Aberrant expression of caspase-14 in epithelial tumors

A Review on Caspases: Key Regulators of Biological Activities and Apoptosis

Caspases are proteolytic enzymes that belong to the cysteine protease family and play a crucial role in homeostasis and programmed cell death. Caspases have been broadly classified by their known roles in apoptosis (caspase-3, caspase-6, caspase-7, caspase-8, and caspase-9 in mammals) and in inflammation (caspase-1, caspase-4, caspase-5, and caspase-12 in humans, and caspase-1, caspase-11, and caspase-12 in mice). Caspases involved in apoptosis have been subclassified by their mechanism of action as either initiator caspases (caspase-8 and caspase-9) or executioner caspases (caspase-3, caspase-6, and caspase-7). Caspases that participate in apoptosis are inhibited by proteins known as inhibitors of apoptosis (IAPs). In addition to apoptosis, caspases play a role in necroptosis, pyroptosis, and autophagy, which are non-apoptotic cell death processes. Dysregulation of caspases features prominently in many human diseases, including cancer, autoimmunity, and neurodegenerative disorders, and increasing evidence shows that altering caspase activity can confer therapeutic benefits. This review covers the different types of caspases, their functions, and their physiological and biological activities and roles in different organisms.

Proximity Proteomics Has Potential for Extracellular Vesicle Identification

Extracellular vesicles (EVs) are biomarkers and mediators of intercellular communication. In biological samples, EVs are secreted by various types of cells. The proteomic identification of proteins expressed in EVs has potential to contribute to research and clinical applications, particularly for cancer. In this study, the proximity-labeling method-based proteomic approach was used for EV identification, labeling membrane components proximal to a given molecule on the EV membrane surface. Due to the small labeling range, proteins on the surface of the same EVs are likely to be labeled by selecting a given EV surface antigen. The protein group of cancer cell-secreted EV (cEV), which abundantly expresses a close homologue of L1 (CHL1), was examined using a model mouse for lung cancer (LC). cEV-expressed proteins were identified by proteomic analysis of enzyme-mediated activation of radical sources by comparing serum EVs from wild-type and LC mice. SLC4A1 was found to be co-expressed in CHL1-expressing EVs, highlighting EVs expressing both CHL1 and SLC4A1 as candidates for cEVs. Serum EVs expressing both CHL1 and caspase 14 were significantly elevated in LC patients compared with healthy individuals. Thus, the combination of proximity labeling and proteomic analysis allows for effective EV identification.

Prognostic significance of mRNA expression of CASPs in gastric cancer

Current studies suggest that the cysteinyl aspartate specific proteinase (caspase/CASP) family may be closely associated with apoptosis. Scientists have suggested that caspases may be a key to the development of more effective anti-cancer therapies. However, the prognostic value of CASP expression in gastric cancer (GC) remains unclear. Using a Kaplan-Meier plotter online database, the predictive prognostic significance of the expression of 12 CASPs genes (CASP1, CASP2, CASP3, CASP4, CASP5, CASP6, CASP7, CASP8, CASP9, CASP10, CASP12 and CASP14) to overall survival (OS) in different clinicopathological features, including Lauren classification, pathological stages, therapies employed and differentiation in gastric cancer patients was explored. The present study revealed that higher CASP1, 2, 3, 4, 5, 6, 7 and 8 mRNA expression was associated with better OS, whereas higher expression of CASP9, 10, 12 and 14 showed an unfavorable OS in all GC patients. Moreover, CASP1 to 8 were all associated with favorable OS in intestinal type and diffuse type classified by Lauren classification. Therefore, the results of the present study suggested that the CASP family may function as new prognostic indicators in GC and may be helpful in making treatment decisions.

