Human myeloma cells express the bone regulating gene Runx2/Cbfa1 and produce osteopontin that is involved in angiogenesis in multiple myeloma patients

Phosphorylated MAPK11 promotes the progression of clear cell renal cell carcinoma by maintaining RUNX2 protein abundance

Previous studies have demonstrated that mitogen-activated protein kinase 11 (MAPK11) functions as an important point of integration in signalling transduction pathways and controlling endocellular processes, including viability of cells, differentiation, proliferation and apoptosis, through the sequence phosphorylation of the substrate protein Ser/Thr kinase protein cascade. Though MAPK 11 plays an important role in various tumours, especially in the invasive and metastatic processes, its expression and molecular mechanism in clear cell renal cell carcinoma (ccRCC) remain unclear. Runt-associated transcription factor 2 (RUNX2), a main transcription factor for osteoblast differentiation and chondrocyte maturation, has high expression in a number of tumours. In this study, the mRNA and protein levels of targeted genes in ccRCC tissues and adjacent tissues are analysed using the Cancer Genome Atlas (TCGA) database and western blotting. The ccRCC cell proliferation was measured with colony formation and EdU assay, and cell migration was examined through transwell assay. The interactive behaviour between proteins was detected with immunoprecipitation. Half-life period of RUNX2 protein was measured with cycloheximide chase assay. The results of the study indicated overexpression of MAPK11 and RUNX2 in ccRCC tissues and cell lines. MAPK11 and RUNX2 promoted the ccRCC cell proliferation and migration. Additionally, physical interaction took place between RUNX2 and P-MAPK11, which functioned to sustain the stability of RUNX2 protein. The high expression of RUNX2 could neutralize the functional degradation in MAPK11. And the outcomes of the study suggest that the P-MAPK11/RUNX2 axis may be used as a potential therapeutic target of ccRCC.

RUNX2 and Cancer

Runt-related transcription factor 2 (RUNX2) is critical for the modulation of chondrocyte osteoblast differentiation and hypertrophy. Recently discovered RUNX2 somatic mutations, expressional signatures of RUNX2 in normal tissues and tumors, and the prognostic and clinical significance of RUNX2 in many types of cancer have attracted attention and led RUNX2 to be considered a biomarker for cancer. Many discoveries have illustrated the indirect and direct biological functions of RUNX2 in orchestrating cancer stemness, cancer metastasis, angiogenesis, proliferation, and chemoresistance to anticancer compounds, warranting further exploration of the associated mechanisms to support the development of a novel therapeutic strategy. In this review, we focus mainly on critical and recent research developments, including RUNX2's oncogenic activities, by summarizing and integrating the findings on somatic mutations of RUNX2, transcriptomic studies, clinical information, and discoveries about how the RUNX2-induced signaling pathway modulates malignant progression in cancer. We also comprehensively discuss RUNX2 RNA expression in a pancancer panel and in specific normal cell types at the single-cell level to indicate the potential cell types and sites for tumorigenesis. We expect this review to shed light on the recent mechanistical findings and modulatory role of RUNX2 in cancer progression and provide biological information that can guide new research in this field.

RUNX2 interacts with SCD1 and activates Wnt/β-catenin signaling pathway to promote the progression of clear cell renal cell carcinoma

BACKGROUND

Previous studies have demonstrated that Runt-associated transcription factor 2 (RUNX2) serves as the main transcription factor for osteoblast differentiation and chondrocyte maturation. RUNX2 is related to a variety of tumors, particularly tumor invasion and metastasis, while the expression and molecular mechanisms of RUNX2 in clear cell renal cell carcinoma (ccRCC) keep to be determined. Stearyl CoA desaturase 1 (SCD1), an endoplasmic reticulum fatty acid desaturase, transfers saturated fatty acids to monounsaturated fatty acids, is expressed highly in numerous malignancies.

METHODS

The Cancer Genome Atlas (TCGA) datebase and Western blot was used to analyzed the mRNA and protein levels of the target gene in ccRCC tissues and adjacent tissues. The proliferation ability of ccRCC cells was tested by colony forming and EdU assay. The migration ability of cells was detected by transwell assay. Immunoprecipitation was utilized to detect protein-protein interaction. Cycloheximide chase assay was used to measure the half-life of SCD1 protein.

RESULTS

In this study, the expressions of RUNX2 and SCD1 are increased in ccRCC tissues as well as ccRCC cell lines. Both RUNX2 and SCD1 could promote proliferation and migration in ccRCC cells. Furthermore, RUNX2 could physically interact with SCD1. In addition, the functional degradation and the inactivation of Wnt/β-catenin signaling pathway triggered by the downregulation of RUNX2 could be partly offset by the overexpression of SCD1.

CONCLUSION

The findings indicate that the RUNX2/SCD1 axis may act as a potential therapeutic target via the Wnt/β-catenin signaling pathway of ccRCC.

Non-coding RNAs and exosomal ncRNAs in multiple myeloma: An emphasis on molecular pathways

One of the most common hematological malignancies is multiple myeloma (MM) that its mortality and morbidity have increased. The incidence rate of MM is suggested to be higher in Europe and various kinds of therapeutic strategies including stem cell transplantation. However, MM treatment is still challenging and gene therapy has been shown to be promising. The non-coding RNAs (ncRNAs) including miRNAs, lncRNAs and circRNAs are considered as key players in initiation, development and progression of MM. In the present review, the role of ncRNAs in MM progression and drug resistance is highlighted to provide new insights for future experiments for their targeting and treatment of MM. The miRNAs affect proliferation and invasion of MM cells, and targeting tumor-promoting miRNAs can induce apoptosis and cell cycle arrest, and reduces proliferation of MM cells. Furthermore, miRNA regulation is of importance for modulating metastasis and chemotherapy response of tumor cells. The lncRNAs exert the same function and determine proliferation, migration and therapy response of MM cells. Notably, lncRNAs mainly target miRNAs in regulating MM progression. The circRNAs also target different molecular pathways in regulating MM malignancy that miRNAs are the most well-known ones. Furthermore, clinical application of ncRNAs in MM is discussed.

CK1α/RUNX2 Axis in the Bone Marrow Microenvironment: A Novel Therapeutic Target in Multiple Myeloma

Simple Summary

Multiple myeloma (MM) is an incurable disease for which novel therapeutic approaches targeting the malignant cells and the associated bone disease are urgently needed. CK1α is a protein kinase that plays a crucial role in the signaling network that sustains plasma cell (PC) survival and bone disease. This protein regulates Wnt/β-catenin signaling, which is fundamental for both MM cell survival and mesenchymal stromal cell (MSC) osteogenic differentiation. In this study, we investigated its involvement in MM–MSC cross-talk. We found that, by lowering CK1α expression levels in co-cultures of MM and MSC cells, expression of RUNX2—the master regulator of osteogenic differentiation—was regulated differently in the two cell types. Our data suggest the possibility of using a specific CK1α inhibitor as part of a novel therapeutic approach to selectively kill malignant PCs and overcome the blocking of osteogenic differentiation induced by MM cells in MSCs.

