Inhibitors of Civ1 kinase belonging to 6-aminoaromatic-2-cyclohexyldiamino purine series as potent anti-fungal compounds

Two Cdc2 Kinase Genes with Distinct Functions in Vegetative and Infectious Hyphae in Fusarium graminearum

Eukaryotic cell cycle involves a number of protein kinases important for the onset and progression through mitosis, most of which are well characterized in the budding and fission yeasts and conserved in other fungi. However, unlike the model yeast and filamentous fungi that have a single Cdc2 essential for cell cycle progression, the wheat scab fungus Fusarium graminearum contains two CDC2 orthologs. The cdc2A and cdc2B mutants had no obvious defects in growth rate and conidiation but deletion of both of them is lethal, indicating that these two CDC2 orthologs have redundant functions during vegetative growth and asexual reproduction. However, whereas the cdc2B mutant was normal, the cdc2A mutant was significantly reduced in virulence and rarely produced ascospores. Although deletion of CDC2A had no obvious effect on the formation of penetration branches or hyphopodia, the cdc2A mutant was limited in the differentiation and growth of infectious growth in wheat tissues. Therefore, CDC2A plays stage-specific roles in cell cycle regulation during infectious growth and sexual reproduction. Both CDC2A and CDC2B are constitutively expressed but only CDC2A was up-regulated during plant infection and ascosporogenesis. Localization of Cdc2A- GFP to the nucleus but not Cdc2B-GFP was observed in vegetative hyphae, ascospores, and infectious hyphae. Complementation assays with chimeric fusion constructs showed that both the N- and C-terminal regions of Cdc2A are important for its functions in pathogenesis and ascosporogenesis but only the N-terminal region is important for its subcellular localization. Among the Sordariomycetes, only three Fusarium species closely related to F. graminearum have two CDC2 genes. Furthermore, F. graminearum uniquely has two Aurora kinase genes and one additional putative cyclin gene, and its orthologs of CAK1 and other four essential mitotic kinases in the budding yeast are dispensable for viability. Overall, our data indicate that cell cycle regulation is different between vegetative and infectious hyphae in F. graminearum and Cdc2A, possibly by interacting with a stage-specific cyclin, plays a more important role than Cdc2B during ascosporogenesis and plant infection.

In the model yeasts and filamentous fungi, CDC2 is an essential gene that encodes the only CDK essential for mitotic cell cycle progression. However, the wheat scab fungus F. graminearum contains two CDC2 orthologs. The cdc2A and cdc2B deletion mutants had no defects in vegetative growth but deletion of both is lethal. Whereas the cdc2B mutant was normal, the cdc2A mutant was almost non-pathogenic, indicating that only Cdc2A is essential in infectious hyphae. Cdc2A and Cdc2B differ in subcellular localization and only localization of Cdc2A to the nucleus was increased in cells active in mitosis. Furthermore, F. graminearum uniquely has two orthologs of Ipl1 Aurora kinase and mutants deleted of orthologs of five essential yeast mitotic kinase genes were viable. However, most of these mutants were significantly reduced in virulence. Overall, our data indicate that F. graminearum differs from the model fungi in CDK and other key mitotic kinase genes, and cell cycle regulation is different between vegetative and infectious hyphae. This is the first report on two Cdc2 kinases in fungi and they differ in subcellular localization and functions during sexual reproduction and plant infection.

Synthesis of novel substituted purine derivatives and identification of the cell death mechanism

Novel 9-(substituted amino/piperazinoethyl)adenines (4-12), 6-(substituted piperazino/amino)purines (15-27), 9-(p-toluenesulfonyl/cyclopentyl/ethoxycarbonylmethyl)-6-(substituted amino/piperazino)purines (28-34, 36, 37, 38-41) were synthesized and evaluated initially for their cytotoxic activities on liver Huh7, breast T47D and colon HCT116 carcinoma cells. N(6)-(4-Trifluoromethylphenyl)piperazine derivative (17) and its 9-(p-toluene-sulfonyl)/9-cyclopentyl analogues (28, 36) had promising cytotoxic activities. Compounds 17, 28 and 36 were further analysed for their cytotoxicity in a panel of a liver cancer cell lines. The compound 36 had better cytotoxic activities (IC50 ≤ 1 μM) than the nucleobase 5-FU and nucleosides fludarabine, cladribine, and pentostatine on Huh7 cells. Cytotoxicity induced by 36 was later identified as senescence associated cell death by SA-β-Gal assay.

Synthesis and anticonvulsant activity of novel purine derivatives

A series of new purines containing triazole and other heterocycle substituents was synthesized and evaluated for their preliminary anticonvulsant activity and neurotoxicity by using the maximal electroshock (MES), subcutaneous pentylenetetrazole (scPTZ) and rotarod neurotoxicity (TOX) tests. Among the compounds studied, 9-decyl-6-(1H-1,2,4-triazol-1-yl)-9H-purine (5e) was the most potent compound, with a median effective dose of 23.4 mg/kg and a high protective index of more than 25.6 after intraperitoneal administration in mice. Compound 5e showed significant oral activity against MES-induced seizures in mice, with an ED50 of 39.4 mg/kg and a PI above 31.6. These results demonstrate that compound 5e possesses better anticonvulsant activity and is safer than the commercially available drugs carbamazepine and valproate in MES, scPTZ and TOX models.

Kinase Cak1 functionally interacts with the PAF1 complex and phosphatase Ssu72 via kinases Ctk1 and Bur1

Protein kinases orthologous with Cak1 of Saccharomyces cerevisiae (ScCak1) appear specific to ascomycetes. ScCak1 phosphorylates Cdc28, the cyclin-dependent kinase (CDK) governing the cell cycle, as well as Kin28, Bur1 and Ctk1, CDKs required for the transcription process performed by RNA polymerase II (RNA Pol II). Using genetic methods, we found that Cak1 genetically interacts with Paf1 and Ctr9, two components belonging to the PAF1 elongation complex needed for histone modifications, and with Ssu72, a protein phosphatase that dephosphorylates serine-5 phosphate in the RNA Pol II C-terminal domain. We present evidence suggesting that the interactions linking Cak1 with the PAF1 complex and with Ssu72 are not direct but mediated via Ctk1 and Bur1. We discuss the possibility that Ssu72 intervenes at the capping checkpoint step of the transcription cycle.