The candidate tumor suppressor CST6 alters the gene expression profile of human breast carcinoma cells: down-regulation of the potent mitogenic, motogenic, and angiogenic factor autotaxin

Cystatin M/E (Cystatin 6): A Janus-Faced Cysteine Protease Inhibitor with Both Tumor-Suppressing and Tumor-Promoting Functions

Alongside its contribution in maintaining skin homeostasis and its probable involvement in fetal and placental development, cystatin M/E (also known as cystatin 6) was first described as a tumor suppressor of breast cancer. This review aims to provide an update on cystatin M/E with particular attention paid to its role during tumorigenesis. Cystatin M/E, which is related to type 2 cystatins, displays the unique property of being a dual tight-binding inhibitor of both legumain (also known as asparagine endopeptidase) and cysteine cathepsins L, V and B, while its expression level is epigenetically regulated via the methylation of the CST6 promoter region. The tumor-suppressing role of cystatin M/E was further reported in melanoma, cervical, brain, prostate, gastric and renal cancers, and cystatin M/E was proposed as a biomarker of prognostic significance. Contrariwise, cystatin M/E could have an antagonistic function, acting as a tumor promoter (e.g., oral, pancreatic cancer, thyroid and hepatocellular carcinoma). Taking into account these apparently divergent functions, there is an urgent need to decipher the molecular and cellular regulatory mechanisms of the expression and activity of cystatin M/E associated with the safeguarding homeostasis of the proteolytic balance as well as its imbalance in cancer.

Cystatins in cancer progression: More than just cathepsin inhibitors

Cystatins are endogenous and reversible inhibitors of cysteine peptidases that are important players in cancer progression. Besides their primary role as regulators of cysteine peptidase activity, cystatins are involved in cancer development and progression through proteolysis-independent mechanisms. Mechanistic studies of cystatin function revealed that they affect all stages of cancer progression including tumor growth, apoptosis, invasion, metastasis and angiogenesis. Recently, the involvement of cystatins in the antitumor immune responses was reported. In this review, we discuss molecular mechanisms and clinical aspects of cystatins in cancer. Altered expression of cystatins in cancer resulting in harmful excessive cysteine peptidase activity has been a subject of several studies in order to find correlations with clinical outcome and therapy response. However, involvement in anti-tumor immune response and signaling cascades leading to cancer progression designates cystatins as possible targets for development of new anti-tumor drugs.

In Silico Analysis Validates Proteomic Findings of Formalin-fixed Paraffin Embedded Cutaneous Squamous Cell Carcinoma Tissue

BACKGROUND

Cutaneous squamous cell carcinoma (cSCC) is a common type of skin cancer but there are no comprehensive proteomic studies on this entity.

MATERIALS AND METHODS

We employed liquid chromatography coupled with tandem mass spectrometry (MS/MS) using formalin-fixed paraffin-embedded (FFPE) cSCC material to study the tumor and normal skin tissue proteomes. Ingenuity Pathway Analysis (IPA) was used to interpret the role of altered proteins in cSCC pathophysiology. Results were validated using the Human Protein Atlas and Oncomine database in silico.

RESULTS

Of 1,310 unique proteins identified, expression of an average of 144 and 88 proteins were significantly (p<0.05) increased and decreased, respectively, in the tumor samples compared to their normal counterparts. IPA analysis revealed disruptions in proteins associated with cell proliferation, apoptosis, and migration. In silico analysis confirmed that proteins corresponding to 12 antibodies, and genes corresponding to 18 proteins were differentially expressed between the two categories, validating our proteomic measurements.

CONCLUSION

Label-free MS-based proteomics is useful for analyzing FFPE cSCC tissues.

