The Folliculin-Fnip1 pathway deleted in human Birt-Hogg-Dube syndrome is required for B cell development.

Birt-Hogg-Dube (BHD) syndrome is an autosomal dominant disorder characterized by hamartomas of skin follicles, cystic lung disease, and renal neoplasia. Affected individuals carry heterozygous mutations in Folliculin (FLCN), a tumor suppressor gene that becomes biallelically inactivated in kidney tumors by second-hit mutations. Similar to other factors implicated in kidney malignancies, Folliculin has been shown to modulate activation of mammalian target of rapamycin (mTOR). However, its precise in vivo function is largely unknown because germline deletion of Flcn results in early embryonic lethality in animal models. We here describe mice deficient in the newly characterized Folliculin-Interacting Protein 1 (Fnip1). In contrast to Flcn, Fnip1-/- mice develop normally, are not susceptible to kidney neoplasia, but display a striking pro-B cell block that is independent of mTOR activity. We show that this developmental arrest results at least in part from impaired V(D)J recombination and caspase-induced cell death, and that pre-recombined V(D)J and Bcl2 transgenes reconstitute pre-B and mature B cell populations respectively. We also demonstrate that conditional deletion of Flcn recapitulates the pro-B cell arrest of Fnip1-/- mice. Our studies thus demonstrate that the Flcn-Fnip complex deregulated in BHD syndrome is absolutely required for B cell differentiation and that it functions both through mTOR dependent and independent pathways. RNASeq data for two pro-B cell subsets (fraction B and CC') isolated from wt and Fnip1-/- mice伯-霍-杜布综合征（Birt-Hogg-Dube syndrome，BHD）是一类常染色体显性遗传病，以皮肤毛囊错构瘤、囊性肺疾病及肾新生物形成为典型特征。受累个体携带卵泡蛋白（Folliculin，FLCN）的杂合突变，该基因为抑癌基因，在肾肿瘤中可通过二次打击突变发生双等位基因失活。与其他参与肾恶性肿瘤发生的因子类似，卵泡蛋白已被证实可调控哺乳动物雷帕霉素靶蛋白（mammalian target of rapamycin，mTOR）的激活，但其确切的体内功能目前仍在很大程度上尚不明确——因为在动物模型中生殖系敲除Flcn会导致早期胚胎致死。本研究报道了新鉴定的卵泡蛋白互作蛋白1（Folliculin-Interacting Protein 1，Fnip1）缺陷小鼠模型。与Flcn敲除小鼠不同，Fnip1全敲除（Fnip1-/-）小鼠发育正常，且未表现出肾肿瘤易感性，但呈现出显著的前B细胞发育阻滞，且该阻滞过程不依赖于mTOR活性。本研究证实，该发育阻滞至少部分源于受损的V(D)J重组与半胱天冬酶介导的细胞死亡；预重组V(D)J与Bcl2转基因可分别重建前B细胞与成熟B细胞群体。此外，本研究还证明，Flcn的条件性敲除可重现Fnip1-/-小鼠的前B细胞发育阻滞表型。综上，本研究表明，在BHD综合征中失调的FLCN-Fnip复合物对B细胞分化不可或缺，其功能同时通过mTOR依赖与非依赖通路发挥作用。本数据集包含从野生型（wild type，wt）与Fnip1-/-小鼠中分离得到的两种前B细胞亚群（B组分与CC'组分）的RNA测序（RNASeq）数据。