TY - JOUR
T1 - LUBAC Suppresses IL-21-Induced Apoptosis in CD40-Activated Murine B Cells and Promotes Germinal Center B Cell Survival and the T-Dependent Antibody Response
AU - Wang, Jingwei
AU - Li, Tianbao
AU - Zan, Hong
AU - Rivera, Carlos E.
AU - Yan, Hui
AU - Xu, Zhenming
N1 - Funding Information:
This work was supported by NIH AI 124172, AI 131034, AI 135599, AI 153506, and DOD BC170448 grants. The UTHSCSA Flow Cytometry Core facility is supported by NIH P30 CA054174 and UL1 TR001120, and Genome Sequencing Facility supported by NIH P30 CA054174, S10 OD021805, and CPRIT Core RP160732 grants.
Publisher Copyright:
© Copyright © 2021 Wang, Li, Zan, Rivera, Yan and Xu.
PY - 2021/4/19
Y1 - 2021/4/19
N2 - B cell activation by Tfh cells, i.e., through CD154 engagement of CD40 and IL-21, and survival within GCs are crucial for the T-dependent Ab response. LUBAC, composed of HOIP, SHARPIN, and HOIL-1, catalyzes linear ubiquitination (Linear M1-Ub) to mediate NF-κB activation and cell survival induced by TNF receptor superfamily members, which include CD40. As shown in this study, B cells expressing the Sharpin null mutation cpdm (Sharpincpdm) could undergo proliferation, CSR, and SHM in response to immunization by a T-dependent Ag, but were defective in survival within GCs, enrichment of a mutation enhancing the BCR affinity, and production of specific Abs. Sharpincpdm B cells stimulated in vitro with CD154 displayed normal proliferation and differentiation, marginally impaired NF-κB activation and survival, but markedly exacerbated death triggered by IL-21. While activating the mitochondria-dependent apoptosis pathway in both Sharpin+/+ and Sharpincpdm B cells, IL-21 induced Sharpincpdm B cells to undergo sustained activation of caspase 9 and caspase 8 of the mitochondria-dependent and independent pathway, respectively, and ultimately caspase 3 in effecting apoptosis. These were associated with loss of the caspase 8 inhibitor cFLIP and reduction in cFLIP Linear M1-Ub, which interferes with cFLIP poly-ubiquitination at Lys48 and degradation. Finally, the viability of Sharpincpdm B cells was rescued by caspase inhibitors but virtually abrogated – together with Linear M1-Ub and cFLIP levels – by a small molecule HOIP inhibitor. Thus, LUBAC controls the cFLIP expression and inhibits the effects of caspase 8 and IL-21-activated caspase 9, thereby suppressing apoptosis of CD40 and IL-21-activated B cells and promoting GC B cell survival.
AB - B cell activation by Tfh cells, i.e., through CD154 engagement of CD40 and IL-21, and survival within GCs are crucial for the T-dependent Ab response. LUBAC, composed of HOIP, SHARPIN, and HOIL-1, catalyzes linear ubiquitination (Linear M1-Ub) to mediate NF-κB activation and cell survival induced by TNF receptor superfamily members, which include CD40. As shown in this study, B cells expressing the Sharpin null mutation cpdm (Sharpincpdm) could undergo proliferation, CSR, and SHM in response to immunization by a T-dependent Ag, but were defective in survival within GCs, enrichment of a mutation enhancing the BCR affinity, and production of specific Abs. Sharpincpdm B cells stimulated in vitro with CD154 displayed normal proliferation and differentiation, marginally impaired NF-κB activation and survival, but markedly exacerbated death triggered by IL-21. While activating the mitochondria-dependent apoptosis pathway in both Sharpin+/+ and Sharpincpdm B cells, IL-21 induced Sharpincpdm B cells to undergo sustained activation of caspase 9 and caspase 8 of the mitochondria-dependent and independent pathway, respectively, and ultimately caspase 3 in effecting apoptosis. These were associated with loss of the caspase 8 inhibitor cFLIP and reduction in cFLIP Linear M1-Ub, which interferes with cFLIP poly-ubiquitination at Lys48 and degradation. Finally, the viability of Sharpincpdm B cells was rescued by caspase inhibitors but virtually abrogated – together with Linear M1-Ub and cFLIP levels – by a small molecule HOIP inhibitor. Thus, LUBAC controls the cFLIP expression and inhibits the effects of caspase 8 and IL-21-activated caspase 9, thereby suppressing apoptosis of CD40 and IL-21-activated B cells and promoting GC B cell survival.
KW - IL-21
KW - SHARPIN
KW - affinity maturation
KW - apoptosis
KW - cFLIP
KW - germinal center B cells
KW - linear ubiquitination
KW - positive selection
UR - http://www.scopus.com/inward/record.url?scp=85105181016&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85105181016&partnerID=8YFLogxK
U2 - 10.3389/fimmu.2021.658048
DO - 10.3389/fimmu.2021.658048
M3 - Article
C2 - 33953720
AN - SCOPUS:85105181016
SN - 1664-3224
VL - 12
JO - Frontiers in immunology
JF - Frontiers in immunology
M1 - 658048
ER -