Effects of dietary supplementation with EPA and/or α-lipoic acid on adipose tissue transcriptomic profile of healthy overweight/obese women following a hypocaloric diet

In obesity, the increment of adiposity levels disrupts the whole body homeostasis, promoting an over production of oxidants and inflammatory mediators. The current study aimed to characterize the transcriptomic changes promoted by supplementation with eicosapentaenoic acid (EPA, 1.3 g/day), α-lipoic acid (0.3 g/day), or both (EPA + α-lipoic acid, 1.3 g/day + 0.3 g/day) in subcutaneous abdominal adipose tissue from overweight/obese healthy women, who followed a hypocaloric diet (30% of total energy expenditure) during ten weeks, by using a microarray approach. At the end of the intervention, a total of 33,297 genes were analyzed using Affymetrix GeneChip arrays. EPA promoted changes in extracellular matrix remodeling gene expression, besides a rise of genes associated with either chemotaxis or wound repair. α-Lipoic acid decreased expression of genes related with cell adhesion and inflammation. Furthermore, α-lipoic acid, especially in combination with EPA, upregulated the expression of genes associated with lipid catabolism while downregulated genes involved in lipids storage. Together, all these data suggest that some of the metabolic effects of EPA and α-lipoic acid could be related to their regulatory actions on adipose tissue metabolism. © 2016 BioFactors, 43(1):117-131, 2017.

Cystatins in immune system

Cystatins comprise a large superfamily of related proteins with diverse biological activities. They were initially characterised as inhibitors of lysosomal cysteine proteases, however, in recent years some alternative functions for cystatins have been proposed. Cystatins possessing inhibitory function are members of three families, family I (stefins), family II (cystatins) and family III (kininogens). Stefin A is often linked to neoplastic changes in epithelium while another family I cystatin, stefin B is supposed to have a specific role in neuredegenerative diseases. Cystatin C, a typical type II cystatin, is expressed in a variety of human tissues and cells. On the other hand, expression of other type II cystatins is more specific. Cystatin F is an endo/lysosome targeted protease inhibitor, selectively expressed in immune cells, suggesting its role in processes related to immune response. Our recent work points on its role in regulation of dendritic cell maturation and in natural killer cells functional inactivation that may enhance tumor survival. Cystatin E/M expression is mainly restricted to the epithelia of the skin which emphasizes its prominent role in cutaneous biology. Here, we review the current knowledge on type I (stefins A and B) and type II cystatins (cystatins C, F and E/M) in pathologies, with particular emphasis on their suppressive vs. promotional function in the tumorigenesis and metastasis. We proposed that an imbalance between cathepsins and cystatins may attenuate immune cell functions and facilitate tumor cell invasion.

Stat3 mediates expression of autotaxin in breast cancer

We determined that signal transducer and activator of transcription 3 (Stat3) is tyrosine phosphorylated in 37% of primary breast tumors and 63% of paired metastatic axillary lymph nodes. Examination of the distribution of tyrosine phosphorylated (pStat3) in primary tumors revealed heterogenous expression within the tumor with the highest levels found in cells on the edge of tumors with relatively lower levels in the central portion of tumors. In order to determine Stat3 target genes that may be involved in migration and metastasis, we identified those genes that were differentially expressed in primary breast cancer samples as a function of pStat3 levels. In addition to known Stat3 transcriptional targets (Twist, Snail, Tenascin-C and IL-8), we identified ENPP2 as a novel Stat3 regulated gene, which encodes autotaxin (ATX), a secreted lysophospholipase which mediates mammary tumorigenesis and cancer cell migration. A positive correlation between nuclear pStat3 and ATX was determined by immunohistochemical analysis of primary breast cancer samples and matched axillary lymph nodes and in several breast cancer derived cell lines. Inhibition of pStat3 or reducing Stat3 expression led to a decrease in ATX levels and cell migration. An association between Stat3 and the ATX promoter, which contains a number of putative Stat3 binding sites, was determined by chromatin immunoprecipitation. These observations suggest that activated Stat3 may regulate the migration of breast cancer cells through the regulation of ATX.

