title: Inhibition of T-type Ca²⁺ channels by endostatin attenuates human glioblastoma cell proliferation and migration.
abstract: OBJECTIVE
  Endostatin (ES) is a c-terminal proteolytic fragment of collagen XVIII with promising antitumour properties in several tumour models, including human glioblastoma. We hypothesized that this peptide could interact with plasma membrane ion channels and modulate their functions.
  
  
  METHODS
  Using cell proliferation and migration assays, patch clamp and Western blot analysis, we studied the effects of ES on the proliferation and migration of human glioblastoma U87 cells, mediated by T-type Ca²⁺ channels.
  
  
  RESULTS
  Extracellular application of ES reversibly inhibited T-type Ca²⁺ channel currents (T-currents) in U87 cells, whereas L-type Ca²⁺ currents were not affected. This inhibitory effect was associated with a hyperpolarizing shift in the voltage-dependence of inactivation but was independent of G-protein and protein tyrosine kinase-mediated pathways. All three α₁ subunits of T-type Ca²⁺ channels (Ca(V) 3), α(1G) (Ca(V) 3.1), α(1H) (Ca(V) 3.2) and α(1I) (Ca(V) 3.3), were endogenously expressed in U87 cells. Using transfected HEK293 or CHO cells, we showed that only Ca(V) 3.1 and Ca(V) 3.2, but not Ca(V) 3.3 or Ca(V) 1.2 (L-type), channel currents were significantly inhibited. More interestingly, ES inhibited the proliferation and migration of U87 cells in a dose-dependent manner. Pretreatment of the cells with the specific T-type Ca²⁺ channel blocker mibefradil occluded these inhibitory effects of ES.
  
  
  CONCLUSIONS
  This study provides the first evidence that the antitumour effects of ES on glioblastoma cells is through direct inhibition of T-type Ca²⁺ channels and gives new insights into the future development of a new class of antiglioblastoma agents that target the proliferation and migration of these cells.
authors.affiliation: The Special Procurement Ward & Department of Neurology, the Second Affiliated Hospital of Soochow University, Suzhou, China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Junhong
authors.initials: J
authors.lastname: Zhang
authors.forename: Dongsheng
authors.initials: D
authors.lastname: Jiang
authors.forename: Dong
authors.initials: D
authors.lastname: Zhang
authors.forename: Zhiyuan
authors.initials: Z
authors.lastname: Qian
authors.forename: Chunfeng
authors.initials: C
authors.lastname: Liu
authors.forename: Jin
authors.initials: J
authors.lastname: Tao
mesh_terms: D020533:Angiogenesis Inhibitors / Q000494:pharmacology; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D016466:CHO Cells; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020747:Calcium Channels, T-Type / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects*; D049109:Cell Proliferation / Q000187:drug effects*; D006224:Cricetinae; D003412:Cricetulus; D043169:Endostatins / Q000494:pharmacology*; D005909:Glioblastoma / Q000188:drug therapy* / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D021122:Protein Subunits / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D020533:Angiogenesis Inhibitors; D000970:Antineoplastic Agents; C121855:CACNA1G protein, human; C479952:CACNA1H protein, human; D002121:Calcium Channel Blockers; D020747:Calcium Channels, T-Type; D043169:Endostatins; D009363:Neoplasm Proteins; D021122:Protein Subunits; D034741:RNA, Small Interfering; D011994:Recombinant Proteins