title: Essential roles of Raf/extracellular signal-regulated kinase/mitogen-activated protein kinase pathway, YY1, and Ca2+ influx in growth arrest of human vascular smooth muscle cells by bilirubin.
abstract: The biological effects of bilirubin, still poorly understood, are concentration-dependent ranging from cell protection to toxicity. Here we present data that at high nontoxic physiological concentrations, bilirubin inhibits growth of proliferating human coronary artery smooth muscle cells by three events. It impairs the activation of Raf/ERK/MAPK pathway and the cellular Raf and cyclin D1 content that results in retinoblastoma protein hypophosphorylation on amino acids S608 and S780. These events impede the release of YY1 to the nuclei and its availability to regulate the expression of genes and to support cellular proliferation. Moreover, altered calcium influx and calpain II protease activation leads to proteolytical degradation of transcription factor YY1. We conclude that in the serum-stimulated human vascular smooth muscle primary cell cultures, bilirubin favors growth arrest, and we propose that this activity is regulated by its interaction with the Raf/ERK/MAPK pathway, effect on cyclin D1 and Raf content, altered retinoblastoma protein profile of hypophosphorylation, calcium influx, and YY1 proteolysis. We propose that these activities together culminate in diminished 5 S and 45 S ribosomal RNA synthesis and cell growth arrest. The observations provide important mechanistic insight into the molecular mechanisms underlying the transition of human vascular smooth muscle cells from proliferative to contractile phenotype and the role of bilirubin in this transition.
authors.affiliation: Medicine, Endocrinology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215, USA.
authors.forename: Marlon
authors.initials: M
authors.lastname: Stoeckius
authors.forename: Anna
authors.initials: A
authors.lastname: Erat
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Fujikawa
authors.forename: Makoto
authors.initials: M
authors.lastname: Hiromura
authors.forename: Anna
authors.initials: A
authors.lastname: Koulova
authors.forename: Leo
authors.initials: L
authors.lastname: Otterbein
authors.forename: Cesario
authors.initials: C
authors.lastname: Bianchi
authors.forename: Edda
authors.initials: E
authors.lastname: Tobiasch
authors.forename: Yossi
authors.initials: Y
authors.lastname: Dagon
authors.forename: Frank W
authors.initials: FW
authors.lastname: Sellke
authors.forename: Anny
authors.initials: A
authors.lastname: Usheva
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D001663:Bilirubin / Q000494:pharmacology*; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D059447:Cell Cycle Checkpoints / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D019938:Cyclin D1 / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects* / Q000502:physiology; D008297:Male; D008856:Microscopy, Fluorescence; D008875:Middle Aged; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D061251:Primary Cell Culture; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000235:genetics / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050986:YY1 Transcription Factor / Q000378:metabolism*; D055815:Young Adult
chemical_list: D012335:RNA, Ribosomal; D016160:Retinoblastoma Protein; D050986:YY1 Transcription Factor; C494698:YY1 protein, human; D019938:Cyclin D1; D019908:Proto-Oncogene Proteins c-raf; D001663:Bilirubin; D002118:Calcium