The Interaction of CD154 with the α5β1 Integrin Inhibits Fas-Induced T Cell Death

Abstract

CD154, a critical regulator of the immune response, is usually associated with chronic inflammatory, autoimmune diseases as well as malignant disorders. In addition to its classical receptor CD40, CD154 is capable of binding other receptors, members of the integrin family, the αIIbβ3, αMβ2 and α5β1. Given the role attributed to integrins and particularly the β1 integrins in inhibiting apoptotic events in normal as well as malignant T cells, we were highly interested in investigating the role of the CD154/α5β1 interaction in promoting survival of malignant T cells contributing as such to tumor development and/or propagation. To support our hypothesis, we first show that soluble CD154 binds to the T-cell acute lymphoblastic leukemia cell line, Jurkat E6.1 in a α5β1-dependent manner. Binding of soluble CD154 to α5β1 integrin of Jurkat cells leads to the activation of key survival proteins, including the p38 and ERK1/2 mitogen-activated protein kinases (MAPKs), phosphoinositide 3 kinase (PI-3K), and Akt. Interestingly, soluble CD154 significantly inhibits Fas-mediated apoptosis in T cell leukemia-lymphoma cell lines, Jurkat E6.1 and HUT78 cells, an important hallmark of T cell survival during malignancy progression. These anti-apoptotic effects were mainly mediated by the activation of the PI-3K/Akt pathway but also involved the p38 and the ERK1/2 MAPKs cascades. Our data also demonstrated that the CD154-triggered inhibition of the Fas-mediated cell death response was dependent on a suppression of caspase-8 cleavage, but independent of de novo protein synthesis or alterations in Fas expression on cell surface. Together, our results highlight the impact of the CD154/α5β1 interaction in T cell function/survival and identify novel targets for the treatment of malignant disorders, particularly of T cell origin.

CD154 inhibits death of T cells via a Cis interaction with the α5β1 integrin

“…Cells were pre-incubated with different concentrations of sCD154 and then treated with the sub-optimum apoptosis-inducing concentration of TRAIL (50 ng/ml) or TNF-α (25 ng/ml) outlined above. Our data show that CD154 was capable of inhibiting TRAIL-and TNF-induced cell death in a dose-dependent manner (Fig 1D), as it did with Fas-induced response previously described [29]. It is important to mention here that we have shown before the capacity of agonistic anti-α5β1Abs to inhibit Fas-induced cell death in Jurkat E6.1cells as does CD154 [29], highly supporting the role of α5β1 integrin in the apoptosis-inhibiting effect of CD154 in Jurkat E6.1 cells.…”

“…inactive form of α5β1, capable of binding CD154 [23], and that binding of sCD154 to these cells was completely abolished by soluble α5β1 confirming the specificity of sCD154 to α5β1 integrin [29].…”

“…We have previously reported that binding of sCD154 to several human T cell lines expressing α5β1 molecules inhibits their Fas-induced death [29]. We therefore hypothesized that such dyad plays an important role in the modulation of T cell death induced by other apoptotic stimuli.…”

“…In some experiments and when indicate, Wortmannin (Millipore Sigma, Bilerica, MA, USA) was used as a control. Cell death was evaluated by FACS analysis as the percentage of death obtained by propidium iodide (Invitrogen, Burlington, ON) staining as we previously described [29].…”

A critical role for both CD40 and VLA5 in angiotensin Il–mediated thrombosis and inflammation

“…This CD40‐VLA5 activated complex induces downstream signaling events, such as MAPK, p38, and ERK1/2, and has also been shown to syner‐gize in the release of inflammatory mediators, such as matrix metalloproteinase‐2 and ‐9, which suggests a crosstalk between these CD40L and VLA5 receptors (35). More recently, it has also been shown that the CD40L–VLA5 interaction promotes the survival of malignant T cells—as demonstrated by the activation of key survival signaling pathways, such as MAPKs (p38 and ERK1 /2) and PI3K—and resistance to Fasmediated apoptosis, an important hallmark of T‐cell malignancies (36).…”