Human squamous cell carcinoma from skin: establishment and characterization of a new cell line (HSC-5)

Investigating Cutaneous Squamous Cell Carcinoma in vitro and in vivo: Novel 3D Tools and Animal Models

Cutaneous Squamous Cell Carcinoma (cSCC) represents the second most common type of skin cancer, which incidence is continuously increasing worldwide. Given its high frequency, cSCC represents a major public health problem. Therefore, to provide the best patients’ care, it is necessary having a detailed understanding of the molecular processes underlying cSCC development, progression, and invasion. Extensive efforts have been made in developing new models allowing to study the molecular pathogenesis of solid tumors, including cSCC tumors. Traditionally, in vitro studies were performed with cells grown in a two-dimensional context, which, however, does not represent the complexity of tumor in vivo. In the recent years, new in vitro models have been developed aiming to mimic the three-dimensionality (3D) of the tumor, allowing the evaluation of tumor cell-cell and tumor-microenvironment interaction in an in vivo-like setting. These models include spheroids, organotypic cultures, skin reconstructs and organoids. Although 3D models demonstrate high potential to enhance the overall knowledge in cancer research, they lack systemic components which may be solved only by using animal models. Zebrafish is emerging as an alternative xenotransplant model in cancer research, offering a high-throughput approach for drug screening and real-time in vivo imaging to study cell invasion. Moreover, several categories of mouse models were developed for pre-clinical purpose, including xeno- and syngeneic transplantation models, autochthonous models of chemically or UV-induced skin squamous carcinogenesis, and genetically engineered mouse models (GEMMs) of cSCC. These models have been instrumental in examining the molecular mechanisms of cSCC and drug response in an in vivo setting. The present review proposes an overview of in vitro, particularly 3D, and in vivo models and their application in cutaneous SCC research.

N-WASP Attenuates Cell Proliferation and Migration through ERK2-Dependent Enhanced Expression of TXNIP

Simple Summary

Neural Wiskott–Aldrich Syndrome Protein (N-WASP) regulates actin cytoskeleton remodeling and can, it has been suggested, suppress several cancers. In this study, HSC-5 cells, a mammalian cell line with reduced N-WASP expression, were used to generate control cells and HSC-5 cells with increased N-WASP expression that is comparable to that of normal keratinocytes. The two cell lines were used to elucidate the regulation of cell proliferation and migration by N-WASP. Our findings suggest that N-WASP increases ERK2-dependent phosphorylation of FOXO1 and increases TXNIP expression, which reduces cell proliferation and migration. This study is the first to propose an antiproliferative role of N-WASP, which is mediated via ERK2, and it suggests new avenues for cancer therapeutic research and treatment.

Abstract

Neural Wiskott–Aldrich Syndrome Protein (N-WASP) regulates actin cytoskeleton remodeling. It has been known that reduced N-WASP expression in breast and colorectal cancers is associated with poor prognosis. Here, we found reduced N-WASP expression in squamous cell carcinoma (SCC) patient samples. The SCC cell line HSC-5 with reduced N-WASP expression was used to generate HSC-5^CN (control) and HSC-5^NW (N-WASP overexpression) cells. HSC-5^NW cells had reduced cell proliferation and migration compared to HSC-5^CN cells. HSC-5^NW cells had increased phospho-ERK2 (extracellular signal-regulated kinase 2), phosphorylated Forkhead box protein class O1 (FOXO1) and reduced nuclear FOXO1 staining compared to HSC-5^CN cells. Proteasome inhibition stabilized total FOXO1, however, not nuclear staining, suggesting that FOXO1 could be degraded in the cytoplasm. Inhibition of ERK2 enhanced nuclear FOXO1 levels and restored cell proliferation and migration of HSC-5^NW to those of HSC-5^CN cells, suggesting that ERK2 regulates FOXO1 activity. The expression of thioredoxin-interacting protein (TXNIP), a FOXO1 target that inhibits thioredoxin and glucose uptake, was higher in HSC-5^NW cells than in HSC-5^CN cells. Knockdown of TXNIP in HSC-5^NW cells restored cell proliferation and migration to those of HSC-5^CN cells. Thus, we propose that N-WASP regulates cell proliferation and migration via an N-WASP-ERK2-FOXO1-TXNIP pathway.

