Alpha2beta1 integrin signaling augments T cell receptor-dependent production of interferon-gamma in human T cells

Abstract

The mechanisms by which β1 integrins modulate T cell costimulation are still poorly defined. In this study, we examined the role of collagen-binding integrins α1β1 and α2β1 in the regulation of interferon-γ (IFN-γ). We demonstrated that ligation of α2β1 integrin with Collagen type I (Coll I) but not α1β1 integrin with Collagen IV (Coll IV) significantly augmented T cell receptor (TCR)-dependent expression and production of IFN-γ by effector T cells. The effect of Coll I was not due to cell adhesion as soluble Coll I also augmented TCR-dependent production of IFN-γ. Inhibition studies indicated that activation of ERK and JNK MAPKs and PI3K/AKT are necessary for both TCR- and TCR + α2β1 integrin-dependent IFN-γ production and that Coll I increases TCR-dependent activation of ERK and JNK MAPKs, and AKT. In addition, our results showed that Coll IV is less potent than Coll I in augmenting TCR-dependent activation of JNK/MAPK, which may explain the differential effect of collagen matrices on TCR-dependent IFN-γ production. Together, these results indicate that the costimulatory effect of Coll I on IFN-γ expression is integrated at the levels of ERK and JNK MAPKs and PI3K/AKT signaling pathways and suggest JNK/MAPK as a major signaling pathway of Coll I costimulation. Thus, our study identifies α2β1 integrin as an important regulatory pathway of IFN-γ expression and provides novel insights into the signaling mechanisms of integrin costimulation in T cells. As such, this study further supports the functional importance that Coll I interactions may have on the control of T cell-dependent Th1 inflammatory diseases.

Introduction

Integrins are α/β heterodimeric membrane proteins that mediate cell–cell interactions and cell adhesion to the surrounding extracellular matrix proteins (ECMp). In addition, integrins elicit a wide variety of intracellular signals that modulate cell growth, proliferation and apoptosis (Giancotti and Ruoslahti, 1999, Lee and Juliano, 2004, Schwartz et al., 1995).

T cells express several members of the β1 integrin family, which following cellular activation mediate their attachment to ECMp (Hemler, 1990, Shimizu and Shaw, 1991, Springer, 1990). T cells interact poorly with constituents of the ECMp in secondary lymphoid organs since in this environment the ECMp is not accessible as it is sheathed by a layer of reticular fibroblasts (Dustin and de Fougerolles, 2001, Krivacic and Levine, 2003). However, T cells interact with ECMp during their migration to injured extravascular tissues and encounter the antigen in an interstitial microenvironment rich in ECMp (Dustin and de Fougerolles, 2001, Krivacic and Levine, 2003). Growing evidence suggests that T cell interactions with ECMp may also contribute to their activation in extravascular tissues and subsequently contribute to regulate T cell-mediated immune and inflammatory responses. Along these lines, several studies have indicated the potential implication of β1 integrins in T cell costimulation. The α4β1 and α5β1 integrins, which bind to fibronectin and to VCAM-1 in the case of α4β1 integrin, are the most studied β1 integrins in T lymphocytes (Pribila et al., 2004, Shimizu and Shaw, 1991). They have been implicated in T cell costimulation leading to IL-2 gene expression and proliferation (Iwata et al., 2000, Kamiguchi et al., 1999, Shimizu et al., 1990). Although expressed only on effector T cells, α1β1 and α2β1 collagen-binding integrins have gained more attention in recent years (Ben-Horin and Bank, 2004, Pribila et al., 2004). These integrins have also been implicated in the costimulation of effector T cells leading to proliferation, and in this context, collagen type I (Coll I) was shown to be a more potent costimulatory ECMp than fibronectin (Rao et al., 2000, Sturm et al., 2004). Furthermore, we have recently demonstrated that Coll I through the α2β1 integrin protects effector T cells from Fas-induced apoptosis, whereas fibronectin and laminin did not (Aoudjit and Vuori, 2000, Gendron et al., 2003). These studies suggest that collagen-binding integrins can be important costimulatory molecules for effector T cells, but the signaling mechanisms by which they mediate costimulation are still poorly defined.

Interferon-γ (IFN-γ) is a crucial cytokine in immune development and function. It is a multi-functional cytokine produced by Th1 cells, cytotoxic T cells and natural killer cells and activates macrophages and cytotoxic T lymphocytes to promote cell-mediated immunity against intracellular pathogens (Boehm et al., 1997, Gattoni et al., 2006). It is also an important cytokine in chronic inflammatory diseases as it activates the inflammatory response of macrophages present at the injured tissue (Boehm et al., 1997, Gattoni et al., 2006). In this regard, recent in vivo studies have implicated collagen-binding integrins in the development of Th1 inflammatory diseases such as delayed type hypersensitivity (DTH) and arthritis (de Fougerolles et al., 2000, Ianaro et al., 2000). Whether β1 integrins and in particular collagen-binding integrins regulate the expression of IFN-γ in T cells and the signaling mechanisms by which they do so are still unclear.

In the present study, we have investigated the regulation of T cell receptor (TCR)-dependent IFN-γ expression by collagen matrices. Our results show that Coll I through its receptor, the α2β1 integrin significantly increases the expression and production of IFN-γ in effector T cells. We also demonstrate that Coll I also augmented TCR-dependent activation of ERK and JNK MAPKs and PI3K/AKT signaling pathways, which are all necessary for IFN-γ expression. Finally, we show that Coll IV to which effector T cells bind through α1β1 integrin is less potent than Coll I in enhancing TCR-mediated activation of JNK/MAPK and was unable to augment the production of IFN-γ. Together, our results identified α2β1 integrin as an important regulatory signaling pathway in T cell activation leading to IFN-γ production and may thus be involved in T cell-mediated inflammatory response.