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The γ-tubulin meshwork assists in the recruitment of PCNA to chromatin in mammalian cells.

ABSTRACT: Changes in the location of γ-tubulin ensure cell survival and preserve genome integrity. We investigated whether the nuclear accumulation of γ-tubulin facilitates the transport of proliferating cell nuclear antigen (PCNA) between the cytosolic and the nuclear compartment in mammalian cells. We found that the γ-tubulin meshwork assists in the recruitment of PCNA to chromatin. Also, decreased levels of γ-tubulin reduce the nuclear pool of PCNA. In addition, the γ-tubulin C terminus encodes a PCNA-interacting peptide (PIP) motif, and a γ-tubulin-PIP-mutant affects the nuclear accumulation of PCNA. In a cell-free system, PCNA and γ-tubulin formed a complex. In tumors, there is a significant positive correlation between TUBG1 and PCNA expression. Thus, we report a novel mechanism that constitutes the basis for tumor growth by which the γ-tubulin meshwork maintains indefinite proliferation by acting as an opportune scaffold for the transport of PCNA from the cytosol to the chromatin.

SUBMITTER: Corvaisier M

PROVIDER: S-EPMC8219688 | biostudies-literature |

REPOSITORIES: biostudies-literature

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The g-tubulin meshwork assists to the transport of cytosolic PCNA to chromatin in mammalian cells

Project description:Changes in the location of g-tubulin ensure cell survival and preserve genome integrity. We investigated whether the nuclear accumulation of g-tubulin facilitates the transport of proliferating cell nuclear antigen (PCNA) between the cytosolic and the nuclear compartment in mammalian cells. We found that the g-tubulin meshwork assists to the recruitment of PCNA to chromatin. Also, decreased levels of g-tubulin affected the nuclear pool of PCNA. In addition, the g-tubulin C terminus encodes a PCNA-interacting peptide (PIP) motif, and a g-tubulin–PIP-mutant affects the nuclear accumulation of PCNA. In a cell-free system, PCNA and g-tubulin formed a complex. In tumors, there is a significant positive correlation between TUBG1 and PCNA expression. Thus, we report a novel mechanism that constitutes the basis for tumor growth by which the g-tubulin meshwork maintains indefinite proliferation by acting as an opportune scaffold for the transport of PCNA from the cytosol to the chromatin.

2021-06-18 | GSE173732 | GEO

The g-tubulin meshwork assists to the transport of cytosolic PCNA to chromatin in mammalian cells

Project description:Changes in the location of g-tubulin ensure cell survival and preserve genome integrity. We investigated whether the nuclear accumulation of g-tubulin facilitates the transport of proliferating cell nuclear antigen (PCNA) between the cytosolic and the nuclear compartment in mammalian cells. We found that the g-tubulin meshwork assists to the recruitment of PCNA to chromatin. Also, decreased levels of g-tubulin reduce the nuclear pool of PCNA. In addition, the g-tubulin C terminus encodes a PCNA-interacting peptide (PIP) motif, and a g-tubulin–PIP-mutant affects the nuclear accumulation of PCNA. In a cell-free system, PCNA and g-tubulin formed a complex. In tumors, there is a significant positive correlation between TUBG1 and PCNA expression. Thus, we report a novel mechanism that constitutes the basis for tumor growth by which the g-tubulin meshwork maintains indefinite proliferation by acting as an opportune scaffold for the transport of PCNA from the cytosol to the chromatin.

2021-04-17 | GSE148798 | GEO

The g-tubulin meshwork assists to the transport of cytosolic PCNA to chromatin in mammalian cells

Project description:The g-tubulin meshwork assists to the transport of cytosolic PCNA to chromatin in mammalian cells

| PRJNA726926 | ENA

The g-tubulin meshwork assists to the transport of cytosolic PCNA to chromatin in mammalian cells

Project description:The g-tubulin meshwork assists to the transport of cytosolic PCNA to chromatin in mammalian cells

| PRJNA625747 | ENA

Gamma-tubulin coordinates nuclear envelope assembly around chromatin.

