title: Apolipoprotein E-mediated cell cycle arrest linked to p27 and the Cox2-dependent repression of miR221/222.
abstract: OBJECTIVE
  In addition to its effects on cholesterol levels, apoE3 has lipid-independent effects that contribute to cardiovascular protection; one of these effects is the ability to inhibit cell cycling in VSMCs. The goal of this study was to identify and characterize cell cycle-regulatory mechanisms responsible for the anti-mitogenic effect of apoE.
  
  
  RESULTS
  Primary VSMCs were stimulated with serum in the absence or presence of apoE3. apoE3 upregulated expression of the cdk inhibitor, p27(kip1), in primary VSMCs, and this effect required Cox2 and activation of PGI(2)-IP signaling. The microRNA family, miR221/222 has recently been identified as a post-translational regulator of p27, and apoE3 inhibited miR221/222 expression in a Cox2- and PGI(2)/IP-dependent manner. Moreover, reconstituted miR222 expression was sufficient to override the effects of apoE on p27 expression and S phase entry. The ability to repress expression of miR221/222 is shared by apoE3-containing HDL but is absent from apoA-1, LDL and apoE-depleted HDL. All three apoE isoforms regulate miR221/222, and the effect is independent of the C-terminal lipid-binding domain. miR221/222 levels are increased in the aortae of apoE3-null mice and reduced when apoE3 expression is reconstituted by adeno-associated virus infection. Thus, regulation of miR221/222 by apoE3 occurs in vivo as well as in vitro.
  
  
  CONCLUSIONS
  ApoE inhibits VSMC proliferation by regulating p27 through miR221/222. Control of cell cycle-regulatory microRNAs adds a new dimension to the spectrum of cardiovascular protective effects afforded by apoE and apoE-HDL.
authors.affiliation: Department of Pharmacology, University of Pennsylvania Perelman School of Medicine, 3620 Hamilton Walk, Philadelphia, PA 19104-6084, USA.
authors.forename: Devashish
authors.initials: D
authors.lastname: Kothapalli
authors.forename: Paola
authors.initials: P
authors.lastname: Castagnino
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Rader
authors.forename: Michael C
authors.initials: MC
authors.lastname: Phillips
authors.forename: Sissel
authors.initials: S
authors.lastname: Lund-Katz
authors.forename: Richard K
authors.initials: RK
authors.lastname: Assoian
mesh_terms: D000818:Animals; D053318:Apolipoprotein E3 / Q000502:physiology*; D059447:Cell Cycle Checkpoints / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000502:physiology*; D051546:Cyclooxygenase 2 / Q000502:physiology*; D008297:Male; D051379:Mice; D035683:MicroRNAs / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000166:cytology
chemical_list: D053318:Apolipoprotein E3; C546122:MIRN221 microRNA, mouse; C546123:MIRN222 microRNA, mouse; D035683:MicroRNAs; D050760:Cyclin-Dependent Kinase Inhibitor p27; C077623:Ptgs2 protein, mouse; D051546:Cyclooxygenase 2