immune system to one that tolerates and enhances tumor growth. Because MDSCs are present in most cancer patients and are potent immune-suppressive cells, MDSCs have been the focus of intense research in recent years. This review describes the history and identification of MDSCs, the role of inflammation and intracellular signaling events governing MDSC accumulation and suppressive activity, immune-suppressive mechanisms utilized by MDSCs, and recent therapeutics that target MDSCs to enhance antitumor immunity.

Rescue of notch-1 signaling in antigen-specific CD8+ T cells overcomes tumor-induced T-cell suppression and enhances immunotherapy in cancer

An impaired antitumor immunity is found in patients with cancer and represents a major obstacle in the successful development of different forms of immunotherapy. Signaling through Notch receptors regulates the differentiation and function of many cell types, including immune cells. However, the effect of Notch in CD8(+) T-cell responses in tumors remains unclear. Thus, we aimed to determine the role of Notch signaling in CD8(+) T cells in the induction of tumor-induced suppression. Our results using conditional knockout mice show that Notch-1 and Notch-2 were critical for the proliferation and IFNγ production of activated CD8(+) T cells and were significantly decreased in tumor-infiltrating T cells. Conditional transgenic expression of Notch-1 intracellular domain (N1IC) in antigen-specific CD8(+) T cells did not affect activation or proliferation of CD8(+) T cells, but induced a central memory phenotype and increased cytotoxicity effects and granzyme B levels. Consequently, a higher antitumor response and resistance to tumor-induced tolerance were found after adoptive transfer of N1IC-transgenic CD8(+) T cells into tumor-bearing mice. Additional results showed that myeloid-derived suppressor cells (MDSC) blocked the expression of Notch-1 and Notch-2 in T cells through nitric oxide-dependent mechanisms. Interestingly, N1IC overexpression rendered CD8(+) T cells resistant to the tolerogenic effect induced by MDSC in vivo. Together, the results suggest the key role of Notch in the suppression of CD8(+) T-cell responses in tumors and the therapeutic potential of N1IC in antigen-specific CD8(+) T cells to reverse T-cell suppression and increase the efficacy of T cell-based immunotherapies in cancer.

Myeloid-derived suppressor cells in cancer: therapeutic, predictive, and prognostic implications

Immune evasion is a hallmark of cancer. While there are multiple different mechanisms that cancer cells employ, myeloid-derived suppressor cells (MDSCs) are one of the key drivers of tumor-mediated immune evasion. MDSCs begin as myeloid cells recruited to the tumor microenvironment, where they are transformed into potent immunosuppressive cells. However, our understanding of the clinical relevance of MDSCs in cancer patients has significantly lagged behind the preclinical literature in part due to the absence of a cognate molecule present in mice, as well as to the considerable heterogeneity of MDSCs. However, if one evaluates the clinical literature through the filter of clinically robust endpoints, such as overall survival, three important phenotypes emerge: promyelocytic, monocytic, and granulocytic. Based on these studies, MDSCs have clear prognostic importance in multiple solid tumors, and emerging data support the utility of circulating MDSCs as a predictive marker for cancer immunotherapy, and even as an early leading marker for predicting clinical response to systemic chemotherapy in patients with advanced solid tumors. More recent preclinical data in immunosuppressed murine models suggest that MDSCs play an important role in tumor progression and the metastatic process that is independent of their immunosuppressive properties. Consequently, targeting MDSCs either in combination with cancer immunotherapy or independently as part of an approach to inhibit the metastatic process appears to be a very clinically promising strategy. We review different approaches to target MDSCs that could potentially be tested in future clinical trials in cancer patients.