肿瘤酸性微环境的研究进展

研究表明,肿瘤转移是恶性肿瘤的临床治疗失败的根本原因。肿瘤转移不仅取决于肿瘤细胞自身的特性,还涉及其与肿瘤酸性微环境之间的相互作用。肿瘤微环境构成非常复杂,可促进肿瘤的增生、转移、侵袭,以及逃避宿主免疫监视和治疗耐药性。肿瘤细胞的生存依赖于在酸性微环境条件下的适应,肿瘤细胞可以通过一些离子交换体维持酸性微环境,缺氧的肿瘤组织酸化可以释放蛋白酶如纤维蛋白酶及MMPs降解细胞外基质、上调VEGF基因表达促进肿瘤新生血管生成等促进肿瘤侵袭转移。近年来,影响肿瘤微环境的因素已经成为癌症研究领域中的新兴话题。     

Role of matrix metalloproteinases in melanoma cell invasion

Cutaneous melanomas are notorious for their tendency to metastasize. Essential steps in this process are the degradation of basement membranes and remodeling of the extracellular matrix (ECM) by proteolytic enzymes such as matrix metalloproteinases (MMPs), which are regulated by their tissue inhibitors (TIMPs). An MMP expression is not restricted to tumor cells but is also found in stromal cells, indicating that stroma-derived proteases may contribute to melanoma progression. The MMPs have been shown to interact with a broad range of non-matrix proteins including adhesion molecules, growth factors and mediators of angiogenesis and apoptosis. In this review, we evaluate new insights into the interplay of MMPs and their molecular partners in melanoma progression.     

Adaptation of the group A Streptococcus adhesin Scl1 to bind fibronectin type III repeats within wound‐associated extracellular matrix: implications for cancer therapy

The human‐adapted pathogen group A Streptococcus (GAS) utilizes wounds as portals of entry into host tissue, wherein surface adhesins interact with the extracellular matrix, enabling bacterial colonization. The streptococcal collagen‐like protein 1 (Scl1) is a major adhesin of GAS that selectively binds to two fibronectin type III (FnIII) repeats within cellular fibronectin, specifically the alternatively spliced extra domains A and B, and the FnIII repeats within tenascin‐C. Binding to FnIII repeats was mediated through conserved structural determinants present within the Scl1 globular domain and facilitated GAS adherence and biofilm formation. Isoforms of cellular fibronectin that contain extra domains A and B, as well as tenascin‐C, are present for several days in the wound extracellular matrix. Scl1‐FnIII binding is therefore an example of GAS adaptation to the host's wound environment. Similarly, cellular fibronectin isoforms and tenascin‐C are present in the tumor microenvironment. Consistent with this, FnIII repeats mediate GAS attachment to and enhancement of biofilm formation on matrices deposited by cancer‐associated fibroblasts and osteosarcoma cells. These data collectively support the premise for utilization of the Scl1‐FnIII interaction as a novel method of anti‐neoplastic targeting in the tumor microenvironment.     

Profiling human protein degradome delineates cellular responses to proteasomal inhibition and reveals a feedback mechanism in regulating proteasome homeostasis

Global change in protein turnover (protein degradome) constitutes a central part of cellular responses to intrinsic or extrinsic stimuli. However, profiling protein degradome remains technically challenging. Recently, inhibition of the proteasome, e.g., by using bortezomib (BTZ), has emerged as a major chemotherapeutic strategy for treating multiple myeloma and other human malignancies, but systematic understanding of the mechanisms for BTZ drug action and tumor drug resistance is yet to be achieved. Here we developed and applied a dual-fluorescence-based Protein Turnover Assay (ProTA) to quantitatively profile global changes in human protein degradome upon BTZ-induced proteasomal inhibition. ProTA and subsequent network analyses delineate potential molecular basis for BTZ action and tumor drug resistance in BTZ chemotherapy. Finally, combined use of BTZ with drugs targeting the ProTA-identified key genes or pathways in BTZ action reduced BTZ resistance in multiple myeloma cells. Remarkably, BTZ stabilizes proteasome subunit PSMC1 and proteasome assembly factor PSMD10, suggesting a previously under-appreciated mechanism for regulating proteasome homeostasis. Therefore, ProTA is a novel tool for profiling human protein degradome to elucidate potential mechanisms of drug action and resistance, which might facilitate therapeutic development targeting proteostasis to treat human disorders.     

