1. ¹Division of Membrane Biology, Department of Biochemistry and Molecular Biology, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Hyogo, Japan
2. ²Laboratory for Developmental Gene Regulation, Brain Science Institute, The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama, Japan
3. ³Laboratory of Lipid Biochemistry, Department of Biochemistry and Molecular Biology, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Hyogo, Japan

Correspondence: Professor T Takenawa, Laboratory of Lipid Biochemistry, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe, Hyogo 650-0017, Japan. E-mail: takenawa@med.kobe-u.ac.jp

⁴These authors equally contributed to this work.

Received 13 August 2008; Revised 8 December 2008; Accepted 31 December 2008; Published online 23 February 2009.

Abstract

The motility of cancer cells in 3D matrices is of two types: mesenchymal motility, in which the cells are elongated and amoeboid motility, in which the cells are round. Amoeboid motility is driven by an actomyosin-based contractile force, which is regulated by the Rho/ROCK pathway. However, the molecular mechanisms underlying the motility of elongated cells remain unknown. Here, we show that the motility of elongated cells is regulated by Rac signaling through the WAVE2/Arp2/3-dependent formation of elongated pseudopodia and cell-substrate adhesion in 3D substrates. The involvement of Rac signaling in cell motility was different in cell lines that displayed an elongated morphology in 3D substrates. In U87MG glioblastoma cells, most of which exhibit mesenchymal motility, inhibition of Rac signaling blocked the invasion of these cells in 3D substrates. In HT1080 fibrosarcoma cells, which display mixed cell motility involving both elongated and rounded cells, inhibition of Rac1 signaling not only blocked mesenchymal motility but also caused a mesenchymal–amoeboid transition. Additionally, Rac1 and RhoA signaling regulated the mesenchymal and amoeboid motility in these cells, respectively, and the inhibition of both pathways dramatically decreased cell invasion. Hence, we could conclude that Rac1 and RhoA signaling simultaneously regulate cell invasion in 3D matrices.