Cathepsin C is a tissue-specific regulator of squamous carcinogenesis

Functional and genomic characterisation of a xenograft model system for the study of metastasis in triple-negative breast cancer

Triple-negative breast cancer (TNBC) represents 10-20% of all human ductal adenocarcinomas and has a poor prognosis relative to other subtypes. Hence, new molecular targets for therapeutic intervention are necessary. Analyses of panels of human or mouse cancer lines derived from the same individual that differ in their cellular phenotypes but not in genetic background have been instrumental in defining the molecular players that drive the various hallmarks of cancer. To determine the molecular regulators of metastasis in TNBC, we completed a rigorous in vitro and in vivo characterisation of four populations of the MDA-MB-231 human breast cancer line ranging in aggressiveness from non-metastatic to spontaneously metastatic to lung, liver, spleen and lymph node. Single nucleotide polymorphism (SNP) array analyses and genome-wide mRNA expression profiles of tumour cells isolated from orthotopic mammary xenografts were compared between the four lines to define both cell autonomous pathways and genes associated with metastatic proclivity. Gene set enrichment analysis (GSEA) demonstrated an unexpected association between both ribosome biogenesis and mRNA metabolism and metastatic capacity. Differentially expressed genes or families of related genes were allocated to one of four categories, associated with either metastatic initiation (e.g. CTSC, ENG, BMP2), metastatic virulence (e.g. ADAMTS1, TIE1), metastatic suppression (e.g. CST1, CST2, CST4, CST6, SCNNA1, BMP4) or metastatic avirulence (e.g. CD74). Collectively, this model system based on MDA-MB-231 cells should be useful for the assessment of gene function in the metastatic cascade and also for the testing of novel experimental therapeutics for the treatment of TNBC.This article has an associated First Person interview with the first author of the paper.

Targeting of cathepsin C induces autophagic dysregulation that directs ER stress mediated cellular cytotoxicity in colorectal cancer cells

As Autophagy is a pivotal mechanism of cancer cell survival and the development of chemotherapeutic resistance; therefore, new approaches are warranted for its targeting which may be fulfilled by cathepsins regulation. Amongst cathepsins, cathepsin C (CTSC) is highly expressed in various cancers and possesses significant therapeutic potential in autoimmune disorders; however, its role in colorectal cancer has not been explored. Herein, we aimed to investigate the role of CTSC in autophagy regulation mediated colorectal carcinoma cell proliferation. Cathepsin C targeting through inhibitors/siRNA leads to the accumulation of light chain 3 II and p62 without affecting the lysosomal integrity, revealed dysfunctional autolysosomal degradation which is also substantiated by proteolytic studies. Cathepsin C inhibition showed comparable autophagy blockade with E64d and augmented the autophagy blockade mediated by bafilomycin. Loss of CTSC function also induced ER stress-mediated JNK phosphorylation accompanied by the translocation of mitochondrial cyt c followed by apoptotic cell death in colorectal carcinoma cells. Taken together, the study reveals that CTSC targeting plays a key role in the regulation of autophagy mediated colorectal cancer cell proliferation. Further investigations are required to determine the functional role of CTSC in other tumors also which may have implications for the therapeutic prevention of cancer in the future.

Characterization of brain tumor initiating cells isolated from an animal model of CNS primitive neuroectodermal tumors

CNS Primitive Neuroectodermal tumors (CNS-PNETs) are members of the embryonal family of malignant childhood brain tumors, which remain refractory to current therapeutic treatments. Current paradigm of brain tumorigenesis implicates brain tumor-initiating cells (BTIC) in the onset of tumorigenesis and tumor maintenance. However, despite their significance, there is currently no comprehensive characterization of CNS-PNETs BTICs. Recently, we described an animal model of CNS-PNET generated by orthotopic transplantation of human Radial Glial (RG) cells - the progenitor cells for adult neural stem cells (NSC) - into NOD-SCID mice brain and proposed that BTICs may play a role in the maintenance of these tumors. Here we report the characterization of BTIC lines derived from this CNS-PNET animal model. BTIC’s orthotopic transplantation generated highly aggressive tumors also characterized as CNS-PNETs. The BTICs have the hallmarks of NSCs as they demonstrate self-renewing capacity and have the ability to differentiate into astrocytes and early migrating neurons. Moreover, the cells demonstrate aberrant accumulation of wild type tumor-suppressor protein p53, indicating its functional inactivation, highly up-regulated levels of onco-protein cMYC and the BTIC marker OCT3/4, along with metabolic switch to glycolysis - suggesting that these changes occurred in the early stages of tumorigenesis. Furthermore, based on RNA- and DNA-seq data, the BTICs did not acquire any transcriptome-changing genomic alterations indicating that the onset of tumorigenesis may be epigenetically driven. The study of these BTIC self-renewing cells in our model may enable uncovering the molecular alterations that are responsible for the onset and maintenance of the malignant PNET phenotype.

