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-霍格-多布综合征（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、囊性肺疾病与肾肿瘤为典型特征。受累个体携带卵泡蛋白（Folliculin，FLCN）的杂合突变，该基因作为肿瘤抑制基因，可在肾肿瘤中通过二次打击突变发生双等位基因失活。与其他参与肾脏恶性肿瘤发生的因子类似，卵泡蛋白已被证实可调控雷帕霉素靶蛋白（mammalian target of rapamycin，mTOR）的激活过程。然而，由于在动物模型中生殖系敲除Flcn会导致早期胚胎致死，其在体内的确切生理功能目前仍未明确。本研究报道了靶向新鉴定的卵泡蛋白互作蛋白1（Folliculin-Interacting Protein 1，Fnip1）的敲除小鼠模型。与Flcn敲除小鼠不同，Fnip1-/-小鼠可正常发育，且不会易患肾肿瘤，但会出现显著的前B细胞阻滞表型，且该阻滞过程不依赖于mTOR活性。研究表明，这一发育停滞至少部分源于受损的V(D)J重排及半胱天冬酶介导的细胞死亡；预重排V(D)J元件与Bcl2转基因可分别重建前B细胞与成熟B细胞群体。此外，本研究证实Flcn的条件性敲除可重现Fnip1-/-小鼠的前B细胞阻滞表型。综上，本研究证明，在BHD综合征中失调的FLCN-Fnip复合物是B细胞分化所必需的，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亚群与CC'亚群）的RNA测序（RNASeq）数据。