ABSTRACT
The TNF superfamily ligands APRIL and BAFF bind with different affinity to two receptors, BCMA and TACI, and induce cell survival and/or proliferation, whereas BAFF also binds specifically to BAFFR. These molecules were considered specific for the immune system. Recently, however, they were also found in epithelial and mesenchymal noncancerous and cancerous tissues and cell lines. In this article, we report that hepatocellular carcinoma (HCC) cell lines HepG2 and Hep3B and HCC specimens express APRIL and BAFF and their receptors BCMA and BAFFR, but not TACI; APRIL/BCMA is enhanced in HCC, compared with normal liver tissue. In contrast to previous reports, APRIL binding to BCMA decreases cell proliferation by inducing G(2)/M cell cycle arrest, whereas BAFF has no effect on cell growth. HCC cells therefore represent a rare system in which these two ligands (APRIL and BAFF) exert a differential effect and may serve as a model for specific APRIL/BCMA actions. We show that the effect of APRIL is mediated via BCMA, which does not activate the classical NF-κB pathway, whereas it induces a novel signaling pathway, which involves JNK2 phosphorylation, FOXO3A activation, and GADD45 transcription. In addition, JNK2 mediates the phosphorylation of Akt, which is activated but does not participate in the antiproliferative effect of APRIL. Furthermore, transcriptome analysis revealed that APRIL modifies genes specifically related to cell cycle modulation, including MCM2/4/5/6, CDC6, PCNA, and POLE2. Our data, therefore, identify a novel APRIL/BCMA signaling pathway in HCC and suggest that APRIL could have a pleiotropic role in tumor biology.
Subject(s)
B-Cell Maturation Antigen/immunology , Cell Cycle Proteins/immunology , DNA-Binding Proteins/immunology , Forkhead Transcription Factors/immunology , G2 Phase Cell Cycle Checkpoints/immunology , Liver/immunology , M Phase Cell Cycle Checkpoints/immunology , MAP Kinase Kinase 7/immunology , Nuclear Proteins/immunology , Transcription Factors/immunology , B-Cell Activating Factor/genetics , B-Cell Activating Factor/immunology , B-Cell Activating Factor/metabolism , B-Cell Maturation Antigen/genetics , B-Cell Maturation Antigen/metabolism , Cell Cycle Proteins/genetics , Cell Cycle Proteins/metabolism , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , Forkhead Box Protein O3 , Forkhead Transcription Factors/genetics , Forkhead Transcription Factors/metabolism , G2 Phase Cell Cycle Checkpoints/genetics , Hep G2 Cells , Humans , Liver/cytology , M Phase Cell Cycle Checkpoints/genetics , MAP Kinase Kinase 7/genetics , MAP Kinase Kinase 7/metabolism , Nuclear Proteins/genetics , Nuclear Proteins/metabolism , Phosphorylation/genetics , Phosphorylation/immunology , Proliferating Cell Nuclear Antigen/genetics , Proliferating Cell Nuclear Antigen/immunology , Proliferating Cell Nuclear Antigen/metabolism , Protein Binding , Transcription Factors/genetics , Transcription Factors/metabolism , Transcription, Genetic/genetics , Transcription, Genetic/immunologyABSTRACT
Naturally occurring Foxp3(+)CD4(+)CD25(+) T regulatory cell (nTreg)-mediated suppression of lung allergic responses is abrogated following ligation of glucocorticoid-induced tumor necrosis receptor (GITR) family-related protein. In vitro stimulation of nTregs with GITR ligand increased phosphorylation of c-Jun N-terminal kinase (JNK) but not extracellular signal-regulated protein kinase (ERK) or p38 MAPK. SP600125, a known JNK inhibitor, prevented GITR-mediated phosphorylation of JNK. Activation of JNK was associated with increases in the upstream mitogen-activated protein kinase kinase 7 (MKK7) and the downstream transcription factor NF-κß. Phosphorylated c-Jun (p-c-Jun), indicative of the activation of JNK, was detected in the immunoprecipitates of nTregs from wild-type but not JNK- or GITR-deficient mice. Treatment with an inhibitor of JNK phosphorylation resulted in complete reversal of all GITR-induced changes in nTreg phenotype and function, with full restoration of suppression of in vivo lung allergic responses and in vitro proliferation of activated CD4(+)CD25(-) T cells. Thus, regulation of JNK phosphorylation plays a central role in T regulatory cell function with therapeutic implications for the treatment of asthma and autoimmune diseases.
