title: Small GTPase Rap1 regulates cell migration through regulation of small GTPase RhoA activity in response to transforming growth factor-β1.
abstract: Transforming growth factor (TGF)-β1 regulates diverse cellular functions. Particularly, TGF-β1 induces monocyte migration to sites of injury or inflammation in early period, whereas TGF-β1 inhibits cell migration in late phase. In this study, we attempted to understand how TGF-β1 suppresses cell migration in late phase. We found that TGF-β1 of short exposure induces the production of chemokines, such as macrophage inflammatory protein (MIP)-1α, by Raw 264.7 cells. However, knock-down of small GTPase RhoA by sh-RhoA inhibited the production of MIP-1α and macrophage migration, suggesting that RhoA is essential for expression of this chemokine. An activator of Epac (exchange proteins directly activated by cAMP; a guanine nucleotide exchange factor of Rap1), 8CPT-2Me-cAMP which leads to Rap1 activation abrogated MIP-1α expression and macrophage migration. Indeed, GTP-RhoA and GTP-Rap1 levels were reciprocally regulated in a time-dependent manner following TGF-β1 stimulation. 8CPT-2Me-cAMP suppressed GTP-RhoA levels, whereas si-Rap1 augmented GTP-RhoA levels and cell migration. TGF-β1 produced cAMP in late period and si-RNAs of Epac1 and Epac2 reduced GTP-Rap1 levels leading to promotion of GTP-RhoA levels. Furthermore, si-RNA of ARAP3 (Rap-dependent RhoGAP) increased GTP-RhoA level and cell migration. Therefore, we propose the mechanism that prolonged TGF-β1 treatment produce cAMP, which activates sequentially Epac, Rap1 and ARAP3, resulting in suppression of RhoA, chemokine expression, and macrophage migration. Contrary to the general concept that Rap1 stimulates cell migration, we demonstrated in this study that Rap1 inhibits cell migration by suppression of RhoA activity in response to TGF-β1.
authors.affiliation: Department of Biochemistry, College of Medicine, Hallym University, Chuncheon, Kangwon-Do, Republic of Korea.
authors.forename: Mi-Young
authors.initials: MY
authors.lastname: Moon
authors.forename: Hee-Jun
authors.initials: HJ
authors.lastname: Kim
authors.forename: Jae-Gyu
authors.initials: JG
authors.lastname: Kim
authors.forename: Jae-Yong
authors.initials: JY
authors.lastname: Lee
authors.forename: Jaebong
authors.initials: J
authors.lastname: Kim
authors.forename: Sung-Chan
authors.initials: SC
authors.lastname: Kim
authors.forename: Ihn-Geun
authors.initials: IG
authors.lastname: Choi
authors.forename: Pyeung-Hyeun
authors.initials: PH
authors.lastname: Kim
authors.forename: Jae-Bong
authors.initials: JB
authors.lastname: Park
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D002465:Cell Movement / Q000187:drug effects; D054405:Chemokine CCL3 / Q000378:metabolism; D018925:Chemokines / Q000378:metabolism; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D013873:Thionucleotides / Q000494:pharmacology; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology*; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D054405:Chemokine CCL3; D018925:Chemokines; C482601:Epac protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D013873:Thionucleotides; D053773:Transforming Growth Factor beta1; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D006160:Guanosine Triphosphate; D000242:Cyclic AMP; D020827:rap1 GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein