Dynamic role of myofibroblasts in oral lesions

Fibroblasts are the most abundant cellular components of connective tissue. They possess phenotypical heterogenicity and may be present in the form of smooth muscle cells or myofibroblasts (MFs). MFs are spindle-shaped cells with stress fibres and well-developed fibronexus, and they display α-smooth muscle actin immunohistochemically and smooth-muscle myofilaments ultrastructurally. MFs play a crucial role in physiological and pathological processes. Derived from various sources, they play pivotal roles not only by synthesizing and producing extracellular matrix components, such as other connective tissue cells, but also are involved in force production. In the tissue remodelling phase of wound closure, integrin-mediated interactions between MFs and type I collagen result in scar tissue formation. The tumour stroma in oral cancer actively recruits various cell types into the tumour mass, where they act as different sources of MFs. This article reviews the importance of MFs and its role in pathological processes such as wound healing, odontogenic cysts and tumours, salivary gland tumours, oral preneoplasia, and oral squamous cell carcinoma. Research oriented on blocking the transdifferentiation of fibroblasts into MFs can facilitate the development of noninvasive therapeutic strategies for the treatment of fibrosis and/or cancer.     

Common gene polymorphisms, cancer progression and prognosis

Neoplastic growth was often regarded as an autonomous process driven by uncontrolled expansion of malignant cell population. This view is now being transformed as it becomes apparent that basically normal regulatory and metabolic mechanisms comprising subcellular processes as well as homo- and heterotypic cell interactions are extensively used by growing tumours throughout all stages of their development. Therefore the role of normal genetic variation emerges as a major factor determining different aspects of neoplastic growth and eventually outcome of the disease. This review is focused on polymorphisms in the genes encoding products acting at post-initiation stages of tumour development. Its four main sections are devoted to gene polymorphisms affecting: (i) growth control at the cellular level (cell proliferation, differentiation and death); (ii) factors involved in tumour invasion and metastasis (immune and inflammatory responses, extracellular matrix remodelling, angiogenesis and cell adhesion); (iii) action of hormones and vitamines on growing tumours; (iv) outcome of cancer therapy (cancer pharmacogenetics). Although active research in this field has been started only recently, some directions (e.g. cancer pharmacogenetics) already demonstrate impressive achievements. At the same time the reliability of results reported by many groups remains questionable mostly due to insufficient statistical power of the studies and often random choice of polymorphisms. It is evident that large studies based upon combined analysis of groups of genes within relevant regulatory and metabolic pathways have a much higher potential value in terms of unravelling prognostically important individual polymorphism profiles.     

Prostate cancer and Hedgehog signalling pathway

The Hedgehog (Hh) family of intercellular signalling proteins have come to be recognised as key mediators in many fundamental processes in embryonic development. Their activities are central to the growth, patterning and morphogenesis of many different regions within the bodies of vertebrates. In some contexts, Hh signals act as morphogens in the dose-dependent induction of distinct cell fates within a target field, in others as mitogens in the regulation of cell proliferation or as inducing factors controlling the form of a developing organ. These diverse functions of Hh proteins raise many intriguing questions about their mode of action. Various studies have now demonstrated the function of Hh signalling in the control of cell proliferation, especially for stem cells and stem-like progenitors. Abnormal activation of the Hh pathway has been demonstrated in a variety of human tumours. Hh pathway activity in these tumours is required for cancer cell proliferation and tumour growth. Recent studies have uncovered the role for Hh signalling in advanced prostate cancer and demonstrated that autocrine signalling by tumour cells is required for proliferation, viability and invasive behaviour. Thus, Hh signalling represents a novel pathway in prostate cancer that offers opportunities for prognostic biomarker development, drug targeting and therapeutic response monitoring. Supported by an unrestricted educational grant from Pfizer.     