Abstract

Multiple myeloma (MM) is a malignant plasma cell (PC) neoplasm, which also displays pathological bone involvement. Clonal expansion of MM cells in the bone marrow causes a perturbation of bone homeostasis that culminates in MM-associated bone disease (MMABD). We previously demonstrated that the S/T kinase CK1α sustains MM cell survival through the activation of AKT and β-catenin signaling. CK1α is a negative regulator of the Wnt/β-catenin cascade, the activation of which promotes osteogenesis by directly stimulating the expression of RUNX2, the master gene regulator of osteoblastogenesis. In this study, we investigated the role of CK1α in the osteoblastogenic potential of mesenchymal stromal cells (MSCs) and its involvement in MM–MSC cross-talk. We found that CK1α silencing in in vitro co-cultures of MMs and MSCs modulated RUNX2 expression differently in PCs and in MSCs, mainly through the regulation of Wnt/β-catenin signaling. Our findings suggest that the CK1α/RUNX2 axis could be a potential therapeutic target for constraining malignant PC expansion and supporting the osteoblastic transcriptional program of MSCs, with potential for ameliorating MMABD. Moreover, considering that Lenalidomide treatment leads to MM cell death through Ikaros, Aiolos and CK1α proteasomal degradation, we examined its effects on the osteoblastogenic potential of MSC compartments.

Role of Extracellular Vesicle-Based Cell-to-Cell Communication in Multiple Myeloma Progression

Multiple myeloma (MM) progression closely depends on the bidirectional crosstalk between tumor cells and the surrounding microenvironment, which leads to the creation of a tumor supportive niche. Extracellular vesicles (EVs) have emerged as key players in the pathological interplay between the malignant clone and near/distal bone marrow (BM) cells through their biologically active cargo. Here, we describe the role of EVs derived from MM and BM cells in reprogramming the tumor microenvironment and in fostering bone disease, angiogenesis, immunosuppression, drug resistance, and, ultimately, tumor progression. We also examine the emerging role of EVs as new therapeutic agents for the treatment of MM, and their potential use as clinical biomarkers for early diagnosis, disease classification, and therapy monitoring.

Runx Transcription Factors in T Cells-What Is Beyond Thymic Development?

Runx proteins (also known as Runt-domain transcription factors) have been studied for a long time as key regulators of cellular differentiation. RUNX2 has been described as essential for osteogenesis, whereas RUNX1 and RUNX3 are known to control blood cell development during different stages of cell lineage specification. However, recent studies show evidence of complex relationships between RUNX proteins, chromatin-modifying machinery, the cytoskeleton and different transcription factors in various non-embryonic contexts, including mature T cell homeostasis, inflammation and cancer. In this review, we discuss the diversity of Runx functions in mature T helper cells, such as production of cytokines and chemokines by different CD4 T cell populations; apoptosis; and immunologic memory acquisition. We then briefly cover recent findings about the contribution of RUNX1, RUNX2 and RUNX3 to various immunologic diseases. Finally, we discuss areas that require further study to better understand the role that Runx proteins play in inflammation and immunity.

Morphogens and growth factor signalling in the myeloma bone-lining niche

Multiple myeloma is a malignancy caused by the clonal expansion of abnormal plasma cells. Myeloma cells have proven to be incredibly successful at manipulating their microenvironment to promote growth and to evade modern therapies. They have evolved to utilise the integral signalling pathways of the bone and bone marrow to drive disease progression. The bone marrow is often described in the context of a single structure that fills the bone cavity and supports normal haematopoiesis. However, within that structure exists two anatomically different niches, the perivascular niche and the endosteal niche. These contain different cell types functioning to support normal immune and blood cell production as well as healthy bone. These cells secrete numerous signalling molecules that can influence myeloma cell biology and behaviour. The endosteal niche is home to specific bone cell lineages and plays a pivotal role in myeloma cell establishment and survival. This review will concentrate on some of the signalling pathways that are hijacked by myeloma cells to shape a favourable environment, and the different influences myeloma cells are exposed to depending on their spatial location within the bone marrow.

Osteopontin: A Key Regulator of Tumor Progression and Immunomodulation

Simple Summary

Anti-PD-1/PD-L1 and anti-CTLA-4-based immune checkpoint blockade (ICB) immunotherapy have recently emerged as a breakthrough in human cancer treatment. Durable efficacy has been achieved in many types of human cancers. However, not all human cancers respond to current ICB immunotherapy and only a fraction of the responsive cancers exhibit efficacy. Osteopontin (OPN) expression is highly elevated in human cancers and functions as a tumor promoter. Emerging data suggest that OPN may also regulate immune cell function in the tumor microenvironment. This review aims at OPN function in human cancer progression and new findings of OPN as a new immune checkpoint. We propose that OPN compensates PD-L1 function to promote tumor immune evasion, which may underlie human cancer non-response to current ICB immunotherapy.

Abstract

OPN is a multifunctional phosphoglycoprotein expressed in a wide range of cells, including osteoclasts, osteoblasts, neurons, epithelial cells, T, B, NK, NK T, myeloid, and innate lymphoid cells. OPN plays an important role in diverse biological processes and is implicated in multiple diseases such as cardiovascular, diabetes, kidney, proinflammatory, fibrosis, nephrolithiasis, wound healing, and cancer. In cancer patients, overexpressed OPN is often detected in the tumor microenvironment and elevated serum OPN level is correlated with poor prognosis. Initially identified in activated T cells and termed as early T cell activation gene, OPN links innate cells to adaptive cells in immune response to infection and cancer. Recent single cell RNA sequencing revealed that OPN is primarily expressed in tumor cells and tumor-infiltrating myeloid cells in human cancer patients. Emerging experimental data reveal a key role of OPN is tumor immune evasion through regulating macrophage polarization, recruitment, and inhibition of T cell activation in the tumor microenvironment. Therefore, in addition to its well-established direct tumor cell promotion function, OPN also acts as an immune checkpoint to negatively regulate T cell activation. The OPN protein level is highly elevated in peripheral blood of human cancer patients. OPN blockade immunotherapy with OPN neutralization monoclonal antibodies (mAbs) thus represents an attractive approach in human cancer immunotherapy.

Runt-related transcription factor 2 influences cell adhesion-mediated drug resistance and cell proliferation in B-cell non-Hodgkin's lymphoma and multiple myeloma

Several lines of evidence show that RUNX2 as a transcription factor is closely involved in carcinogenesis in a variety of human cancers. Cell adhesion-mediated drug resistance (CAM-DR) is an important part of the mechanism underlying drug resistance in hematological tumors. In this study, we investigated the biological function of RUNX2 in B-cell Non-Hodgkin's lymphoma (B-NHL) and multiple myeloma (MM). We assessed the expression of RUNX2 in suspension and adhesion model by western blot in B-NHL and MM. Adhesion assay, flow cytometry and CCK-8 were utilized to examine the role and mechanism of RUNX2 in CAM-DR and proliferation in B-NHL and MM. RUNX2 was highly expressed in adherent B-NHL and MM cells compared to suspension cells, and knockdown the expression of RUNX2 could reverse CAM-DR. Besides, RUNX2 could promote the proliferation of B-NHL and MM cells. Furthermore, RUNX2 participated the process of CAM-DR and proliferation by regulating the AKT/GSK-3β pathway. Developing RUNX2 inhibitor may be a possible strategy for drug resistance.

