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EGFR Signaling Is Required for TGF-1–Mediated COX-2 Induction in Human Bronchial Epithelial Cells

¹ Lung Cancer Research Program, Jonsson Comprehensive Cancer Center, UCLA, Los Angeles, California; ² Veterans Affairs Greater Los Angeles Healthcare Center, Los Angeles, California; ³ Hamon Center for Therapeutic Oncology Research, University of Texas Southwestern Medical Center, Dallas, Texas; ⁴ Dallas Veterans Affairs Medical Center, Dallas, Texas; ⁵ Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas; and ⁶ Department of Pathology and Laboratory Medicine, David Geffen School of Medicine, UCLA, Los Angeles, California

Correspondence and requests for reprints should be addressed to Dr. Steven M. Dubinett, Lung Cancer Research Program, David Geffen School of Medicine at UCLA, 37-131 CHS, 10833 Le Conte Ave, Room 37-131 CHS, Los Angeles, CA 90095. E-mail: sdubinett{at}mednet.ucla.edu

Cyclooxygenase-2 (COX-2) is a key enzyme in the production of prostaglandins and thromboxanes from free arachidonic acid. Increasing evidence suggests that COX-2 plays a role in tumorigenesis. A variety of stimuli induce COX-2 and it is overexpressed in many tumors, including non–small cell lung cancer (NSCLC). We studied the regulation of COX-2 expression in immortalized human bronchial epithelial cells (HBECs) by transforming growth factor-1 (TGF-1) and epidermal growth factor (EGF) because these two growth factors are present in both the pulmonary milieu of those at risk for lung cancer as well as in the tumor microenvironment. EGF significantly enhanced TGF-1–mediated induction of COX-2 and corresponding prostaglandin E2 (PGE2) production. TGF-1 and EGF induced COX-2 at the transcriptional and post-transcriptional levels. EGF receptor (EGFR) inhibition, neutralizing antibody against amphiregulin, or mitogen-activated protein kinase kinase (MEK) inhibition blocked TGF-1–mediated COX-2 induction. COX-2 induction by TGF-1 depended upon Smad3 signaling and required the activity of EGFR or its downstream mediators. Autocrine amphiregulin signaling maintains EGFR in a constitutively active state in HBECs, allowing for COX-2 induction by TGF-1. Thus, EGFR ligands, which are abundant in the pulmonary microenvironment of those at risk for lung cancer, potentiate and are required for COX-2 induction by TGF-1 in HBEC. These findings emphasize the central role of EGFR signaling in COX-2 induction by TGF-1 and suggest that inhibition of EGFR signaling should be investigated further for lung cancer prevention.

Key Words: cyclooxygenase-2 • transforming growth factor-1 • epidermal growth factor receptor • lung cancer • Smad3

CLINICAL RELEVANCE Our findings regarding cooperation between transforming growth factor-1 and epidermal growth factor receptor (EGFR) signaling events in COX-2 regulation in human bronchial epithelial cells are novel and suggest that inhibition of EGFR signaling should be investigated further for lung cancer prevention.