Crosstalk between tumor and stroma modifies CLIC4 cargo in extracellular vesicles

Mouse models of breast cancer have revealed that tumor-bearing hosts must express the oxidoreductase CLIC4 to develop lung metastases. In the absence of host CLIC4, primary tumors grow but the lung premetastatic niche is defective for metastatic seeding. Primary breast cancer cells release EVs that incorporate CLIC4 as cargo and circulate in plasma of wildtype tumor-bearing hosts. CLIC4-deficient breast cancer cells also form tumors in wildtype hosts and release EVs in plasma, but these EVs lack CLIC4, suggesting that the tumor is the source of the plasma-derived EVs that carry CLIC4 as cargo. Paradoxically, circulating EVs are also devoid of CLIC4 when CLIC4-expressing primary tumors are grown in CLIC4 knockout hosts. Thus, the incorporation of CLIC4 (and perhaps other factors) as EV cargo released from tumors involves specific signals from the surrounding stroma determined by its genetic composition. Since CLIC4 is also detected in circulating EVs from human breast cancer patients, future studies will address its association with disease.

Irreversible cell cycle exit associated with senescence is mediated by constitutive MYC degradation

Cells can irreversibly exit the cell cycle and become senescent to safeguard against uncontrolled proliferation. While the p53-p21 and p16-Rb pathways are thought to mediate senescence, they also mediate reversible cell cycle arrest (quiescence), raising the question of whether senescence is actually reversible or whether alternative mechanisms underly the irreversibility associated with senescence. Here, we show that senescence is irreversible and that commitment to and maintenance of senescence are mediated by irreversible MYC degradation. Senescent cells start dividing when a non-degradable MYC mutant is expressed, and quiescent cells convert to senescence when MYC is knocked down. In early oral carcinogenesis, epithelial cells exhibit MYC loss and become senescent as a safeguard against malignant transformation. Later stages of oral premalignant lesions exhibit elevated MYC levels and cellular dysplasia. Thus, irreversible cell cycle exit associated with senescence is mediated by constitutive MYC degradation, but bypassing this degradation may allow tumor cells to escape during cancer initiation.

Murine models of HRAS-mediated cutaneous skeletal hypophosphatemia syndrome suggest bone as the FGF23 excess source

Cutaneous Skeletal Hypophosphatemia Syndrome (CSHS) is a mosaic RASopathy characterized by the association of dysplastic skeletal lesions, congenital skin nevi of epidermal and/or melanocytic origin, and fibroblast growth factor-23 (FGF23)-mediated hypophosphatemia. The primary physiological source of circulating FGF23 is bone cells. However, several reports have suggested skin lesions as the source of excess FGF23 in CSHS. Consequently, without convincing evidence of efficacy, many patients with CSHS have undergone painful removal of cutaneous lesions in an effort to normalize blood phosphate levels.This study aims to elucidate whether the source of FGF23 excess in CSHS is RAS mutation-bearing bone or skin lesions. Towards this end, we analyzed the expression and activity of Fgf23 in two mouse models expressing similar HRAS/Hras activating mutations in a mosaic-like fashion in either bone or epidermal tissue. We found that HRAS hyperactivity in bone, not skin, caused excess of bioactive intact FGF23, hypophosphatemia and osteomalacia.Our findings support RAS-mutated dysplastic bone as the primary source of physiologically active FGF23 excess in patients with CSHS. This evidence informs the care of patients with CSHS, arguing against the practice of nevi removal to decrease circulating, physiologically active FGF23.

RAS oncogene signal strength regulates matrisomal gene expression and tumorigenicity of mouse keratinocytes

Environmental and molecular carcinogenesis are linked by the discovery that chemical carcinogen induced-mutations in the Hras or Kras genes drives tumor development in mouse skin. Importantly, enhanced expression or allele amplification of the mutant Ras gene contributes to selection of initiated cells, tumor persistence, and progression. To explore the consequences of Ras oncogene signal strength, primary keratinocytes were isolated and cultured from the LSL-HrasG12D and LSL-KrasG12D C57BL/6J mouse models and the mutant allele was activated by adeno-Cre recombinase. Keratinocytes expressing one (H) or two (HH) mutant alleles of HrasG12D, one KrasG12D allele (K), or one of each (HK) were studied. All combinations of activated Ras alleles stimulated proliferation and drove transformation marker expression, but only HH and HK formed tumors. HH, HK, and K sustained long-term keratinocyte growth in vitro, while H and WT could not. RNA-Seq yielded two distinct gene expression profiles; HH, HK, and K formed one cluster while H clustered with WT. Weak MAPK activation was seen in H keratinocytes but treatment with a BRAF inhibitor enhanced MAPK signaling and facilitated tumor formation. K keratinocytes became tumorigenic when they were isolated from mice where the LSL-KrasG12D allele was backcrossed from the C57BL/6 onto the FVB/N background. All tumorigenic keratinocytes but not the non-tumorigenic precursors shared a common remodeling of matrisomal gene expression that is associated with tumor formation. Thus, RAS oncogene signal strength determines cell-autonomous changes in initiated cells that are critical for their tumor-forming potential.

The oxidoreductase CLIC4 is required to maintain mitochondrial function and resistance to exogenous oxidants in breast cancer cells

The chloride intracellular channel-4 (CLIC4) is one of the six highly conserved proteins in the CLIC family that share high structural homology with GST-omega in the GST superfamily. While CLIC4 is a multifunctional protein that resides in multiple cellular compartments, the discovery of its enzymatic glutaredoxin-like activity in vitro suggested that it could function as an antioxidant. Here, we found that deleting CLIC4 from murine 6DT1 breast tumor cells using CRISPR enhanced the accumulation of reactive oxygen species (ROS) and sensitized cells to apoptosis in response to H₂O₂ as a ROS-inducing agent. In intact cells, H₂O₂ increased the expression of both CLIC4 mRNA and protein. In addition, increased superoxide production in 6DT1 cells lacking CLIC4 was associated with mitochondrial hyperactivity including increased mitochondrial membrane potential and mitochondrial organelle enlargement. In the absence of CLIC4, however, H₂O₂-induced apoptosis was associated with low expression and degradation of the antiapoptotic mitochondrial protein Bcl2 and the negative regulator of mitochondrial ROS, UCP2. Furthermore, transcriptomic profiling of H₂O₂-treated control and CLIC4-null cells revealed upregulation of genes associated with ROS-induced apoptosis and downregulation of genes that sustain mitochondrial functions. Accordingly, tumors that formed from transplantation of CLIC4-deficient 6DT1 cells were highly necrotic. These results highlight a critical role for CLIC4 in maintaining redox-homeostasis and mitochondrial functions in 6DT1 cells. Our findings also raise the possibility of targeting CLIC4 to increase cancer cell sensitivity to chemotherapeutic drugs that are based on elevating ROS in cancer cells.

Host CLIC4 expression in the tumor microenvironment is essential for breast cancer metastatic competence

The TGF-β-regulated Chloride Intracellular Channel 4 (CLIC4) is an essential participant in the formation of breast cancer stroma. Here, we used data available from the TCGA and METABRIC datasets to show that CLIC4 expression was higher in breast cancers from younger women and those with early-stage metastatic disease. Elevated CLIC4 predicted poor outcome in breast cancer patients and was linked to the TGF-β pathway. However, these associations did not reveal the underlying biological contribution of CLIC4 to breast cancer progression. Constitutive ablation of host Clic4 in two murine metastatic breast cancer models nearly eliminated lung metastases without reducing primary tumor weight, while tumor cells ablated of Clic4 retained metastatic capability in wildtype hosts. Thus, CLIC4 was required for host metastatic competence. Pre- and post-metastatic proteomic analysis identified circulating pro-metastatic soluble factors that differed in tumor-bearing CLIC4-deficient and wildtype hosts. Vascular abnormalities and necrosis increased in primary tumors from CLIC4-deficient hosts. Transcriptional profiles of both primary tumors and pre-metastatic lungs of tumor-bearing CLIC4-deficient hosts were consistent with a microenvironment where inflammatory pathways were elevated. Altogether, CLIC4 expression in human breast cancers may serve as a prognostic biomarker; therapeutic targeting of CLIC4 could reduce primary tumor viability and host metastatic competence.

