Multi-stage chemical carcinogenesis in mouse skin: fundamentals and applications

The mouse oral carcinoma (MOC) model: A 10-year retrospective on model development and head and neck cancer investigations

Preclinical models of cancer have long been paramount to understanding tumor development and advancing the treatment of cancer. Creating preclinical models that mimic the complexity and heterogeneity of human tumors is a key challenge in the advancement of cancer therapy. About ten years ago, we created the mouse oral carcinoma (MOC) cell line models that were derived from 7, 12-dimethylbenz(a) anthracene (DMBA)-induced mouse oral squamous cell cancers. This model has been used in numerous investigations, including studies on tumor biology and therapeutics. We have seen remarkable progress in cancer immunology in recent years, and these cell lines, which are syngeneic to C57BL/6 background, have also been used to study the anti-tumor immune response. Herein, we aim to review the MOC model from its development and characterization to its use in non-immunological and immunological preclinical head and neck squamous cell carcinoma (HNSCC) studies. Integrating and refining these MOC model studies and extending findings to other systems will provide crucial insights for translational approaches aimed at improving head and neck cancer treatment.

Role of hair follicles in the pathogenesis of arsenical-induced cutaneous damage

Arsenical vesicants cause skin inflammation, blistering, and pain. The lack of appropriate animal models causes difficulty in defining their molecular pathogenesis. Here, Ptch1+/- /C57BL/6 mice were employed to investigate the pathobiology of the arsenicals lewisite and phenylarsine oxide (PAO). Following lewisite or PAO challenge (24 h), the skin of animals becomes grayish-white, thick, leathery, and wrinkled with increased bi-fold thickness, Draize score, and necrotic patches. In histopathology, infiltrating leukocytes (macrophages and neutrophils), epidermal-dermal separation, edema, apoptotic cells, and disruption of tight and adherens junction proteins can be visualized. PCR arrays and nanoString analyses showed significant increases in cytokines/chemokines and other proinflammatory mediators. As hair follicles (HFs), which provide an immune-privileged environment, may affect immune cell trafficking and consequent inflammatory responses, we compared the pathogenesis of these chemicals in this model to that in Ptch1+/- /SKH-1 hairless mice. Ptch1+/- /SKH-1 mice have rudimentary, whereas Ptch1+/- /C57BL/6 mice have well-developed HFs. Although no significant differences were observed in qualitative inflammatory responses between the two strains, levels of cytokines/chemokines differed. Importantly, the mechanism of inflammation was identical; both reactive oxygen species induction and consequent activation of unfolded protein response signaling were similar. These data reveal that the acute molecular pathogenesis of arsenicals in these two murine models is similar.

The Roles of Skin Langerhans Cells in Immune Tolerance and Cancer Immunity

Langerhans cells (LC) are a unique population of tissue-resident macrophages with dendritic cell (DC) functionality that form a network of cells across the epidermis of the skin. Their location at the skin barrier suggests an important role for LC as immune sentinels at the skin surface. The classification of LC as DC over the past few decades has driven the scientific community to extensively study how LC function as DC-like cells that prime T cell immunity. However, LC are a unique type of tissue-resident macrophages, and recent evidence also supports an immunoregulatory role of LC at steady state and during specific inflammatory conditions, highlighting the impact of cutaneous environment in shaping LC functionality. In this mini review, we discuss the recent literature on the immune tolerance function of LC in homeostasis and disease conditions, including malignant transformation and progression; as well as LC functional plasticity for adaption to microenvironmental cues and the potential connection between LC population heterogeneity and functional diversity. Future investigation into the molecular mechanisms that LC use to integrate different microenvironment cues and adapt immunological responses for controlling LC functional plasticity is needed for future breakthroughs in tumor immunology, vaccine development, and treatments for inflammatory skin diseases.

Defect of IL17 Signaling, but Not Centrinone, Inhibits the Development of Psoriasis and Skin Papilloma in Mouse Models

Patients with psoriasis tend to develop skin cancer, and the hyperproliferation of the epidermis is a histopathological hallmark of both psoriasis and cutaneous squamous cell carcinoma (SCC), indicating that they may share pathogenic mechanisms. Interleukin-17 (IL17) stimulates the proliferation of the epidermis, leading to psoriasis. Overexpression of Polo-like kinase 4 (PLK4), which controls centriole duplication, has been identified in SCC, which also shows the hyperproliferation of keratinocytes. To investigate the cooperation between IL17 signaling and centriole duplication in epidermal proliferation, we established psoriasis and skin papilloma models in wild type (WT), IL17 receptor A (T779A) knockin (Il17ra(T779A)-KI), and IL17 receptor C knockout (Il17rc-KO) mouse strains. Bioinformatics, Western blot, immunohistochemical staining, colony formation, and real-time PCR were used to determine the effect of IL17 signaling and centrinone on epithelial proliferation. In the psoriasis model, compared to WT and Il17ra(T779A)-KI, Il17rc-KO dramatically suppressed epidermal thickening. The proliferation of keratinocytes significantly decreased in this order from WT to Il17ra(T779A)-KI and Il17rc-KO mice. In the skin papilloma model, Il17ra(T779A)-KI significantly decreased tumor burden compared to the WT, while Il17rc-KO abolished papilloma development. However, centrinone, a selective inhibitor of PLK4, did not affect skin lesion formation in either model. Our data demonstrated that Il17ra(T779A)-KI and Il17rc-KO prevent the development of psoriasis and tumorigenesis in the skin, while the topical administration of centrinone does not have any effect.

Upregulated integrin α11 in the stroma of cutaneous squamous cell carcinoma promotes skin carcinogenesis

Integrin α11β1 is a collagen-binding integrin that is needed to induce and maintain the myofibroblast phenotype in fibrotic tissues and during wound healing. The expression of the α11 is upregulated in cancer-associated fibroblasts (CAFs) in various human neoplasms. We investigated α11 expression in human cutaneous squamous cell carcinoma (cSCC) and in benign and premalignant human skin lesions and monitored its effects on cSCC development by subjecting α11-knockout (Itga11^−/−) mice to the DMBA/TPA skin carcinogenesis protocol. α11-deficient mice showed significantly decreased tumor cell proliferation, leading to delayed tumor development and reduced tumor burden. Integrin α11 expression was significantly upregulated in the desmoplastic tumor stroma of human and mouse cSCCs, and the highest α11 expression was detected in high-grade tumors. Our results point to a reduced ability of α11-deficient stromal cells to differentiate into matrix-producing and tumor-promoting CAFs and suggest that this is one causative mechanism underlying the observed decreased tumor growth. An unexpected finding in our study was that, despite reduced CAF activation, the α11-deficient skin tumors were characterized by the presence of thick and regularly aligned collagen bundles. This finding was attributed to a higher expression of TGFβ1 and collagen crosslinking lysyl oxidases in the Itga11^-/- tumor stroma. In summary, our data suggest that α11β1 operates in a complex interactive tumor environment to regulate ECM synthesis and collagen organization and thus foster cSCC growth. Further studies with advanced experimental models are still needed to define the exact roles and molecular mechanisms of stromal α11β1 in skin tumorigenesis.

The landscape of genetic alterations of UVB-induced skin tumors in DNA repair-deficient mice

Non-melanoma skin cancer (NMSC) is mainly caused by ultraviolet (UV)-induced somatic mutations and is characterized by UV signature modifications. Xeroderma pigmentosum group A (Xpa) knockout mice exhibit extreme UV-induced photo-skin carcinogenesis, along with a photosensitive phenotype. We performed whole-exome sequencing (WES) of squamous cell carcinoma (SCC) samples after repetitive ultraviolet B (UVB) exposure to investigate the differences in the landscape of somatic mutations between Xpa knockout and wild-type mice. Although the tumors that developed in mice harbored UV signature mutations in a similar set of cancer-related genes, the pattern of transcriptional strand asymmetry was largely different; UV signature mutations in Xpa knockout and wild-type mice preferentially occurred in transcribed and non-transcribed strands, respectively, reflecting a deficiency in transcription-coupled nucleotide excision repair in Xpa knockout mice. Serial time point analyses of WES for a tumor induced by only a single UVB exposure showed pathogenic mutations in Kras, Fat1, and Kmt2c, which may be driver genes for the initiation and promotion of SCC in Xpa knockout mice. Furthermore, the inhibitory effects on tumor production in Xpa knockout mice by the anti-inflammatory CXCL1 monoclonal antibody affected the pattern of somatic mutations, wherein the transcriptional strand asymmetry was attenuated and the activated signal transduction was shifted from the RAS/RAF/MAPK to the PIK3CA pathway.

