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.

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.

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.

The transcription factor CBFB suppresses breast cancer through orchestrating translation and transcription

Translation and transcription are frequently dysregulated in cancer. These two processes are generally regulated by distinct sets of factors. The CBFB gene, which encodes a transcription factor, has recently emerged as a highly mutated driver in a variety of human cancers including breast cancer. Here we report a noncanonical role of CBFB in translation regulation. RNA immunoprecipitation followed by deep sequencing (RIP-seq) reveals that cytoplasmic CBFB binds to hundreds of transcripts and regulates their translation. CBFB binds to mRNAs via hnRNPK and enhances translation through eIF4B, a general translation initiation factor. Interestingly, the RUNX1 mRNA, which encodes the transcriptional partner of CBFB, is bound and translationally regulated by CBFB. Furthermore, nuclear CBFB/RUNX1 complex transcriptionally represses the oncogenic NOTCH signaling pathway in breast cancer. Thus, our data reveal an unexpected function of CBFB in translation regulation and propose that breast cancer cells evade translation and transcription surveillance simultaneously through downregulating CBFB.

CBFB is highly mutated in breast cancers and is known to interact with RUNX proteins to regulate transcription. Here, the authors describe a non-canonical role of CBFB in translation regulation in which it binds to mRNAs through hnRNPK, facilitating translation by eIF4B.

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.

Abstract 1042: CLIC4 is incorporated into extracellular vesicles of murine breast cancer cells and may influence metastatic burden

Chloride intracellular channel 4 (CLIC4) is an evolutionarily conserved, 29kD, dimorphic protein that contributes to TGF-β signaling by preventing the de-phosphorylation of phospho-SMAD2/3 upon nuclear translocation. In several cancer types, CLIC4 is excluded from the nucleus and downregulated in the cytoplasm of the tumor cells as the tumor progresses, suggesting that CLIC4 acts as tumor suppressor. In a parallel sequence, CLIC4 becomes upregulated in the stromal compartment, where it enhances tumor growth and invasion. Recent reports have suggested that CLIC4 is detectable in the serum of cancer patients and incorporated into extracellular vesicles, and has potential as a biomarker. We hope to gain a better understanding of the role that CLIC4 plays in the tumor stromal and epithelial compartments as well as their respective release of extracellular vesicles. Using in-vitro and in-vivo assays, we have conducted experiments using the FVB mouse MMTV-c-MYC 6DT1 breast cancer model. By CRISPR/ Cas9 system, CLIC4 was deleted from wild type 6DT1 cells. Following clonal selection, the loss of the CLIC4 protein at both the cellular and released vesicle level was validated. Both functional assays on CLIC4 deleted clones and evaluation of their extra-cellular vesicles were undertaken in order to further understand their tumorigenic and metastatic capabilities. In-vitro, CLIC4 was not necessary for vesicle biogenesis and its deletion did not have a significant effect on cellular proliferation. In vivo, selected clones were orthotopically injected into the 4th mammary fat pad of wild type FVB mice. Compared to wild type 6DT1 clones, CLIC4 deleted clones formed primary tumors that had greater mass but a fewer number of lung metastasis. Future studies are designed to isolate vesicles circulating in tumor bearing hosts to determine their stromal or epithelial origin and to provide a better understanding of the role that CLIC4 may play in tumor growth, creating a metastatic niche and as a potential serological biomarker.

Citation Format: Alayna B. Craig-Lucas, Vanesa C. Sanchez, Abigail Read, Ji Lou, Anjali Shukla, Stuart H. Yuspa. CLIC4 is incorporated into extracellular vesicles of murine breast cancer cells and may influence metastatic burden [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1042. doi:10.1158/1538-7445.AM2017-1042

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 1924: miR-142-3p is a candidate mediator of chloride intracellular channel 4 (CLIC4) loss during squamous cancer progression

Chloride intracellular channel 4 (CLIC4) is a broadly expressed protein that has been implicated in multiple cellular processes, including cellular differentiation and apoptosis. As a soluble factor, CLIC4 translocates to the nucleus following exposure to a variety of stimuli, including TGF-β, TNF-α, and etoposide. Nuclear CLIC4 potentiates TGF-β signaling by preventing the dephosphorylation of phospho-SMAD2 and 3 and promotes growth arrest. Although its primary function is as a tumor suppressor, CLIC4 expression is progressively diminished during cancer progression and CLIC4 protein is excluded from the nucleus of many human epithelial neoplasms and squamous cell carcinoma (SCC) cell lines. To date, no gene deletions or mutations have been identified to account for this phenomenon; thus, identifying the mechanism of CLIC4 loss is our primary focus. To determine if epigenetic gene silencing is responsible, we evaluated the methylation status of the CLIC4 promoter in a progression panel (normal, papilloma, SCC) of epithelial cell lines by performing bisulfite sequencing. No differential promoter methylation was found between the cell lines, suggesting that the regulation may be post-transcriptional or post-translational. Because microRNAs (miRNAs) are known to regulate gene expression by mediating the degradation or translational repression of target mRNAs, we performed a bioinformatic analysis of the CLIC4 3’ UTR, which revealed a large number of putative targeting miRNAs. One such miRNA, miR-142-3p, has been predicted to target CLIC4 by multiple algorithms and has been shown to interact with the CLIC4 3’ UTR by high-throughput sequencing and crosslinking immunoprecipitation. We confirmed the functional activity of miR-142-3p against the CLIC4 3’ UTR by using a 3’ UTR luciferase reporter assay and a miR-142-3p mimic. miR-142-3p is high in the tumor tissue and plasma of patients with head and neck SCC and is correlated with worse prognosis, where CLIC4 expression is known to be low. Thus, miR-142-3p may be responsible for mediating CLIC4 loss in squamous lesions and warrants further investigation.

Citation Format: Brandi L. Carofino, Stuart H. Yuspa. miR-142-3p is a candidate mediator of chloride intracellular channel 4 (CLIC4) loss during squamous cancer progression. [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 1924.

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.

Science Signaling Podcast for 21 June 2016: MET and skin cancer

This Podcast features an interview with Stuart Yuspa, senior author of a Research Article that appears in the 21 June 2016 issue of Science Signaling, about how activation of the receptor tyrosine kinase MET stimulates the formation of squamous cell carcinoma in the skin. Hepatocyte growth factor (HGF) is produced by mesenchymal cells and stimulates MET, which is present on the surface of epithelial cells. HGF-MET signaling directs the proliferation and migration of epithelial cells during the development of various organs and is important during wound healing. Aberrant MET activation has been implicated in several types of cancer, including squamous cell carcinoma. Using a model in which mice overexpressing HGF develop spontaneous squamous cell carcinomas in the skin, Cataisson et al found that MET promoted the development of squamous tumors by stimulating the synthesis and release of ligands that activate the epidermal growth factor receptor (EGFR). This mechanism was similar to that through which oncogenic RAS promotes skin tumors. Blocking EGFR signaling caused HGF-induced squamous tumors to regress, suggesting that EGFR inhibitors might be useful for treating squamous cell carcinomas.Listen to Podcast.

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.

Inhibition of calcium-induced terminal differentiation of epidermal cells by ouabain and A23187

Mouse epidermal basal cells can be selectively grown in a medium containing 0.02-0.1 mM Ca++. Terminal differentiation with squame formation and cell death is induced by elevating extracellular Ca++ to greater than 0.1mM. A variety of agents were studied as modifiers of this calcium-induced terminal differentiation. Other than Ca++, no inorganic cation tested was active in inducing or preventing differentiation. Organic cations, local anesthetics, quercetin, and the ionophore X 537A were also without effect. Limited non-toxic exposures to macromolecular synthesis inhibitors or microtubule and microfilament disruptors, and prolonged exposure to indomethacin or protease inhibitors did not alter differentiation. The skin tumor promoter 12-O-tetradecanoylphorbol-13-acetate markedly accelerated calcium-induced epidermal differentiation while the ionophore A23187 and the Na+-K+ATPase inhibitor ouabain (at non-toxic concentrations) clearly inhibited the induction by calcium. These results suggest that epidermal differentiation is specifically triggered by elevation of extracellular calcium but may be mediated by the flux or intracellular levels of other ions, particularly Na+ or K+.

Alterations in epidermal functions resulting from exposure to initiators and promoters of carcinogenesis

Mouse epidermal basal cells can be selectively cultivated in medium with a [Ca++] of 0.02-0.09 mM. Terminal differentiation and sloughing of mature keratinocytes occurs when the [Ca++] is increased to 1.2-1.4 mM. When basal cell cultures are exposed to chemical initiators of carcinogenesis, colonies of cells which resist Ca++ -induced differentiation evolve. Likewise basal cells derived from mouse skin initiated in vivo yield foci which resist terminal differentiation. This defect in the commitment to terminal differentiation appears to be an essential change in initiated cells in skin and is also characteristic of malignant epidermal cells. When normal basal cell cultures are exposed to the potent tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), there is induction of epidermal transglutaminase, an enzyme which is characteristic of terminally differentiating epidermal cells. Morphological differentiation is observed in about 50% of the population, and these cells are lost from the culture. The cells which remain are resistant to induced differentiation by either 1.2 mM Ca++ medium or a second exposure to TPA if the exposure interval is 4 days. These cells are directly stimulated (without an initial inhibition) to proliferate by a second TPA exposure, suggesting that this population is responsive only to the mitogenic effects of the promoter. With a 10-day interval between exposures, responsiveness to both TPA and 1.2 mM Ca++ return to control patterns. These results indicate that exposure to TPA induces differentiation in some basal cells while stimulating proliferation in others. Such responses could lead to clonal expansion of epidermal cells which fail to respond to differentiation signals, such as initiated cells.

Chemical carcinogenesis studies in mouse epidermal cell cultures

Studies of tumor induction on mouse skin have provided insight into the basis biology of chemical carcinogenesis, but molecular mechanisms have been more difficult to elucidate. Mouse epidermal cell cultures have proven to be a valuable model for performing mechanistic studies. Previous data have indicated that such cultures proliferate and differentiate in a manner highly analogous to epidermis in vivo. In addition, carcinogen metabolism, DNA repair, and responses to tumor promoters are quite similar in mouse skin in vivo and in vitro. Recent data have extended these observations toward defining the biological characteristics of initiated cells and elucidating the mechanism of action of promoters and antipromoters. When mouse epidermis is cultured under conditions of low extracellular Ca++, proliferation is enhanced and terminal differentiation is inhibited. Addition of Ca++ induces terminal differentiation. If cells are treated with carcinogens under low Ca++ conditions and subsequently switched to standard Ca++, cell colonies which do not terminally differentiate evolve. Such colonies continue to synthesize keratin, are subculturable, and may represent preneoplastic cells. In other experiments, epidermal cells derived from mouse skin treated with carcinogens in vivo also demonstrate prolonged in vitro survival and subculturability while controls have a limited lifespan. Such studies suggest that biological alterations can be detected in epidermal cells exposed to carcinogens well before and the phenotypic expression of neoplasia. Exposure of epidermal cells to phorbol-ester tumor promoters induces ornithine decarboxylase (ODC). This induction is enhanced by corticosteroids and markedly inhibited by retinoids. Ultraviolet light also induces ODC in epidermal cells, but kinetic studies suggest that the early pathway of induction (afferent to the nucleus) is different from that of phorbol esters. The later pathways (efferent from the nucleus-i.e., transcription and translation) appear to be similar. Retinoids have only a minor suppressive effect on ODC induction by UV while corticosteroids enhance UV induction to the same extent as seen with phorbol esters These results suggest that the site of retinoids is in the afferent pathway while steroids act on the efferent pathway.

Chloride channels in cancer: Focus on chloride intracellular channel 1 and 4 (CLIC1 AND CLIC4) proteins in tumor development and as novel therapeutic targets

In recent decades, growing scientific evidence supports the role of ion channels in the development of different cancers. Both potassium selective pores and chloride permeabilities are considered the most active channels during tumorigenesis. High rate of proliferation, active migration, and invasiveness into non-neoplastic tissues are specific properties of neoplastic transformation. All these actions require partial or total involvement of chloride channel activity. In this context, this class of membrane proteins could represent valuable therapeutic targets for the treatment of resistant tumors. However, this encouraging premise has not so far produced any valid new channel-targeted antitumoral molecule for cancer treatment. Problematic for drug design targeting ion channels is their vital role in normal cells for essential physiological functions. By targeting these membrane proteins involved in pathological conditions, it is inevitable to cause relevant side effects in healthy organs. In light of this, a new protein family, the chloride intracellular channels (CLICs), could be a promising class of therapeutic targets for its intrinsic individualities: CLIC1 and CLIC4, in particular, not only are overexpressed in specific tumor types or their corresponding stroma but also change localization and function from hydrophilic cytosolic to integral transmembrane proteins as active ionic channels or signal transducers during cell cycle progression in certain cases. These changes in intracellular localization, tissue compartments, and channel function, uniquely associated with malignant transformation, may offer a unique target for cancer therapy, likely able to spare normal cells. This article is part of a special issue itled "Membrane Channels and Transporters in Cancers."

Detection of differential fetal and adult expression of chloride intracellular channel 4 (CLIC4) protein by analysis of a green fluorescent protein knock-in mouse line

Background

Chloride Intracellular Channel 4 (CLIC4) is one of seven members in the closely related CLIC protein family. CLIC4 is involved in multiple cellular processes including apoptosis, cellular differentiation, inflammation and endothelial tubulogenesis. Despite over a decade of research, no comprehensive in situ expression analysis of CLIC4 in a living organism has been reported. In order to fulfill this goal, we generated a knock-in mouse to express Green Fluorescent Protein (GFP) from the CLIC4 locus, thus substituting the GFP coding region for CLIC4. We used GFP protein expression to eliminate cross reaction with other CLIC family members.

Results

We analyzed CLIC4 expression during embryonic development and adult organs. During mid and late gestation, CLIC4 expression is modulated particularly in fetal brain, heart, thymus, liver and kidney as well as in developing brown adipose tissue and stratifying epidermis. In the adult mouse, CLIC4 is highly expressed globally in vascular endothelial cells as well as in liver, lung alveolar septae, pancreatic acini, spermatogonia, renal proximal tubules, cardiomyocytes and thymic epithelial cells. Neural expression included axonal tracks, olfactory bulb, Purkinje cell layer and dentate gyrus. Renal CLIC4 expression was most pronounced in proximal tubules, although altered renal function was not detected in the absence of CLIC4. Myeloid cells and B cells of the spleen are rich in CLIC4 expression as are CD4 and CD8 positive T cells.

Conclusions

In a comprehensive study detailing CLIC4 expression in situ in a mouse model that excludes cross reaction with other family members, we were able to document previously unreported expression for CLIC4 in developing fetus, particularly the brain. In addition, compartmentalized expression of CLIC4 in specific adult tissues and cells provides a focus to explore potential functions of this protein not addressed previously.