HSP70 inhibition by the small-molecule 2-phenylethynesulfonamide impairs protein clearance pathways in tumor cells

The evolutionarily conserved stress-inducible HSP70 molecular chaperone plays a central role in maintaining protein quality control in response to various forms of stress. Constitutively elevated HSP70 expression is a characteristic of many tumor cells and contributes to their survival. We recently identified the small-molecule 2-phenylethyenesulfonamide (PES) as a novel HSP70 inhibitor. Here, we present evidence that PES-mediated inhibition of HSP70 family proteins in tumor cells results in an impairment of the two major protein degradation systems, namely, the autophagy-lysosome system and the proteasome pathway. HSP70 family proteins work closely with the HSP90 molecular chaperone to maintain the stability and activities of their many client proteins, and PES causes a disruption in the HSP70/HSP90 chaperone system. As a consequence, many cellular proteins, including known HSP70/HSP90 substrates, accumulate in detergent-insoluble cell fractions, indicative of aggregation and functional inactivation. Overall, PES simultaneously disrupts several cancer critical survival pathways, supporting the idea of targeting HSP70 as a potential approach for cancer therapeutics.     

The extracellular matrix: a dynamic niche in cancer progression

The local microenvironment, or niche, of a cancer cell plays important roles in cancer development. A major component of the niche is the extracellular matrix (ECM), a complex network of macromolecules with distinctive physical, biochemical, and biomechanical properties. Although tightly controlled during embryonic development and organ homeostasis, the ECM is commonly deregulated and becomes disorganized in diseases such as cancer. Abnormal ECM affects cancer progression by directly promoting cellular transformation and metastasis. Importantly, however, ECM anomalies also deregulate behavior of stromal cells, facilitate tumor-associated angiogenesis and inflammation, and thus lead to generation of a tumorigenic microenvironment. Understanding how ECM composition and topography are maintained and how their deregulation influences cancer progression may help develop new therapeutic interventions by targeting the tumor niche.     

Hypoxia inducible factor(HIF) in the tumor microenvironment:friend or foe?

Hypoxia acts as an important regulator of physiological and pathological processes. Hypoxia inducible factors (HIFs) are the central players involved in the cellular adaptation to hypoxia and are regulated by oxygen sensing EGLN prolyl hydroxylases. Hypoxia affects many aspects of cellular growth through both redox effects and through the stabilization of HIFs. The HIF isoforms likely have differential effects on tumor growth via alteration of metabolism, growth, and self-renewal and are likely highly context-dependent. In some tumors such as renal cell carcinoma, the EGLN/HIF axis appears to drive tumorigenesis, while in many others HIF1 and HIF2 may actually have a tumor suppressive role. An emerging role of HIF biology is its effects on the tumor microenvironment. The EGLN/HIF axis plays a key role in regulating the function of the various components of the tumor microenvironment, which include cancer-associated fibroblasts, endothelial cells, immune cells, and the extracellular matrix (ECM). Here, we discuss hypoxia and the diverse roles of HIFs in the setting of tumorigenesis and the maintenance of the tumor microenvironment as well as possible future directions of the field.     

Role of the ubiquitin–proteasome system on macrophages in the tumor microenvironment

Tumor-associated macrophages (TAMs) are key components of the tumor microenvironment, and their different polarization states play multiple roles in tumors by secreting cytokines, chemokines, and so on, which are closely related to tumor development. In addition, the enrichment of TAMs is often associated with poor prognosis of tumors. Thus, targeting TAMs is a potential tumor treatment strategy, in which therapeutic approaches such as reducing TAMs numbers, remodeling TAMs phenotypes, and altering their functions are being extensively investigated. Meanwhile, the ubiquitin–proteasome system (UPS), an important mechanism of protein hydrolysis in eukaryotic cells, participates in cellular processes by regulating the activity and stability of key proteins. Interestingly, UPS plays a dual role in the process of tumor development, and its role in TAMs deserve to be investigated in depth. This review builds on this foundation to further explore the multiple roles of UPS on TAMs and identifies a promising approach to treat tumors by targeting TAMs with UPS.     

Tumor microenvironment: the role of the tumor stroma in cancer

The tumor microenvironment, composed of non-cancer cells and their stroma, has become recognized as a major factor influencing the growth of cancer. The microenvironment has been implicated in the regulation of cell growth, determining metastatic potential and possibly determining location of metastatic disease, and impacting the outcome of therapy. While the stromal cells are not malignant per se, their role in supporting cancer growth is so vital to the survival of the tumor that they have become an attractive target for chemotherapeutic agents. In this review, we will discuss the various cellular and molecular components of the stromal environment, their effects on cancer cell dynamics, and the rationale and implications of targeting this environment for control of cancer. Additionally, we will emphasize the role of the bone marrow-derived cell in providing cells for the stroma.     