RAS induced senescence of skin keratinocytes is mediated through Rho-associated protein kinase (ROCK)

Cellular senescence is a well-documented response to oncogene activation in many tissues. Multiple pathways are invoked to achieve senescence indicating its importance to counteract the transforming activities of oncogenic stimulation. We now report that the Rho-associated protein kinase (ROCK) signaling pathway is a critical regulator of oncogene-induced senescence in skin carcinogenesis. Transformation of mouse keratinocytes with oncogenic RAS upregulates ROCK activity and initiates a senescence response characterized by cell enlargement, growth inhibition, upregulation of senescence associated β-galactosidase (SAβgal) expression, and release of multiple pro-inflammatory factors comprising the senescence-associated secretory phenotype (SASP). The addition of the ROCK inhibitor Y-27632 and others prevents these senescence responses and maintains proliferating confluent RAS transformed keratinocyte cultures indefinitely. Mechanistically, oncogenic RAS transformation is associated with upregulation of cell cycle inhibitors p15Ink4b , p16Ink4a , and p19Arf and downregulation of p-AKT, all of which are reversed by Y-27632. RNA-seq analysis of Y-27632 treated RAS-transformed keratinocytes indicated that the inhibitor reduced growth-inhibitory gene expression profiles and maintained expression of proliferative pathways. Y-27632 also reduced the expression of NF-κB effector genes and the expression of IκBζ downstream mediators. The senescence inhibition from Y-27632 was reversible, and upon its removal, senescence reoccurred in vitro with rapid upregulation of cell cycle inhibitors, SASP expression, and cell detachment. Y-27632 treated cultured RAS-keratinocytes formed tumors in the absence of the inhibitor when placed in skin orthografts suggesting that factors in the tumor microenvironment can overcome the drive to senescence imparted by overactive ROCK activity.

Endogenous retroviruses promote homeostatic and inflammatory responses to the microbiota

The microbiota plays a fundamental role in regulating host immunity. However, the processes involved in the initiation and regulation of immunity to the microbiota remain largely unknown. Here, we show that the skin microbiota promotes the discrete expression of defined endogenous retroviruses (ERVs). Keratinocyte-intrinsic responses to ERVs depended on cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes protein (STING) signaling and promoted the induction of commensal-specific T cells. Inhibition of ERV reverse transcription significantly impacted these responses, resulting in impaired immunity to the microbiota and its associated tissue repair function. Conversely, a lipid-enriched diet primed the skin for heightened ERV- expression in response to commensal colonization, leading to increased immune responses and tissue inflammation. Together, our results support the idea that the host may have co-opted its endogenous virome as a means to communicate with the exogenous microbiota, resulting in a multi-kingdom dialog that controls both tissue homeostasis and inflammation.

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.

Mus musculus papillomavirus 1 is a key driver of skin cancer development upon immunosuppression

Epidemiological and experimental data implicate cutaneous human papillomavirus infection as co-factor in the development of cutaneous squamous cell carcinomas (cSCCs), particularly in immunocompromised organ transplant recipients (OTRs). Herein, we established and characterized a skin cancer model, in which Mus musculus papillomavirus 1 (MmuPV1) infection caused cSCCs in cyclosporine A (CsA)-treated mice, even in the absence of UV light. Development of cSCCs and their precursors were observed in 70% of MmuPV1-infected, CsA-treated mice on back as well as on tail skin. Immunosuppression by systemic CsA, but not UV-B irradiation, was a prerequisite, as immunocompetent or UV-B-irradiated mice did not develop skin malignancies after infection. In the virus-driven cSCCs the MmuPV1-E6/E7 oncogenes were abundantly expressed, and transcriptional activity and productive infection demonstrated. MmuPV1 infection induced the expression of phosphorylated H2AX, but not degradation of proapoptotic BAK in the cSCCs. Transfer of primary cells, established from a MmuPV1-induced cSCC from back skin, into athymic nude mice gave rise to secondary cSCCs, which lacked viral DNA, demonstrating that maintenance of the malignant phenotype was virus independent. This papillomavirus-induced skin cancer model opens future investigations into viral involvement, pathogenesis, and cancer surveillance, aiming at understanding and controlling the high incidence of skin cancer in OTRs.

Head and neck squamous cancer progression is marked by CLIC4 attenuation in tumor epithelium and reciprocal stromal upregulation of miR-142-3p, a novel post-transcriptional regulator of CLIC4

Chloride intracellular channel 4 (CLIC4) is a tumor suppressor implicated in processes including growth arrest, differentiation, and apoptosis. CLIC4 protein expression is diminished in the tumor parenchyma during progression in squamous cell carcinoma (SCC) and other neoplasms, but the underlying mechanisms have not been identified. Data from The Cancer Genome Atlas suggest this is not driven by genomic alterations. However, screening and functional assays identified miR-142-3p as a regulator of CLIC4. CLIC4 and miR-142-3p expression are inversely correlated in head and neck (HN) SCC and cervical SCC, particularly in advanced stage cancers. In situ localization revealed that stromal immune cells, not tumor cells, are the predominant source of miR-142-3p in HNSCC. Furthermore, HNSCC single-cell expression data demonstrated that CLIC4 is lower in tumor epithelial cells than in stromal fibroblasts and endothelial cells. Tumor-specific downregulation of CLIC4 was confirmed in an SCC xenograft model concurrent with immune cell infiltration and miR-142-3p upregulation. These findings provide the first evidence of CLIC4 regulation by miRNA. Furthermore, the distinct localization of CLIC4 and miR-142-3p within the HNSCC tumor milieu highlight the limitations of bulk tumor analysis and provide critical considerations for both future mechanistic studies and use of miR-142-3p as a HNSCC biomarker.

Role of Retinoic Acid Receptor-γ in DNA Damage-Induced Necroptosis

DNA-damaging compounds, commonly used as chemotherapeutic drugs, are known to trigger cells to undergo programmed cell death such as apoptosis and necroptosis. However, the molecular mechanism of DNA damage-induced cell death is not fully understood. Here, we report that RARγ has a critical role in DNA damage-induced programmed cell death, specifically in necroptosis. The loss of RARγ abolishes the necroptosis induced by DNA damage. In addition, cells that lack RARγ are less susceptible to extrinsic apoptotic pathway activated by DNA-damaging agents whereas the intrinsic apoptotic pathway is not affected. We demonstrate that RARγ is essential for the formation of RIPK1/RIPK3 death complex, known as Ripoptosome, in response to DNA damage. Furthermore, we show that RARγ plays a role in skin cancer development by using RARγ1 knockout mice and human squamous cell carcinoma biopsies. Hence, our study reveals that RARγ is a critical component of DNA damage-induced cell death.

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RARγ plays a key role in DNA damage-induced cell death

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RARγ is essential for RIPK1-mediated necroptosis and apoptosis following DNA damage

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RARγ is required for the formation of Ripoptosome in response to DNA damage

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Loss of RARγ correlates with skin cancer development

T-Cell Deletion of MyD88 Connects IL17 and IκBζ to RAS Oncogenesis

Cancer development requires a favorable tissue microenvironment. By deleting Myd88 in keratinocytes or specific bone marrow subpopulations in oncogenic RAS-mediated skin carcinogenesis, we show that IL17 from infiltrating T cells and IκBζ signaling in keratinocytes are essential to produce a permissive microenvironment and tumor formation. Both normal and RAS-transformed keratinocytes respond to tumor promoters by activating canonical NF-κB and IκBζ signaling, releasing specific cytokines and chemokines that attract Th17 cells through MyD88-dependent signaling in T cells. The release of IL17 into the microenvironment elevates IκBζ in normal and RAS-transformed keratinocytes. Activation of IκBζ signaling is required for the expression of specific promoting factors induced by IL17 in normal keratinocytes and constitutively expressed in RAS-initiated keratinocytes. Deletion of Nfkbiz in keratinocytes impairs RAS-mediated benign tumor formation. Transcriptional profiling and gene set enrichment analysis of IκBζ-deficient RAS-initiated keratinocytes indicate that IκBζ signaling is common for RAS transformation of multiple epithelial cancers. Probing The Cancer Genome Atlas datasets using this transcriptional profile indicates that reduction of IκBζ signaling during cancer progression associates with poor prognosis in RAS-driven human cancers. IMPLICATIONS: The paradox that elevation of IκBζ and stimulation of IκBζ signaling through tumor extrinsic factors is required for RAS-mediated benign tumor formation while relative IκBζ expression is reduced in advanced cancers with poor prognosis implies that tumor cells switch from microenvironmental dependency early in carcinogenesis to cell-autonomous pathways during cancer progression.

