ICK1, a cyclin-dependent protein kinase inhibitor from Arabidopsis thaliana interacts with both Cdc2a and CycD3, and its expression is induced by abscisic acid

Cyclin-dependent kinase (CDK) inhibitor genes encode low molecular weight proteins which have important functions in cell cycle regulation, development and perhaps also in tumorigenesis. The first plant CDK inhibitor gene ICK1 was recently identified from Arabidopsis thaliana . Although the C-terminal domain of ICK1 contained an important consensus sequence with the mammalian CDK inhibitor p27^Kip1, the remainder of the deduced ICK1 sequence showed little similarity to any known CDK inhibitors. In vitro assays showed that recombinant ICK1 exhibited unique kinase inhibitory properties. In the present study we characterized ICK1 in terms of its gene structure, its interaction with both A. thaliana Cdc2a and CycD3, and its induction by the plant growth regulator, abscisic acid (ABA). ICK1 was expressed at a relatively low level in the tissues surveyed. However, ICK1 was induced by ABA, and along with ICK1 induction there was a decrease in Cdc2-like histone H1 kinase activity. These results suggest a molecular mechanism by which plant cell division might be inhibited by ABA. ICK1 clones were also identified from independent yeast two-hybrid screens using the CycD3 construct. The implication that ICK1 protein could interact with both Cdc2a and CycD3 was confirmed by in vitro binding assays. Furthermore, deletion analysis indicated that different regions of ICK1 are required for the interactions with Cdc2a and CycD3. These results provide a mechanistic basis for understanding the role of CDK inhibitors in cell cycle regulation in plant cells.     

Isolation of Complementary DNAs Coding for a Receptor for Activated C Kinase (RACK) from Zebrafish (Danio rerio) and Tilapia (Oreochromis niloticus): Constitutive Developmental and Tissue Expression

We have cloned and sequenced complementary DNAs coding for a receptor for activated C kinase (RACK) from two species of teleost fishes, zebrafish (Danio rerio) and tilapia (Oreochromis niloticus). The tilapia clone is 1063 nucleotides long, and the zebrafish clone is 1069 nucleotides long. Both clones contain an open reading frame coding for the complete RACK protein of 317 amino acids. Northern hybridization analysis using these clones as probes detected a 1.2-kb band, indicating that these are nearly full-length cDNA clones. In tilapia, RACK messenger RNA was expressed in all tissues examined. In situ hybridization detected the presence of mRNA for this RACK sequence in unfertilized eggs and embryos (development up to 24 hours) from zebrafish. Received July 13, 1998; accepted January 14, 1999     

Loss of CDKN2A expression is a frequent event in primary invasive melanoma and correlates with sensitivity to the CDK4/6 inhibitor PD0332991 in melanoma cell lines

We have investigated the potential for the p16‐cyclin D‐CDK4/6‐retinoblastoma protein pathway to be exploited as a therapeutic target in melanoma. In a cohort of 143 patients with primary invasive melanoma, we used fluorescence in situ hybridization to detect gene copy number variations (CNVs) in CDK4, CCND1, and CDKN2A and immunohistochemistry to determine protein expression. CNVs were common in melanoma, with gain of CDK4 or CCND1 in 37 and 18% of cases, respectively, and hemizygous or homozygous loss of CDKN2A in 56%. Three‐quarters of all patients demonstrated a CNV in at least one of the three genes. The combination of CCND1 gain with either a gain of CDK4 and/or loss of CDKN2A was associated with poorer melanoma‐specific survival. In 47 melanoma cell lines homozygous loss, methylation or mutation of CDKN2A gene or loss of protein (p16^INK4A) predicted sensitivity to the CDK4/6 inhibitor PD0332991, while RB1 loss predicted resistance.     

酿酒酵母Cdk1抑制蛋白的研究进展

细胞周期蛋白依赖性激酶1(cyclin-dependent kinase 1,Cdk1)是真核生物细胞周期调控的核心,也是维持基因组稳定性的重要激酶,其活性受到严格调控.CDK抑制蛋白(cyclin-dependent kinase inhibitor,CKI)是调节其活性的一类关键负调控因子,CKI功能失活导致细胞不受控制地增殖,促进癌症的发生发展.酿酒酵母作为细胞周期研究的重要模式生物,在揭示CDK活性调控机制中发挥着重要作用.酿酒酵母中已发现的Cdk1抑制蛋白CKI包括Far1、Sic1以及最近鉴定的Cip1蛋白.这三个CKI蛋白在不同细胞时期中,通过抑制Cdk1活性调控细胞周期的进程.此外,CKI还在应对环境胁迫,保持基因组稳定性中发挥重要作用.本文对酿酒酵母Cdk1抑制蛋白CKI的研究进展,尤其是CKI在细胞周期运转及胁迫应答中的作用做出综述,以期为细胞周期及癌症的基础研究提供模式依据.     

Characterisation of the double genome structure of modern sugarcane cultivars (Saccharum spp.) by molecular cytogenetics

Cultivated sugarcane clones (Saccharum spp., 2n=100 to 130) are derived from complex interspecific hybridizations between the speciesS. officinarum andS. spontaneum. Using comparative genomic DNA in situ hybridization, we demonstrated that it is possible to distinguish the chromosomes contributed by these two species in an interspecific F1 hybrid and a cultivated clone, R570. In the interspecific F1 studied, we observed n+n transmission of the parental chromosomes instead of the peculiar 2n+n transmission usually described in such crosses. Among the chromosomes of cultivar R570 (2n=107–115) about 10% were identified as originating fromS. spontaneum and about 10% were identified as recombinant chromosomes between the two speciesS. officinarum andS. spontaneum. This demonstrated for the first time the occurrence of recombination between the chromosomes of these two species. The rDNA sites were located by in situ hybridization in these two species and the cultivar R570. This supported different basic chromosome numbers and chromosome structural differences between the two species and provided a first bridge between physical and genetical mapping in sugarcane.