title: Roles of Serine/Threonine Phosphatases in Low-Dose Endothelial Monocyte-Activating Polypeptide-II-Induced Opening of Blood-Tumor Barrier.
abstract: Previous studies have demonstrated that low-dose endothelial monocyte-activating polypeptide-II (EMAP-II) induces blood-tumor barrier (BTB) opening via RhoA/Rho kinase/PKC-α/β signaling pathway. In a recent study, we revealed that low-dose EMAP-II induced significant increases in expression levels of serine/threonine (Ser/Thr) phosphatase (PP)1 and 2A in rat brain microvascular endothelial cells (RBMECs) of BTB model. In addition, PKC-ζ/PP2A signaling pathway is involved in EMAP-II-induced BTB hyperpermeability. The present study further investigated the exact roles of PPs in this process. In an in vitro BTB model, low-dose EMAP-II (0.05 nM) induced a significant increase in PP1 activity in RBMECs. There was an interaction between PKC-α/β and PP1 in RBMECs. Inhibition of PKC-α/β activity with GÖ6976 completely blocked EMAP-II-induced activation of PP1. Conversely, inhibition of PP1 activity with tautomycin had no effect on EMAP-II-induced PKC-α/β activation. Like GÖ6976, tautomycin significantly prevented EMAP-II-induced BTB hyperpermeability and MLC phosphorylation in RBMECs. Also, in this study, EMAP-II induced a marked redistribution of occludin and a significant dephosphorylation of occludin on Ser/Thr residues in RBMECs. Similar with GÖ6976 pretreatment, tautomycin pretreatment dramatically diminished EMAP-II-induced redistribution of occludin. Furthermore, pretreatment with tautomycin significantly inhibited EMAP-II-induced dephosphorylation of occludin on Ser residues. However, pretreatment with okadaic acid (an inhibitor of PP2A) significantly prevented changes in Ser-phosphorylated occludin induced by EMAP-II treatment. Collectively, this study demonstrates that low-dose EMAP-II increases BTB permeability via a RhoA/Rho kinase/PKC-α/β/PP1 signaling pathway and that PP1/PP2A-mediated Ser/Thr dephosphorylation of occludin plays an important role in EMAP-II-induced BTB hyperpermeability.
authors.affiliation: Department of Neurosurgery, Shengjing Hospital, China Medical University, Shenyang, Liaoning Province, 110004, People's Republic of China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Li
authors.forename: Xiao-Bai
authors.initials: XB
authors.lastname: Liu
authors.forename: Yun-hui
authors.initials: YH
authors.lastname: Liu
authors.forename: Yi-xue
authors.initials: YX
authors.lastname: Xue
authors.forename: Ping
authors.initials: P
authors.lastname: Wang
authors.forename: Li-bo
authors.initials: LB
authors.lastname: Liu
authors.forename: Jing
authors.initials: J
authors.lastname: Liu
authors.forename: Yi-long
authors.initials: YL
authors.lastname: Yao
authors.forename: Jun
authors.initials: J
authors.lastname: Ma
mesh_terms: D000818:Animals; D002199:Capillary Permeability; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000378:metabolism*; D005910:Glioma / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D062793:Occludin / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054645:Protein Phosphatase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D062793:Occludin; C531571:Rapgef4 protein, rat; D054460:rho-Associated Kinases; D011493:Protein Kinase C; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D020742:rhoA GTP-Binding Protein