VEGF/VEGFR-Targeted Therapy and Immunotherapy in Non-small Cell Lung Cancer: Targeting the Tumor Microenvironment

Non-small cell lung cancer (NSCLC) is the leading cause of death by cancer worldwide. Despite developments in therapeutic approaches for the past few decades, the 5-year survival rate of patients with NSCLC remains low. NSCLC tumor is a complex, heterogeneous microenvironment, comprising blood vessels, cancer cells, immune cells, and stroma cells. Vascular endothelial growth factors (VEGFs) are a major mediator to induce tumor microvasculature and are associated with the progression, recurrence, and metastasis of NSCLC. Current treatment medicines targeting VEGF/VEGF receptor (VEGFR) pathway, including neutralizing antibodies to VEGF or VEGFR and receptor tyrosine kinase inhibitors, have shown good treatment efficacy in patients with NSCLC. VEGF is not only an important angiogenic factor but also an immunomodulator of tumor microenvironment (TME). VEGFs can suppress antigen presentation, stimulate activity of regulatory T (Treg) cells, and tumor-associated macrophages, which in turn promote an immune suppressive microenvironment in NSCLC. The present review focuses on the angiogenic and non-angiogenic functions of VEGF in NSCLC, especially the interaction between VEGF and the cellular components of the TME. Additionally, we discuss recent preclinical and clinical studies to explore VEGF/VEGFR-targeted compounds and immunotherapy as novel approaches targeting the TME for the treatment of NSCLC.     

Matrix metalloproteinases in tumor-host cell communication

The microenvironment or stroma immediately surrounding tumor cells consists of a three-dimensional extracellular matrix (ECM) and stromal cells such as fibroblasts and inflammatory cells. The matrix metalloproteinases (MMPs) constitute a family of over 24 members, which collectively are capable of degrading virtually the entire ECM. Strict regulation of MMP expression is critical in order to maintain proper ECM homeostasis, but in disease states such as cancer there is often a high level of MMP activity at the tumor-stroma interface. Several studies have documented the importance of MMP-mediated ECM destruction in the successful dissemination of several tumor types, but it has become increasingly clear that they are also involved in earlier stages of tumorigenesis. MMPs are implicated in a wide variety of roles that can assist tumor initiation, growth, migration, angiogenesis, the selection of apoptosis-resistant subpopulations, and in invasion and metastasis. Interestingly, the factors responsible for many of these effects are derived from the cell surfaces of the tumor or stromal cells or are embedded in the ECM. Therefore, the MMPs can no longer be thought of solely as ECM destructionists, but as part of an elegant communication system through which the tumor interacts with the stroma.     

Roles of metalloproteases in metastatic niche

Metalloproteinases (MMPs) are a cluster of at least 23 enzymes belonging to the more wide family of endopeptidases called Metzincins, whose structure is characterized by the presence of a zinc ion at the catalytic site. Although the general view of MMPs as physiologic scissors involved in extracellular matrix (ECM) degradation and tissue remodeling is still valid, additional functions have recently emerged, including the ability to cleave non ECM molecules such as growth factors, cytokines and chemokines from their membrane-anchored proforms. These functions are utilized by tumor cells and are fundamental in the determination of tumor progression and invasion. The effect of MMPs activity in cancer progression has been traditionally associated with the acquisition by tumor cells of an invasive phenotype, an indispensable requisite for the metastatic spreading of cancer cells. In addition to the traditional view, a new role for MMPs in creating a favourable microenvironment has been proposed, so that MMPs are not only involved in cell invasion, but also in signaling pathways that control cell growth, inflammation, or angiogenesis. Finally, recent evidence suggest a role of MMPs in the so called "pre-metastatic niche" that is the hypothesis of an early distant modification of the premetastatic site by primary cancer cells. This new hypothesis is changing our traditional view about MMPs and provides important insights into the effective time window for the therapeutic use of MMP inhibitors. In this review we provide the main available data about the ability of MMPs in creating a suitable microenvironment for tumor growth in metastatic sites and we indicate the implication of these data on the potential use of MMP inhibitors in the metastatic therapy.     

Angiogenesis in gynecological cancers and the options for anti-angiogenesis therapy

Angiogenesis is required in cancer, including gynecological cancers, for the growth of primary tumors and secondary metastases. Development of anti-angiogenesis therapy in gynecological cancers and improvement of its efficacy have been a major focus of fundamental and clinical research. However, survival benefits of current anti-angiogenic agents, such as bevacizumab, in patients with gynecological cancer, are modest. Therefore, a better understanding of angiogenesis and the tumor microenvironment in gynecological cancers is urgently needed to develop more effective anti-angiogenic therapies, either or not in combination with other therapeutic approaches. We describe the molecular aspects of (tumor) blood vessel formation and the tumor microenvironment and provide an extensive clinical overview of current anti-angiogenic therapies for gynecological cancers. We discuss the different phenotypes of angiogenic endothelial cells as potential therapeutic targets, strategies aimed at intervention in their metabolism, and approaches targeting their (inflammatory) tumor microenvironment.     

