title: EphA4-mediated Rho activation via Vsm-RhoGEF expressed specifically in vascular smooth muscle cells.
abstract: Rho-kinase, an effector of Rho GTPase, increases the contractility of vascular smooth muscle by phosphorylating myosin light chain (MLC) and by inactivating MLC phosphatase. A wide variety of extracellular stimuli activate RhoA via G protein-coupled receptors. In the present study, we demonstrate a novel cell-cell interaction-mediated Rho activation signaling pathway in vascular smooth muscle cells (VSMCs). Among many receptor tyrosine kinases, the Eph family receptors are unique in that they require cell-cell interaction to engage their ligands, ephrin. We found that a novel VSMC-specific guanine nucleotide exchange factor (GEF) for Rho (Vsm-RhoGEF/KIAA0915) was expressed specifically in VSMCs of several organs including the heart, aorta, liver, kidney, and spleen, as examined by the immunohistochemical analysis using a specific antibody against Vsm-RhoGEF. Based on the association of Vsm-RhoGEF with EphA4 in quiescent cells, we tested whether EphA4 and Vsm-RhoGEF were expressed in the same tissue and further studied the molecular mechanism of Vsm-RhoGEF regulation by EphA4. Immunohistochemical analysis showed that EphA4 and Vsm-RhoGEF expression overlapped in VSMCs. Additionally, tyrosine phosphorylation of Vsm-RhoGEF induced by EphA4 upon ephrin-A1 stimulation enhanced the Vsm-RhoGEF activity for RhoA. The requirement of Vsm-RhoGEF for ephrin-A1-induced assembly of actin stress fibers in VSMCs was shown by the overexpression of a dominant-negative form of VSM-RhoGEF and by the depletion of Vsm-RhoGEF using RNA interference. These results suggested that ephrin-A1-triggered EphA4-Vsm-RhoGEF-RhoA pathway is involved in the cell-cell interaction-mediated RhoA activation that regulates vascular smooth muscle contractility.
authors.affiliation: Department of Structural Analysis, National Cardiovascular Center Research Institute, Fujishirodai 5-7-1, Suita, Osaka 565-8565, Japan.
authors.forename: Hisakazu
authors.initials: H
authors.lastname: Ogita
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kunimoto
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kamioka
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Sawa
authors.forename: Michitaka
authors.initials: M
authors.lastname: Masuda
authors.forename: Naoki
authors.initials: N
authors.lastname: Mochizuki
mesh_terms: D000818:Animals; D002460:Cell Line; D036382:Ephrin-A1 / Q000494:pharmacology; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011233:Precipitin Tests; D011485:Protein Binding; D051381:Rats; D036122:Receptor, EphA4 / Q000378:metabolism*; D064067:Rho Guanine Nucleotide Exchange Factors; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D036382:Ephrin-A1; D020662:Guanine Nucleotide Exchange Factors; D064067:Rho Guanine Nucleotide Exchange Factors; D014443:Tyrosine; D006160:Guanosine Triphosphate; D036122:Receptor, EphA4; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein