Tumors are unique organs defined by abnormal signaling and context

Seed Becoming Soil: A New Paradigm of the Ewing Sarcoma Tumor Microenvironment

Cells in the tumor microenvironment, including cancer-associated fibroblasts (CAF), contribute to tumor growth and immune evasion. A recent study of Ewing sarcoma identified "CAF-like" tumor cells that mimic the protumorigenic features of CAFs. These findings highlight the role of cell plasticity in tumor growth. See related article by Wrenn et al., p. 5140.

cFLIP downregulation is an early event required for endoplasmic reticulum stress-induced apoptosis in tumor cells

Protein misfolding or unfolding and the resulting endoplasmic reticulum (ER) stress frequently occur in highly proliferative tumors. How tumor cells escape cell death by apoptosis after chronic ER stress remains poorly understood. We have investigated in both two-dimensional (2D) cultures and multicellular tumor spheroids (MCTSs) the role of caspase-8 inhibitor cFLIP as a regulator of the balance between apoptosis and survival in colon cancer cells undergoing ER stress. We report that downregulation of cFLIP proteins levels is an early event upon treatment of 2D cultures of colon cancer cells with ER stress inducers, preceding TNF-related apoptosis-inducing ligand receptor 2 (TRAIL-R2) upregulation, caspase-8 activation, and apoptosis. Maintaining high cFLIP levels during ER stress by ectopic expression of cFLIP markedly inhibits ER stress-induced caspase-8 activation and apoptosis. Conversely, cFLIP knockdown by RNA interference significantly accelerates caspase-8 activation and apoptosis upon ER stress. Despite activation of the proapoptotic PERK branch of the unfolded protein response (UPR) and upregulation of TRAIL-R2, MCTSs are markedly more resistant to ER stress than 2D cultures of tumor cells. Resistance of MCTSs to ER stress-induced apoptosis correlates with sustained cFLIP_L expression. Interestingly, resistance to ER stress-induced apoptosis is abolished in MCTSs generated from cFLIP_L knockdown tumor cells. Overall, our results suggest that controlling cFLIP levels in tumors is an adaptive strategy to prevent tumor cell's demise in the unfavorable conditions of the tumor microenvironment.

Beyond Neurons: Long Distance Communication in Development and Cancer

Cellular communication is important in all aspects of tissue and organism functioning, from the level of single cells, two discreet populations, and distant tissues of the body. Long distance communication networks integrate individual cells into tissues to maintain a complex organism during development, but when communication between cells goes awry, disease states such as cancer emerge. Herein we discuss the growing body of evidence suggesting that communication methods known to be employed by neurons, also exist in other cell types. We identify three major areas of long-distance communication: bioelectric signaling, tunneling nanotubes (TNTs), and macrophage modulation of networks, and draw comparisons about how these systems operate in the context of development and cancer. Bioelectric signaling occurs between cells through exchange of ions and tissue-level electric fields, leading to changes in biochemical gradients and molecular signaling pathways to control normal development and tumor growth and invasion in cancer. TNTs transport key morphogens and other cargo long distances, mediating electrical coupling, tissue patterning, and malignancy of cancer cells. Lastly macrophages maintain long distance signaling networks through trafficking of vesicles during development, providing communication relays and priming favorable microenvironments for cancer metastasis. By drawing comparisons between non-neural long distance signaling in the context of development and cancer we aim to encourage crosstalk between the two fields to cultivate new hypotheses and potential therapeutic strategies.

The paradoxical role of matrix metalloproteinase-11 in cancer

The microenvironment surrounding the tumor affects biological processes, such as cell proliferation, angiogenesis, apoptosis, and invasion. Therefore, the ability to change these environments is an important attribute for tumor cells to obtain specific functions necessary for growth and metastasis. Matrix metalloproteinases (MMPs) are zinc-dependent proteolytic metalloenzymes that facilitate protease-dependent tumor progression by degrading extracellular matrix (ECM) proteins, releasing cytokines, growth factors, and other cell surface molecules. As one of the most widely studied MMPs, MMP-11 is an important protease that is expressed in cancer cells, stromal cells, and the adjacent microenvironment. MMP-11 has a dual effect on tumors. On one hand, MMP-11 promotes tumor development by inhibiting apoptosis and promoting the migration and invasion of cancer cells in the early stage. On the other hand, in animal models, MMP-11 has a protective effect on tumor growth and metastasis at an advanced stage. Based on current findings regarding the importance of MMP-11 in altering the tumor microenvironment, there is a need to further understand how stromal cells and the ECM regulate tumor progression, which may result in the re-examination of MMPs as drug targets for cancer and other diseases. In this review, we summarize the dual role of MMP-11 in cancer and its potential clinical significance.

Elucidate growth control mechanisms using reconstructed spatiotemporal distributions of signaling events

A fundamental biological question is how diverse and complex signaling and patterning is controlled correctly to generate distinct tissues, organs, and body plans, but incorrectly in diseased cells and tissues. Signaling pathways important for growth control have been identified, but to identify the mechanisms their transient and context-dependent interactions encode is more difficult. Currently computational systems biology aims to infer the control mechanisms by investigating quantitative changes of gene expression and protein concentrations, but this inference is difficult in nature. We propose it is desirable to explicitly simulate events and orders of gene regulation and protein interactions, which better elucidate control mechanisms, and report a method and tool with three examples. The Drosophila wing model includes Wnt, PCP, and Hippo pathways and mechanical force, incorporates well-confirmed experimental findings, and generates novel results. The other two examples illustrate the building of three-dimensional and large-scale models. These examples support that reconstructed spatiotemporal distributions of key signaling events help elucidate growth control mechanisms. As biologists pay increasing attention to disordered signaling in diseased cells, to develop new modeling methods and tools for conducting new computational studies is important.

Cell Force-Driven Basement Membrane Disruption Fuels EGF- and Stiffness-Induced Invasive Cell Dissemination from Benign Breast Gland Acini

Local basement membrane (BM) disruption marks the initial step of breast cancer invasion. The activation mechanisms of force-driven BM-weakening remain elusive. We studied the mechanical response of MCF10A-derived human breast cell acini with BMs of tuneable maturation to physical and soluble tumour-like extracellular matrix (ECM) cues. Traction force microscopy (TFM) and elastic resonator interference stress microscopy (ERISM) were used to quantify pro-invasive BM stress and protrusive forces. Substrate stiffening and mechanically impaired BM scaffolds induced the invasive transition of benign acini synergistically. Robust BM scaffolds attenuated this invasive response. Additional oncogenic EGFR activation compromised the BMs’ barrier function, fuelling invasion speed and incidence. Mechanistically, EGFR-PI3-Kinase downstream signalling modulated both MMP- and force-driven BM-weakening processes. We show that breast acini form non-proteolytic and BM-piercing filopodia for continuous matrix mechanosensation, which significantly push and pull on the BM and ECM under pro-invasive conditions. Invasion-triggered acini further shear and compress their BM by contractility-based stresses that were significantly increased (3.7-fold) compared to non-invasive conditions. Overall, the highest amplitudes of protrusive and contractile forces accompanied the highest invasiveness. This work provides a mechanistic concept for tumour ECM-induced mechanically misbalanced breast glands fuelling force-driven BM disruption. Finally, this could facilitate early cell dissemination from pre-invasive lesions to metastasize eventually.

Tumor Microenvironment and Nitric Oxide: Concepts and Mechanisms

The cancer tissue exists not as a single entity, but as a combination of different cellular phenotypes which, taken together, dramatically contribute to the entirety of their ecosystem, collectively termed as the tumor microenvironment (TME). The TME is composed of both immune and nonimmune cell types, stromal components, and vasculature-all of which cooperate to promote cancer progression. Not all immune cells, however, are immune-suppressive; some of them can promote the immune microenvironment to fight the invading and uncontrollably dividing cell populations at the initial stages of tumor growth. Yet, many of these processes and cellular phenotypes fall short, and the immune ecosystem more often than not ends up stabilizing in favor of the "resistant" resident cells that begin clonal expansion and may progress to metastatic forms. Stromal components, making up the extracellular matrix and basement membrane, are also not the most innocuous: CAFs embedded throughout secrete proteases that allow the onset of one of the most invasive processes-angiogenesis-through destruction of the ECM and the basement membrane. Vasculature formation, because of angiogenesis, is the largest invader of the TME and the reason metastasis happens. Vasculature is so sporadic and omnipresent in the TME that most drug therapies are mainly focused on stopping this uncontrollable process. As the tumor continues to grow, different processes are constantly supplying it with the ingredients favorable for tumor progression and eventual metastasis. For example, angiogenesis promotes blood vessel formation that will allow the bona fide escape of tumor cells to take place. Another process like hypoxia will present itself in several forms throughout the tumor (mild or acute, cycling or permanent), starting mechanisms such as epithelial to mesenchymal transitions (EMT) of resident cells and inadvertently placing the cells in such a stressful condition that production of ROS and DNA damage is unavoidable. DNA damage can induce mutagenicity while allowing resistant cells to survive. This is where drugs and treatments can subsequently suffer in effectiveness. Finally, another molecule has just surfaced as being a very important player in the TME: nitric oxide. Often overlooked and equated with ROS and initially assigned in the category of pathogenic molecules, nitric oxide can definitely do some damage by causing metabolic reprogramming and promotion of immunosuppressive phenotypes at low concentrations. However, its actions seem to be extremely dose-dependent, and this issue has become a hot target of current treatment goals. Shockingly, nitric oxide, although omnipresent in the TME, can have a positive effect on targeting the TME broadly. Thus, while the TME is a myriad of cellular phenotypes and a combination of different tumor-promoting processes, each process is interconnected into one whole: the tumor microenvironment.

Cancer-Associated Fibroblasts: Understanding Their Heterogeneity

Simple Summary

Cancer-associated fibroblasts (CAFs) play an important contributory role in the microenvironment of tumors. They originate from different cells, have multiple pro-and anti-tumorigenic functions in tumors and their presence is variable among cancer types. Recently, there has been evidence that CAFs represent a highly heterogeneous group of cells that can now be characterized and identified at the single cell level. This review article summarizes our recent understanding of the highly heterogeneous nature of the origin, phenotype and function of CAFs and how such understanding will lead to a more precise approach to target or use CAFs and their precursor cells in the treatment of cancer.

Abstract

The tumor microenvironment (TME) plays a critical role in tumor progression. Among its multiple components are cancer-associated fibroblasts (CAFs) that are the main suppliers of extracellular matrix molecules and important contributors to inflammation. As a source of growth factors, cytokines, chemokines and other regulatory molecules, they participate in cancer progression, metastasis, angiogenesis, immune cell reprogramming and therapeutic resistance. Nevertheless, their role is not fully understood, and is sometimes controversial due to their heterogeneity. CAFs are heterogeneous in their origin, phenotype, function and presence within tumors. As a result, strategies to target CAFs in cancer therapy have been hampered by the difficulties in better defining the various populations of CAFs and by the lack of clear recognition of their specific function in cancer progression. This review discusses how a greater understanding of the heterogeneous nature of CAFs could lead to better approaches aimed at their use or at their targeting in the treatment of cancer.

Potentiality, Limitations, and Consequences of Different Experimental Models to Improve Photodynamic Therapy for Cancer Treatment in Relation to Antiangiogenic Mechanism

The relevance of experimentally gained information represents a long-term debating issue in the field of molecular biology research. The loss of original conditions in the in vitro environment affects various biological mechanisms and cellular interactions. Consequently, some biochemical mechanisms are lost or critically altered. Analyses in these modified conditions could, therefore, distort the relevancy of experimentally gained information. In some cases, the similarities with original conditions are so small that utilization of simpler in vitro models seems impossible, or could occur in a very limited way. To conclude, the study of more complex phenomena places higher demands on the complexity of the experimental model. The latest information highlights the fact that the tumor angiogenesis mechanism has very complex features. This complexity can be associated with a wide range of angiogenic factors expressed by a variety of malignant and non-malignant cells. Our article summarizes the results from various experimental models that were utilized to analyze a photodynamic therapy effect on tumor angiogenic mechanisms. Additionally, based on the latest information, we present the most important attributes and limitations of utilized experimental models. We also evaluate the essential problems associated with angiogenic mechanism induction after photodynamic therapy application.

Luminal MCF-12A & myoepithelial-like Hs 578Bst cells form bilayered acini similar to human breast

The epithelium's functional unit is the bilayered acinus, made of a layer of luminal cells, surrounded by a layer of basal cells mainly composed of myoepithelial cells.

Aim

The aim of this study was to develop a reproducible and manipulable 3D co-culture model of the bilayered acinus in vitro to study the interactions between the two layers.

Materials & methods

Two different combinations of cell lines were co-cultured in Matrigel: SCp2 and SCg6 mice cells, or MCF-12A and Hs 578Bst human cell lines.

Results

Confocal microscopy analysis showed that only MCF-12A and Hs 578Bst cells could form some bilayered acini. This in vitro bilayered acini model will allow us to understand the role of interactions between luminal and myoepithelial cells in the normal breast development.

Multi-omic molecular profiling of lung cancer in COPD

Chronic obstructive pulmonary disease (COPD) is a known risk factor for developing lung cancer but the underlying mechanisms remain unknown. We hypothesise that the COPD stroma contains molecular mechanisms supporting tumourigenesis.We conducted an unbiased multi-omic analysis to identify gene expression patterns that distinguish COPD stroma in patients with or without lung cancer. We obtained lung tissue from patients with COPD and lung cancer (tumour and adjacent non-malignant tissue) and those with COPD without lung cancer for profiling of proteomic and mRNA (both cytoplasmic and polyribosomal). We used the Joint and Individual Variation Explained (JIVE) method to integrate and analyse across the three datasets.JIVE identified eight latent patterns that robustly distinguished and separated the three groups of tissue samples (tumour, adjacent and control). Predictive variables that associated with the tumour, compared to adjacent stroma, were mainly represented in the transcriptomic data, whereas predictive variables associated with adjacent tissue, compared to controls, were represented at the translatomic level. Pathway analysis revealed extracellular matrix and phosphatidylinositol-4,5-bisphosphate 3-kinase-protein kinase B signalling pathways as important signals in the tumour adjacent stroma.The multi-omic approach distinguishes tumour adjacent stroma in lung cancer and reveals two stromal expression patterns associated with cancer.

Unraveling the Role of Angiogenesis in Cancer Ecosystems

Activation of the tumor and stromal cell-driven angiogenic program is one of the first requirements in the tumor ecosystem for growth and dissemination. The understanding of the dynamic angiogenic tumor ecosystem has rapidly evolved over the last decades. Beginning with the canonical sprouting angiogenesis, followed by vasculogenesis and intussusception, and finishing with vasculogenic mimicry, the need for different neovascularization mechanisms is further explored. In addition, an overview of the orchestration of angiogenesis within the tumor ecosystem cellular and molecular components is provided. Clinical evidence has demonstrated the effectiveness of traditional vessel-directed antiangiogenics, stressing on the important role of angiogenesis in tumor establishment, dissemination, and growth. Particular focus is placed on the interaction between tumor cells and their surrounding ecosystem, which is now regarded as a promising target for the development of new antiangiogenics.

Nanoparticle-based hyperthermia, a local treatment modulating the tumor extracellular matrix

The structural complexity and physical properties of the tumor microenvironment negatively affect the penetration and efficiency of conventional anticancer drugs. While previously underestimated, the tumor microenvironment now becomes a potential target for cancer treatment. This microenvironment can be modulated either systemically by pharmacological means, or locally, through physical effects mediated by certain nanoparticles. Some of them, such as magnetic, plasmonic or carbon-based nanoparticles, can generate heat on demand in a spatially and temporally controlled manner. In addition, the nanoparticles can be either activated by light or magnetic stimuli. The impact of the resulting local heating can be observed on the ultrastructural level, as it strongly affects the organization of collagen fibers, and on the macroscopic level, since the thermal damages alter the mechanical properties of the tumor. Nanoparticle-based hyperthermia thus improves the effect of conventional anticancer drugs, as it allows their better penetration through the altered extracellular matrix. Here we suggest the use of nanoparticle-generated hyperthermia, obtained after magnetic or light activation, as an adjuvant treatment to prime the tumor microenvironment and improve the efficacy of chemotherapy.

Quantitative evaluation and reversion analysis of the attractor landscapes of an intracellular regulatory network for colorectal cancer

BACKGROUND

Cancer reversion, converting the phenotypes of a cancer cell into those of a normal cell, has been sporadically observed throughout history. However, no systematic analysis has been attempted so far.

RESULTS

To investigate this from a systems biological perspective, we have constructed a logical network model of colorectal tumorigenesis by integrating key regulatory molecules and their interactions from previous experimental data. We identified molecular targets that can reverse cancerous cellular states to a normal state by systematically perturbing each molecular activity in the network and evaluating the resulting changes of the attractor landscape with respect to uncontrolled proliferation, EMT, and stemness. Intriguingly, many of the identified targets were well in accord with previous studies. We further revealed that the identified targets constitute stable network motifs that contribute to enhancing the robustness of attractors in cancerous cellular states against diverse regulatory signals.

CONCLUSIONS

The proposed framework for systems analysis is applicable to the study of tumorigenesis and reversion of other types of cancer.

A holistic approach to dissecting SPARC family protein complexity reveals FSTL-1 as an inhibitor of pancreatic cancer cell growth

SPARC is a matricellular protein that is involved in both pancreatic cancer and diabetes. It belongs to a wider family of proteins that share structural and functional similarities. Relatively little is known about this extended family, but evidence of regulatory interactions suggests the importance of a holistic approach to their study. We show that Hevin, SPOCKs, and SMOCs are strongly expressed within islets, ducts, and blood vessels, suggesting important roles for these proteins in the normal pancreas, while FSTL-1 expression is localised to the stromal compartment reminiscent of SPARC. In direct contrast to SPARC, however, FSTL-1 expression is reduced in pancreatic cancer. Consistent with this, FSTL-1 inhibited pancreatic cancer cell proliferation. The complexity of SPARC family proteins is further revealed by the detection of multiple cell-type specific isoforms that arise due to a combination of post-translational modification and alternative splicing. Identification of splice variants lacking a signal peptide suggests the existence of novel intracellular isoforms. This study underlines the importance of addressing the complexity of the SPARC family and provides a new framework to explain their controversial and contradictory effects. We also demonstrate for the first time that FSTL-1 suppresses pancreatic cancer cell growth.

The effect of LOXL2 in hepatocellular carcinoma

Lysyl oxidase-like 2 (LOXL2) is key in the hepatocellular carcinoma (HCC) tumor microenvironment and metastatic niche formation. However, its effect on proliferation and clinical parameters in HCC require further elucidation. The present study aimed to investigate LOXL2 expression in HCC from in vitro and clinical aspects. The present study constructed LOXL2-small interfering RNA with a lentiviral vector, investigated the effect of LOXL2 on proliferation using HCC cell lines via a series of assays, including reverse transcription-quantitative polymerase chain reaction, cell counting, colony formation, assessment of cell cycle and apoptosis using flow cytometry, MTT and BrdU. Furthermore, 80 tissue samples from HCC patients at The First Affiliated Hospital of Dalian Medical University (Dalian, China) from 2007 to 2010. Immunohistochemical staining was used to clinically verify LOXL2 expression. The results of the present study demonstrate that LOXL2 silencing decreased cell numbers, proliferation, colony formations and cell growth, induced cell cycle arrest and increased apoptosis. Clinically, expression levels of LOXL2 was markedly increased in matched adjacent non-tumor tissue (ANT) samples compared with levels in tumor tissue (TT) samples, and this gradually increased with higher histological grade and more advanced TNM classification in the matched ANT and TT samples. LOXL2 was determined to promote proliferation of HCC and demonstrated to be highly expressed in HCC ANT samples compared with TT samples.