Proteoglycan control of cell movement during wound healing and cancer spreading.

By virtue of their multifunctional nature, proteoglycans (PGs) are thought to govern the process of cell movement in numerous physiological and pathological contexts, spanning from early embryonic development to tumour invasion and metastasis. The precise mode by which they influence this process is still fragmentary, but evidence is accruing that they may affect it in a multifaceted manner. PGs bound to the plasma membrane mediate the polyvalent interaction of the cell with matrix constituents and with molecules of the neighbouring cells' surfaces; they modulate the activity of receptors implicated in the recognition of these components; and they participate in the perception and convergence of growth- and motility-promoting cues contributed by soluble factors. Through some of these interactions several PGs transduce to pro-motile cells crucial intracellular signals that are likely to be essential for their mobility. A regulated shedding of certain membrane-intercalated PGs seems to provide an additional level of control of cell movement. Coincidentally, matrix-associated PGs may govern cell migration by structuring permissive and non-permissive migratory paths and, when directly secreted by the moving cells, may alternatively create favourable or hostile microenvironments. To exert this latter, indirect effect on cell movement, matrix PGs strongly rely upon their primary molecular partners, such as hyaluronan, link proteins, tenascins, collagens and low-affinity cell surface receptors, whereas a further finer control is provided by a highly regulated proteolytic processing of the PGs accounted by both the migrating cells themselves and cells of their surrounding tissues. Overall, PGs seem to play an important role in determining the migratory phenotype of a cell by initiating, directing and terminating cell movement in a spatio-temporally controlled fashion. This implies that the "anti-adhesive and/or "anti-migratory" properties that have previously been assigned to certain PGs may be re-interpreted as being a means by which these macromolecules elaborate haptotaxis-like mechanisms imposing directionality upon the moving cells. Since these conditions would allow cells to be led to given tissue locations and become immobilized at these sites, a primary function may be ascribed to PGs in the dictation of a "stop or go" choice of the migrating cells.     

Cadmium pyrithione suppresses tumor growth in vitro and in vivo through inhibition of proteasomal deubiquitinase

The ubiquitin–proteasome system (UPS) is indispensable to the protein quality control in eukaryotic cells. Due to the remarkable clinical success of using proteasome inhibitors for clinical treatment of multiple myeloma, it is anticipated that targeting the UPS upstream of the proteasome step be an effective strategy for cancer therapy. Deubiquitinases (DUB) are proteases that remove ubiquitin from target proteins and therefore regulate multiple cellular processes including some signaling pathways altered in cancer cells. Thus, targeting DUB is a promising strategy for cancer drug discovery. Previously, we have reported that metal complexes, such as copper and gold complexes, can disrupt the UPS via suppressing the activity of 19S proteasome-associated DUBs and/or of the 20S proteasomes, thereby inducing cancer cell death. In this study, we found that cadmium pyrithione (CdPT) treatment led to remarkable accumulation of ubiquitinated proteins in cultured cancer cells and primary leukemia cells. CdPT potently inhibited the activity of proteasomal DUBs (USP14 and UCHL5), but slightly inhibited 20S proteasome activity. The anti-cancer activity of CdPT was associated with triggering apoptosis via caspase activation. Moreover, treatment with CdPT inhibited proteasome function and repressed tumor growth in animal xenograft models. Our results show that cadmium-containing complex CdPT may function as a novel proteasomal DUB inhibitor and suggest appealing prospects for cancer treatment.     

Heparin--a unique stimulator of human colon cancer cells' growth

The cancer microenvironment and the interactions between cancer and surrounding tissue cells are thought to play a pivotal role in tumor development and progression. Glycosaminoglycans (GAGs)/proteoglycans (PGs) are major constituents of the extracellular matrix, the composition of which may affect various cellular functions. In the present study, the effects of GAGs on the proliferation of HT29, SW1116, and HCT116 human colon cancer cell lines were examined using exogenously added GAGs, an inhibitor of endogenous GAG sulfation and specific glycosidase digestions. Our results demonstrate that colon cancer cell growth was exclusively stimulated by exogenously added heparin and insensitive to endogenous GAGs/PGs production, in a sulfation pattern-related manner. Treatment of the tested cell lines with the FGF-2 neutralizing antibody showed that the stimulatory effect of heparin on the cells' growth was not FGF-2-dependent. Responsiveness of colon cancer cell lines to exogenous heparin/heparan sulfate may play a role in their growth and metastasis.     