The cancer-related transcription factor RUNX2 modulates expression and secretion of the matricellular protein osteopontin in osteosarcoma cells to promote adhesion to endothelial pulmonary cells and lung metastasis

Osteosarcomas are bone tumors that frequently metastasize to the lung. Aberrant expression of the transcription factor, runt-related transcription factor 2 (RUNX2), is a key pathological feature in osteosarcoma and associated with loss of p53 and miR-34 expression. Elevated RUNX2 may transcriptionally activate genes mediating tumor progression and metastasis, including the RUNX2 target gene osteopontin (OPN/SPP1). This gene encodes a secreted matricellular protein produced by osteoblasts to regulate bone matrix remodeling and tissue calcification. Here we investigated whether and how the RUNX2/OPN axis regulates lung metastasis of osteosarcoma. Importantly, RUNX2 depletion attenuates lung metastasis of osteosarcoma cells in vivo. Using next-generation RNA-sequencing, protein-based assays, as well as the loss- and gain-of-function approaches in selected osteosarcoma cell lines, we show that osteopontin messenger RNA levels closely correlate with RUNX2 expression and that RUNX2 controls the levels of secreted osteopontin. Elevated osteopontin levels promote heterotypic cell-cell adhesion of osteosarcoma cells to human pulmonary microvascular endothelial cells, but not in the presence of neutralizing antibodies. Collectively, these findings indicate that the RUNX2/OPN axis regulates the ability of osteosarcoma cells to attach to pulmonary endothelial cells as a key step in metastasis of osteosarcoma cells to the lung.

Prognostic significance of osteopontin in acute myeloid leukemia: A meta-analysis

Osteopontin (OPN) has been investigated in the field of tumor research for several years. However, the prognostic role of OPN overexpression in acute myeloid leukemia (AML) remains controversial. A meta-analysis of four studies, including a total of 492 patients, was performed to determine the association of OPN with overall survival (OS) in AML patients. The random-effects model of Der Simonian and Laird was used to synthesize data; hazard ratio (HR) with its 95% confidence interval (CI) was used as the effect size estimate. It was observed that serum-based OPN was inversely correlated with OS and the difference was statistically significant (HR=1.83; 95% CI: 1.43-2.35; P<0.001). Experimental findings indicate that OPN overexpression is associated with a poor prognosis in AML and may be of prognostic value for AML stage and metastasis.

Runx3 and Cell Fate Decisions in Pancreas Cancer

The RUNX family transcription factors are critical regulators of development and frequently dysregulated in cancer. RUNX3, the least well characterized of the three family members, has been variously described as a tumor promoter or suppressor, sometimes with conflicting results and opinions in the same cancer and likely reflecting a complex role in oncogenesis. We recently identified RUNX3 expression as a crucial determinant of the predilection for pancreatic ductal adenocarcinoma (PDA) cells to proliferate locally or promulgate throughout the body. High RUNX3 expression induces the production and secretion of soluble factors that support metastatic niche construction and stimulates PDA cells to migrate and invade, while simultaneously suppressing proliferation through increased expression of cell cycle regulators such as CDKN1A/p21 ^WAF1/CIP1 . RUNX3 expression and function are coordinated by numerous transcriptional and post-translational inputs, and interactions with diverse cofactors influence whether the resulting RUNX3 complexes enact tumor suppressive or tumor promoting programs. Understanding these exquisitely context-dependent tumor cell behaviors has the potential to inform clinical decision-making including the most appropriate timing and sequencing of local vs. systemic therapies.

Contact of myeloma cells induces a characteristic transcriptome signature in skeletal precursor cells -Implications for myeloma bone disease

Physical interaction of skeletal precursors with multiple myeloma cells has been shown to suppress their osteogenic potential while favoring their tumor-promoting features. Although several transcriptome analyses of myeloma patient-derived mesenchymal stem cells have displayed differences compared to their healthy counterparts, these analyses insufficiently reflect the signatures mediated by tumor cell contact, vary due to different methodologies, and lack results in lineage-committed precursors. To determine tumor cell contact-mediated changes on skeletal precursors, we performed transcriptome analyses of mesenchymal stem cells and osteogenic precursor cells cultured in contact with the myeloma cell line INA-6. Comparative analyses confirmed dysregulation of genes which code for known disease-relevant factors and additionally revealed upregulation of genes that are associated with plasma cell homing, adhesion, osteoclastogenesis, and angiogenesis. Osteoclast-derived coupling factors, a dysregulated adipogenic potential, and an imbalance in favor of anti-anabolic factors may play a role in the hampered osteoblast differentiation potential of mesenchymal stem cells. Angiopoietin-Like 4 (ANGPTL4) was selected from a list of differentially expressed genes as a myeloma cell contact-dependent target in skeletal precursor cells which warranted further functional analyses. Adhesion assays with full-length ANGPTL4-coated plates revealed a potential role of this protein in INA-6 cell attachment. This study expands knowledge of the myeloma cell contact-induced signature in the stromal compartment of myelomatous bones and thus offers potential targets that may allow detection and treatment of myeloma bone disease at an early stage.

Osteoblast-derived paracrine factors regulate angiogenesis in response to mechanical stimulation

Angiogenesis is a process by which new blood vessels emerge from existing vessels through endothelial cell sprouting, migration, proliferation, and tubule formation. Angiogenesis during skeletal growth, homeostasis and repair is a complex and incompletely understood process. As the skeleton adapts to mechanical loading, we hypothesized that mechanical stimulation regulates "osteo-angio" crosstalk in the context of angiogenesis. We showed that conditioned media (CM) from osteoblasts exposed to fluid shear stress enhanced endothelial cell proliferation and migration, but not tubule formation, relative to CM from static cultures. Endothelial cell sprouting was studied using a dual-channel collagen gel-based microfluidic device that mimics vessel geometry. Static CM enhanced endothelial cell sprouting frequency, whereas loaded CM significantly enhanced both frequency and length. Both sprouting frequency and length were significantly enhanced in response to factors released from osteoblasts exposed to fluid shear stress in an adjacent channel. Osteoblasts released angiogenic factors, of which osteopontin, PDGF-AA, IGBP-2, MCP-1, and Pentraxin-3 were upregulated in response to mechanical loading. These data suggest that in vivo mechanical forces regulate angiogenesis in bone by modulating "osteo-angio" crosstalk through release of paracrine factors, which we term "osteokines".

