TSC2 regulates lysosome biogenesis via a non-canonical RAGC and TFEB-dependent mechanism

Abstract

Tuberous Sclerosis Complex (TSC) is caused by TSC1 or TSC2 mutations, resulting in hyperactivation of the mechanistic target of rapamycin complex 1 (mTORC1). Transcription factor EB (TFEB), a master regulator of lysosome biogenesis, is negatively regulated by mTORC1 through a RAG GTPase-dependent phosphorylation. Here we show that lysosomal biogenesis is increased in TSC-associated renal tumors, pulmonary lymphangioleiomyomatosis, kidneys from Tsc2+/− mice, and TSC1/2-deficient cells via a TFEB-dependent mechanism. Interestingly, in TSC1/2-deficient cells, TFEB is hypo-phosphorylated at mTORC1-dependent sites, indicating that mTORC1 is unable to phosphorylate TFEB in the absence of the TSC1/2 complex. Importantly, overexpression of folliculin (FLCN), a GTPase activating protein for RAGC, increases TFEB phosphorylation at the mTORC1 sites in TSC2-deficient cells. Overexpression of constitutively active RAGC is sufficient to relocalize TFEB to the cytoplasm. These findings establish the TSC proteins as critical regulators of lysosomal biogenesis via TFEB and RAGC and identify TFEB as a driver of the proliferation of TSC2-deficient cells.

The SZT2 Interactome Unravels New Functions of the KICSTOR Complex

“…A similar effect was seen in TSC1 deficient macrophages [58]. In contrast, a recent publication reported that renal tumors, lymphangioleiomyomatosis, and kidneys from TSC2 heterozygous mice display increased lysosomal biogenesis that occurs due to hypo-phosphorylation and nuclear translocation of TFEB [104]. In the SZT2 KOs we observed increased phosphorylation of TFEB, ruling out a contribution of this transcription factor.…”

A Compendium of Information on the Lysosome

“…As with mTORC1, TFEB is also recruited to the lysosome by RagC/D and this recruitment is dependent on the GTPase activating protein for RagC/D, Folliculin (FLCN) ( Martina and Puertollano, 2013 ; Petit et al, 2013 ). Non-canonically, mTORC1’s inhibitory phosphorylation of TFEB was demonstrated to also be dependent on the Tuberous Sclerosis Complex (TSC) 1 and 2 upstream of mTORC1 in pathogenic TSC models ( Alesi et al, 2021 ). The pathogenic phosphorylation of TFEB was also demonstrated to be RagC dependent.…”

Seventh BHD international symposium: recent scientific and clinical advancement

“…Dr Lisa Henske (Brigham and Women's Hospital, Harvard Medical School, USA) presented their work on upregulation of lysosomes and lysosomal genes in TSC1deficient and TSC2-deficient cells. The transcription factors TFEB and TFE3 are unexpectedly localized to the nucleus in TSC1-deficient and TSC2-deficient cells and in FLCN-deficient cells [25], where they regulate lysosomal biogenesis and cell proliferation. In agreement, the Ballabio group has recently shown that TFEB is responsible for renal cyst formation in a mouse model of BHD [27].…”