miR-221/222 compensates for Skp2-mediated p27 degradation and is a primary target of cell cycle regulation by prostacyclin and cAMP

PLoS One. 2013;8(2):e56140. doi: 10.1371/journal.pone.0056140. Epub 2013 Feb 7.


p27(kip1) (p27) is a cdk-inhibitory protein with an important role in the proliferation of many cell types. SCF(Skp2) is the best studied regulator of p27 levels, but Skp2-mediated p27 degradation is not essential in vivo or in vitro. The molecular pathway that compensates for loss of Skp2-mediated p27 degradation has remained elusive. Here, we combine vascular injury in the mouse with genome-wide profiling to search for regulators of p27 during cell cycling in vivo. This approach, confirmed by RT-qPCR and mechanistic analysis in primary cells, identified miR-221/222 as a compensatory regulator of p27. The expression of miR221/222 is sensitive to proteasome inhibition with MG132 suggesting a link between p27 regulation by miRs and the proteasome. We then examined the roles of miR-221/222 and Skp2 in cell cycle inhibition by prostacyclin (PGI(2)), a potent cell cycle inhibitor acting through p27. PGI(2) inhibited both Skp2 and miR221/222 expression, but epistasis, ectopic expression, and time course experiments showed that miR-221/222, rather than Skp2, was the primary target of PGI(2). PGI(2) activates Gs to increase cAMP, and increasing intracellular cAMP phenocopies the effect of PGI(2) on p27, miR-221/222, and mitogenesis. We conclude that miR-221/222 compensates for loss of Skp2-mediated p27 degradation during cell cycling, contributes to proteasome-dependent G1 phase regulation of p27, and accounts for the anti-mitogenic effect of cAMP during growth inhibition.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Cell Cycle / genetics*
  • Cyclic AMP / metabolism*
  • Cyclin-Dependent Kinase Inhibitor p27 / metabolism*
  • Down-Regulation / genetics
  • Epoprostenol / metabolism*
  • Male
  • Mice
  • MicroRNAs / genetics*
  • MicroRNAs / metabolism
  • Muscle, Smooth, Vascular / cytology
  • Proteolysis*
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • S-Phase Kinase-Associated Proteins / metabolism*


  • MIRN221 microRNA, mouse
  • MIRN222 microRNA, mouse
  • MicroRNAs
  • RNA, Messenger
  • S-Phase Kinase-Associated Proteins
  • Cyclin-Dependent Kinase Inhibitor p27
  • Epoprostenol
  • Cyclic AMP