Abstract
It is generally assumed that cells interrogate the mechanical properties of their environment by pushing and pulling on the extracellular matrix (ECM). For instance, acto-myosin-dependent contraction forces exerted at focal adhesions (FAs) allow the cell to actively probe substrate elasticity. Here, we report that a subset of long-lived and flat clathrin-coated structures (CCSs), also termed plaques, are contractility-independent mechanosensitive signaling platforms. We observed that plaques assemble in response to increasing substrate rigidity and that this is independent of FAs, actin and myosin-II activity. We show that plaque assembly depends on αvβ5 integrin, and is a consequence of frustrated endocytosis whereby αvβ5 tightly engaged with the stiff substrate locally stalls CCS dynamics. We also report that plaques serve as platforms for receptor-dependent signaling and are required for increased Erk activation and cell proliferation on stiff environments. We conclude that CCSs are mechanotransduction structures that sense substrate rigidity independently of cell contractility.
Highlights
It is generally assumed that cells interrogate the mechanical properties of their environment by pushing and pulling on the extracellular matrix (ECM)
When HeLa cells were grown on collagen-coated glass, ventral plasma membrane clathrin-coated structures (CCSs) marked with the α-adaptin subunit of the clathrin adaptor AP-2 appeared as a mix of dot-like, diffraction-limited structures corresponding to clathrin-coated pits (CCPs), and large, heterogeneous structures corresponding to plaques, as previously reported[11,12,14] (Fig. 1a)
Similar to HeLa cells, HepG2 and Caco-2 cell lines harbored both dynamic CCPs and large, static CCSs when cultured on glass or on 31 kPa gels while only short-lived CCPs were detectable on softer gels (Supplementary Fig. 2b–e)
Summary
It is generally assumed that cells interrogate the mechanical properties of their environment by pushing and pulling on the extracellular matrix (ECM). We report that a subset of long-lived and flat clathrin-coated structures (CCSs), termed plaques, are contractility-independent mechanosensitive signaling platforms. We report that plaques serve as platforms for receptor-dependent signaling and are required for increased Erk activation and cell proliferation on stiff environments. Contractile forces generated by the acto-myosin network and transmitted to the substrate at integrin-rich cell adhesions endow these adhesions to grow and mature into focal adhesions (FAs), in a matrix rigiditydependent manner[7,8]. Clathrin-coated structures (CCSs) are mostly described to control the uptake of cell-surface receptors, including some integrins. Plaque formation on stiff environments is independent of cell contractility but is the consequence of a frustrated endocytosis process whereby αvβ5-integrin prevents CCSs budding by anchoring the structure to the substrate. We propose that clathrin-coated plaques are mechanosensitive structures instructing the cell about the rigidity of its environment
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