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First published online 21 October 2008
doi: 10.1242/jcs.029769

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Signaling through urokinase and urokinase receptor in lung cancer cells requires interactions with β1 integrins

Pulmonary and Critical Care Division, Department of Medicine, Cardiovascular Research Institute, University of California San Francisco, San Francisco, CA 94143, USA

^* Author for correspondence (e-mail: ying.wei{at}ucsf.edu)

Accepted 14 August 2008

The urokinase receptor (uPAR) is upregulated upon tumor cell invasion and correlates with poor lung cancer survival. Although a cis-interaction with integrins has been ascribed to uPAR, whether this interaction alone is critical to urokinase (uPA)- and uPAR-dependent signaling and tumor promotion is unclear. Here we report the functional consequences of point mutations of uPAR (H249A-D262A) that eliminate β1 integrin interactions but maintain uPA binding, vitronectin attachment and association with V integrins, caveolin and epidermal growth factor receptor. Disruption of uPAR interactions with β1 integrins recapitulated previously reported findings with β1-integrin-derived peptides that attenuated matrix-dependent ERK activation, MMP expression and in vitro migration by human lung adenocarcinoma cell lines. The uPAR mutant cells acquired enhanced capacity to adhere to vitronectin via uPAR–Vβ5-integrin, rather than through the uPAR–3β1-integrin complex and they were unable to initiate uPA signaling to activate ERK, Akt or Stat1. In an orthotopic lung cancer model, uPAR mutant cells exhibited reduced tumor size compared with cells expressing wild-type uPAR. Taken together, the results indicate that uPAR–β1-integrin interactions are essential to signals induced by integrin matrix ligands or uPA that support lung cancer cell invasion in vitro and progression in vivo.

Key words: Urokinase, Urokinase receptor, Integrin, Signaling, Lung cancer