Cell death induced autophagy contributes to terminal differentiation of skin and skin appendages

In the adult mammalian skin, cells are constantly renewing, differentiating and moving upward, to finally die in a yet not fully understood manner. Here, we provide evidence that macroautophagy/autophagy has a dual role in the skin. In addition to its known catabolic protective role as an evolutionary conserved upstream regulator of lysosomal degradation, we show that autophagy induced cell death (CDA) occurs in epithelial lineage-derived organs, such as the inter-follicular epidermis, the sebaceous- and the Harderian gland. By utilizing GFP-LC3 transgenic and ATG7-deficient mice, we show that CDA is initiated during terminal differentiation at a stage when the cells have become highly resistant to apoptosis. In these transitional cells, the Golgi compartment expands, which accounts for the formation of primary lysosomes, and the nucleus starts to condense. During CDA a burst of autophagosome formation is observed, first the endoplasmic reticulum (ER) is phagocytosed followed by autophagy of the nucleus. By this selective form of cell death, most of the cytoplasmic organelles are degraded, but structural proteins remain intact. In the absence of autophagy, consequently, parts of the ER, ribosomes, and chromatin remain. A burst of autophagy was stochastically observed in single cells of the epidermis and collectively in larger areas of ductal cells, arguing for a coordinated induction. We conclude that autophagy is an integral part of cell death in keratinocyte lineage cells and participates in their terminal cell fate.

Abbreviations: Atg7: autophagy related 7; BECN1: beclin 1; CDA: cell death-induced autophagy; Cre: Cre-recombinase; DAPI: 4′,6-diamidino-2-phenylindole; ER: endoplasmatic reticulum; GFP: green fluorescent protein; HaGl: haderian gland; IVL: involucrin; KRT14: keratin 14; LD: lipid droplet; LSM: laser scanning microscope; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; PN: perinuclear space; RB: residual body; rER: rough endoplasmatic reticulum; SB: sebum; SG-SC: stratum granulosum – stratum corneum; SGl: sebaceous gland; SQSTM1: sequestosome 1; TEM: transmission electron microscopy; TUNEL: terminal deoxynucleotidyl transferase dUTP nick end labelling.

How Does Chronic Cigarette Smoke Exposure Affect Human Skin? A Global Proteomics Study in Primary Human Keratinocytes

Cigarette smoking has been associated with multiple negative effects on human skin. Long-term physiological effects of cigarette smoke are through chronic and not acute exposure. Molecular alterations due to chronic exposure to cigarette smoke remain unclear. Primary human skin keratinocytes chronically exposed to cigarette smoke condensate (CSC) showed a decreased wound-healing capacity with an increased expression of NRF2 and MMP9. Using quantitative proteomics, we identified 4728 proteins, of which 105 proteins were overexpressed (≥2-fold) and 41 proteins were downregulated (≤2-fold) in primary skin keratinocytes chronically exposed to CSC. We observed an alteration in the expression of several proteins involved in maintenance of epithelial barrier integrity, including keratin 80 (5.3 fold, p value 2.5 × 10-7), cystatin A (3.6-fold, p value 3.2 × 10-3), and periplakin (2.4-fold, p value 1.2 × 10-8). Increased expression of proteins associated with skin hydration, including caspase 14 (2.2-fold, p value 4.7 × 10-2) and filaggrin (3.6-fold, p value 5.4 × 10-7), was also observed. In addition, we report differential expression of several proteins, including adipogenesis regulatory factor (2.5-fold, p value 1.3 × 10-3) and histone H1.0 (2.5-fold, p value 6.3 × 10-3) that have not been reported earlier. Bioinformatics analyses demonstrated that proteins differentially expressed in response to CSC are largely related to oxidative stress, maintenance of skin integrity, and anti-inflammatory responses. Importantly, treatment with vitamin E, a widely used antioxidant, could partially rescue adverse effects of CSC exposure in primary skin keratinocytes. The utility of antioxidant-based new dermatological formulations in delaying or preventing skin aging and oxidative damages caused by chronic cigarette smoke exposure warrants further clinical investigations and multi-omics research.

