In Saccharomyces cerevisiae, the Inositol Polyphosphate Kinase Activity of Kcs1p Is Required for Resistance to Salt Stress, Cell Wall Integrity, and Vacuolar Morphogenesis

Abstract

A problem for inositol signaling is to understand the significance of the kinases that convert inositol hexakisphosphate to diphosphoinositol polyphosphates. This kinase activity is catalyzed by Kcs1p in the yeast Saccharomyces cerevisiae. A kcs1⌬ yeast strain that was transformed with a specifically "kinase-dead" kcs1p mutant did not synthesize diphosphoinositol polyphosphates, and the cells contained a fragmented vacuolar compartment. Biogenesis of the yeast vacuole also required another functional domain in Kcs1p, which contains two leucine heptad repeats. The kinase activity of Kcs1p was also found to sustain cell growth and integrity of the cell wall and to promote adaptive responses to salt stress. Thus, the synthesis of diphosphoinositol polyphosphates has wide ranging physiological significance. Furthermore, we showed that these phenotypic responses to Kcs1p deletion also arise when synthesis of precursor material for the diphosphoinositol polyphosphates is blocked in arg82⌬ cells. This metabolic block was partially bypassed, and the phenotype was partially rescued, when Kcs1p was overexpressed in the arg82⌬ cells. This was due, in part, to the ability of Kcs1p to phosphorylate a wider range of substrates than previously appreciated. Our results show that diphosphoinositol polyphosphate synthase activity is essential for biogenesis of the yeast vacuole and the cell's responses to certain environmental stresses.

Telomere maintenance by intracellular signals: New kid on the block?

“…Snyder's group (4) thinks that there might be a hitherto unrecognized relationship between inositol pyrophosphates and PIKK-related processes, after they observed that yeast became immune to the toxic, growth-impeding effects of wortmannin and caffeine, if the IP 6 kinase gene, KCS1, was deleted. These results were a little surprising, because earlier reports contrarily indicated that kcs1⌬ cells were hypersensitive to both wortmannin (10) and caffeine (11). Nevertheless, Snyder's group was prompted by its observations to study the effects on telomere length when inositol pyrophosphate synthesis was targeted genetically.…”

Inositol pyrophosphates modulate cell cycle independently of alteration in telomere length

“…There are numerous ways how inositol pyrophosphates may regulate cell cycle progression, this may include events on vacuole biogenesis and cell wall integrity (Dubois et al, 2002), proper endocytic trafficking (Saiardi et al, 2002), cyclin-CDK-CDK inhibitor complex (Lee et al, 2007), chromatin remodelling (Steger et al, 2003) or RNA polymerase Imediated rRNA transcription (Thota et al, 2015) and for all of them understanding of structural analysis of diphosphoinositol polyphosphate kinase is crucial (Shears et al, 2013). Furthermore, above all of them, two might be of particular significance.…”

“…A major role of Ipk2 and its products, IP 4 and IP 5 , is transcriptional regulation by modulation of the chromatin remodelling in response to nutrients (Odom et al, 2000;Steger et al, 2003). The yeast Ipk1 and its product, IP 6 , which is generated by phosphorylation of IP 5 , regulate mRNA export through conjunction with Gle1 which regulates the activity of the DEAD-box protein Dbp5 at the nuclear pore complexes cytoplasmic face (York et al, 1999;Folkman et al, 2014) and nonhomologous end joining (Hanakahi et al, 2000). The synthesis of diphosphoinositol phosphates or pyrophosphates in yeasts is mediated by two kinases: Kcs1 phosphorylates IP 5 into 5-PP-IP 4 , and IP 6 into 5-PP-IP 5 (IP 7 ); Vip1 phosphorylates IP 6 into IP 7 isomer 1-PP-IP 5 .…”

HSP90 regulates cell survival via inositol hexakisphosphate kinase-2

“…Cellular IP7 was measured as described previously (8,21). Details are found in SI Materials and Methods.…”

“…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.…”