Topical Application of a Dual ABC Transporter Substrate and NF-κB Inhibitor Blocks Multiple Sources of Cutaneous Inflammation in Mouse Skin

Among the molecular signals underlying cutaneous inflammation is the transcription complex NF-κB, its upstream modulators, and cytokines and chemokines that are the downstream proinflammatory effectors. Central to NF-κB activation is IκB kinase (IKK), which phosphorylates IκBα, releasing NF-κB to the nucleus. In a screening of a kinase inhibitor library, we identified two IKK inhibitors that were high-affinity substrates for p-glycoprotein (ABCB1), the multidrug resistance protein known to facilitate transdermal drug delivery. ACHP (2-amino-6-[2-(cyclopropylmethoxy)-6-hydroxyphenyl]-4-(4-piperidinyl)-3-pyridinecarbonitrile) and IKK 16 prevented both nuclear translocation of NF-κB and activation of a NF-κB reporter and reduced the induction of cytokine and chemokine transcripts in human or mouse keratinocytes by IL-1α, tumor necrosis factor-α, and phorbol myristate acetate. ACHP, but not IKK 16, was nontoxic to mouse or human keratinocytes at any dose tested. In mice, topical ACHP prevented the cutaneous inflammation induced by topical phorbol myristate acetate or imiquimod, reduced the inflammation from erythema doses of artificial sunlight, and lowered the tumor incidence of mice treated with 7,12-dimethyl benzanthracene when applied before phorbol myristate acetate. Topical ACHP also reduced the NF-κB and IL-17 inflammatory signature after multiple doses of imiquimod. Thus, ACHP and IKK 16 hit their NF-κB target in mouse and human keratinocytes, and ACHP is an effective topical nonsteroidal anti-inflammatory in mice.

A novel DLX3-PKC integrated signaling network drives keratinocyte differentiation

Epidermal homeostasis relies on a well-defined transcriptional control of keratinocyte proliferation and differentiation, which is critical to prevent skin diseases such as atopic dermatitis, psoriasis or cancer. We have recently shown that the homeobox transcription factor DLX3 and the tumor suppressor p53 co-regulate cell cycle-related signaling and that this mechanism is functionally involved in cutaneous squamous cell carcinoma development. Here we show that DLX3 expression and its downstream signaling depend on protein kinase C α (PKCα) activity in skin. We found that following 12-O-tetradecanoyl-phorbol-13-acetate (TPA) topical treatment, DLX3 expression is significantly upregulated in the epidermis and keratinocytes from mice overexpressing PKCα by transgenic targeting (K5-PKCα), resulting in cell cycle block and terminal differentiation. Epidermis lacking DLX3 (DLX3cKO), which is linked to the development of a DLX3-dependent epidermal hyperplasia with hyperkeratosis and dermal leukocyte recruitment, displays enhanced PKCα activation, suggesting a feedback regulation of DLX3 and PKCα. Of particular significance, transcriptional activation of epidermal barrier, antimicrobial peptide and cytokine genes is significantly increased in DLX3cKO skin and further increased by TPA-dependent PKC activation. Furthermore, when inhibiting PKC activity, we show that epidermal thickness, keratinocyte proliferation and inflammatory cell infiltration are reduced and the PKC-DLX3-dependent gene expression signature is normalized. Independently of PKC, DLX3 expression specifically modulates regulatory networks such as Wnt signaling, phosphatase activity and cell adhesion. Chromatin immunoprecipitation sequencing analysis of primary suprabasal keratinocytes showed binding of DLX3 to the proximal promoter regions of genes associated with cell cycle regulation, and of structural proteins and transcription factors involved in epidermal differentiation. These results indicate that Dlx3 potentially regulates a set of crucial genes necessary during the epidermal differentiation process. Altogether, we demonstrate the existence of a robust DLX3–PKCα signaling pathway in keratinocytes that is crucial to epidermal differentiation control and cutaneous homeostasis.

Cell autonomous or systemic EGFR blockade alters the immune-environment in squamous cell carcinomas

Targeting mutations and amplifications in the EGFR has been successful precision therapy for cancers of the lung, oral cavity and gastrointestinal track. However, a systemic immune reaction manifested by dose-limiting inflammation in the skin and gut has been a consistent adverse effect. To address the possibility that intra-tumoral immune changes contribute to the anti-cancer activity of EGFR inhibition, squamous cancers were produced by syngeneic orthografts of either EGFR null or wildtype mouse primary keratinocytes transduced with an oncogenic H-ras retrovirus. Flow cytometric, RNA and Bioplex immunoassay analyses of the tumor immune milieu were performed. Cancers forming from keratinocytes genetically depleted of EGFR were smaller than wildtype cancers and had fewer infiltrating FoxP3 Treg cells, lower Foxp3 RNA and a lower percentage of CD4 PD1 positive cells indicating a tumor cell autonomous regulation of its microenvironment. Hosts bearing wildtype cancers treated with gefitinib for 1 week showed a trend for smaller tumors. In this short term pharmacological model, there was also a trend to reduced FoxP3 cells and FoxP3 RNA in the tumors of treated mice as well as a substantial increase in the ratio of IL-1A/IL-1RA transcripts. These results suggest that relatively brief systemic inhibition of EGFR signaling alters the immune environment of the targeted cancer. Together these data imply that an EGFR dependent Treg function supports the growth of squamous cancers and is a target for the therapeutic activity of EGFR inhibition.

Abstract 5165: ADAM17: a common effector for RAS and MET-driven transformation of primary keratinocytes

The purpose of the current study is to determine the contribution of the metalloproteinase ADAM17 (a disintegrin and metalloprotease 17) to the transformation driven by activated MET or oncogenic RAS in primary keratinocytes. Transgenic keratinocytes overexpressing HGF (MT-HGF) to activate MET and keratinocytes transduced with an oncogenic RAS share identical phenotypic and biochemical features of transformation and produce squamous tumors in vivo. In both keratinocyte populations, these common features arise from autocrine activation of EGFR through elevated expression and release of EGFR ligands. Amphiregulin (AREG) blockade in MT-HGF keratinocytes decreases MET-mediated EGFR transactivation. Inhibition of EGFR ablates the initiated signature of MT-HGF keratinocytes in vitro and causes regression of tumors from MT-HGF keratinocytes tranplanted in vivo. Deletion or knock-down of ADAM17 decreases EGFR activation in both RAS and MT-HGF keratinocytes and reverses the transformation associated gene signature in RAS keratinocytes. Using AREG release as an indicator of ADAM17 activity, we determined that knock-down of either the SRC kinase or inactive Rhomboid 2 (iRhom2) reduces the ability of keratinocytes to release AREG upon HGF stimulation. Collectively our data suggest that MET-mediated transformation of keratinocytes occurs through EGFR transactivation and that ADAM17 is a necessary effector for RAS and MET-driven transformation.

Citation Format: Christophe Cataisson, Mary Klosterman, Kelly Shibuya, Glenn Merlino, Stuart H. Yuspa. ADAM17: a common effector for RAS and MET-driven transformation of primary keratinocytes. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5165.

MET signaling in keratinocytes activates EGFR and initiates squamous carcinogenesis

The receptor tyrosine kinase MET is abundant in many human squamous cell carcinomas (SCCs), but its functional significance in tumorigenesis is not clear. We found that the incidence of carcinogen-induced skin squamous tumors was substantially increased in transgenic MT-HGF (mouse metallothionein-hepatocyte growth factor) mice, which have increased abundance of the MET ligand HGF. Squamous tumors also erupted spontaneously on the skin of MT-HGF mice that were promoted by wounding or the application of 12-O-tetradecanoylphorbol 13-acetate, an activator of protein kinase C. Carcinogen-initiated tumors had Ras mutations, but spontaneous tumors did not. Cultured keratinocytes from MT-HGF mice and oncogenic RAS-transduced keratinocytes shared phenotypic and biochemical features of initiation that were dependent on autocrine activation of epidermal growth factor receptor (EGFR) through increased synthesis and release of EGFR ligands, which was mediated by the kinase SRC, the pseudoproteases iRhom1 and iRhom2, and the metallopeptidase ADAM17. Pharmacological inhibition of EGFR caused the regression of MT-HGF squamous tumors that developed spontaneously in orthografts of MT-HGF keratinocytes combined with dermal fibroblasts and implanted onto syngeneic mice. The global gene expression profile in MET-transformed keratinocytes was highly concordant with that in RAS-transformed keratinocytes, and a core RAS/MET coexpression network was activated in precancerous and cancerous human skin lesions. Tissue arrays revealed that many human skin SCCs have abundant HGF at both the transcript and protein levels. Thus, through the activation of EGFR, MET activation parallels a RAS pathway to contribute to human and mouse cutaneous cancers.