Differential patterns of stromelysin-2 (MMP-10) and MT1-MMP (MMP-14) expression in epithelial skin cancers

Co-expression of several members of the matrix metalloproteinase (MMP) family is characteristic of human malignant tumours. To investigate the role of stromelysin-2 (MMP-10) in growth and invasion of skin tumours, we studied cutaneous carcinomas with high metastatic capacity (squamous cell carcinomas, SCCs), only locally destructive tumours (basal cell carcinomas, BCCs) and pre-malignant lesions (Bowen's disease and actinic keratosis) using in situ hybridization. Expression of MMP-10 was compared with that of stromelysin-1 (MMP-3) and of MT1-MMP, the expression of which has been shown to correlate with tumour invasiveness. MMP-10 was expressed in 13/21 SSCs and 11/19 BCCs only in epithelial laminin-5 positive cancer cells, while premalignant lesions were entirely negative. MT1-MMP mRNA was detected in 19/21 SCCs both in epithelial cancer cells and stromal fibroblasts and in 14/18 BCCs only in fibroblasts. The level of MMP-10 was upregulated in a cutaneous SCC cell line (UT-SCC-7) by transforming growth factor-alpha and keratinocyte growth factor, and by interferon-gamma in combination with transforming growth factor-beta1 and tumour necrosis factor-alpha both in UT-SCC-7 and HaCaT cells. Our results show that MMP-10 expression does not correlate with the invasive behaviour of tumours as assessed by their histology and MT1-MMP expression, but may be induced by the wound healing and inflammatory matrix remodelling events associated with skin tumours.     

Matrix metalloproteinases and oral cancer

For tumours to invade and metastasise, neoplastic cells must be capable of degrading the extracellular matrix (ECM), and accessing blood vessels and lymphatics. This process is mediated in the pericellular environment and is a highly controlled cascade of events utilising the same mechanisms that normal cells use for migrating through tissue barriers, for example, in development and wound healing. Proteolytic enzymes from several families, including matrix metalloproteinases (MMPs), are involved in ECM remodelling. Increased production of these enzymes has been associated with the invasive and/or metastatic phenotype in many tumours. Several MMPs have been shown to play a role in the invasion and metastasis of oral carcinoma, and it is increasingly apparent that tumour cells, as well as producing endogenous MMP, are capable of utilising MMP produced by tumour stromal cells, indicating an active role for stroma in tumour invasion. It is not clear whether a particular invasive system is favoured by oral carcinoma, but it is likely that further understanding of the interactions between carcinoma and stromal cells will provide an opportunity to refine the therapeutic interventions that are currently being tested.     

Cancer metastasis as a non-healing wound

Most cancer deaths are caused by metastasis: recurrence of disease by disseminated tumour cells at sites distant from the primary tumour. Large numbers of disseminated tumour cells are released from the primary tumour, even during the early stages of tumour growth. However, only a minority survive as potential seeds for future metastatic outgrowths. These cells must adapt to a relatively inhospitable microenvironment, evade immune surveillance and progress from the micro- to macro-metastatic stage to generate a secondary tumour. A pervasive driver of this transition is chronic inflammatory signalling emanating from tumour cells themselves. These signals can promote migration and engagement of stem and progenitor cell function, events that are also central to a wound healing response. In this review, we revisit the concept of cancer as a non-healing wound, first introduced by Virchow in the 19th century, with a new tumour cell-intrinsic perspective on inflammation and focus on metastasis. Cellular responses to inflammation in both wound healing and metastasis are tightly regulated by crosstalk with the surrounding microenvironment. Targeting or restoring canonical responses to inflammation could represent a novel strategy to prevent the lethal spread of cancer.Subject terms: Tumour heterogeneity, Metastasis, Cancer microenvironment, Cancer stem cells     

Molecular and cellular mechanisms of lymphangiogenesis.

Lymphangiogenesis is the growth and formation of new lymphatic vessels. It occurs in normally developing tissues and in pathological processes like inflammation, wound healing, lymphoedema and in cancer. New molecular markers that are specific to the lymphatic endothelium include: podoplanin, prox-1 and LYVE-1. The molecular mechanisms of lymphangiogenesis are not clear, but vascular endothelial growth factors (VEGF-C and VEGF-D) within tumours may simulate endothelial cells within tumour tissues to grow and generate new lymphatics. We report the current knowledge of molecular and cellular mechanisms of lymphangiogenesis.     