S100A7 acts as a dual regulator in promoting proliferation and suppressing squamous differentiation through GATA-3/caspase-14 pathway in A431 cells

S100A7 is expressed in many squamous cell carcinomas (SCCs), such as SCC of the skin, and well-differentiated SCC always displays stronger staining of this protein. A431 cells, an epidermal cancer cell line, were selected as a cell model to investigate the roles and mechanism of S100A7 in SCC of the skin. In this study, we demonstrated that the overexpression of S100A7 in A431 cells significantly promoted cell proliferation in vitro and tumor growth in vivo, whereas it suppressed the expression of GATA-3, caspase-14 and three squamous differentiation markers, keratin-1, TG-1 and involucrin. Conversely, the overexpression of caspase-14 not only significantly decreased cell proliferation and delayed tumor growth but also markedly induced the expression of three squamous differentiation markers, whereas S100A7 and GATA-3 were not influenced. Further evidence showed that silencing GATA-3 greatly inhibited the expression of caspase-14 and three differentiation markers, while the expression of S100A7 was not changed; contrary results were obtained when overexpressing GATA-3. Importantly, restoring the expression of GATA-3 and caspase-14 in A431-S100A7 cells could bypass the ability of S100A7 to increase cell viability and repress squamous differentiation. These data suggested that S100A7 expression in SCC may play an important role in the maintenance of SCC cell dedifferentiation, at least in SCC of the skin.

Aberrant expression of caspase 14 in salivary gland carcinomas

OBJECTIVES

Caspase 14 is reduced in adenocarcinomas of the stomach and colon. In contrast, breast and lung adenocarcinomas frequently show an overexpression of caspase 14. Salivary gland adenocarcinomas have not been evaluated for potential aberrant caspase 14 expression.

MATERIALS AND METHODS

Samples from salivary gland carcinomas (n = 43) were analysed by immunohistochemistry (caspase 14, filaggrin, GATA3 and Ki67) and fluorescence in situ hybridization.

RESULTS

Caspase 14 is not expressed in normal salivary glands, while in a subfraction of carcinomas (32%) an aberrant expression was found. Filaggrin could not be detected. Caspase 14 staining was not associated with tumour dedifferentiation, GATA3 expression or amplification of gene locus 19p13.

CONCLUSION

In summary, aberrant expression of caspase 14 can be found in a subfraction of salivary gland carcinomas but could not be used as a biomarker for a specific carcinoma subtype of the salivary gland.

Comprehensive evaluation of caspase-14 in vulvar neoplasia: an opportunity for treatment with black raspberry extract

OBJECTIVE

The aim of this study is to determine the expression of caspase-14, a key protein in maturation of squamous epithelia, in archival malignant and premalignant vulvar squamous lesions and examine in-vitro effects of a black raspberry extract (BRB-E) on a vulvar squamous cell carcinoma (VSCC) cell line.

METHODS

VSCC cell cultures were exposed to different BRB-E concentrations and used to create cell blocks. Immunohistochemistry for caspase-14 was performed on cell block sections, whole tissue sections, and a tissue microarray consisting of normal vulvar skin, lichen sclerosus (LS), classic and differentiated vulvar intraepithelial neoplasia (cVIN and dVIN respectively), and VSCC.

RESULTS

LS demonstrated abnormal full thickness (5/11) or absent (1/11) caspase-14 staining. dVIN often showed markedly reduced expression (4/7), and cVIN occasionally demonstrated either absent or reduced caspase-14 (6/22). VSCC predominantly had absent or markedly reduced caspase-14 (26/28). VSCC cell cultures demonstrated a significant increase in caspase-14 (p=0.013) after BRB-E treatment: 7.3% (±2.0%) of untreated cells showed caspase-14 positivity, while 21.3% (±8.9%), 21.7% (±4.8%), and 22.6% (±5.3%) of cells were positive for caspase-14 after treatment with 200, 400, and 800 μg/mL BRB-E, respectively. Pair-wise comparisons between the treatment groups and the control demonstrated significant differences between no treatment with BRB-E and each of these treatment concentrations (Dunnett's adjusted p-values: 0.024, 0.021, and 0.014, respectively).

CONCLUSIONS

Caspase-14 is frequently decreased in premalignant and malignant vulvar squamous lesions, and is upregulated in VSCC cell culture by BRB-E. BRB-E should be further explored and may ultimately be incorporated in topical preparations.

Expression of caspase 14 and filaggrin in oral squamous carcinoma

Caspase 14 is one of the latter discovered members of the caspase enzyme family and, although sharing sequence homologies with the other caspases, it is not involved in apoptosis. Together with its co-factor filaggrin, it plays an important role in skin barrier formation. It is already known that caspase 14 proteins are reduced during neoplastic dedifferentiation in cervical intraepithelial neoplasms and in invasive cervical carcinomas. Oral squamous carcinoma tissues have not been systematically evaluated for caspase 14 expression yet. Formalin-fixed and paraffin-embedded samples from oral squamous carcinomas (n = 36 tumours from 34 patients), metastases (n = 15) and controls (leukoplakia, n = 10) were analysed by immunohistochemistry. In carcinomas, human papilloma virus (HPV) infection was tested by PCR. Here we demonstrate that, in oral epithelia, caspase 14 is expressed mainly by cells of the intermediate and superficial cell layers while filaggrin is expressed only in keratinising foci in leukoplakia. Caspase 14 and filaggrin are co-localised. In invasive oral carcinomas, reduced expression of caspase 14 was detectable in 47 % of tumours but was not associated with keratinisation, tumour differentiation or HPV infection. Filaggrin was detectable in a subfraction of tumours (56 %) and was restricted to keratinising areas of the carcinomas. In summary, in contrast to cervical carcinomas, partial loss of caspase 14 is not associated with dedifferentiation in neoplastic lesions of the oral mucosa or HPV infection.

Caspase-14 suppresses GCM1 acetylation and inhibits placental cell differentiation

Glial cell missing 1 (GCM1) transcription factor regulates placental cell fusion into the syncytiotrophoblast. Caspase-14 is proteolytically activated to mediate filaggrin processing during keratinocyte differentiation. Interestingly, altered expression of nonactivated caspase-14 proenzyme is associated with tumorigenesis and diabetic retinopathy, suggesting that caspase-14 may perform physiological functions independently of its protease activity. Here, we performed tandem affinity purification coupled with mass spectrometry analysis to identify caspase-14 proenzyme as a GCM1-interacting protein that suppresses GCM1 activity and syncytiotrophoblast differentiation. Immunohistochemistry revealed that caspase-14 and GCM1 colocalize to placental cytotrophoblast cells at 8 wk of gestation and syncytiotrophoblast layer at term. Further, we demonstrated that caspase-14 mRNA level is decreased by 40% in placental BeWo cells treated with forskolin (FSK). To the contrary, stimulation of GCM1-regulated placental cell fusion and human chorionic gonadotropin β (hCGβ) expression by FSK is enhanced by caspase-14 knockdown. Indeed, GCM1 protein level is increased by 40% in the caspase-14-knockdown BeWo cells. Because GCM1 is stabilized by acetylation, we subsequently showed that caspase-14 impedes the interaction between GCM1 and cAMP response element-binding protein (CREB)-binding protein (CBP) to suppress CBP-mediated acetylation and transcriptional coactivation of GCM1. Therefore, caspase-14 can suppress placental cell differentiation through down-regulation of GCM1 activity.

Gata-3 negatively regulates the tumor-initiating capacity of mammary luminal progenitor cells and targets the putative tumor suppressor caspase-14

The transcription factor Gata-3 is a definitive marker of luminal breast cancers and a key regulator of mammary morphogenesis. Here we have explored a role for Gata-3 in tumor initiation and the underlying cellular mechanisms using a mouse model of "luminal-like" cancer. Loss of a single Gata-3 allele markedly accelerated tumor progression in mice carrying the mouse mammary tumor virus promoter-driven polyomavirus middle T antigen (MMTV-PyMT mice), while overexpression of Gata-3 curtailed tumorigenesis. Through the identification of two distinct luminal progenitor cells in the mammary gland, we demonstrate that Gata-3 haplo-insufficiency increases the tumor-initiating capacity of these progenitors but not the stem cell-enriched population. Overexpression of a conditional Gata-3 transgene in the PyMT model promoted cellular differentiation and led to reduced tumor-initiating capacity as well as diminished angiogenesis. Transcript profiling studies identified caspase-14 as a novel downstream target of Gata-3, in keeping with its roles in differentiation and tumorigenesis. A strong association was evident between GATA-3 and caspase-14 expression in preinvasive ductal carcinoma in situ samples, where GATA-3 also displayed prognostic significance. Overall, these studies identify GATA-3 as an important regulator of tumor initiation through its ability to promote the differentiation of committed luminal progenitor cells.

