ATG conjugation-dependent/independent mechanisms underlie lysosomal stress-induced TFEB regulation

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Transcription Factor EB (TFEB) is a key regulator of autophagy and lysosomal biogenesis.
• TFEB activation is triggered by cellular stresses, including lysosomal damage, but its regulatory mechanisms remain incompletely understood.
• Existing knowledge links TFEB activation during lysosomal damage to the ATG conjugation system, which modifies ATG8 proteins.

Purpose of the Study:

• To elucidate the underlying mechanisms of TFEB activation during cellular stress.
• To identify novel regulators and pathways involved in TFEB regulation.
• To establish a unified understanding of TFEB regulatory mechanisms in response to various cellular stresses.

Main Methods:

• Investigated TFEB regulation during lysosomal damage, distinguishing between ATG conjugation-dependent and -independent pathways.
• Identified and characterized novel TFEB regulators: APEX1 (Mode I) and CCT7/TRIP6 (Mode II).
• Utilized biochemical assays and cell-based studies to analyze protein interactions and TFEB stability/activation.

Main Results:

• Discovered an ATG conjugation-independent TFEB regulation (Mode I) involving APEX1, which enhances TFEB stability.
• Identified an ATG conjugation-dependent TFEB regulation (Mode II) mediated by CCT7 and/or TRIP6, which appear to block TFEB activation.
• Demonstrated that both Mode I and Mode II are involved in TFEB activation by various cellular stresses, suggesting a broader regulatory role.

Conclusions:

• TFEB regulation involves at least two distinct modes, one independent and one dependent on the ATG conjugation system.
• APEX1, CCT7, and TRIP6 are identified as novel key players in TFEB regulation under different stress conditions.
• These findings provide a more comprehensive framework for understanding TFEB's role in cellular stress responses.