Endothelial progenitor cells in hematologic malignancies

Studies carried out in the last years have improved the understanding of the cellular and molecular mechanisms controlling angiogenesis during adult life in normal and pathological conditions. Some of these studies have led to the identification of some progenitor cells that sustain angiogenesis through indirect, paracrine mechanisms (hematopoietic angiogenic cells) and through direct mechanisms, i.e., through their capacity to generate a progeny of phenotypically and functionally competent endothelial cells [endothelial colony forming cells (ECFCs)]. The contribution of these progenitors to angiogenetic processes under physiological and pathological conditions is intensively investigated. Angiogenetic mechanisms are stimulated in various hematological malignancies, including chronic myeloid leukemia (CML), acute myeloid leukemia (AML), myelodysplastic syndromes and multiple myeloma, resulting in an increased angiogenesis that contributes to disease progression. In some of these conditions there is preliminary evidence that some endothelial cells could derive from the malignant clone, thus leading to the speculation that the leukemic cell derives from the malignant transformation of a hemangioblastic progenitor, i.e., of a cell capable of differentiation to the hematopoietic and to the endothelial cell lineages. Our understanding of the mechanisms underlying increased angiogenesis in these malignancies not only contributed to a better knowledge of the mechanisms responsible for tumor progression, but also offered the way for the discovery of new therapeutic targets.

RUNX2 and the PI3K/AKT axis reciprocal activation as a driving force for tumor progression

From the first reported role of the transcription factor RUNX2 in osteoblast and chondrocyte differentiation and migration to its involvement in promigratory/proinvasive behavior of breast, prostate, and thyroid cancer cells, osteosarcoma, or melanoma cells, RUNX2 currently emerges as a key player in metastasis. In this review, we address the interaction of RUNX2 with the PI3K/AKT signaling pathway, one of the critical axes controlling cancer growth and metastasis. AKT, either by directly phosphorylating/activating RUNX2 or phosphorylating/inactivating regulators of RUNX2 stability or activity, contributes to RUNX2 transcriptional activity. Reciprocally, the activation of the PI3K/AKT pathway by RUNX2 regulation of its different components has been described in non-transformed and transformed cells. This mutual activation in the context of cancer cells exhibiting constitutive AKT activation and high levels of RUNX2 might constitute a major driving force in tumor progression and aggressiveness.

The Forkhead Transcription Factor FOXP2 Is Required for Regulation of p21WAF1/CIP1 in 143B Osteosarcoma Cell Growth Arrest

Mutations of the forkhead transcription factor FOXP2 gene have been implicated in inherited speech-and-language disorders, and specific Foxp2 expression patterns in neuronal populations and neuronal phenotypes arising from Foxp2 disruption have been described. However, molecular functions of FOXP2 are not completely understood. Here we report a requirement for FOXP2 in growth arrest of the osteosarcoma cell line 143B. We observed endogenous expression of this transcription factor both transiently in normally developing murine osteoblasts and constitutively in human SAOS-2 osteosarcoma cells blocked in early osteoblast development. Critically, we demonstrate that in 143B osteosarcoma cells with minimal endogenous expression, FOXP2 induced by growth arrest is required for up-regulation of p21^WAF1/CIP1. Upon growth factor withdrawal, FOXP2 induction occurs rapidly and precedes p21^WAF1/CIP1 activation. Additionally, FOXP2 expression could be induced by MAPK pathway inhibition in growth-arrested 143B cells, but not in traditional cell line models of osteoblast differentiation (MG-63, C2C12, MC3T3-E1). Our data are consistent with a model in which transient upregulation of Foxp2 in pre-osteoblast mesenchymal cells regulates a p21-dependent growth arrest checkpoint, which may have implications for normal mesenchymal and osteosarcoma biology.

Myeloma cell-derived Runx2 promotes myeloma progression in bone

The progression of multiple myeloma (MM) is governed by a network of molecular signals, the majority of which remain to be identified. Recent studies suggest that Runt-related transcription factor 2 (Runx2), a well-known bone-specific transcription factor, is also expressed in solid tumors, where expression promotes both bone metastasis and osteolysis. However, the function of Runx2 in MM remains unknown. The current study demonstrated that (1) Runx2 expression in primary human MM cells is significantly greater than in plasma cells from healthy donors and patients with monoclonal gammopathy of undetermined significance; (2) high levels of Runx2 expression in MM cells are associated with a high-risk population of MM patients; and (3) overexpression of Runx2 in MM cells enhanced tumor growth and disease progression in vivo. Additional studies demonstrated that MM cell-derived Runx2 promotes tumor progression through a mechanism involving the upregulation of Akt/β-catenin/Survivin signaling and enhanced expression of multiple metastatic genes/proteins, as well as the induction of a bone-resident cell-like phenotype in MM cells. Thus, Runx2 expression supports the aggressive phenotype of MM and is correlated with poor prognosis. These data implicate Runx2 expression as a major regulator of MM progression in bone and myeloma bone disease.

Exosomal miR-135b shed from hypoxic multiple myeloma cells enhances angiogenesis by targeting factor-inhibiting HIF-1

Exosomes are small endosome-derived vesicles containing a wide range of functional proteins, mRNA, and miRNA. Exosomal miRNA from cancer cells helps modulate the microenvironment. In multiple myeloma (MM), the massive proliferation of malignant plasma cells causes hypoxia. To date, the majority of in vitro hypoxia studies of cancer cells have used acute hypoxic exposure (3-24 hours). Thus, we attempted to clarify the role of MM-derived exosomes in hypoxic bone marrow by using MM cells grown continuously in vitro under chronic hypoxia (hypoxia-resistant MM [HR-MM] cells). The HR-MM cells produced more exosomes than the parental cells under normoxia or acute hypoxia conditions, and miR-135b was significantly upregulated in exosomes from HR-MM cells. Exosomal miR-135b directly suppressed its target factor-inhibiting hypoxia-inducible factor 1 (FIH-1) in endothelial cells. Finally, exosomal miR-135b from HR-MM cells enhanced endothelial tube formation under hypoxia via the HIF-FIH signaling pathway. This in vitro HR myeloma cell model will be useful for investigating MM cell-endothelial cell interactions under hypoxic conditions, which may mimic the in vivo bone marrow microenvironment. Although tumor angiogenesis is regulated by various factors, exosomal miR-135b may be a target for controlling MM angiogenesis.

