Abstract
Autophagy is a cellular recycling program which efficiently reduces the cellular burden of ageing. Autophagy is characterised by nucleation of isolation membranes, which grow in size and further expand to form autophagosomes, engulfing cellular material to be degraded by fusion with lysosomes (vacuole in yeast). Autophagosomal membranes do not bud from a single cell organelle, but are generated de novo. Several lipid sources for autophagosomal membranes have been identified, but the whole process of their generation is complex and not entirely understood. In this study, we investigated how the mitochondrial outer membrane protein porin 1 (Por1), the yeast orthologue of mammalian voltage-dependent anion channel (VDAC), affects autophagy in yeast. We show that POR1 deficiency reduces the autophagic capacity and leads to changes in vacuole and lipid homeostasis. We further investigated whether limited phosphatidylethanolamine (PE) availability in por1∆ was causative for reduced autophagy by overexpression of the PE-generating phosphatidylserine decarboxylase 1 (Psd1). Altogether, our results show that POR1 deficiency is associated with reduced autophagy, which can be circumvented by additional PSD1 overexpression. This suggests a role for Por1 in Psd1-mediated autophagy regulation.
Highlights
Macroautophagy, hereafter referred to as autophagy, represents a cellular recycling mechanism, which regulates degradation of misfolded, oxidised, aggregated, or unneeded proteins
We suggest that porin 1 (Por1) harbours essential functions in the co-ordination of lipid synthesis and inter-organelle communication, which impact the regulation of autophagy
We detected liberation of free GFP from GFP–Atg8 in yeast cultures grown on YPD media by immunoblotting, which revealed a decrease in basic autophagy levels in por1∆ at both 24 and 48 h after inoculation (Figure 1a)
Summary
Macroautophagy, hereafter referred to as autophagy, represents a cellular recycling mechanism, which regulates degradation of misfolded, oxidised, aggregated, or unneeded proteins. The lipid material making up the autophagosomal membrane does not derive from a single organelle, but uses multiple lipid sources, such as the ER [3], mitochondria [4], Golgi [5,6], plasma membrane [7,8], endosomes [9,10], and lipid droplets [11,12]. It has recently been suggested that the extension of the autophagosomal membrane occurs de novo at ER–autophagosome contacts. This process involves Faa1-mediated channelling of activated fatty acids into phospholipids, which are used in autophagosomal membrane expansion [13]. The availability of fatty acids [14,15,16] and phosphatidylethanolamine (PE) [17] has further been shown to be a limiting factor for autophagy
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