Dynamic control of β1 integrin adhesion by the plexinD1-sema3E axis

Abstract

Plexins and semaphorins comprise a large family of receptorligand pairs controlling cell guidance in nervous, immune, and vascular systems. How plexin regulation of neurite outgrowth, lymphoid trafficking, and vascular endothelial cell branching is linked to integrin function, central to most directed movement, remains unclear. Here we show that on developing thymocytes, plexinD1 controls surface topology of nanometer-scaled β1 integrin adhesion domains in cis, whereas its ligation by sema3E in trans regulates individual β1 integrin catch bonds. Loss of plexinD1 expression reduces β1 integrin clustering, thereby diminishing avidity, whereas sema3E ligation shortens individual integrin bond lifetimes under force to reduce stability. Consequently, both decreased expression of plexinD1 during developmental progression and a thymic medulla-emanating sema3E gradient enhance thymocyte movement toward the medulla, thus enforcing the orchestrated lymphoid trafficking required for effective immune repertoire selection. Our results demonstrate plexin-tunable molecular features of integrin adhesion with broad implications for many cellular processes.thymocyte development | mechanobiology | integrin activation | autoimmunity | central tolerance I t is well established that plexins and their semaphorin ligands regulate biological processes in multiple physiological domains including axon pathfinding (1, 2), angiogenesis (3), and immunity (4). Although plexins harbor potential for regulating small GTPases that mediate cytoskeletal remodeling, either through a direct cytoplasmic GTPase-activating protein (GAP) domain and Rac/Rho-GTPase binding domain or through sequestration of guanidine nucleotide exchange factor (GEF) proteins to the membrane-proximal cytoplasmic face, there is little consensus on plexin signaling pathways in a complex physiological context (5).While studying the molecular interactions controlling mouse thymocyte development, we identified plexinD1 as a critical mediator for thymocytes destined to mature into T lymphocytes populating the mammalian immune system (6). Plxnd1 encoding plexinD1 is transcriptionally regulated at a key intermediate stage of thymocyte development. Double-negative (DN) thymocytes lacking expression of CD4 and CD8 as well as plexinD1 differentiate in the thymic cortex into largely nondividing CD4 + CD8 + double-positive (DP) thymocytes that display surface αβ T-cell receptors (TCRs) and express plexinD1 (6). Despite being highly mobile (7), DP thymocytes remain sequestered in the cortex in frequent physical association with thymic epithelial cells (TECs), moving toward the thymic medulla via chemokine guidance only subsequent to TCR stimulation by self-derived peptide/MHC complexes (pMHC) that induce CD69 expression and support cell survival, i.e., positive selection (8, 9). CD69 + DP cells differentiate further into CD4 + CD8 − or CD4 − CD8 + singlepositive (SP) thymocytes, translocating to the thymic medulla to complete their maturation (10, 11). While traversing the thymus, immatu...

Pre-T Cell Receptors (Pre-TCRs) Leverage Vβ Complementarity Determining Regions (CDRs) and Hydrophobic Patch in Mechanosensing Thymic Self-ligands

“…1). 3) The mechanosensor operates far from thermal equilibrium, driven by an energetically rich environment using energy harvested from cell motility and other surveillance operations regulated by chemokines, integrins, plexins, and semaphorins (25,37). Although the pre-TCR and TCR␣␤ have similar energetic requirements, the pre-TCR exhibits more reversible transitioning (Fig.…”

Altered proliferative ability of neuronal progenitors in PlexinA1 mutant mice

“…Thus, reduced adhesion of PlexinA1 knockdown cells would suggest that loss of receptor function perturbs attachment to laminin. Plexins associate with integrins (Basile et al, 2007; Choi et al, 2014), which are known laminin receptors (Tomaselli et al, 1988). Thus, it is possible that PlexinA1 could be acting as an integrin coreceptor required for laminin binding and attachment to the ECM.…”

Dynamic catch of a Thy-1–α5β1+syndecan-4 trimolecular complex

“…Surprisingly, we find a complex mechanical regulation of adhesive bonds at the single-molecule level: tensile force prolongs the bond lifetime (that is, catch bonds). In contrast to the well-known catch bonds of bimolecular systems, such as cell adhesion receptors (integrins 28,38,39 , selectins 40,41 , glycoprotein Iba 30,42 , E-cadherin 43 and FimH 44 ), the T-cell receptor 31 and cytoskeletal linkages 45,46 , the Thy-1 catch bond is strongly correlated with a bond-stiffening phenotype, termed 'dynamic catch', which partially shifts force to the already engaged but unstretched coreceptor Syn4. Thus, the data reveal a unique, previously unreported class of receptor-ligand bonds whereby force tightens co-receptor engagement that is required for forcemediated adhesion signalling.…”