Identification of novel growth factor-responsive genes in neuroendocrine gastrointestinal tumour cells

Targeting growth-regulatory pathways is a promising approach in cancer treatment. A prerequisite to the development of such therapies is characterisation of tumour growth regulation in the particular tumour cell type of interest. In order to gain insight into molecular mechanisms underlying proliferative responses in neuroendocrine (NE) gastrointestinal (GI) tumours, we investigated gene expression in human carcinoid BON cells after exposure to gastrin, hepatocyte growth factor (HGF), pituitary adenylate cyclase-activating polypeptide or epidermal growth factor. We particularly focused on gastrin- and HGF-induced gene expression, and identified 95 gastrin- and 101 HGF-responsive genes. The majority of these genes are known mediators of processes central in tumour biology, and a number of them have been associated with poor prognosis and metastasis in cancer patients. Furthermore, we identified 12 genes that were regulated by all four factors, indicating that they may be universally regulated during NE GI tumour cell proliferation. Our findings provide useful hypotheses for further studies aimed to search for new therapeutic targets as well as tumour markers in NE GI tumours.     

The impact of O2 availability on human cancer

During the past century it has been established that regions within solid tumours experience mild to severe O(2) deprivation owing to aberrant vascular function. These hypoxic regions are associated with altered cellular metabolism, as well as increased resistance to radiation and chemotherapy. As discussed in this Timeline, over the past decade work from many laboratories has elucidated the mechanisms by which hypoxia-inducible factors (HIFs) modulate tumour cell metabolism, angiogenesis, growth and metastasis. The central role played by intra-tumoural hypoxia and HIF in these processes has made them attractive therapeutic targets in the treatment of multiple human malignancies.     

The sodium channel β1 subunit mediates outgrowth of neurite‐like processes on breast cancer cells and promotes tumour growth and metastasis

Voltage‐gated Na⁺ channels (VGSCs) are heteromeric proteins composed of pore‐forming α subunits and smaller β subunits. The β subunits are multifunctional channel modulators and are members of the immunoglobulin superfamily of cell adhesion molecules (CAMs). β1, encoded by SCN1B, is best characterized in the central nervous system (CNS), where it plays a critical role in regulating electrical excitability, neurite outgrowth and migration during development. β1 is also expressed in breast cancer (BCa) cell lines, where it regulates adhesion and migration in vitro. In the present study, we found that SCN1B mRNA/β1 protein were up‐regulated in BCa specimens, compared with normal breast tissue. β1 upregulation substantially increased tumour growth and metastasis in a xenograft model of BCa. β1 over‐expression also increased vascularization and reduced apoptosis in the primary tumours, and β1 over‐expressing tumour cells had an elongate morphology. In vitro, β1 potentiated outgrowth of processes from BCa cells co‐cultured with fibroblasts, via trans‐homophilic adhesion. β1‐mediated process outgrowth in BCa cells required the presence and activity of fyn kinase, and Na⁺ current, thus replicating the mechanism by which β1 regulates neurite outgrowth in CNS neurons. We conclude that when present in breast tumours, β1 enhances pathological growth and cellular dissemination. This study is the first demonstration of a functional role for β1 in tumour growth and metastasis in vivo. We propose that β1 warrants further study as a potential biomarker and targeting β1‐mediated adhesion interactions may have value as a novel anti‐cancer therapy.     

