Antigen (Ag)-driven B cells undergo antibody (Ab) affinity maturation and class switching in germinal center (GC) B cells. GANP is one of the molecules required for Ab affinity maturation. We herein found an increase of IgE in B cell ganp-deficient mice and studied the signal transduction pathway regulated by GANP. GANP suppresses the STAT-mediated transcription activity in GC B cells with the regulation of arginine methyltransferase activity by the interaction with JAK-binding protein arginine methyltransferase (PRMT) 5 and JAK1/JAK3 that are responsible for STAT6 activation. The prmt5 mRNA was up-regulated in B cells after stimulation in vitro and in vivo in GC B cells. The loss of GANP caused up-regulation of phosphorylation and arginine dimethylation of STAT6 in B cells after stimulation with LPS and IL-4 in vitro. On the contrary, GANP over-expressed B cells in ganp gene-transgenic mice showed a low STAT6 phosphorylation after stimulation. The over-expression of PRMT5 caused the up-regulation of STAT6-mediated gene transcription, which was also suppressed by the co-transfection of GANP, in luciferase reporter assay. GANP down-regulates JAK1/JAK3 to STAT6-signaling with regulation of arginine methylation activity, which might be responsible for the B cell endogenous suppressive mechanism of hyper-IgE.
Bibliographical noteFunding Information:
We thank Drs. N. Araki and A. Irie (Kumamoto University) for their help to determine the amino acid sequence. We also acknowledge technical assistance by H. Nizato and Y. Kawasho, and secretary help of F. Higashi. This work was supported by Special Coordination Funds for Promoting Science and Technology from the Ministry of Education, Culture, Sports, Science, and Technology of Japan, by the grant from Core Research for Evolutional Science and Technology (CREST) of the Japan Science and Technology Agency (N.S.), and by JSPS KAKENHI 17590440 (H.I.). The authors have no conflicting financial interests.
- Arginine methylation
- GC B-cells