Genetic ablation of epidermal EGFR reveals the dynamic origin of adverse effects of anti-EGFR therapy

Cancer patients treated with anti-EGFR (epidermal growth factor receptor) drugs often develop a dose-limiting pruritic rash of unknown etiology. The aims of our study were to define causal associations from a clinical study of cutaneous and systemic changes in patients treated with gefitinib and use these to develop and characterize a mouse model that recapitulates the human skin rash syndrome caused by anti-EGFR therapy. We examined the patients' plasma before and after treatment with gefitinib and documented changes in chemokines and leukocyte counts associated with the extent of rash or the presence of pruritus. We established a parallel mouse model by ablating EGFR in the epidermis. These mice developed skin lesions similar to the human rash. Before lesion development, we detected increased mRNA expression of chemokines in the skin associated with early infiltration of macrophages and mast cells and later infiltration of eosinophils, T cells, and neutrophils. As the skin phenotype evolved, changes in blood counts and circulating chemokines reproduced those seen in the gefitinib-treated patients. Crossing the mutant mice with mice deficient for tumor necrosis factor-α (TNF-α) receptors, MyD88, NOS2, CCR2, T cells, or B cells failed to reverse the skin phenotype. However, local depletion of macrophages provided partial resolution, suggesting that this model can identify targets that may be effective in preventing the troublesome and dose-limiting skin response to anti-EGFR drugs. These results highlight the importance of EGFR signaling in maintaining skin immune homeostasis and identify a macrophage contribution to a serious adverse consequence of cancer chemotherapy.

Aberrant chloride intracellular channel 4 expression contributes to endothelial dysfunction in pulmonary arterial hypertension

BACKGROUND

Chloride intracellular channel 4 (CLIC4) is highly expressed in the endothelium of remodeled pulmonary vessels and plexiform lesions of patients with pulmonary arterial hypertension. CLIC4 regulates vasculogenesis through endothelial tube formation. Aberrant CLIC4 expression may contribute to the vascular pathology of pulmonary arterial hypertension.

METHODS AND RESULTS

CLIC4 protein expression was increased in plasma and blood-derived endothelial cells from patients with idiopathic pulmonary arterial hypertension and in the pulmonary vascular endothelium of 3 rat models of pulmonary hypertension. CLIC4 gene deletion markedly attenuated the development of chronic hypoxia-induced pulmonary hypertension in mice. Adenoviral overexpression of CLIC4 in cultured human pulmonary artery endothelial cells compromised pulmonary endothelial barrier function and enhanced their survival and angiogenic capacity, whereas CLIC4 shRNA had an inhibitory effect. Similarly, inhibition of CLIC4 expression in blood-derived endothelial cells from patients with idiopathic pulmonary arterial hypertension attenuated the abnormal angiogenic behavior that characterizes these cells. The mechanism of CLIC4 effects involves p65-mediated activation of nuclear factor-κB, followed by stabilization of hypoxia-inducible factor-1α and increased downstream production of vascular endothelial growth factor and endothelin-1.

CONCLUSION

Increased CLIC4 expression is an early manifestation and mediator of endothelial dysfunction in pulmonary hypertension.

Opposing functions of psoriasin (S100A7) and koebnerisin (S100A15) in epithelial carcinogenesis

The S100 protein family is involved in epithelial cell maturation and inflammation. Some S100 members are dysregulated during carcinogenesis and have been established as tumor markers. Psoriasin (S100A7) and koebnerisin (S100A15) are highly homologous proteins that have been first described in psoriasis, which is characterized by disturbed epidermal maturation and chronic inflammation. Despite their homology, both S100 proteins are distinct in expression and function through different receptors but synergize as chemoattractants and pro-inflammatory 'alarmins' to promote inflammation. Psoriasin and koebnerisin are further regulated with tumor progression in epithelial cancers. In tumor cells, high cytoplasmic expression of psoriasin and koebnerisin may prevent oncogenic activity, whereas their nuclear translocation and extracellular secretion are associated with tumor progression and poor prognosis. The present review outlines these opposing effects of psoriasin and koebnerisin in multifunctional pathways and mechanisms that are known to affect tumor cells ('seeds'), tumor environment ('soil') and tumor cell metastasis ('seeding') thereby influencing epithelial carcinogenesis.