The role of the coagulation system in tumour angiogenesis

The coagulation system, which is activated in most cancer patients, has an important role in tumour biology. It may make a substantial contribution to tumour angiogenesis, which represents an imbalance in the normal mechanisms that allow organised healing after injury. The recently recognised, but steadily growing, knowledge of the relationship between the coagulation and angiogenesis pathways has research and clinical implications. Manipulation of these systems may minimise both the neoangiogenesis essential for tumour growth and associated thromboembolic complications. However, since surgery is the primary treatment for most cancers, the angiogenesis of wound healing and haemostatic competence must be maintained. In this article, we summarise the complex interactions between the coagulation system and the angiogenic process that occur in cancer growth. We focus upon the contributions of the vascular endothelium, platelets, and coagulation factors to the angiogenic process and explore the coagulation system as a therapeutic target.     

A model of self-maintenance of in vivo malignant growth not dependent on tumour type or origin: syndrome of everlasting wound healing

The common mechanism of permanent growth maintenance in all types of malignant tumours is proposed. According to the model, the main event, stimulating tumour growth is the stochastic but permanent death of a proportion of tumour cells as a result of inherent genetic instability of tumour cell genome (chromosome fragility). Dead cells trigger the complex and multicomponent process of wound healing, manifesting in stimulation of cell proliferation, angiogenesis, cell migration and other events. Stimulation of proliferation of tumour cells leads to further production of dead (necrotic) cells and as a result to further stimulation of wound healing system etc. The nature of genetic instability of malignant cells, as proposed, is connected with arising of heritable uninemic (uniduplex) structures in pieces of some chromosomes or in whole chromosomes or sometimes even in whole genomes. Uninemic areas possess extremely high incidence of spontaneous chromosome aberrations due to failure of the mechanism of repair of DNA double-strand breaks in the absence of second DNA copy. The theory is based on the binemic structure of normal eukaryote chromosomes. Possible approaches to the mechanisms of cancer therapy are discussed.     

Plasminogen activator system and its clinical significance in patients with a malignant disease

Urokinase (uPA) plays an essential role in the activation of plasminogen to plasmin, a serine protease participating in the activation of matrixmetaloproteinases, latent elastases, growth factors and cytokines involved in the degradation of extracellular matrix elements. Together with its receptor (uPAR), tissue activator (tPA) and urokinase inhibitors (PAI-1, PAI-2, PAI-3 and protease nexin), it forms the plasminogen activator system (PAS), a component of metastatic cascade importantly contributing to the invasive growth and angiogenesis of malignant tumours. Plasminogen activator inhibitor 1 inhibits uPA-dependent invasiveness of some cancer cell lines. The vitronectin-PAI-1 complex inhibits migration of smooth muscle cells by binding alpha(v)beta3 integrin to vitronectin. PAI-1 or its deficiency interferes with signalling pathways such as PI3K/Akt and JAK/STAT and it is included in the processes of maintaining the integrity of the endothelial cells and thereby regulation of cell death. PAI-1 affects apoptosis by reducing cell adhesion and functioning of intracellular signalling pathways. The individual components of PAS undoubtedly play an important role in angiogenesis and metastasising of malignant tumours. In the near future, results of published studies with various types of cancer could be reflected in diagnostic and therapeutic algorithms and, at the same time, could serve as the goal for targeted therapies.     

