Biology subjects

Kalappurakkal, J. M.

Publications and source records attributed to Kalappurakkal, J. M..

3 recordsLinked to original sources

bioRxiv2021

Cortical actin flow activates an alpha-catenin clutch to assemble adherens junctions

Adherens junctions allow cell contact to inhibit epithelial migration. But a long-standing puzzle is how locomotion is downregulated when E-cadherin adhesions form at surfaces perpendicular, but not those parallel, to the direction of migration. We now show that this arises from coupling between E-cadherin adhesions and the retrograde cortical flows of leader cells in migrating epithelia. At interfaces perpendicular to the direction of motion, such flows are antiparallel, which generates a tensile signal that induces the actin-binding domain of -catenin to promote lateral growth of nascent adhesions and inhibit the lamellipodial activity necessary for migration. At interfaces parallel to the direction of motion, by contrast, cortical flows are aligned and no such mechanical inhibition takes place. Therefore, -catenin mechanosensitivity in the clutch between E-cadherin and cortical F-actin allows cells to interpret the direction of motion via cortical flows and trigger the first signal for contact to inhibit locomotion.

cell biology↗

bioRxiv2019

Phosphorylation of Nephrin induces phase separated domains that move through actomyosin contraction

The plasma membrane of eukaryotic cells is organized into lipid and protein microdomains, whose assembly mechanisms and functions are incompletely understood. We demonstrate that proteins in the Nephrin/Nck/N-WASP actin-regulatory pathway cluster into micron-scale domains at the basal plasma membrane upon triggered phosphorylation of transmembrane Nephrin. The domains are persistent but readily exchange components with their surroundings, and their formation is dependent on the number of Nck SH3 domains, suggesting they are phase separated polymers assembled through multivalent interactions among the three proteins. The domains form independent of the actin cytoskeleton, but acto-myosin contractility induces their rapid lateral movement. Nephrin phosphorylation induces larger clusters at the cell periphery, which are associated with extensive actin assembly and dense filopodia. Our studies illustrate how multivalent interactions between proteins at the plasma membrane can produce micron-scale organization of signaling molecules, and how the resulting clusters can both respond to and control the actin cytoskeleton.

cell biology↗

bioRxiv2017

Acto-myosin driven functional nanoclusters of GPI-anchored proteins are generated by integrin receptor signaling

GPI-anchored protein (GPI-AP) nanoclusters are generated by cortical acto-myosin activity. While our understanding of the physical principles behind this process is emerging, the molecular machinery required for the generation of these nanoclusters is unknown. Here, we show that ligand-mediated membrane receptor signaling triggers nanocluster formation. Both soluble and surface-tethered RGD ligands bind the {beta}1-integrin receptor and activate focal adhesion and src-kinases, resulting in RhoA signaling. This cascade ultimately triggers actin-nucleation via specific formins, driving nanoclustering of both GPI-APs and a model transmembrane protein with an actin-binding domain. Integrin signaling concurrently results in talin mediated activation of vinculin. This is necessary for the coupling of the dynamic actin machinery to the inner leaflet driving GPI-AP nanoclustering. Disruption of GPI-AP nanoclustering in either GPI-anchor remodeling mutants or in cells that express vinculin mutants, provide evidence that these nanoclusters are necessary for activating cell spreading, a hallmark of integrin function.

cell biology↗