The unique disulfide bond-stabilized W1 β4-β1 loop in the α4 β-propeller domain regulates integrin α4β7 affinity and signaling

Mucin-Like Domain of Mucosal Addressin Cell Adhesion Molecule-1 Facilitates Integrin α4β7-Mediated Cell Adhesion Through Electrostatic Repulsion

The homing of lymphocytes from blood to gut-associated lymphoid tissue is regulated by interaction between integrin α4β7 with mucosal vascular addressin cell adhesion molecule 1 (MAdCAM-1) expressed on the endothelium of high endothelial venules (HEVs). However, the molecular basis of mucin-like domain, a specific structure of MAdCAM-1 regulating integrin α4β7-mediated cell adhesion remains obscure. In this study, we used heparan sulfate (HS), which is a highly acidic linear polysaccharide with a highly variable structure, to mimic the negative charges of the extracellular microenvironment and detected the adhesive behaviors of integrin α4β7 expressing 293T cells to immobilized MAdCAM-1 in vitro. The results showed that HS on the surface significantly promoted integrin α4β7-mediated cell adhesion, decreased the percentage of cells firmly bound and increased the rolling velocities at high wall shear stresses, which was dependent on the mucin-like domain of MAdCAM-1. Moreover, breaking the negative charges of the extracellular microenvironment of CHO-K1 cells expressing MAdCAM-1 with sialidase inhibited cell adhesion and rolling velocity of 293T cells. Mechanistically, electrostatic repulsion between mucin-like domain and negative charges of the extracellular microenvironment led to a more upright conformation of MAdCAM-1, which facilitates integrin α4β7-mediated cell adhesion. Our findings elucidated the important role of the mucin-like domain in regulating integrin α4β7-mediated cell adhesion, which could be applied to modulate lymphocyte homing to lymphoid tissues or inflammatory sites.

Extracellular Redox Regulation of α7β Integrin-Mediated Cell Migration Is Signaled via a Dominant Thiol-Switch

While adhering to extracellular matrix (ECM) proteins, such as laminin-111, cells temporarily produce hydrogen peroxide at adhesion sites. To study the redox regulation of α7β1 integrin-mediated cell adhesion to laminin-111, a conserved cysteine pair within the α-subunit hinge region was replaced for alanines. The molecular and cellular effects were analyzed by electron and atomic force microscopy, impedance-based migration assays, flow cytometry and live cell imaging. This cysteine pair constitutes a thiol-switch, which redox-dependently governs the equilibrium between an extended and a bent integrin conformation with high and low ligand binding activity, respectively. Hydrogen peroxide oxidizes the cysteines to a disulfide bond, increases ligand binding and promotes cell migration toward laminin-111. Inversely, extracellular thioredoxin-1 reduces the disulfide, thereby decreasing laminin binding. Mutation of this cysteine pair into the non-oxidizable hinge-mutant shows molecular and cellular effects similar to the reduced wild-type integrin, but lacks redox regulation. This proves the existence of a dominant thiol-switch within the α subunit hinge of α7β1 integrin, which is sufficient to implement activity regulation by extracellular redox agents in a redox-regulatory circuit. Our data reveal a novel and physiologically relevant thiol-based regulatory mechanism of integrin-mediated cell-ECM interactions, which employs short-lived hydrogen peroxide and extracellular thioredoxin-1 as signaling mediators.

Kindlin-3 Is Essential for the Resting α4β1 Integrin-mediated Firm Cell Adhesion under Shear Flow Conditions

Integrin-mediated rolling and firm cell adhesion are two critical steps in leukocyte trafficking. Integrin α4β1 mediates a mixture of rolling and firm cell adhesion on vascular cell adhesion molecule-1 (VCAM-1) when in its resting state but only supports firm cell adhesion upon activation. The transition from rolling to firm cell adhesion is controlled by integrin activation. Kindlin-3 has been shown to bind to integrin β tails and trigger integrin activation via inside-out signaling. However, the role of kindlin-3 in regulating resting α4β1-mediated cell adhesion is not well characterized. Herein we demonstrate that kindlin-3 was required for the resting α4β1-mediated firm cell adhesion but not rolling adhesion. Knockdown of kindlin-3 significantly decreased the binding of kindlin-3 to β1 and down-regulated the binding affinity of the resting α4β1 to soluble VCAM-1. Notably, it converted the resting α4β1-mediated firm cell adhesion to rolling adhesion on VCAM-1 substrates, increased cell rolling velocity, and impaired the stability of cell adhesion. By contrast, firm cell adhesion mediated by Mn(2+)-activated α4β1 was barely affected by knockdown of kindlin-3. Structurally, lack of kindlin-3 led to a more bent conformation of the resting α4β1. Thus, kindlin-3 plays an important role in maintaining a proper conformation of the resting α4β1 to mediate both rolling and firm cell adhesion. Defective kindlin-3 binding to the resting α4β1 leads to a transition from firm to rolling cell adhesion on VCAM-1, implying its potential role in regulating the transition between integrin-mediated rolling and firm cell adhesion.

Bioinformatic description of immunotherapy targets for pediatric T-cell leukemia and the impact of normal gene sets used for comparison

Pediatric lymphoid leukemia has the highest cure rate of all pediatric malignancies, yet due to its prevalence, still accounts for the majority of childhood cancer deaths and requires long-term highly toxic therapy. The ability to target B-cell ALL with immunoglobulin-like binders, whether anti-CD22 antibody or anti-CD19 CAR-Ts, has impacted treatment options for some patients. The development of new ways to target B-cell antigens continues at rapid pace. T-cell ALL accounts for up to 20% of childhood leukemia but has yet to see a set of high-value immunotherapeutic targets identified. To find new targets for T-ALL immunotherapy, we employed a bioinformatic comparison to broad normal tissue arrays, hematopoietic stem cells (HSC), and mature lymphocytes, then filtered the results for transcripts encoding plasma membrane proteins. T-ALL bears a core T-cell signature and transcripts encoding TCR/CD3 components and canonical markers of T-cell development predominate, especially when comparison was made to normal tissue or HSC. However, when comparison to mature lymphocytes was also undertaken, we identified two antigens that may drive, or be associated with leukemogenesis; TALLA-1 and hedgehog interacting protein. In addition, TCR subfamilies, CD1, activation and adhesion markers, membrane-organizing molecules, and receptors linked to metabolism and inflammation were also identified. Of these, only CD52, CD37, and CD98 are currently being targeted clinically. This work provides a set of targets to be considered for future development of immunotherapies for T-ALL.