Identification of PI3K regulatory subunit p55γ as a novel inhibitor of vascular smooth muscle cell proliferation and neointimal formation.
OBJECTIVE
Phosphatidylinositol 3 kinases (PI3Ks) play a pivotal role in vascular physiology and pathophysiology. We aimed to investigate the role of p55γ, a regulatory subunit of PI3Ks, in vascular smooth muscle cell (VSMC) proliferation and neointimal formation.


RESULTS
We identified p55γ as an important factor that suppresses VSMC proliferation and injury-evoked neointimal formation. Western blot and mRNA analyses showed that p55γ expression declined in balloon-injured rat carotid arteries and in response to PDGF-BB and serum treatment in cultured VSMCs. Overexpression of p55γ inhibited, whereas short hairpin RNA knockdown of p55γ promoted PDGF-BB- and serum-induced VSMC proliferation. Importantly, in vivo adenoviral gene transfer of p55γ into carotid arteries attenuated, while knockdown of p55γ enhanced balloon injury-induced neointimal formation. Furthermore, p55γ sequentially up-regulated p53 and p21, resulting in cell-cycle arrest in S phase; small-interfering RNA knockdown of either p53 or p21 blocked p55γ-induced VSMC growth arrest. Mechanistically, p55γ interacted with and stabilized p53 protein by blocking mouse double minute 2 homologue-mediated p53 ubiquitination and degradation, subsequently activating its target gene p21. Concurrently, p55γ up-regulated Bcl-xl expression, resulting in non-apoptotic growth arrest effect.


CONCLUSIONS
These findings mark p55γ as a novel upstream regulator of the p53-p21 signalling pathway that negatively regulates VSMC proliferation, suggesting that malfunction of p55γ may trigger vascular proliferative disorders.
Institute of Molecular Medicine, Peking University, Yiheyuan Road 5, Haidian District, Beijing 100871, China.
Geng
G
Li
Institute of Molecular Medicine, Peking University, Yiheyuan Road 5, Haidian District, Beijing 100871, China.
Ning
N
Xie
Institute of Molecular Medicine, Peking University, Yiheyuan Road 5, Haidian District, Beijing 100871, China.
Yuan
Y
Yao
Institute of Molecular Medicine, Peking University, Yiheyuan Road 5, Haidian District, Beijing 100871, China.
Yan
Y
Zhang
Institute of Molecular Medicine, Peking University, Yiheyuan Road 5, Haidian District, Beijing 100871, China.
Jiaojiao
J
Guo
Institute of Molecular Medicine, Peking University, Yiheyuan Road 5, Haidian District, Beijing 100871, China.
Yuanqing
Y
Feng
Institute of Molecular Medicine, Peking University, Yiheyuan Road 5, Haidian District, Beijing 100871, China.
Fengxiang
F
Lv
Institute of Molecular Medicine, Peking University, Yiheyuan Road 5, Haidian District, Beijing 100871, China State Key Laboratory of Biomembrane and Membrane Biotechnology, Peking University, Beijing 100871, China Center for Life Sciences, Peking University, Yiheyuan Road 5, Haidian District, Beijing 100871, China.
Rui-Ping
RP
Xiao
Institute of Molecular Medicine, Peking University, Yiheyuan Road 5, Haidian District, Beijing 100871, China caochunmei@pku.edu.cn.
Chun-Mei
CM
Cao
D000818:Animals; D020212:Carotid Artery Injuries / Q000201:enzymology / Q000473:pathology; D059447:Cell Cycle Checkpoints; D049109:Cell Proliferation; D002478:Cells, Cultured; D058543:Class Ia Phosphatidylinositol 3-Kinase / Q000235:genetics / Q000378:metabolism*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006801:Humans; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000201:enzymology* / Q000473:pathology*; D058426:Neointima / Q000201:enzymology* / Q000473:pathology / Q000517:prevention & control*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D015854:Up-Regulation; D051020:bcl-X Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
D058543:Class Ia Phosphatidylinositol 3-Kinase; D050759:Cyclin-Dependent Kinase Inhibitor p21; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051736:Proto-Oncogene Proteins c-mdm2; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; D051020:bcl-X Protein; C494813:Bcl2l1 protein, rat; C497208:Mdm2 protein, rat; C523442:PIK3R3 protein, human
Neointimal formation; Restenosis; Vascular smooth muscle cell proliferation; p55γ