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B Cell Development sans B Cell Receptor Responsiveness Due to Unfolded Protein Response-Triggered Mef2c Protein Degradation.

Authors :
Yi-Ting Chen
Yu-Chia Su
Kung, John T.
Source :
Journal of Immunology. 11/15/2018, Vol. 201 Issue 10, p2885-2898. 14p.
Publication Year :
2018

Abstract

BCR engagement leads to activation and clonal expansion of B cells. The I-A12% mutant mouse possesses a branch site point mutation in the H2-Aa gene that causes highly reduced I-Aa protein expression. As I-A is a heterodimer made up of I-Aa and I-Ab, reduced I-Aa results not only in reduced surface I-A expression but also in an excess of unpaired I-Ab. B cells that develop in I-A12% mice proliferated in response to LPS stimulation but failed to do so upon BCR stimulation. Developing I-A12% B cells were engaged in unfolded protein response due to an excess of unpaired I-Ab. BCR responsiveness was restored by transduced I-Aa expression and by BiP, the unfolded protein response sensor. Reducing the load of unpaired I-Ab also restored BCR responsiveness of I-A12% B cells. Mef2c protein, a transcription factor required for BCR-stimulated proliferation, was missing in I-A12% B cells, and that transduced Mef2c expression restored BCR responsiveness. Mef2c protein appeared in I-A12% B cells after addition of proteasome inhibitors. Mef2c degradation was mediated by Skp2 E3 ligase, and that knockdown of Skp2 mRNA in I-A12% B cells restored BCR responsiveness. Our results point to a generalized incompatibility between BCR responsiveness and increased Skp2 stability. They also imply the existence of regulatory mechanisms other than Ig gene rearrangement that govern Mef2c turnover in a specific, exquisite, and dynamic fashion. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
00221767
Volume :
201
Issue :
10
Database :
Academic Search Index
Journal :
Journal of Immunology
Publication Type :
Academic Journal
Accession number :
132884625
Full Text :
https://doi.org/10.4049/jimmunol.1800685