Epidermal Growth Factor-Induced Tumor Cell Invasion and Metastasis Initiated by Dephosphorylation and Downregulation of Focal Adhesion Kinase

Abstract

Upregulated epidermal growth factor (EGF) receptor (EGFR) expression and EGFR-induced signaling have been correlated with progression to invasion and metastasis in a wide variety of carcinomas, but the mechanism behind this is not well understood. We show here that, in various human carcinoma cells that overexpress EGFR, EGF treatment induced rapid tyrosine dephosphorylation of focal adhesion kinase (FAK) associated with downregulation of its kinase activity. The downregulation of FAK activity was both required and sufficient for EGF-induced refractile morphological changes, detachment of cells from the extracellular matrix, and increased tumor cell motility, invasion, and metastasis. Tumor cells with downregulated FAK activity became less adherent to the extracellular matrix. However, once cells started reattaching, FAK activity was restored by activated integrin signaling. Moreover, this process of readhesion and spreading could not be abrogated by further EGF stimulation. Interruption of transforming growth factor alpha-EGFR autocrine regulation with an EGFR tyrosine kinase inhibitor led to a substantial increase in FAK tyrosine phosphorylation and inhibition of tumor cell invasion in vitro. Consistent with this, FAK tyrosine phosphorylation was reduced in cells from tumors growing in transplanted, athymic, nude mice, which have an intact autocrine regulation of the EGFR. We suggest that the dynamic regulation of FAK activity, initiated by EGF-induced downregulation of FAK leading to cell detachment and increased motility and invasion, followed by integrin-dependent reactivation during readhesion, plays a role in EGF-associated tumor invasion and metastasis.

ACKNOWLEDGMENTS

We thank Jeffrey Travers (Indiana University School of Medicine) for KB cells and technical assistance, Peter Vogt and Binghua Jiang (The Scripps Research Institute) for DU145 cells, David Schlaepfer (The Scripps Research Institute) for pcDNA3.1FRNK and pcDNA3.1L1034S-FRNK expression vectors, David Foster (The City University of New York) for A431 cells, MDA-MB468 cells, and NIH 3T3 EGFR cells, and Armand Hornia, Nigel Carter, and Joel Leverson for helpful discussions.

This work was supported by a Pioneer Fund Fellowship (Z.L.) and by USPHS grants CA14195 and CA82863 (T.H.). T.H. is a Frank and Else Schilling American Cancer Society Research Professor.