Calcium/calmodulin regulates signaling at the α1A adrenoceptor

Abstract

Cardiovascular functions are mediated by multiple 7-pass transmembrane receptors whose activation promotes contraction or relaxation of the tissues. The α 1 adrenoceptor type 1A plays important roles in the control of vascular tone and myocardial contractility via Ca 2+ -dependent actions. Here, using novel FRET-based biosensors, we identified a novel Ca 2+ -dependent interaction between calmodulin (CaM) and the human α 1A adrenoceptor at the juxtamembranous region of its 4 th submembrane domain (SMD4 JM , a.a. 333-361). SMD4 JM houses the known nuclear localization signal of α 1A adrenoceptor (NLS, a.a. 334-349). We found that NLS itself also interacts with CaM, but with lower affinity and Ca 2+ sensitivity, indicating that full interaction between CaM and α 1A receptor in this region requires segment a.a. 333-361. Combined K353Q/ L356A substitutions in the non-NLS segment of SMD4 JM cause a 3.5-fold reduction in the affinity of CaM-SMD4 JM interaction. Overexpression of wild-type α 1A adrenoceptor in cells enhances phosphorylation of the extracellular signal-regulated kinases 1/2 (ERK1/2) stimulated by A61603, while overexpression of the K353Q/L356A α 1A receptor mutant significantly reduces this signal. Norepinephrine stimulates intracellular Ca 2+ signals that are higher in cells overexpressing wildtype receptor but lower in cells overexpressing the K353Q/L356A receptor compared to nontransfected cells in the same microscopic environments. These data support a novel and important role for Ca 2+ -dependent CaM interaction at SMD4 JM in α 1A adrenoceptor-mediated signaling.

Adrenergic Receptor Regulation of Mitochondrial Function in Cardiomyocytes

“…However, considerable evidence suggests that a1A activation increases intracellular calcium and, hence, likely increases mitochondrial calcium indirectly. Structurally, the fourth membrane subdomain of the human a1A-AR has been shown to interact directly with the calcium-binding messenger protein calmodulin, 137 implicating a1A-AR activation in calcium regulation. Mice with transgenic a1A-AR overexpression (66-fold and 170-fold) have increased intracellular calcium signaling.…”