Keratinocyte p38δ loss inhibits Ras-induced tumor formation, while systemic p38δ loss enhances skin inflammation in the early phase of chemical carcinogenesis in mouse skin

p38δ expression and/or activity are increased in human cutaneous malignancies, including invasive squamous cell carcinoma (SCC) and head and neck SCC, but the role of p38δ in cutaneous carcinogenesis has not been well-defined. We have reported that mice with germline loss of p38δ exhibited a reduced susceptibility to skin tumor development compared with wild-type mice in the two-stage 7,12-dimethylbenz(a)anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA) chemical skin carcinogenesis model. Here, we report that p38δ gene ablation inhibited the growth of tumors generated from v-ras(Ha) -transformed keratinocytes in skin orthografts to nude mice, indicating that keratinocyte-intrinsic p38δ is required for Ras-induced tumorigenesis. Gene expression profiling of v-ras(Ha) -transformed p38δ-null keratinocytes revealed transcriptional changes associated with cellular responses linked to tumor suppression, such as reduced proliferation and increased differentiation, cell adhesion, and cell communications. Notably, a short-term DMBA/TPA challenge, modeling the initial stages of chemical skin carcinogenesis treatment, elicited an enhanced inflammation in p38δ-null skin compared with skin of wild-type mice, as assessed by measuring the expression of pro-inflammatory cytokines, including IL-1β, IL-6, IL-17, and TNFα. Additionally, p38δ-null skin and p38δ-null keratinocytes exhibited increased p38α activation and signaling in response to acute inflammatory challenges, suggesting a role for p38α in stimulating the elevated inflammatory response in p38δ-null skin during the initial phases of the DMBA/TPA treatment compared with similarly treated p38δ(+/+) skin. Altogether, our results indicate that p38δ signaling regulates skin carcinogenesis not only by keratinocyte cell-autonomous mechanisms, but also by influencing the interaction between between the epithelial compartment of the developing skin tumor and its stromal microenvironment.

Biological activity of the bryostatin analog Merle 23 on mouse epidermal cells and mouse skin

Bryostatin 1, a complex macrocyclic lactone, is the subject of multiple clinical trials for cancer chemotherapy. Although bryostatin 1 biochemically functions like the classic mouse skin tumor promoter phorbol 12-myristate 13-acetate (PMA) to bind to and activate protein kinase C, paradoxically, it fails to induce many of the typical phorbol ester responses, including tumor promotion. Intense synthetic efforts are currently underway to develop simplified bryostatin analogs that preserve the critical functional features of bryostatin 1, including its lack of tumor promoting activity. The degree to which bryostatin analogs maintain the unique pattern of biological behavior of bryostatin 1 depends on the specific cellular system and the specific response. Merle 23 is a significantly simplified bryostatin analog that retains bryostatin like activity only to a limited extent. Here, we show that in mouse epidermal cells the activity of Merle 23 was either similar to bryostatin 1 or intermediate between bryostatin 1 and PMA, depending on the specific parameter examined. We then examined the hyperplastic and tumor promoting activity of Merle 23 on mouse skin. Merle 23 showed substantially reduced hyperplasia and was not tumor promoting at a dose comparable to that for PMA. These results suggest that there may be substantial flexibility in the design of bryostatin analogs that retain its lack of tumor promoting activity. © 2016 Wiley Periodicals, Inc.

Abstract 1642: Bryostatin 1 and the simplified analog Merle 23 have similar and opposing properties on mouse epidermal cells and mouse skin

Protein kinase C (PKC) is differentially regulated in a range of cancers and has become an attractive therapeutic target. A number of natural compounds exist that have been found to regulate PKCs, and the biological responses of each compound can vary. The PKC activator PMA is an established tumor promoter, while others, such as the bryostatins, are non-tumor promoting and have inhibitory effects on the PKC pathway. Because of its effects on the PKC pathway, bryostatin 1 is currently in clinical trials as an anti-cancer agent. Limited availability and the difficulty involved in synthesizing bryostatin 1 make its use as an anti-cancer agent less attractive. Merle 23, a simplified synthetic analog of bryostatin 1, could be an alternative to bryostatin 1 if it acted similarly. Initial investigations of Merle 23 have revealed biological responses both similar to bryostatin 1 and similar to PMA, depending on the system. In U937 leukemia cells Merle 23 acts similar to PMA, and in the LNCaP prostate cancer cell line it behaves more like bryostatin 1. Its behavior in mouse skin is of particular interest, since this is the system in which the tumor promoting activity of PMA and the anti-tumor promoting activity of bryostatin 1 have been characterized. The activity of Merle 23 was compared to PMA and bryostatin 1 in mouse epidermal cells and mouse skin. In mouse primary keratinocytes PMA produces a prolonged morphological response, while the morphological response to bryostatin 1 is transient. The response to Merle 23 is intermediate, but more similar to bryostatin 1. When applied simultaneously, Merle 23, like bryostatin 1, is able to protect the cells from the morphological response induced by PMA. In the PKC pathway, all three compounds promote similar levels of initial PKCδ activation and ERK1/2 phosphorylation. By 24 hrs, however, the responses differ. At high concentrations, bryostatin 1 protects PKCδ from down regulation whereas Merle 23 does not. Bryostatin 1 is also much more potent for down regulation of PKCα, whereas Merle 23 and PMA are similar. The inflammatory response was measured by monitoring the transcript levels of various genes involved in inflammation. PMA induced the largest increase in transcript levels, while Merle 23 was more similar to bryostatin 1. Short-term in vivo analysis reveals no epidermal thickening in response to low doses of Merle 23 whereas the corresponding dose of PMA induced significant hyperplasia. The in vivo analysis of Merle 23 is ongoing. The results presented suggest that Merle 23 behaves more similarly to bryostatin 1 in the mouse epidermal cells at the level of biological response, raising the possibility that it may likewise be non-promoting. The results emphasize that the structure activity relations responsible for the distinct behavior between PMA and bryostatin 1 are distinct for different cellular systems and different biological endpoints.

Citation Format: Jessica Kelsey, Noemi Kedei, Christophe Cataisson, Mark Petersen, Stuart Yuspa, Gary Keck, Peter Blumberg. Bryostatin 1 and the simplified analog Merle 23 have similar and opposing properties on mouse epidermal cells and mouse skin. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1642. doi:10.1158/1538-7445.AM2014-1642

Endothelial cell tube formation assay for the in vitro study of angiogenesis

Angiogenesis is a vital process for normal tissue development and wound healing, but is also associated with a variety of pathological conditions. Using this protocol, angiogenesis may be measured in vitro in a fast, quantifiable manner. Primary or immortalized endothelial cells are mixed with conditioned media and plated on basement membrane matrix. The endothelial cells form capillary like structures in response to angiogenic signals found in conditioned media. The tube formation occurs quickly with endothelial cells beginning to align themselves within 1 hr and lumen-containing tubules beginning to appear within 2 hr. Tubes can be visualized using a phase contrast inverted microscope, or the cells can be treated with calcein AM prior to the assay and tubes visualized through fluorescence or confocal microscopy. The number of branch sites/nodes, loops/meshes, or number or length of tubes formed can be easily quantified as a measure of in vitro angiogenesis. In summary, this assay can be used to identify genes and pathways that are involved in the promotion or inhibition of angiogenesis in a rapid, reproducible, and quantitative manner.

MyD88 and its divergent toll in carcinogenesis

Toll-like and interleukin-1 (IL-1) family receptors recognize microbial or endogenous ligands and inflammatory mediators, respectively, and with the exception of Toll-like receptor 3 (TLR3), signal via the adaptor molecule myeloid differentiation factor 88 (MyD88). MyD88 is involved in oncogene-induced cell intrinsic inflammation and in cancer-associated extrinsic inflammation, and as such MyD88 contributes to skin, liver, pancreatic, and colon carcinogenesis, as well as sarcomagenesis. MyD88 is also protective, for example in oncogenic virus carcinogenesis or, acting downstream of IL-18R to strengthen mucosal repair, in azoxymethane (AOM)/dextran sulfate sodium (DSS)-induced colon carcinogenesis. Here, we discuss the mechanisms of the divergent effects of MyD88 and the balance of its protumor role in cancer-enhancing inflammation and immunity and its antitumor role in tissue homeostasis, repair, and immunity against the tumor or oncogenic pathogens.

