ReviewTumor cell- and microenvironment-specific roles of cysteine cathepsins in mouse models of human cancers
Introduction
The lysosome hosts a large variety of more than 60 degradative enzymes [1]. Among the lysosomal proteases the Clan CA family C1 peptidases, the so called cysteine cathepsins, comprise the largest group with 11 members [2]. These are cathepsin B (CtsB), cathepsin C (CtsC), cathepsin F (CtsF), cathepsin H (CtsH), cathepsin K (CtsK), cathepsin L (CtsL), cathepsin O (CtsO), cathepsin S (CtsS), cathepsin V (CtsV, also cathepsin L2), cathepsin W (CtsW), and cathepsin Z (CtsZ, also cathepsin X). Mice lack CtsV but express eight cathepsin L-like cathepsins specifically in the placenta [3,4]. The cysteine cathepsins have been investigated extensively for their diverse roles in cancer [5,6]. Cell-based assays revealed their involvement in regulation of proliferation, death, and motility of cancer cells. Proteomic analyses have started to identify the relevant substrates of the cathepsin proteases. Furthermore, clinical as well as histopathological studies have evaluated the role of cathepsins as markers for prognosis and therapy response. The important link between mechanistic in vitro experiments and clinical relevance has been provided by animal studies, mostly employing laboratory mice as model system. Systematic preclinical cancer treatment trials with cathepsin inhibitors have been rarely performed because of limited selectivity and poor pharmacokinetics of the existing small molecules for cathepsin inhibition [[7], [8], [9], [10]]. Hence, genetic approaches have been widely used to study the in vivo roles of cathepsin proteases in cancer cells and in cells of the tumor microenvironment. Here we will review the evidence obtained for the differential roles of cysteine cathepsins in murine cancer models during the past 15 years.
There are two principal approaches to study cancer in mice [11,12]. In the first approach – so called de novo carcinogenesis models – normal cells of living mice are gradually transformed to invasive and eventually metastatic cancer cells upon the action of mutagenic chemicals or by genetic activation or inactivation of oncogenes or tumor suppressors, respectively (Table 1). Both genetic and chemical induction of tumors allow to study the classical stepwise carcinogenesis process including the gradual adaptation of the tumor microenvironment concerning matrix remodeling, angiogenesis, and tumor-associated inflammation. These models, however, are usually laborious and often require extensive time periods of one year or even longer to achieve end-stage tumors.
The second approach to study cancer in mice is the transfer of cancer cells into the animals (Fig. 1). Those models have the advantage of a well-defined start of the experiment, highly reproducible growth rates and usually well manageable tumor growth periods of a few weeks. Their disadvantage is that the injected cancer cells have already undergone the full malignant transformation process. Therefore, the co-evolution of cancer cells and their environment cannot be readily studied in those models. The transfer of human cancer cells or tumor specimen into mice is generally complicated by an unwanted clearance of the foreign cells by the mouse immune system. To allow for tumor growth, human material is usually injected into immunocompromised mice lacking at least T- and B-cells. Naturally, these so called xenograft tumor models do not mimic the immunological situation in patients with an intact immune system. The more widespread use of immunologically humanized mice is likely to overcome these limitations [13]. The injection of mouse cancer cells into recipient mice of the same genetic background does not face the challenge of immunological graft rejection. Therefore, these syngeneic allograft models have been popular for the study of host responses to a cancer (Fig. 1). The matter is further complicated by the fact that the cancer cells are often injected subcutaneously to the flanks of mice, an anatomical site noticeably different to the tissue from which the initial tumor originated. Those heterotopic models are clearly inferior to orthotopic models, in which the cells are injected into the tissue of origin thereby mimicking the site-specific conditions far more accurately [14].
Many published reports used genetic tools to downregulate or overexpress cathepsins in cancer cells and subjected them to xenograft in vivo studies. Those studies provided valuable insights into cancer cell autonomous functions of the cathepsins and some explored even combinatory effects of CtsB and matrix metalloprotease 9 (MMP9) or CtsB and urokinase-type plasminogen activator receptor (uPAR) downregulations in orthotopic models [15,16]. However, due to the limitations of the xenograft approach we will focus this review on the models of de novo carcinogenesis and to syngeneic allograft approaches that allowed to address the role of cathepsins in non-malignant tumor-associated cells.
