Multi-functional protein, involved in both the cellular response to amino acid availability and in the regulation of glycolysis (PubMed:17028174, PubMed:18663353, PubMed:21209915, PubMed:24081491, PubMed:24095279, PubMed:31672913, PubMed:31704029, PubMed:32612235, PubMed:34381247, PubMed:36103527, PubMed:37079666). GTPase-activating protein that plays a key role in the cellular response to amino acid availability through regulation of the non-canonical mTORC1 signaling cascade controlling the MiT/TFE factors TFEB and TFE3 (PubMed:17028174, PubMed:18663353, PubMed:21209915, PubMed:24081491, PubMed:24095279, PubMed:24448649, PubMed:31672913, PubMed:31704029, PubMed:32612235, PubMed:36103527, PubMed:37079666). Activates mTORC1 by acting as a GTPase-activating protein: specifically stimulates GTP hydrolysis by RagC/RRAGC or RagD/RRAGD, promoting the conversion to the GDP-bound state of RagC/RRAGC or RagD/RRAGD, and thereby activating the kinase activity of mTORC1 (PubMed:24095279, PubMed:31672913, PubMed:31704029, PubMed:32612235, PubMed:37079666).

The GTPase-activating activity is inhibited during starvation and activated in presence of nutrients (PubMed:31672913, PubMed:32612235). Acts as a key component for non-canonical mTORC1-dependent control of the MiT/TFE factors TFEB and TFE3, while it is not involved in mTORC1-dependent phosphorylation of canonical RPS6KB1/S6K1 and EIF4EBP1/4E-BP1 (PubMed:21209915, PubMed:24081491, PubMed:31672913, PubMed:32612235). In low-amino acid conditions, the lysosomal folliculin complex (LFC) is formed on the membrane of lysosomes, which inhibits the GTPase-activating activity of FLCN, inactivates mTORC1 and maximizes nuclear translocation of TFEB and TFE3 (PubMed:31672913).

Upon amino acid restimulation, RagA/RRAGA (or RagB/RRAGB) nucleotide exchange promotes disassembly of the LFC complex and liberates the GTPase-activating activity of FLCN, leading to activation of mTORC1 and subsequent cytoplasmic retention of TFEB and TFE3 (PubMed:31672913). Indirectly acts as a positive regulator of Wnt signaling by promoting mTOR-dependent cytoplasmic retention of MiT/TFE factor TFE3 (PubMed:31272105). Required for the exit of hematopoietic stem cell from pluripotency by promoting mTOR-dependent cytoplasmic retention of TFE3, thereby increasing Wnt signaling (PubMed:30733432).

Acts as an inhibitor of browning of adipose tissue by regulating mTOR-dependent cytoplasmic retention of TFE3 (By similarity). Involved in the control of embryonic stem cells differentiation; together with LAMTOR1 it is necessary to recruit and activate RagC/RRAGC and RagD/RRAGD at the lysosomes, and to induce exit of embryonic stem cells from pluripotency via non-canonical, mTOR-independent TFE3 inactivation (By similarity). In response to flow stress, regulates STK11/LKB1 accumulation and mTORC1 activation through primary cilia: may act by recruiting STK11/LKB1 to primary cilia for activation of AMPK resided at basal bodies, causing mTORC1 down-regulation (PubMed:27072130).

Together with FNIP1 and/or FNIP2, regulates autophagy: following phosphorylation by ULK1, interacts with GABARAP and promotes autophagy (PubMed:25126726). Required for starvation-induced perinuclear clustering of lysosomes by promoting association of RILP with its effector RAB34 (PubMed:27113757). Regulates glycolysis by binding to lactate dehydrogenase LDHA, acting as an uncompetitive inhibitor (PubMed:34381247)

Interacts (via C-terminus) with FNIP1 or FNIP2 (via C-terminus) (PubMed:17028174, PubMed:18403135, PubMed:18663353, PubMed:27353360, PubMed:36103527). Component of the lysosomal folliculin complex (LFC), composed of FLCN, FNIP1 (or FNIP2), RagA/RRAGA or RagB/RRAGB GDP-bound, RagC/RRAGC or RagD/RRAGD GTP-bound, and Ragulator (PubMed:31672913, PubMed:31704029, PubMed:36103527). Interaction with FNIP1 or FNIP2 mediates indirect interaction with the PRKAA1, PRKAB1 and PRKAG1 subunits of 5'-AMP-activated protein kinase (AMPK) (PubMed:17028174).

Interacts with HSP90AA1 in the presence of FNIP1 (PubMed:27353360). Interacts with HSP70, STUB1, CDC37, AHSA1, CCT2, STIP1, PTGES3 and PPP5C (PubMed:27353360). Interacts with GABARAP; interaction takes place in the presence of FNIP1 and/or FNIP2 (PubMed:25126726).

Interacts with RILP; the interaction is direct and promotes association between RILP and RAB34 (PubMed:27113757). Interacts with KIF3A and KIF3B (PubMed:27072130). Interacts with lactate dehydrogenase LDHA, but not LDHB; the interaction is direct, may preferentially bind LDHA dimers rather than tetramers, and regulates LDHA activity, acting as an uncompetitive inhibitor (PubMed:34381247)

Expressed in most tissues tested, including skin, lung, kidney, heart, testis and stomach

• Birt-Hogg-Dube syndrome 1 (BHD1)

  A form of Birt-Hogg-Dube syndrome, a rare genodermatosis usually manifesting in adulthood and characterized by multiple fibrofolliculomas, trichodiscomas, and acrochordons. Patients with this syndrome have an increased susceptibility to develop renal cell carcinoma, lung cysts, and spontaneous pneumothorax. Inheritance is autosomal dominant.

• Primary spontaneous pneumothorax (PSP)

  Condition in which air is present in the pleural space in the absence of a precipitating event, such as trauma or lung disease. This results in secondary collapse of the lung, either partially or completely, and some degree of hypoxia. PSP is relatively common, with an incidence between 7.4-18/100'000 for men and 1.2-6/100'000 for women and a dose-dependent, increased risk among smokers.

  Most cases are sporadic, typically occurring in tall, thin men aged 10-30 years and generally while at rest. Familial PSP is rarer and usually is inherited as an autosomal dominant condition with reduced penetrance, although X-linked recessive and autosomal recessive inheritance have also been suggested.

• Renal cell carcinoma (RCC)

  Renal cell carcinoma is a heterogeneous group of sporadic or hereditary carcinoma derived from cells of the proximal renal tubular epithelium. It is subclassified into clear cell renal carcinoma (non-papillary carcinoma), papillary renal cell carcinoma, chromophobe renal cell carcinoma, collecting duct carcinoma with medullary carcinoma of the kidney, and unclassified renal cell carcinoma. Clear cell renal cell carcinoma is the most common subtype.