The Multifaceted Role of the Lysosomal Protease Cathepsins in Kidney Disease

Kidney disease is worldwide the 12th leading cause of death affecting 8–16% of the entire population. Kidney disease encompasses acute (short-lasting episode) and chronic (developing over years) pathologies both leading to renal failure. Since specific treatments for acute or chronic kidney disease are limited, more than 2 million people a year require dialysis or kidney transplantation. Several recent evidences identified lysosomal proteases cathepsins as key players in kidney pathophysiology. Cathepsins, originally found in the lysosomes, exert important functions also in the cytosol and nucleus of cells as well as in the extracellular space, thus participating in a wide range of physiological and pathological processes. Based on their catalytic active site residue, the 15 human cathepsins identified up to now are classified in three different families: serine (cathepsins A and G), aspartate (cathepsins D and E), or cysteine (cathepsins B, C, F, H, K, L, O, S, V, X, and W) proteases. Specifically in the kidney, cathepsins B, D, L and S have been shown to regulate extracellular matrix homeostasis, autophagy, apoptosis, glomerular permeability, endothelial function, and inflammation. Dysregulation of their expression/activity has been associated to the onset and progression of kidney disease. This review summarizes most of the recent findings that highlight the critical role of cathepsins in kidney disease development and progression. A better understanding of the signaling pathways governed by cathepsins in kidney physiopathology may yield novel selective biomarkers or therapeutic targets for developing specific treatments against kidney disease.

Inhibitory effect of Triperygium wilfordii polyglucoside on dipeptidyl peptidase I in vivo and in vitro

BACKGROUD

Dipeptidyl peptidase I (DPPI), a lysosomal cysteine protease is derived from granule immune cells including mast cell, neutrophils, and toxicity T cells. DPPI can activate serine proteases by removal of dipeptides from N-termini of the pro-proteases, resulting in granule immune cells activation which involved in physiological or pathological responses. Triperygium Wilfordii Polyglucoside (TWP) is one of the traditional Chinese medicines, and commonly used in rheumatoid arthritis (RA) treatment. The present study intended to evaluate the effects of TWP on DPPI activity.

METHODS

In vivo and in vitro studies were carried out to investigate the functions of TWP or triptolide (TP) on DPPI activities in serum, tissues of CIA rats. Rats were divided into five groups randomly: normal group, untreated CIA rat group, TWP treatment CIA groups (the low dose 2.5mg/100g body-weight and high dose 5mg/100g body-weight), and TP treatment CIA group (4μg/100g body-weight). Arthritis development was monitored visually, and joint pathology was examined radiologically. Total protein concentrations in synovial fluids (SFs) were determined by BCA method. Serums and tissue homogenates from CIA rats were collected and DPPI activities were detected using fluorescence substrate GF-AFC. The in vitro interactions between DPPI in serums or in tissue homogenates and TWP or TP were assessed.

RESULTS

TWP-treated CIA rats showed a significant improvement in bone erosion. TWP significantly suppressed paw swelling and total protein concentration in the SFs of CIA rats compared with untreated CIA rats. The elevated activities of DPPI in serums or tissues of CIA rats were significantly inhibited by TWP, but not by TP in vivo. The inhibitory effects of TWP on DPPI activities were also confirm by in vitro study.

CONCLUSION

One of the therapeutic functions of TWP in RA treatment could be inhibiting DPPI activity in serums and synovial tissue produced during RA development, and then reducing inflammatory serine proteases activities and further recovering CIA rats from RA symptoms.

