Project description:It is important to understand how cells can maintain and exit human pluripotency. We exploited the metabolic and epigenetic differences between naïve and primed pluripotent cells to design a CRISPR-Cas9 screen for identifying genes that promote the exit from naïve pluripotency. Among the known and novel regulators of this early step of human development, we identified the tumor suppressor folliculin (FLCN). Flcn is important for implantation of the mouse embryo into the uterus and has been shown to regulate the exit of pluripotency in mouse through activation of Esrrb. However, the function of FLCN is unknown in human embryonic stem cells (hESC). Knock-out (KO) of FLCN revealed that it is not essential to maintain the naïve pluripotent state but is required for the exit of that state, in part by controlling the localization of the transcription factor TFE3. While mainly found in the cytoplasm of cells exiting the naïve state, FLCN KO resulted in TFE3 nuclear localization. TFE3 targets up-regulated in FLCN KO exit assay were members of Wnt pathway and ESRRB. Treatment of FLCN KO hESC with a Wnt inhibitor rescued the phenotype and allowed the cells to exit the naïve state. In contrast, the lack of rescue in ESRRB/FLCN double KO lines suggested that ESRRB was not responsible for the FLCN mutant phenotype. Using co-immunoprecipitation and mass spectrometry analysis we identified unique FLCN binding partners, in addition to known FLCN interactors, at various stages of pluripotency. The interactions of FLCN with components of the mTOR pathway (mTORC1 and mTORC2) revealed a mechanism of FLCN function during exit from naïve pluripotency.
Project description: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
Project description:Growing tumors exist in metabolically compromised environments that require activation of multiple pathways to scavenge nutrients to support accelerated rates of growth. The FLCN tumor suppressor complex (FLCN, FNIP1, FNIP2) has been implicated in the regulation of energy homeostasis via two metabolic master kinases: AMPK and mTORC1. Loss-of-function mutations of the FLCN tumor suppressor complex have only been reported in renal tumors in patients with the rare Birt-Hogg-Dube syndrome. Here we reveal that FLCN, FNIP1, and FNIP2 are downregulated in many human cancers including poor prognosis invasive basal-like breast carcinomas where AMPK and TFE3 targets are activated compared to the luminal, less aggressive subtypes. We show that FLCN loss in luminal subtypes promotes tumor growth through TFE3 activation and subsequent induction of several pathways including autophagy, lysosomal biogenesis, aerobic glycolysis, and angiogenesis. Strikingly, induction of aerobic glycolysis and angiogenesis in FLCN deficient cells was dictated by the activation of PGC-1⍺/HIF-1⍺ pathway, which we show to be TFE3-dependent, directly linking TFE3 to Warburg metabolic reprogramming and angiogenesis. Thus, FLCN loss induces TFE3-dependent breast tumor growth through activation of multiple mechanisms, including previously unreported roles in aerobic glycolysis and angiogenesis. These findings could point to a general role of a deregulated FLCN/TFE3 tumor suppressor pathway in human cancers.
Project description:Using co-immunoprecipitation and mass spectrometry analysis we identify unique FLCN binding partners. The interactions of FLCN with components of the mTOR pathway (mTORC1 and mTORC2) reveal a mechanism of FLCN function during exit from naïve pluripotency.
Project description: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.
Project description:Renal tumors that arise in individuals with BHD Syndrome represent a molecularly distinct form of renal cancer. In addition, BHD syndrome is due to a mutation the folliculin gene (FLCN). While the folliculin gene is an important tumor suppressor gene, the molecular function of this gene is not well defined. By analyzing tumor samples that contain FLCN mutations, we demonstrate that the FLCN gene is an important regulator of mitochondrial function. Gene expression profiling of BHDS tumors and normal kidney tissues
Project description:Renal tumors that arise in individuals with BHD Syndrome represent a molecularly distinct form of renal cancer. In addition, BHD syndrome is due to a mutation the folliculin gene (FLCN). While the folliculin gene is an important tumor suppressor gene, the molecular function of this gene is not well defined. By analyzing tumor samples that contain FLCN mutations, we demonstrate that the FLCN gene is an important regulator of mitochondrial function.
Project description:The “Warburg effect” describes the use of aerobic glycolysis by cancer cells to fuel their growth. Lactate dehydrogenase-A (LDHA) is key to this process and catalyzes the interconversion of pyruvate and lactate. Here we used a proteomic approach to identify LDHA as a binding partner of the tumor suppressor FLCN. Canonically, LDHA is thought to be a substrate-regulated enzyme, however our data show that FLCN uncompetitively inhibits LDHA activity by restricting movement of its active site loop. This inhibition appears to be critical in normal cells, as we show FLCN binds to and tightly regulates LDHA activity in order to preserve metabolic homeostasis. Pathogenic mutations of FLCN are associated with LDHA hyperactivity and kidney tumor formation, suggesting a mechanism for FLCN tumor suppressive function. We have identified a cell-permeant ten amino acid peptide based on the FLCN sequence that enters these tumors and inhibits LDHA ex vivo. In a broader context, renal cell carcinomas experience the Warburg effect and show FLCN dissociation from LDHA. Cells that experience this metabolic shift depend on the hyperactivity of LDHA, as previous work has shown attenuation or inhibition of LDHA leads to programmed cell death. Treating these cells with the FLCN-derived peptide causes apoptosis, strongly suggesting that the glycolytic shift of cancer cells is the result of FLCN inactivation or disassociation from LDHA. Taken together, FLCN-mediated inhibition of LDHA provides a new paradigm for the regulation of glycolysis.
Project description:Birt-Hogg-Dubé syndrome is an autosomal dominantly inherited disorder that is characterized by the clinical triad of benign skin tumors - so-called fibrofolliculomas, recurrent pneumothoraces due to pulmonary cysts and the formation of kidney tumors. The molecular function of Folliculin (FLCN), the protein product of the BHD gene mutated in this syndrome, has remained elusive to a large extent. Animal models such as mouse, rat and canine models have been used to elucidate parts of the pathway in which FLCN plays a role showing it to interfere with AMP-kinase and mTOR signaling. Caenorhabditis elegans provides - due to its simple genetic amenability and large brood size - the perfect tool to study signal transduction pathways in detail. Thus, we decided to examine F22D3.2 (flcn-1) - a putative orthologue of FLCN in the nematode. We established the first gene expression profiles of a strain harboring a mutation in flcn-1 compared to WTN2 allowing for a first insight into the function of this gene in C. elegans. This study examines the transcriptome of the flcn-1 mutant strain RB1035 in comparison to WTN2 in order to identify differentially regulated genes. RNA was prepared from pre-reproductive adults in both WTN2 and RB1035 (harboring a flcn-1 mutant allele, mutant worms had been backcrossed wo WTN2 8 times) using biological triplicates. RNA was labeled and hybridized to Agilent C. elegans whole genome microarrays and scanned using a Agilent Technologies Scanner G2505C US22502540.
Project description:The bHLH transcription factor Tfe3 is a powerful regulator of pluripotency and we report a genome-wide analysis of Tfe3 occupancy in mouse ES cells. Nuclear localization of Tfe3 is inhibited by a protein complex containing the tumor-suppressor Folliculin (Flcn) and we also determine Tfe3 binding sites in ES cells expressing an shRNA targeting Flcn. Specificity is controlled for by using unspecific IgGs and ES cells expressing an shRNA targeting Tfe3. ChIP-Seq profiling of Tfe3 in ES cells