mTORC1 feedback to AKT modulates lysosomal biogenesis through MiT/TFE regulation
Kaushal Asrani, … , Michael Skaro, Tamara L. Lotan
Kaushal Asrani, … , Michael Skaro, Tamara L. Lotan
Published December 2, 2019; First published September 17, 2019
Citation Information: J Clin Invest. 2019;129(12):5584-5599. https://doi.org/10.1172/JCI128287.
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Categories: Research Article Metabolism Oncology

mTORC1 feedback to AKT modulates lysosomal biogenesis through MiT/TFE regulation

Abstract

The microphthalmia family of transcription factors (MiT/TFEs) controls lysosomal biogenesis and is negatively regulated by the nutrient sensor mTORC1. However, the mechanisms by which cells with constitutive mTORC1 signaling maintain lysosomal catabolism remain to be elucidated. Using the murine epidermis as a model system, we found that epidermal Tsc1 deletion resulted in a phenotype characterized by wavy hair and curly whiskers, and was associated with increased EGFR and HER2 degradation. Unexpectedly, constitutive mTORC1 activation with Tsc1 loss increased lysosomal content via upregulated expression and activity of MiT/TFEs, whereas genetic deletion of Rheb or Rptor or prolonged pharmacologic mTORC1 inactivation had the reverse effect. This paradoxical increase in lysosomal biogenesis by mTORC1 was mediated by feedback inhibition of AKT, and a resulting suppression of AKT-induced MiT/TFE downregulation. Thus, inhibiting hyperactive AKT signaling in the context of mTORC1 loss-of-function fully restored MiT/TFE expression and activity. These data suggest that signaling feedback loops work to restrain or maintain cellular lysosomal content during chronically inhibited or constitutively active mTORC1 signaling, respectively, and reveal a mechanism by which mTORC1 regulates upstream receptor tyrosine kinase signaling.

Authors

Kaushal Asrani, Sanjana Murali, Brandon Lam, Chan-Hyun Na, Pornima Phatak, Akshay Sood, Harsimar Kaur, Zoya Khan, Michaël Noë, Ravi K. Anchoori, C. Conover Talbot Jr., Barbara Smith, Michael Skaro, Tamara L. Lotan

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Figure 5

mTORC1 activates lysosomal gene expression.

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mTORC1 activates lysosomal gene expression. (A) qRT-PCR showing upregula...
(A) qRT-PCR showing upregulation of lysosomal CLEAR target gene transcripts in Tsc1-cre keratinocytes compared with empty controls (r = 4, error bars represent SEM; P values are by Student’s t test). Expression of lysosomal CLEAR gene targets is increased in Tsc1-cKO epidermis (B) and Tsc1-cKO keratinocytes (C), compared with WT controls, by immunoblot analyses. (D) Expression of lysosomal proteins is increased in Tsc1-cKO keratinocytes compared with empty controls, and is downregulated in response to Torin1 (1 μM, 24 hours), by immunoblot analyses. Ctsb, LAMP1, and Ctsd were immunoblotted separately using a different biological replicate. (E) Immunostaining for Ctsb and LAMP1 showing expansion of the lysosomal compartment in basal keratinocytes of Tsc1-cKO epidermis compared with WT controls; white lines demarcate dermal-epidermal junction. Scale bar: 150 μm. (F) Tsc1-cre keratinocytes treated with the lysosomal V-ATPase inhibitor Bafilomycin A1 (100 nm)rescued EGFR expression in a time-dependent manner.