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 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

Abstract 5635: Development of a high-throughput cell and fluorescent image-based ABCB1-mediated efflux assay for screening inhibitors of ABCB1

ABCB1, also known as P-glycoprotein (P-gp) or multidrug resistance protein 1 (MDR1), is a membrane-associated multidrug transporter of the ATP-binding cassette (ABC) transporter family. It is one of the most widely studied transporters that enable cancer cells to develop drug resistance. Reliable high-throughput assays that can identify compounds that interact with ABCB1 are crucial for developing new therapeutic drugs. A high-throughput assay for measuring ABCB1-mediated calcein AM efflux was developed using the IncuCyteFLR technology. Time- and dose-dependent accumulation of fluorescent calcein in ABCB1-overexpressing KB-V1 cells was recorded using the IncuCyteFLR. Validation of the assay was performed with known ABCB1 inhibitors, XR9576, verapamil, and cyclosporin A, all of which displayed dose-dependent inhibition of ABCB1-mediated calcein AM efflux in this assay. A kinase inhibitor library and other compounds with known therapeutic targets were screened. The assay is highly reproducible and inhibitors for ABCB1-mediated efflux were identified from the kinase inhibitor library. Among compounds with known targets, BEZ235, BI 2536, IKK 16, and Ispinesib (SB-715992) inhibited calcein AM efflux in a dose-dependent manner and were also active in the flow cytometry based efflux assay. BEZ235, BI 2536, and IKK 16 also successfully competed with radiolabeled photoaffinity substrate [125I]iodoarylazidoprazosin (IAAP) for binding to ABCB1. Inhibition of ABCB1 lowered the IC50 value of BI 2536 treated ABCB1-overexpressing cancer cells. Phase and fluorescent images taken by the IncuCyteFLR provided additional opportunities for evaluating compounds that are cytotoxic or produce false positive signals. This high-throughput assay provides an efficient, reliable, and simple technique for screening libraries of natural and synthetic compounds to identify ABCB1 inhibitors. The same approach may be applied to screen inhibitors of other ABC transporters when suitable cell lines and fluorescent substrates are used.

Citation Format: Megan R. Ansbro, Suneet Shukla, Suresh V. Ambudkar, Stuart H. Yuspa, Luowei Li. Development of a high-throughput cell and fluorescent image-based ABCB1-mediated efflux assay for screening inhibitors of ABCB1. [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 5635. doi:10.1158/1538-7445.AM2013-5635

Abstract 1418: CLIC4 regulates carcinogenesis in a TGF-β context-dependent manner

CLIC4 is a 28kD, ubiquitously expressed, redox-regulated, multifunctional protein. It is dimorphic and can transition between membrane bound or soluble forms in the cytoplasm. Cytoplasmic CLIC4 translocates to the nucleus in multiple cell types under conditions of metabolic stress and nuclear CLIC4 causes growth arrest, terminal differentiation and apoptosis. In vivo, CLIC4 is nuclear in quiescent epithelial cells with little stromal expression. In contrast, nuclear CLIC4 is lost from tumor epithelium and is highly upregulated in tumor stroma. We show that CLIC4 expression is reduced in chemically induced mouse skin papillomas, mouse and human squamous carcinomas and squamous cancer cell lines. The extent of reduction in CLIC4 coincides with progression of squamous tumors from benign to malignant. Adenoviral targeting of CLIC4 to the nucleus of tumor cells in orthografts of oncogenic ras transformed keratinocytes inhibits tumor growth, while elevation of CLIC4 in transgenic epidermis reduces de novo chemically induced skin tumor formation. In parallel, overexpression of exogenous CLIC4 in squamous tumor orthografts suppresses tumor growth. These results identify CLIC4 as a tumor suppressor. We show that CLIC4 is an integral intermediate in TGF-β signaling, that overexpressing CLIC4 in tumor cell lines restores TGF-β mediated growth inhibition, and tumor cells in vivo overexpressing CLIC4 have enhanced TGF-β signaling. We have also analyzed the substantial upregulation of CLIC4 in tumor stroma. Reconstituting orthografts of mammary or squamous tumors with stromal cells overexpressing CLIC4 enhances tumor growth.Correspondingly, tumor growth is significantly inhibited in orthografts of tumor cells to hosts that lack stromal CLIC4. CLIC4 expression is increased in stromal cells by conditioned medium from tumor cells in a TGF-β dependent manner. In stromal cells genetically deleted of CLIC4, the conversion of fibroblasts to cancer associated myofibroblasts by TGF-β through p38 activation is prevented. CLIC4 is essential for preventing the de-activation of p38 by its phosphatase PPM1a. Stromal cells that overexpress CLIC4 enhance tumor cell invasion and EMT in vitro. Thus CLIC4, like TGF-β, has context dependent dual influence on tumor cell growth and progression. CLIC4 is an attractive therapeutic target both in cancer stages where TGF-β signal augmentation or inhibition is required due to responses in separate tissue compartments. Targeting CLIC4 would also be a more specific approach in therapy that would mitigate some of the severe side effects of global targeting of the multifunctional TGF-β pathway.

Citation Format: Anjali Shukla, Rebecca Edwards, Yihan Yang, Alexandra Hahn, VC Padmakumar, Andrew Ryscavage, Kwang S. Suh, Stuart H. Yuspa. CLIC4 regulates carcinogenesis in a TGF-β context-dependent manner. [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 1418. doi:10.1158/1538-7445.AM2013-1418

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.