Abstract 2454: Comparison of the activity of the bryostatin derivative Merle 23 with that of bryostatin 1 and phorbol ester in mouse epidermal cells

Tumor promoting phorbol esters, such as PMA, are potent activators of the PKC pathway. The bryostatins, marine natural products, activate PKCs similarly to phorbol esters but paradoxically inhibit most phorbol ester responses, including skin tumor promotion. Because of this inhibitory activity on the PKC pathway, bryostatin 1 has been the subject of extensive clinical trials. Serious impediments to clinical development, however, have been the scarcity of natural supplies coupled with great structural complexity, making synthesis problematic. Recent synthetic advances are now yielding simplified structural derivatives. Here, we compare the behavior of the bryostatin derivative Merle 23 with that of bryostatin 1 and phorbol 12-myristate 13-acetate (PMA) in mouse epidermal cells. While having similar binding activity on PKC as does bryostatin 1, Merle 23 behaves like PMA rather than like bryostatin 1 in U937 human leukemia cells but conversely behaves more like bryostatin 1 in the human prostate cancer cell line LNCaP. As a first step in assessing whether Merle 23 possesses or lacks skin tumor promoting activity, its activity in mouse primary keratinocyte cultures was assessed. PMA induces a prominent, prolonged morphological response in keratinocytes. Bryostatin 1 induces a similar initial response, which is however very transient. The morphological response to Merle 23 is more prolonged than for bryostatin 1 but much shorter than for PMA. For initial activation of PKCδ or induction of ERK1/2 phosphorylation, all three ligands show similar activity. By 24 hrs, however, bryostatin 1 is much more potent for down regulation of PKCα, whereas Merle 23 and PMA are similar. For PKCδ, bryostatin 1 at higher concentrations protects PKCδ from down regulation whereas Merle 23 does not. Transcriptional responses of various inflammation genes were monitored by qPCR. PMA causes the greatest increase in transcript levels for all genes investigated. In many cases bryostatin 1 induces a smaller response and the response to Merle 23 generally resembles that of bryostatin 1. While these studies are ongoing, they suggest that Merle 23 largely behaves like bryostatin 1 in the mouse epidermal cells. Our findings emphasize the important role of cellular context in determining the pattern of behavior of Merle 23. An important implication is that different cellular environments reveal different structure activity relations for bryostatin 1-like behavior. Finally, our studies raise the possibility that Merle 23, which is significantly simplified relative to bryostatin 1 in its upper two rings, may be non-promoting, at least in the mouse skin tumor promotion system.

Citation Format: Jessica Kelsey, Noemi Kedei, Christophe Cataisson, Mark Petersen, Stuart Yuspa, Gary Keck, Peter Blumberg. Comparison of the activity of the bryostatin derivative Merle 23 with that of bryostatin 1 and phorbol ester in mouse epidermal cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2454. doi:10.1158/1538-7445.AM2013-2454

Abstract 1064: The combined activation of MET signaling and PKCα is sufficient to induce tumors in mouse skin

Aberrant activation of MET signaling has been identified in multiple cancers but its relation to cancer-associated inflammation has not been explored. To address this issue in the context of skin carcinogenesis, a double transgenic mouse model (MT1-HGF/ K5-PKCα or DT) was generated. K5-PKCα mice that overexpress PKCα in basal keratinocytes develop a strong neutrophilic cutaneous inflammatory response upon topical TPA (12-tetradecanoylphorbol-13-acetate) application. These mice were crossed with MT1-HGF mice that overexpress HGF under a metallothionein promoter to create MT1-HGF/ K5-PKCα double transgenic (DT) mice and their respective controls. We observed that DT animals were very sensitive to squamous carcinogenesis. Using a low promoting dose of TPA that primarily activates PKCα in K5-PKCα or DT mice yielded an average of 6 tumors per mouse in the DT group; single transgenic K5-PKCα or MT-HGF mice developed an average of 1 tumor while WT developed none at this TPA dose. We hypothesize that in DT mice, keratinocyte-derived HGF synergizes with PKCα to drive tumor promotion and increase tumor growth. Primary keratinocytes derived from MT1-HGF or DT mice display a phenotype reminiscent of EGFR activated cells: increased expression of pro-inflammatory factors, upregulation of Keratin 8 (K8) and downregulation of K1 and K10 mRNAs. Indeed western blot analysis shows that EGFR is transactivated in MT1-HGF and DT keratinocytes and cell proliferation is elevated as well but not in K5-PKCα or WT keratinocytes. The release of CXCL1,a hallmark of RAS transformation, is augmented in RAS-keratinocyte cell culture supernatants with MT1-HGF and DT keratinocytes producing the most in the absence of RAS-transduction. Blockade of EGFR or IL-1 activity can mitigate the HGF-induced RAS-phenotype. K5-PKCα and DT mice exhibit the same acute inflammatory response and regenerative epidermal hyperplasia following low dose TPA treatment. When promoted for 10 weeks with TPA, 100% of DT mice but none of the single transgenic controls developed squamous papillomas in the absence of DMBA-mediated initiation. Our data suggest that the synergistic activity of Met and PKCα can substitute for the lack of RAS mutation during skin carcinogenesis. It remains to be determined if that mechanism could provide an alternate route to transformation in human skin tumors lacking RAS mutations.

Citation Format: Christophe Cataisson, Fan Liu, Lisa N. Wright, Anne Zhuang, Glenn Merlino, Stuart H. Yuspa. The combined activation of MET signaling and PKCα is sufficient to induce tumors in mouse skin. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1064. doi:10.1158/1538-7445.AM2013-1064

Abstract 1081: Rapamycin is a chemopreventive and chemotherapeutic agent for ras-driven epidermal squamous cell carcinoma: evidence from mouse models

Braf inhibitors are clinically important agents for the treatment of advanced melanoma however secondary cutaneous tumors are a common side effect; non-melanoma skin cancers (NMSCs) arise in 15-30% of patients on Braf inhibitor therapy and 60% of these harbor ras mutations. NMSC also occurs in 40% of organ transplant patients receiving immunosuppressive therapy, and switching from a calcineurin inhibitor-containing regimen to rapamycin reduces the incidence. To examine the effect of rapamycin on ras-driven epidermal squamous cell tumors, we treated mutant K-RasLA2 mice with rapamycin or vehicle by intraperitoneal injection and found that rapamycin prevented the development of squamous skin tumors (0/21 vs 6/24; p=0.04), and also rapidly reduced the tumor size. To explore this effect we employed a syngeneic orthotopic grafting model using H-Ras mutant primary murine keratinocytes to determine if rapamycin could hamper the ability of a Braf inhibitor to enhance squamous skin tumor growth. Similar to results in the K-RasLA2 model, rapamycin alone diminished the growth of tumors (size difference; 334.5 vs 22.3mm3; p=0.03), and decreased the volume even more in the presence of a Braf inhibitor (size difference; 699.6 vs 17.6 mm3; p=0.02). Treatment of established tumors with rapamycin resulted in significant tumor shrinkage even in the continuous presence of a Braf inhibitor. Size reduction was 78.7% and 66.7% in Braf inhibitor untreated and treated groups respectively. In vitro, Braf inhibition enhanced mutant H-Ras-induced activation of the Raf-ERK and mTOR pathways in keratinocytes, while rapamycin addition blocked the activation of signaling pathways and decreased cell proliferation. Taken together, rapamycin prevents murine skin tumor development arising from oncogenic mutations in two distinct types of ras gene alleles, and reduced the tumor size by inhibiting downstream oncogenic pathways. Rapamycin may have clinical application as a chemopreventive and therapeutic agent for patients at high risk to develop ras-driven NMSC, including those receiving Braf inhibitors.

