An Autophagy-Independent Role for ATG41 in Sulfur Metabolism During Zinc Deficiency

Abstract

1The Zap1 transcription factor of Saccharomyces cerevisiae is a key regulator in the genomic 2 responses to zinc deficiency. Among the genes regulated by Zap1 during zinc deficiency is the 3 autophagy-related gene ATG41. Here, we report that Atg41 is required for growth in zinc-4 deficient conditions but not when zinc is abundant or when other metals are limiting. 5Consistent with a role for Atg41 in macroautophagy, we show that nutritional zinc deficiency 6 induces autophagy and that mutation of ATG41 diminishes that response. Several experiments 7 indicated that the importance of ATG41 function to growth during zinc deficiency is not 8 because of its role in macroautophagy but rather is due to one or more autophagy-independent 9 functions. For example, rapamycin treatment fully induced autophagy in zinc-deficient atg41Δ 10 mutants but failed to improve growth. In addition, atg41Δ mutants showed a far more severe 11 growth defect than any of several other autophagy mutants tested, and atg41Δ mutants 12 showed increased Hsf1 activity, an indicator of protein homeostasis stress, while other 13 autophagy mutants did not. An autophagy-independent function for ATG41 in sulfur 14 metabolism during zinc deficiency was suggested by analyzing the transcriptome of atg41Δ 15 mutants during the transition from zinc-replete to deficient conditions. Analysis of sulfur 16 metabolites confirmed that Atg41 is needed for the normal accumulation of methionine, 17 homocysteine, and cysteine in zinc-deficient cells. Therefore, we conclude that Atg41 plays 18 roles in both macroautophagy and sulfur metabolism during zinc deficiency. 19 20 4

Zinc Deficiency Induces Autophagy in HT-22 Mouse Hippocampal Neuronal Cell Line

“…The mechanism by which autophagy protects hippocampal neurons from zinc deficiency has not yet been elucidated. A study in yeast showed that zinc deficiency caused autophagy, and genetic blockade of autophagy inhibited cellular growth [ 11 , 16 ]. Metallothioneins (MTs), proteins that bind zinc and buffer intracellular zinc levels, are degraded in lysosomes [ 20 , 21 ].…”

“…However, studies on zinc deficiency models without prior stress exposure to autophagy-related conditions are still lacking. We identified only two studies in yeast, which suggested that zinc deficiency induces autophagy [ 11 , 16 ]. The effect of zinc deficiency on autophagy has not been well studied.…”

Restricted glycolysis is a primary cause of the reduced growth rate of zinc-deficient yeast cells

“…specific transporters responsible for Zn uptake into the cell and its trafficking between compartments) ( 1 ) and those for the adaptive response (which do not affect Zn availability, but help cells better tolerate the stress of Zn deficiency) ( 15 , 16 ). Adaptive response factors include enzymes that help maintain phospholipid synthesis in low Zn ( 17 , 18 ), antioxidant proteins that help ZnD cells maintain redox homeostasis ( 19 ), and factors affecting the stability of the Zn proteome ( 20 , 21 , 22 ).…”