Epidermal Growth Factor Receptor Controls Flat Dysplastic Aberrant Crypt Foci Development and Colon Cancer Progression in the Rat Azoxymethane Model

Abstract

Purpose: Colonic carcinogenesis deranges growth-regulating epidermal growth factor receptors (EGFR). We previously showed that EGFR signals were up-regulated in human aberrant crypt foci (ACF), putative colon cancer precursors. The azoxymethane model of colon cancer recapitulates many aspects of human colonic tumors. Recent studies indicate that flat dysplastic ACF with increased h-catenin are tumor precursors in this model. We asked, therefore, if EGFR signals are required for flat dysplastic ACF development and cancer progression. Experimental Design: Rats received azoxymethane or saline, and standard chow or chow supplemented with gefitinib, an EGFR inhibitor, for 44 weeks. EGFR signals were quantified in normal colon, flat ACF, and tumors by computerized analysis of immunostains and Western blots. K-ras mutations were assessed by PCR and mRNA for egfr ligands by quantitative real-time PCR. Results: EGFR inhibition with gefitinib decreased the incidence of flat dysplastic ACF from 66% to 36% and tumors from 71% to 22% (P < 0.05). This inhibitor also reduced the overexpressions of cyclin D1 and Cox-2 in flat ACF. Furthermore, in flat ACF, EGFR blockade decreased the upregulation of c-Jun, FosB, phosphorylated active signal transducers and activators of transcription 3, and CCAAT/enhancer binding protein-h, potential regulators of cyclin D1 and Cox-2. In colonic tumors, EGFR blockade significantly decreased angiogenesis, proliferation, and progression while also increasing apoptosis (P < 0.05). Gefitinib also inhibited the activations of extracellular signal^regulated kinase, Src, and AKT pathways in tumors. Conclusions: We have shown for the first time that EGFR promotes the development of flat dysplastic ACF and the progression of malignant colonic tumors. Furthermore, we have mechanistically identified several transcription factors and their targets as EGFR effectors in colonic carcinogenesis.Colonic carcinogenesis is characterized by the accumulation of activating mutations in proto-oncogenes and inhibiting mutations in tumor suppressor genes. These mutations dysregulate pathways, including epidermal growth factor receptor (EGFR) signals that control cell growth, maturation, and cell death. Up-regulations of EGFRs and ligands have been described in many tumors, including colon cancers (1). Recently, we reported that EGFR signals were up-regulated in human aberrant crypt foci (ACF) identified in situ using image magnification chromoendoscopy (2). ACF are the earliest identifiable lesions in experimental colonic carcinogenesis and dysplastic ACF are believed to be precursors of colon cancer (3).EGFR (ErbB1) is a member of the ErbB family of receptor tyrosine kinases which also includes ErbB2, ErbB3, and ErbB4 (4). Ligand binding induces a conformational change, causing receptors to dimerize and activating the receptor's intrinsic tyrosine kinase. ErbB2 is unique in that it has no identified ligand, but is the preferred heterodimeric partner for other members. EGFR signals activate multiple pathways i...

Mucin‐depleted foci show strong activation of inflammatory markers in 1,2‐dimethylhydrazine‐induced carcinogenesis and are promoted by the inflammatory agent sodium dextran sulfate

“…21,[32][33][34] On the other hand, increased COX-2 has been documented in large or flat dysplastic AOM-induced ACF. 35,36 In agreement with these latter reports, we also found a modest, but significant increase in COX-2 expression in ACF. Importantly, when analysing MDF, that we consider the precursor lesions of colon cancer, we found a strong increase in COX-2, higher than that found in ACF or tumours.…”

Phase IIa Clinical Trial of Curcumin for the Prevention of Colorectal Neoplasia

“…This finding raises the question of the in-vivo mechanism(s) by which curcumin may have cancer-preventive effects in the setting of early pre-invasive neoplastic lesions. Potential mechanisms may involve down-regulating different signaling cascades such as epidermal growth factor receptor (EGFR) or insulin-like growth factor receptor (IGFR) signaling, either of which has been linked to ACF formation (38, 39) and is known to be inhibited by curcumin in cell-culture models (40). Alternatively, curcumin may act via influencing Notch signaling, as shown in pancreatic cell lines (41), and Wnt signaling, as shown in breast-cancer stem cells (42).…”

The Renin–Angiotensin System Mediates EGF Receptor–Vitamin D Receptor Cross-Talk in Colitis-Associated Colon Cancer

“…In prior studies we demonstrated that EGFR signals play a critical role in colonic tumorigenesis (6, 48, 49). The AT1 receptor can transactivate EGFR (24).…”

“…Prior studies showed that EGFR promotes colonic tumor development, whereas vitamin D inhibits tumorigenesis in models of colon cancer (6, 8, 32, 47-49). To examine how VDR alters colonic tumorigenesis and EGFR signals, we treated Vdr −/− and Vdr +/+ mice with AOM/DSS.…”