These results suggest that 1143532-39-1 CCG-1423 inhibits the seruminduced nuclear import of MRTF-B and Phactr1. However, CCG- 1423 did not affect the subcellular localization of constitutively nuclear Mycd. CCG-1423,whichwasoriginally identified asaninhibitor ofRhoA signaling, is thought to be theMRTF-Ainhibitor becauseCCG- 1423 reduces cell growth and migration and blocks the nuclear accumulation of MRTF-A,. However, the mode of inhibitory action is yet to be determined. In this study, we addressed our hypothesis that CCG-1423 directly inhibits MRTF-A1616113-45-1 cost binding to importin a/b1. Our novel findings are as follows: CCG-1423 inhibits the interaction betweenMRTF-Aandimportina/b1but not G-actin binding toMRTF-A, Apull-down assay usingCCG-1423 Sepharose revealed direct and specific binding of CCG-1423 to MRTF-A. Furthermore, the functional NLS of MRTF-A is the binding site for CCG-1423, In the presence of G-actin, MRTF-A preferentially forms a complex with G-actin rather than CCG-1423 because of its high binding affinity for G-actin, indicating competitive binding of G-actin and CCG-1423 to the N-terminal region of MRTF-A containing three RPEL motifs and NB, but it remains elusive whether or not all basic amino acid rich NLS bind to CCG- 1423,and CCG-1423isexpectedto specificallybindto theNLSsof RPEL-containing proteins such as Mycd family members and Phactr1. These results suggest that CCG-1423 prevents the interaction between MRTF-A and importin a/b1 by masking NB, resulting in inhibition of the nuclear import of MRTF-A and that Gactin- free MRTF-A is the more likely CCG-1423 target protein. These molecular mechanisms are schematically summarized in Figure 7.Asimilar inhibitory action is expected tobe applicable to the interaction between MRTF-B or Phactr1 and importin a/b1. CCG-1423 inhibits the interaction between MRTF-A and importin a/b1. We demonstrated that CCG-1423 binds directly and specifically to MRTF-A under mediation by NB and that the basic amino acids in the NB sequence play a critical role in CCG-1423 binding to NB. Because the sequences of NBs of Mycd family members are identical, CCG-1423 is expected to bind to each of the NB sequences of MRTF-B and Mycd. Actually, we demonstrated that CCG-1423 binds to MRTF-B under mediation by NB.
