Cell cycle events regulator

II. PROTEIN KINASE ACTIVITY AND REGULATION OF CELL CYCLE EVENTS IN THE YEAST AND SELECTED VERTEBRATE MODEL SYSTEMS... 

All eukaryotic cells have checkpoint regulation.32 A deletion in a gene encoding a checkpoint regulator abolishes the strict follow-up of one cell-cycle event after the other. Kim Nasmyth,33 therefore wants the term checkpoint to be applied only to those controls that ensure the ordered sequence of cell-cycle events. Following his definition, checkpoints are in essence inhibitory signalling pathways that keep a cell-cycle transition in check until the preceding operation is completed. 

It was also reported that menthol suppressed the viabihty of human malignant melanoma cell line, G-361 and was proposed that the influx of calcium through activation of TRPM8 channels may be responsible for the regulation of cell cycle events leading to cell death in such melanoma cells [27]. 

Gautier Returning to the nuclear cytoplasmic ratio, in a situation where you don t block any event in the cell cycle, such as experiments in frogs where a mosaic is made between the diploid and tetraploid tissue, the tetraploid cells are twice as large. There is some regulation here the amount of DNA is somehow influencing the size of the cell. 

Whether the DNA replication checkpoint directly affects the Plxl activation pathway for Cdc25C has not yet been established. It is possible that the replication checkpoint arrests the cell cycle prior to initiation of the Plxl kinase cascade. Further characterization of upstream components of the cascade should reveal whether it is directly regulated by replication checkpoint activation. Such a characterization will also have importance for other M phase events, inasmuch as Plxl also regulates bipolar spindle formation, APC activation and cytokinesis (Qian et al 1998, 1999). These multiple functions of Plxl are associated with changes in localization of Plxl, and are most likely mediated by protein—protein interaction with the polo box motif in the non-catalytic C-terminal half of Plxl. 

Although further studies are needed to clarify the mechanism(s) of lycopene interference with cell signaling leading to down-regulation of cyclin Dl and ultimately to cell cycle arrest in both normal and tumor cells, these reports suggest that the reduction in cyclin Dl by lycopene treatment may be a key event in the ability of the carotenoid to arrest cell cycle progression. 

The normally functioning cellular counterparts of the oncogenes, called protooncogenes are also important regulators of biological processes. They are localized in different cell compartments, are expressed at different stages of the cell cycle, and appear to be involved in the cascade of events that maintain the ordered procession through the cell cycle. 

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