Disease relevance of PHO85

• Each of the fusion proteins, LacZ-Pho80 and LacZ-Pho85, was produced into Escherichia coli and used as an antigen to raise antibodies in a rabbit [1].

High impact information on PHO85

• The ability of cells to react appropriately to nutritional cues is of fundamental importance, and in budding yeast, a small number of intracellular protein kinases, PKA, Snf1p/AMP-activated kinase, TOR, Gcn2p, and the cyclin-dependent kinase Pho85p have key roles [2].
• We show that phosphorylation of Pho4 by a nuclear complex of a cyclin with a cyclin-dependent kinase, Pho80-Pho85, triggers its export from the nucleus [3].
• Cell cycle control by a complex of the cyclin HCS26 (PCL1) and the kinase PHO85 [4].
• A complex consisting of the cyclin-dependent kinase (CDK) PHO85 and the cyclin PHO80 phosphorylates and is thought to inactivate the transcription factor PHO4 when yeast cells are grown in medium containing high concentrations of phosphate [5].
• Here it is reported that PHO80 has homology to yeast cyclins and interacts with PHO85, a p34cdc2/CDC28-related protein kinase [6].

Biological context of PHO85

• Analysis of Ser-to-Ala mutations at the three potential Gsy2p phosphorylation sites in pho85 cells implicated Ser-654 and/or Thr-667 in PHO85 control of glycogen synthase [7].
• In Saccharomyces cerevisiae, PHO85 encodes a cyclin-dependent protein kinase (Cdk) with multiple roles in cell cycle and metabolic controls [8].
• Other cellular roles for Pho85 cyclin-Cdk complexes are suggested by the multiple phenotypes associated with deletion of PHO85, in addition to Start defects and deregulated acid phosphatase gene expression [9].
• We described several unique phenotypes associated with the deletion of the PHO85 gene including growth defects on a variety of carbon sources and hyperaccumulation of glycogen in rich medium high in Pi [10].
• Our studies suggest that Pho85 associates with multiple cyclins and that subsets of cyclins may direct Pho85 to perform distinct roles in cell growth and division [9].

Anatomical context of PHO85

• Though vac5-1 is recessive, pho80 delta or pho85 delta strains do not show a defect in vacuole inheritance, suggesting that vac5-1 is not a complete loss-of-function allele [11].
• The signal transduction pathway that mediates this response consists of components that resemble those used to regulate the eukaryotic cell cycle; these include a cyclin-dependent kinase or CDK (Pho85), a cyclin (Pho80) and a CDK inhibitor (Pho81) [12].
• Like Cdk5, Pho85 has been implicated in actin cytoskeleton regulation through phosphorylation of an actin-regulatory protein [13].
• Paradoxically, phosphorylation of Tau-4R isolated from kinase Pho85-deficient yeast was dramatically increased resulting in very poor binding to microtubules [14].

Associations of PHO85 with chemical compounds

• However, unlike pho85 mutants, pcl8 pcl10 cells had normal morphologies, grew on glycerol, and showed proper regulation of acid phosphatase gene expression [8].
• The activity of one of these, GPK2, was inhibited by olomoucine, which potently inhibits cyclin-dependent protein kinases, and contained an approximately 36-kDa species that reacted with antibodies to Pho85p [7].
• Phosphorylation by Pho85 cyclin-dependent kinase acts as a signal for the down-regulation of the yeast sphingoid long-chain base kinase Lcb4 during the stationary phase [15].
• In this review we present information on the regulation of the activity of the enzymes implicated in the pathways of synthesis and degradation of glycogen and trehalose as well as on the transcriptional control of the genes encoding them. cAMP and the protein kinases Snf1 and Pho85 appear as major actors in this regulation [16].
• An in vitro assay showed that a glutathione S-transferase-Pho81p fusion protein inhibits the Pho85p protein kinase [17].

Physical interactions of PHO85

• Interactions between Pho85 cyclin-dependent kinase complexes and the Swi5 transcription factor in budding yeast [18].
• Although Pho85 is not essential for viability, Pcl1,2-Pho85 kinase complexes become essential for Start in the absence of Cln1,2-Cdc28 kinases [9].
• PCL2 interacted with the cdk PHO85 in vivo and in vitro and formed a kinase complex that had G1-periodic activity [19].
• Additionally, we show that Pcl7 interacts with the phosphate-regulated cyclin-cdk inhibitor Pho81, and that the regulation of the Pcl7-Pho85 complex in response to changes in phosphate levels is dependent on Pho81 [20].
• Gcn4 degradation depends on the ubiquitination complex SCF(CDC4) and requires phosphorylation by the cyclin-dependent kinase Pho85 [21].

Enzymatic interactions of PHO85

• The PHO80 protein was found to be phosphorylated in the presence of PHO85 protein [1].
• Previous work has shown that Rvs167p can be phosphorylated in vitro by the cyclin-dependent kinase Pho85p complexed with its cyclin Pcl2p [22].
• Pho85 and other G1 Cdks appear to phosphorylate Sic1 at different sites in vivo [23].
• Many known substrates of the G1 forms of Pho85 are also phosphorylated by the homologous Cdk Cln-Cdc28, suggesting parallel or overlapping roles [24].

Regulatory relationships of PHO85

• Mutation of the type-1 protein phosphatase encoded by GLC7 only partially suppresses the glycogen phenotype of the pho85 mutant [10].
• Mutation of PHO85 suppressed the glycogen storage deficiency of snf1 or glc7-1 mutants in which glycogen synthase is locked in an inactive state [8].
• Two contiguous regions upstream of the GSY2 coding region are necessary for negative control by the cyclin-dependent protein kinase Pho85, one of which is a 14-bp G/C-rich sequence [25].
• The CDK inhibitor PHO81 inhibits the kinase activity of the PHO80-PHO85 complex when Saccharomyces cerevisiae cells are grown in medium depleted of phosphate [5].
• We propose that Rvs167p is activated by phosphorylation in its GPA region by the Pcl-Pho85p kinase [26].

Other interactions of PHO85

• The vacuole inheritance defect in vac5-1 cells is dependent on the presence of the Pho85 kinase and its targets Pho4p and Pho2p [11].
• Pho85p, a cyclin-dependent protein kinase, and the Snf1p protein kinase act antagonistically to control glycogen accumulation in Saccharomyces cerevisiae [7].
• In addition, two other G1 cyclins, Pcl1 and Pcl2, associate with a second Cdk, Pho85, to contribute to Start [9].
• Induction of autophagy in pho85 mutants entering the stationary phase was exaggerated compared to the level in wild-type cells, but was blocked in apg1 pho85 mutants [27].
• We show that deletion of PHO85, which encodes a cyclin-dependent protein kinase, causes reduced transcription of HO and that this reduction is dependent on ASH1 [28].

Analytical, diagnostic and therapeutic context of PHO85

• We found that all of the new genes encode proteins that interacted with Pho85 in an affinity chromatography assay [9].
• Co-immunoprecipitation experiments using in vitro translated proteins showed that Pcl9 and Pho85 form a complex [29].
• Using the affinity-purified antibodies in Western blotting experiments, the PHO85 protein was detected as a 36 kDa and the PHO80 protein as a 34 kDa protein [1].
• Gel filtration of yeast cell lysates demonstrated that most Pho85p was present as a monomer, although a portion coeluted in high-molecular-weight fractions with Pcl10p and Gsy2p [30].

References