1. ¹The Second Department of Surgery, Faculty of Medicine, Kagawa University, Kagawa, Japan
2. ²Department of Pathology and Host Defense, Faculty of Medicine, Kagawa University, Kagawa, Japan
3. ³Life Science Research Center, Kagawa University, Kagawa, Japan
4. ⁴The Fifth Department of Oncology and the Department of Thoracic Surgery, Kitano Hospital, Tazuke Kofukai Medical Research Institute, Osaka, Japan

Correspondence: Dr C-L Huang, The Second Department of Surgery, Faculty of Medicine, Kagawa University, 1750-1, Miki-cho, Kita-gun, Kagawa 761-0793, Japan. E-mail: chuang@kms.ac.jp

Received 8 August 2005; Revised 15 March 2006; Accepted 30 March 2006; Published online 8 May 2006.

Abstract

Motility-related protein-1 (MRP-1/CD9) is involved in cell motility. We studied the change in the actin cytoskeleton, and the expression of actin-related protein (Arp) 2 and Arp3 and the Wiskott–Aldrich syndrome protein (WASP) family according to MRP-1/CD9 gene transduction into HT1080 cells. The frequency of cells with lamellipodia was significantly lower in MRP-1/CD9-transfected HT1080 cells than in control HT1080 cells (P<0.0001). MRP-1/CD9 gene transduction affected the subcellular localization of Arp2 and Arp3 proteins. Furthermore, MRP-1/CD9 gene transduction induced a downregulation of WAVE2 expression (P<0.0001). However, no difference was observed in the expression of Arp2, Arp3 or other WASPs. A neutralizing anti-MRP-1/CD9 monoclonal antibody inhibited downregulation of WAVE2 in MRP-1/CD9-transfected HT1080 cells (P<0.0001), and reversed the morphological effects of MRP-1/CD9 gene transduction. Furthermore, downregulation of WAVE2 by transfection of WAVE2-specific small interfering RNA (siRNA) mimicked the morphological effects of MRP-1/CD9 gene transduction and suppressed cell motility. However, transfection of each siRNA for Wnt1, Wnt2b1 or Wnt5a did not affect WAVE2 expression. Transfection of WAVE2-specific siRNA also did not affect expressions of these Wnts. These results indicate that MRP-1/CD9 regulates the actin cytoskeleton by downregulating of the WAVE2, through the Wnt-independent signal pathway.