Human Papillomavirus and the Stroma: Bidirectional Crosstalk during the Virus Life Cycle and Carcinogenesis

Human papillomaviruses (HPVs) are double-stranded DNA (dsDNA) tumor viruses that are causally associated with human cancers of the anogenital tract, skin, and oral cavity. Despite the availability of prophylactic vaccines, HPVs remain a major global health issue due to inadequate vaccine availability and vaccination coverage. The HPV life cycle is established and completed in the terminally differentiating stratified epithelia, and decades of research using in vitro organotypic raft cultures and in vivo genetically engineered mouse models have contributed to our understanding of the interactions between HPVs and the epithelium. More recently, important and emerging roles for the underlying stroma, or microenvironment, during the HPV life cycle and HPV-induced disease have become clear. This review discusses the current understanding of the bidirectional communication and relationship between HPV-infected epithelia and the surrounding microenvironment. As is the case with other human cancers, evidence suggests that the stroma functions as a significant partner in tumorigenesis and helps facilitate the oncogenic potential of HPVs in the stratified epithelium.

The Future of Cysteine Cathepsins in Disease Management

Since the discovery of the key role of cathepsin K in bone resorption, cysteine cathepsins have been investigated by pharmaceutical companies as drug targets. The first clinical results from targeting cathepsins by activity-based probes and substrates are paving the way for the next generation of molecular diagnostic imaging, whereas the majority of antibody-drug conjugates currently in clinical trials depend on activation by cathepsins. Finally, cathepsins have emerged as suitable vehicles for targeted drug delivery. It is therefore timely to review the future of cathepsins in drug discovery. We focus here on inflammation-associated diseases because dysregulation of the immune system accompanied by elevated cathepsin activity is a common feature of these conditions.

Cystatin C deficiency suppresses tumor growth in a breast cancer model through decreased proliferation of tumor cells

Cysteine cathepsins are proteases that, in addition to their important physiological functions, have been associated with multiple pathologies, including cancer. Cystatin C (CstC) is a major endogenous inhibitor that regulates the extracellular activity of cysteine cathepsins. We investigated the role of cystatin C in mammary cancer using CstC knockout mice and a mouse model of breast cancer induced by expression of the polyoma middle T oncoprotein (PyMT) in the mammary epithelium. We showed that the ablation of CstC reduced the rate of mammary tumor growth. Notably, a decrease in the proliferation of CstC knockout PyMT tumor cells was demonstrated ex vivo and in vitro, indicating a role for this protease inhibitor in signaling pathways that control cell proliferation. An increase in phosphorylated p-38 was observed in CstC knockout tumors, suggesting a novel function for cystatin C in cancer development, independent of the TGF-β pathway. Moreover, proteomic analysis of the CstC wild-type and knockout PyMT primary cell secretomes revealed a decrease in the levels of 14-3-3 proteins in the secretome of knock-out cells, suggesting a novel link between cysteine cathepsins, cystatin C and 14-3-3 proteins in tumorigenesis, calling for further investigations.

Low expression of angiotensinogen and dipeptidyl peptidase 1 in saliva of patients with proliferative verrucous leukoplakia

AIM

To elucidate the profile of the salivary proteome.

METHODS

Unstimulated whole mouth saliva was collected from 30 volunteers [15 proliferative verrucous leukoplakia (PVL) patients and 15 controls] and proteins were submitted for mass spectrometry-based proteomics using the discovery approach, followed by analyses of variance and logistic regression tests.

RESULTS

A total of two hundred and eighty-three proteins were confidently identified in saliva. By combining two low abundance proteins from the PVL group, angiotensinogen (AGT) and dipeptidyl peptidase 1 (DPP1), a model for group differentiation was built with a concordance index of 94.2%, identifying both proteins as potential etiologic biomarkers for PVL.

CONCLUSION

This study suggests that both AGT and DPP1 may be involved in developmental mechanisms of PVL.

TAILS N-Terminomics and Proteomics Show Protein Degradation Dominates over Proteolytic Processing by Cathepsins in Pancreatic Tumors

Deregulated cathepsin proteolysis occurs across numerous cancers, but in vivo substrates mediating tumorigenesis remain ill-defined. Applying 8-plex iTRAQ terminal amine isotopic labeling of substrates (TAILS), a systems-level N-terminome degradomics approach, we identified cathepsin B, H, L, S, and Z in vivo substrates and cleavage sites with the use of six different cathepsin knockout genotypes in the Rip1-Tag2 mouse model of pancreatic neuroendocrine tumorigenesis. Among 1,935 proteins and 1,114 N termini identified by TAILS, stable proteolytic products were identified in wild-type tumors compared with one or more different cathepsin knockouts (17%-44% of 139 cleavages). This suggests a lack of compensation at the substrate level by other cathepsins. The majority of neo-N termini (56%-83%) for all cathepsins was consistent with protein degradation. We validated substrates, including the glycolytic enzyme pyruvate kinase M2 associated with the Warburg effect, the ER chaperone GRP78, and the oncoprotein prothymosin-alpha. Thus, the identification of cathepsin substrates in tumorigenesis improves the understanding of cathepsin functions in normal physiology and cancer.

Immune Regulation of the Metastatic Process: Implications for Therapy

Metastatic disease is the major cause of fatalities in cancer patients, but few therapies are designed to target the metastatic process. Cancer cells must perform a number of steps to successfully establish metastatic foci, including local invasion, intravasation, survival, extravasation, and growth in ectopic tissue. Due to the nonrandom distribution of metastasis, it has long been recognized that the tissue microenvironment must be an important determinant of colonization. More recently it has been established in animal models that immune cells regulate the metastatic process, including a dominant role for monocytes and macrophages, and emerging roles for neutrophils and various lymphocyte populations. While most research has focused on the early dissemination process, patients usually present clinically with disseminated, if not macroscopic, disease. Identifying pathways by which immune cells regulate growth and therapeutic resistance within metastatic sites is therefore key to the development of pharmacological agents that will significantly extend patient survival.

Combined deletion of cathepsin protease family members reveals compensatory mechanisms in cancer

In this study, Akkari et al. show the stage-dependent effects of simultaneously deleting cathepsin B (CtsB) and CtsS in a murine pancreatic neuroendocrine tumor model. They also identified CtsZ as the compensatory protease that regulates the acquired tumor-promoting functions of lesions deficient in both CtsB and CtsS, thus providing insight into a novel mechanism regulating tumorigenesis.

Proteases are important for regulating multiple tumorigenic processes, including angiogenesis, tumor growth, and invasion. Elevated protease expression is associated with poor patient prognosis across numerous tumor types. Several multigene protease families have been implicated in cancer, including cysteine cathepsins. However, whether individual family members have unique roles or are functionally redundant remains poorly understood. Here we demonstrate stage-dependent effects of simultaneously deleting cathepsin B (CtsB) and CtsS in a murine pancreatic neuroendocrine tumor model. Early in tumorigenesis, the double knockout results in an additive reduction in angiogenic switching, whereas at late stages, several tumorigenic phenotypes are unexpectedly restored to wild-type levels. We identified CtsZ, which is predominantly supplied by tumor-associated macrophages, as the compensatory protease that regulates the acquired tumor-promoting functions of lesions deficient in both CtsB and CtsS. Thus, deletion of multiple cathepsins can lead to stage-dependent, compensatory mechanisms in the tumor microenvironment, which has potential implications for the clinical consideration of selective versus pan-family cathepsin inhibitors in cancer.

HDAC Inhibitors Enhance T-Cell Chemokine Expression and Augment Response to PD-1 Immunotherapy in Lung Adenocarcinoma

PURPOSE

A significant limitation of checkpoint blockade immunotherapy is the relatively low response rate (e.g., ∼20% with PD-1 blockade in lung cancer). In this study, we tested whether strategies that increase T-cell infiltration to tumors can be efficacious in enhancing immunotherapy response.

EXPERIMENTAL DESIGN

We performed an unbiased screen to identify FDA-approved oncology agents with an ability to enhance T-cell chemokine expression with the goal of identifying agents capable of augmenting immunotherapy response. Identified agents were tested in multiple lung tumor models as single agents and in combination with PD-1 blockade. Additional molecular and cellular analysis of tumors was used to define underlying mechanisms.