Therapeutic Potential of Matrix Metalloproteinase Inhibition in Breast Cancer

Matrix metalloproteinases (MMPs) are a family of zinc endopeptidases that cleave nearly all components of the extracellular matrix as well as many other soluble and cell‐associated proteins. MMPs have been implicated in normal physiological processes, including development, and in the acquisition and progression of the malignant phenotype. Disappointing results from a series of clinical trials testing small molecule, broad spectrum MMP inhibitors as cancer therapeutics led to a re‐evaluation of how MMPs function in the tumor microenvironment, and ongoing research continues to reveal that these proteins play complex roles in cancer development and progression. It is now clear that effective targeting of MMPs for therapeutic benefit will require selective inhibition of specific MMPs. Here, we provide an overview of the MMP family and its biological regulators, the tissue inhibitors of metalloproteinases (TIMPs). We then summarize recent research from model systems that elucidate how specific MMPs drive the malignant phenotype of breast cancer cells, including acquisition of cancer stem cell features and induction of the epithelial–mesenchymal transition, and we also outline clinical studies that implicate specific MMPs in breast cancer outcomes. We conclude by discussing ongoing strategies for development of inhibitors with therapeutic potential that are capable of selectively targeting the MMPs most responsible for tumor promotion, with special consideration of the potential of biologics including antibodies and engineered proteins based on the TIMP scaffold. J. Cell. Biochem. 118: 3531–3548, 2017. © 2017 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals, Inc.     

Effect of Endothelin-1 on proliferation,migration and fibrogenic gene expression in human RPE cells

The pathology of the fibrotic proliferative vitreoretinopathy (PVR) membrane represents an excessive wound healing response characterised by cells’ proliferation, migration and secretion of extracellular matrix molecules (ECMs). Retinal pigment epithelial (RPE) cells are a major cellular component of the fibrotic membrane. Endothelin-1 (ET-1) has been reported to be involved in the development of PVR in vivo research. However, little is known about the role of ET-1 in RPE cells in vitro. In the present study, we investigated the role of ET-1 in the proliferation, migration and secretion of ECMs (such as type I collagen and fibronectin) in RPE cells in vitro. Our results illustrated that ET-1 promoted the proliferation, migration and secretion of ECMs through the protein kinase B (Akt) and extracellular signal-regulated kinase (Erk) signaling pathways in RPE cells in vitro. These findings strongly suggested that ET-1 may play a vital role in the development of PVR.     

Components of the hepatocellular carcinoma microenvironment and their role in tumor progression

This review summarizes recently published data on the mechanisms of tumor cell interaction with the tumor microenvironment. Tumor stroma influences the processes of hepatocarcinogenesis, epithelial-to-mesenchymal transition, invasion, and metastasis. The tumor microenvironment includes both cellular and noncellular components. Main cellular components of hepatocellular carcinoma (HCC) stroma are tumor-associated fibroblasts, hepatic stellate cells, immune cells, and endothelial cells that produce extracellular components of tumor microenvironment such as extracellular matrix, various proteins, proteolytic enzymes, growth factors, and cytokines. The noncellular components of the stroma modulate signaling pathways in tumor cells and stimulate invasion and metastasis. The tumor microenvironment composition and organization can serve as prognostic factors in HCC pathogenesis. Current approaches in HCC targeted therapy are aimed at creating efficient strategies for interrupting tumor interactions with the stroma. Recent data on the composition and role of the microenvironment in HCC pathogenesis, as well as new developments in antitumor drug design are discussed.     

Matrix metalloproteinases and their expression in mammary gland

The matrix metalloproteinases (MMPs) are a family of zine-dependent endopeptidases that play a key role in both normal and pathological processes involving tissue remodeling events.The expression of these proteolytic enzymes is highly regulated by a balance between extracellular matrix (ECM) deposition and its degradation,and is controlled by growth factors,cytokines,hormones,as well as interactions with the ECM macromolecules.Furthermore,the activity of the MMPs is regulated by their natural endogenous inhibitors,which are members of the tissue inhibitor of metalloproteinases (TIMP) family.In the normal mammary gland,MMPs are expressed during ductal development,lobulo-alveolar development in pregnancy and involution after lactation.Under pathological conditions,such as tumorigenesis,the dysregulated expression of MMPs play a role in tumor initiation,progression and malignant conversion as well as facilitating invasion and metastasis of malignant cells through degradation of the ECM and basement membranes.