title: Calpain-6, a microtubule-stabilizing protein, regulates Rac1 activity and cell motility through interaction with GEF-H1.
abstract: Crosstalk between microtubules and actin filaments is crucial for various cellular functions, including cell migration, spreading and cytokinesis. The Rac1 GTPase plays a key role in such crosstalk at the leading edge of migrating cells in order to promote lamellipodial formation. However, the mechanism underlying the link between microtubules and Rac1 activation remains unclear. Here, we show that calpain-6 (CAPN6), a non-proteolytic calpain with microtubule-binding and -stabilizing activity, might participate in this crosstalk. Small interfering RNA (siRNA)-induced knockdown of Capn6 in NIH 3T3 cells resulted in Rac1 activation, which promoted cell migration, spreading and lamellipodial protrusion. This increase in Rac1 activity was abolished by knockdown of the Rho guanine nucleotide exchange factor GEF-H1 (officially known as Arhgef2). CAPN6 and GEF-H1 colocalized with microtubules and also interacted with each other through specific domains. Upon knockdown of Capn6, GEF-H1 was shown to translocate from microtubules to the lamellipodial region and to interact with Rac1. By contrast, RhoA activity was decreased upon knockdown of Capn6, although low levels of active RhoA or the presence of RhoA molecules appeared to be required for the Capn6-knockdown-induced Rac1 activation. We suggest that CAPN6 acts as a potential regulator of Rac1 activity, through a mechanism involving interaction with GEF-H1, to control lamellipodial formation and cell motility.
authors.affiliation: Department of Physiological Chemistry and Metabolism, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Tonami
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Kurihara
authors.forename: Satoshi
authors.initials: S
authors.lastname: Arima
authors.forename: Koichi
authors.initials: K
authors.lastname: Nishiyama
authors.forename: Yasunobu
authors.initials: Y
authors.lastname: Uchijima
authors.forename: Tomoichiro
authors.initials: T
authors.lastname: Asano
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sorimachi
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kurihara
mesh_terms: D000818:Animals; D002154:Calpain / Q000235:genetics / Q000378:metabolism*; D002465:Cell Movement; D005786:Gene Expression Regulation; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008870:Microtubules / Q000737:chemistry* / Q000378:metabolism*; D041681:NIH 3T3 Cells; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D011554:Pseudopodia / Q000378:metabolism; D064067:Rho Guanine Nucleotide Exchange Factors; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: C577402:Arhgef2 protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D011518:Proto-Oncogene Proteins; D064067:Rho Guanine Nucleotide Exchange Factors; D002154:Calpain; C403234:Capn6 protein, mouse; D020830:rac1 GTP-Binding Protein