GPR174 signals via Gαs to control a CD86-containing gene expression program in B cells [0h and 4h culture]

GPR174 is abundantly expressed in B and T lymphocytes and has a role in restraining T cell responses, but the function of GPR174 in B cells is less clear. Here we report that upon in vitro culture B cells undergo a spontaneous GPR174-dependent activation process that is associated with marked changes in gene expression, including upregulation of Cd86, Nr4a1, Ccr7 and phosphodiesterases. B cells lacking Gas show a block in induction of the GPR174-dependent program. Spontaneous upregulation of CD86 in cultured B cells is dependent on protein kinase A. Both GPR174- and Gas-deficient B cells show enhanced survival in culture. In vivo, GPR174 contributes to NUR77 expression in follicular B cells and is needed for establishing a marginal zone compartment of normal size. Treatment of mice with lysophosphatidylserine (lysoPS), a GPR174 ligand, is sufficient to promote CD86 upregulation by follicular B cells. These findings demonstrate that GPR174 can signal via Gas to modulate B cell gene expression and show this can occur in vivo in response to lysoPS. Additionally, the findings illuminate a pathway that might be targeted to improve systems for the in vitro study of B cell responses. Follicular B cells were isolated from adult mice (N=3 per genotype) for RNA-seq either immediately post-sort or following 1 or 4 hours of culture in complete RPMI 1640 (containing 10% FBS, 10 mM HEPES, 55 µM 2-mercaptoethanol, 2 mM glutamine and 50 IU penicillin/streptomycin)

GPR174在B淋巴细胞与T淋巴细胞中高丰度表达，对T细胞应答具有抑制作用，但其在B细胞中的功能尚不明晰。
本研究发现，体外培养条件下，B细胞会发生依赖GPR174的自发性活化过程，该过程伴随基因表达的显著改变，包括Cd86、Nr4a1、Ccr7与磷酸二酯酶的上调。缺失Gas的B细胞无法诱导GPR174依赖的基因表达程序。培养的B细胞中CD86的自发上调依赖于蛋白激酶A。GPR174缺陷与Gas缺陷的B细胞在培养过程中均表现出存活能力增强。
在体内环境中，GPR174可促进滤泡B细胞中NUR77的表达，且对维持正常大小的边缘区B细胞区室不可或缺。以溶血磷脂酰丝氨酸（lysophosphatidylserine，lysoPS）——一种GPR174配体——处理小鼠，即可诱导滤泡B细胞上调CD86。
本研究结果证实，GPR174可通过Gas信号通路调控B细胞的基因表达，且该调控效应可在体内响应lysoPS时发生。
此外，本研究揭示了一条可用于优化体外B细胞应答研究体系的潜在靶向通路。
研究人员从成年小鼠中分离滤泡B细胞（每个基因型n=3），分别在分选后即刻，或于完全RPMI 1640培养基（含10%胎牛血清（FBS）、10 mM羟乙基哌嗪乙硫磺酸（HEPES）、55 μM 2-巯基乙醇、2 mM谷氨酰胺以及50 IU青霉素/链霉素）中培养1小时或4小时后，进行RNA测序（RNA-seq）。