Therapeutic implications of melanoma heterogeneity

Over the last decade, the treatment of metastatic melanoma has been revolutionized by the translation of molecular insights into therapeutic benefit for patients. These include advances in immunotherapeutic and small-molecule approaches aimed at destroying cells with immunogenic antigens or gene mutations. Despite these advances, the limited durability of clinical response and eventual disease progression underscores a need for better understanding of mechanisms underlying tumor development. Current targeted therapies are developed partly based on the rationale that tumors are primarily clonal with respect to mutant oncogene or cell surface antigen target. However, with the advancement of cell isolation and transplantation approaches coupled with deep sequencing and mutation detection techniques, it has become increasingly clear that tumors are polyclonal. As a result, sensitive malignant cells are eradicated by treatment while the remaining tumor cell populations are conferred varying degrees of resistance and survival advantages by harbouring or acquiring certain epigenetic and genetic abnormalities. Tumor heterogeneity thus represents a major obstacle to the successful application of current therapies. Gaining insights into the cellular and molecular aspects of tumor diversity will not only facilitate the development and selection of therapeutic targets but also promote the evolution of precision medicine. In this viewpoint, we will discuss the implications of tumor heterogeneity for the treatment of metastatic melanoma and propose approaches to accelerate the translation of scientific discovery into improved clinical outcomes.

Progress towards understanding heterotypic interactions in multi-culture models of breast cancer

Microenvironments in primary tumors and metastases include multiple cell types whose dynamic and reciprocal interactions are central to progression of the disease. However, the literature involving breast cancer studied in vitro is dominated by cancer cells in mono-culture or co-cultured with one other cell type. For in vitro studies of breast cancer the inclusion of multiple cell types has led to models that are more representative of in vivo behaviors and functions as compared to more traditional monoculture. Here, we review foundational co-culture techniques and their adaptation to multi-culture (including three or more cell types). Additionally, while macroscale methods involving conditioned media, direct contact, and indirect interactions have been informative, we examined many advances that have been made more recently using microscale systems with increased control over cellular and structural complexity. Throughout this discussion we consider the benefits and limitations of current multi-culture methods and the significant results they have produced.

Adiponectin induces CXCL1 secretion from cancer cells and promotes tumor angiogenesis by inducing stromal fibroblast senescence

Adiponectin is an adipocyte-specific adipocytokine with proliferative and pro-angiogenic effects that regulates many biological processes, including immunity, insulin resistance, and inflammation. The oncogenic role of adiponectin has been implicated in several cancer types. Stromal cells within tumor contribute tumor growth and angiogenesis; however, it is not clear that how adiponectin regulates stromal cell-mediated tumorigenesis. In this study, using the tumor xenograft models, we demonstrated that tumor development was severely impaired in mouse subcutaneous cancer tissue and metastasis tumor tissue in adiponectin knockout mice. Our results indicated adiponectin deficiency resulted in decrease of blood vessel and stromal senescent fibroblasts in subcutaneous and metastasis tumor tissue. These observations were confirmed in vitro, in which co-cultured tumor cells and fibroblasts treated with adiponectin promoted ECs tube formation. A secretion of CXCL1 by adiponectin-treated tumor cells was observed during the process of inducing stromal fibroblast senescence. Furthermore, stromal cells senescence was through p53 and p16 pathways. Taken together, our results indicate that adiponectin promotes stromal cell senescence within invasive colon cancer contributing to angiogenesis and tumor growth in part through the production of CXCL1 and may serve as a therapeutic target for tumor patients. © 2015 Wiley Periodicals, Inc.

Recapitulating the Tumor Ecosystem Along the Metastatic Cascade Using 3D Culture Models

Advances in cancer research have shown that a tumor can be likened to a foreign species that disrupts delicately balanced ecological interactions, compromising the survival of normal tissue ecosystems. In efforts to mitigate tumor expansion and metastasis, experimental approaches from ecology are becoming more frequently and successfully applied by researchers from diverse disciplines to reverse engineer and re-engineer biological systems in order to normalize the tumor ecosystem. We present a review on the use of 3D biomimetic platforms to recapitulate biotic and abiotic components of the tumor ecosystem, in efforts to delineate the underlying mechanisms that drive evolution of tumor heterogeneity, tumor dissemination, and acquisition of drug resistance.

The double-edged sword: conserved functions of extracellular hsp90 in wound healing and cancer

Heat shock proteins (Hsps) represent a diverse group of chaperones that play a vital role in the protection of cells against numerous environmental stresses. Although our understanding of chaperone biology has deepened over the last decade, the “atypical” extracellular functions of Hsps have remained somewhat enigmatic and comparatively understudied. The heat shock protein 90 (Hsp90) chaperone is a prototypic model for an Hsp family member exhibiting a duality of intracellular and extracellular functions. Intracellular Hsp90 is best known as a master regulator of protein folding. Cancers are particularly adept at exploiting this function of Hsp90, providing the impetus for the robust clinical development of small molecule Hsp90 inhibitors. However, in addition to its maintenance of protein homeostasis, Hsp90 has also been identified as an extracellular protein. Although early reports ascribed immunoregulatory functions to extracellular Hsp90 (eHsp90), recent studies have illuminated expanded functions for eHsp90 in wound healing and cancer. While the intended physiological role of eHsp90 remains enigmatic, its evolutionarily conserved functions in wound healing are easily co-opted during malignancy, a pathology sharing many properties of wounded tissue. This review will highlight the emerging functions of eHsp90 and shed light on its seemingly dichotomous roles as a benevolent facilitator of wound healing and as a sinister effector of tumor progression.

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

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

Non-collagenous ECM proteins in blood vessel morphogenesis and cancer

BACKGROUND

The extracellular matrix (ECM) is constituted by diverse composite structures, which determine the specific to each organ, histological architecture and provides cells with biological information, mechanical support and a scaffold for adhesion and migration. The pleiotropic effects of the ECM stem from the dynamic changes in its molecular composition and the ability to remodel in order to effectively regulate biological outcomes. Besides collagens, fibronectin and laminin are two major fiber-forming constituents of various ECM structures.