Project description:The cytosolic role of ?-tubulin as a microtubule organizer has been studied thoroughly, but its nuclear function is poorly understood. Here, we show that ?-tubulin is located throughout the chromatin of demembranated Xenopus laevis sperm and, as the nucleus is formed, ?-tubulin recruits lamin B3 and nuclear membranes. Immunodepletion of ?-tubulin impairs X. laevis assembly of both the lamina and the nuclear membrane. During nuclear formation in mammalian cell lines, ?-tubulin establishes a cellular protein boundary around chromatin that coordinates nuclear assembly of the daughter nuclei. Furthermore, expression of a ?-tubulin mutant that lacks the DNA-binding domain forms chromatin-empty nuclear like structures and demonstrate that a constant interplay between the chromatin-associated and the cytosolic pools of ?-tubulin is required and, when the balance between pools is impaired, aberrant nuclei are formed. We therefore propose that the nuclear protein meshwork formed by ?-tubulin around chromatin coordinates nuclear formation in eukaryotic cells.

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Recruitment of the gamma-tubulin ring complex to Drosophila salt-stripped centrosome scaffolds.

Project description:Extracting isolated Drosophila centrosomes with 2 M KI generates salt-resistant scaffolds that lack the centrosomal proteins CP190, CP60, centrosomin, and gamma-tubulin. To clarify the role of these proteins in microtubule nucleation by centrosomes and to identify additional centrosome components required for nucleation, we have developed an in vitro complementation assay for centrosome function. Centrosome aster formation is reconstituted when these inactive, salt-stripped centrosome scaffolds are supplemented with a soluble fraction of a Drosophila embryo extract. The CP60 and CP190 can be removed from this extract without effect, whereas removing the gamma-tubulin destroys the complementing activity. Consistent with these results, we find no evidence that these three proteins form a complex together. Instead, gamma-tubulin is found in two distinct protein complexes of 240,000 and approximately 3,000,000 D. The larger complex, which is analogous to the Xenopus gamma-tubulin ring complex (gammaTuRC) (Zheng, Y., M.L. Wong, B. Alberts, and T. Mitchison. 1995. Nature. 378:578-583), is necessary but not sufficient for complementation. An additional factor found in the extract is required. These results provide the first evidence that the gammaTuRC is required for microtubule nucleation at the centrosome.

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The role of Xgrip210 in gamma-tubulin ring complex assembly and centrosome recruitment.

Project description:The gamma-tubulin ring complex (gammaTuRC), purified from the cytoplasm of vertebrate and invertebrate cells, is a microtubule nucleator in vitro. Structural studies have shown that gammaTuRC is a structure shaped like a lock-washer and topped with a cap. Microtubules are thought to nucleate from the uncapped side of the gammaTuRC. Consequently, the cap structure of the gammaTuRC is distal to the base of the microtubules, giving the end of the microtubule the shape of a pointed cap. Here, we report the cloning and characterization of a new subunit of Xenopus gammaTuRC, Xgrip210. We show that Xgrip210 is a conserved centrosomal protein that is essential for the formation of gammaTuRC. Using immunogold labeling, we found that Xgrip210 is localized to the ends of microtubules nucleated by the gammaTuRC and that its localization is more distal, toward the tip of the gammaTuRC-cap structure, than that of gamma-tubulin. Immunodepletion of Xgrip210 blocks not only the assembly of the gammaTuRC, but also the recruitment of gamma-tubulin and its interacting protein, Xgrip109, to the centrosome. These results suggest that Xgrip210 is a component of the gammaTuRC cap structure that is required for the assembly of the gammaTuRC.

| S-EPMC2150686 | biostudies-literature

The centrosomal recruitment of γ-tubulin and its microtubule nucleation activity is α-fodrin guided.