Citation Format: Hiroshi Kitagawa, Christophe Cataisson, Alessandra Handisurya, Patricia M. Day, Stuart H. Yuspa, Phillip A. Dennis. Rapamycin is a chemopreventive and chemotherapeutic agent for ras-driven epidermal squamous cell carcinoma: evidence from mouse models. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1081. doi:10.1158/1538-7445.AM2013-1081

Targeted disruption of glutathione peroxidase 4 in mouse skin epithelial cells impairs postnatal hair follicle morphogenesis that is partially rescued through inhibition of COX-2

Selenoproteins are essential molecules for the mammalian antioxidant network. We previously demonstrated that targeted loss of all selenoproteins in mouse epidermis disrupted skin and hair development and caused premature death. In the current study we targeted specific selenoproteins for epidermal deletion to determine whether similar phenotypes developed. Keratinocyte-specific knockout mice lacking either the glutathione peroxidase 4 (GPx4) or thioredoxin reductase 1 (TR1) gene were generated by cre-lox technology using K14-cre. TR1 knockout mice had a normal phenotype in resting skin while GPx4 loss in epidermis caused epidermal hyperplasia, dermal inflammatory infiltrate, dysmorphic hair follicles and alopecia in perinatal mice. Unlike epidermal ablation of all selenoproteins, mice ablated for GPx4 recovered after 5 weeks and had a normal lifespan. GPx1 and TR1 were upregulated in the skin and keratinocytes of GPx4 knockout mice. GPx4 deletion reduces keratinocyte adhesion in culture and increases lipid peroxidation and COX-2 levels in cultured keratinocytes and whole skin. Feeding a COX-2 inhibitor to nursing mothers partially prevents development of the abnormal skin phenotype in knockout pups. These data link the activity of cutaneous GPx4 to the regulation of COX-2 and hair follicle morphogenesis and provide insight into the function of individual selenoprotein activity in maintaining cutaneous homeostasis.

IL-1R-MyD88 signaling in keratinocyte transformation and carcinogenesis

Constitutively active RAS plays a central role in the development of human cancer and is sufficient to induce tumors in two-stage skin carcinogenesis. RAS-mediated tumor formation is commonly associated with up-regulation of cytokines and chemokines that mediate an inflammatory response considered relevant to oncogenesis. In this study, we report that mice lacking IL-1R or MyD88 are less sensitive to topical skin carcinogenesis than their respective wild-type (WT) controls. MyD88(-/-) or IL-1R(-/-) keratinocytes expressing oncogenic RAS are hyperproliferative and fail to up-regulate proinflammatory genes or down-regulate differentiation markers characteristic of RAS-expressing WT keratinocytes. Although RAS-expressing MyD88(-/-) keratinocytes form only a few small tumors in orthotopic grafts, IL-1R-deficient RAS-expressing keratinocytes retain the ability to form tumors in orthotopic grafts. Using both genetic and pharmacological approaches, we find that the differentiation and proinflammatory effects of oncogenic RAS in keratinocytes require the establishment of an autocrine loop through IL-1α, IL-1R, and MyD88 leading to phosphorylation of IκBα and NF-κB activation. Blocking IL-1α-mediated NF-κB activation in RAS-expressing WT keratinocytes reverses the differentiation defect and inhibits proinflammatory gene expression. Collectively, these results demonstrate that MyD88 exerts a cell-intrinsic function in RAS-mediated transformation of keratinocytes.

Gene from a psoriasis susceptibility locus primes the skin for inflammation

Psoriasis is a common complex genetic disease characterized by hyperplasia and inflammation in the skin; however, the relative contributions of epidermal cells and the immune system to disease pathogenesis remain unclear. Linkage studies have defined a psoriasis susceptibility locus (PSORS4) on 1q21, the epidermal differentiation complex, which includes genes for small S100 calcium-binding proteins. These proteins are involved in extracellular and intracellular signaling during epithelial host defense, linking innate and adaptive immunity. Inflammation-prone psoriatic skin constitutively expresses elevated concentrations of S100A7 (psoriasin) and S100A15 (koebnerisin) in the epidermis. Here, we report that genetically modified mice expressing elevated amounts of doxycycline-regulated mS100a7a15 in skin keratinocytes demonstrated an exaggerated inflammatory response when challenged by exogenous stimuli such as abrasion (Koebner phenomenon). This immune response was characterized by immune cell infiltration and elevated concentrations of T helper 1 (T(H)1) and T(H)17 proinflammatory cytokines, which have been linked to the pathogenesis of psoriasis and were further amplified upon challenge. Both inflammation priming and amplification required mS100a7a15 binding to the receptor of advanced glycation end products (RAGE). mS100a7a15 potentiated inflammation by acting directly as a chemoattractant for leukocytes, further increasing the number of inflammatory cells infiltrating the skin. This study provides a pathogenetic psoriasis model using a psoriasis candidate gene to link the epidermis and innate immune system in inflammation priming, highlighting the S100A7A15-RAGE axis as a potential therapeutic target.

Inflammasome sensor Nlrp1b-dependent resistance to anthrax is mediated by caspase-1, IL-1 signaling and neutrophil recruitment

Bacillus anthracis infects hosts as a spore, germinates, and disseminates in its vegetative form. Production of anthrax lethal and edema toxins following bacterial outgrowth results in host death. Macrophages of inbred mouse strains are either sensitive or resistant to lethal toxin depending on whether they express the lethal toxin responsive or non-responsive alleles of the inflammasome sensor Nlrp1b (Nlrp1b^S/S or Nlrp1b^R/R, respectively). In this study, Nlrp1b was shown to affect mouse susceptibility to infection. Inbred and congenic mice harboring macrophage-sensitizing Nlrp1b^S/S alleles (which allow activation of caspase-1 and IL-1β release in response to anthrax lethal toxin challenge) effectively controlled bacterial growth and dissemination when compared to mice having Nlrp1b^R/R alleles (which cannot activate caspase-1 in response to toxin). Nlrp1b^S-mediated resistance to infection was not dependent on the route of infection and was observed when bacteria were introduced by either subcutaneous or intravenous routes. Resistance did not occur through alterations in spore germination, as vegetative bacteria were also killed in Nlrp1b^S/S mice. Resistance to infection required the actions of both caspase-1 and IL-1β as Nlrp1b^S/S mice deleted of caspase-1 or the IL-1 receptor, or treated with the Il-1 receptor antagonist anakinra, were sensitized to infection. Comparison of circulating neutrophil levels and IL-1β responses in Nlrp1b^S/S,Nlrp1b^R/R and IL-1 receptor knockout mice implicated Nlrp1b and IL-1 signaling in control of neutrophil responses to anthrax infection. Neutrophil depletion experiments verified the importance of this cell type in resistance to B. anthracis infection. These data confirm an inverse relationship between murine macrophage sensitivity to lethal toxin and mouse susceptibility to spore infection, and establish roles for Nlrp1b^S, caspase-1, and IL-1β in countering anthrax infection.

In this study, we show that anthrax lethal toxin activation of Nlrp1b in toxin-sensitive mouse macrophages imparts resistance to infection. Inbred and congenic mice harboring macrophage-sensitizing Nlrp1b alleles control bacterial growth and dissemination independent of infection route or effects on germination efficiency. Knockout mice demonstrate that resistance imparted by Nlrp1b requires caspase-1 activity and IL-1 signaling. Mice in which lethal toxin activates the Nlrp1b inflammasome show an IL-1β response and increased neutrophil recruitment leading to increased resistance to infection. Neutrophil depletion experiments verify the importance of this cell type in resistance to B. anthracis infection. These data confirm an inverse relationship between murine macrophage sensitivity to lethal toxin and mouse susceptibility to spore infection and demonstrate that the activation of the inflammasome in response to anthrax infection in mice is a protective event that occurs through IL-1β induction of neutrophil recruitment.

Loss of syndecan-1 is associated with malignant conversion in skin carcinogenesis

Syndecan-1 (sdc-1) is a cell surface proteoglycan that mediates the interaction of cells with their matrix, influencing attachment, migration, and response to growth factors. In keratinocytes, loss of sdc-1 delays wound healing, reduces migration, and increases Transforming growth factor beta (TGFbeta) 1 expression. In this study we show that sdc-1 expression is significantly reduced in basal cell, squamous cell, and metastatic human skin cancers compared to normal human skin. In experimental mouse skin tumor induction, compared to wildtype (wt) BALB/c mice, papilloma formation in sdc-1 null mice was reduced by 50% and the percent of papillomas converting to squamous cell carcinoma (SCC) was enhanced. sdc-1 expression on wt mouse papillomas decreased as they converted to SCC. Furthermore, papillomas forming on sdc-1 null mice expressed suprabasal alpha3 and beta4 integrins; suprabasal beta4 integrin is a marker of a high risk for progression. While the proliferative response to phorbol-12-myristate-13-acetate (TPA) did not differ among the genotypes, sdc-1 null mice had an enhanced inflammatory response and retained higher levels of total TGFbeta1 within their skin after TPA treatment. sdc-1 null keratinocytes, transduced in vitro by oncogenic ras(Ha), expressed higher levels of beta4 integrin and had enhanced pSmad2 signaling and reduced senescence when compared to wt ras(Ha)-transduced keratinocytes. When ras(Ha)-transduced cells of both genotypes were grafted onto nude mice, null tumors converted to SCC with higher frequency confirming the skin painting experiments. These data indicate that sdc-1 is important both early in the development of skin tumors and in progression of skin cancers suggesting that reduced expression of sdc-1 could be a useful marker for progression in neoplastic skin lesions.