SCOPE OF REVIEW

This review will focus on the properties and the biological functions of non-collagenous extracellular matrix especially on laminin and fibronectin that are currently emerging as important regulators of blood vessel formation and function in health and disease.

MAJOR CONCLUSIONS

The ECM is a fundamental component of the microenvironment of blood vessels, with activities extending beyond providing a vascular scaffold; extremely versatile it directly or indirectly modulates all essential cellular functions crucial for angiogenesis, including cell adhesion, migration, proliferation, differentiation and lumen formation. Specifically, fibronectin and laminins play decisive roles in blood vessel morphogenesis both during embryonic development and in pathological conditions, such as cancer.

GENERAL SIGNIFICANCE

Emerging evidence demonstrates the importance of ECM function during embryonic development, organ formation and tissue homeostasis. A wealth of data also illustrates the crucial role of the ECM in several human pathophysiological processes, including fibrosis, skeletal diseases, vascular pathologies and cancer. Notably, several ECM components have been identified as potential therapeutic targets for various diseases, including cancer. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Are the somatic mutation and tissue organization field theories of carcinogenesis incompatible?

Two drastically different approaches to understanding the forces driving carcinogenesis have crystallized through years of research. These are the somatic mutation theory (SMT) and the tissue organization field theory (TOFT). The essence of SMT is that cancer is derived from a single somatic cell that has successively accumulated multiple DNA mutations, and that those mutations occur on genes which control cell proliferation and cell cycle. Thus, according to SMT, neoplastic lesions are the results of DNA-level events. Conversely, according to TOFT, carcinogenesis is primarily a problem of tissue organization: carcinogenic agents destroy the normal tissue architecture thus disrupting cell-to-cell signaling and compromising genomic integrity. Hence, in TOFT the DNA mutations are the effect, and not the cause, of the tissue-level events. Cardinal importance of successful resolution of the TOFT versus SMT controversy dwells in the fact that, according to SMT, cancer is a unidirectional and mostly irreversible disease; whereas, according to TOFT, it is curable and reversible. In this paper, our goal is to outline a plausible scenario in which TOFT and SMT can be reconciled using the framework and concepts of the self-organized criticality (SOC), the principle proven to be extremely fruitful in a wide range of disciplines pertaining to natural phenomena, to biological communities, to large-scale social developments, to technological networks, and to many other subjects of research.

Of plasticity and specificity: dialectics of the microenvironment and macroenvironment and the organ phenotype

The study of biological form and how it arises is the domain of the developmental biologists; but once the form is achieved, the organ poses a fascinating conundrum for all the life scientists: how are form and function maintained in adult organs throughout most of the life of the organism? That they do appears to contradict the inherently plastic nature of organogenesis during development. How do cells with the same genetic information arrive at, and maintain such different architectures and functions, and how do they keep remembering that they are different from each other? It is now clear that narratives based solely on genes and an irreversible regulatory dynamics cannot answer these questions satisfactorily, and the concept of microenvironmental signaling needs to be added to the equation. During development, cells rearrange and differentiate in response to diffusive morphogens, juxtacrine signals, and the extracellular matrix (ECM). These components, which constitute the modular microenvironment, are sensitive to cues from other tissues and organs of the developing embryo as well as from the external macroenvironment. On the other hand, once the organ is formed, these modular constituents integrate and constrain the organ architecture, which ensures structural and functional homeostasis and therefore, organ specificity. We argue here that a corollary of the above is that once the organ architecture is compromised in adults by mutations or by changes in the microenvironment such as aging or inflammation, that organ becomes subjected to the developmental and embryonic circuits in search of a new identity. But since the microenvironment is no longer embryonic, the confusion leads to cancer: hence as we have argued, tumors become new evolutionary organs perhaps in search of an elusive homeostasis.

Tumor-secreted LOXL2 activates fibroblasts through FAK signaling

Cancer-associated fibroblasts enhance cancer progression when activated by tumor cells through mechanisms not yet fully understood. Blocking mammary tumor cell-derived lysyl oxidase-like 2 (LOXL2) significantly inhibited mammary tumor cell invasion and metastasis in transgenic and orthotopic mouse models. Here, we discovered that tumor-derived LOXL2 directly activated stromal fibroblasts in the tumor microenvironment. Genetic manipulation or antibody inhibition of LOXL2 in orthotopically grown mammary tumors reduced the expression of α-smooth muscle actin (α-SMA). Using a marker for reticular fibroblasts, it was determined that expression of α-SMA was localized to fibroblasts recruited from the host tissue. This marker also revealed that the matrix present in tumors with reduced levels of LOXL2 was more scattered compared with control tumors which exhibited matrices with dense, parallel alignments. Importantly, in vitro assays revealed that tumor-derived LOXL2 and a recombinant LOXL2 protein induced fibroblast branching on collagen matrices, as well as increased fibroblast-mediated collagen contraction and invasion of fibroblasts through extracellular matrix. Moreover, LOXL2 induced the expression of α-SMA in fibroblasts grown on collagen matrices. Mechanistically, it was determined that LOXL2 activated fibroblasts through integrin-mediated focal adhesion kinase activation. These results indicate that inhibition of LOXL2 in tumors not only reduces tumor cell invasion but also attenuates the activation of host cells in the tumor microenvironment.

IMPLICATIONS

These findings reveal new insight into the mechanisms of fibroblast activation, a novel function of LOXL2, and further highlight the importance of generating LOXL2-targeted therapies for the prevention of tumor progression and metastasis.

Molecular mechanism of the "feedback loop" model of carcinogenesis

It is commonly accepted that cancer is a genetic disease. The current prevailing theory of carcinogenesis is the somatic mutation theory of carcinogenesis and metastasis (SMT). This theory postulates that mutations in epithelial cells lead to uncontrolled proliferation of tumor cells in a cell-autonomous fashion. This cell-autonomy is increasingly criticized. Current data suggest that the tumor microenvironment is also strongly involved in carcinogenesis. Recently, we published a hypothesis that considers the important contribution of the tumor microenvironment in carcinogenesis and complements the classical clonal evolution model.

Essentially, this “feedback loop model” (FBM) postulates that the physiological communication between cancer cells and stromal cells in inflammatory or proliferative conditions is altered by anomalous signal processing within the parenchymal cells. The inability of parenchymal cells to correctly finalize the intercellular communication might result in a perpetuation of the activated state of cells and the tumor micromilieu. The FBM is unique among the tissue-based models because in this model tumor and stromal cells interact together in a reciprocal manner to form the cancer phenotype. Contrary to the SMT, the FBM postulates that mutated genes act in a cell-heteronomous fashion, not in a cell-autonomously fashion.