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.

Synthetic lethal kinases in Ras/p53 mutant squamous cell carcinoma

The oncogene Ras and the tumor suppressor gene p53 are frequently co-mutated in human cancer and mutations in Ras and p53 can cooperate to generate a more malignant cell state. To discover novel druggable targets for cancers carrying co-mutations in Ras and p53, we performed arrayed, kinome focused siRNA and oncology drug phenotypic screening utilizing a set of syngeneic Ras mutant squamous cell carcinoma (SCC) cell lines that also carried co-mutations in selected p53 pathway genes. These cell lines were derived from SCCs from carcinogen-treated inbred mice which harbored germline deletions or mutations in Trp53, p19Arf, Atm, or Prkdc. Both siRNA and drug phenotypic screening converge to implicate the phosphoinositol kinases, receptor tyrosine kinases, MAP kinases, as well as cell cycle and DNA damage response genes as targetable dependencies in SCC. Differences in functional kinome profiles between Ras mutant cell lines reflect incomplete penetrance of Ras synthetic lethal kinases and indicate that co-mutations cause a rewiring of survival pathways in Ras mutant tumors. This study describes the functional kinomic landscape of Ras/p53 mutant chemically-induced squamous cell carcinoma in both the baseline unperturbed state and following DNA damage and nominates candidate therapeutic targets, including the Nek4 kinase, for further development.

Structural anatomy of Protein Kinase C C1 domain interactions with diacylglycerol and other agonists

Diacylglycerol (DAG) is a versatile lipid whose 1,2-sn-stereoisomer serves both as second messenger in signal transduction pathways that control vital cellular processes, and as metabolic precursor for downstream signaling lipids such as phosphatidic acid. Effector proteins translocate to available DAG pools in the membranes by using conserved homology 1 (C1) domains as DAG-sensing modules. Yet, how C1 domains recognize and capture DAG in the complex environment of a biological membrane has remained unresolved for the 40 years since the discovery of Protein Kinase C (PKC) as the first member of the DAG effector cohort. Herein, we report the high-resolution crystal structures of a C1 domain (C1B from PKCδ) complexed to DAG and to each of four potent PKC agonists that produce different biological readouts and that command intense therapeutic interest. This structural information details the mechanisms of stereospecific recognition of DAG by the C1 domains, the functional properties of the lipid-binding site, and the identities of the key residues required for the recognition and capture of DAG and exogenous agonists. Moreover, the structures of the five C1 domain complexes provide the high-resolution guides for the design of agents that modulate the activities of DAG effector proteins.

Inhibition of Fibroblast Growth Factor Receptor Attenuates Ultraviolet B-Induced Skin Carcinogenesis

Altered FGFR signaling has been shown to play a role in a number of cancers. However, the role of FGFR signaling in the development and progression of ultraviolet B-induced (UVB) induced cutaneous squamous cell carcinoma (cSCC) remains unclear. In the current study, the effect of UVB radiation on FGFR activation and its downstream signaling in mouse skin epidermis was examined. In addition, the impact of FGFR inhibition on UVB-induced signaling and skin carcinogenesis was also investigated. Exposure of mouse dorsal skin to UVB significantly increased phosphorylation of FGFRs in the epidermis as well as activation of downstream signaling pathways, including AKT/mTOR, STATs and MAPK. Topical application of the pan-FGFR inhibitor AZD4547 to mouse skin prior to exposure to UVB significantly inhibited FGFR phosphorylation as well as mTORC1, STAT3 and MAPK activation (i.e., phosphorylation). Moreover, AZD4547 pretreatment significantly inhibited UVB-induced epidermal hyperplasia and hyperproliferation and reduced infiltration of mast cells and macrophages into the dermis. AZD4547 treatment also significantly inhibited mRNA expression of inflammatory genes in the epidermis. Finally, mice treated topically with AZD4547 prior to UVB exposure showed decreased cSCC incidence and increased survival rate. Collectively, the current data supports the hypothesis that inhibition of FGFR in epidermis may provide a new strategy to prevent and/or treat UVB-induced cSCC.

Anti-inflammatory, Antinociceptive, and Antitumorigenesis Activities of Terminalia Bellerica (Gaertn.) Roxb. in Animal Models

Previous pharmacological research has demonstrated that Terminalia bellerica (Gaertn.) Roxb. (TB) extract possesses several pharmacological activities. However, there is scant evidence documenting the therapeutic activities of TB extract on inflammation, pain, and cancers. Our study examined the in vivo anti-inflammation, antinociception, and antitumorigenesis effects of TB extract and investigated possible mechanisms for those effects. Anti-inflammation activities of TB extract were evaluated using ethyl phenylpropiolate (EPP)- and arachidonic acid (AA)-induced ear edema models, a cotton pellet-induced granulation formation model, and a carrageenan-induced hind paw edema model. An antinociceptive property of TB extract was assessed using a formalin-induced nociception test. An anticarcinogenesis effect was investigated using a 7,12-dimethylbenz( a) anthracene (DMBA) and 12- O-tetradecanoylphorbol-13-acetate (TPA)-induced tumorigenesis model. In the study, TB extract exhibited significant anti-inflammatory effects against EPP-induced ear edema and carrageenan-induced hind paw edema in rats. However, the TB extract showed insignificant inhibitory activity against AA-induced ear edema and cotton pellet-induced granuloma. A dose-dependent decrease in analgesic activity was observed with TB extract evidenced by decreased licking time in formalin-induced pain in mice in both the early and late phases. TB extract also significantly inhibited DMBA/TPA-induced mouse skin tumorigenesis. In conclusion, TB extract possesses anti-inflammatory, analgesic, and anticarcinogenesis properties which act, at least in part, through inhibitory effects of inflammatory mediator production.

Dehydroepiandrosterone, Cancer, and Aging

The biological significance of dehydroepiandrosterone (DHEA) which, in the form of its sulfated ester is the most abundant steroid hormone in human plasma, is an enigma. Over the past years, numerous investigators have reported preclinical findings that DHEA has preventive and therapeutic efficacy in treating major age-associated diseases, including cancer, atherosclerosis, diabetes, obesity, as well as ameliorating the deleterious effects of excess cortisol exposure. Epidemiological studies have also found that low DHEA(S) levels predict an increased all-cause mortality. However, clinical trials, in which oral doses of DHEA at 50 mg-100 mg have been administered to elderly individuals for up to two years, have produced no clear evidence of benefit in parameters such as body composition, peak volume of oxygen consumption, muscle strength, or insulin sensitivity. I discuss why clinical trials, which use doses of DHEA in the 100 mg range, which are the human equivalent of about 1/20^th the doses used in animal studies, are an inadequate test of DHEA's therapeutic potential. I also discuss three mechanisms of DHEA action that very likely contribute to its biological effects in animal studies. Lastly, I describe the development of a DHEA analog which lacks DHEA's androgenic and estrogenic action and that demonstrates enhanced potency and is currently in clinical trials. The use of such analogs may provide a better understanding of DHEA's potential therapeutic utility.

