Cyclin D1/cdk2 kinase is present in a G1 phase-specific protein complex Yi1 that binds to the mouse thymidine kinase gene promoter

Effects of nanoplastic exposure on the growth performance and molecular characterization of growth-associated genes in juvenile Macrobrachium nipponense

Nanoplastic pollution has become a major issue in the aquatic environment while there are few studies examined the effects of nanoplastic exposure on crustaceans. To investigate this issue, we exposed juvenile shrimp, Macrobrachium nipponense to 75 nm polystyrene with 0, 5, 10, 20 and 40 mg/L nanoplastics concentrations for 28 days. The effects of nanoplastic exposure on the microstructure of the hepatopancreas, digestive enzyme activity and expression of growth-related genes were studied. The results showed that (1) adverse effects on the hepatopancreas were positively correlated with nanoplastic concentration; (David et al.) the activity of lipase, trypsin and pepsin was initially promoted and then inhibited with increasing nanoplastic concentration, whereas the activity of amylase was not significantly affected; (3) molting-associated genes were initially promoted and then inhibited with increasing nanoplastic concentration; (4) CDK2 gene was first cloned and molecular characteristics were analyzed. (5) polystyrene nanoplastics concentration >10 mg/L showed inhibition effect on CDK2 expression. These results indicated that nanoplastics affect the growth, digestive enzyme activity, hepatopancreas function and growth-related gene expression. Capsule: Our results identified the effects of nanoplastics on the growth performance of Macrobrachium nipponense in terms of digestion and molting.

Role of p27Kip1 as a transcriptional regulator

The protein p27Kip1 is a member of the Cip/Kip family of cyclin-dependent kinase (Cdk) inhibitors. It interacts with both the catalytic and the regulatory subunit (cyclin) and introduces a region into the catalytic cleave of the Cdk inducing its inactivation. Its inhibitory capacity can be modulated by specific tyrosine phosphorylations. p27Kip1 also behaves as a transcriptional regulator. It associates with specific chromatin domains through different transcription factors. ChIP on chip, ChIP-seq and expression microarray analysis allowed the identification of the transcriptional programs regulated by p27Kip1. Thus, important cellular functions as cell division cycle, respiration, RNA processing, translation and cell adhesion, are under p27Kip1 regulation. Moreover, genes involved in pathologies as cancer and neurodegeneration are also regulated by p27Kip1, suggesting its implication in these pathologies. The carboxyl moiety of p27Kip1 can associate with different proteins, including transcriptional regulators. In contrast, its NH2-terminal region specifically interacts with cyclin-Cdk complexes. The general mechanistic model of how p27Kip1 regulates transcription is that it associates by its COOH region to the transcriptional regulators on the chromatin and by the NH2-domain to cyclin-Cdk complexes. After Cdk activation it would phosphorylate the specific targets on the chromatin leading to gene expression. This model has been demonstrated to apply in the transcriptional regulation of p130/E2F4 repressed genes involved in cell cycle progression. We summarize in this review our current knowledge on the role of p27Kip1 in the regulation of transcription, on the transcriptional programs under its regulation and on its relevance in pathologies as cancer and neurodegeneration.

Progesterone receptor-cyclin D1 complexes induce cell cycle-dependent transcriptional programs in breast cancer cells

The progesterone receptor (PR) and its coactivators are direct targets of activated cyclin-dependent kinases (CDKs) in response to peptide growth factors, progesterone, and deregulation of cell cycle inhibitors. Herein, using the T47D breast cancer model, we probed mechanisms of cell cycle-dependent PR action. In the absence of exogenous progestin, the PR is specifically phosphorylated during the G2/M phase. Accordingly, numerous PR target genes are cell cycle regulated, including HSPB8, a heat-shock protein whose high expression is associated with tamoxifen resistance. Progestin-induced HSPB8 expression required cyclin D1 and was insensitive to antiestrogens but blocked by antiprogestins or inhibition of specificity factor 1 (SP1). HSPB8 expression increased with or without ligand when cells were G2/M synchronized or contained high levels of cyclin D1. Knockdown of PRs abrogated ligand-independent HSPB8 expression in synchronized cells. Notably, PRs and cyclin D1 copurified in whole-cell lysates of transiently transfected COS-1 cells and in PR-positive T47D breast cancer cells expressing endogenous cyclin D1. PRs, cyclin D1, and SP1 were recruited to the HSPB8 promoter in progestin-treated T47D breast cancer cells. Mutation of PR Ser345 to Ala (S345A) or inhibition of CDK2 activity using roscovitine disrupted PR/cyclin D1 interactions with DNA and blocked HSPB8 mRNA expression. Interaction of phosphorylated PRs with SP1 and cyclin D1 provides a mechanism for targeting transcriptionally active PRs to selected gene promoters relevant to breast cancer progression. Understanding the functional linkage between PRs and cell cycle regulatory proteins will provide keys to targeting novel PR/cyclin D1 cross talk in both hormone-responsive disease and HSPB8-high refractory disease with high HSPB8 expression.