Cutaneous retinoic acid levels determine hair follicle development and downgrowth

Retinoic acid (RA) is essential during embryogenesis and for tissue homeostasis, whereas excess RA is well known as a teratogen. In humans, excess RA is associated with hair loss. In the present study, we demonstrate that specific levels of RA, regulated by Cyp26b1, one of the RA-degrading enzymes, are required for hair follicle (hf) morphogenesis. Mice with embryonic ablation of Cyp26b1 (Cyp26b1(-/-)) have excessive endogenous RA, resulting in arrest of hf growth at the hair germ stage. The altered hf development is rescued by grafting the mutant skin on immunodeficient mice. Our results show that normalization of RA levels is associated with reinitiation of hf development. Conditional deficiency of Cyp26b1 in the dermis (En1Cre;Cyp26b1f/-) results in decreased hair follicle density and specific effect on hair type, indicating that RA levels also influence regulators of hair bending. Our results support the model of RA-dependent dermal signals regulating hf downgrowth and bending. To elucidate target gene pathways of RA, we performed microarray and RNA-Seq profiling of genes differentially expressed in Cyp26b1(-/-) skin and En1Cre;Cyp26b1f/- tissues. We show specific effects on the Wnt-catenin pathway and on members of the Runx, Fox, and Sox transcription factor families, indicating that RA modulates pathways and factors implicated in hf downgrowth and bending. Our results establish that proper RA distribution is essential for morphogenesis, development, and differentiation of hfs.

Genetic ablation of cyclooxygenase-2 in keratinocytes produces a cell-autonomous defect in tumor formation

Using a mouse skin tumor model, we reported previously that cyclooxygenase-2 (COX-2) deficiency reduced papilloma formation. However, this model did not differentiate between the effects of systemic COX-2-deficiency and keratinocyte-specific COX-2 deficiency on tumor formation. To determine whether keratinocyte-specific COX-2 deficiency reduced papilloma formation, v-H-ras-transformed COX-2+/+ and COX-2-/- keratinocytes were grafted onto nude mice and tumor development was compared. Transformed COX-2+/+ and COX-2-/- keratinocytes expressed similar levels of H-ras, epidermal growth factor receptor and phospho-extracellular signal-regulated kinase 1/2 in vitro; and COX-2-deficiency did not reduce uninfected or v-H-ras infected keratinocyte replication. In contrast, tumors arising from grafted transformed COX-2+/+ and COX-2-/- keratinocytes expressed similar levels of H-ras, but COX-2 deficiency reduced phospho-extracellular signal-regulated kinase 1/2 and epidermal growth factor receptor levels 50-60% and tumor volume by 80% at 3 weeks. Two factors appeared to account for the reduced papilloma size. First, papillomas derived from COX-2-/- keratinocytes showed about 70% decreased proliferation, as measured by bromodeoxyuridine incorporation, compared with papillomas derived from COX-2+/+ keratinocytes. Second, keratin 1 immunostaining of papillomas indicated that COX-2-/- keratinocytes prematurely initiated terminal differentiation. Differences in the levels of apoptosis and vascularization did not appear to be contributing factors as their levels were similar in tumors derived from COX-2-/- and COX-2+/+ keratinocytes. Overall, the data are in agreement with our previous observations that decreased papilloma number and size on COX-2-/- mice resulted from reduced keratinocyte proliferation and accelerated keratinocyte differentiation. Furthermore, the data indicate that deficiency/inhibition of COX-2 in the initiated keratinocyte is an important determinant of papilloma forming ability.

Spontaneous skin erosions and reduced skin and corneal wound healing characterize CLIC4(NULL) mice

Cutaneous wound healing is a complex process involving blood clotting, inflammation, migration of keratinocytes, angiogenesis, and, ultimately, tissue remodeling and wound closure. Many of these processes involve transforming growth factor-β (TGF-β) signaling, and mice lacking components of the TGF-β signaling pathway are defective in wound healing. We show herein that CLIC4, an integral component of the TGF-β pathway, is highly up-regulated in skin wounds. We genetically deleted murine CLIC4 and generated a colony on a C57Bl/6 background. CLIC4(NULL) mice were viable and fertile but had smaller litters than did wild-type mice. After 6 months of age, up to 40% of null mice developed spontaneous skin erosions. Reepithelialization of induced full-thickness skin wounds and superficial corneal wounds was delayed in CLIC4(NULL) mice, resolution of inflammation was delayed, and expression of β4 integrin and p21 was reduced in lysates of constitutive and wounded CLIC4(NULL) skin. The induced level of phosphorylated Smad2 in response to TGF-β was reduced in cultured CLIC4(NULL) keratinocytes relative to in wild-type cells, and CLIC4(NULL) keratinocytes migrated slower than did wild-type keratinocytes and did not increase migration in response to TGF-β. CLIC4(NULL) keratinocytes were also less adherent on plates coated with matrix secreted by wild-type keratinocytes. These results indicate that CLIC4 participates in skin healing and corneal wound reepithelialization through enhancement of epithelial migration by a mechanism that may involve a compromised TGF-β pathway.

