An EGFR-Sox9 Signaling Cascade Links Urothelial Development, Regeneration, and Cancer
S Ling, X Chang, T Lee, L Marchionni, X He, BW Simons, Z Huang, D Sidransky, G Netto, DM Berman. Johns Hopkins Medical Institutions, Baltimore
Background: Like many carcinomas, urothelial carcinoma (UrCa) is associated with chronic injury. This association is poorly understood, but could elucidate the etiology and treatment of this disease.
Design: Using western blot and immunohistochemistry, we investigated expression of the transcriptional regulator SRY-related HMG box 9 (SOX9), total and activated forms of Epidermal growth factor receptor (EGFR) and mitogen activated protein kinase (MAPK) proteins, as well as EGFR ligands in injured benign and malignant urothelial cells and tissue samples. Sox9 function was assayed for growth and invasion using human BFTC-905 UrCa cells transfected with scrambled (control) or specific short hairpin RNA expression vectors. A selection of both benign and malignant urothelial cell lines were cultured with EGFR and MAPK pathway agonists and antagonists, hydrogen peroxide, urea, and NaCl.
Results: We identified induction of the Sox9 in urothelial regeneration and in UrCa. In mouse bladder, Sox9 expression showed two spikes of increased expression -- first during embryonic growth and again during physiologic regeneration postnatally. In adults, and in cultured benign human urothelial cells, Sox9 protein was markedly induced by a variety of injuries, including systemic administration of the carcinogen cyclophosphamide, culture with hydrogen peroxide, and osmotic stress. Sox9 is a known target of MAPK signaling, which also induced Sox9 in urothelial injury and resulted from upregulation of Heparin binding EGF-like growth factor (HB-EGF) and amphiregulin through EGFR. EGFR expression was highest in the urothelial basal layer, normally protected from urinary EGFR ligands by overlying superficial cells. With chronic breaches of urothelial integrity, EGFR-Sox9 stimulation may promote urothelial carcinogenesis, as Sox9 expression was significantly upregulated in invasive human UrCa samples (n=82) and cell lines. The EGFR-Sox9 signaling axis operated in UrCa cells and was required for cell migration and invasion.
Conclusions: These results identify a novel, potentially oncogenic signaling axis that links urothelial injury to UrCa. Inhibiting the operation of this pathway is possible through a variety of pharmacologic approaches and may play a role in prevention and treatment of UrCa.
Tuesday, March 23, 2010 1:45 PM
Platform Session: Section H, Tuesday Afternoon