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[PSI+] prion propagation is controlled by inositol polyphosphates.

ABSTRACT: The yeast prions [PSI+] and [URE3] are folded in-register parallel β-sheet amyloids of Sup35p and Ure2p, respectively. In a screen for antiprion systems curing [PSI+] without protein overproduction, we detected Siw14p as an antiprion element. An array of genetic tests confirmed that many variants of [PSI+] arising in the absence of Siw14p are cured by restoring normal levels of the protein. Siw14p is a pyrophosphatase specifically cleaving the β phosphate from 5-diphosphoinositol pentakisphosphate (5PP-IP₅), suggesting that increased levels of this or some other inositol polyphosphate favors [PSI+] propagation. In support of this notion, we found that nearly all variants of [PSI+] isolated in a WT strain were lost upon loss of ARG82, which encodes inositol polyphosphate multikinase. Inactivation of the Arg82p kinase by D131A and K133A mutations (preserving Arg82p's nonkinase transcription regulation functions) resulted the loss of its ability to support [PSI+] propagation. The loss of [PSI+] in arg82Δ is independent of Hsp104's antiprion activity. [PSI+] variants requiring Arg82p could propagate in ipk1Δ (IP₅ kinase), kcs1Δ (IP₆ 5-kinase), vip1Δ (IP₆ 1-kinase), ddp1Δ (inositol pyrophosphatase), or kcs1Δ vip1Δ mutants but not in ipk1Δ kcs1Δ or ddp1Δ kcs1Δ double mutants. Thus, nearly all [PSI+] prion variants require inositol poly-/pyrophosphates for their propagation, and at least IP₆ or 5PP-IP₄ can support [PSI+] propagation.

SUBMITTER: Wickner RB

PROVIDER: S-EPMC5635934 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Pseudohyphal growth is a nutrient-regulated program in which budding yeast form multicellular filaments of elongated and connected cells. Filamentous growth is required for virulence in pathogenic fungi and provides an informative model of stress-responsive signaling. The genetics and regulatory networks modulating pseudohyphal growth have been studied extensively, but little is known regarding the changes in metabolites that enable pseudohyphal filament formation. Inositol signaling molecules are an important class of metabolite messengers encompassing highly phosphorylated and diffusible inositol polyphosphates (InsPs). We report here that the InsP biosynthesis pathway is required for wild-type pseudohyphal growth. Under nitrogen-limiting conditions that can induce filamentation, InsPs exhibit characteristic profiles, distinguishing the InsP7 pyrophosphate isoforms 1PP-InsP5 and 5PP-InsP5. Deletion and overexpression analyses of InsP kinases identify elevated levels of 5PP-InsP5 relative to 1PP-InsP5 in mutants exhibiting hyper-filamentous growth. Overexpression of KCS1, which promotes formation of inositol pyrophosphates, is sufficient to drive pseudohyphal filamentation on medium with normal nitrogen levels. We find that the kinases Snf1p (AMPK), Kss1p, and Fus3p (MAPKs), required for wild-type pseudohyphal growth, are also required for wild-type InsP levels. Deletion analyses of the corresponding kinase genes indicate elevated InsP3 levels and an absence of exaggerated 5PP-InsP5 peaks in trace profiles from snf1Δ/Δ and kss1Δ/Δ mutants exhibiting decreased pseudohyphal filamentation. Elevated 5PP-InsP5:1PP-InsP5 ratios are present in the hyperfilamentous fus3 deletion mutant. Collectively, the data identify the presence of elevated 5PP-InsP5 levels relative to other inositol pyrophosphates as an in vivo marker of hyper-filamentous growth, while providing initial evidence for the regulation of InsP signaling by pseudohyphal growth kinases.

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[PSI+] prion propagation is controlled by inositol polyphosphates.

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