Basic fibroblast growth factor upregulates survivin expression in hepatocellular carcinoma cells via a protein kinase B-dependent pathway

Basic fibroblast growth factor (bFGF) plays an important role in tumor angiogenesis. Several studies have reported that bFGF may influence cell apoptosis through different signaling pathways. The aim of the present investigation was to study the effect of bFGF on the activities of protein kinase B (PKB)/survivin and cell apoptosis in hepatocellular carcinoma cells (Bel-7402). We treated Bel-7402 cells with bFGF and wortmannin [phosphatidylinositol 3-kinase (PI3K)-specific inhibitor] separately to observe the expression of PKB and survivin detected with RT-PCR and western blotting. The cell cycle and apoptosis were assayed with flow cytometry. We found a significant increase in PKB expression in the group treated with 25 ng/ml bFGF for 10 min (P<0.05), and this effect was significantly inhibited by pretreatment with wortmannin (200 nM) for 1 h. After treatment with 10 ng/ml bFGF, the expression of survivin mRNA in Bel-7402 cells increased significantly, and reached the peak at 16 h (P<0.05); however, this effect could be significantly inhibited by pretreatment with wortmannin (200 mM) in a time-dependent manner. Following incubation with 25 ng/ml bFGF for 10 min, the apoptosis rate and M phase were significantly decreased and S phase cells increased compared with the wortmannin (200 nM)-treated group. When this group was pretreated with wortmannin (200 nM) for 1 h, the apoptosis rate and S phase were significantly increased, M phase cells decreased. The results revealed that wortmannin could induce high apoptosis rates in hepatocellular carcinoma cells, and bFGF could inhibit the cell apoptosis induced by wortmannin. These findings indicate that bFGF could rapidly activate the PKB activities, enhance the expression of survivin and the proliferation of hepatocellular carcinoma cells via the PI3K pathway, thus it may serve as a novel molecule for early targeting therapy of hepatocellular carcinoma.

The modulation of MSC integrin expression by RGD presentation

Biomaterials designed to mimic the intricate native extracellular matrix (ECM) can use a variety of techniques to control the behavior of encapsulated cells. Common methods include controlling the mechanical properties of the material, incorporating bioactive signals, spatially patterning bioactive signals, and controlling the time-release of bioactive signals. Further design parameters like bioactive signal distribution can be used to manipulate cell behavior. Efforts on clustering adhesion peptides have focused on seeding cells on top of a biomaterial. Here we report the effect of clustering the adhesion peptide RGD on mouse mesenchymal stem cells encapsulated inside three-dimensional hyaluronic acid hydrogels. The clustered bioactive signals resulted in significant differences in both cell spreading and integrin expression. These results indicate that signal RGD peptide clustering is an additional hydrogel design parameter can be used to influence and guide the behavior of encapsulated cells.

Global consensus theorem and self-organized criticality: unifying principles for understanding self-organization, swarm intelligence and mechanisms of carcinogenesis

Complex biological systems manifest a large variety of emergent phenomena among which prominent roles belong to self-organization and swarm intelligence. Generally, each level in a biological hierarchy possesses its own systemic properties and requires its own way of observation, conceptualization, and modeling. In this work, an attempt is made to outline general guiding principles in exploration of a wide range of seemingly dissimilar phenomena observed in large communities of individuals devoid of any personal intelligence and interacting with each other through simple stimulus-response rules. Mathematically, these guiding principles are well captured by the Global Consensus Theorem (GCT) equally applicable to neural networks and to Lotka-Volterra population dynamics. Universality of the mechanistic principles outlined by GCT allows for a unified approach to such diverse systems as biological networks, communities of social insects, robotic communities, microbial communities, communities of somatic cells, social networks and many other systems. Another cluster of universal laws governing the self-organization in large communities of locally interacting individuals is built around the principle of self-organized criticality (SOC). The GCT and SOC, separately or in combination, provide a conceptual basis for understanding the phenomena of self-organization occurring in large communities without involvement of a supervisory authority, without system-wide informational infrastructure, and without mapping of general plan of action onto cognitive/behavioral faculties of its individual members. Cancer onset and proliferation serves as an important example of application of these conceptual approaches. In this paper, the point of view is put forward that apparently irreconcilable contradictions between two opposing theories of carcinogenesis, that is, the Somatic Mutation Theory and the Tissue Organization Field Theory, may be resolved using the systemic approaches provided by GST and SOC.

Impact of tumor microenvironment and epithelial phenotypes on metabolism in breast cancer

PURPOSE

Cancer cells have altered metabolism, with increased glucose uptake, glycolysis, and biomass production. This study conducted genomic and metabolomic analyses to elucidate how tumor and stromal genomic characteristics influence tumor metabolism.

EXPERIMENTAL DESIGN

Thirty-three breast tumors and six normal breast tissues were analyzed by gene expression microarray and by mass spectrometry for metabolites. Gene expression data and clinical characteristics were evaluated in association with metabolic phenotype. To evaluate the role of stromal interactions in altered metabolism, cocultures were conducted using breast cancer cells and primary cancer-associated fibroblasts (CAF).

RESULTS

Across all metabolites, unsupervised clustering resulted in two main sample clusters. Normal breast tissue and a subset of tumors with less aggressive clinical characteristics had lower levels of nucleic and amino acids and glycolysis byproducts, whereas more aggressive tumors had higher levels of these Warburg-associated metabolites. While tumor-intrinsic subtype did not predict metabolic phenotype, metabolic cluster was significantly associated with expression of a wound response signature. In cocultures, CAFs from basal-like breast cancers increased glucose uptake and basal-like epithelial cells increased glucose oxidation and glycogen synthesis, suggesting interplay of stromal and epithelial phenotypes on metabolism. Cytokine arrays identified hepatocyte growth factor (HGF) as a potential mediator of stromal-epithelial interaction and antibody neutralization of HGF resulted in reduced expression of glucose transporter 1 (GLUT1) and decreased glucose uptake by epithelium.

CONCLUSIONS

Both tumor/epithelial and stromal characteristics play important roles in metabolism. Warburg-like metabolism is influenced by changes in stromal-epithelial interactions, including altered expression of HGF/Met pathway and GLUT1 expression.