Project description:The regulation and recruitment of γ-TuRCs, the prime nucleator of microtubules, to the centrosome are still thrust areas of research. The interaction of fodrin, a sub-plasmalemmal cytoskeletal protein, with γ-tubulin is a new area of interest. To understand the cellular significance of this interaction, we show that depletion of α-fodrin brings in a significant reduction of γ-tubulin in neural cell centrosomes making it functionally under-efficient. This causes a loss of nucleation ability that cannot efficiently form microtubules in interphase cells and astral microtubules in mitosis. Fluorescence Recovery after Photobleaching (FRAP) experiment implies that α-fodrin is important in the recruitment of γ-tubulin to the centrosome resulting in the aforementioned effects. Further, our experiments indicate that the interaction of α-fodrin with certain pericentriolar matrix proteins such as Pericentrin and CDK5RAP2 are crucial for the recruitment of γ-tubulin to the centrosome. Earlier we reported that α-fodrin limits the nucleation potential of γ-TuRC. In that context, this study suggests that α-fodrin is a γ-tubulin recruiting protein to the centrosome thus preventing cytoplasmic microtubule nucleation and thereby compartmentalizing the process to the centrosome for maximum efficiency. Summary statementα-fodrin is a γ-tubulin interacting protein that controls the process of γ-tubulin recruitment to the centrosome and thereby regulates the microtubule nucleation capacity spatially and temporally.

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Gamma-tubulin is required for proper recruitment and assembly of Kar9-Bim1 complexes in budding yeast.

Project description:Microtubule plus-end-interacting proteins (+TIPs) promote the dynamic interactions between the plus ends (+ends) of astral microtubules and cortical actin that are required for preanaphase spindle positioning. Paradoxically, +TIPs such as the EB1 orthologue Bim1 and Kar9 also associate with spindle pole bodies (SPBs), the centrosome equivalent in budding yeast. Here, we show that deletion of four C-terminal residues of the budding yeast gamma-tubulin Tub4 (tub4-delta dsyl) perturbs Bim1 and Kar9 localization to SPBs and Kar9-dependent spindle positioning. Surprisingly, we find Kar9 localizes to microtubule +ends in tub4-delta dsyl cells, but these microtubules fail to position the spindle when targeted to the bud. Using cofluorescence and coaffinity purification, we show Kar9 complexes in tub4-delta dsyl cells contain reduced levels of Bim1. Astral microtubule dynamics is suppressed in tub4-delta dsyl cells, but it are restored by deletion of Kar9. Moreover, Myo2- and F-actin-dependent dwelling of Kar9 in the bud is observed in tub4-delta dsyl cells, suggesting defective Kar9 complexes tether microtubule +ends to the cortex. Overproduction of Bim1, but not Kar9, restores Kar9-dependent spindle positioning in the tub4-delta dsyl mutant, reduces cortical dwelling, and promotes Bim1-Kar9 interactions. We propose that SPBs, via the tail of Tub4, promote the assembly of functional +TIP complexes before their deployment to microtubule +ends.

| S-EPMC1635365 | biostudies-literature

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Project description:The γ-tubulin ring complex (γ-TuRC) is a key part of microtubule-organizing centers (MTOCs) that control microtubule polarity, organization and dynamics in eukaryotes. Understanding regulatory mechanisms of γ-TuRC function is of fundamental importance, as this complex is central to many cellular processes, including chromosome segregation, fertility, neural development, T-cell cytotoxicity and respiration. The fission yeast microtubule motor kinesin-14 Pkl1 regulates mitosis by binding to the γ-tubulin small complex (γ-TuSC), a subunit of γ-TuRC. Here we investigate the binding mechanism of Pkl1 to γ-TuSC and its functional consequences using genetics, biochemistry, peptide assays and cell biology approaches in vivo and in vitro. We identify two critical elements in the Tail domain of Pkl1 that mediate γ-TuSC binding and trigger release of γ-tubulin from γ-TuRC. Such action disrupts the MTOC and results in failed mitotic spindle assembly. This study is the first demonstration that a motor protein directly affects the structural composition of the γ-TuRC, and we provide details of this mechanism that may be of broad biological importance.

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