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Modeling the Transcriptional Consequences of Epidermal Growth Factor Receptor Ablation in Ras-Initia

ABSTRACT: EGFR targeted therapy is in clinical use to treat squamous cell carcinoma of the head and neck and other cancers of lining epithelium. Activating Ras mutations are a negative prognostic factor for response to EGFR ablation therapy in multiple cancer types. Furthermore, the major adverse consequence of this therapy is an acneiform papulopustular eruption on normal skin. To better understand Ras signaling in an EGFR depleted environment, we performed gene expression profiling on oncogenic Ras transformed and wildtype mouse keratinocytes with EGFR ablated chronically by genetic deletion or acutely by drug treatment. We were able to identify 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 wildtype Ras reduces ontologies favoring cell cycle control and transcription while ablation in the context of oncogenic Ras enriches ontologies for ion channels and membrane transporters, particularly focused on calcium homeostasis. The study showed substantial differences in ontologies between chronic EGFR ablation and acute pharmacological ablation, both with and without Ras activation. Pathway and biochemical analysis indicates that activation of p38α is a response to both acute and chronic abrogation of EGFR signaling under conditions of Ras activation. This was confirmed in oncogenic RAS transformed human keratinocytes and in tumors developing in orthografts of EGFR ablated mouse keratinocytes transformed by oncogenic Ras. EGFR ablation in the absence of oncogenic Ras revealed Erk and IL-1β related pathways. These findings reveal previously unrecognized interactions between Ras and EGFR signaling in squamous tumor cells that could influence the therapeutic response to EGFR ablation therapy.

ORGANISM(S): Mus musculus

PROVIDER: GSE29415 | GEO | 2012/01/11

SECONDARY ACCESSION(S): PRJNA141535

REPOSITORIES: GEO

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Project description:MET expression is elevated in a majority of human skin cancers but its contributions to pathogenesis have not been evaluated. In a mouse model of constitutive overexpression of HGF (MT-HGF), the incidence of squamous cell skin tumors induced by initiation with 7,12-dimethylbenz(a)anthracene (DMBA) followed by exposure to 12-O-tetradecanoyl-phorbol-13-acetate (TPA) is increased fivefold over control groups. Half of these tumors carry Hras1 or Kras mutations. Without DMBA initiation, tumors also erupt on MT-HGF mouse skin but only when TPA promotion is enhanced by crossing these mice with mice overexpressing cutaneous PKCα. None of these tumors have Ras mutations. In culture, MT-HGF keratinocytes share identical MET mediated phenotypic and biochemical features with wildtype keratinocytes transformed by oncogenic RAS. In both cell types, these common features of initiated keratinocytes arise from autocrine activation of EGFR through elevated expression and release of EGFR ligands. Inhibition of EGFR ablates the initiated signature of MT-HGF keratinocytes in vitro and causes regression of MT-HGF induced tumors in vivo. Global gene expression data indicate that MT-HGF and RAS transformed keratinocytes share largely an identical profile of over 5000 mRNAs. Gene ontology analysis reveals the most affected concordant signature is enriched for functions relevant to tissue development and response to wounding, accompanied by cytokine and growth factor activity, and peptidase and endopeptidase activity previously not linked to initiated keratinocytes. Furthermore, gene co-expression analysis in skin cancer patients revealed a core RAS/MET co-expression network considerably activated in pre cancerous and cancerous lesions. Thus MET activation though EGFR contributes to human cutaneous cancers, and inhibitors could be efficacious in advanced lesions such as those seen in transplant recipient patients. In this dataset with provide gene expression data from primary mouse keratinocytes in culture.

Project description:We have compared the response to TGFbeta1 in normal and v-rasHa transduced primary mouse keratinocytes using NCI cDNA microarrays. This analysis reveals that Ha-ras alters global TGFbeta1 mediated gene expression in a gene specific manner. The expression pattern of TGFbeta1 immediate early response genes and down regulation of cell cycle control genes is not altered by Ha-ras but the induction of most extracellular matrix genes is blocked. Using Smad3 null keratinocytes, we find that the majority of TGFbeta1 responsive genes in primary keratinocytes are Smad3 dependent, but patterns of transcriptional responses suggest that the ability of Ha-ras to block TGFbeta1 mediated gene expression is not dependent on Smad3. However, the combination of oncogenic ras and loss of Smad3 prevents the TGFbeta1 dependent suppression of genes associated with cell cycle progression and apoptosis observed with either genotype alone. In addition several extracellular matrix genes are super-repressed by TGFbeta1 in the Ha-ras Smad3 null keratinocytes. These data provide a genomic framework for understanding how disruptions of TGFbeta signaling and oncogenic ras cooperate to promote premalignant progression of primary keratinocytes. Keywords: time series design RNA from Balb/c primary and ras keratinocytes treated for 1, 6, 24, and 48 hours with TGFbeta1 at 1ng/ml was compared to RNA from the corresponding untreated controls. For each timepoint sample from primary and ras cells, multiple arrays (including dye swaps) were analyzed. There are 6, 7, 6, and 5 arrays analyzed for RNA from primary keratinocytes treated for 1, 6, 24, and 48 hours as compared to RNA from untreated primary cells, respectively. There are 6, 8, 7, and 5 arrays analyzed for RNA from ras keratinocytes treated for 1, 6, 24, and 48 hours as compared to RNA from untreated ras cells, respectively. There are 50 arrays analyzed for the Balb/c time-course dataset. RNA from Smad3 WT and KO primary and ras keratinocytes treated 48 hours with TGFbeta1 were compared to RNA from its untreated corresponding controls. There are 6 arrays analyzed for the Smad3 WT/KO data set. There are 56 arrays in this series.

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Modeling the Transcriptional Consequences of Epidermal Growth Factor Receptor Ablation in Ras-Initia

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