Recombinant snake venom cystatin inhibits the growth, invasion and metastasis of B16F10 cells and MHCC97H cells in vitro and in vivo

Studies have shown that expression of snake venom cystatin (sv-cystatin) in mouse melanoma cells and human gastric carcinoma cells can inhibit their invasion and metastasis. To advance the research into the biological features and pharmaceutical applications of sv-cystatin, we investigated the expression of recombinant sv-cystatin in an optimized Pichia pastoris system. Approximately 5 mg/L of bioactive sv-cystatin was obtained with a purity of 95.08%. Kinetic analyses of recombinant sv-cystatin revealed highly effective inhibitory efficiency against papain (Ki = 2.67 nM). We further investigated the effects of recombinant sv-cystatin on the invasion and metastasis of B16F10 cells and MHCC97H cells in vitro and in vivo. Matrigel invasion assays showed significant inhibition of recombinant sv-cystatin on the tumor cells in vitro. For experimental lung colonization assays, C57BL/6 mice inoculated in the lateral tail vein with B16F10 cells were treated with three i.v. injections of recombinant sv-cystatin (25 and 50 mg/kg) 24 h before cell inoculation, and 2 h and 24 h after cell inoculation. Administration of recombinant sv-cystatin significantly suppressed the formation of lung tumor colonies. For spontaneous metastasis assays, MHCC97H cells were inoculated s.c. into nude mice. After 24 h, recombinant sv-cystatin was administered by i.p. injections at 25, 50 or 100 mg/kg once daily for 5 days. Administration of recombinant sv-cystatin significantly decreased the formation of lung tumor colonies. Taken together, recombinant sv-cystatin inhibits the invasion and metastasis of tumor cells in vitro and in vivo. These results may facilitate the future evaluation of the pharmaceutical applications of sv-cystatin.

Cystatin M loss is associated with the losses of estrogen receptor, progesterone receptor, and HER4 in invasive breast cancer

Introduction

This study was aimed at understanding the clinicopathological significance of cystatin M loss, and investigating possible factors responsible for cystatin M loss in breast cancer.

Methods

The expression of estrogen receptor (ER), progesterone receptor (PR), HER2, HER4, and cystatin M was retrospectively analyzed using immunohistochemistry in 117 patients with ductal carcinoma in situ (DCIS) and in 175 patients with invasive breast cancer (IBC). The methylation status of CST6 gene encoding cystatin M was evaluated using methylation-specific polymerase chain reaction (PCR) in formalin-fixed paraffin-embedded tissues from 292 participants and using pyrosequencing in fresh-frozen tumor and matched normal tissues from 51 IBC patients.

Results

Cystatin M loss was found in 9 (8%) of 117 patients with DCIS and in 99 (57%) of 175 with invasive breast cancer (IBC) (P < 0.0001). Cystatin M loss was found in 58 (57%) of 101 HER2-negative IBCs and in 41 (55%) of 74 HER2-positive IBCs, and this difference was not statistically significant (P = 0.97). However, cystatin M loss was significantly associated with the loss of ER (P = 0.01), PR (P = 0.002), and HER4 (P = 0.003) in IBCs. Cystatin M loss occurred in 34 (76%) of the 45 HER4-negative IBCs and in 65 (50%) of the 130 HER4-positive IBCs. Multivariate analysis showed that cystatin M loss occurred at a 3.57 times (95% CI = 1.28 to 9.98; P = 0.01) higher prevalence in the triple-negative IBCs of ER, PR, and HER4 than in other subtypes, after adjusting for age. The quantity of CST6 methylation was associated with ER loss (P = 0.0002) in IBCs but not with the loss of PR (P = 0.64) or HER4 (P = 0.87).

Conclusions

The present study suggests that cystatin M loss may be associated with the losses of ER, PR, and HER4 in IBC.

Regulation of lysophosphatidate signaling by autotaxin and lipid phosphate phosphatases with respect to tumor progression, angiogenesis, metastasis and chemo-resistance