Section snippets
Cysteine cathepsins in invasive growth and angiogenesis of pancreatic cancers
The Rip1-Tag2 mouse model is a seminal transgenic model to study oncogene-induced de novo carcinogenesis [17]. The rat insulin promoter (Rip1) directs expression of the Simian virus 40 large T-antigen (Tag2) specifically to the endocrine β-cells of the pancreas. This causes induction of pancreatic neuroendocrine tumors that develop progressively towards invasive pancreatic β-cell carcinomas [18]. In the first study on cathepsins in this model, collective cysteine cathepsin inhibition by the
Exploring the role of stroma-derived cathepsins in the tumor microenvironment using tumor cell transplantation models
It is commonly accepted that epithelial cells bearing oncogenic mutations are not solely responsible for carcinoma progression [[66], [67], [68], [69], [70]]. Rather, tumors develop in a complex relationship of cancer cells with their surrounding stroma. The stroma consists of endothelial and other vasculature cells, resident cells like fibroblasts, and tumor-associated immune cells including leukocytes and macrophages [68,69] as well as ECM components [71]. This tumor microenvironment actively
Concluding remarks
The efforts to elucidate specific in vivo roles of cysteine cathepsins in complex immunocompetent models revealed in many instances their tumor-promoting role in cancer cells, tumor-associated immune cells, or both. However, in some models the genetic manipulation of cathepsins had no influence on cancer growth or metastasis (Table 1). Even worse, knock-out of CtsL had a detrimental effect in some cancer models (see Section 2.4; Table 1). Hence, for upholding cathepsin inhibition as therapeutic
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The Deutsche Forschungsgemeinschaft (DFG) SFB 850 subproject B7, DFG-grant RE1584/6-2 and the German Cancer Consortium (DKTK) program Oncogenic Pathways project L627 support the work in the Reinheckel laboratory.
References (99)
- et al.
Cysteine cathepsins: from structure, function and regulation to new frontiers
Biochim. Biophys. Acta, Proteins Proteomics
(2012) Emerging functions of placental cathepsins
Placenta
(2008)- et al.
Identification and pre-clinical testing of a reversible cathepsin protease inhibitor reveals anti-tumor efficacy in a pancreatic cancer model
Biochimie
(2010) - et al.
A preclinical model for erα-positive breast cancer points to the epithelial microenvironment as determinant of luminal phenotype and hormone response
Cancer Cell
(2016) - et al.
Cathepsin cysteine proteases are effectors of invasive growth and angiogenesis during multistage tumorigenesis
Cancer Cell
(2004) - et al.
Cathepsin S controls angiogenesis and tumor growth via Matrix-derived angiogenic factors
J. Biol. Chem.
(2006) - et al.
Pancreatic ductal adenocarcinoma: State-of-the-art 2017 and new therapeutic strategies
Cancer Treat. Rev.
(2017) - et al.
Trp53R172H and KrasG12D cooperate to promote chromosomal instability and widely metastatic pancreatic ductal adenocarcinoma in mice
Cancer Cell
(2005) - et al.
Cellular transformation by Simian Virus 40 and Murine Polyoma Virus T antigens
Semin. Cancer Biol.
(2009) - et al.
Progression to malignancy in the polyoma middle T oncoprotein mouse breast cancer model provides a reliable model for human diseases
Am. J. Pathol.
(2003)
Stress-resistant translation of Cathepsin L mRNA in breast cancer progression
J. Biol. Chem.
Cystatins in cancer progression: more than just cathepsin inhibitors
Biochimie
Multistage carcinogenesis in mouse skin
Pharmacol. Ther.
ApcMin: a mouse model for intestinal and mammary tumorigenesis
Eur. J. Cancer
Cathepsin L targeting in cancer treatment
Pharmacol. Ther.
Cathepsin D in pancreatic acinar cells is implicated in cathepsin B and L degradation, but not in autophagic activity
Biochem. Biophys. Res. Commun.
