Inositol pyrophosphates regulate cell death and telomere length through phosphoinositide 3-kinase-related protein kinases - PubMed (original) (raw)

Adolfo Saiardi et al. Proc Natl Acad Sci U S A. 2005.

Abstract

Inositol pyrophosphates physiologically regulate vesicular endocytosis, ribosomal disposition, and directly phosphorylate proteins. Here we demonstrate roles in cell death and regulation of telomere length. Lethal actions of wortmannin and caffeine are selectively abolished in yeast mutants that cannot synthesize inositol pyrophosphates. Wortmannin and caffeine appear to act through the phosphoinositide 3-kinase-related protein kinases Tel1 and Mec1, known regulators of telomere length. Inositol pyrophosphates physiologically antagonize the actions of these kinases, which is demonstrated by the fact that yeast mutants with reduced or elevated levels of inositol pyrophosphates, respectively, display longer and shorter telomeres.

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Figures

Fig. 1.

Fig. 1.

Absence of inositol pyrophosphates confers wortmannin resistance. Serial dilutions (7-fold) of cells were planted in synthetic media containing 10 μg/ml wortmannin (Right) or vehicle alone (Left) and incubated at 30°C for 72 h. Indicated to the left are the different genotypes and strain backgrounds analyzed. Strains _ipmk_Δ and _ip6k_Δ were transformed with empty vector (p415) or a vector carrying their respective WT gene (p415yIPMK and p415yIP6K). Indicated to the right are the presence (yes) or absence (no) of inositol pyrophosphates in the different strains as described in Fig. 2 or as published in ref. .

Fig. 2.

Fig. 2.

Intracellular levels of inositol polyphosphates. WT, _yIP6K_-null (_ip6k_Δ), _IPK1_-null (_ipk1_Δ), and double-mutant yIP6K- and _IPK1_-null (_ipk1_Δ_ip6k_Δ) yeast were radiolabeled with [3H]inositol. Inositol polyphosphates were extracted and analyzed by HPLC as described in ref. ; standards used to identify the different inositol polyphosphate species were described in ref. .

Fig. 3.

Fig. 3.

Absence of inositol pyrophosphates confers caffeine resistance. Serial dilutions (7-fold) of cells were planted in synthetic media containing 15 mM (Center) or 20 mM(Right) of caffeine or vehicle alone (Left) and incubated at 30°C for 72 h (vehicle and 15 mM caffeine) or 96 h (20 mM caffeine). Indicated to the left are the genotypes analyzed.

Fig. 4.

Fig. 4.

Inositol pyrophosphates control telomere length. Genomic DNA was extracted from yeast grown in yeast extract/peptone/dextrose, digested by _Pst_I, and analyzed by using a telomere probe as described in Materials and Methods. (A) Yeast with defects in inositol pyrophosphate synthesis (described in Fig. 2) display associated telomere defects that were rescued by the introduction of specified plasmids. Strains _ipk1_Δ and _ip6k_Δ were transformed with empty vector (p415) or a vector carrying their respective gene (p415IPK1 and p415yIP6K). (B) The analysis of the double-mutants _ipk1_Δ_tel1_Δ and _ip6k1_Δ_tel1_Δ reveals that the shortened telomeres present in _tel1_Δ yeast are not affected by changes in inositol pyrophosphate levels. The lines indicate the range of the WT telomere lengths observed.

Comment in

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