title: miR-221/222 compensates for Skp2-mediated p27 degradation and is a primary target of cell cycle regulation by prostacyclin and cAMP.
abstract: 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.
authors: Department of Pharmacology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
authors: Paola
authors: P
authors: Castagnino
authors: Devashish
authors: D
authors: Kothapalli
authors: Elizabeth A
authors: EA
authors: Hawthorne
authors: Shu-Lin
authors: SL
authors: Liu
authors: Tina
authors: T
authors: Xu
authors: Shilpa
authors: S
authors: Rao
authors: Yuval
authors: Y
authors: Yung
authors: Richard K
authors: RK
authors: Assoian
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000235:genetics*; D000242:Cyclic AMP / Q000378:metabolism*; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism*; D015536:Down-Regulation / Q000235:genetics; D011464:Epoprostenol / Q000378:metabolism*; D008297:Male; D051379:Mice; D035683:MicroRNAs / Q000235:genetics* / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000166:cytology; D059748:Proteolysis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D044786:S-Phase Kinase-Associated Proteins / Q000378:metabolism*
chemical_list: C546122:MIRN221 microRNA, mouse; C546123:MIRN222 microRNA, mouse; D035683:MicroRNAs; D012333:RNA, Messenger; D044786:S-Phase Kinase-Associated Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D011464:Epoprostenol; D000242:Cyclic AMP