Resistance to chemical carcinogenesis induction via a dampened inflammatory response in naked mole-rats

Naked mole-rats (NMRs) have a very low spontaneous carcinogenesis rate, which has prompted studies on the responsible mechanisms to provide clues for human cancer prevention. However, it remains unknown whether and how NMR tissues respond to experimental carcinogenesis induction. Here, we show that NMRs exhibit extraordinary resistance against potent chemical carcinogenesis induction through a dampened inflammatory response. Although carcinogenic insults damaged skin cells of both NMRs and mice, NMR skin showed markedly lower immune cell infiltration. NMRs harbour loss-of-function mutations in RIPK3 and MLKL genes, which are essential for necroptosis, a type of necrotic cell death that activates strong inflammation. In mice, disruption of Ripk3 reduced immune cell infiltration and delayed carcinogenesis. Therefore, necroptosis deficiency may serve as a cancer resistance mechanism via attenuating the inflammatory response in NMRs. Our study sheds light on the importance of a dampened inflammatory response as a non-cell-autonomous cancer resistance mechanism in NMRs.

Naked mole rats are found to be resistant to cancer development through dampened inflammatory response due to genetically determined impaired necroptosis, with essential necroptosis genes RIPK3 and MLKL containing mutations causing premature stop codons.

Loss of Tpl2 activates compensatory signaling and resistance to EGFR/MET dual inhibition in v-RAS transduced keratinocytes

Cutaneous squamous cell carcinoma (cSCC) is the second most common form of skin cancer in the United States, affecting one million people per year. Patients with aggressive disease have limited treatment options and high mortality, highlighting the need to identify new biomarkers linked to poor clinical outcome. HRAS mutations are found in skin papillomas and cSCCs and increase in frequency when MAP3K family members are inhibited, suggesting a link between blockade of mitogen-activated protein kinase (MAPK) signaling and initiation of RAS-primed cells. Tpl2, a MAP3K gene, can serve as a tumor suppressor gene in cSCC. We have previously shown that upon Tpl2 ablation, mice have heightened sensitivity to aberrant RAS signaling. Tpl2-/- mice display significantly higher numbers of papillomas and cSCCs in two-stage chemical carcinogenesis studies and increased tumorigenicity of keratinocytes expressing oncogenic v-rasHa in nude mouse skin grafts. In part, this is mediated through increased mesenchymal-epithelial transition factor (MET) receptor activity. Epidermal Growth Factor Receptor (EGFR) is reported to be an essential factor for MET-driven carcinogenesis and MET activation may confer resistance to EGFR therapies, suggesting that the concurrent use of both an EGFR inhibitor and a MET inhibitor may show promise in advanced cSCCs. In this study we assessed whether normal or Ras-transformed Tpl2-/- keratinocytes have aberrant EGFR signaling and whether concomitant treatment with EGFR/MET tyrosine kinase inhibitors was more effective than single agents in reducing growth and angiogenic potential of Ras-transformed keratinocytes. Tpl2-/- keratinocytes exhibited increased HER-2 and STAT-3 under basal conditions and elevated p-MET and p-EGFR when transduced with oncogenic RAS. Inhibition of MET by Capmatinib increased p-EGFR in Tpl2-/- keratinocytes and papillomas, and inhibition of EGFR by Gefitinib increased HER2 and HER3 signaling in both genotypes. Treatment of keratinocytes with EGFR and MET inhibitors, in combination, significantly enhanced endothelial tube formation, MMP-9 activity and activation of other RTKs, with more pronounced effects when Tpl2 was ablated. These data indicate that Tpl2 cross-talks with both EGFR and MET signaling pathways. Upon inhibition of EGFR/MET signaling, a myriad of escape mechanisms exists in keratinocytes to overcome targeted drug effects.

Functional polymorphism in Pak1-3'UTR alters skin tumor susceptibility by alternative polyadenylation

We identified a functional single nucleotide polymorphism (SNP) in the 3' untranslated region (UTR) of p21-activated kinase 1 (Pak1) that is responsible for the Skin tumor modifier of MSM 1a locus. Candidate SNPs in the 3'UTR of Pak1 from resistance strain MSM/Ms were introduced into susceptible strain FVB/N using CRISPR/Cas9. DMBA/TPA skin carcinogenesis experiments revealed an SNP (Pak1-3'UTR-6^C>T: rs31627325) that strongly suppressed skin tumors. Furthermore, Muscleblind-Like Splicing Regulator 1 bound more strongly to FVB-allele (6^C/C) and regulated the transcript length in the 3'UTR of Pak1 and tumorigenesis via polyadenylation. Therefore, the alternative polyadenylation of Pak1 is cis-regulated by rs31627325.

Salivary Exosome Proteomics and Bioinformatics Analysis in 7,12-Dimethylbenz[a]anthracene-Induced Oral Cancer with Radiation Therapy-A Syrian Golden Hamster Model

Exosomes carry cellular proteins and contain molecules that can be potential biomarkers of diseases. This study used a Syrian golden hamster model of 7,12-dimethylbenz[a]anthracene (DMBA)-induced oral squamous cell carcinoma with radiation therapy to exclude the confounding factors that may affect outcomes in clinical studies, and re-examine the role of exosomes during tumorigenesis. We used data-dependent acquisition-based quantitative proteomics and bioinformatics analyses and found unique proteins present (desmocollin-2) or absent (Glucagon-cAMP-PKA-CREB pathway-related proteins) in the salivary exosomes of the pre-radiation DMBA-treated group (PreD). Comparing our data to other studies, salivary exosomes in the PreD group were found carrying proteins that the tumor mass does not express and lacking the proteins needed during tumorigenesis. Immunohistochemistry staining showed p53 expression but a negative apoptotic signal in the PreD tumor tissue. We thus suggest that inhibition of desmocollin-2 expression in tumor tissue may impede the activation of cell apoptosis. However, both the origin of the salivary exosomes and main role of the salivary exosome proteins should be clarified in future studies.

KLF5, a Novel Therapeutic Target in Squamous Cell Carcinoma

Squamous cell carcinomas (SCCs) are the most common ectodermal cancers, and result in more than 300,000 deaths per year. The Krüppel-like family of transcription factors play a critical role in cancer pathogenesis. The Krüppel-like factor 5 gene (KLF5), which is a member of Krüppel-like family, has been reported to promote cancer cell proliferation and tumorigenesis. In this review, we discuss the roles of KLF5 in different SCCs and the mechanisms by which KLF5 transcriptionally regulates its target gene expression in the pathogenesis and progression of SCCs. Due to its significant functions in cell proliferation and differentiation, KLF5 could be a novel diagnostic biomarker and therapeutic target for the treatment of SCCs.

Loss of epidermal MCPIP1 is associated with aggressive squamous cell carcinoma

BACKGROUND

Squamous cell carcinoma (SCC) of the skin is a common form of nonmelanoma skin cancer. Monocyte chemotactic protein 1-induced protein 1 (MCPIP1), also called Regnase-1, is an RNase with anti-inflammatory properties. In normal human skin, its expression is predominantly restricted to the suprabasal epidermis. The main aim of this study was to investigate whether MCPIP1 is involved in the pathogenesis of SCC.

METHODS

We analyzed the distribution of MCPIP1 in skin biopsies of patients with actinic keratoses (AKs) and SCCs. To explore the mechanisms by which MCPIP1 may modulate tumorigenesis in vivo, we established a mouse model of chemically induced carcinogenesis.

RESULTS

Skin expression of MCPIP1 changed during the transformation of precancerous lesions into cutaneous SCC. MCPIP1 immunoreactivity was high in the thickened area of the AK epidermis but was predominantly restricted to keratin pearls in fully developed SCC lesions. Accelerated development of chemically induced skin tumors was observed in mice with loss of epidermal MCPIP1 (Mcpip1^eKO). Papillomas that developed in Mcpip1^eKO mouse skin were larger and characterized by elevated expression of markers typical of keratinocyte proliferation and tumor angiogenesis. This phenotype was correlated with enhanced expression of IL-6, IL-33 and transforming growth factor-beta (TGF-β). Moreover, our results demonstrated that in keratinocytes, the RNase MCPIP1 is essential for the negative regulation of genes encoding SCC antigens and matrix metallopeptidase 9.

CONCLUSIONS

Overall, our results provide a mechanistic understanding of how MCPIP1 contributes to the development of epidermoid carcinoma.