In vitro evaluation of the suppressor potential of conditioned medium from benign myoepithelial cells from pleomorphic adenoma in malignant cell invasion

Tumoral invasion process is the result of a complex interaction between the tumor cells and microenvironment which plays an important role in modulating the growth and invasion of the cancer. The myoepithelial cells, present in glandular organs such as the breast and salivary glands, seem to exert paracrine effects on the glandular epithelium, acting as natural tumor suppressors. To verify the influence of the benign myoepithelial cells in the invasion of malignant cells, simulating an in situ carcinoma ex pleomorphic adenoma, we have cultured three different high-potential invasive malignant tumors (breast ductal adenocarcinoma, melanoma and oral squamous cell carcinoma) in conditioned medium of myoepithelial cells from salivary gland pleomorphic adenomas using transwell chambers with 8-μm pores membrane coated with matrigel. After 96 h, quantitative analyses of the results were performed by calculating the invasion index (number of cells that invaded in relation to the total number of cells). The results showed that there was a reduction of the invasion index mean for the three different malignant tumors. This study supports a tumoral suppressor function of the myoepithelial cells from pleomorphic adenoma in in vitro invasion process.

Critical choices for modeling breast cancer in transgenic mouse models

Modeling breast cancer in the mouse has helped to better define the heterogeneity of human breast cancer. In the recent past, it has become evident that some limitations have restricted the potential benefits that can be achieved with this approach. In this review, we highlight some key points that should be taken into account when the mouse is used, with special emphasis on transgenic models.

Feedback within the inter-cellular communication and tumorigenesis in carcinomas

The classical somatic mutation theory (SMT) of carcinogenesis and metastasis postulates that malignant transformation occurs in cells that accumulate a sufficient amount of mutations in the appropriate oncogenes and/or tumor suppressor genes. These mutations result in cell-autonomous activation of the mutated cell and a growth advantage relative to neighboring cells. However, the SMT cannot completely explain many characteristics of carcinomas. Contrary to the cell-centered view of the SMT with respect to carcinogenesis, recent research has revealed evidence that the tumor microenvironment plays a role in carcinogenesis as well. In this review, we present a new model that accommodates the role of the tumor microenvironment in carcinogenesis and complements the classical SMT. Our "feedback" model emphasizes the role of an altered spatiotemporal communication between epithelial and stromal cells during carcinogenesis: a dysfunctional intracellular signaling in tumorigenic epithelial cells leads to inappropriate cellular responses to stimuli from associated stromal or inflammatory cells. Thus, a positive feedback loop of the information flow between parenchymal and stromal cells results. This constant communication between the stromal cells and the tumor cells causes a perpetually activated state of tumor cells analogous to resonance disaster.

Evolving models of tumor origin and progression

History of cancer disease models clearly illustrates the evolving nature of these concepts. Since such models undergo continual revisions and additions as a result of underlying medical research, they also tend to reorganize knowledge and allow perceiving previously unseen relationships. Growth of medical thought has been influenced for many centuries by an ancient Hippocratic concept of disease seen as a disturbance in bodily “humors.” True mechanisms of cell and tissue injury started to be elucidated only with the advent of postmortem pathological findings. Concerning cancer, when first disease-producing bacteria were identified in the nineteenth century, also neoplasms were treated as infectious diseases. Foreign organisms were thought to be present inside tumors. However, this hypothesis could not be confirmed by microscopic or histochemical studies. The latter suggested, instead, that tumors were rather formed by abnormal cells. Cancer was then started to be regarded as a disease of cells. This interpretation was radically altered by later developments in genetics which suggested that neoplasms can be treated as genetic diseases as pathologic cellular lesions are caused by mutations in specific genes. More recent models have compared carcinogenesis to evolutionary processes. Due to genetic instability, successive mutations, appearing in cells, lead to selection of cancer cells which feature specific phenotypic traits. The newest data indicate that there may be also a link between cancer and mutated stem cells. The review discusses main concepts of tumor origin forwarded since the beginnings of the nineteenth century.

Basic fibroblast growth factor in an animal model of spontaneous mammary tumor progression

Although basic fibroblast growth factor (FGF2) was the first pro-angiogenic molecule discovered, it has numerous activities on the growth and differentiation of non-vascular cell types. FGF2 is both stimulatory and inhibitory, depending on the cell type evaluated, the experimental design used and the context in which it is tested. Here, we investigated the effects of manipulating endogenous FGF2 on the development of mammary cancer to determine whether its endogenous contribution in vivo is pro- or anti-tumorigenic. Specifically, we examined the effects of FGF2 gene dosing in a cross between a spontaneous breast tumor model (PyVT+ mice) and FGF2-/- (FGF KO) mice. Using these mice, the onset and progression of mammary tumors was determined. As predicted, female FGF2 WT mice developed mammary tumors starting around 60 days after birth and by 80 days, 100% of FGF2 WT female mice had mammary tumors. In contrast, 80% of FGF2 KO female mice had no palpable tumors until nearly three weeks later (85 days) at times when 100% of the WT cohort was tumor positive. All FGF KO mice were tumor-bearing by 115 days. When we compared the onset of mammary tumor development and the tumor progression curves between FGF het and FGF KO mice, we observed a difference, which suggested a gene dosing effect. Analysis of the tumors demonstrated that there were significant differences in tumor size depending on FGF2 status. The delay in tumor onset supports a functional role for FGF2 in mammary tumor progression, but argues against an essential role for FGF2 in overall mammary tumor progression.

Building the niche: the role of the S100 proteins in metastatic growth

Communication between cancer cells and stromal cells, often mediated by extracellular molecules in the tumor microenvironment, plays a central role in tumorigenesis and metastasis. The establishment of a pro-inflammatory milieu is increasingly recognized as an important consequence of these interactions. The family of S100 Ca2+-binding proteins has been implicated in many aspects of the interaction between cancer cells and stromal cells, and contributes to the formation of an inflammatory tumor microenvironment. Focusing on S100A4, S100A8 and S100A9, in this review we discuss the role these proteins play in primary tumors and in the development of metastases, in particular during the formation of pre-metastatic niches.

The tumor microenvironment is a dominant force in multidrug resistance

The emergence of clinical drug resistance is still one of the most challenging factors in cancer treatment effectiveness. Until more recently, the assumption has been that random genetic lesions are sufficient to explain the progression of malignancy and escape from chemotherapy. Here we propose an additional perspective, one in which the tumor cells despite the malignant genome could find a microenvironment either within the tumor or as a dormant cell to remain polar and blend into an organized context. Targeting this dynamic interplay could be considered a new avenue to prevent therapeutic resistance, and may even provide a promising effective cancer treatment.

