title: Regulation of cardiac CACNB2 by microRNA-499: Potential role in atrial fibrillation.
abstract: The L-type calcium channel (LTCC) is one of the major ion channels that are known to be associated with the electrical remodeling of atrial fibrillation (AF). In AF, there is significant downregulation of the LTCC, but the underlying mechanism for such downregulation is not clear. We have previously reported that microRNA-499 (miR-499) is significantly upregulated in patients with permanent AF and thatKCNN3,the gene that encodes the small-conductance calcium-activated potassium channel 3 (SK3), is a target of miR-499. We found that CACNB2, an important subunit of the LTCC, is also a target of miR-499. We hypothesize that miR-499 plays an important role in AF electrical remodeling by regulating the expression ofCACNB2and the LTCC. In atrial tissue from patients with permanent AF, CACNB2 was significantly downregulated by 67% (n= 4,p< 0.05) compared to those from patients with no history of AF. Transfection of miR-499 mimic into HL-1 cells, a mouse hyperplastic atrial cardiac myocyte cell-line, resulted in the downregulation of CACNB2 protein expression, while that of miR-499 inhibitor upregulated CACNB2 protein expression. Binding of miR-499 to the 3' untranslated region ofCACNB2was confirmed by luciferase reporter assay and by the increased presence ofCACNB2mRNA in Argonaute pulled-down microRNA-induced silencing complexes after transfection with the miR-499 mimic. In addition, downregulation of CACNB2 resulted in the downregulation of protein levels of the pore-forming α-subunit (CACNA1C). In conclusion, upregulation of atrial miR-499 induces the downregulation of CACNB2 expression and may contribute to the electrical remodeling in AF.
authors.affiliation: Department of Cardiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: Tian-You
authors.initials: TY
authors.lastname: Ling
authors.affiliation: Department of Cardiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: Xiao-Li
authors.initials: XL
authors.lastname: Wang
authors.affiliation: Department of Cardiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Chai
authors.affiliation: Department of Cardiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: Tong
authors.initials: T
authors.lastname: Lu
authors.affiliation: Department of Cardiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: John M
authors.initials: JM
authors.lastname: Stulak
authors.affiliation: Department of Cardiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: Lyle D
authors.initials: LD
authors.lastname: Joyce
authors.affiliation: Department of Cardiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: Richard C
authors.initials: RC
authors.lastname: Daly
authors.affiliation: Department of Cardiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Greason
authors.affiliation: Department of Cardiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: Li-Qun
authors.initials: LQ
authors.lastname: Wu
authors.affiliation: Department of Cardiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: Win-Kuang
authors.initials: WK
authors.lastname: Shen
authors.affiliation: Department of Cardiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: Yong-Mei
authors.initials: YM
authors.lastname: Cha
authors.affiliation: Department of Cardiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: Hon-Chi
authors.initials: HC
authors.lastname: Lee
keywords: AF, atrial fibrillation; Ago, Argonaute; CACNA1C, voltage-dependent calcium channel α-1C subunit; CACNB2, voltage-dependent calcium channel β-2 subunit; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; LTCC, L-type calcium channel; SR, sinus rhythm; UTR, untranslated region; miR-499, microRNA-499; miRISC, microRNA-inducing silencing complex