RESULTS

We found that histone deacetylase (HDAC) inhibitors (HDACi) increased expression of multiple T-cell chemokines in cancer cells, macrophages, and T cells. Using the HDACi romidepsin in vivo, we observed increased chemokine expression, enhanced T-cell infiltration, and T-cell-dependent tumor regression. Importantly, romidepsin significantly enhanced the response to PD-1 blockade immunotherapy in multiple lung tumor models, including nearly complete rejection in two models. Combined romidepsin and PD-1 blockade also significantly enhanced activation of tumor-infiltrating T cells.

CONCLUSIONS

These results provide evidence for a novel role of HDACs in modulating T-cell chemokine expression in multiple cell types. In addition, our findings indicate that pharmacologic induction of T-cell chemokine expression represents a conceptually novel approach for enhancing immunotherapy response. Finally, these results suggest that combination of HDAC inhibitors with PD-1 blockade represents a promising strategy for lung cancer treatment. Clin Cancer Res; 22(16); 4119-32. ©2016 AACR.

Neutrophilic Cathepsin C Is Maturated by a Multistep Proteolytic Process and Secreted by Activated Cells during Inflammatory Lung Diseases

The cysteine protease cathepsin C (CatC) activates granule-associated proinflammatory serine proteases in hematopoietic precursor cells. Its early inhibition in the bone marrow is regarded as a new therapeutic strategy for treating proteolysis-driven chronic inflammatory diseases, but its complete inhibition is elusive in vivo Controlling the activity of CatC may be achieved by directly inhibiting its activity with a specific inhibitor or/and by preventing its maturation. We have investigated immunochemically and kinetically the occurrence of CatC and its proform in human hematopoietic precursor cells and in differentiated mature immune cells in lung secretions. The maturation of proCatC obeys a multistep mechanism that can be entirely managed by CatS in neutrophilic precursor cells. CatS inhibition by a cell-permeable inhibitor abrogated the release of the heavy and light chains from proCatC and blocked ∼80% of CatC activity. Under these conditions the activity of neutrophil serine proteases, however, was not abolished in precursor cell cultures. In patients with neutrophilic lung inflammation, mature CatC is found in large amounts in sputa. It is secreted by activated neutrophils as confirmed through lipopolysaccharide administration in a nonhuman primate model. CatS inhibitors currently in clinical trials are expected to decrease the activity of neutrophilic CatC without affecting those of elastase-like serine proteases.

Mouse Models of Tumor Immunotherapy

Immunotherapy is now evolving into a major therapeutic option for cancer patients. Such clinical advances also promote massive interest in the search for novel immunotherapy targets, and to understand the mechanism of action of current drugs. It is projected that a series of novel immunotherapy agents will be developed and assessed for their therapeutic activity. In light of this, in vivo experimental mouse models that recapitulate human malignancies serve as valuable tools to validate the efficacy and safety profile of immunotherapy agents, before their transition into clinical trials. In this review, we will discuss the major classes of experimental mouse models of cancer commonly used for immunotherapy assessment and provide examples to guide the selection of appropriate models. We present some new data concerning the utility of a carcinogen-induced tumor model for comparing immunotherapies and combining immunotherapy with chemotherapy. We will also highlight some recent advances in experimental modeling of human malignancies in mice that are leading towards personalized therapy in patients.

Neutrophils in the Tumor Microenvironment

Neutrophils are the first responders to sites of acute tissue damage and infection. Recent studies suggest that in addition to neutrophil apoptosis, resolution of neutrophil inflammation at wounds can be mediated by reverse migration from tissues and transmigration back into the vasculature. In settings of chronic inflammation, neutrophils persist in tissues, and this persistence has been associated with cancer progression. However, the role of neutrophils in the tumor microenvironment remains controversial, with evidence for both pro- and anti-tumor roles. Here we review the mechanisms that regulate neutrophil recruitment and resolution at sites of tissue damage, with a specific focus on the tumor microenvironment. We discuss the current understanding as to how neutrophils alter the tumor microenvironment to support or hinder cancer progression, and in this context outline gaps in understanding and important areas of inquiry.