Plasma levels of osteopontin and vascular endothelial growth factor in association with clinical features and parameters of tumor burden in patients with multiple myeloma

The aim of this pilot study was to determine the plasma levels of osteopontin (OPN) and vascular endothelial growth factor (VEGF) and find possible association between them and main clinical features and parameters of tumor burden in patient with multiple myeloma (MM). Plasma levels of OPN and VEGF were determined in 44 newly diagnosed MM patients and 24 healthy persons by ELISA method. These values were compared with the presence of anemia, renal dysfunction, and bone lesions as myeloma related clinical manifestations and with serum beta-2 microglobulin and Durie-Salmon clinical stage as prognosticators related to tumor mass. The value of OPN was significantly higher in MM patients with evident bone lesions (P = 0.03) and there was also a positive correlation with serum beta-2 microglobulin (r = 0.366; P = 0.04). Furthermore, patients with lower Durie-Salmon stage had significantly lower OPN and VEGF levels (P = 0.05; P = 0.04, resp.). Our preliminary results found positive association between plasma level of OPN, tumor burden, and bone destruction. Further analysis should provide information about the possible use of OPN as useful clinical biomarker for monitoring bone disease and tumor mass, as well as a prognostic factor, or a possible target for pharmacological intervention.

Expression of osteoblast and osteoclast regulatory genes in the bone marrow microenvironment in multiple myeloma: only up-regulation of Wnt inhibitors SFRP3 and DKK1 is associated with lytic bone disease

Multiple myeloma (MM) lytic bone disease (LBD) is caused by osteoclast activation and osteoblast inhibition. RANK/RANKL/OPG play central roles in osteoclast activation and Wnt inhibitor DKK1 in osteoblast inhibition. The role of other Wnt inhibitors is less clear. We evaluated gene expression of osteoclast regulators (RANK, RANKL, OPG, TRAIL, MIP1A), Wnt inhibitors (DKK1, SFRP2, SFRP3, sclerostin, WIF1) and osteoblast transcription factors (RUNX2, osterix) by quantitative reverse transcriptase polymerase chain reaction (RT-PCR) in the bone marrow (BM) microenvironment using snap-frozen BM biopsies, thereby achieving minimal post-sampling manipulation, and gene expression profiling (GEP) data, reflecting the in vivo situation. We analyzed 110 biopsies from newly diagnosed patients with MM and monoclonal gammopathy of unknown significance (MGUS) and healthy volunteers. LBD was evaluated using standard radiographs and the bone resorption marker CTX-1. Protein levels were evaluated by enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry. Among Wnt inhibitors, only SFRP3 and DKK1 were significantly overexpressed in advanced LBD, correlating with protein levels. SFRP3 correlated with CTX-1. Our findings support osteoblast inhibition as the driving force behind MM LBD.

Intraclonal heterogeneity is a critical early event in the development of myeloma and precedes the development of clinical symptoms

The mechanisms involved in progression from monoclonal gammopathy of undetermined significance (MGUS) and smoldering myeloma (SMM) to malignant multiple myeloma (MM) and plasma cell leukemia (PCL) are poorly understood but believed to involve the sequential acquisition of genetic hits. We performed exome and whole genome sequencing on a series of MGUS (n=4), high risk (HR)-SMM (n=4), MM (n=26) and PCL (n=2) samples, including four cases who transformed from HR-SMM to MM, to determine the genetic factors which drive progression of disease. The pattern and number of non-synonymous mutations show that the MGUS disease stage is less genetically complex than MM, and HR-SMM is similar to presenting MM. Intraclonal heterogeneity is present at all stages and using cases of HR-SMM, which transformed to MM, we show that intraclonal heterogeneity is a typical feature of the disease. At the HR-SMM stage of disease the majority of the genetic changes necessary to give rise to MM are already present. These data suggest that clonal progression is the key feature of transformation of HR-SMM to MM and as such the invasive clinically predominant clone typical of MM is already present at the SMM stage and would be amenable to therapeutic intervention at that stage.

Hypoxia-inducible factor (HIF)-1α suppression in myeloma cells blocks tumoral growth in vivo inhibiting angiogenesis and bone destruction

Hypoxia-inducible transcription factor-1 (HIF-1α) is overexpressed in multiple myeloma (MM) cells within the hypoxic microenvironment. Herein, we explored the effect of persistent HIF-1α inhibition by a lentivirus short hairpin RNA pool on MM cell growth either in vitro or in vivo and on the transcriptional and pro-angiogenic profiles of MM cells. HIF-1α suppression did not have a significant impact on MM cell proliferation and survival in vitro although, increased the antiproliferative effect of lenalidomide. On the other hand, we found that HIF-1α inhibition in MM cells downregulates the pro-angiogenic genes VEGF, IL8, IL10, CCL2, CCL5 and MMP9. Pro-osteoclastogenic cytokines were also inhibited, such as IL-7 and CCL3/MIP-1α. The effect of HIF-1α inhibition was assessed in vivo in nonobese diabetic/severe combined immunodeficiency mice both in a subcutaneous and an intratibial MM model. HIF-1α inhibition caused a dramatic reduction in the weight and volume of the tumor burden in both mouse models. Moreover, a significant reduction of the number of vessels and vascular endothelial growth factors (VEGFs) immunostaining was observed. Finally, in the intratibial experiments, HIF-1α inhibition significantly blocked bone destruction. Overall, our data indicate that HIF-1α suppression in MM cells significantly blocks MM-induced angiogenesis and reduces MM tumor burden and bone destruction in vivo, supporting HIF-1α as a potential therapeutic target in MM.

Prognostic value of hepatocyte growth factor, syndecan-1, and osteopontin in multiple myeloma and monoclonal gammopathy of undetermined significance

Our aim was to compare serum levels of selected biological parameters in different phases of multiple myeloma (MM) and monoclonal gammopathy of undetermined significance (MGUS) to determine their diagnostic and prognostic potential. A cohort of 234 individuals was assessed for serum levels of hepatocyte growth factor (HGF), syndecan-1/CD₁₃₈ (SYN), and osteopontin (OPN). The patients with MM (N = 156) were divided into 3 groups: at the time of diagnosis (N = 45), in relapse/progression (N = 56), and in remission (N = 50). The analysis revealed significant differences of all three parameters in comparison of active and remission phase MM. Moreover, the parameters in active myeloma were significantly higher than in MGUS. Within the comparison of active disease (newly diagnosed and relapsing), there was no significant difference. Similar results were in remission phase MM and MGUS. There was no relationship of pretreatment levels of the parameters to therapeutic response. We conclude that serum levels of HGF, OPN, and SYN correspond to the activity of MM and might become useful in differentiation of MGUS, asymptomatic MM, and overt/symptomatic form of MM. The levels of all three parameters behave accordingly with MM activity. Pretreatment measurement without the assessment of their kinetics, however, has no relationship to therapeutic response.