Anti-Malignant Effect of Tensile Loading to Adherens Junctions in Cutaneous Squamous Cell Carcinoma Cells

Actomyosin contractility regulates various cellular processes including proliferation and differentiation while dysregulation of actomyosin activity contributes to cancer development and progression. Previously, we have reported that actomyosin-generated tension at adherens junctions is required for cell density-dependent inhibition of proliferation of normal skin keratinocytes. However, it remains unclear how actomyosin contractility affects the hyperproliferation ability of cutaneous squamous cell carcinoma (cSCC) cells. In this study, we find that actomyosin activity is impaired in cSCC cells both in vitro and in vivo. External application of tensile loads to adherens junctions by sustained mechanical stretch attenuates the proliferation of cSCC cells, which depends on intact adherens junctions. Forced activation of actomyosin of cSCC cells also inhibits their proliferation in a cell-cell contact-dependent manner. Furthermore, the cell cycle arrest induced by tensile loading to adherens junctions is accompanied by epidermal differentiation in cSCC cells. Our results show that the degree of malignant properties of cSCC cells can be reduced by applying tensile loads to adherens junctions, which implies that the mechanical status of adherens junctions may serve as a novel therapeutic target for cSCC.

Deep neural network for the determination of transformed foci in Bhas 42 cell transformation assay

Bhas 42 cell transformation assay (CTA) has been used to estimate the carcinogenic potential of chemicals by exposing Bhas 42 cells to carcinogenic stimuli to form colonies, referred to as transformed foci, on the confluent monolayer. Transformed foci are classified and quantified by trained experts using morphological criteria. Although the assay has been certified by international validation studies and issued as a guidance document by OECD, this classification process is laborious, time consuming, and subjective. We propose using deep neural network to classify foci more rapidly and objectively. To obtain datasets, Bhas 42 CTA was conducted with a potent tumor promotor, 12-O-tetradecanoylphorbol-13-acetate, and focus images were classified by experts (1405 images in total). The labeled focus images were augmented with random image processing and used to train a convolutional neural network (CNN). The trained CNN exhibited an area under the curve score of 0.95 on a test dataset significantly outperforming conventional classifiers by beginners of focus judgment. The generalization performance of unknown chemicals was assessed by applying CNN to other tumor promotors exhibiting an area under the curve score of 0.87. The CNN-based approach could support the assay for carcinogenicity as a fundamental tool in focus scoring.

Loss of integrin α9β1 on tumor keratinocytes enhances the stromal vasculature and growth of cutaneous tumors

Angiogenesis is critical to tumor progression and the function of integrins in tumor angiogenesis is complex. Here we report that loss of integrin α9β1 expression from epidermal tumor cells is critical to maintain persistent stromal vessel density. Forced expression of α9 in transformed mouse keratinocytes dramatically reduces vessel density in allograft tumors, in vivo, compared to the same cells lacking α9β1. Moreover, α9 mRNA expression is dramatically reduced in mouse and human epidermal tumors as is α9β1-dependent gene regulation. Loss of tumor cell α9β1 occurs through at least two mechanisms: (1) ITGA9 gene copy number loss in human tumors, and (2) epigenetic silencing in mouse and human tumors. Importantly, we show that reversal of epigenetic silencing of Itga9 restores α9 expression in mouse keratinocytes, and that human tumors without ITGA9 copy number loss have increased promoter methylation. Our data suggest that for epidermal tumorigenesis to occur, tumor cells must avoid the tumor and angiogenic suppressive effects of α9β1 by repressing its expression through deletion and/or epigenetic silencing, thereby promoting stromal development and tumor growth.

IL-13Rα1 Suppresses Tumor Progression in Two-stage Skin Carcinogenesis Model by Regulating Regulatory T Cells

Type 2-inflammation-related cytokine Interleukin (IL)-13 plays a protective role in experimental papilloma induction in mice. To understand mechanisms by which IL-13 contributes to papilloma formation we utilized IL-13Rα1 knockout (KO) mice in widely used DMBA/TPA two-stage skin carcinogenesis protocol that mimics the development of Squamous Cell Carcinoma (SCC). KO mice developed more papillomas and significantly faster than wild-type (WT) mice. Papilloma development reduced Tregs in WT mice, but substantially less in KO mice. In line with this, IL-2 and IL-10 levels decreased in WT mice, but not in KO mice. Furthermore, systemic IL-5 and Thymic Stromal Lymphopoietin (TSLP) levels were elevated, while IL-22 was decreased during papilloma formation in the skin of KO mice. Polymorphonuclear Myeloid-derived suppressor cells (PMN-MDSCs) were decreased in the KO mice at the early phase of papilloma induction. We demonstrate that IL-13Rα1 protects from papilloma development in chemically induced skin carcinogenesis and our results provide further insights into the protective role of functional IL-4 and IL-13 signaling via type II IL-4R in tumor development.

Lymphatic Dysfunction Exacerbates Cutaneous Tumorigenesis and Psoriasis-Like Skin Inflammation through Accumulation of Inflammatory Cytokines

Lymphatic transport plays an important role in coordinating local immune responses. However, the biologic effects of impaired lymphatic flow in vivo are not fully understood. In this study, we investigated the roles of the lymphatic system in skin carcinogenesis and psoriasis-like inflammation using k-cyclin transgenic (kCYC^+/-) mice, which demonstrate severe lymphatic dysfunction. kCYC^+/- mice showed augmented tumor growth in the two-stage skin carcinogenesis model and severe clinical scores in imiquimod-induced psoriasis-like skin inflammation compared with wild-type mice. Although mRNA levels of inflammatory cytokines in skin after topical application of 12-O-tetradecanoylphorbol-13-acetate or imiquimod were comparable between kCYC^+/- and wild-type mice, protein levels of inflammatory cytokines, such as IL-17A, IL-22, and IL-23, were significantly upregulated in kCYC^+/- mice in both models. Consistently, signal transducer and activator of transcription 3 pathway and NF-κB signaling were augmented in epidermal keratinocytes in kCYC^+/- mice. These results suggest that lymphatic dysfunction in kCYC^+/- mice caused accumulation of inflammatory cytokines, leading to the exacerbation of two-stage skin carcinogenesis and imiquimod-induced psoriasis-like skin inflammation. These findings add insight into the clinical problems of secondary malignancies and inflammatory dermatoses that may occur with extremity lymphedema.

NR2F2 controls malignant squamous cell carcinoma state by promoting stemness and invasion and repressing differentiation

The nongenetic mechanisms required to sustain malignant tumor state are poorly understood. During the transition from benign tumors to malignant carcinoma, tumor cells need to repress differentiation and acquire invasive features. Using transcriptional profiling of cancer stem cells from benign tumors and malignant skin squamous cell carcinoma (SCC), we identified the nuclear receptor NR2F2 as uniquely expressed in malignant SCC. Using genetic gain of function and loss of function in vivo, we show that NR2F2 is essential for promoting the malignant tumor state by controlling tumor stemness and maintenance in mouse and human SCC. We demonstrate that NR2F2 promotes tumor cell proliferation, epithelial-mesenchymal transition and invasive features, while repressing tumor differentiation and immune cell infiltration by regulating a common transcriptional program in mouse and human SCCs. Altogether, we identify NR2F2 as a key regulator of malignant cancer stem cell functions that promotes tumor renewal and restricts differentiation to sustain a malignant tumor state.

DNAM-1 promotes inflammation-driven tumor development via enhancing IFN-γ production

DNAM-1 is an activating immunoreceptor on T cells and natural killer (NK) cells. Expression levels of its ligands, CD155 and CD112, are upregulated on tumor cells. The interaction of DNAM-1 on CD8 + T cells and NK cells with the ligands on tumor cells plays an important role in tumor immunity. We previously reported that mice deficient in DNAM-1 showed accelerated growth of tumors induced by the chemical carcinogen 7,12-dimethylbenz[a]anthracene (DMBA). Contrary to those results, we show here that tumor development induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) together with DMBA was suppressed in DNAM-1-deficient mice. In this model, DNAM-1 enhanced IFN-γ secretion from conventional CD4 + T cells to promote inflammation-related tumor development. These findings suggest that, under inflammatory conditions, DNAM-1 contributes to tumor development via conventional CD4 + T cells.