Cysteine cathepsin proteases: regulators of cancer progression and therapeutic response

Cysteine cathepsin protease activity is frequently dysregulated in the context of neoplastic transformation. Increased activity and aberrant localization of proteases within the tumour microenvironment have a potent role in driving cancer progression, proliferation, invasion and metastasis. Recent studies have also uncovered functions for cathepsins in the suppression of the response to therapeutic intervention in various malignancies. However, cathepsins can be either tumour promoting or tumour suppressive depending on the context, which emphasizes the importance of rigorous in vivo analyses to ascertain function. Here, we review the basic research and clinical findings that underlie the roles of cathepsins in cancer, and provide a roadmap for the rational integration of cathepsin-targeting agents into clinical treatment.

Cell cycle- and cancer-associated gene networks activated by Dsg2: evidence of cystatin A deregulation and a potential role in cell-cell adhesion

Cell-cell adhesion is paramount in providing and maintaining multicellular structure and signal transmission between cells. In the skin, disruption to desmosomal regulated intercellular connectivity may lead to disorders of keratinization and hyperproliferative disease including cancer. Recently we showed transgenic mice overexpressing desmoglein 2 (Dsg2) in the epidermis develop hyperplasia. Following microarray and gene network analysis, we demonstrate that Dsg2 caused a profound change in the transcriptome of keratinocytes in vivo and altered a number of genes important in epithelial dysplasia including: calcium-binding proteins (S100A8 and S100A9), members of the cyclin protein family, and the cysteine protease inhibitor cystatin A (CSTA). CSTA is deregulated in several skin cancers, including squamous cell carcinomas (SCC) and loss of function mutations lead to recessive skin fragility disorders. The microarray results were confirmed by qPCR, immunoblotting, and immunohistochemistry. CSTA was detected at high level throughout the newborn mouse epidermis but dramatically decreased with development and was detected predominantly in the differentiated layers. In human keratinocytes, knockdown of Dsg2 by siRNA or shRNA reduced CSTA expression. Furthermore, siRNA knockdown of CSTA resulted in cytoplasmic localization of Dsg2, perturbed cytokeratin 14 staining and reduced levels of desmoplakin in response to mechanical stretching. Both knockdown of either Dsg2 or CSTA induced loss of cell adhesion in a dispase-based assay and the effect was synergistic. Our findings here offer a novel pathway of CSTA regulation involving Dsg2 and a potential crosstalk between Dsg2 and CSTA that modulates cell adhesion. These results further support the recent human genetic findings that loss of function mutations in the CSTA gene result in skin fragility due to impaired cell-cell adhesion: autosomal-recessive exfoliative ichthyosis or acral peeling skin syndrome.

Lysosomal protein turnover contributes to the acquisition of TGFβ-1 induced invasive properties of mammary cancer cells

Background

Normal epithelial cells and carcinoma cells can acquire invasiveness by epithelial-to-mesenchymal transition (EMT), a process of considerable cellular remodeling. The endosomal/lysosomal compartment is a principal site of intracellular protein degradation. Lysosomal cathepsin proteases are secreted during cancer progression. The established pro-metastatic role of specific cysteine cathepsins has until now been ascribed to their contribution to extracellular matrix remodeling. We hypothesized that cysteine cathepsins affect transforming growth factor β-1 (TGFβ-1)-induced EMT of normal and malignant mammary epithelial cells.

Methods

The role of lysosomal proteolysis in TGFβ-1-induced EMT and invasion was investigated in a normal and a novel malignant murine mammary epithelial cell line. The contribution of cysteine cathepsins was determined by addition of the general cysteine cathepsin inhibitor E64d. Hallmarks of EMT were analyzed by molecular- and cell-biologic analyses including real-time cell migration/invasion assays. A quantitative proteome comparison using stable isotopic labeling with amino acids in culture (SILAC) showed the effect of E64d on TGFβ-1 induced proteome changes. Lysosomal patterning and junctional adhesion molecule A (Jam-a) localization and abundance were analyzed by immunofluorescence.

