Role of the VLA-4 molecule in T cell costimulation. Identification of the tyrosine phosphorylation pattern induced by the ligation of VLA-4.

Abstract

The very late activated Ag (VLA) molecules not only mediate T cell adhesions, but also provide costimulation in a TCR/CD3-dependent manner. However, little is known about the signals mediated by the ligation of VLA molecules. Previous work from our laboratory identified a 105-kDa protein that is predominantly phosphorylated on tyrosine residue upon engagement of VLA-4 in a human T lymphoblastic cell line, H9, and in peripheral T cells. In the present study, we have shown that the A and B epitope of VLA-4 plays a key role in VLA-4-mediated T cell costimulation. Moreover, we have demonstrated that the solid phase cross-linking of VLA-4 using Ab (against A and B) or the CS-1 region of fibronectin, stimulated tyrosine phosphorylation of 140-, 120-, 80- to 70-, 60- to 55-, 50-, and 45-kDa proteins in addition to the 105-kDa protein. In contrast, Ab ligation of the C epitope of VLA-4 mainly induced tyrosine phosphorylation of pp105, weakly induced other protein tyrosine phosphorylation, and additionally induced only minimal T cell costimulation. Using immunoblotting, we have identified some of the tyrosine-phosphorylated proteins to be phospholipase C gamma (pp140), pp125 focal adhesion kinase (pp120), paxillin (pp70 and pp50), p59fyn/p56lck (pp60-55), and mitogen-activated protein kinase (pp45). Since solid phase cross-linking of VLA-4 by B2 epitope-specific Ab induced T cell costimulation most strongly via the CD3 pathway, our results suggested that the above tyrosine-phosphorylated proteins may play an important role in VLA-4-mediated T cell costimulatory signaling events.

Phenotypic characterization of single CD4+ T cells harboring genetically intact and inducible HIV genomes

“…Importantly, α4β1 expression enriched for intact and replication-competent proviruses in all samples tested and may represent an interesting addition to previously described flow cytometry panels aimed at isolating HIV-infected cells 83 . The combination of α4 and β1 integrins, also known as the adhesion molecule VLA-4, is involved in trafficking of immune cells to inflammatory sites as well as in T cell co-stimulation 84 . It was recently demonstrated that expression of VLA-4 on resting CD4+ T cells favors their susceptibility to HIV infection in vitro 85 suggesting that VLA-4 may contribute to the reseeding of the reservoir by promoting the migration of resting CD4+ T cells to inflammatory tissues and facilitating their de novo infection during ART 86,87 .…”

Correction: Effects of Natalizumab Treatment on Foxp3+ T Regulatory Cells

“…Integrins including alpha-4 integrin (VLA-4) are so called bi-directional signalling molecules that connect to the cytoskeleton and activate intracellular signalling pathways [10]. Ligation of VLA-4, which forms an essential part of the immunological synapse, was demonstrated to provide costimulatory signals to T cells [11][12][13] and anti-VLA-4 therapy was suggested to modulate the activation of lymphocytes in experimental animal models of MS [25]. Accordingly, direct effects of Natalizumab on the homeostasis of Tregs and their immunobiological functions appear feasible.…”

“…In addition to bead-based suppression assays we used allogeneic immature and mature DC to challenge T effector cells. Since VLA-4 is part of the immunological synapse and has been suggested to be involved in costimulation [11][12][13] we first investigated whether Natalizumab influences the outcome of DC-T cell encounters by modulating T cell proliferation. However, Natalizumab (20 mg/ml) did not impact the percentage of proliferating T cells in response to immature DC (23,96+/ 210,57 vs. 24,58+/214,02) or mature DC (39,324+/214,77 vs. 39,178+/216,67) as determined by CFSE dilution assays (n = 5, Figure 4c).…”

“…The therapeutic target of Natalizumab belongs to the large group of integrins, which are considered bi-directional signalling molecules [10]. VLA-4 forms an essential part of the immunological synapse and ligation of VLA-4 was demonstrated to provide costimulatory signals to T cells [11][12][13]. However, despite strong clinical evidence for the use of Natalizumab in patients, knowledge on biological effects on different immune cell populations in MS patients in vivo is still marginal [13][14][15].…”