Early growth response 1 is an early signal inducing Cav3.2 T-type calcium channels during cardiac hypertrophy.
OBJECTIVE
The Cav3.2 T-channel plays a pivotal role in inducing calcineurin/nuclear factor of activated T cell (NFAT) signalling during cardiac hypertrophy. Because calcineurin/NFAT signalling is induced early after pressure overload, we hypothesized that Cav3.2 is induced by an early signal. Our aim is to investigate when and how Cav3.2 is induced during cardiac hypertrophy.


RESULTS
The evolutionary conserved promoter Cav3.2-3500 from mouse genome was validated to express the reporter gene as endogenous Cav3.2 in cell lines and transgenic (Tg; Cav3.2-3500-Luc) mice. The early induction of luciferase in Tg mice and Cav3.2 mRNA in wild-type mice after transverse aortic banding (TAB) surgery supported our hypothesis that Cav3.2 is induced early during cardiac hypertrophy. The TAB-responding element [-81 to -41 bp upstream of the transcription start site (TSS) of mouse Cav3.2] was identified by in vivo gene transfer by injecting reporter constructs into the left ventricle followed by TAB surgery. Electrophoresis mobility shift assay and chromatin immunoprecipitation assays revealed that Egr1 bound to the TAB-responding element of Cav3.2. Egr1 level was increased with increased Cav3.2 mRNA level at 3 days after TAB. To demonstrate that Egr1 indeed regulates Cav3.2 expression after hypertrophic stimulation, knockdown of Egr1 with short hairpin RNA prevented the phenylephrine-induced up-regulation of Cav3.2 expression and cellular hypertrophy in neonatal rat ventricular myocytes (NRVMs) and H9c2 cells. Furthermore, overexpression of Cav3.2 in Egr1-knockdown cells restored the phenylephrine-induced hypertrophy.


CONCLUSIONS
Cav3.2 is induced early by Egr1 during cardiac hypertrophy and Cav3.2 is an important mediator of Egr1 in regulating cardiac hypertrophy.
Molecular Medicine Program, Taiwan International Graduate Program, Institute of Biomedical Sciences, Academia Sinica, 128 Academia Rd Sec 2, Taipei 11529, Taiwan.
Shao-Chun
SC
Hsu
Ya-Ting
YT
Chang
Chien-Chang
CC
Chen
D000818:Animals; D001665:Binding Sites; D020747:Calcium Channels, T-Type / Q000235:genetics / Q000502:physiology*; D006332:Cardiomegaly / Q000209:etiology / Q000378:metabolism*; D051766:Early Growth Response Protein 1 / Q000502:physiology*; D005260:Female; D005786:Gene Expression Regulation; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL
C504883:Cacna1h protein, mouse; D020747:Calcium Channels, T-Type; D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse
Cardiac hypertrophy; Cav3.2; Egr1; T-type calcium channel; Transcriptional regulation