Toll‑like receptor 4 plays a tumor‑suppressive role in cutaneous squamous cell carcinoma

Toll‑like receptor 4 (TLR4), a key regulator of the innate immune system, is expressed not only in immune cells, but also in a number of cancer cells. A biological role for TLR4 in cutaneous squamous cell carcinoma (SCC), however, is unclear. In this study, we first examined TLR4 expression and localization in cases of SCC, actinic keratosis (AK) and Bowen's disease (BD) by immunohistochemistry. TLR4 expression was significantly higher in the SCC than in the AK or BD tissues. We then determined the TLR4 expression level in vivo, in 3 histological subtypes of SCC. TLR4 expression in poorly differentiated SCC was significantly lower compared with that of the moderately and well‑differentiated type. In addition, the CD44 immunoreactivity tended to be high in the cell membrane of poorly differentiated SCC. Of note, poorly differentiated SCC is a risk factor of unfavorable outcomes in affected patients. We then assessed the biological role of TLR4 in HSC‑1 and HSC‑5 SCC cells and HaCaT human keratinocytes. TLR4 knockdown by transfection with siRNA accelerated HSC‑1 and HaCaT cell migration and invasion compared to the control siRNA‑transfected cells. TLR4 knockdown resulted in an increased CD44 expression and in an enhanced filopodia protrusion formation, particularly in HSC‑1. On the whole, these results suggest that a reduced TLR4 expression enhances the malignant features in SCC cases and cultured SCC cell lines. TLR4 may thus play an anti‑tumor role in cutaneous SCC.

Overexpression of CDC42SE1 in A431 Cells Reduced Cell Proliferation by Inhibiting the Akt Pathway

Cell division cycle 42 (CDC42), a small Rho GTPase, plays a critical role in many cellular processes, including cell proliferation and survival. CDC42 interacts with the CRIB (Cdc42- and Rac-interactive binding) domain of CDC42SE1, a small effector protein of 9 kDa. We found that the expression of CDC42SE1 was reduced in human skin cancer samples relative to matched perilesional control. Exogenous expression of CDC42SE1 but not CDC42SE1^H38A (mutation within CRIB domain) in A431 cells (A431^SE1, A431^SE1-H38A) reduced cell proliferation. Antibody microarray analysis of A431^Ctrl and A431^SE1 lysate suggested that reduced A431^SE1 cells proliferation was due to inhibition of Akt pathway, which was confirmed by the reduced P-Akt and P-mTOR levels in A431^SE1 cells compared to A431^Ctrl cells. This suggests that CDC42SE1 modulates the CDC42-mediated Akt pathway by competing with other effector proteins to bind CDC42. A431^SE1 cells formed smaller colonies in soft agar compared to A431^Ctrl and A431^SE1-H38A cells. These findings correlate with nude mice xenograft assays, where A431^SE1 cells formed tumors with significantly-reduced volume compared to the tumors formed by A431^Ctrl cells. Our results suggest that CDC42SE1 is downregulated in skin cancer to promote tumorigenesis, and thus CDC42SE1 might be an important marker of skin cancer progression.

Insulin-like growth factor 2 mRNA-binding protein-3 as a marker for distinguishing between cutaneous squamous cell carcinoma and keratoacanthoma

In the histopathological diagnosis of cutaneous tumors, the differential diagnosis of squamous cell carcinoma (SCC) with crateriform architecture and keratoacanthoma (KA) is often difficult so an accurate understanding of the biological features and the identification of reliable markers of SCC and KA are crucial issues. Insulin-like growth factor 2 mRNA-binding protein-3 (IGF2BP3, also known as IMP3) is thought of as a bona fide oncofetal protein, which is overexpressed and is involved in cell proliferation, migration, and invasion in several kinds of tumors. However, the role of IMP3 in cutaneous SCC and KA has not been well studied. Therefore, we focused on studying the biological functions of IMP3 in SCC and KA. In human skin SCC cell lines, HSC-1 and HSC-5, and the human keratinocyte cell line, HaCaT, IMP3 mRNA levels were significantly higher than that of normal human skin. The knockdown of IMP3 expression reduced the proliferation of HSC-1, and significantly reduced invasion by HSC-1 and HSC-5. In contrast, the knockdown of IMP3 did not significantly affect invasion by HaCaT cells. In immunohistochemical studies of SCC and KA tissues, the Ki-67 labeling index (LI) of the suprabasal cell layer was significantly higher in SCC, compared with KA tissues and the tumor-free margin (TFM) adjacent to SCC and KA. Most SCC tissues stained strongly positive for IMP3, but KA tissues and TFM were mostly negative for IMP3. The Ki-67 LI of the IMP3-positive group was significantly higher than that of the IMP3-negative group in the suprabasal cell layer of SCC. These results suggest that IMP3 plays an important role in proliferation and, more significantly, in the invasion of SCC, and may be a suitable marker for the histopathological diagnosis of SCC with a crateriform architecture and KA. Furthermore, IMP3 may potentially be a new therapeutic target for SCC.

