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Rho-dependent control of the Citron kinase, Sticky, drives midbody ring maturation.

ABSTRACT: Rho-dependent proteins control assembly of the cytokinetic contractile ring, yet it remains unclear how those proteins guide ring closure and how they promote subsequent formation of a stable midbody ring. Citron kinase is one important component required for midbody ring formation but its mechanisms of action and relationship with Rho are controversial. Here, we conduct a structure-function analysis of the Drosophila Citron kinase, Sticky, in Schneider's S2 cells. We define two separable and redundant RhoGEF/Pebble-dependent inputs into Sticky recruitment to the nascent midbody ring and show that each input is subsequently required for retention at, and for the integrity of, the mature midbody ring. The first input is via an actomyosin-independent interaction between Sticky and Anillin, a key scaffold also required for midbody ring formation. The second input requires the Rho-binding domain of Sticky, whose boundaries we have defined. Collectively, these results show how midbody ring biogenesis depends on the coordinated actions of Sticky, Anillin, and Rho.

SUBMITTER: El-Amine N

PROVIDER: S-EPMC6743463 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Tissue-specific control of midbody microtubule stability by Citron kinase through modulation of TUBB3 phosphorylation.

Project description:Cytokinesis, the physical separation of daughter cells at the end of cell cycle, is commonly considered a highly stereotyped phenomenon. However, in some specialized cells this process may involve specific molecular events that are still largely unknown. In mammals, loss of Citron-kinase (CIT-K) leads to massive cytokinesis failure and apoptosis only in neuronal progenitors and in male germ cells, resulting in severe microcephaly and testicular hypoplasia, but the reasons for this specificity are unknown. In this report we show that CIT-K modulates the stability of midbody microtubules and that the expression of tubulin β-III (TUBB3) is crucial for this phenotype. We observed that TUBB3 is expressed in proliferating CNS progenitors, with a pattern correlating with the susceptibility to CIT-K loss. More importantly, depletion of TUBB3 in CIT-K-dependent cells makes them resistant to CIT-K loss, whereas TUBB3 overexpression increases their sensitivity to CIT-K knockdown. The loss of CIT-K leads to a strong decrease in the phosphorylation of S444 on TUBB3, a post-translational modification associated with microtubule stabilization. CIT-K may promote this event by interacting with TUBB3 and by recruiting at the midbody casein kinase-2α (CK2α) that has previously been reported to phosphorylate the S444 residue. Indeed, CK2α is lost from the midbody in CIT-K-depleted cells. Moreover, expression of the nonphosphorylatable TUBB3 mutant S444A induces cytokinesis failure, whereas expression of the phospho-mimetic mutant S444D rescues the cytokinesis failure induced by both CIT-K and CK2α loss. Altogether, our findings reveal that expression of relatively low levels of TUBB3 in mitotic cells can be detrimental for their cytokinesis and underscore the importance of CIT-K in counteracting this event.

| S-EPMC4832100 | biostudies-literature

Citron kinase controls a molecular network required for midbody formation in cytokinesis.

Project description:Cytokinesis partitions cytoplasmic and genomic materials at the end of cell division. Failure in this process causes polyploidy, which in turn can generate chromosomal instability, a hallmark of many cancers. Successful cytokinesis requires cooperative interaction between contractile ring and central spindle components, but how this cooperation is established is poorly understood. Here we show that Sticky (Sti), the Drosophila ortholog of the contractile ring component Citron kinase (CIT-K), interacts directly with two kinesins, Nebbish [the fly counterpart of human kinesin family member 14 (KIF14)] and Pavarotti [the Drosophila ortholog of human mitotic kinesin-like protein 1 (MKLP1)], and that in turn these kinesins interact with each other and with another central spindle protein, Fascetto [the fly ortholog of protein regulator of cytokinesis 1 (PRC1)]. Sti recruits Nebbish to the cleavage furrow, and both proteins are required for midbody formation and proper localization of Pavarotti and Fascetto. These functions require Sti kinase activity, indicating that Sti plays both structural and regulatory roles in midbody formation. Finally, we show that CIT-K's role in midbody formation is conserved in human cells. Our findings indicate that CIT-K is likely to act at the top of the midbody-formation hierarchy by connecting and regulating a molecular network of contractile ring components and microtubule-associated proteins.

| S-EPMC3683733 | biostudies-literature

Cross-regulation between Aurora B and Citron kinase controls midbody architecture in cytokinesis.

