The Putative Lipid Transporter, Arv1, Is Required for Activating Pheromone-Induced MAP Kinase Signaling in Saccharomyces cerevisiae

Abstract

Saccharomyces cerevisiae haploid cells respond to extrinsic mating signals by forming polarized projections (shmoos), which are necessary for conjugation. We have examined the role of the putative lipid transporter, Arv1, in yeast mating, particularly the conserved Arv1 homology domain (AHD) within Arv1 and its role in this process. Previously it was shown that arv1 cells harbor defects in sphingolipid and glycosylphosphatidylinositol (GPI) biosyntheses and may harbor sterol trafficking defects. Here we demonstrate that arv1 cells are mating defective and cannot form shmoos. They lack the ability to initiate pheromone-induced G1 cell cycle arrest, due to failure to polarize PI(4,5)P 2 and the Ste5 scaffold, which results in weakened MAP kinase signaling activity. A mutant Ste5, Ste5 Q59L, which binds more tightly to the plasma membrane, suppresses the MAP kinase signaling defects of arv1 cells. Filipin staining shows arv1 cells contain altered levels of various sterol microdomains that persist throughout the mating process. Data suggest that the sterol trafficking defects of arv1 affect PI(4,5)P 2 polarization, which causes a mislocalization of Ste5, resulting in defective MAP kinase signaling and the inability to mate. Importantly, our studies show that the AHD of Arv1 is required for mating, pheromone-induced G1 cell cycle arrest, and for sterol trafficking.

Proper Sterol Distribution Is Required for Candida albicans Hyphal Formation and Virulence

“…Expressing the ScAHD alone can restore mating to Scarv1 cells (Villasmil et al 2011), suggesting it can substitute for full-length ScArv1 function under some circumstances. To determine if the AHD could substitute for full-length ScArv1 in conferring virulence, a Caarv1/Caarv1 strain was generated expressing a single Caarv1 AHD allele, and it was tested using a murine model of disseminated candidiasis.…”

“…arv1 cells are hypersusceptible to the ergosterol-binding agent nystatin, suggesting a mislocalization of sterol to the plasma membrane (Tinkelenberg et al 2000). Cells lacking Arv1 accumulate several unknown sterol intermediates, suggesting these cells have defects in sterol synthesis (Kajiwara et al 2008), and they harbor lipid distribution defects, as they cannot polarize phosphatidylinositol 4,5 phosphate (PIP 2 ) during yeast mating (Fei et al 2008; Villasmil et al 2011). Mutant cells also have defects in organelle lipid morphology and homeostasis (Georgiev et al 2013; Schechtmans et al 2011), and they are highly sensitive to fatty acid supplementation (Ruggles et al 2014).…”

Sphingolipids regulate telomere clustering by affecting transcriptional levels of genes involved in telomere homeostasis

“…It is notable that CLN1 and CLN2, which encode G1 cyclins involved in regulation of the cell cycle, were strongly upregulated in the arv1Δ mutant (supplementary material Table S5). Because G1 cyclins negatively regulate the pheromone response pathway (Bloom and Cross, 2007;Doncic et al, 2011), the increased expression of CLN1 and CLN2, and decreased expression of MFA2 might contribute to the defects in pheromone-induced G1 cell cycle arrest and mating that have been observed in the arv1Δ mutant (Villasmil et al, 2011). A particularly intriguing finding is the downregulation of EST3 (supplementary material Table S6), which encodes a non-catalytic component of telomerase.…”

Mice lacking have reduced signs of metabolic syndrome and non-alcoholic fatty liver disease

“…Our results strongly suggest that complete loss of Arv1 protects mice from acquiring MetS and NAFLD in response to a HFD challenge. While it is still up for debate as to what is the function of ARV1 (13)(14)(15)18,19,41), evidence is accumulating that suggests it's involvement in maintaining proper sterol distribution (16,20,42,43).…”

“…S. cerevisiae cells lacking ARV1 have defects in PL (phospholipid), SL (sphingolipid), GPI (glycosylphosphatidylinositol) and sterol syntheses, and lack the ability to localize sterol and mobilize PIP 2 (phosphatidylinositol 4,5 bisphosphate) (13)(14)(15)(16). arv1 deficient cells are hypersensitive to the PS (phosphatidylserine) binding agent, papuamide-B, suggesting a mislocalization of PS to the plasma membrane (17).…”