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(Circulation Research. 2009;104:1373.)
© 2009 American Heart Association, Inc.

Cellular Biology

L-Type Calcium Channel C Terminus Autoregulates Transcription

Elizabeth Schroder, Miranda Byse, Jonathan Satin

From the Department of Physiology, University of Kentucky, Lexington.

Correspondence to Jonathan Satin, University of Kentucky, Department of Physiology, 800 Rose St, MS508, Lexington, KY 40536-0298. E-mail jsatin1{at}uky.edu

Calcium homeostasis is critical for cardiac myocyte function and must be tightly regulated. The guiding hypothesis of this study is that a carboxyl-terminal cleavage product of the cardiac L-type calcium channel (Ca_V1.2) autoregulates expression. First, we confirmed that the Ca_V1.2 C terminus (CCt) is cleaved in murine cardiac myocytes from mature and developing ventricle. Overexpression of full-length CCt caused a 34±8% decrease of Ca_V1.2 promoter activity, and truncated CCt caused an 80±3% decrease of Ca_V1.2 promoter (n=12). The full-length CCt distributes into cytosol and nucleus. A deletion mutant of CCt has a greater relative affinity for the nucleus than full-length CCt, and this is consistent with increased repression of Ca_V1.2 promoter activity by truncated CCt. Chromatin immunoprecipitation analysis revealed that CCt interacts with the Ca_V1.2 promoter in adult ventricular cardiac myocytes at promoter modules containing Nkx2.5/Mef2, C/EBp, and a cis regulatory module. The next hypothesis tested was that CCt contributes to transcriptional signaling associated with cellular hypertrophy. We explored whether fetal cardiac myocyte Ca_V1.2 was regulated by serum in vitro. We tested atrial natriuretic factor promoter activity as a positive control and measured the serum response of Ca_V1.2 promoter, protein, and L-type current (I_Ca,L) from fetal mouse ventricular myocytes. Serum increased atrial natriuretic factor promoter activity and cell size as expected. Serum withdrawal increased Ca_V1.2 promoter activity, mRNA, and I_Ca,L. Moreover, serum withdrawal decreased the relative nuclear localization of CCt. A combination of promoter deletion mutant analyses, and the response of promoter mutants to serum withdrawal support the conclusion that CCt, a proteolytic fragment of Ca_V1.2, autoregulates Ca_V1.2 expression in cardiac myocytes. These data support the novel mechanism that a mobile segment of Ca_V1.2 links Ca handling to nuclear signaling.

Key Words: L-type Ca²⁺ channels • L-type Ca²⁺ current • Ca²⁺ channels • Ca²⁺ regulation • transcriptional regulation