Fractalkine-Induced Endothelial Cell Migration Requires MAP Kinase Signaling

Background/Aims: Angiogenesis is a well-established char- acteristic in the rheumatoid arthritis (RA) synovial pannus. We have previously demonstrated that fractalkine (Fkn/ CX3CL1) expression is significantly increased in the RA joint and that fractalkine induces angiogenesis. In this work we studied mechanisms through which Fkn functions as an an- giogenic mediator. Methods: Human microvascular endo- thelial cells (HMVECs) and human umbilical vein endothelial cells (HUVECs) were stimulated with Fkn and analyzed by Western blotting or stained with Alexa Fluor 488 phalloidin for F-actin to characterize the time frame of cytoskeletal re- arrangement. Fkn-induced HUVEC chemotaxis was per- formed in the presence and absence of MAP kinase inhibi- tors. Results: Phalloidin staining of F-actin revealed signifi- cant cytoskeletal rearrangements in HUVECs and HMVECs starting as early as 10 min after Fkn stimulation. Western blotting demonstrated that HUVEC and HMVEC stimulation with Fkn for 1-30 min resulted in phosphorylation of JNK. Fkn also induces significant phosphorylation of Erk 1/2 in HUVECs over a time course ranging from 1 to 15 min. A some- what similar time course (5-15 min) was detected for Erk 1/2 phosphorylation in HMVECs. Inhibitors of either JNK or Erk