Loss of TAK1 increases cell traction force in a ROS-dependent manner to drive epithelial-mesenchymal transition of cancer cells

Epithelial–mesenchymal transition (EMT) is a crucial step in tumor progression, and the TGFβ–SMAD signaling pathway as an inductor of EMT in many tumor types is well recognized. However, the role of non-canonical TGFβ–TAK1 signaling in EMT remains unclear. Herein, we show that TAK1 deficiency drives metastatic skin squamous cell carcinoma earlier into EMT that is conditional on the elevated cellular ROS level. The expression of TAK1 is consistently reduced in invasive squamous cell carcinoma biopsies. Tumors derived from TAK1-deficient cells also exhibited pronounced invasive morphology. TAK1-deficient cancer cells adopt a more mesenchymal morphology characterized by higher number of focal adhesions, increase surface expression of integrin α5β1 and active Rac1. Notably, these mutant cells exert an increased cell traction force, an early cellular response during TGFβ1-induced EMT. The mRNA level of ZEB1 and SNAIL, transcription factors associated with mesenchymal phenotype is also upregulated in TAK1-deficient cancer cells compared with control cancer cells. We further show that TAK1 modulates Rac1 and RhoA GTPases activities via a redox-dependent downregulation of RhoA by Rac1, which involves the oxidative modification of low-molecular weight protein tyrosine phosphatase. Importantly, the treatment of TAK1-deficient cancer cells with Y27632, a selective inhibitor of Rho-associated protein kinase and antioxidant N-acetylcysteine augment and hinders EMT, respectively. Our findings suggest that a dysregulated balance in the activation of TGFβ–TAK1 and TGFβ–SMAD pathways is pivotal for TGFβ1-induced EMT. Thus, TAK1 deficiency in metastatic cancer cells increases integrin:Rac-induced ROS, which negatively regulated Rho by LMW-PTP to accelerate EMT.

Downregulation of keratins 8, 18 and 19 influences invasiveness of human cultured squamous cell carcinoma and adenocarcinoma cells

Keratin (K) expression index has been reported to be related to cell invasion activity in adenocarcinoma. In a previous study, we observed a negative correlation between K expression and cell invasion activity; i.e., when many Ks are expressed in the cells, the cell activity is low. To further elucidate the correlation between Ks and invasion activity, RNA interference experiments of K8, K18 and K19 were carried out to clarify the essential role of Ks using T24 and HEC-1 as typical squamous cell carcinoma and adenocarcinoma cells, respectively. K8 small interfering RNA (siRNA) was most effective against K18 and K19 expression and demonstrated the strongest effect on relative invasion activity among the siRNAs used. These results suggest that K8/K18 or K8/K19 filaments may play roles in internal cell structure and invasion activity. Moreover, K18 and K19 were capable of substituting for each other, and K18 or K19 formed filaments with K8. In addition, cells treated with K8 siRNA demonstrated high invasion activity, which was approximately double that observed with control siRNA in HEC-1 cells. The order of effects was K8>K19>K18 in the two cell lines. The above results suggest that K8 may play a signifiant role in invasive functions in epithelial and metastatic cells.

Reduced expression and aberrant localization of p120catenin in human squamous cell carcinoma of the skin

BACKGROUND

p120catenin (p120ctn), a member of the Armadillo protein family, is ubiquitously expressed and binds to classical cadherins together with other catenins to participate in the adherens junction. p120ctn has numerous isoforms generated through extensive splicing and alternative usage of translation initiation codons. Although the involvement of p120ctn in cell growth control has been postulated, little has so far been known about its expression patterns in the skin and epidermal tumors.

OBJECTIVE

To identify the isoforms expressed in benign and malignant keratinocytes and to analyze the expression patterns of p120ctn in epidermal tumor specimens.

METHODS

HaCaT, DJM-1, BSCC-93, HSC-1, HSC-5 and A431 cells along with normal skin tissue were subjected to RT-PCR to identify the expressed isoforms. For immunofluorescence study, surgical specimens including 29 squamous cell carcinomas (SSCs), 4 basal cell carcinomas (BCCs) and 4 seborrheic keratoses as well as 3 normal skin samples were stained with specific antibodies to detect p120ctn and E-cadherin.

RESULTS

RT-PCR revealed that the isoform 3A was predominantly expressed with faint expression of the isoform 4 and that there was no difference in expressed isoforms between the examined cell lines. Immunofluorescent staining indicated that the expression of p120ctn was significantly reduced in all of the examined squamous cell carcinomas and that p120ctn was frequently localized in cytoplasm. In benign tumors and normal samples, p120ctn was properly expressed in cell-cell boundaries. Furthermore, there were several SCCs where E-cadherin continued to be expressed with no expression of p120ctn.

