Nicola Alesi, MD, PhD - "Non canonical regulation of TFEB by mTORC1 underlies Tuberous Sclerosis Complex"

  • What seminar
  • When Sep 30, 2022 from 12:00 PM to 01:00 PM (Europe/Berlin / UTC200)
  • Where Tigem Auditorium Vesuvius
  • Contact Name
  • Contact Phone 08119230659
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Nicola Alesi, MD, PhD
Department of Medicine
Brigham and Women's Hospital,
Harvard Medical School,
Boston, MA, USA


Short CV

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 unexpectedly increased in TSC-associated pulmonary LAM, renal tumors, kidneys from Tsc2+/− mice, and TSC1/2-deficient cells via a TFEB-dependent mechanism. Importantly, TFEB knockout in a kidney-specific mouse model of TSC (KspCre; Tsc2fl/fl) almost completely abolishes kidney cyst formation and normalizes the kidney to body weight ratio (KspCre; Tsc2fl/fl Tfebfl/fl). In KspCre; Tsc2fl/fl mice average lifespan is 90-days, TFEB knockdown restores normal lifespan. Similarly, renal cystogenesis is almost completely abolished in an inducible total body mouse model of TSC (Cagg-CreERT2; Tsc2fl/fl) after TFEB knockdown (CreERT2; Tsc2fl/fl Tfebfl/fl). Interestingly, in this model also body weight is fixed by TFEB knockdown. RNA-sequencing performed in these mouse models identified the lysosome and the endosome pathways as the top 2 most upregulated pathways in Tsc2-null mouse kidneys. These effects of TFEB are unexpected, since in cells with hyperactive mTORC1 TFEB should be phosphorylated and sequestered in the cytoplasm. Instead, in TSC1/2-deficient cells, TFEB is hypo-phosphorylated at mTORC1-dependent sites (S142, S211), resulting in nuclear localization and hyperactivation. Importantly, overexpression of folliculin (FLCN), a GTPase activating protein for RAGC, increases TFEB phosphorylation at the mTORC1 sites in TSC2-deficient cells, suggesting a cooperation between TSC2 and FLCN in the regulation of TFEB. Moreover, overexpression of constitutively active RAGC is sufficient to relocalize TFEB to the cytoplasm, decreasing thereby the activity.

These findings establish the TSC proteins as critical regulators of lysosomal biogenesis via TFEB and RAGC and identify TFEB as a key factor in TSC pathogenesis independent of mTORC1 hyperactivation