Global gene expression profiling in mouse plasma cell tumor precursor and bystander cells reveals potential intervention targets for plasma cell neoplasia

Tumor progression usually proceeds through several sequential stages, any of which could be targets for interrupting the progression process if one understood these steps at the molecular level. We extracted nascent plasma cell tumor (PCT) cells from within inflammatory oil granulomas (OG) isolated from IP pristane-injected BALB/c.iMyc(Eμ) mice at 5 different time points during tumor progression. We used laser capture microdissection to collect incipient PCT cells and analyzed their global gene expression on Affymetrix Mouse Genome 430A microarrays. Two independent studies were performed with different sets of mice. Analysis of the expression data used ANOVA and Bayesian estimation of temporal regulation. Genetic pathway analysis was performed using MetaCore (GeneGo) and IPA (Ingenuity). The gene expression profiles of PCT samples and those of undissected OG samples from adjacent sections showed that different genes and pathways were mobilized in the tumor cells during tumor progression, compared with their stroma. Our analysis implicated several genetic pathways in PCT progression, including biphasic (up- and then down-regulation) of the Spp1/osteopontin-dependent network and up-regulation of mRNA translation/protein synthesis. The latter led to a biologic validation study that showed that the AMPK-activating diabetes drug, metformin, was a potent specific PCT inhibitor in vitro.

Biological aspects of angiogenesis in multiple myeloma

Multiple myeloma (MM) is a hematological malignancy characterized by the aberrant expansion of malignant plasma cells within the bone marrow (BM). One of the hallmarks of this disease is the close interaction between myeloma cells and neighboring cells within the BM. Angiogenesis, through the activation of endothelial cells, plays an essential role in MM biology. In the current review, we describe the angiogenesis process in MM by identifying the interacting cells, the pro- and anti-angiogenic cytokines modulated, and the extracellular matrix degrading proteases liable to participate in the pathophysiology. Finally, we highlight the impact of hypoxia (through hypoxia-inducible factor-1) and constitutive activation of nuclear factor-κB in this tumor-induced neo-vascularization.

Angiogenesis and multiple myeloma

The bone marrow microenvironment in multiple myeloma is characterized by an increased microvessel density. The production of pro-angiogenic molecules is increased and the production of angiogenic inhibitors is suppressed, leading to an "angiogenic switch". Here we present an overview of the role of angiogenesis in multiple myeloma, the pro-angiogenic factors produced by myeloma cells and the microenvironment, and the mechanisms involved in the myeloma-induced angiogenic switch. Current data suggest that the increased bone marrow angiogenesis in multiple myeloma is due to the aberrant expression of angiogenic factors by myeloma cells, the subsequent increase in pro-angiogenic activity of normal plasma cells as a result of myeloma cell angiogenic activity, and the increased number of plasma cells overall. Hypoxia also contributes to the angiogenic properties of the myeloma marrow microenvironment. The transcription factor hypoxia-inducible factor-1α is overexpressed by myeloma cells and affects their transcriptional and angiogenic profiles. In addition, potential roles of the tumor suppressor gene inhibitor of growth family member 4 and homeobox B7 have also been recently highlighted as repressors of angiogenesis and pro-angiogenic related genes, respectively. This complex pathogenetic model of myeloma-induced angiogenesis suggests that several pro-angiogenic molecules and related genes in myeloma cells and the microenvironment are potential therapeutic targets.

Inducible expression of Runx2 results in multiorgan abnormalities in mice

Runx2 is a transcription factor controlling skeletal development, and is also expressed in extraskeletal tissues where its function is not well understood. Existing Runx2 mutant and transgenic mouse models do not allow the necessary control of Runx2 expression to understand its functions in different tissues. We generated conditional, doxycyline-inducible, triple transgenic mice (CMV-Cre;ROSA26-neo(flox/+)-rtTA;Tet-O-Runx2) to investigate the effects of wide spread overexpression of Runx2. Osteoblasts isolated from CMV-Cre;ROSA26-neo(flox/+)-rtTA; Tet-O-Runx2 mice demonstrated a dose-dependent effect of doxycycline to stimulate Runx2 transgene expression. Doxycycline administration to CMV-Cre;ROSA26-neo(flox/+)-rtTA;Tet-O-Runx2 mice induced Runx2 transgene expression in all tissues tested, with the highest levels observed in kidney, ovary, and bone. Runx2 overexpression resulted in deceased body size and reduced viability. With regard to bone, Runx2 overexpressing mice paradoxically displayed profound osteopenia and diminished osteogenesis. Induced expression of Runx2 in extraskeletal tissues resulted in ectopic calcification and induction of the osteogenic program in a limited number of tissues, including lung and muscle. In addition, the triple transgenic mice showed evidence of a myeloproliferative disorder and an apparent inhibition of lymphocyte development. Thus, overexpression of Runx2 both within and outside of the skeleton can have diverse biological effects. Use of tissue specific Cre mice will allow this model to be used to conditionally and inducibly overexpress Runx2 in different tissues and provide a means to study the post-natal tissue- and cell context-dependent functions of Runx2.

Calciphylaxis: a review

Human calciphylaxis reflects a form of severe tissue compromise attributable to a unique microangiopathy that combines features of vascular thrombotic occlusion with endoluminal calcification. While most frequently described in patients with renal failure, it is seen in other settings, such as multiple myeloma; polyneuropathy, organomegaly, endocrinopathy, M protein, and skin changes (POEMS) syndrome; cirrhosis; and rheumatoid arthritis. Although most commonly involving the skin, calciphylaxis can affect other organs including the heart and gastrointestinal tract, in which cases it falls under the appellation of systemic calciphylaxis. There are cases in which the main pathology is one of endovascular thrombosis of the vessels of the fat without discernible calcification or one manifesting a pseudoangiosarcomatous pattern, hence adding to the histomorphologic spectrum of calciphylaxis. A variety of factors contribute to this severe occlusive microangiopathy, including an underlying procoagulant state and ectopic neo-osteogenesis of the microvasculature through varied mechanisms, including increased osteopontin production by vascular smooth muscle or reduced synthesis of fetuin and GLA matrix protein, important inhibitors of ectopic neo-osteogenesis. Certain factors adversely affect outcome, including truncal and genital involvement and systemic forms of calciphylaxis. With a better understanding of its pathophysiology, more-effective therapies, such as sodium thiosulfate and biphosphanates to reduce reactive oxygen species and receptor activator of nuclear factor κβ-mediated nuclear factor κβ activity, respectively, are being developed.

TGF-β-related mechanisms of bone destruction in multiple myeloma

In destructive bone lesions of multiple myeloma (MM), osteoclastic bone resorption is enhanced, while bone formation is suppressed with impaired osteoblast differentiation from their progenitor cells. As a result, a strong negative balance in bone turnover develops in MM bone lesions. The suppression of bone formation is mainly due to a secretion of Wnt signal inhibitors, secreted Frizzled-related protein (sFRP)-2 and 3 and dikkopf1 (DKK1). In addition, the enhanced bone resorption in MM bone lesions causes a marked increase in the release and activation of transforming growth factor (TGF)-β. Although TGF-β enhances the recruitment and proliferation of osteoblast progenitors, TGF-β potently inhibits later phases of osteoblast differentiation and maturation and suppresses matrix mineralization. Thus, TGF-β also plays a role in the suppression of bone formation in MM bone lesions. In fact, when TGF-β action is suppressed by inhibitors of TGF-β type I receptor kinase, the inhibition of terminal differentiation of osteoblasts and mineralization is abrogated. While immature mesenchymal stromal cells support the growth and survival of MM cells, mature osteoblasts enhance MM cell apoptosis and cell cycle arrest. Thus, the inhibition of TGF-β signaling by TGF-β type I receptor kinase inhibitor causes not only an enhancement of bone formation but also a suppression of MM cell growth. Inhibition of TGF-β signaling can become a new therapeutic approach against MM.

