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

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. Overall design: Keratinocyte samples were collected from CD-1 EGFR total wild type and knock-out mice. Each of these were treated with 3 different EGFR tyrosine kinase inhibitors (AG1478, Erlotinib, PD153035) in combination with and without ras transduction. Control samples included untreated keratinocyte samples. Universal mouse reference RNA was used as the reference sample. Most groups contained 5 biological replicates, one being a reverse fluoro for a total of 63 samples.