Lessons learned from Art Pardee in cell cycle, science, and life

This essay is written to honor Dr Art Pardee's 85th birthday (July 13, 2006). In this essay, I have summarized the lessons I learned from Art and the cell-cycle research I performed in Art's laboratory during my postdoctoral training period. I have also summarized some research from my own laboratory that has been inspired by the lessons I learned from Art, including the interactions between cell cycle and cell death regulators and discovery of novel polyphenol- and copper-based proteasome inhibitors. Finally, I have discussed the potential use of these proteasome inhibitors in cancer prevention and treatment.

Construction of a cyclin D1-Cdk2 fusion protein to model the biological functions of cyclin D1-Cdk2 complexes

Cyclin D1 is frequently overexpressed in human breast cancers, and cyclin D1 overexpression correlates with poor prognosis. Cyclin D1-Cdk2 complexes were previously observed in human breast cancer cell lines, but their role in cell cycle regulation and transformation was not investigated. This report demonstrates that Cdk2 in cyclin D1-Cdk2 complexes from mammary epithelial cells is phosphorylated on the activating phosphorylation site, Thr(160). Furthermore, cyclin D1-Cdk2 complexes catalyze Rb phosphorylation on multiple sites in vitro. As a model to investigate the biological and biochemical functions of cyclin D1-Cdk2 complexes, and the mechanisms by which cyclin D1 activates Cdk2, a cyclin D1-Cdk2 fusion gene was constructed. The cyclin D1-Cdk2 fusion protein expressed in epithelial cells was phosphorylated on Thr(160) and catalyzed the phosphorylation of Rb on multiple sites in vitro and in vivo. Kinase activity was not observed if either the cyclin D1 or Cdk2 domain was mutationally inactivated. Mutational inactivation of the cyclin D1 domain prevented activating phosphorylation of the Cdk2 domain on Thr(160). These results indicate that the cyclin D1 domain of the fusion protein activated the Cdk2 domain through an intramolecular mechanism. Cells stably expressing the cyclin D1-Cdk2 fusion protein exhibited several hallmarks of transformation including hyperphosphorylation of Rb, resistance to TGFbeta-induced growth arrest, and anchorage-independent proliferation in soft agar. We propose that cyclin D1-Cdk2 complexes mediate some of the transforming effects of cyclin D1 and demonstrate that the cyclin D1-Cdk2 fusion protein is a useful model to investigate the biological functions of cyclin D1-Cdk2 complexes.

Quantitative analysis of cyclin D1 messenger RNA expression in head and neck squamous cell carcinomas

Cyclin D1 is thought to play a critical role in the G1/S phase transition of the cell cycle. Amplification of this gene has been reported in several types of human neoplasms including breast, lung, esophageal, and head and neck tumors. In this study, we have analyzed the relative level of expression of cyclin D1 messenger RNA (mRNA) in fresh specimens of head and neck squamous cell carcinoma (HNSCC), and investigated the concordance of the overexpression of cyclin D1 mRNA with gene amplification. Levels of cyclin D1 mRNA were analyzed by a modified method of competitive reverse transcription-polymerase chain reaction and levels of cyclin D1 gene amplification were evaluated by Southern blot hybridization in a series of 23 matched normal mucosas and HNSCC. Overexpression of cyclin D1 mRNA was observed in 10 of 23 cases (43.5%) of HNSCC, ranging from 2 to 50-fold higher than the normal control. Twelve of 23 cases could be evaluated by Southern blot hybridization, and gene amplification was found in only 2 of 12 cases (16.7%). These findings suggest that cyclin D1 plays an important role in tumorigenesis of HNSCC, and gene amplification is not one of the major mechanisms for overexpression of cyclin D1.

Role of protein kinase activity in apoptosis

The transmission of signals from the plasma membrane to the nucleus involves a number of different pathways all of which have in common protein modification. The modification is primarily in the form of phosphorylation which leads to the activation of a series of protein kinases. It is now evident that these pathways are common to stimuli that lead to mitogenic and apoptotic responses. Even the same stimuli under different physiological conditions can cause either cell proliferation or apoptosis. Activation of specific protein kinases can in some circumstances protect against cell death, while in others it protects the cell against apoptosis. Some of the pathways involved lead to activation of transcription factors and the subsequent induction of genes involved in the process of cell death or proliferation. In other cases, such as for the tumour suppressor gene product p53, activation may be initiated both at the level of gene expression or through pre-existing proteins. Yet in others, while the initial steps in the pathway are ill-defined, it is clear that downstream activation of a series of cystein proteases is instrumental in pushing the cell towards apoptosis. In this report we review the involvement of protein kinases at several different levels in the control of cell behaviour.

Mammalian deoxyribonucleoside kinases

The mammalian deoxyribonucleoside kinases are deoxycytidine kinase, thymidine kinase 1 and 2 and deoxyguanosine kinase. These enzymes phosphorylate deoxyribonucleosides and thereby provide an alternative to de novo synthesis of DNA precursors. Their activities are essential for the activation of several chemotherapeutically important nucleoside analogues. In recent years, these enzymes have been thoroughly characterised with regard to structure, substrate specificity and patterns of expression. In this review, these results are reviewed and furthermore, the physiologic metabolic role of the anabolic enzymes is discussed in relation to catabolic pathways. The significance of this information for the development of therapeutic protocols and choice of animal model systems is discussed. Finally, alternative pathways for nucleoside analogue phosphorylation are surveyed, such as the phosphotransfer capacity of 5'-nucleotidase.