CONCLUSION

Reduced expression and aberrant localization of p120ctn are among the most common events during the development and/or progression of SCCs.

Secretory component (polymeric immunoglobulin receptor) expression on human keratinocytes by stimulation with interferon-gamma and differences in response

Secretory IgA (sIgA) is a major protective factor in the mucosal immune system because of its great ability to form complexes with bacteria. Secretory component (SC) is an 80-kDa glycoprotein, a component of sIgA, which functions as a polymeric immunoglobulin receptor for IgA and aids the secretion of sIgA from the epithelial surface. We studied SC production by keratinocytes which were involved in the inflammatory process using interferon-gamma (IFN-gamma) as one of the major inflammatory promoters produced by helper T cells. Using two human squamous cell carcinoma cell lines (HSCs) and normal human keratinocytes (NHKs), results from flow cytometric analysis, enzyme-linked immunosorbent assay (ELISA), and Northern blotting revealed that HSCs produced SC when stimulated with IFN-gamma, although their responses differed; one line exhibited enhanced SC production whereas the production in the other line was suppressed. NHKs also exhibited SC expression on the cell surface by means of immunocytochemical analysis, flow cytometry and ELISA, however the responses were also different in each strain. Although the reason for the diversity of SC expression on keratinocytes is not clear, these differences may influence epidermal sIgA secretion level.

Keratin specificity analyses of eight anti-keratin monoclonal antibodies, and their immunostaining patterns in normal skin using formalin-fixed and paraffin-embedded tissue specimens

Keratin specificity analyses of eight anti-keratin antibodies (34 beta B4 (K1), 35 beta H11 (K8), Ks 13.1 (K13), Ks 19.1 (K19), PKK1, LP34 (CK1), KL1 and AE1) using keratin protein derived from normal thigh epidermis, normal parotid gland and a human squamous cell carcinoma cell line (HSC-5) were performed, and compared with those described in the data sheets. The reactivities of LP34, KL1 and PKK1 were markedly different from those mentioned in the data sheets. The immunostaining pattern of these antibodies in normal skin using formalin-fixed and paraffin-embedded tissue specimens was also examined. The staining patterns of suprabasal keratinocytes (K1, K13, CK1 and KL1 positive), basal cells of the epidermis (PKK1 and AE1 positive), inner cells of the ducts (K8, K13, CK1, KL1 and AE1 positive) and secretory cells of sweat glands (K8, K19, PKK1, KL1 and AE1 positive), mature cells (K8 and KL1 positive) and peripheral cells (CK1, KL1 and AE1 positive) of sebaceous glands and outer root sheaths (PKK1, CK1, KL1 and AE1 positive) were specific. Thus, we conclude that the differentiation of epidermis and skin appendages is possible by immunostaining with these eight anti-keratin antibodies using formalin-fixed and paraffin-embedded tissue specimens with proper protease pretreatment.

Occurrence of differentiated keratin peptide(K1) in cultured human squamous cell carcinomas

To date, the largest keratin peptide(K1, 68 KD) has been absent in cultured human squamous cell carcinomas. Using a low salt aqueous solution, not containing high salt and Triton X-100, as a washing buffer for keratin extraction, followed by two dimensional polyacrylamide gel electrophoresis, immunological techniques and Northern blot analysis, we demonstrated K1 peptide in two kinds of cultured human squamous cell carcinomas. Until now keratin extraction has been done using high salt/Triton X-100 solution during which K1 peptide may be removed together developed an affinity with the buffer. Many investigators may have therefore overlooked K1.

Autocrine secretion of an EGF-like substance by a cell line (HSC-1) derived from a human skin squamous cell carcinoma

The presence of EGF-autocrine secretion was investigated in a cell line derived from a human squamous cell carcinoma (HSC-1). The cell line was found to secrete the epidermal growth factor (EGF)-like substance. Meanwhile, normal human and uninvolved and involved psoriatic epidermal cells did not show any evidence of EGF secretion in culture. Not was any evidence of EGF secretion observed in vitro in several malignant cell lines other than HSC-1 derived from human squamous cell carcinomas, adenocarcinoma and melanoma. The addition of EGF did not stimulate, but rather inhibited, the growth of HSC-1 cells in GIT medium as well as Dulbecco's modified essential medium with low concentrations of fetal calf serum (0.5-1%) in vitro. Overexpression of EGF receptors is known to occur in HSC-1. The results suggest that HSC-1 cells exhibit autocrine secretion of the EGF-like substance but not autostimulation in anchorage-dependent cell culture.