Epidermal growth factor receptor controls flat dysplastic aberrant crypt foci development and colon cancer progression in the rat azoxymethane model.
OBJECTIVE
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 beta-catenin are tumor precursors in this model. We asked, therefore, if EGFR signals are required for flat dysplastic ACF development and cancer progression.


METHODS
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 up-regulation of c-Jun, FosB, phosphorylated active signal transducers and activators of transcription 3, and CCAAT/enhancer binding protein-beta, 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.
Dougherty
Urszula
U
Department of Medicine, University of Chicago Hospitals and Clinics, Chicago, IL 60637, USA.
Sehdev
Amikar
A
Cerda
Sonia
S
Mustafi
Reba
R
Little
Nathaniel
N
Yuan
Weihua
W
Jagadeeswaran
Sujatha
S
Chumsangsri
Anusara
A
Delgado
Jorge
J
Tretiakova
Maria
M
Joseph
Loren
L
Hart
John
J
Cohen
Ezra E W
EE
Aluri
Lata
L
Fichera
Alessandro
A
Bissonnette
Marc
M
D000818:Animals; D001397:Azoxymethane / Q000633:toxicity; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000502:physiology; D003110:Colonic Neoplasms / Q000209:etiology* / Q000517:prevention & control; D056741:Cyclin D; D016213:Cyclins / Q000032:analysis; D018450:Disease Progression; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000502:physiology*; D000077156:Gefitinib; D008297:Male; D011230:Precancerous Conditions / Q000209:etiology* / Q000517:prevention & control; D011799:Quinazolines / Q000627:therapeutic use; D051381:Rats; D011916:Rats, Inbred F344; D050796:STAT3 Transcription Factor / Q000502:physiology; D018808:Transcription Factor AP-1 / Q000502:physiology
D022782:CCAAT-Enhancer-Binding Protein-beta; D056741:Cyclin D; D016213:Cyclins; D011799:Quinazolines; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D018808:Transcription Factor AP-1; D066246:ErbB Receptors; D001397:Azoxymethane; D000077156:Gefitinib