Results

We found increased lysosome activity during EMT of malignant mammary epithelial cells. Cysteine cathepsin inhibition had no effect on the induction of the TGFβ-1-induced EMT program on transcriptional level. Protease inhibition did not affect invasion of TGFβ-1 treated normal mammary epithelial cells, but reduced the invasion of murine breast cancer cells. Remarkably, reduced invasion was also evident if E64d was removed 24 h before the invasion assay in order to allow for recovery of cathepsin activity. Proteome analyses revealed a high abundance of lysosomal enzymes and lysosome-associated proteins in cancer cells treated with TGFβ-1 and E64d. An accumulation of those proteins and of lysosomal vesicles was further confirmed by independent methods. Interestingly, E64d caused lysosomal accumulation of Jam-a, a tight junction component facilitating epithelial cell-cell adhesion.

Conclusion

Our results demonstrate an important role of lysosomal proteolysis in cellular remodeling during EMT and a pivotal contribution of lysosomal cysteine cathepsins to TGFβ-1 induced acquisition of breast cancer cell invasiveness. These findings provide an additional rationale to use cathepsin inhibitors to stall tumor metastasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0313-5) contains supplementary material, which is available to authorized users.

Pericellular proteolysis in cancer

Pericellular proteases have long been associated with cancer invasion and metastasis due to their ability to degrade extracellular matrix components. Recent studies demonstrate that proteases also modulate tumor progression and metastasis through highly regulated and complex processes involving cleavage, processing, or shedding of cell adhesion molecules, growth factors, cytokines, and kinases. In this review, we address how cancer cells, together with their surrounding microenvironment, regulate pericellular proteolysis. We dissect the multitude of mechanisms by which pericellular proteases contribute to cancer progression and discuss how this knowledge can be integrated into therapeutic opportunities.

HPV16-E7 expression in squamous epithelium creates a local immune suppressive environment via CCL2- and CCL5- mediated recruitment of mast cells

Human Papillomavirus (HPV) 16 E7 protein promotes the transformation of HPV infected epithelium to malignancy. Here, we use a murine model in which the E7 protein of HPV16 is expressed as a transgene in epithelium to show that mast cells are recruited to the basal layer of E7-expressing epithelium, and that this recruitment is dependent on the epithelial hyperproliferation induced by E7 by inactivating Rb dependent cell cycle regulation. E7 induced epithelial hyperplasia is associated with increased epidermal secretion of CCL2 and CCL5 chemokines, which attract mast cells to the skin. Mast cells in E7 transgenic skin, in contrast to those in non-transgenic skin, exhibit degranulation. Notably, we found that resident mast cells in E7 transgenic skin cause local immune suppression as evidenced by tolerance of E7 transgenic skin grafts when mast cells are present compared to the rejection of mast cell-deficient E7 grafts in otherwise competent hosts. Thus, our findings suggest that mast cells, recruited towards CCL2 and CCL5 expressed by epithelium induced to proliferate by E7, may contribute to an immunosuppressive environment that enables the persistence of HPV E7 protein induced pre-cancerous lesions.

Cathepsin B: multiple roles in cancer

Proteases, including intracellular proteases, play roles at many different stages of malignant progression. Our focus here is cathepsin B, a lysosomal cysteine cathepsin. High levels of cathepsin B are found in a wide variety of human cancers, levels that often induce secretion and association of cathepsin B with the tumor cell membrane. In experimental models, such as transgenic models of murine pancreatic and mammary carcinomas, causal roles for cathepsin B have been demonstrated in initiation, growth/tumor cell proliferation, angiogenesis, invasion, and metastasis. Tumor growth in transgenic models is promoted by cathepsin B in tumor-associated cells, for example, tumor-associated macrophages, as well as in tumor cells. In transgenic models, the absence of cathepsin B has been associated with enhanced apoptosis, yet cathepsin B also has been shown to contribute to apoptosis. Cathepsin B is part of a proteolytic pathway identified in xenograft models of human glioma; targeting only cathepsin B in these tumors is less effective than targeting cathepsin B in combination with other proteases or protease receptors. Understanding the mechanisms responsible for increased expression of cathepsin B in tumors and association of cathepsin B with tumor cell membranes is needed to determine whether targeting cathepsin B could be of therapeutic benefit.