Expression of CCRL2 Inhibits Tumor Growth by Concentrating Chemerin and Inhibiting Neoangiogenesis

Simple Summary

Chemerin is a multifunctional protein regulating inflammation, immune responses, and metabolism. It was also shown to display anti-tumoral properties in various cancer models. CMKLR1 is the main functional receptor of chemerin. C-C motif chemokine receptor-like 2 (CCRL2) is another receptor binding chemerin with high affinity but failing to signal through any known signaling pathway. CCRL2 is strongly upregulated by inflammatory signals and was shown to regulate inflammatory reactions in diverse pathological conditions. Expression of CCRL2 was described in many types of human tumors such as melanoma, neuroblastoma, prostate, breast, and gastric cancer. However, its functional role in cancer has not been studied much so far. We investigate in this study how CCRL2 expression can influence the distribution of chemerin and thereby its biological activity in different tumoral contexts.

Abstract

CCRL2 belongs to the G protein-coupled receptor family and is one of the three chemerin receptors. It is considered as a non-signaling receptor, presenting chemerin to cells expressing the functional chemerin receptor ChemR23/CMKLR1 and possibly GPR1. In the present work, we investigate the role played by CCRL2 in mouse cancer models. Loss of function of Ccrl2 accelerated the development of papillomas in a chemical model of skin carcinogenesis (DMBA/TPA), whereas the growth of B16 and LLC tumor cell grafts was delayed. Delayed tumor growth was also observed when B16 and LLC cells overexpress CCRL2, while knockout of Ccrl2 in tumor cells reversed the consequences of Ccrl2 knockout in the host. The phenotypes associated with CCRL2 gain or loss of function were largely abrogated by knocking out the chemerin or Cmklr1 genes. Cells harboring CCRL2 could concentrate bioactive chemerin and promote the activation of CMKLR1-expressing cells. A reduction of neoangiogenesis was observed in tumor grafts expressing CCRL2, mimicking the phenotype of chemerin-expressing tumors. This study demonstrates that CCRL2 shares functional similarities with the family of atypical chemokine receptors (ACKRs). Its expression by tumor cells can significantly tune the effects of the chemerin/CMKLR1 system and act as a negative regulator of tumorigenesis.

PHLDA3 is an important downstream mediator of p53 in squamous cell carcinogenesis

Squamous cell carcinomas (SCCs) are one of the most frequent solid cancer types in humans and are derived from stratified epithelial cells found in various organs. SCCs derived from various organs share common important properties including genomic abnormalities in the tumor suppressor gene p53. There is a carcinogen-induced mouse model of SCC which produces benign papilloma, some of which progress to advanced carcinoma and metastatic SCCs. These SCCs undergo key genetic alterations that are conserved between human and mice, including alterations in the genomic p53 sequence, and is therefore an ideal system to study the mechanisms of SCC tumorigenesis. Using this SCC model, we show that the PHLDA3 gene, a p53 target gene encoding an Akt repressor, is involved in the suppression of benign and metastatic tumor development. Loss of PHLDA3 induces an epithelial-mesenchymal transition (EMT) and can complement p53 loss in the formation of metastatic tumors. We also show that in human SCC patients, low PHLDA3 expression is associated with poorer prognosis. Collectively, this study identifies PHLDA3 as an important downstream molecule of p53 involved in SCC development and progression.

Oh, the Mutations You'll Acquire! A Systematic Overview of Cutaneous Squamous Cell Carcinoma

Nearly two million cases of cutaneous squamous cell carcinoma (cSCC) are diagnosed every year in the United States alone. cSCC is notable for both its prevalence and its propensity for invasion and metastasis. For many patients, surgery is curative. However, patients experiencing immunosuppression or recurrent, advanced, and metastatic disease still face limited therapeutic options and significant mortality. cSCC forms after decades of sun exposure and possesses the highest known mutation rate of all cancers. This mutational burden complicates efforts to identify the primary factors driving cSCC initiation and progression, which in turn hinders the development of targeted therapeutics. In this review, we summarize the mutations and alterations that have been observed in patients’ cSCC tumors, affecting signaling pathways, transcriptional regulators, and the microenvironment. We also highlight novel therapeutic opportunities in development and clinical trials.

miR-22 promotes stem cell traits via activating Wnt/β-catenin signaling in cutaneous squamous cell carcinoma

Emerging evidence suggests that the cancer stem cells (CSCs) are key culprits of cancer metastasis and drug resistance. Understanding mechanisms regulating the critical oncogenic pathways and CSCs function could reveal new diagnostic and therapeutic strategies. We now report that miR-22, a miRNA critical for hair follicle stem/progenitor cell differentiation, promotes tumor initiation, progression, and metastasis by maintaining Wnt/β-catenin signaling and CSCs function. Mechanistically, we find that miR-22 facilitates β-catenin stabilization through directly repressing citrullinase PAD2. Moreover, miR-22 also relieves DKK1-mediated repression of Wnt/β-catenin signaling by targeting a FosB-DDK1 transcriptional axis. miR-22 knockout mice showed attenuated Wnt/β-catenin activity and Lgr5+ CSCs penetrance, resulting in reduced occurrence, progression, and metastasis of chemically induced cutaneous squamous cell carcinoma (cSCC). Clinically, miR-22 is abundantly expressed in human cSCC. Its expression is even further elevated in the CSCs proportion, which negatively correlates with PAD2 and FosB expression. Inhibition of miR-22 markedly suppressed cSCC progression and increased chemotherapy sensitivity in vitro and in xenograft mice. Together, our results revealed a novel miR-22-WNT-CSCs regulatory mechanism in cSCC and highlight the important clinical application prospects of miR-22, a common target molecule for Wnt/β-catenin signaling and CSCs, for patient stratification and therapeutic intervention.

Skin Cancers and the Contribution of Rho GTPase Signaling Networks to Their Progression

Skin cancers are the most common cancers worldwide. Among them, melanoma, basal cell carcinoma of the skin and cutaneous squamous cell carcinoma are the three major subtypes. These cancers are characterized by different genetic perturbations even though they are similarly caused by a lifelong exposure to the sun. The main oncogenic drivers of skin cancer initiation have been known for a while, yet it remains unclear what are the molecular events that mediate their oncogenic functions and that contribute to their progression. Moreover, patients with aggressive skin cancers have been known to develop resistance to currently available treatment, which is urging us to identify new therapeutic opportunities based on a better understanding of skin cancer biology. More recently, the contribution of cytoskeletal dynamics and Rho GTPase signaling networks to the progression of skin cancers has been highlighted by several studies. In this review, we underline the various perturbations in the activity and regulation of Rho GTPase network components that contribute to skin cancer development, and we explore the emerging therapeutic opportunities that are surfacing from these studies.

Combined intermittent fasting and ERK inhibition enhance the anti-tumor effects of chemotherapy via the GSK3β-SIRT7 axis

Dietary interventions such as intermittent fasting (IF) have emerged as an attractive strategy for cancer therapies; therefore, understanding the underlying molecular mechanisms is pivotal. Here, we find SIRT7 decline markedly attenuates the anti-tumor effect of IF. Mechanistically, AMP-activated protein kinase (AMPK) phosphorylating SIRT7 at T263 triggers further phosphorylation at T255/S259 by glycogen synthase kinase 3β (GSK3β), which stabilizes SIRT7 by decoupling E3 ligase UBR5. SIRT7 hyperphosphorylation achieves anti-tumor activity by disrupting the SKP2-SCF E3 ligase, thus preventing SKP2-mediated K63-linked AKT polyubiquitination and subsequent activation. In contrast, GSK3β-SIRT7 axis is inhibited by EGF/ERK2 signaling, with ERK2 inactivating GSK3β, thus accelerating SIRT7 degradation. Unfavorably, glucose deprivation or chemotherapy hijacks the GSK3β-SIRT7 axis via ERK2, thus activating AKT and ensuring survival. Notably, Trametinib, an FDA-approved MEK inhibitor, enhances the efficacy of combination therapy with doxorubicin and IF. Overall, we have revealed the GSK3β-SIRT7 axis that must be fine-tuned in the face of the energetic and oncogenic stresses in malignancy.

