Regulation of focal adhesion formation by a vinculin-Arp2/3 hybrid complex

Abstract

Focal adhesions (FAs) are large multi-protein complexes that act as transmembrane links between the extracellular matrix and the actin cytoskeleton. Recently, FAs were extensively characterized, yet the molecular mechanisms underlying their mechanical and signalling functions remain unresolved. To address this question, we isolated protein complexes containing different FA components, from chicken smooth muscle, and characterized their properties. Here we identified 'hybrid complexes' consisting of the actin-nucleating subunits of Arp2/3 and either vinculin or vinculin and a-actinin. We further show that suppression of p41-ARC, a central component of native Arp2/3, which is absent from the hybrid complexes, increases the levels of the Arp2/3-nucleating core in FA sites and stimulates FA growth and dynamics. In contrast, overexpression of p41-ARC adversely affects FAs. These results support the view that Arp2/3 can form modular 'hybrid complexes' containing an actinnucleating 'functional core', and 'anchoring domains' (vinculin/p41-ARC) that regulate its subcellular localization.

Jack of all trades: functional modularity in the adherens junction

“…It is well-established that the Arp2/3 complex physically associates with E-cadherin [48], though the direct binding partner is not known. One potential candidate is vinculin, which is known to recruit Arp2/3 into focal adhesions [29,49 ]. Another candidate is cortactin, which binds Arp2/3 and has known interactions with p120-catenin and ZO-1 [50][51][52].…”

The inner workings of stress fibers − from contractile machinery to focal adhesions and back

“…We begin our discussion of this aspect with the observation that actin filaments are continuously polymerized in focal adhesions (Chorev et al, 2014;Skau et al, 2015;Tojkander et al, 2015). The newly formed actin filaments are then treadmilled away along the attached stress fibers towards the cell center, at a velocity of 0.02-0.4 µm/min (Endlich et al, 2007;Russell et al, 2011;Tojkander et al, 2015).…”

Caveolin 1 (Cav-1) and actin-related protein 2/3 complex, subunit 1B (ARPC1B) expressions as prognostic indicators for oral squamous cell carcinoma (OSCC)

“…In the current study, underexpression of ARPC1B protein showed significant association with advanced disease stage and lymph node metastasis. This could be explained by the findings from a recent study which demonstrated that low expression of ARPC1B gene would promote the activities of Arp2/3-nucleating core in focal adhesions sites involved in cell migration and adhesion [30]. Down regulation of the Arp2/3 complex may also be attributed to methylation of its subunit p41-Arc, leading to loss of expression and development of dysplastic morphology.…”

“…In addition, Zucchini et al [31] suggested that the down regulation of ARPC1B in osteosarcoma might be one of the causal effects that leads to inhibition of metastasis by decreasing dynamic actin disassembly that is crucial for cancer cell migration. These observations reflect the migration activity of ARPC1B in regulation of the focal adhesions and actin filaments which promotes tumor cell metastasis [30]. Although loss of ARPC1B has been reported in various cancers, the mechanism of this gene in OSCC remains unclear, and further downstream analysis should be performed to clarify its role in oral carcinogenesis.…”