Evidence from clinical, animal and cell culture studies demonstrates that increased autotaxin (ATX) expression is responsible for enhancing tumor progression, cell migration, metastases, angiogenesis and chemo-resistance. These effects depend mainly on the rapid formation of lysophosphatidate (LPA) by ATX. Circulating LPA has a half-life of about 3 min in mice and it is degraded by the ecto-activities of lipid phosphate phosphatases (LPPs). These enzymes also hydrolyze extracellular sphingosine 1-phosphate (S1P), a potent signal for cell division, survival and angiogenesis. Many aggressive tumor cells express high ATX levels and low LPP activities. This favors the formation of locally high LPA and S1P concentrations. Furthermore, LPPs attenuate signaling downstream of the activation of G-protein coupled receptors and receptor tyrosine kinases. Therefore, we propose that the low expression of LPPs in many tumor cells makes them hypersensitive to growth promoting and survival signals that are provided by LPA, S1P, platelet-derived growth factor (PDGF) and epidermal growth factor (EGF). One of the key signaling pathways in this respect appears to be activation of phospholipase D (PLD) and phosphatidate (PA) production. This is required for the transactivations of the EGFR and PDGFR and also for LPA-induced cell migration. PA also increases the activities of ERK, mTOR, myc and sphingosine kinase-1 (SK-1), which provide individual signals for cells division, survival, chemo-resistance and angiogenesis. This review focuses on the balance of signaling by bioactive lipids including LPA, phosphatidylinositol 3,4,5-trisphosphate, PA and S1P versus the action of ceramides. We will discuss how these lipid mediators interact to produce an aggressive neoplastic phenotype.

Cystatin M expression is reduced in gastric carcinoma and is associated with promoter hypermethylation

Cystatin M is a secreted inhibitor of lysosomal cysteine proteases and increasing evidences indicate that it is a novel target for epigenetic silencing during mammary tumorigenesis. Aberrant promoter methylation is a well-known mechanism that participates in cystatin M silencing in breast cancer. However, the role of cystatin M in the gastric cancer remains to be elucidated. Immunohistochemistry was used to investigate the expression of cystatin M in 60 gastric carcinomas. Hypermethylation of cystatin M promoter was evaluated by the methylation-specific PCR (MSP) method in gastric carcinomas (tumor and paired adjacent non-tumor tissues). Reverse-transcriptase PCR and BSP were also performed on gastric cancer cell lines before and after treatment with 5-aza-2'-deoxycytidine (5-Aza-dC). Lost expression of cystatin M was observed in 42 of 60 (70%) gastric carcinomas. 55% (33 of 60) of primary tumors analyzed displayed cystatin M promoter hypermethylation, indicating that this aberrant characteristic is common in gastric malignancies. Moreover, a statistically significant inverse association was found between cystatin M methylation status and expression of the cystatin M protein in tumor tissues (p=0.027). We also found that patients with cystatin M promoter methylation had a significantly shorter survival time than those without this methylation (p=0.020). These results suggest that cystatin M promoter hypermethylation is one of the molecular mechanisms that accounts for reduced cystatin M gene expression in gastric carcinomas.

ATX-LPA receptor axis in inflammation and cancer

Lysophosphatidic acid (LPA, 1- or 2-acyl-sn-glycerol 3-phosphate) mediates a plethora of physiological and pathological activities via interactions with a series of high affinity G protein-coupled receptors (GPCR). Both LPA receptor family members and autotaxin (ATX/LysoPLD), the primary LPA-producing enzyme, are aberrantly expressed in many human breast cancers and several other cancer lineages. Using transgenic mice expressing either an LPA receptor or ATX, we recently demonstrated that the ATX-LPA receptor axis plays a causal role in breast tumorigenesis and cancer-related inflammation, further validating the ATX-LPA receptor axis as a rich therapeutic target in cancer.

Autotaxin

Autotaxin is a protein of approximately 900 amino acids discovered in the early 1990s. Over the past 15 years, a strong association between cancer cells and autotaxin production has been observed. Recent publications indicate that autotaxin and the capacity of cancer to metastasise are intimately linked. The discovery of new molecular targets in pharmacology is a mixture of pure luck, hard work and industrial strategy. Despite a crucial and desperate need for new therapeutic tools, many targets are approached in oncology, but only a few are validated and end up at the patient bed. Outside the busy domain of kinases, few targets have been discovered that can be useful in treating cancer, particularly metastatic processes. The fortuitous relationship between autotaxin and lysophosphatidic acid renders the results of observations made in the diabetes/obesity context considerably important. The literature provides observations that may aid in redesigning experiments to validate autotaxin as a potential oncology target.

