Loss of actin dynamics leads to VDAC dependent MAPK signalling and altered lipid homeostasis that promotes cell death in yeast cells

Abstract

The dynamic nature of the actin cytoskeleton controls many cellular processes and a loss of its plasticity has been linked to accelerated cell ageing. Cofilin is an actin-binding protein that controls actin dynamics and is linked to mitochondrial signalling pathways that control drug resistance and cell death. Here we show that cofilin driven stabilisation of actin dynamics leads to a loss in cell wall integrity, vacuole fragmentation and disruption of lipid homeostasis, lipid droplet accumulation and the promotion of necrosis. Our data suggest that these phenotypes are triggered by the inappropriate activation of Protein Kinase C (PKC) which leads to constitutive MAPK signalling. Cofilin-driven activation of the MAPK Slt2 requires the presence of the voltage dependent anion channel (VDAC), which resides in the mitochondrial outer membrane, referred to as Porin 1 (Por1) in yeast. This provides further evidence for a link between actin regulation and mitochondrial signalling. Porin has recently been implicated in lipid transport and we find that prevention of excessive lipid droplet accumulation, achieved by deleting the LRO1 and DGA1 genes, was sufficient to prevent Slt2 activation and restore cellular homeostasis in actin stabilised cells. These data suggest that the integrity of the actin cytoskeleton is essential to maintain the fidelity of MAPK signalling and that this in turn is crucial for the maintenance of lipid homeostasis and cell health in S. cerevisiae. Our data also suggest that chronic actin stabilisation leads to mitochondrial VDAC-dependent Slt2 activation and altered, pro-death, cell fate in yeast cells.

Phospholipids are imported into mitochondria by VDAC, a dimeric beta barrel scramblase

“…5d), indicating that these proteins are the principal lipid importers of the OMM. Consistent with this, depletion of VDACs in yeast and mammalian cells caused a reduction in the levels of cardiolipin [54][55][56] , a lipid whose synthesis requires the import of phospholipid precursors from the ER. However, the residual (<10% of total) scramblase activity in por1Δpor2Δ mitochondria (Fig.…”