The combination of intermittent fasting and chemotherapy can improve the response to treatment. Here, the authors show that SIRT7 activation is required to inactivate Akt during intermittent fasting and that the combination of intermittent fasting and inhibitors that block the Erk pathway can improve efficacy of treatment.

The RATIOnal Role of Polyamines in Epidermal Differentiation

Polyamines have been implicated in skin tumorigenesis; however, their role in epidermal homeostasis remains obscure. In a new article in the Journal of Investigative Dermatology, Rahim et al. (2021) report that keratinocyte differentiation requires a shift in polyamine ratios that is mediated by AMD1. Results suggest that targeting polyamine availability might be useful in the treatment of hyperproliferative skin disorders.

Animal Models of Metastatic Lesions to the Spine: a Focus on Epidural Spinal Cord Compression

Epidural spinal cord compression (ESCC) secondary to spine metastases is one of the most devastating sequelae of primary cancer as it may lead to muscle weakness, paresthesia, pain, and paralysis. Spine metastases occur through a multi-step process that can result in eventual ESCC; however, the lack of a preclinical model to effectively recapitulate each step of this metastatic cascade and the symptom burden of ESCC has limited our understanding of this disease process. In this review, we discuss animal models that best recapitulate ESCC; we start with a broad discussion of commonly used models of bone metastasis and end with a focused discussion of models used to specifically study ESCC. Orthotopic models offer the most authentic recapitulation of metastasis development; however, they rarely result in symptomatic ESCC and are challenging to replicate. Conversely, models that involve injection of tumor cells directly into the bloodstream or bone better mimic the symptoms of ESCC; however, they provide limited insight into the epithelial to mesenchymal transition (EMT) and natural hematogenous spread of tumor cell. Therefore, until an ideal model is created, it is critical to select an animal model that is specifically designed to answer the scientific question of interest.

Efficient In Vitro and In Vivo Anti-Inflammatory Activity of a Diamine-PEGylated Oleanolic Acid Derivative

Recent evidence has shown that inflammation can contribute to all tumorigenic states. We have investigated the anti-inflammatory effects of a diamine-PEGylated derivative of oleanolic acid (OADP), in vitro and in vivo with inflammation models. In addition, we have determined the sub-cytotoxic concentrations for anti-inflammatory assays of OADP in RAW 264.7 cells. The inflammatory process began with incubation with lipopolysaccharide (LPS). Nitric oxide production levels were also determined, exceeding 75% inhibition of NO for a concentration of 1 µg/mL of OADP. Cell-cycle analysis showed a reversal of the arrest in the G0/G1 phase in LPS-stimulated RAW 264.7 cells. Furthermore, through Western blot analysis, we have determined the probable molecular mechanism activated by OADP; the inhibition of the expression of cytokines such as TNF-α, IL-1β, iNOS, and COX-2; and the blocking of p-IκBα production in LPS-stimulated RAW 264.7 cells. Finally, we have analyzed the anti-inflammatory action of OADP in a mouse acute ear edema, in male BL/6J mice treated with OADP and tetradecanoyl phorbol acetate (TPA). Treatment with OADP induced greater suppression of edema and decreased the ear thickness 14% more than diclofenac. The development of new derivatives such as OADP with powerful anti-inflammatory effects could represent an effective therapeutic strategy against inflammation and tumorigenic processes.

Calcium Fructoborate Prevents Skin Cancer Development in Balb-c Mice: Next Part, Reverse Inflammation, and Metabolic Alteration

Metabolic alterations and inflammation are regarded as hallmarks of cancer. Glycolytic flux and intermediate accumulation lead to the production of building blocks and NADPH which is important in protecting the cell from oxidative damage. Inflammation causes the release of mediators responsible for regulating molecular mechanism affecting metabolic pathways. CaFB due to its cis-diol-rich feature may have the potential to interact with molecules taking part in cancer development. This study was aimed to investigate the effects of CaFB on metabolic alterations and inflammation in 7,12-dimethylbenz(a)anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA)-induced skin cancer. For this purpose, 92 Balb-c mice were distributed into 6 groups as control, CaFB, DMBA/TPA (D-T), treatment 1 (T1), 2 (T2), and 3(T3). Apart from control and CaFB in other groups, tumors initiated with 97.5-nmol DMBA and 6.5-nmol TPA. Treatment groups received 3 mg/kg/day CaFB with DMBA (T1), with TPA (T2), and after tumor formation (T3). In the D-T group, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity, 6-phosphogluconate dehydrogenase (PGD), glutathione (GSH), interleukin 6 (IL-6), (IL-1β), tumor necrosis factor-α (TNF-α) levels increased (p < 0.001) while malondialdehyde (MDA) levels decreased (p < 0.001) compared with that in control. CaFB application ameliorated DMBA-TPA effect according to the distribution time. It is noteworthy to consider CaFB as a potential preventive agent in skin cancer development.

Vitamin D and Vitamin D Analogs as Adjuncts to Field Therapy Treatments for Actinic Keratoses: Current Research and Future Approaches

Actinic keratoses (AK), also known as solar keratoses, are precancerous hyperkeratotic papules caused by long-term exposure to ultraviolet radiation. Management of AK prior to progression to cutaneous malignancy represents an important window of intervention. This is important on a population level, given the high incidence, morbidity, financial costs, and the low but measurable risk of mortality from cutaneous neoplasia. Treatments for AK have been refined for many years with significant progress over the past decade. Those recent advancements lead to questions about current treatment paradigms and the role of harnessing the immune system in field therapies. Recent studies suggest a key interplay between vitamin D and cancer immunity; in particular, the systemic and/or topical vitamin D analogs can augment field therapies used for severe actinic damage. In this review, we will examine the literature supporting the use of vitamin D-directed therapies to improve field therapy approaches. An enhanced understanding of these recent concepts with a focus on mechanisms is important in the optimized management of AK. These mechanisms will be critical in guiding whether selected populations, including those with immunosuppression, heritable cancer syndromes, and other risk factors for skin cancer, can benefit from these new concepts with vitamin D analogs and whether the approaches will be as effective in these populations as in immunocompetent patients.

Mdm2 phosphorylation by Akt regulates the p53 response to oxidative stress to promote cell proliferation and tumorigenesis

We have shown previously that phosphorylation of Mdm2 by ATM and c-Abl regulates Mdm2-p53 signaling and alters the effects of DNA damage in mice, including bone marrow failure and tumorigenesis induced by ionizing radiation. Here, we examine the physiological effects of Mdm2 phosphorylation by Akt, another DNA damage effector kinase. Surprisingly, Akt phosphorylation of Mdm2 does not alter the p53-mediated effects of ionizing radiation in cells or mice but regulates the p53 response to oxidative stress. Akt phosphorylation of Mdm2 serine residue 183 increases nuclear Mdm2 stability, decreases p53 levels, and prevents senescence in primary cells exposed to reactive oxidative species (ROS). Using multiple mouse models of ROS-induced cancer, we show that Mdm2 phosphorylation by Akt reduces senescence to promote Kras^G12D-driven lung cancers and carcinogen-induced papilloma and hepatocellular carcinomas. Collectively, we document a unique physiologic role for Akt-Mdm2-p53 signaling in regulating cell growth and tumorigenesis in response to oxidative stress.