HOXB7 expression by myeloma cells regulates their pro-angiogenic properties in multiple myeloma patients

The deregulation of the homeobox genes as homeoboxB (HOXB)-7 has been previously associated to tumor progression and angiogenesis; here we investigated the potential role of HOXB7 in the pro-angiogenic properties of multiple myeloma (MM) cells. We found that HOXB7 was expressed in 10 out of 22 MM patients analyzed at the diagnosis related to high bone marrow angiogenesis and overexpressed in about 40% of myeloma cell lines compared with normal plasma cells. Enforced HOXB7 expression in MM cells by a lentiviral vector significantly modified their transcriptional and angiogenic profile, checked by combined microarray and angiogenesis PCR analyses, upregulating VEGFA, FGF2, MMP2, WNT5a and PDGFA and downregulating thrombospoindin-2. The pro- and anti-angiogenic HOXB7-related gene signature was also validated in a large independent dataset of MM patients. Accordingly, MM-induced vessel formation was significantly increased by HOXB7 overexpression both in vitro angiogenic and chorioallantoic membrane assays, as well as the HOXB7 silencing by small interfering RNA inhibited the production of angiogenic factors, and the pro-angiogenic properties of MM cells. Finally, in SCID-NOD mice we confirmed that HOXB7 overexpression by MM cells stimulated tumor growth, increased MM-associated angiogenesis and the expression of pro-angiogenic genes by microarray analysis supporting the critical role of HOXB7 in the angiogenic switch in MM.

Runx2 in normal tissues and cancer cells: A developing story

The Runx transcription factors are essential for mammalian development, most notably in the haematopoietic and osteogenic lineages. Runx1 and its binding partner, CBFbeta, are frequently targeted in acute leukaemia but evidence is accumulating that all three Runx genes may have a role to play in a wider range of cancers, either as tumour promoters or tumour suppressors. Whilst Runx2 is renowned for its role as a master regulator of bone development we discuss here its expression pattern and putative functions beyond this lineage. Furthermore, we review the evidence that RUNX2 promotes neoplastic development in haematopoietic lineages and in advanced mammary and prostate cancer.

RARalpha2 expression is associated with disease progression and plays a crucial role in efficacy of ATRA treatment in myeloma

Specific genetic alterations in multiple myeloma (MM) may cause more aggressive diseases. Paired gene array analysis on 51 samples showed that retinoic acid (RA) receptor alpha (RARalpha) expression significantly increased at relapse compared with diagnosis. RARalpha encodes 2 major isoforms: RARalpha1 and RARalpha2. In this study, we examined the function of RARalpha2 in MM. Reverse transcription-polymerase chain reaction (RT-PCR) revealed ubiquitous RARalpha1 expression in MM cells, but RARalpha2 was expressed in 26 (32%) of 80 newly diagnosed patients and 10 (28%) of 36 MM cell lines. Patients with RARalpha2 expression had a significantly shorter overall survival on identical treatments. The presence of RARalpha2 remained significant on multivariate analysis. Knockdown of RARalpha2 but not RARalpha1 induced significant MM cell death and growth inhibition, and overexpressing RARalpha2 activated STAT3 and mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathways. Interestingly, all-trans retinoic acid (ATRA) treatment induced potent cell death and growth inhibition in RARalpha2(+) but not RARalpha2(-) MM cells; overexpressing RARalpha2 in RARalpha2-deficient MM cells restored sensitivity to ATRA. Furthermore, ATRA treatment significantly inhibited the growth of RARalpha2-overexpressing MM tumors in severe combined immunodeficiency (SCID) mouse model. These findings provide a rationale for RA-based therapy in aggressive RARalpha2(+) MM.

Role of osteopontin in breast cancer patients

AIM AND BACKGROUND

In breast cancer, as in almost all neoplastic diseases, the prognosis is strictly related to the invasive capacity, local and distant, that characterizes the growth of all tumors. Since the mechanisms that regulate replication of the neoplastic cells, with consequent capacity to metastasize, are not completely known, identification of new markers represents the gold standard of research in the stratification of patients with such a pathology. Osteopontin, a specific phosphoglycoprotein isolated from extracellular bone matrix and actively involved in mechanisms of bone reabsorption, appears to play a key role in osteoclastogenesis at the level of the skeleton in some pathologic situations. It has been found that patients with metastatic bone lesions from breast or prostate cancer present, with respect to subjects without repetitive bone lesions, elevated serum levels of the protein, indicating that osteopontin could play an important role in the development and progression of the neoplastic disease at the bone level.

METHODS AND STUDY DESIGN

The authors studied 26 patients with breast cancer, evaluating as a marker also serum osteopontin levels.

RESULTS AND CONCLUSIONS

The results, although obtained on a small number of patients, showed that osteopontin evaluation in breast cancer patients can be a particularly interesting method of research in staging of the disease as well as in the prognosis, thereby attributing a role of a biotumoral marker also in the follow-up of the therapy.

Novel anti-myeloma agents and angiogenesis

During the last decade several novel agents have been used in the management of patients with multiple myeloma. Immunomodulatory drugs and proteasome inhibitors exert their efficacy both directly by inducing apoptosis of myeloma cells and indirectly through the interruption of the interactions between myeloma and stromal cells in the bone marrow (BM) microenvironment. These interactions are crucial for myeloma cell growth and survival. The adherence of myeloma cells to BM stromal cells leads to the overproduction of several cytokines with angiogenic properties that enhance the survival and growth of myeloma cells through paracrine and autocrine loops. The correlation of these molecules with clinical features and survival of myeloma patients supports the importance of angiogenesis in the pathogenesis of the disease and reveals these cytokines as suitable targets for the development of novel anti-myeloma therapies. This review summarises all available preclinical and clinical data for the effect of novel agents that are used in myeloma therapy, such as thalidomide, lenalidomide, bortezomib and VEGF inhibitors, on angiogenesis, which is at least partially responsible for their remarkable anti-myeloma efficacy.

NF-kappaB in the pathogenesis and treatment of multiple myeloma

PURPOSE OF REVIEW

This review aims to summarize recent advances in the mechanisms through which the activation of the transcription factor NF-kappaB contributes to the pathogenesis of multiple myeloma.

RECENT FINDINGS

This transcription factor regulates expression of numerous genes involved in multiple myeloma pathogenesis, including growth, survival, immortalization, angiogenesis and metastasis. Recently, mutations of NF-kappaB signaling molecules have been identified in multiple myeloma cells. In addition, interactions between multiple myeloma cells and the bone marrow environment play critical roles in NF-kappaB activation as well as in multiple myeloma pathogenesis. Moreover, several drugs that are effective against multiple myeloma, including bortezomib, thalidomide, lenalidomide and arsenic trioxide, have been found to block activation of NF-kappaB. The combination of conventional chemotherapeutic drugs and those that block NF-kappaB activation has now proven to be effective in the treatment of multiple myeloma.

