Macronucleophagy maintains cell viability under nitrogen starvation by modulating micronucleophagy

Area of Science:

• Cell Biology
• Molecular Biology
• Yeast Genetics

Background:

• Autophagy is essential for cellular homeostasis, involving lysosome/vacuole-mediated degradation.
• Nitrogen starvation in Saccharomyces cerevisiae induces both macronucleophagy and micronucleophagy.
• The interplay between different autophagy modes, particularly concerning nuclear degradation, remains poorly understood.

Purpose of the Study:

• To elucidate the mechanism by which Atg39-mediated macronucleophagy influences micronucleophagy.
• To investigate the relationship between macronucleophagy and micronucleophagy under nitrogen starvation.
• To understand how disruptions in macronucleophagy affect nuclear component degradation and cell survival.

Main Methods:

• Genetic analysis of Saccharomyces cerevisiae mutants with defects in Atg39-mediated macronucleophagy.
• Microscopy and biochemical assays to monitor nuclear component transport into the vacuole.
• Analysis of protein localization and degradation at the nucleus-vacuole junction (NVJ).

Main Results:

• Defective Atg39-mediated macronucleophagy leads to hyperactivated micronucleophagy.
• Accumulation of the micronucleophagy component Nvj1 in macronucleophagy-deficient cells.
• Blocking micronucleophagy rescues cell death in Atg39-mutant cells under nitrogen starvation.

Conclusions:

• Macronucleophagy acts as a negative regulator of micronucleophagy to prevent excessive nuclear degradation.
• The Atg39-mediated pathway is crucial for maintaining nuclear and cellular homeostasis during nutrient stress.
• Dysregulation of the balance between macroautophagy and microautophagy can lead to cell death.