HS1-Associated Protein X-1 Regulates Carcinoma Cell Migration and Invasion via Clathrin-Mediated Endocytosis of Integrin αvβ6

Alan G Ramsay,John F Marshall,Melanie D Keppler,Mona Jazayeri,Maddy Parsons,Paul Weinreb,Shelia Violette,Ian R Hart,Gareth J Thomas

doi:10.1158/0008-5472.can-07-0318

Abstract

Enhanced expression levels of integrin alphavbeta6 have been linked to more aggressive invasive carcinoma cell behavior and poorer clinical prognosis. However, how alphavbeta6 determines invasion and the dynamics of integrin alphavbeta6 regulation in tumor cells are poorly understood. We have identified the 35-kDa HS1-associated protein X-1 (HAX-1) protein as a novel binding partner of the beta6 cytoplasmic tail using a yeast two-hybrid screen. We show that alphavbeta6-dependent migration is blocked following small interfering RNA (siRNA)-mediated depletion of HAX-1 in oral squamous cell carcinoma cell lines. Using both siRNA and membrane-permeable peptides, we show that alphavbeta6-dependent migration and invasion require HAX-1 to bind directly to beta6 and thereby regulate clathrin-mediated endocytosis of alphavbeta6 integrins. Progression of oral cancer is associated with enhanced expression of alphavbeta6 and HAX-1 proteins in patient tissue. This report establishes that integrin endocytosis is required for alphavbeta6-dependent carcinoma cell motility and invasion and suggests that this process is an important mechanism in cancer progression.

Highlights

Integrins are heterodimeric cell-surface receptors, comprising noncovalently associated a and h subunits [1]
We report that reduction of HS1associated protein X-1 (HAX-1) levels by small interfering RNA suppresses avh6-dependent carcinoma cell migration by down-regulating avh6 endocytosis via a clathrin-mediated pathway
The demonstration that HAX-1 is a binding partner for the ATP-binding cassette–type proteins and that it, together with cortactin, is involved in their internalization via clathrin-coated vesicles suggests a role in receptor endocytosis [33]

Summary

Introduction

Integrins are heterodimeric cell-surface receptors, comprising noncovalently associated a and h subunits [1]. They mediate cell-cell and cell-extracellular matrix interactions involved in cell migration, proliferation, differentiation, and apoptosis [1,2,3,4], processes essential in tumor cell invasion [5]. Whereas avh expression is low or absent on resting epithelial cells, de novo or increased expression occurs during wound healing responses [7] and in cancers such as oral [8], ovarian [9], and colorectal [10] carcinomas. Because avh promotes invasion in vitro, this localization suggests an active role in tumor cell invasion [12,13,14,15] and increased expression has been correlated with a dramatic reduction in survival of patients with colorectal cancer [10]

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Conclusion