Biomolecular self-defense and futility of high-specificity therapeutic targeting

Robustness has been long recognized to be a distinctive property of living entities. While a reasonably wide consensus has been achieved regarding the conceptual meaning of robustness, the biomolecular mechanisms underlying this systemic property are still open to many unresolved questions. The goal of this paper is to provide an overview of existing approaches to characterization of robustness in mathematically sound terms. The concept of robustness is discussed in various contexts including network vulnerability, nonlinear dynamic stability, and self-organization. The second goal is to discuss the implications of biological robustness for individual-target therapeutics and possible strategies for outsmarting drug resistance arising from it. Special attention is paid to the concept of swarm intelligence, a well studied mechanism of self-organization in natural, societal and artificial systems. It is hypothesized that swarm intelligence is the key to understanding the emergent property of chemoresistance.

Novel stromal biomarkers in human breast cancer tissues provide evidence for the more malignant phenotype of estrogen receptor-negative tumors

Research efforts were focused on genetic alterations in epithelial cancer cells. Epithelial-stromal interactions play a crucial role in cancer initiation, progression, invasion, angiogenesis, and metastasis; however, the active role of stroma in human breast tumorigenesis in relation to estrogen receptor (ER) status of epithelial cells has not been explored. Using proteomics and biochemical approaches, we identified two stromal proteins in ER-positive and ER-negative human breast cancer tissues that may affect malignant transformation in breast cancer. Two putative biomarkers, T-cell receptor alpha (TCR-α) and zinc finger and BRCA1-interacting protein with a KRAB domain (ZBRK1), were detected in leukocytes of ER-positive and endothelial cells of ER-negative tissues, respectively. Our data suggest an immunosuppressive role of leukocytes in invasive breast tumors, propose a multifunctional nature of ZBRK1 in estrogen receptor regulation and angiogenesis, and demonstrate the aggressiveness of ER-negative human breast carcinomas. This research project may identify new stromal drug targets for the treatment of breast cancer patients.

Functional heterogeneity of breast fibroblasts is defined by a prostaglandin secretory phenotype that promotes expansion of cancer-stem like cells

Fibroblasts are important in orchestrating various functions necessary for maintaining normal tissue homeostasis as well as promoting malignant tumor growth. Significant evidence indicates that fibroblasts are functionally heterogeneous with respect to their ability to promote tumor growth, but markers that can be used to distinguish growth promoting from growth suppressing fibroblasts remain ill-defined. Here we show that human breast fibroblasts are functionally heterogeneous with respect to tumor-promoting activity regardless of whether they were isolated from normal or cancerous breast tissues. Rather than significant differences in fibroblast marker expression, we show that fibroblasts secreting abundant levels of prostaglandin (PGE2), when isolated from either reduction mammoplasty or carcinoma tissues, were both capable of enhancing tumor growth in vivo and could increase the number of cancer stem-like cells. PGE2 further enhanced the tumor promoting properties of fibroblasts by increasing secretion of IL-6, which was necessary, but not sufficient, for expansion of breast cancer stem-like cells. These findings identify a population of fibroblasts which both produce and respond to PGE2, and that are functionally distinct from other fibroblasts. Identifying markers of these cells could allow for the targeted ablation of tumor-promoting and inflammatory fibroblasts in human breast cancers.

Role of tumor vascular architecture in drug delivery

Tumor targeted drug delivery has the potential to improve cancer care by reducing non-target toxicities and increasing the efficacy of a drug. Tumor targeted delivery of a drug from the systemic circulation, however, requires a thorough understanding of tumor pathophysiology. A growing or receding (under the impact of therapy) tumor represents a dynamic environment with changes in its angiogenic status, cell mass, and extracellular matrix composition. An appreciation of the salient characteristics of tumor vascular architecture and the unique biochemical markers that may be used for targeting drug therapy is important to overcome barriers to tumor drug therapy and to facilitate targeted drug delivery. This review discusses the unique aspects of tumor vascular architecture that need to be overcome or exploited for tumor targeted drug delivery.

Apoptotic cell signaling in cancer progression and therapy

Apoptosis is a tightly regulated cell suicide program that plays an essential role in the development and maintenance of tissue homeostasis by eliminating unnecessary or harmful cells. Impairment of this native defense mechanism promotes aberrant cellular proliferation and the accumulation of genetic defects, ultimately resulting in tumorigenesis, and frequently confers drug resistance to cancer cells. The regulation of apoptosis at several levels is essential to maintain the delicate balance between cellular survival and death signaling that is required to prevent disease. Complex networks of signaling pathways act to promote or inhibit apoptosis in response to various cues. Apoptosis can be triggered by signals from within the cell, such as genotoxic stress, or by extrinsic signals, such as the binding of ligands to cell surface death receptors. Various upstream signaling pathways can modulate apoptosis by converging on, and thereby altering the activity of, common central control points within the apoptotic signaling pathways, which involve the BCL-2 family proteins, inhibitor of apoptosis (IAP) proteins, and FLICE-inhibitory protein (c-FLIP). This review highlights the role of these fundamental regulators of apoptosis in the context of both normal apoptotic signaling mechanisms and dysregulated apoptotic pathways that can render cancer cells resistant to cell death. In addition, therapeutic strategies aimed at modulating the activity of BCL-2 family proteins, IAPs, and c-FLIP for the targeted induction of apoptosis are briefly discussed.

Remodeling and homeostasis of the extracellular matrix: implications for fibrotic diseases and cancer

Dynamic remodeling of the extracellular matrix (ECM) is essential for development, wound healing and normal organ homeostasis. Life-threatening pathological conditions arise when ECM remodeling becomes excessive or uncontrolled. In this Perspective, we focus on how ECM remodeling contributes to fibrotic diseases and cancer, which both present challenging obstacles with respect to clinical treatment, to illustrate the importance and complexity of cell-ECM interactions in the pathogenesis of these conditions. Fibrotic diseases, which include pulmonary fibrosis, systemic sclerosis, liver cirrhosis and cardiovascular disease, account for over 45% of deaths in the developed world. ECM remodeling is also crucial for tumor malignancy and metastatic progression, which ultimately cause over 90% of deaths from cancer. Here, we discuss current methodologies and models for understanding and quantifying the impact of environmental cues provided by the ECM on disease progression, and how improving our understanding of ECM remodeling in these pathological conditions is crucial for uncovering novel therapeutic targets and treatment strategies. This can only be achieved through the use of appropriate in vitro and in vivo models to mimic disease, and with technologies that enable accurate monitoring, imaging and quantification of the ECM.