Project description:Cytokinesis culminates in the final separation, or abscission, of the two daughter cells at the end of cell division. Abscission relies on an organelle, the midbody, which forms at the intercellular bridge and is composed of various proteins arranged in a precise stereotypic pattern. The molecular mechanisms controlling midbody organization and function, however, are obscure. Here we show that proper midbody architecture requires cross-regulation between two cell division kinases, Citron kinase (CIT-K) and Aurora B, the kinase component of the chromosomal passenger complex (CPC). CIT-K interacts directly with three CPC components and is required for proper midbody architecture and the orderly arrangement of midbody proteins, including the CPC. In addition, we show that CIT-K promotes Aurora B activity through phosphorylation of the INCENP CPC subunit at the TSS motif. In turn, Aurora B controls CIT-K localization and association with its central spindle partners through phosphorylation of CIT-K's coiled coil domain. Our results identify, for the first time, a cross-regulatory mechanism between two kinases during cytokinesis, which is crucial for establishing the stereotyped organization of midbody proteins.

| S-EPMC4821246 | biostudies-literature

Opposing actions of septins and Sticky on Anillin promote the transition from contractile to midbody ring.

Project description:During cytokinesis, closure of the actomyosin contractile ring (CR) is coupled to the formation of a midbody ring (MR), through poorly understood mechanisms. Using time-lapse microscopy of Drosophila melanogaster S2 cells, we show that the transition from the CR to the MR proceeds via a previously uncharacterized maturation process that requires opposing mechanisms of removal and retention of the scaffold protein Anillin. The septin cytoskeleton acts on the C terminus of Anillin to locally trim away excess membrane from the late CR/nascent MR via internalization, extrusion, and shedding, whereas the citron kinase Sticky acts on the N terminus of Anillin to retain it at the mature MR. Simultaneous depletion of septins and Sticky not only disrupted MR formation but also caused earlier CR oscillations, uncovering redundant mechanisms of CR stability that can partly explain the essential role of Anillin in this process. Our findings highlight the relatedness of the CR and MR and suggest that membrane removal is coordinated with CR disassembly.

| S-EPMC3824009 | biostudies-literature

Overexpression of Citron Rho-Interacting Serine/Threonine Kinase Associated with Poor Outcome in Bladder Cancer.

Project description:Objective: Citron Rho-Interacting Serine/Threonine Kinase (CIT) was originally identified as a binding partner of active forms of the small GTPases Rho and Rac. This kinase participated in the regulation of cytokinesis and loss of CIT was associated with chromosomal instability. Here, we assume that CIT might be a potential prognostic biomarker for bladder cancer. Materials and Methods: The expression and prognostic significance of CIT mRNA were validated on 5 published microarray data sets, including 948 bladder cancer cases. To further confirm the results, we collected 54 non-carcinomatous human bladder tissue samples and 315 bladder cancer tissues from Zhejiang Provincial People's Hospital to detect the protein level of CIT based on the immunohistochemistry analysis. The Kaplan-Meier method and Cox proportional hazards regression model were used in survival analysis. Results: Analysis results showed that high CIT expression was associated with tumor size (p=0.0001), tumor grade (p<0.0001), smoking status (p=0.0143), TNM stage (p=0.0024), pathological tumor stage (p<0.0001) and aggressive phenotypes of bladder cancer. Independent and pooled survival analyses both indicated that overexpression of CIT was significantly associated with poor survival of bladder cancers. Conclusions: In conclusion, these findings indicated that overexpression of CIT was significantly associated with poor survival outcome in bladder cancers. CIT might serve as a promising prognostic biomarker and therapeutic target for bladder cancers.

| S-EPMC7196275 | biostudies-literature

Citron Rho-interacting kinase silencing causes cytokinesis failure and reduces tumor growth in multiple myeloma.

Project description:Citron Rho-interacting serine/threonine kinase (CIT) is a serine/threonine kinase that acts as a key component of the midbody and is essential for cytokinesis. CIT has been reported to be highly expressed in some tumor tissues and to play a role in cancer proliferation; however, the significance of CIT has not been investigated in multiple myeloma (MM). Here, we identified, by protein microarray and immunohistochemistry, that CIT is 1 of the upregulated proteins in the plasma cells of MM patients compared with healthy controls. Analysis of a gene expression profile data set showed that MM patients with high CIT gene expression had significantly worse overall survival compared with MM patients with low CIT gene expression. CIT silencing in MM cell lines induced cytokinesis failure and resulted in decreased MM cell proliferation in vitro and in vivo. TP53 expression was found to be an independent predictor of CIT dependency, with low-TP53 cell lines exhibiting a strong dependency on CIT. This study provides the rationale for CIT being a potential therapeutic target in MM in future trials.

| S-EPMC6457230 | biostudies-literature

Genetic and systems level analysis of Drosophila sticky/citron kinase and dFmr1 mutants reveals common regulation of genetic networks.

