The Roles Of Centrosomal Protein FOR20in Cell Cycle Progression

Cell cycle progression is one of the fundamental activities of organisms. Cell cycle progression is involved in both physiological and pathological progresses. Out of control of cell cycle progression is involved in numerous of diseases such as cancer. Previous studies demonstrate that cell cycle is very complicated process, which regulated a bunch of molecules and signaling pathways. Microtubules, as one of the major cytoskeleton, play important roles in cell cycle progression. The balance between polymerization and depolymerizaion of microtubules needs to be very well regulated to keep cell cycle progression normally processed. Microtubules dynamics defects are found to be correlated with some kinds of diseases. So during the past decades lots of people try to investigate cell cycle progression by focusing on microtubule regulation to uncover the mechanisms underlying diseases.In normal physiological condition microtubule dynamics is precisely regulated. Proteins associate with centrosomes or microtubules are always involved in microtubule dynamics regulation. NudC/Lisl/dynein (Nuclear distribution gene C/lissencephaly1/dynein) is a conservative signaling pathway that our lab focuses on during the past few years. Our data and previous studies reveal that NudC/Lisl/dynein related proteins are not only found to be localized to centrosomes but also involved in microtubule dynamics regulation. We identified three NudC homology genes in mammalian cells which are all play roles in microtubule dynamics regulation. However, as the signaling center of NudC/Lis1/dynein pathway, Lisl is not thoroughly studied in terms of whether it also has multiple homology genes in mammalian cells. Based on the domain analysis of Lis1protein and combined with bioinformatics strategy we found a LisH domain (Lis Homology), which is a conserve domain in the N-terminus of Lisl, containing protein FOR20(FOP related protein of20kDa).Part I:The Role of Centrosomal Protein FOR20in S-phase ProgressionCentrosomes are required for efficient cell-cycle progression mainly by directing microtubule dynamics and facilitating G1/S and G2/M transitions. However, the role of centrosomes in S-phase progression is largely unknown. Here, we report that depletion of FOR20, a conserved centrosomal protein, inhibits S-phase progression and prevents targeting of Plkl (Polo-like kinase1) to centrosomes, where FOR20interacts with Plkl. Ablation of Plkl also significantly induces S-phase defects, which are reversed by ectopic expression of Plkl, even a kinase-dead mutant, but not a mutant that fails to localize to centrosomes. Exogenous expression of centrosome-tethered Plkl, but not wild-type Plkl, overrides FOR20depletion-induced S-phase defects independent of its kinase activity. Thus, these data indicate that recruitment of Plk1to centrosomes by FOR20may act as a signal to license efficient progression of S-phase. This represents a hitherto uncharacterized role of centrosomes in cell cycle regulation. And the data indicates that it may exsist a Plkl related centrosomal check point for S-phase progression.Part II:The Role of FOR20in CytokinesisMidbody is a complex structure between two daughter cells during cytokinesis which defines the site where the eventual abscission takes place and physically separates the two daughter cells. Lots of midbody localized proteins are found to be involved in cytokinesis regulation. However, which of those midbody localized proteins are essential for cytokinesis regulation and the detail mechnisams underlying that are still not well understood. Our Further investigation about FOR20revealed that it is not only localizes to centrosomes but also recruited to midbodies during cytokinesis. Some midbody localized proteins such as Plk1and Aroura B are recruited to midzone at Anaphase before they are eventually targeted to midbody during cytokinesis. However, the midbody localization pattern of FOR20is totally different with those kinds of classic midbody localized proteins. It is directly recruited to midbody during its formation. Knock down experiments indicated that depletion of endogenous FOR20result to significant abscission defects. The abscission process is dramatically prolonged. However, the midbody formation is not impaired by FOR20depeletion. As we previously demonstrate FOR20is essential for S-phase progression by recruiting P1k1to centrosmes, but here, the role of FOR20plays at midbody for cytokinesis is independent of Plkl.In summary, LisH domain containing protein FOR20plays important roles in cell cycle progression. The study of Lisl homology gene FOR20makes us know better about roles of NudC/Lisl/dynein signaling pathway in cell cycle regulation. And potentially, it may provide a new target for cell cycle related diseases treatment.