Neuroectoderm-specific deletion of cathepsin D in mice models human inherited neuronal ceroid lipofuscinosis type 10
Biochimie
Accessories to the crime: functions of cells recruited to the tumor microenvironment
Cancer Cell
The organizing principle: microenvironmental influences in the normal and malignant breast
Differentiation
Biophysics of tumor microenvironment and cancer metastasis - a mini review
Comput. Struct. Biotechnol. J.
Hallmarks of cancer: the next generation
Cell.
Complexity of cancer protease biology: Cathepsin K expression and function in cancer progression
Semin. Cancer Biol.
Dual contrasting roles of cysteine cathepsins in cancer progression: apoptosis versus tumour invasion
Biochimie
Cysteine cathepsins: cellular roadmap to different functions
Biochimie
Stefin A-functionalized liposomes as a system for cathepsins S and L-targeted drug delivery
Biochimie
Imaging of extracellular cathepsin S activity by a selective near infrared fluorescence substrate-based probe
Biochimie
The proteome of lysosomes
Proteomics
Specialized roles for cysteine cathepsins in health and disease
J. Clin. Invest.
Cysteine cathepsins: multifunctional enzymes in cancer
Nat. Rev. Cancer
Cysteine cathepsin proteases: regulators of cancer progression and therapeutic response
Nat. Rev. Cancer
Macrophages and cathepsin proteases blunt chemotherapeutic response in breast cancer
Genes Dev.
Trial of the cysteine cathepsin inhibitor JPM-OEt on early and advanced mammary cancer stages in the MMTV-PyMT-transgenic mouse model
Biol. Chem.
Multiple roles for cysteine cathepsins in cancer
Cell Cycle
Genetically engineered mouse models in oncology research and cancer medicine
EMBO Mol. Med.
The origins of oncomice: a history of the first transgenic mice genetically engineered to develop cancer
Genes Dev.
Humanized mouse models of clinical disease
Annu. Rev. Pathol. Mech. Dis.
Cathepsin B and uPAR regulate self-renewal of glioma-initiating cells through GLI-regulated Sox2 and Bmi1 expression
Carcinogenesis
Targeting MMP-9, uPAR, and cathepsin B inhibits invasion, migration and activates apoptosis in prostate cancer cells
Cancer Gene Ther.
Heritable formation of pancreatic β-cell tumours in transgenic mice expressing recombinant insulin/simian virus 40 oncogenes
Nature
A second signal supplied by insulin-like growth factor II in oncogene-induced tumorigenesis
Nature
Distinct functions of macrophage-derived and cancer cell-derived cathepsin Z combine to promote tumor malignancy via interactions with the extracellular matrix
Genes Dev.
Combined deletion of cathepsin protease family members reveals compensatory mechanisms in cancer
Genes Dev.
Deletion of cathepsin H perturbs angiogenic switching, vascularization and growth of tumors in a mouse model of pancreatic islet cell cancer
Biol. Chem.
Distinct roles for cysteine cathepsin genes in multistage tumorigenesis
Genes Dev.
Cathepsin B promotes the progression of pancreatic ductal adenocarcinoma in mice
Gut
Secreted cathepsin L generates endostatin from collagen XVIII
EMBO J.
Cathepsin L is required for endothelial progenitor cell–induced neovascularization
Nat. Med.
Deficiency for the cysteine protease Cathepsin L Impairs Myc-Induced tumorigenesis in a mouse model of pancreatic neuroendocrine cancer
PLoS One
Differences in secretion of the proteinase cathepsin B at the edges of human breast carcinomas and fibroadenomas
Nature
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2022, Encyclopedia of Cell Biology: Volume 1-6, Second EditionXPA is susceptible to proteolytic cleavage by cathepsin L during lysis of quiescent cells
2022, DNA RepairCitation Excerpt :We conclude that a cysteine protease is primarily responsible for acting on the C-terminus of XPA. Interestingly, previous studies have shown that the expression and/or activity of several cathepsin proteins, which are a major class of cysteine proteases [29,30], are elevated in quiescent and/or confluent cells [31,32]. Consistent with this data, we found that expression of both cathepsin B and L (CTSB and CTSL) were significantly elevated at the protein level in lysates from confluent HaCaT cells in comparison to sub-confluent, proliferating cells (Fig. 2B and Fig. S5B).
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