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Régis Giet

Publications and source records attributed to Régis Giet.

6 recordsLinked to original sources
PubMed2005

Drosophila Nek2 protein kinase knockdown leads to centrosome maturation defects while overexpression causes centrosome fragmentation and cytokinesis failure.

The Nima-related kinase 2 (Nek2) has been implicated in the regulation of centrosome integrity and separation in several species and is a candidate for cell transformation. We now show that reduction of levels of the Drosophila Nek2 by RNAi in cultured cells leads to both dispersal of centrosomal antigens and formation of ectopic bodies of centrosomal antigens. Overexpression of the active DmNek2 kinase resulted in an increase in the number of mitotic cells with fragmented centrosomes. The DmNek2 protein kinase is associated with punctuate bodies within the centrosome consistent with its presence on centrioles. In addition, it is present at lower levels on the midbody during cytokinesis. Midbody association was enhanced following overexpression, whereupon the DmNek2 protein kinase also localised to the cell cortex becoming concentrated in the region of the cleavage furrow in late telophase. Many of such cells showed abnormalities in the organisation of anillin and actin in the cleavage furrow that was associated with formation of ectopic membrane protrusions between each daughter cell. We discuss potential roles for DmNek2 in maintaining centrosome integrity in mitosis, during cytokinesis, and consequently for the fidelity of chromosome segregation.

Actins↗
PubMed2005

Aurora kinases, aneuploidy and cancer, a coincidence or a real link?

As Aurora kinases are overexpressed in a large number of cancers, and ectopic expression of Aurora generates polyploid cells containing multiple centrosomes, it has been tempting to suggest that Aurora overexpression provokes genetic instability underlying the tumorigenesis. However, examination of the evidence suggests a more complex relationship. Overexpression of Aurora-A readily transforms rat-1 and NIH3T3 cells, but not primary cells, whereas overexpression of Aurora-B induces metastasis after implantation of tumors in nude mice. Why do polyploid cells containing abnormal centrosome numbers induced by Aurora not get eliminated at cell-cycle checkpoints? Does this phenotype determine the origin of cancer or does it only promote tumor progression? Would drugs against Aurora family members be of any help for cancer treatment? These and related questions are addressed in this review (which is part of the Chromosome Segregation and Aneuploidy series).

Aneuploidy↗
PubMed2004

The E2-C vihar is required for the correct spatiotemporal proteolysis of cyclin B and itself undergoes cyclical degradation.

BACKGROUND: Proteolytic degradation of mitotic regulatory proteins first requires these targets to be ubiquitinated. This is regulated at the level of conjugation of ubiquitin to substrates by the anaphase-promoting complex/cyclosome (APC/C) ubiquitin-protein ligase. Substrate specificity and temporal activity of the APC/C has been thought to lie primarily with its two activators, Cdc20/Fizzy and Cdh1/Fizzy-related. RESULTS: Here, we show that reduction in the E2 ubiquitin-conjugating enzyme (UBC) of the E2-C family that is encoded by the Drosophila gene vihar (vih), by either mutation or RNAi, leads to an accumulation of cells in a metaphase-like state. Cyclin B accumulates to high levels in all mitotic vih cells, particularly at the spindle poles. Vihar E2-C is present in the cytoplasm of mitotic cells but also associates with centrosomes, and its own degradation is initiated at the metaphase-anaphase transition. Expression of destruction D box mutants of vihar in the syncytial embryo results in mitotic arrest at late anaphase. In contrast to hypomorphic mutants, Cyclin B is degraded at the spindle poles and accumulates in the equatorial region of the spindle. CONCLUSIONS: In Drosophila, the Vihar E2 UBC contributes to the spatiotemporal control of Cyclin B degradation that first occurs at the spindle poles. APC/C-mediated proteolysis of Vihar E2-C autoinactivates the APC/C at the centrosome before a second wave of proteolysis to degrade Cyclin B on the rest of the spindle and elsewhere in the cell.

Anaphase-Promoting Complex-Cyclosome↗
PubMed2003

Aurora A and mitotic commitment.

A remarkable study published in this issue of Cell reveals a key role of Aurora A protein kinase in G2/M progression. To achieve this role, Aurora A acts in conjunction with the LIM protein Ajuba, which functions as an activating factor.

Animals↗
PubMed2002

Drosophila Aurora A kinase is required to localize D-TACC to centrosomes and to regulate astral microtubules.

Disruption of the function of the A-type Aurora kinase of Drosophila by mutation or RNAi leads to a reduction in the length of astral microtubules in syncytial embryos, larval neuroblasts, and cultured S2 cells. In neuroblasts, it can also lead to loss of an organized centrosome and its associated aster from one of the spindle poles, whereas the centrosome at the other pole has multiple centrioles. When centrosomes are present at the poles of aurA mutants or aurA RNAi spindles, they retain many antigens but are missing the Drosophila counterpart of mammalian transforming acidic coiled coil (TACC) proteins, D-TACC. We show that a subpopulation of the total Aurora A is present in a complex with D-TACC, which is a substrate for the kinase. We propose that one of the functions of Aurora A kinase is to direct centrosomal organization such that D-TACC complexed to the MSPS/XMAP215 microtubule-associated protein may be recruited, and thus modulate the behavior of astral microtubules.

Adenosine Triphosphate↗