Role of the JNK/c-Jun/AP-1 signaling pathway in galectin-1-induced T-cell death

Abstract

Galectin-1 (gal-1), an endogenous β-galactoside-binding protein, triggers T-cell death through several mechanisms including the death receptor and the mitochondrial apoptotic pathway. In this study we first show that gal-1 initiates the activation of c-Jun N-terminal kinase (JNK), mitogen-activated protein kinase kinase 4 (MKK4), and MKK7 as upstream JNK activators in Jurkat T cells. Inhibition of JNK activation with sphingomyelinase inhibitors (20 μM desipramine, 20 μM imipramine), with the protein kinase C-δ (PKCδ) inhibitor rottlerin (10 μM), and with the specific PKCθ pseudosubstrate inhibitor (30 μM) indicates that ceramide and phosphorylation by PKCδ and PKCθ mediate gal-1-induced JNK activation. Downstream of JNK, we observed increased phosphorylation of c-Jun, enhanced activating protein-1 (AP-1) luciferase reporter, and AP-1/DNA-binding in response to gal-1. The pivotal role of the JNK/c-Jun/AP-1 pathway for gal-1-induced apoptosis was documented by reduction of DNA fragmentation after inhibition JNK by SP600125 (20 μM) or inhibition of AP-1 activation by curcumin (2 μM). Gal-1 failed to induce AP-1 activation and DNA fragmentation in CD3-deficient Jurkat 31-13 cells. In Jurkat E6.1 cells gal-1 induced a proapoptotic signal pattern as indicated by decreased antiapoptotic Bcl-2 expression, induction of proapoptotic Bad, and increased Bcl-2 phosphorylation. The results provide evidence that the JNK/c-Jun/AP-1 pathway plays a key role for T-cell death regulation in response to gal-1 stimulation.

The Involvement of CD146 and Its Novel Ligand Galectin-1 in Apoptotic Regulation of Endothelial Cells

“…Finally, it has been previously shown that endothelial cells secrete Galectin-1 upon inflammatory conditions (34). Moreover, Galectin-1 can induce apoptosis of T lymphocytes and can regulate bcl-2 expression (35,36). Along the same line, CD146 expression is both up-regulated at the membrane and secreted after TNF␣ treatment (12), and its overexpression leads to activation of survival and anti-apoptotic pathways (37).…”

Impact of Exogenous Galectin-9 on Human T Cells

“…In sharp contrast with our findings about gal-9, several of these studies pointed out some kind of interdependence between T cell activation and apoptosis induction. For example, Brandt et al (59) reported apoptosis induction in Jurkat cells treated with galectin-1 requiring an intact TCR-CD3 complex. It is important to notice that in the study of Brandt et al (59), the concentrations of galectin-1 were in the range of 600 -1800 nM instead of about 30 nM gal-9 in our own work.…”

Glycobiology of cell death: when glycans and lectins govern cell fate

“…41 Mechanistically, this lectin triggers endonuclease G nuclear translocation, 42 p56/Lck tyrosine phosphorylation 43 and activator protein-1 activation. 44,45 Moreover, galectin-1 stimulates the release of ceramide and promotes c-Jun N-terminal kinase (JNK) activation. As a result, Bcl-2 accumulation is condensed and Bcl-2 phosphorylation is elevated, generating heterodimerization with the proapoptotic protein Bax.…”

“…These molecular events lead to caspase-3 and -9 activation resulting in T-cell death. 45 Expression of core-2 O-glycans (Galb1-3 [N-acetyl glucosamine] b1-6 GalNAc) on the surface of T cells allows clustering of CD45, which facilitates galectin-1-induced apoptosis. 46 The absence of this glycan and particularly the presence of a2-6-linked sialic acid on CD45 N-glycans counteract inhibition of CD45 tyrosine phosphatase activity, which is an essential step in galectin-1-induced cell death.…”