Thyroid Hormone Enhances Angiogenesis and the Warburg Effect in Squamous Cell Carcinomas

Simple Summary

Cancer cells rewire their metabolism to promote growth, survival, proliferation, and long-term maintenance. Aerobic glycolysis is a prominent trait of many cancers; contextually, glutamine addiction, enhanced glucose uptake and aerobic glycolysis sustain the metabolic needs of rapidly proliferating cancer cells. Thyroid hormone (TH) is a positive regulator of tumor progression and metastatic conversion of squamous cell carcinoma (SCC). Accordingly, overexpression of the TH activating enzyme, D2, is associated with metastatic SCC. The aim of our study was to assess the ability of TH and its activating enzyme in promoting key tracts of cancer progression such as angiogenesis, response to hypoxia and metabolic adaptation. By performing in vivo and in vitro studies, we demonstrate that TH induces VEGF-A in cancer cells and fosters aerobic glycolysis inducing pro-glycolytic mediators, thus implying that TH signal attenuation represents a therapeutic tool to contrast tumor angiogenesis and tumor progression.

Abstract

Cancer angiogenesis is required to support energetic demand and metabolic stress, particularly during conditions of hypoxia. Coupled to neo-vasculogenesis, cancer cells rewire metabolic programs to sustain growth, survival and long-term maintenance. Thyroid hormone (TH) signaling regulates growth and differentiation in a variety of cell types and tissues, thus modulating hyper proliferative processes such as cancer. Herein, we report that TH coordinates a global program of metabolic reprogramming and induces angiogenesis through up-regulation of the VEGF-A gene, which results in the enhanced proliferation of tumor endothelial cells. In vivo conditional depletion of the TH activating enzyme in a mouse model of cutaneous squamous cell carcinoma (SCC) reduces the concentration of TH in the tumoral cells and results in impaired VEGF-A production and attenuated angiogenesis. In addition, we found that TH induces the expression of the glycolytic genes and fosters lactate production, which are key traits of the Warburg effect. Taken together, our results reveal a TH–VEGF-A–HIF1α regulatory axis leading to enhanced angiogenesis and glycolytic flux, which may represent a target for SCC therapy.

Topical arginase inhibition decreases growth of cutaneous squamous cell carcinoma

Cutaneous squamous cell carcinomas (cSCC) are among the most commonly diagnosed malignancies, causing significant morbidity and mortality. Tumor-associated macrophage (TAM) expression of arginase is implicated in tumor progression, and therapeutic use of arginase inhibitors has been studied in various cancers. However, investigating potential cSCC immunotherapies including arginase inhibition in pre-clinical models is hampered by the lack of appropriate tumor models in immunocompetent mice. PDV is a cSCC cell line derived from chemical carcinogenesis of mouse keratinocytes. PDVC57 cells were derived from a PDV tumor in C57BL/6 (B6) mice. Unlike PDV, PDVC57 tumors grow consistently in B6 mice, and have increased TAMs, decreased dendritic and T cell intra-tumor infiltration. Arginase inhibition in cSCC tumors using Nω-hydroxy-nor-arginine (nor-NOHA) reduced tumor growth in B6 mice but not immunodeficient Rag1-deficient mice. nor-NOHA administration increased dendritic and T cell tumor-infiltration and PD-1 expression. The combination of nor-NOHA and anti-PD-1 therapy with nivolumab enhanced anti-PD-1 therapeutic efficacy. This study demonstrates the therapeutic potential of transcutaneous arginase inhibition in cSCC. A competent immune microenvironment is required for tumor growth inhibition using this arginase inhibitor. Synergistic co-inhibition of tumor growth in these results, supports further examination of transcutaneous arginase inhibition as a therapeutic modality for cSCC.

Curcumin Nanoemulsions Stabilized with Modified Phosphatidylcholine on Skin Carcinogenesis Protocol

BACKGROUND

Cancer is one of the main causes of death by disease; several alternative treatments have been developed to counteract this condition. Curcumin (diferuloylmethane), extracted from the rhizome of Curcuma longa, has antioxidant, anti-inflammatory, and anti-cancer properties; however, it has low water solubility and poor intestinal absorption. Carrier systems, such as nanoemulsions, can increase the bioavailability of lipophilic bioactive compounds.

OBJECTIVE

To evaluate the effect of curcumin nanoemulsions prepared with lecithin modified with medium-chain fatty acids as an emulsifier, on the expression of the Cdk4, Ccne2, Casp8 and Cldn4 genes involved in the carcinogenesis process in K14E6 transgenic mice.

METHODS

The emulsifier was prepared by interesterification of medium-chain fatty acids, pure lecithin, and immobilized phospholipase-1 on Duolite A568. An Ultraturrax homogenizer and a Branson Ultrasonic processor were used for the preparation of nano-emulsions, and a Zetasizer evaluated the particle size. qRT-PCR analysis was performed to quantify the cancer-related genes expressed in the K14E6 mice. The development and evolution of skin carcinogenesis were assessed through histological analysis to compare cell morphology.

RESULTS

Ca 59% of the MCFA were incorporated via esterification into the PC within 12 hours of the reaction. An emulsifier yield used to formulate the NE of 86% was achieved. Nanoemulsions with a particle size of 44 nm were obtained. The curcumin nano-emulsion group had a 91.81% decrease in the tumorigenesis index and a reduction in tumor area of 89.95% compared to the sick group. Histological analysis showed that the group administered with free curcumin developed a microinvasive squamous cell carcinoma, as opposed to the group with nanoemulsion which presented only a slight inflammation. In gene expression, only a significant difference in Cdk4 was observed in the nanoemulsion group.

Generation of a tissue-specific transgenic model for K8 phosphomutants: A tool to investigate the role of K8 phosphorylation during skin carcinogenesis in vivo

Keratin 8/18, the predominant keratin pair of simple epithelia, is known to be aberrantly expressed in several squamous cell carcinomas (SCCs), where its expression is often correlated with increased invasion, neoplastic progression, and poor prognosis. The majority of keratin 8/18 structural and regulatory functions are governed by posttranslational modifications, particularly phosphorylation. Apart from filament reorganization, cellular processes including cell cycle, cell growth, cellular stress, and apoptosis are known to be orchestrated by K8 phosphorylation at specific residues in the head and tail domains. Even though deregulation of K8 phosphorylation at two significant sites (Serine⁷³ /Serine⁴³¹ ) has been implicated in neoplastic progression of SCCs by various in vitro studies, including ours, it is reported to be highly context-dependent. Therefore, to delineate the precise role of Kereatin 8 phosphorylation in cancer initiation and progression, we have developed the tissue-specific transgenic mouse model expressing Keratin 8 wild type and phosphodead mutants under Keratin 14 promoter. Subjecting these mice to 7,12-dimethylbenz(a)anthracene/12-O-tetradecanoylphorbol-13-acetate-mediated skin carcinogenesis revealed that Keratin 8 phosphorylation may lead to an early onset of tumors compared to Keratin 8 wild-type expressing mice. Conclusively, the transgenic mouse model developed in the present study ascertained a positive impact of Keratin 8 phosphorylation on the neoplastic transformation of skin-squamous cells.

Loss of DLX3 tumor suppressive function promotes progression of SCC through EGFR-ERBB2 pathway

Cutaneous squamous cell carcinoma (cSCC) ranks second in the frequency of all skin cancers. The balance between keratinocyte proliferation and differentiation is disrupted in the pathological development of cSCC. DLX3 is a homeobox transcription factor which plays pivotal roles in embryonic development and epidermal homeostasis. To investigate the impact of DLX3 expression on cSCC prognosis, we carried out clinicopathologic analysis of DLX3 expression which showed statistical correlation between tumors of higher pathologic grade and levels of DLX3 protein expression. Further, Kaplan-Meier survival curve analysis demonstrated that low DLX3 expression correlated with poor patient survival. To model the function of Dlx3 in skin tumorigenesis, a two-stage dimethylbenzanthracene (DMBA)/12-O-tetradecanoylphorbol 13-acetate (TPA) study was performed on mice genetically depleted of Dlx3 in skin epithelium (Dlx3cKO). Dlx3cKO mice developed significantly more tumors, with more rapid tumorigenesis compared to control mice. In Dlx3cKO mice treated only with DMBA, tumors developed after ~16 weeks suggesting that loss of Dlx3 has a tumor promoting effect. Whole transcriptome analysis of tumor and skin tissue from our mouse model revealed spontaneous activation of the EGFR-ERBB2 pathway in the absence of Dlx3. Together, our findings from human and mouse model system support a tumor suppressive function for DLX3 in skin and underscore the efficacy of therapeutic approaches that target EGFR-ERBB2 pathway.

Clinically relevant aberrant Filip1l DNA methylation detected in a murine model of cutaneous squamous cell carcinoma

BACKGROUND

Cutaneous squamous cell carcinomas (cSCC) are among the most common and highly mutated human malignancies. Understanding the impact of DNA methylation in cSCC may provide avenues for new therapeutic strategies.

METHODS

We used reduced-representation bisulfite sequencing for DNA methylation analysis of murine cSCC. Differential methylation was assessed at the CpG level using limma. Next, we compared with human cSCC Infinium HumanMethylation BeadArray data. Genes were considered to be of major relevance when they featured at least one significantly differentially methylated CpGs (RRBS) / probes (Infinium) with at least a 30% difference between tumour vs. control in both a murine gene and its human orthologue. The human EPIC Infinium data were used to distinguish two cSCC subtypes, stem-cell-like and keratinocyte-like tumours.

FINDINGS

We found increased average methylation in mouse cSCC (by 12.8%, p = 0.0011) as well as in stem-cell like (by 3.1%, p=0.002), but not keratinocyte-like (0.2%, p = 0.98), human cSCC. Comparison of differentially methylated genes revealed striking similarities between human and mouse cSCC. Locus specific methylation changes in mouse cSCC often occurred in regions of potential regulatory function, including enhancers and promoters. A key differentially methylated region was located in a potential enhancer of the tumour suppressor gene Filip1l and its expression was reduced in mouse tumours. Moreover, the FILIP1L locus showed hypermethylation in human cSCC and lower expression in human cSCC cell lines.

INTERPRETATION

Deregulation of DNA methylation is an important feature of murine and human cSCC that likely contributes to silencing of tumour suppressor genes, as shown for Filip1l.

FUNDING

British Skin Foundation, Cancer Research UK.

Epidermal Integrin α3β1 Regulates Tumor-Derived Proteases BMP-1, Matrix Metalloprotease-9, and Matrix Metalloprotease-3

As the major cell surface receptors for the extracellular matrix, integrins regulate adhesion and migration and have been shown to drive tumor growth and progression. Previous studies showed that mice lacking integrin α3β1 in the epidermis fail to form skin tumors during two-step chemical tumorigenesis, indicating a protumorigenic role for α3β1. Furthermore, genetic ablation of α3β1 in established skin tumors caused their rapid regression, indicating an essential role in the maintenance of tumor growth. In this study, analysis of immortalized keratinocyte lines and their conditioned media support a role for α3β1 in regulating the expression of several extracellular proteases of the keratinocyte secretome, namely BMP-1, matrix metalloprotease (MMP)-9, and MMP-3. Moreover, immunofluorescence revealed reduced levels of each protease in α3β1-deficient tumors, and RNA in situ hybridization showed that their expression was correspondingly reduced in α3β1-deficient tumor cells in vivo. Bioinformatic analysis confirmed that the expression of BMP1, MMP9, and MMP3 genes correlate with the expression of ITGA3 (gene encoding the integrin α3 subunit) in human squamous cell carcinoma and that high ITGA3 and MMP3 associate with poor survival outcome in these patients. Overall, our findings identify α3β1 as a regulator of several proteases within the secretome of epidermal tumors and as a potential therapeutic target.

Functional cooperation between ASK1 and p21Waf1/Cip1 in the balance of cell-cycle arrest, cell death and tumorigenesis of stressed keratinocytes

Both CDKN1A (p21 ^Waf1/Cip1) and Apoptosis signal-regulating kinase 1 (ASK1) play important roles in tumorigenesis. The role of p21 ^Waf1/Cip1 in attenuating ASK1-induced apoptosis by various stress conditions is well established. However, how ASK1 and p21 ^Waf1/Cip1 functionally interact during tumorigenesis is still unclear. To address this aspect, we crossed ASK1 knockout (ASK1KO) mice with p21 ^Waf1/Cip1 knockout (p21KO) mice to compare single and double-mutant mice. We observed that deletion of p21 ^Waf1/Cip1 leads to increased keratinocyte proliferation but also increased cell death. This is mechanistically linked to the ASK1 axis-induced apoptosis, including p38 and PARP. Indeed, deletion of ASK1 does not alter the proliferation but decreases the apoptosis of p21KO keratinocytes. To analyze as this interaction might affect skin carcinogenesis, we investigated the response of ASK1KO and p21KO mice to DMBA/TPA-induced tumorigenesis. Here we show that while endogenous ASK1 is dispensable for skin homeostasis, ASK1KO mice are resistant to DMBA/TPA-induced tumorigenesis. However, we found that epidermis lacking both p21 and ASK1 reacquires increased sensitivity to DMBA/TPA-induced tumorigenesis. We demonstrate that apoptosis and cell-cycle progression in p21KO keratinocytes are uncoupled in the absence of ASK1. These data support the model that a critical event ensuring the balance between cell death, cell-cycle arrest, and successful divisions in keratinocytes during stress conditions is the p21-dependent ASK1 inactivation.

Cutaneous Squamous Cell Carcinoma Development Is Associated with a Temporal Infiltration of ILC1 and NK Cells with Immune Dysfunctions

NK cells and tissue-resident innate lymphoid cells (ILCs) are innate effectors found in the skin. To investigate their temporal dynamics and specific functions throughout the development of cutaneous squamous cell carcinoma (cSCC), we combined transcriptomic and immunophenotyping analyses in mouse and human cSCCs. We identified an infiltration of NK cells and ILC1s as well as the presence of a few ILC3s. Adoptive transfer of NK cells in NK cell‒ and ILC-deficient Nfil3^-/- mice revealed a role for NK cells in early control of cSCC. During tumor progression, we identified a population skewing with the infiltration of atypical ILC1 secreting inflammatory cytokines but reduced levels of IFN-γ at the papilloma stage. NK cells and ILC1s were functionally impaired, with reduced cytotoxicity and IFN-γ secretion associated with the downregulation of activating receptors. They also showed a high degree of heterogeneity in mouse and human cSCCs with the expression of several markers of exhaustion, including TIGIT on NK cells and PD-1 and TIM-3 on ILC1s. Our data show an enrichment in inflammatory ILC1 at the precancerous stage together with impaired antitumor functions in NK cells and ILC1 that could contribute to the development of cSCC and thus suggest that future immunotherapies should take both ILC populations into account.

Integrin α3β1 Is a Key Regulator of Several Protumorigenic Pathways during Skin Carcinogenesis

Integrin α3β1 plays a crucial role in tumor formation in the two-stage chemical carcinogenesis model (DMBA and TPA treatment). However, the mechanisms whereby the expression of α3β1 influences key oncogenic drivers of this established model are not known yet. Using an in vivo mouse model with epidermal deletion of α3β1 and in vitro Matrigel cultures of transformed keratinocytes, we demonstrate the central role of α3β1 in promoting the activation of several protumorigenic signaling pathways during the initiation of DMBA/TPA‒driven tumorigenesis. In transformed keratinocytes, α3β1-mediated focal adhesion kinase/Src activation leads to in vitro growth of spheroids and to strong Akt and STAT 3 activation when the α3β1-binding partner tetraspanin CD151 is present to stabilize cell‒cell adhesion and promote Smad2 phosphorylation. Remarkably, α3β1 and CD151 can support Akt and STAT 3 activity independently of α3β1 ligation by laminin-332 and as such control the essential survival signals required for suprabasal keratin-10 expression during keratinocyte differentiation. These data demonstrate that α3β1 together with CD151 regulate the signaling pathways that control the survival of differentiating keratinocytes and provide a mechanistic understanding of the essential role of α3β1 in early stages of skin cancer development.