SUMMARY

Recent studies further underscore the critical role of NF-kappaB in multiple myeloma pathogenesis and have provided the rationale for multiple myeloma therapy with NF-kappaB-specific inhibitors combined with conventional chemotherapeutic drugs.

Small integrin-binding ligand N-linked glycoproteins (SIBLINGs): multifunctional proteins in cancer

Numerous components and pathways are involved in the complex interplay between cancer cells and their environment. The family of glycophosphoproteins comprising osteopontin, bone sialoprotein, dentin matrix protein 1, dentin sialophosphoprotein and matrix extracellular phosphoglycoprotein - small integrin-binding ligand N-linked glycoproteins (SIBLINGs) - are emerging as important players in many stages of cancer progression. From their detection in various human cancers to the demonstration of their key functional roles during malignant transformation, invasion and metastasis, the SIBLINGs are proteins with potential as diagnostic and prognostic tools, as well as new therapeutic targets.

Extravasation and homing mechanisms in multiple myeloma

Multiple myeloma (MM) is a malignant B-cell disorder characterized by a monoclonal expansion of plasma cells (PC) in the bone marrow (BM). During the main course of disease evolution, MM cells depend on the BM microenvironment for their growth and survival. Reciprocal interactions between MM cells and the BM mediate not only MM cell growth, but also protect them against apoptosis and cause bone disease and angiogenesis. A striking feature of MM represents the predominant localization and retention of MM cells in the BM. Although BM PC indeed represent the main neoplastic cell type, small numbers of MM cells can also be detected in the peripheral blood circulation. It can be assumed that these circulating cells represent the tumour-spreading component of the disease. This implicates that MM cells have the capacity to (re)circulate, to extravasate and to migrate to the BM (homing). In analogy to the migration and homing of normal leucocytes, the BM homing of MM cells is mediated by a multistep process of extravasation with adhesion to the endothelium, invasion of the subendothelial basement membrane, followed by further migration within the stroma, mediated by chemotactic factors. At the end stage of disease, MM cells are thought to develop autocrine growth supporting loops that enable them to survive and proliferate in the absence of the BM microenvironment and to become stroma-independent. In this stage, the number of circulating cells increases and growth at extramedullary sites can occur, associated with alteration in adhesion molecule and chemokine receptor expression. This review summarizes the recent progress in the study of the extravasation and homing mechanisms of MM cells.

Regulation and functional role of the Runt-related transcription factor-2 in pancreatic cancer

Recent evidence suggests that Runt-related transcription factors play a role in different human tumours. In the present study, the localisation of the Runt-related transcription factor-2 (Runx2), its transcriptional activity, as well as its regulation of expression was analysed in human pancreatic ductal adenocarcinoma (PDAC). Quantitative real-time PCR and immunohistochemistry were used for Runx2 expression and localisation analysis. Runt-related transcription factor-2 expression was silenced using specific siRNA oligonucleotides in pancreatic cancer cells (Panc-1) and immortalised pancreatic stellate cells (IPSCs). Overexpression of Runx2 was achieved using a full-length expression vector. TGF-β1, BMP2, and other cytokines were assessed for their potential to regulate Runx2 expression. There was a 6.1-fold increase in median Runx2 mRNA levels in PDAC tissues compared to normal pancreatic tissues (P<0.0001). Runt-related transcription factor-2 was localised in pancreatic cancer cells, tubular complexes, and PanIN lesions of PDAC tissues as well as in tumour-associated fibroblasts/stellate cells. Coculture of IPSCs and Panc-1 cells, as well as treatment with TGF-β1 and BMP2, led to increased Runx2 expression in Panc-1 cells. Runt-related transcription factor-2 overexpression was associated with decreased MMP1 release as well as decreased growth and invasion of Panc-1 cells. These effects were reversed by Runx2 silencing. In conclusion, Runx2 is overexpressed in PDAC, where it is regulated by certain cytokines such as TGF-β1 and BMP2 in an auto- and paracrine manner. In addition, Runx2 has the potential to regulate the transcription of extracellular matrix modulators such as SPARC and MMP1, thereby influencing the tumour microenvironment.

Inhibition of osteopontin would suppress angiogenesis in gastric cancer

Osteopontin (OPN) plays an important role in tumorigenesis, tumor invasion, and metastasis in many types of cancers, including gastric cancer. Recently, much interest has been focused on the role of OPN in tumor angiogenesis. Our previous studies have shown that OPN is overexpressed, and associated with mean microvessel density in, the tissue samples of patients with gastric cancer. In the present study, we aimed to further determine and provide evidence for the role of OPN in gastric-cancer-associated angiogenesis by diminishing OPN expression in gastric cancer cells using the small interference RNA method, and then evaluate the effects of OPN on gastric cancer-associated angiogenesis by in vivo and in vitro assays. Our results revealed that reduced OPN production by gastric cancer cells would reduce the proliferation, migration, and tube formation of human umbilical vein endothelial cells, and lead to a lower microvessel density, i.e., angiogenesis, in transplanted tumors of mice. These data confirm the positive role of OPN in gastric-cancer-associated angiogenesis.

The new tumor-suppressor gene inhibitor of growth family member 4 (ING4) regulates the production of proangiogenic molecules by myeloma cells and suppresses hypoxia-inducible factor-1 alpha (HIF-1alpha) activity: involvement in myeloma-induced angiogenesis

Angiogenesis has a critical role in the pathophysiology of multiple myeloma (MM); however, the molecular mechanisms underlying this process are not completely elucidated. The new tumor-suppressor gene inhibitor of growth family member 4 (ING4) has been recently implicated in solid tumors as a repressor of angiogenesis. In this study, we found that ING4 expression in MM cells was correlated with the expression of the proangiogenic molecules interleukin-8 (IL-8) and osteopontin (OPN). Moreover, we demonstrate that ING4 suppression in MM cells up-regulated IL-8 and OPN, increasing the hypoxia inducible factor-1alpha (HIF-1alpha) activity and its target gene NIP-3 expression in hypoxic condition. In turn, we show that the inhibition of HIF-1alpha by siRNA suppressed IL-8 and OPN production by MM cells under hypoxia. A direct interaction between ING4 and the HIF prolyl hydroxylase 2 (HPH-2) was also demonstrated. Finally, we show that ING4 suppression in MM cells significantly increased vessel formation in vitro, blunted by blocking IL-8 or OPN. These in vitro observations were confirmed in vivo by finding that MM patients with high IL-8 production and microvascular density (MVD) have significantly lower ING4 levels compared with those with low IL-8 and MVD. Our data indicate that ING4 exerts an inhibitory effect on the production of proangiogenic molecules and consequently on MM-induced angiogenesis.