Extracellular Matrix: Surface Proteoglycans

Chemical mapping of the surface interactome of PIEZO1 identifies CADM1 as a modulator of channel inactivation

The propeller-shaped blades of the PIEZO1 and PIEZO2 ion channels partition into the plasma membrane and respond to indentation or stretching of the lipid bilayer, thus converting mechanical forces into signals that can be interpreted by cells, in the form of calcium flux and changes in membrane potential. While PIEZO channels participate in diverse physiological processes, from sensing the shear stress of blood flow in the vasculature to detecting touch through mechanoreceptors in the skin, the molecular details that enable these mechanosensors to tune their responses over a vast dynamic range of forces remain largely uncharacterized. To survey the molecular landscape surrounding PIEZO channels at the cell surface, we employed a mass spectrometry-based proteomic approach to capture and identify extracellularly exposed proteins in the vicinity of PIEZO1. This PIEZO1-proximal interactome was enriched in surface proteins localized to cell junctions and signaling hubs within the plasma membrane. Functional screening of these interaction candidates by calcium imaging and electrophysiology in an overexpression system identified the adhesion molecule CADM1/SynCAM that slows the inactivation kinetics of PIEZO1 with little effect on PIEZO2. Conversely, we found that CADM1 knockdown accelerates inactivation of endogenous PIEZO1 in Neuro-2a cells. Systematic deletion of CADM1 domains indicates that the transmembrane region is critical for the observed effects on PIEZO1, suggesting that modulation of inactivation is mediated by interactions in or near the lipid bilayer.

Molecular recognition and proteoglycan mimic arrangement: modulating cisplatin toxicity

We have demonstrated that cisplatin (CP), an anticancer drug, showed a preference for binding the sulfated-L-iduronic acid (S-L-IdoA) unit over the sulfated-D-glucuronic acid unit of heparan sulfate. The multivalency of S-L-IdoA, such as in the proteoglycan mimic, resulted in distinct modes of cell-surface engineering in normal and cancer cells, with these disparities having a significant impact on CP-mediated toxicity.