Food for thought: How cell adhesion coordinates nutrient sensing

Cell adhesion controls cell survival and proliferation via multiple mechanisms. Rabanal-Ruiz et al. (2021. J. Cell Biol. https://doi. org/10.1083/jcb.202004010) demonstrate that focal adhesions are key signaling hubs for cellular nutrient sensing and signaling

The complexity of integrins in cancer and new scopes for therapeutic targeting

Cancer is a complex disease and progresses within a dynamically evolving extracellular matrix that controls virtually every aspect of the tumour and tumour-associated cells. Interactions with the extracellular microenvironment are predominately mediated by a family of cell-surface transmembrane receptors called integrins. Integrin–matrix engagement leads to the formation of adhesion plaques, consisting of signalling and adaptor proteins, at the plasma membrane that link the extracellular matrix to the regulation of the cell cytoskeleton. In this review, we will highlight exciting data that identify new roles for integrins and integrin-dependent signalling in cancer away from the plasma membrane, discuss the implications of integrin-dependent regulation of Met and ErbB2 growth factor receptors and highlight the role of specific integrins in different stages of cancer development including maintenance of cancer stem cells.</p

The cell biologist's guide to super-resolution microscopy

Fluorescence microscopy has become a ubiquitous method to observe the location of specific molecular components within cells. However, the resolution of light microscopy is limited by the laws of diffraction to a few hundred nanometers, blurring most cellular details. Over the last two decades, several techniques - grouped under the 'super-resolution microscopy' moniker - have been designed to bypass this limitation, revealing the cellular organization down to the nanoscale. The number and variety of these techniques have steadily increased, to the point that it has become difficult for cell biologists and seasoned microscopists alike to identify the specific technique best suited to their needs. Available techniques include image processing strategies that generate super-resolved images, optical imaging schemes that overcome the diffraction limit and sample manipulations that expand the size of the biological sample. In this Cell Science at a Glance article and the accompanying poster, we provide key pointers to help users navigate through the various super-resolution methods by briefly summarizing the principles behind each technique, highlighting both critical strengths and weaknesses, as well as providing example images

Filopodome Mapping Identifies p130Cas as a Mechanosensitive Regulator of Filopodia Stability

in filopodia tips, predicts critical roles for PIs in regulating filopodia ultra-structure and function. Our mapping further reveals that filopodia adhesions consist of a unique set of proteins, the filopodome, that are distinct from classical nascent adhesions, focal adhesions, and fibrillar adhesions. Using live imaging, we observe that filopodia adhesions can give rise to nascent adhesions, which, in turn, form focal adhesions. We demonstrate that p130Cas (BCAR1) is recruited to filopodia tips via its C-terminal Cas family homology domain (CCHD) and acts as a mechanosensitive regulator of filopodia stability. Finally, we demonstrate that our map based on myosin-X-induced filopodia can be translated to endogenous filopodia and fascin- and IRSp53-mediated filopodia

Fluctuation-Based Super-Resolution Traction Force Microscopy

Cellular mechanics play a crucial role in tissue homeostasis and are often misregulated in disease. Traction force microscopy is one of the key methods that has enabled researchers to study fundamental aspects of mechanobiology; however, traction force microscopy is limited by poor resolution. Here, we propose a simplified protocol and imaging strategy that enhances the output of traction force microscopy by increasing i) achievable bead density and ii) the accuracy of bead tracking. Our approach relies on super-resolution microscopy, enabled by fluorescence fluctuation analysis. Our pipeline can be used on spinning-disk confocal or widefield microscopes and is compatible with available analysis software. In addition, we demonstrate that our workflow can be used to gain biologically relevant information and is suitable for fast long-term live measurement of traction forces even in light-sensitive cells. Finally, using fluctuation-based traction force microscopy, we observe that filopodia align to the force field generated by focal adhesions

Syndecan-4 phosphorylation is a control point for integrin recycling

Precise spatiotemporal coordination of integrin adhesion complex dynamics is essential for efficient cell migration. For cells adherent to fibronectin, differential engagement of α5β1 and αVβ3 integrins is used to elicit changes in adhesion complex stability, mechanosensation, matrix assembly, and migration, but the mechanisms responsible for receptor regulation have remained largely obscure. We identify phosphorylation of the membrane-intercalated proteoglycan syndecan-4 as an essential switch controlling integrin recycling. Src phosphorylates syndecan-4 and, by driving syntenin binding, leads to suppression of Arf6 activity and recycling of αVβ3 to the plasma membrane at the expense of α5β1. The resultant elevation in αVβ3 engagement promotes stabilization of focal adhesions. Conversely, abrogation of syndecan-4 phosphorylation drives surface expression of α5β1, destabilizes adhesion complexes, and disrupts cell migration. These data identify the dynamic spatiotemporal regulation of Src-mediated syndecan-4 phosphorylation as an essential switch controlling integrin trafficking and adhesion dynamics to promote efficient cell migration

SHANK proteins limit integrin activation by directly interacting with Rap1 and R-Ras

SHANK3, a synaptic scaffold protein and actin regulator, is widely expressed outside of the central nervous system with predominantly unknown function. Solving the structure of the SHANK3 N-terminal region revealed that the SPN domain is an unexpected Ras-association domain with high affinity for GTP-bound Ras and Rap G-proteins. The role of Rap1 in integrin activation is well established but the mechanisms to antagonize it remain largely unknown. Here, we show that SHANK1 and SHANK3 act as integrin activation inhibitors by sequestering active Rap1 and R-Ras via the SPN domain and thus limiting their bioavailability at the plasma membrane. Consistently, SHANK3 silencing triggers increased plasma membrane Rap1 activity, cell spreading, migration and invasion. Autism-related mutations within the SHANK3 SPN domain (R12C and L68P) disrupt G-protein interaction and fail to counteract integrin activation along the Rap1-RIAM-talin axis in cancer cells and neurons. Altogether, we establish SHANKs as critical regulators of G-protein signalling and integrin-dependent processes