The biology of cystatin M/E and its cognate target proteases

Cystatin M/E is a member of a superfamily of evolutionarily-related cysteine protease inhibitors that provide regulatory and protective functions against uncontrolled proteolysis by cysteine proteases. Although most cystatins are ubiquitously expressed, high levels of cystatin M/E expression are mainly restricted to the epithelia of the skin (epidermis, hair follicles, sebaceous glands, and sweat glands) and to a few extracutaneous tissues. The identification of its physiological targets and the localization of these proteases in skin have suggested a regulatory role for cystatin M/E in epidermal differentiation. In vitro biochemical approaches as well as the use of in vivo mouse models have revealed that cystatin M/E is a key molecule in a biochemical pathway that controls skin barrier formation by the regulation of both crosslinking and desquamation of the stratum corneum. Cystatin M/E directly controls the activity of cathepsin V, cathepsin L, and legumain, thereby regulating the processing of transglutaminases. Misregulation of this pathway by unrestrained protease activity, as seen in cystatin M/E-deficient mice, leads to abnormal stratum corneum and hair follicle formation, as well as to severe disturbance of skin barrier function. Here, we review the current knowledge on cystatin M/E in skin barrier formation and its potential role as a tumor suppressor gene.

Invasion suppressor cystatin E/M (CST6): high-level cell type-specific expression in normal brain and epigenetic silencing in gliomas

DNA hypermethylation-mediated gene silencing is a frequent and early contributor to aberrant cell growth and invasion in cancer. Malignant gliomas are the most common primary brain tumors in adults and the second most common tumor in children. Morbidity and mortality are high in glioma patients because tumors are resistant to treatment and are highly invasive into surrounding brain tissue rendering complete surgical resection impossible. Invasiveness is regulated by the interplay between secreted proteases (eg, cathepsins) and their endogenous inhibitors (cystatins). In our previous studies we identified cystatin E/M (CST6) as a frequent target of epigenetic silencing in glioma. Cystatin E/M is a potent inhibitor of cathepsin B, which is frequently overexpressed in glioma. Here, we study the expression of cystatin E/M in normal brain and show that it is highly and moderately expressed in oligodendrocytes and astrocytes, respectively, but not in neurons. Consistent with this, the CST6 promoter is hypomethylated in all normal samples using methylation-specific PCR, bisulfite genomic sequencing, and pyrosequencing. In contrast, 78% of 28 primary brain tumors demonstrated reduced/absent cystatin E/M expression using a tissue microarray and this reduced expression correlated with CST6 promoter hypermethylation. Interestingly, CST6 was expressed in neural stem cells (NSC) and markedly induced upon differentiation, whereas a glioma tumor initiating cell (TIC) line was completely blocked for CST6 expression by promoter methylation. Analysis of primary pediatric brain tumor-derived lines also showed CST6 downregulation and methylation in nearly 100% of 12 cases. Finally, ectopic expression of cystatin E/M in glioma lines reduced cell motility and invasion. These results demonstrate that epigenetic silencing of CST6 is frequent in adult and pediatric brain tumors and occurs in TICs, which are thought to give rise to the tumor. CST6 methylation may therefore represent a novel prognostic marker and therapeutic target specifically altered in TICs.

Autotaxin (ATX): a multi-functional and multi-modular protein possessing enzymatic lysoPLD activity and matricellular properties

Recent studies have established that autotaxin (ATX), also known as phosphodiesterase Ialpha/autotaxin (PD-Ialpha/ATX) or (ecto)nucleotide pyrophosphatase/phosphodiesterase 2 [(E)NPP2], represents a multi-functional and multi-modular protein. ATX was initially thought to function exclusively as a phosphodiesterase/pyrophosphatase. However, it has become apparent that this enzymatically active site, which is ultimately responsible for ATX's originally discovered property of tumor cell motility stimulation, mediates the conversion of lysophosphatidylcholine (LPC) to lysophosphatidic acid (LPA). In addition, a separate functionally active domain, here referred to as the Modulator of Oligodendrocyte Remodeling and Focal adhesion Organization (MORFO) domain, was discovered in studies analyzing the role of ATX during the differentiation of myelinating cells of the central nervous system (CNS), namely oligodendrocytes. This novel domain was found to mediate anti-adhesive, i.e. matricellular, properties and to promote morphological maturation of oligodendrocytes. In this review, we summarize our current understanding of ATX's structure-function domains and discuss their contribution to the presently known main functional roles of ATX.

