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. 2014 Oct 29;13(23):3707–3726. doi: 10.4161/15384101.2014.965003

Figure 4.

Figure 4.

A depletion of PE in the extracellular leaflet of the PM is a characteristic trait of POA-induced liponecrotic PCD, perhaps due to the ability of POA to trigger the alkaline-pH- and lipid-asymmetry-responsive Rim101 signaling pathway. (A) Outline of the Rim101 signaling pathway operating in yeast cells. This pathway can be induced by alkalinisation of culture medium and/or in response to certain changes in asymmetrical distribution of some species of PL across the PM bilayer. The pathway includes the pH sensing protein complex on the PM and the proteolytic processing complex for the transcriptional factor Rim101p on the endosomal membrane. After Rim101p is proteolytically processed by the protease Rim13p on the surface of the endosome, its cleaved form is delivered to the nucleus. In the nucleus, cleaved Rim101p activates transcription of the RSB1 gene by suppressing its repressor, Nrg1p. A protein product of the RSB1 gene is a putative sphingoid long-chain base-specific translocase/transporter within the PM. This protein stimulates the Lem3p-dependent transport of PE from the outer (extracellular) leaflet of the PM to its inner (intracellular) leaflet and suppresses the Yor1p-dependent transport of PE across the PM bilayer in the opposite direction. See text for additional details. The names of proteins whose lack causes a decrease or increase of the susceptibility of yeast to POA-induced liponecrosis are displayed in blue or red color, respectively. Activation arrows and inhibition bars denote pro-death processes (displayed in red color) or pro-survival processes (displayed in blue color) for liponecrotic PCD. (B) WT, lem3Δ and yor1Δ cells were recovered at days 1, 2 and 4 of culturing in YP medium initially containing 0.2% glucose as carbon source. Each cell suspension was divided into 2 equal aliquots. Cells in one of these aliquots were treated for 2 h with 0.15 mM POA; cells in the other aliquot remained untreated. Cells in each aliquot were then diluted in YP medium containing 2% glucose and supplemented with 25 μM cinnamycin. Both aliquots were incubated for 8 h, and the total number of cells in each aliquot was determined using a hemacytometer. Data are presented as means ± SEM (n = 5–6). Abbreviations: ESCRT-III, endosomal sorting complex (type III) required for transport; PE, phosphatidylethanolamine; PL, phospholipids; PM, plasma membrane; POA, palmitoleic acid; PS, phosphatidylserine; TAG, triacylglycerols.