Ablation of cyclase-associated protein 2 (CAP2) leads to cardiomyopathy

Abstract

Cyclase-associated proteins are highly conserved proteins that have a role in the regulation of actin dynamics. Higher eukaryotes have two isoforms, CAP1 and CAP2. To study the in vivo function of CAP2, we generated mice in which the CAP2 gene was inactivated by a gene-trap approach. Mutant mice showed a decrease in body weight and had a decreased survival rate. Further, they developed a severe cardiac defect marked by dilated cardiomyopathy (DCM) associated with drastic reduction in basal heart rate and prolongations in atrial and ventricular conduction times. Moreover, CAP2-deficient myofibrils exhibited reduced cooperativity of calciumregulated force development. At the microscopic level, we observed disarrayed sarcomeres with development of fibrosis. We analyzed CAP2's role in actin assembly and found that it sequesters G-actin and efficiently fragments filaments. This activity resides completely in its WASP homology domain. Thus CAP2 is an essential component of the myocardial sarcomere and is essential for physiological functioning of the cardiac system, and a deficiency leads to DCM and various cardiac defects.

The role of cyclase-associated protein in regulating actin filament dynamics – more than a monomer-sequestration factor

“…This activity has been demonstrated for CAPs from budding yeast (Freeman et al, 1995), Dictyostelium (Gottwald et al, 1996), Arabidopsis (Chaudhry et al, 2007), C. elegans (CAS-1 and CAS-2) (Nomura et al, 2012;Nomura and Ono, 2013), pig platelets (ASP-56/CAP1) (Gieselmann and Mann, 1992), humans (CAP2) (Peche et al, 2013) and Cryptosporidium (C-CAP) (Hliscs et al, 2010). The effect of CAP on actin elongation is somewhat controversial; Freeman et al (Freeman et al, 1995) reported that yeast Srv2/CAP inhibits the incorporation of G-actin to either pointed or barbed ends of actin filaments, whereas Mattila et al reported that yeast Srv2/CAP specifically inhibits the incorporation of G-actin to the barbed end.…”

“…1A). The C-terminal half of CAP can bind to one molecule of G-actin (Freeman et al, 1995), and WH2 and CARP bind independently to G-actin (Chaudhry et al, 2010;Makkonen et al, 2013;Mattila et al, 2004;Peche et al, 2013), suggesting that they separately contact G-actin. An Nterminal part of WH2 from other proteins, such as WASP, was found to bind to G-actin at a cleft between its subdomains 1 and 3 (Dominguez, 2007), and WH2 of CAP might bind to G-actin in a similar manner.…”

“…1B), but how these residues interact with ADF/cofilin-bound F-actin is unknown. In mammalian CAP2, the WH2 domain is sufficient to sever actin filaments in the absence of ADF/cofilin at a neutral pH (Peche et al, 2013), but its requirement for filament severing in the context of full-length CAP2 still needs to be determined.…”

“…In mammalian skeletal and cardiac muscles, CAP2 is localized in the nucleus and diffused in the cytoplasm in skeletal myoblasts and embryonic cardiomyocytes, whereas, in differentiated skeletal myotubes and cardiomyocytes, it localizes to the M-lines, which are at the center of the thick filaments (Peche et al, 2007). CAP2-null mice die earlier than wild-type mice and show a phenotype that is typically associated with dilated cardiomyopathy, including enlarged heart with dilated ventricle and atrium, increased fibrosis, and impaired heart function (Peche et al, 2013;Jeffrey Field, University of Pennsylvania, personal communication). Furthermore, the myofibrils in skeletal and cardiac muscles from CAP2-null mice are disorganized with disturbed M-lines, thin filaments and Z-discs (Peche et al, 2013).…”

Mammalian Adenylyl Cyclase-associated Protein 1 (CAP1) Regulates Cofilin Function, the Actin Cytoskeleton, and Cell Adhesion

“…Taken together, CAP1 appears to be required in most cells, yet CAP2 appears to have unique roles required for specific cells or tissues. Most studies so far have been on CAP1, although recent studies have shed light on the role of CAP2 in the cardiovascular system (23,24).…”