Methylation-dependent silencing of CST6 in primary human breast tumors and metastatic lesions

CST6 is a breast tumor suppressor gene that is expressed in normal breast epithelium, but is epigenetically silenced as a consequence of promoter hypermethylation in metastatic breast cancer cell lines. In the current study, we investigated the expression and methylation status of CST6 in primary breast tumors and lymph node metastases. 25/45 (56%) primary tumors and 17/20 (85%) lymph node metastases expressed significantly lower levels of cystatin M compared to normal breast tissue. Bisulfite sequencing demonstrated CST6 promoter hypermethylation in 11/23 (48%) neoplastic lesions analyzed, including 3/11 (27%) primary tumors and 8/12 (67%) lymph node metastases. In most cases (12/23, 52%), the expression of cystatin M directly reflected CST6 promoter methylation status. In remaining lesions (8/23, 35%) loss of cystatin M was not associated with CST6 promoter hypermethylation, indicating that other mechanisms can account for loss of CST6 expression. These results show that methylation-dependent silencing of CST6 occurs in a subset of primary breast cancers, but more frequently in metastatic lesions, possibly reflecting progression-related genomic events. To examine this possibility, primary breast tumors and matched lymph node metastases were analyzed. In 2/3 (67%) patients, primary tumors were positive for cystatin M and negative for CST6 promoter methylation, and matched metastatic lesions lacked cystatin M expression and CST6 was hypermethylated. This observation suggests that progression-related epigenetic alterations in CST6 gene expression can accompany metastatic spread from a primary tumor site. Overall, the results of the current investigation suggest that methylation-dependent epigenetic silencing of CST6 represents an important mechanism for loss of CST6 during breast tumorigenesis and/or progression to metastasis.

Regulation and biological activities of the autotaxin-LPA axis

Autotaxin (ATX), or nucleotide pyrophosphatase/phosphodiesterase 2 (NPP2), is an exo-enzyme originally identified as a tumor cell autocrine motility factor. ATX is unique among the NPPs in that it primarily functions as a lysophospholipase D, converting lysophosphatidylcholine into the lipid mediator lysophosphatidic acid (LPA). LPA acts on specific G protein-coupled receptors to elicit a wide range of cellular responses, ranging from cell proliferation and migration to neurite remodeling and cytokine production. While LPA signaling has been studied extensively over the last decade, we are only now beginning to explore the properties and biological importance of ATX as the major LPA-producing phospholipase. In this review, we highlight recent advances in our understanding of the ATX-LPA axis, giving first an update on LPA action and then focusing on ATX, in particular its regulation, its link to cancer and its vital role in vascular development.

Frequent epigenetic inactivation of cystatin M in breast carcinoma

Cystatin M is a potent endogenous inhibitor of lysosomal cysteine proteases. In breast carcinoma, cystatin M expression is frequently downregulated. It has been shown that cystatin M expression suppressed growth and migration of breast cancer cells. We examined the methylation status of the CpG island promoter of cystatin M in four breast cancer cell lines (MDAMB231, ZR75-1, MCF7 and T47D), in 40 primary breast carcinoma and in corresponding normal tissue probes by combined bisulphite restriction analysis. To investigate the effects of cystatin M expression on the growth of breast carcinoma, cystatin M was transfected in T47D. The cystatin M promoter was highly methylated in all four-breast cancer cell lines. Primary breast tumours were significantly more frequently methylated compared to normal tissue samples (60 vs 25%; P=0.006 Fisher's exact test). Treatment of breast cancer cells with 5-aza-2'-deoxycytidine (5-Aza-CdR), reactivated the transcription of cystatin M. Transfection of breast carcinoma cells with cystatin M caused a 30% decrease in colony formation compared to control transfection (P=0.002). Our results show that cystatin M is frequently epigenetically inactivated during breast carcinogenesis and cystatin M expression suppresses the growth of breast carcinoma. These data suggest that cystatin M may encode a novel epigenetically inactivated candidate tumour suppressor gene.