Induction of microRNA-1 by myocardin in smooth muscle cells inhibits cell proliferation.
OBJECTIVE
Myocardin is a cardiac- and smooth muscle-specific transcription co-factor that potently activates the expression of downstream target genes. Previously, we demonstrated that overexpression of myocardin inhibited the proliferation of smooth muscle cells (SMCs). Recently, myocardin was reported to induce the expression of microRNA-1 (miR-1) in cardiomyocytes. In this study, we investigated whether myocardin induces miR-1 expression to mediate its inhibitory effects on SMC proliferation.


RESULTS
Using tetracycline-regulated expression (T-REx) inducible system expressing myocardin in human vascular SMCs, we found that overexpression of myocardin resulted in significant induction of miR-1 expression and inhibition of SMC proliferation, which was reversed by miR-1 inhibitors. Consistently, introduction of miR-1 into SMCs inhibited their proliferation. We isolated spindle-shaped and epithelioid human SMCs and demonstrated that spindle-shaped SMCs were more differentiated and less proliferative. Correspondingly, spindle-shaped SMCs had significantly higher expression levels of both myocardin and miR-1 than epithelioid SMCs. We identified Pim-1, a serine/threonine kinase, as a target gene for miR-1 in SMCs. Western blot and luciferase reporter assays further confirmed that miR-1 targeted Pim-1 directly. Furthermore, neointimal lesions of mouse carotid arteries displayed downregulation of myocardin and miR-1 with upregulation of Pim-1.


CONCLUSIONS
Our data demonstrate that miR-1 participates in myocardin-dependent of SMC proliferation inhibition.
Department of Biochemistry and Molecular Biology, Libin Cardiovascular Institute of Alberta, University of Calgary, Health Sciences Center, 3330 Hospital Drive NW, Calgary, Alberta, Canada.
Jie
J
Chen
Hao
H
Yin
Yulan
Y
Jiang
Sarvan Kumar
SK
Radhakrishnan
Zhan-Peng
ZP
Huang
Jingjing
J
Li
Zhan
Z
Shi
Elisabeth P C
EP
Kilsdonk
Yu
Y
Gui
Da-Zhi
DZ
Wang
Xi-Long
XL
Zheng
D000818:Animals; D001011:Aorta / Q000166:cytology / Q000378:metabolism; D002339:Carotid Arteries / Q000166:cytology / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D049109:Cell Proliferation; D002478:Cells, Cultured; D015536:Down-Regulation / Q000502:physiology; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D035683:MicroRNAs / Q000378:metabolism*; D023421:Models, Animal; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D051573:Proto-Oncogene Proteins c-pim-1 / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D015534:Trans-Activators / Q000378:metabolism*; D000099251:Myocardin
D035683:MicroRNAs; D009687:Nuclear Proteins; D051573:Proto-Oncogene Proteins c-pim-1; D015534:Trans-Activators; D000099251:Myocardin; C544547:MIRN1 microRNA, human