title: Betulinic acid enhances TGF-β signaling by altering TGF-β receptors partitioning between lipid-raft/caveolae and non-caveolae membrane microdomains in mink lung epithelial cells.
abstract: BACKGROUND
  TGF-β is a key modulator in the regulation of cell proliferation and migration, and is also involved in the process of cancer development and progression. Previous studies have indicated that TGF-β responsiveness is determined by TGF-β receptor partitioning between lipid raft/caveolae-mediated and clathrin-mediated endocytosis. Lipid raft/caveolae-mediated endocytosis facilitates TGF-β degradation and thus suppressing TGF-β responsiveness. By contrast, clathrin-mediated endocytosis results in Smad2/3-dependent endosomal signaling, thereby promoting TGF-β responsiveness. Because betulinic acid shares a similar chemical structure with cholesterol and has been reported to insert into the plasma membrane, we speculate that betulinic acid changes the fluidity of the plasma membrane and modulates the signaling pathway associated with membrane microdomains. We propose that betulinic acid modulates TGF-β responsiveness by changing the partitioning of TGF-β receptor between lipid-raft/caveolae and non-caveolae microdomain on plasma membrane.
  
  
  METHODS
  We employed sucrose-density gradient ultracentrifugation and confocal microscopy to determine membrane localization of TGF-β receptors and used a luciferase assay to examine the effects of betulinic acid in TGF-β-stimulated promoter activation. In addition, we perform western blotting to test TGF-β-induced Smad2 phosphorylation and fibronectin production.
  
  
  CONCLUSIONS
  Betulinic acid induces translocation of TGF-β receptors from lipid raft/caveolae to non-caveolae microdomains without changing total level of TGF-β receptors. The betulinic acid-induced TGF-β receptors translocation is rapid and correlate with the TGF-β-induced PAI-1 reporter gene activation and growth inhibition in Mv1Lu cells.
authors.affiliation: Department of Biological Science, National Sun Yat-sen University, Kaohsiung, 804, Taiwan, ROC. chunlinchen@mail.nsysu.edu.tw.|Doctoral Degree Program in Marine Biotechnology, National Sun Yat-sen University and Academia Sinica, Kaohsiung, 804, Taiwan, ROC. chunlinchen@mail.nsysu.edu.tw.|Center for Stem Cell Research, Kaohsiung Medical University, Kaohsiung, 807, Taiwan, ROC. chunlinchen@mail.nsysu.edu.tw.
authors.forename: C L
authors.initials: CL
authors.lastname: Chen
authors.affiliation: Department of Biological Science, National Sun Yat-sen University, Kaohsiung, 804, Taiwan, ROC. lovelyjean@mail.tyhs.edu.tw.
authors.forename: C Y
authors.initials: CY
authors.lastname: Chen
authors.affiliation: Department of Biological Science, National Sun Yat-sen University, Kaohsiung, 804, Taiwan, ROC. yingpinkingdom@gmail.com.
authors.forename: Y P
authors.initials: YP
authors.lastname: Chen
authors.affiliation: Department of Biological Science, National Sun Yat-sen University, Kaohsiung, 804, Taiwan, ROC. yabihu@kmu.edu.tw.|Graduate Institute of Clinical Pharmacy, College of Pharmacy, Kaohsiung Medical University, Kaohsiung, 807, Taiwan, ROC. yabihu@kmu.edu.tw.|Center for Stem Cell Research, Kaohsiung Medical University, Kaohsiung, 807, Taiwan, ROC. yabihu@kmu.edu.tw.
authors.forename: Y B
authors.initials: YB
authors.lastname: Huang
authors.affiliation: Graduate Institute of Clinical Pharmacy, College of Pharmacy, Kaohsiung Medical University, Kaohsiung, 807, Taiwan, ROC. tanukikimo@yahoo.com.tw.|Center for Stem Cell Research, Kaohsiung Medical University, Kaohsiung, 807, Taiwan, ROC. tanukikimo@yahoo.com.tw.
authors.forename: M W
authors.initials: MW
authors.lastname: Lin
authors.affiliation: Division of Gastroenterology, Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung, 807, Taiwan, ROC. dechwu@yahoo.com.|Center for Stem Cell Research, Kaohsiung Medical University, Kaohsiung, 807, Taiwan, ROC. dechwu@yahoo.com.
authors.forename: D C
authors.initials: DC
authors.lastname: Wu
authors.affiliation: Department of Biological Science, National Sun Yat-sen University, Kaohsiung, 804, Taiwan, ROC. hungtu@kmu.edu.tw.|Division of Pathology, Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung, 807, Taiwan, ROC. hungtu@kmu.edu.tw.
authors.forename: H T
authors.initials: HT
authors.lastname: Huang
authors.affiliation: Taiwan Ocean Research Institute, National Applied Research Laboratories, Kaohsiung, 852, Taiwan, ROC. mylalex@tori.narl.org.tw.
authors.forename: M Y
authors.initials: MY
authors.lastname: Liu
authors.affiliation: Department of Biological Science, National Sun Yat-sen University, Kaohsiung, 804, Taiwan, ROC. hwchang@faculty.nsysu.edu.tw.
authors.forename: H W
authors.initials: HW
authors.lastname: Chang
authors.affiliation: Department of Biological Science, National Sun Yat-sen University, Kaohsiung, 804, Taiwan, ROC. yubow0611@gmail.com.
authors.forename: Y C
authors.initials: YC
authors.lastname: Kao
authors.affiliation: Department of Biological Science, National Sun Yat-sen University, Kaohsiung, 804, Taiwan, ROC. houy1543@gmail.com.
authors.forename: P H
authors.initials: PH
authors.lastname: Yang
mesh_terms: D000818:Animals; D002460:Cell Line; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D008168:Lung / Q000166:cytology / Q000378:metabolism*; D021962:Membrane Microdomains / Q000378:metabolism*; D008907:Mink; D053978:Pentacyclic Triterpenes; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D014315:Triterpenes / Q000494:pharmacology*; D000094062:Betulinic Acid
chemical_list: D053978:Pentacyclic Triterpenes; D018125:Receptors, Transforming Growth Factor beta; D016212:Transforming Growth Factor beta; D014315:Triterpenes; D000094062:Betulinic Acid