Abstract 388: mS100a7a15 enhances mammary tumor growth and metastasis by recruiting tumor associated macrophages

mS100a7a15 is the murine ortholog of human S100A7 and S100A15 proteins. Both S100A7 and S100A15 have been shown to play an important role in breast cancer. S100A7 has been shown to be highly expressed in high grade ductal carcinoma in situ and invasive breast cancers. Its expression is also related to poor prognosis and associated with increased inflammatory infiltrates and various inflammatory disorders. However, the exact mechanism by which S100A7 or S100A15 enhances breast cancer growth is not known. In the present study, we determined the molecular mechanisms by which mS100a7a15 enhances growth by overexpressing mS100a7a15 in MDA-MB-231 cells. We showed that mS100a7a15 enhances expression of proinflammatory molecules CXCL1 and CXCL8. In addition, we observed that supernatants obtained from mS100a7a15 overexpressing cells enhanced chemotaxis of murine RAW264.7 macrophages. Further elucidation revealed that mS100a7/a15 mediates its effects by binding to receptor for advanced glycation end products (RAGE). We further analyzed the role of mS100a7a15 on modulation of tumor growth and inflammatory pathways in breast cancer by generating inducible bi-transgenic MMTV-rtTA; mS100a7a15 mice (MMTV-mS100a7a15). These mice showed enhanced mS100a7a15 protein expression upon doxycycline treatment. Mammary glands isolated from these mice showed enhanced hyperplasia upon doxycycline treatment for 3 months compared to uninduced mice. Further studies revealed enhanced recruitment of macrophages in mammary glands and activation of STAT3 in induced mice. Orthotopic implantation of MVT-1 breast tumor cells (derived from MMTV-c-Myc; MMTV-VEGF mice) into the mammary glands of these mice showed enhanced tumor growth and metastasis in doxycycline treated mice compared to the control. Tumors and lung tissues obtained from these mice showed enhanced pro-metastatic gene expression and recruitment of F4/80 and CD206 positive M2 tumor-associated macrophages (TAM). However, no difference was observed in CD3+ and CD4+ T lymphocytes. Further elucidation of the role of macrophages by in vivo depletion of macrophages using clodronate liposomes revealed that mS100a7a15-mediated recruitment of TAM is important for tumor growth, angiogenesis and metastasis. Furthermore, mice treated with STAT3 inhibitors showed reduced mS100a7a15-induced hyperplasia. STAT3 has been shown to regulate expression of various inflammatory molecules. These studies using a novel mS100a7a15 bi-transgenic model system demonstrate that mS100a7a15 enhances breast tumor growth and metastasis by enhancing inflammatory signals that result in enhanced recruitment of TAM.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 388. doi:1538-7445.AM2012-388

CLIC4 is a tumor suppressor for cutaneous squamous cell cancer

Chloride intracellular channel (CLIC) 4 is a member of a redox-regulated, metamorphic multifunctional protein family, first characterized as intracellular chloride channels. Current knowledge indicates that CLICs participate in signaling, cytoskeleton integrity and differentiation functions of multiple tissues. In metabolically stressed skin keratinocytes, cytoplasmic CLIC4 is S-nitrosylated and translocates to the nucleus where it enhances transforming growth factor-β (TGF-β) signaling by protecting phospho-Smad 2 and 3 from dephosphorylation. CLIC4 expression is diminished in multiple human epithelial cancers, and the protein is excluded from the nucleus. We now show that CLIC4 expression is reduced in chemically induced mouse skin papillomas, mouse and human squamous carcinomas and squamous cancer cell lines, and the protein is excluded from the nucleus. The extent of reduction in CLIC4 coincides with progression of squamous tumors from benign to malignant. Inhibiting antioxidant defense in tumor cells increases S-nitrosylation and nuclear translocation of CLIC4. Adenoviral-mediated reconstitution of nuclear CLIC4 in squamous cancer cells enhances TGF-β-dependent transcriptional activity and inhibits growth. Adenoviral targeting of CLIC4 to the nucleus of tumor cells in orthografts inhibits tumor growth, whereas elevation of CLIC4 in transgenic epidermis reduces de novo chemically induced skin tumor formation. In parallel, overexpression of exogenous CLIC4 in squamous tumor orthografts suppresses tumor growth and enhances TGF-β signaling. These results indicate that CLIC4 suppresses the growth of squamous cancers, that reduced CLIC4 expression and nuclear residence detected in cancer cells is associated with the altered redox state of tumor cells and the absence of detectable nuclear CLIC4 in cancers contributes to TGF-β resistance and enhances tumor development.

Increased retinoic acid levels through ablation of Cyp26b1 determine the processes of embryonic skin barrier formation and peridermal development

The process by which the periderm transitions to stratified epidermis with the establishment of the skin barrier is unknown. Understanding the cellular and molecular processes involved is crucial for the treatment of human pathologies, where abnormal skin development and barrier dysfunction are associated with hypothermia and perinatal dehydration. For the first time, we demonstrate that retinoic acid (RA) levels are important for periderm desquamation, embryonic skin differentiation and barrier formation. Although excess exogenous RA has been known to have teratogenic effects, little is known about the consequences of elevated endogenous retinoids in skin during embryogenesis. Absence of cytochrome P450, family 26, subfamily b, polypeptide 1 (Cyp26b1), a retinoic-acid-degrading enzyme, results in aberrant epidermal differentiation and filaggrin expression, defective cornified envelopes and skin barrier formation, in conjunction with peridermal retention. We show that these alterations are RA dependent because administration of exogenous RA in vivo and to organotypic skin cultures phenocopy Cyp26b1(-/-) skin abnormalities. Furthermore, utilizing the Flaky tail (Ft/Ft) mice, a mouse model for human ichthyosis, characterized by mutations in the filaggrin gene, we establish that proper differentiation and barrier formation is a prerequisite for periderm sloughing. These results are important in understanding pathologies associated with abnormal embryonic skin development and barrier dysfunction.

CLIC4 and Schnurri-2: a dynamic duo in TGF-beta signaling with broader implications in cellular homeostasis and disease

CLIC4 is a highly conserved, multifunctional member of the chloride intracellular channel family of proteins. The protein is largely cytoplasmic but translocates to the nucleus upon a variety of stimuli including TGF-beta, TNF-alpha and etoposide. Nuclear resident CLIC4 causes growth arrest, terminal differentiation and apoptosis. Recently, it was discovered that TGF-beta causes CLIC4 to associate with Schnurri-2 and together they translocate to the nucleus and dissociate thereafter. The nuclear function of CLIC4 was further illuminated by the discovery that CLIC4 enhances TGF-beta signaling by associating with phospho-Smad2 and 3 and preventing their dephosphorylation. Enhanced TGF-beta dependent gene expression and growth inhibition are downstream consequences of this activity of CLIC4. In this article, we speculate on other consequences of the CLIC4 relation to TGF-beta signaling and the potential for CLIC4 to participate in other cellular functions related to normal homeostasis and disease.

S100A7 enhances mammary tumorigenesis through upregulation of inflammatory pathways

S100A7/psoriasin, a member of the epidermal differentiation complex, is widely overexpressed in invasive estrogen receptor (ER)α-negative breast cancers. However, it has not been established whether S100A7 contributes to breast cancer growth or metastasis. Here, we report the consequences of its expression on inflammatory pathways that impact breast cancer growth. Overexpression of human S100A7 or its murine homologue mS100a7a15 enhanced cell proliferation and upregulated various proinflammatory molecules in ERα-negative breast cancer cells. To examine in vivo effects, we generated mice with an inducible form of mS100a7a15 (MMTV-mS100a7a15 mice). Orthotopic implantation of MVT-1 breast tumor cells into the mammary glands of these mice enhanced tumor growth and metastasis. Compared with uninduced transgenic control mice, the mammary glands of mice where mS100a7a15 was induced exhibited increased ductal hyperplasia and expression of molecules involved in proliferation, signaling, tissue remodeling, and macrophage recruitment. Furthermore, tumors and lung tissues obtained from these mice showed further increases in prometastatic gene expression and recruitment of tumor-associated macrophages (TAM). Notably, in vivo depletion of TAM inhibited the effects of mS100a7a15 induction on tumor growth and angiogenesis. Furthermore, introduction of soluble hS100A7 or mS100a7a15 enhanced chemotaxis of macrophages via activation of RAGE receptors. In summary, our work used a powerful new model system to show that S100A7 enhances breast tumor growth and metastasis by activating proinflammatory and metastatic pathways.

Modeling the transcriptional consequences of epidermal growth factor receptor ablation in Ras-initiated squamous cancer

PURPOSE

Epidermal growth factor receptor (EGFR)-targeted therapy is in clinical use to treat squamous cell carcinoma of the head and neck and other cancers of lining epithelium. RAS mutations in these tumors are a negative prognostic factor for response, and skin inflammation is an adverse reaction to therapy. We investigated transcriptional and biochemical changes that could account for the confounding effects of RAS activation and inflammation in a squamous tissue.

EXPERIMENTAL DESIGN

We carried out gene expression profiling on oncogenic Ras-transformed and wild-type mouse and human keratinocytes with EGFR ablated chronically by genetic deletion or acutely by drug treatment and followed leads provided by pathway analysis with biochemical studies.

RESULTS

We identified a 25-gene signature specific to the Ras-EGFR ablation interaction and a distinct 19-gene EGFR ablation signature on normal keratinocytes. EGFR ablation in the context of wild-type Ras reduces ontologies favoring cell-cycle control and transcription, whereas oncogenic Ras enriches ontologies for ion channels and membrane transporters, particularly focused on calcium homeostasis. Ontologies between chronic EGFR ablation and acute pharmacologic ablation were unique, both with and without Ras activation. p38α is activated in response to abrogation of EGFR signaling under conditions of Ras activation in both mouse and human keratinocytes and in RAS-transformed tumor orthografts of EGFR-ablated mouse keratinocytes. EGFR ablation in the absence of oncogenic Ras revealed Erk and interleukin-1β-related pathways.

CONCLUSION

These findings reveal unrecognized interactions between Ras and EGFR signaling in squamous tumor cells that could influence the therapeutic response to EGFR ablation therapy.