Mechanisms of organ selective tumour growth by bloodborne cancer cells

The sites of tumour development for 6 rat tumours injected into syngeneic rats via different vascular routes was determined. Xenografts of human tumours were also injected intra-arterially (i.a.) into immunosuppressed rats. Following intravenous (i.v.) and intraportal (i.ptl.) injection of cells tumour colonies localized in lung and liver respectively due to tumour cell arrest. Arterially injected radiolabelled cells disseminated and arrested in a similar distribution to cardiac output and did not 'home' to any organs. Following arterial injection of unlabelled tumour cells colonies grew in many organs. While the pattern of growth for a particular tumour varied with the cell dose, the 'arterial patterns' for all of the tumours studied followed a similar pattern. Some organs (eg adrenals, ovaries and periodontal ligament) were consistently preferred, others (eg skin and skeletal muscle) only supported tumour growth following the delivery of large numbers of cells, while in some tissues (eg spleen and intestines) tumour never grew. Viable tumour cells could be demonstrated by bioassay in many organs for up to 24h after i.a. injection. However tumour growth only occurred in certain organs and the pattern of this growth was not related to the number of tumour cells arrested or their rate of autolysis. This site preference could be expressed quantitatively as the probability of an arrested cell developing into a tumour and was considered a 'soil effect'. Site preference was not directly related to organ vascularity. Organ colonisation was promoted by steroid treatment but the mechanism was unclear and was not secondary to T-cell immunosuppression or prostaglandin synthesis suppression. The adrenal glands were preferred sites of tumour growth but pharmacological manipulation of adrenal function did not alter tumour growth to this organ. Sites of injury and healing were preferred sites of tumour colonisation and this could not be accounted for by increased delivery of tumour cells to these regions. The possibility that the macrophage component of the inflammatory response promoted tumour growth was suggested from studies in which the interval between trauma and inoculation of tumour cells was varied as well as by promotion of intraperitoneal (i.p.) tumour growth by a macrophage infiltrate.     

Normoxic and hypoxic regulation of vascular endothelial growth factor (VEGF) by astrocytoma cells is mediated by Ras

Vascular endothelial growth Factor (VEGF) has been identified as a key angiogenic factor involved in the growth and malignant progression of tumours. Glioblastoma multiforme (GBM) are the most common primary human brain tumours, histo-pathologically characterized by intense tumour angiogenesis. GBMs do not harbour oncogenic Ras mutations, but there is a functional up-regulation of Ras signaling through activation of receptor tyrosine kinases overexpressed by these tumours. We demonstrate that Ras pathway activation regulates VEGF secretion in astrocytoma cell lines. Ras pathway inhibition was carried out using genetic and pharmacologic techniques. Astrocytoma cells that were transfected to express the dominant inhibitory mutant H-Ras(N17) demonstrated a reduction in VEGF secretion under both normoxic and hypoxic conditions. Cells treated with the farnesyl transferase inhibitor L-744,832 demonstrated similar reductions in VEGF secretion. Furthermore, astrocytoma cells expressing a constitutively phosphorylated and truncated EGF-R common in GBMs (EGFRvIII or p140(EGF-R)) demonstrate further elevations in Ras activation, resulting in a further increase in VEGF secretion. We have previously demonstrated that activation of Ras plays a vital role in transducing mitogenic signals in human malignant astrocytoma cells. Our present results further extend the role of Ras activation in modulating tumour angiogenesis in these tumours. We propose that Ras may contribute to the angiogenic switch in astrocytomas.     

Cancer and thromboembolic disease: pathogenic mechanisms

Almost all types of cancer are associated with an activation of coagulation. However, elevation of haemostatic markers of coagulation does not predict venous thrombosis. Multiple and interdependent processes between the tumour and the patient induce a hypercoagulable state. Tumour procoagulant activity, host inflammatory responses and extrinsic factors are involved. Tumour cells express the procoagulants, tissue factor and cancer procoagulant. They also release inflammatory cytokines and vascular endothelial growth factor, substances that enhance procoagulant activity and angiogenesis. Tumour-induced coagulation is intrinsically involved with tumour growth, angiogenesis and metastasis.     

Vascular endothelial growth-factor production is stimulated in response to growth-factors in human glioma-cells

Neovascularization is essential for tumour growth and is mediated by physiological substances produced by tumours. Vascular endothelial growth factor (VEGF) is one such potent angiogenic factor. Human gliomas, the most important class of intrinsic brain tumours, express VEGF both in vivo and in vitro. Factors involved in the control of VEGF production by glioma cells are not well known. In this study, we investigated the role of basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), and platelet derived growth factors (PDGF) on VEGF production by four different glioma cell lines in vitro. With the exception of PDGF A/A and B/B in one cell line, all growth factors differentially stimulated VEGF production in all cell lines investigated. These data suggest that VEGF production in human glioma may be regulated by other growth factors which are also known to be expressed in such tumours.