Inositol pyrophosphates regulate cell death and telomere length through phosphoinositide 3-kinase-related protein kinases

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.wortmannin ͉ yeast ͉ caffeine I nositol polyphosphates mediate diverse forms of cell signaling, with the best characterized, inositol 1,4,5-trisphosphate (IP 3 ), releasing calcium from intracellular stores (1). Inositol hexakisphosphate (IP 6 ) (also known as phytic acid), the most abundant inositol polyphosphate present in eukaryotes (2), is the precursor of diphosphoinositol polyphosphates, a class of phosphorylated inositols containing one or more pyrophosphate moieties on the inositol ring (3, 4). The pyrophosphate moieties of diphosphoinositol-pentakisphosphate (PP-IP 5 or IP 7 ) and bis-diphosphoinositol-tetrakisphosphate ([PP] 2 -IP 4 or IP 8 ) contain energetic bonds that turn over rapidly (3, 4), possibly indicating a molecular switching role. Recently, we showed that IP 7 physiologically transfers the ␤-phosphate of the pyrophosphate moiety to several target proteins (5), implying a major role in intracellular signaling. Yeast lacking the inositol pyrophosphate-forming enzyme, IP 6 kinase (yIP6K; also designated KCS1; ORF DRO17c) (6, 7), display defective vesicular endocytosis (8). yIP6K-deficient (ip6k⌬) yeast also manifest slow cell growth (9), sensitivity to environmental stresses (10), and abnormal ribosomal functions (5). In the present study, we demonstrate the involvement of inositol pyrophophates in signaling cascades that mediate cell death and telomere length. ip6k⌬ yeast are resistant to the lethal effects of wortmannin and caffeine, drugs that inhibit the activity of phosphoinositide 3-kinase (PI3K)-related protein kinases. Mutant yeast with elevated or reduced levels of inositol pyrophosphates respectively possess shorter and longer telomeres. Materials and MethodsYeast Growth Conditions and Drug Treatments. Yeast were grown in synthetic medium supplemented with a complete or appropriate amino acid mixture of the Synthetic Complete supplement purchased from Qbiogene (Carlsbad, Ca). Wortmannin and caffeine (Sigma) were added to the synthetic media from concentrated stocks prepared in DMSO and water, respectively. Yeast Strains, Plasmid Preparation, and HPLC Analyses of InositolPhosphates. Yeast strains used in this study were described in refs. 7-9 or generated by standard mating and tetrad dissection techniques. The plasmids p415yIP6K and p415IPK1 were generated by ...

HSP90 regulates cell survival via inositol hexakisphosphate kinase-2

“…IP6K2 can up-regulate DR4 and caspase 8 and inhibit NF-␤ signaling via interactions with TRAF2 (23,24). In yeast, inositol pyrophosphates modulate cell death and telomere length by antagonizing yeast homologues of ataxia telangiectasia mutated (ATM) kinase, a regulator of the DNA damage response and cell death in higher organisms (12). IP7(5) competes with the lipid PI(3,4,5)P3 for binding to PH domains (16).…”

“…IP6K-deficient yeast manifest major abnormalities in vesicular endocytosis (8)(9)(10) and telomere length (11,12). Abundant evidence implicates PP-IPs in vesicular trafficking.…”

The “Other” Inositols and Their Phosphates: Synthesis, Biology, and Medicine (with Recent Advances inmyo‐Inositol Chemistry)

“…The synthesis of analogues of 5PP-Ins(1,2,3,4,6)P 5 (not shown), such as compound 218, is an important step in elucidating the mechanism of its natural parent pyrophosphate, associated with cellular functions such as repair of damaged DNA. [233] Several analogues possessing a methylene bisphosphonate at the 1D-position with phosphate groups at the 2-, 3-, 5-and 6-positions and a variety of substituents at the 4-position have been reported (Scheme 30).…”

Inositol pyrophosphates modulate cell cycle independently of alteration in telomere length

“…Furthermore, as ipk1 cells are unable to synthesize IP 6 , IP 7 or IP 8, but will accumulate alternative inositol pyrophosphates, PP-IP 4 and (PP) 2 -IP 3 and have telomeres slightly shorter than wild type (Saiardi et al, 2005;York et al, 2005), therefore herein we have investigated how overexpression of Kcs1 affects the level of alternative inositol pyrophosphates, telomere length and progression of cells through the cell cycle.…”

“…(PP) 2 -IP 4 (IP 8 ) is generated by either Kcs1-mediated phosphorylation of 1-PP-IP 5 or Vip1-mediated phosphorylation of 5-PP-IP 5 (Tsui and York, 2010). Kcs1 has been reported to modulate telomere length by generation of 5-PP-IP 4 (Saiardi et al, 2005;York et al, 2005), and Vip1-generated IP 7 binds to the cyclin-CDK-CDK inhibitor complex to regulate transcription of the yeast phosphate (Pi)-responsive (PHO) genes (Lee et al, 2007).…”