Cyclase-associated Protein 1 (CAP1) Promotes Cofilin-induced Actin Dynamics in Mammalian Nonmuscle Cells

Abstract

Cyclase-associated proteins (CAPs) are highly conserved actin monomer binding proteins present in all eukaryotes. However, the mechanism by which CAPs contribute to actin dynamics has been elusive. In mammals, the situation is further complicated by the presence of two CAP isoforms whose differences have not been characterized. Here, we show that CAP1 is widely expressed in mouse nonmuscle cells, whereas CAP2 is the predominant isoform in developing striated muscles. In cultured NIH3T3 and B16F1 cells, CAP1 is a highly abundant protein that colocalizes with cofilin-1 to dynamic regions of the cortical actin cytoskeleton. Analysis of CAP1 knockdown cells demonstrated that this protein promotes rapid actin filament depolymerization and is important for cell morphology, migration, and endocytosis. Interestingly, depletion of CAP1 leads to an accumulation of cofilin-1 into abnormal cytoplasmic aggregates and to similar cytoskeletal defects to those seen in cofilin-1 knockdown cells, demonstrating that CAP1 is required for proper subcellular localization and function of ADF/cofilin. Together, these data provide the first direct in vivo evidence that CAP promotes rapid actin dynamics in conjunction with ADF/cofilin and is required for several central cellular processes in mammals.

Mammalian CAP (Cyclase-associated protein) in the world of cell migration

“…Available evidence from a number of species such as Dictyostelium 7,26 suggests that CAP1 may facilitate cell polarization. In mammalian cells, CAP1 is enriched at the leading edge of migrating cells, 7,25,27 and we have also observed similar localization in multiple mammalian cell lines such as HeLa and hTERT-HPNE pancreas cells (unpublished observations). We speculate that CAP1 at the leading edge may promote local actin dynamics, which facilitates cell polarization and subsequent migration.…”

“…While most data suggesting that CAP1 interacts with cofilin are from in vitro studies, there is some evidence that they interact in cells because depletion of mammalian CAP1 causes cofilin to accumulate into cytoplasmic aggregates 5,25 and remain dephosphorylated. 5 Aggregation is likely to prevent cofilin from functioning to facilitate actin filament dynamics.…”

“…In CAP1-depleted NIH3T3 fibroblasts, B16F1, and HeLa cells, common actin cytoskeletal (and morphological) alterations observed include enhanced actin stress fibers and enlarged cell size. 5,25 The enhanced stress fibers in the CAP1 knockdowns are likely to be caused by the reduced rate of the actin filament turnover and reduced G-actinsequestering. While stress fibers generate tension force needed to pull the trailing edge forward during cell movement, enhanced stress fibers is typically associated with reduced motility.…”

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

“…WH2 motifs are intrinsically disordered, adopting an a-helical structure only upon binding to actin [11]. CAP in lower eukaryotes as well as mouse CAP1 are involved in cell polarity, motility, and receptor-mediated endocytosis [12][13][14]. Additionally, mammalian CAP1 was shown to be a proapoptotic protein [15].…”

Adenylate cyclase-associated protein 1 overexpressed in pancreatic cancers is involved in cancer cell motility

“…33,34 In addition to those genetic studies, CAP1 knockdown results in aberrant cell morphology and reduced migration in mouse cells. 35 These reports suggest that a failure of actin turnover by aberrations in CAP1 orthologs induces abnormalities in cell morphology, polarity, and motility. In our study, protruding of the lamellipodium was induced by serum stimulation and was inhibited by CAP1 knockdown, suggesting that CAP1 was involved in serum-induced lamellipodium formation.…”