Expressions of caspase-14 in human middle ear cholesteatoma

OBJECTIVES

Cholesteatoma is characterized by an excessive proliferation and differentiation of keratinocytes with a progressive accumulation of keratin debris. Caspase-14 is a novel regulator of keratinocyte terminal differentiation. The purpose of this study was to investigate the expression patterns and localizations of caspase- 14 in cholesteatoma and in normal external auditory canal (EAC) epithelium.

METHODS

The expression levels of caspase-14 mRNA were evaluated through real-time polymerase chain reaction (PCR) and Western blotting. Cholesteatoma and normal EAC epithelium were immunostained with a monoclonal antibody to caspase-14. The localizations of immunoreactivity to the caspase-14 antibody were compared between cholesteatoma and normal EAC epithelium through immunohistochemical staining.

RESULTS

As shown by real-time reverse-transcription PCR, the expression level of caspase-14 mRNA in cholesteatoma epithelium was significantly higher than in normal EAC epithelium. Caspase-14 protein was detected in both normal EAC and cholesteatoma, but its expression was shown to be greater in cholesteatoma on Western blot analysis. As shown with immunohistochemical staining, caspase-14 protein was primarily expressed in the granular layer and the upper parts of the spinous layer in cholesteatoma epithelium and in the superficial layer of normal EAC epithelium. The expression of caspase-14 was more intense in cholesteatoma tissues than in normal EAC epithelium.

CONCLUSION

The increased level of caspase-14 expression in cholesteatoma tissues may play a role in terminal differentiation of epithelium and accumulation of keratin debris from external matrix.

Caspase-14 reveals its secrets

Caspase-14 is a unique member of the evolutionarily conserved family of cysteinyl aspartate-specific proteinases, which are mainly involved in inflammation and apoptosis. However, recent evidence also implicates these proteases in proliferation and differentiation. Although most caspases are ubiquitously expressed, caspase-14 expression is confined mainly to cornifying epithelia, such as the skin. Moreover, caspase-14 activation correlates with cornification, indicating that it plays a role in terminal keratinocyte differentiation. The determination of in vitro conditions for caspase-14 activity paved the way to identifying its substrates. The recent development of caspase-14-deficient mice underscored its importance in the correct degradation of (pro)filaggrin and in the formation of the epidermal barrier that protects against dehydration and UVB radiation. Here, we review the current knowledge on caspase-14 in skin homeostasis and disease.

Mutational analysis of caspase-14 gene in common carcinomas

AIMS

Whereas most caspases play roles in apoptosis and/or inflammation, caspase-14 plays a main role in epithelial differentiation. In cancers, expression of caspase-14 is frequently altered and is associated with some clinicopathological characteristics, suggesting caspase-14 might contribute to the pathogenesis of cancers. As a potential mechanism of caspase-14 alterations in cancers, we explored the possibility that mutation of caspase-14 gene is a characteristic of human cancers.

METHODS

We analysed the entire coding region and all splice sites of human caspase-14 gene for the detection of somatic mutations in a series of 345 cancers, including 105 colorectal, 60 gastric, 60 hepatocellular, 60 breast and 60 lung carcinomas, by a single-strand conformation polymorphism (SSCP) assay.

RESULTS

Overall, we detected two somatic mutations of caspase-14 gene, which consisted of one missense mutation (S32Y) and one silent mutation (T234T). The caspase-14 mutations were detected in two of 105 colorectal carcinomas (1.9%), but not in other carcinomas.

CONCLUSION

These data indicate that caspase-14 gene is rarely mutated in colorectal carcinomas, but not mutated in gastric, lung, breast and hepatocellular carcinomas. The data also suggest that the caspase-14 mutation may not be a direct target of inactivation in tumorigenesis of common carcinomas.