PDGF-BB regulates p27 expression through ERK-dependent RNA turn-over in vascular smooth muscle cells.
Cyclin-dependent kinase inhibitor p27, a critical determinant for cell cycle progression, is an important regulation target of mitogenic signals during arterial injury. In this study, we show in rat aortic smooth muscle cells that PDGF-BB down-regulated p27 protein and mRNA in an ERK-dependent mechanism. Inhibition of ERK, but not other subtypes of the mitogen-activated protein kinase family, prevented the reduction of p27 protein and mRNA. Conversely, direct activation of ERK via adenovirus-mediated expression of a constitutively active form of MEK led to a reduction of p27 protein and mRNA, further supporting the central role of ERK in regulation of p27 expression. Rapamycin, which potently inhibited PDGF-induced activation of p70 S6 kinase as well as proliferation of smooth muscle cells, did not alter the expression of p27. To delineate the molecular mechanism underlying the p27 down-regulation, we examined the effect of PDGF-BB on p27 promoter activity as well as mRNA stability. Stimulation with PDGF-BB significantly shortened the half-life of p27 mRNA without affecting its promoter activity. To further understand the PDGF-stimulated p27 mRNA turnover, we inserted the 5'- and/or 3'-untranslated regions of p27 cDNA into a non-PDGF-responsive luciferase gene. Only those chimeric genes that contained the 3'-untranslated region responded to PDGF-BB with reduced expression. Moreover, inhibition of ERK completely prevented the effect of PDGF on the chimera expression. In summary, our data suggest that p27 is down-regulated by PDGF-BB in vascular smooth muscle cells through an ERK-dependent posttranscriptional mechanism.
Sakakibara
Kenji
K
Department of Surgery, Division of Vascular Surgery, Weill Medical College of Cornell University, New York, New York 10021, USA.
Kubota
Kenji
K
Worku
Berhane
B
Ryer
Evan J
EJ
Miller
Jeffrey P
JP
Koff
Andrew
A
Kent
K Craig
KC
Liu
Bo
B
D020413:3' Untranslated Regions / Q000378:metabolism; D000818:Animals; D000925:Anticoagulants / Q000494:pharmacology*; D001011:Aorta / Q000166:cytology; D000077214:Becaplermin; D018797:Cell Cycle Proteins / Q000235:genetics*; D002478:Cells, Cultured; D050760:Cyclin-Dependent Kinase Inhibitor p27; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000502:physiology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D020574:Proto-Oncogene Proteins c-sis; D020871:RNA Stability / Q000187:drug effects*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics*
D020413:3' Untranslated Regions; D000925:Anticoagulants; C493962:Cdkn1b protein, rat; D018797:Cell Cycle Proteins; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D012333:RNA, Messenger; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D000077214:Becaplermin; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D048049:Extracellular Signal-Regulated MAP Kinases; D046988:Proteasome Endopeptidase Complex