The human promyelocytic leukemia protein is a tumor suppressor for murine skin carcinogenesis

Expression of the PMLRARalpha fusion dominant-negative oncogene in the epidermis of transgenic mice resulted in spontaneous skin tumors attributed to changes in both the PML and RAR pathways [Hansen et al., Cancer Res 2003; 63:5257-5265]. To determine the contribution of PML to skin tumor susceptibility, transgenic mice were generated on an FVB/N background, that overexpressed the human PML protein in epidermis and hair follicles under the control of the bovine keratin 5 promoter. PML was highly expressed in the epidermis and hair follicles of these mice and was also increased in cultured keratinocytes where it was confined to nuclear bodies. While an overt skin phenotype was not detected in young transgenic mice, expression of keratin 10 (K10) was increased in epidermis and hair follicles and cultured keratinocytes. As mice aged, they exhibited extensive alopecia that was accentuated on the C57BL/6J background. Following skin tumor induction with 7, 12-dimethylbenz[a]anthracene (DMBA) as initiator and 12-O-tetradecanoylphorbol-13-acetate (TPA) as promoter, papilloma multiplicity and size were decreased in the transgenic mice by 35%, and the conversion of papillomas to carcinomas was delayed. Cultured transgenic keratinocytes underwent premature senescence and upregulated transcripts for p16 and Rb but not p19 and p53. Together, these changes suggest that PML participates in regulating the growth and differentiation of keratinocytes that likely influence its activity as a suppressor for tumor development.

TGF-beta signalling is regulated by Schnurri-2-dependent nuclear translocation of CLIC4 and consequent stabilization of phospho-Smad2 and 3

CLIC4 (chloride intracellular channel 4), a multifunctional protein that traffics between the cytoplasm and nucleus, interacts with Schnurri-2, a transcription factor in the bone morphogenetic protein (BMP) signalling pathway. Here we show that transforming growth factor beta (TGF-beta) promotes the expression of CLIC4 and Schnurri-2 as well as their association in the cytoplasm and their translocation to the nucleus. In the absence of CLIC4 or Schnurri-2, TGF-beta signalling is abrogated. Direct nuclear targeting of CLIC4 enhances TGF-beta signalling and removes the requirement for Schnurri-2. Nuclear CLIC4 associates with phospho (p)-Smad2 and p-Smad3, protecting them from dephosphorylation by nuclear phosphatases. An intact TGF-beta signalling pathway is essential for CLIC4-mediated growth-arrest. These results newly identify Schnurri-2 and CLIC4 as modifiers of TGF-beta signalling through their stabilization of p-Smad2 and 3 in the nucleus.

Inducible cutaneous inflammation reveals a protumorigenic role for keratinocyte CXCR2 in skin carcinogenesis

Transgenic mice that overexpress PKCalpha in the epidermis (K5-PKCalpha mice) exhibit acute CXCR2-mediated intraepidermal neutrophilic inflammation and a strong epidermal hyperplasia in response to application of 12-O-tetradecanoylphorbol-13-acetate (TPA). We now show that hyperplasia is independent of infiltrating neutrophils. Furthermore, when K5-PKCalpha mice were initiated with 7,12-dimethylbenz(a)anthracene (DMBA) and promoted with a low dose of TPA, 58% of K5-PKCalpha mice developed skin papillomas that progressed to carcinoma, whereas wild-type mice did not develop tumors. We confirmed that CXCR2 is expressed by keratinocytes and showed that transformation by oncogenic ras (a hallmark of DMBA initiation) or TPA exposure induced all CXCR2 ligands. Ras induction of CXCR2 ligands was mediated by autocrine activation of epidermal growth factor receptor and nuclear factor-kappaB, and potentiated by PKCalpha. Oncogenic ras also induced CXCR2 ligands in keratinocytes genetically ablated for CXCR2. However, ras transformed CXCR2 null keratinocytes formed only small skin tumors in orthotopic skin grafts to CXCR2 intact hosts, whereas transformed wild-type keratinocytes produced large tumors. In vitro, CXCR2 was essential for CXCR2 ligand-stimulated migration of ras-transformed keratinocytes and for ligand activation of the extracellular signal-regulated kinase (ERK) and Akt pathways. Both migration and activation of ERK and Akt were restored by CXCR2 reconstitution of CXCR2 null keratinocytes. Thus, activation of CXCR2 on ras-transformed keratinocytes has both promigratory and protumorigenic functions. The up-regulation of CXCR2 ligands after initiation by oncogenic ras and promotion with TPA in the mouse skin model provides a mechanism to stimulate migration by both autocrine and paracrine pathways and contribute to tumor development.

CXCR2 ligands and G-CSF mediate PKCalpha-induced intraepidermal inflammation

Transgenic mice overexpressing PKCalpha in the epidermis (K5-PKCalpha mice) exhibit an inducible severe intraepidermal neutrophilic inflammation and systemic neutrophilia when PKCalpha is activated by topical 12-O-tetradecanoylphorbol-13-acetate (TPA). This inducible model of cutaneous inflammation was used to define mediators of skin inflammation that may have clinical relevance. Activation of cutaneous PKCalpha increased the production of the chemotactic factors cytokine-induced neutrophil chemoattractant (KC) and macrophage inflammatory protein 2 (MIP-2) in murine plasma. TPA treatment of cultured K5-PKCalpha keratinocytes also released KC and MIP-2 into culture supernatants through an NF-kappaB-dependent pathway. MIP-2 and KC mediated the infiltration of neutrophils into the epidermis, since this was prevented by ablating CXCR2 in K5-PKCalpha mice or administering neutralizing antibodies against KC or MIP-2. The neutrophilia resulted from PKCalpha-mediated upregulation of cutaneous G-CSF released into the plasma independent of CXCR2. These responses could be inhibited by topical treatment with a PKCalpha-selective inhibitor. Inhibiting PKCalpha also reduced the basal and TNF-alpha- or TPA-induced expression of CXCL8 in cultured psoriatic keratinocytes, suggesting that PKCalpha activity may contribute to psoriatic inflammation. Thus, skin can be the source of circulating factors that have both local and systemic consequences, and these factors, their receptors, and possibly PKCalpha could be therapeutic targets for inhibition of cutaneous inflammation.

The mouse S100A15 ortholog parallels genomic organization, structure, gene expression, and protein-processing pattern of the human S100A7/A15 subfamily during epidermal maturation

The calcium-binding proteins of the human S100A7/A15 (hS100A7/A15) subfamily are differentially expressed in normal and pathological epidermis. The hS100A7 (psoriasin) and S100A15 reside in a chromosomal cluster of highly similar paralogs. To exploit the power of mouse models for determining functions of gene products, the corresponding S100A7/A15 ortholog was cloned and examined in murine skin. The single mouse S100A15 (mS100A15) gene encodes a protein of 104 amino acids with a predicted molecular weight of 12,870 Da and two EF-hand calcium binding sites. Using gene-specific primers and specific antibodies, expression of mS100A15 in both skin and isolated keratinocytes is confined to differentiating granular and cornified epidermal cells. Immunoblotting of epidermal extracts revealed a series of high molecular weight bands that are also recognized by an antibody for transglutaminase-mediated protein crosslinks. mS100A15 expression is upregulated in cultured keratinocytes induced to differentiate by calcium or phorbol esters. Maximal induction occurs concordantly with expression of late differentiation markers. Induction is enhanced in keratinocytes overexpressing protein kinase Calpha and is dependent on activator protein-1 transcription factors. The regulation, expression pattern and crosslinking of mS100A15 are consistent with the characteristics of the human orthologs, providing a valid surrogate model to study changes in these proteins associated with cutaneous pathologies.

Protein Kinase Cα-Mediated Chemotaxis of Neutrophils Requires NF-κB Activity but Is Independent of TNFα Signaling in Mouse Skin In Vivo

Protein kinase C (PKC) isoforms are major regulators of cutaneous homeostasis and mediate inflammation in response to 12-O-tetradecanoylphorbol-13-acetate (TPA). We have previously reported that transgenic mice overexpressing PKCalpha in the skin exhibit severe intraepidermal neutrophilic inflammation and keratinocyte apoptosis when treated topically with TPA. Activation of PKCalpha increases the production of TNFalpha and the transcription of chemotactic factors (MIP-2, KC, S100A8/A9), vascular endothelial growth factor, and GM-CSF in K5-PKCalpha keratinocytes. In response to PKCalpha activation, NF-kappaB translocates to the nucleus and this is associated with IkappaB phosphorylation and degradation. Preventing IkappaB degradation reduces both the expression of inflammation-associated genes and chemoattractant release. To determine whether TNFalpha mediated NF-kappaB translocation and subsequent expression of proinflammatory factors, K5-PKCalpha mice were treated systemically with a dimeric soluble form of p75 TNFR (etanercept) or crossed with mice deficient for both TNFR isoforms, and keratinocytes were cultured in the presence of TNFalpha-neutralizing Abs. The in vivo treatment and TNFR deficiency did not prevent inflammation, and the in vitro treatment did not prevent NF-kappaB nuclear translocation after TPA. Together these results implicate PKCalpha as a regulator of a subset of cutaneous cytokines and chemokines responsible for intraepidermal inflammation independent of TNFalpha. PKCalpha inhibition may have therapeutic benefit in some human inflammatory skin disorders.

Activation of cutaneous protein kinase C alpha induces keratinocyte apoptosis and intraepidermal inflammation by independent signaling pathways

Skin keratinocytes are major mediators of host immune responses. The skin is also a target for immunologically based inflammation in many pathological states. Activation of protein kinase C (PKC) can induce cutaneous inflammation, but the precise role of each of six cutaneous PKC isoforms (alpha, delta, epsilon, eta, zeta, mu) that regulate normal skin homeostasis or contribute to skin pathology has not been clarified. We generated transgenic mice that overexpress PKCalpha in the basal layer of the epidermis and the outer root sheath of hair follicles under the regulation of the bovine keratin 5 promoter. K5-PKCalpha transgenic mice exhibit severe intraepidermal neutrophilic inflammation and disruption of the epidermis and upper hair follicles when treated topically with 12-O-tetradecanoylphorbol-13-acetate (TPA). Both TPA and UVB cause apoptosis in transgenic skin, but only TPA evokes intraepidermal inflammation. TPA also induces apoptosis in cultured transgenic keratinocytes, and this is prevented by an AP-1 dominant-negative construct. However, inhibiting AP-1 in vivo does not abrogate intraepidermal inflammation. Transcripts for specific cytokines and chemokines are elevated in TPA-treated cultured transgenic keratinocytes, and conditioned culture medium from these cells promotes neutrophil migration in vitro. Chemokine expression and neutrophil migration are not diminished by inhibiting AP-1. Thus, PKCalpha activation induces keratinocyte apoptosis via an AP-1-dependent pathway and mediates chemokine induction and intraepidermal inflammation independently. This model system will be useful to define specific chemokines regulated by PKCalpha that promote intraepidermal neutrophilic inflammation, a condition that characterizes several human cutaneous diseases such as pustular psoriasis and acute generalized exanthematous pustulosis.

Constitutive production of parathyroid hormone-related protein (PTHrP) by fibroblasts derived from normal and pathological human breast tissue

Parathyroid hormone-related protein (PTHrP) is expressed in the mammary gland and appears to be critical to the morphogenesis of this structure. PTHrP production in the breast is generally attributed to epithelial cells. Because the stromal component of the breast produces factors implicated in proliferation and differentiation of mammary epithelial tissue and tumors, the aim of this study was to investigate the PTHrP expression by mammary fibroblasts from breast cancer tumors and normal breast. PTHrP antibodies labeled intralobular fibroblasts in normal breast and stromal fibroblasts that surround tumor cells. PTHrP was constitutively produced by the cultured mammary fibroblasts, independent of serum stimulation. Normal (15.83 +/- 1.72 fmol/10(6) cells) and pathological breast fibroblasts (19.87 +/- 5.76) secreted similar amounts of PTHrP. PTH/PTHrP receptor mRNA was detected by RT-PCR in all the samples tested. Fibroblasts from normal breast were both PTH and PTHrP-cAMP responsive (453 +/- 133% and 513 +/- 133%, respectively, from basal stimulation), whereas pathological breast fibroblasts were minimally PTHrP-cAMP responsive (183 +/- 36%). The production of other fibroblastic factors implicated in tumor growth and invasiveness was also examined. Interleukin-6 (IL-6), tumor necrosis factor-alpha (INF-alpha), and pro-matrix metalloproteinase (MMP)-1 were not affected by the status of the tissue. In contrast, increased levels of pro-MMP-2 were produced in fibroblasts that originated from pathological (290 +/- 62 ng/10(6) cells) samples compared with those from normal donors (125 +/- 41 ng/10(6) cells). PTHrP production was correlated with TNF-alpha and pro-MMP-2 production. However, inhibition with specific neutralizing antibodies against TNF-alpha or PTHrP, or with a PTHrP antagonist, showed that these factors did not regulate each other. In conclusion, breast fibroblasts are constitutive PTHrP-producing cells with the potential for autocrine signaling through the PTH/PTHrP receptor.

Ets-1 activates parathyroid hormone-related protein gene expression in tumorigenic breast epithelial cells

Parathyroid hormone-related protein (PTHrP) is produced by many tumors not associated with humoral hypercalcemia, including breast cancers. In this study, we used three human immortalized mammary epithelial cell lines that differ in tumorigenicity and PTHrP expression. Using RT-PCR we investigated 5' and 3' alternative splicing of PTHrP transcripts and promoter usage in the lines. Increased levels of P3-derived transcripts and the 1-139 mRNA isoform were observed in the most tumorigenic cell line. Transient transfection experiments identified elements close to P3 promoter that appeared to account for a portion of differential PTHrP expression among the three cell lines. Using site-directed mutagenesis, a previously described Ets-1/Sp1 binding site upstream of P3 was determined to be crucial for full activity of this promoter. RT-PCR and western blot evaluation of Ets family member expression found that Ese-1 was present in all three lines, but that appreciable levels of Ets-1 protein were present exclusively in the most tumorigenic line. Cotransfection of Ets-1 expression vectors activated PTHrP reporter constructs in the most tumorigenic line but not in the other cell lines. These findings suggest a potential mechanism by which PTHrP transcription may be regulated as a consequence of events that promote tumorigenic behavior in breast epithelial cells.

Src family kinases phosphorylate protein kinase C delta on tyrosine residues and modify the neoplastic phenotype of skin keratinocytes

Protein kinase C delta (PKC delta) is tyrosine-phosphorylated and catalytically inactive in mouse keratinocytes transformed by a ras oncogene. In several other model systems, Src kinases are upstream regulators of PKC delta. To examine this relationship in epidermal carcinogenesis, v-ras transformed mouse keratinocytes were treated with a selective Src kinase inhibitor (PD 173958). PD 173958 decreased autophosphorylation of Src, Fyn, and Lyn kinases and prevented tyrosine phosphorylation of the Src kinase substrate p120. PD 173958 also prevented PKC delta tyrosine phosphorylation and activated PKC delta as detected by membrane translocation. Expression of keratinocyte differentiation markers increased in PD 173958-treated v-ras-keratinocytes, and fluid-filled domes emerged, indicative of tight junction formation. Antisense PKC delta or bryostatin 1 inhibited dome formation, while overexpression of PKC delta in the presence of PD 173958 enhanced the formation of domes. Plasmids encoding phenylalanine mutants of PKC delta tyrosine residues 64 and 565 induced domes in the absence of PD 173958, while phenylalanine mutants of tyrosine residues 52, 155, and 187 were inactive. Thus, Src kinase mediated post-translational modification of PKC delta on specific tyrosine residues in ras-transformed mouse keratinocytes inactivates PKC delta and contributes to alterations in the differentiated phenotype and tight junction formation associated with neoplasia.