Project description:BackgroundIn Drosophila, the genes sticky and dFmr1 have both been shown to regulate cytoskeletal dynamics and chromatin structure. These genes also genetically interact with Argonaute family microRNA regulators. Furthermore, in mammalian systems, both genes have been implicated in neuronal development. Given these genetic and functional similarities, we tested Drosophila sticky and dFmr1 for a genetic interaction and measured whole genome expression in both mutants to assess similarities in gene regulation.ResultsWe found that sticky mutations can dominantly suppress a dFmr1 gain-of-function phenotype in the developing eye, while phenotypes produced by RNAi knock-down of sticky were enhanced by dFmr1 RNAi and a dFmr1 loss-of-function mutation. We also identified a large number of transcripts that were misexpressed in both mutants suggesting that sticky and dFmr1 gene products similarly regulate gene expression. By integrating gene expression data with a protein-protein interaction network, we found that mutations in sticky and dFmr1 resulted in misexpression of common gene networks, and consequently predicted additional specific phenotypes previously not known to be associated with either gene. Further phenotypic analyses validated these predictions.ConclusionThese findings establish a functional link between two previously unrelated genes. Microarray analysis indicates that sticky and dFmr1 are both required for regulation of many developmental genes in a variety of cell types. The diversity of transcripts regulated by these two genes suggests a clear cause of the pleiotropy that sticky and dFmr1 mutants display and provides many novel, testable hypotheses about the functions of these genes. As both of these genes are implicated in the development and function of the mammalian brain, these results have relevance to human health as well as to understanding more general biological processes.

| S-EPMC2610033 | biostudies-literature

Centrosome-dependent asymmetric inheritance of the midbody ring in Drosophila germline stem cell division.

Project description:Many stem cells, including Drosophila germline stem cells (GSCs), divide asymmetrically, producing one stem cell and one differentiating daughter. Cytokinesis is often asymmetric, in that only one daughter cell inherits the midbody ring (MR) upon completion of abscission even in apparently symmetrically dividing cells. However, whether the asymmetry in cytokinesis correlates with cell fate or has functional relevance has been poorly explored. Here we show that the MR is asymmetrically segregated during GSC divisions in a centrosome age-dependent manner: male GSCs, which inherit the mother centrosome, exclude the MR, whereas female GSCs, which we here show inherit the daughter centrosome, inherit the MR. We further show that stem cell identity correlates with the mode of MR inheritance. Together our data suggest that the MR does not inherently dictate stem cell identity, although its stereotypical inheritance is under the control of stemness and potentially provides a platform for asymmetric segregation of certain factors.

| S-EPMC3890347 | biostudies-literature

The midbody ring scaffolds the abscission machinery in the absence of midbody microtubules.

Project description:Abscission completes cytokinesis to form the two daughter cells. Although abscission could be organized from the inside out by the microtubule-based midbody or from the outside in by the contractile ring-derived midbody ring, it is assumed that midbody microtubules scaffold the abscission machinery. In this paper, we assess the contribution of midbody microtubules versus the midbody ring in the Caenorhabditis elegans embryo. We show that abscission occurs in two stages. First, the cytoplasm in the daughter cells becomes isolated, coincident with formation of the intercellular bridge; proper progression through this stage required the septins (a midbody ring component) but not the membrane-remodeling endosomal sorting complex required for transport (ESCRT) machinery. Second, the midbody and midbody ring are released into a specific daughter cell during the subsequent cell division; this stage required the septins and the ESCRT machinery. Surprisingly, midbody microtubules were dispensable for both stages. These results delineate distinct steps during abscission and highlight the central role of the midbody ring, rather than midbody microtubules, in their execution.

| S-EPMC3824018 | biostudies-literature

[Citron Rho-interacting serine/threonine kinase knockdown suppresses prostate cancer cell proliferation and metastasis by blocking Hippo-YAP pathway].

Project description:OBJECTIVE:Citron Rho-interacting serine/threonine kinase (CIT) was identified recently as an oncogene involved in the progression of various malignant tumors, but its role in prostate cancer (PCa) remains unclear. In this study, we aimed to investigate the biological functions of CIT in PCa. METHODS:We analyzed the expression of CIT in PCa tissues and its clinical correlations based on the Cancer Genome Atlas (TCGA) and Memorial Sloan-Kettering Cancer Center (MSKCC) dataset. We then examined the effects of RNA interference-mediated CIT silencing on the proliferation, migration and invasion of PC-3 cells using cell counting kit-8, wound healing assay and Transwell assay. We also investigated the effect of CIT silencing on epithelial-mesenchymal transition (EMT) and Hippo-Yap signaling pathway in the cells using Western blotting. RESULTS:CIT expression was significantly elevated in PCa tissues from TCGA cohort (P < 0.05). MSKCC dataset analysis showed that an elevated expression of CIT was significantly correlated with N stage (P=0.001), distant metastasis (P < 0.001), Gleason score (P=0.010) and PSA (P=0.004). In cultured PC-3 cells, knockdown of CIT significantly inhibited cell proliferation, migration and invasion, reversed the EMT phenotype and decreased the expression and activity of YAP. CONCLUSIONS:CIT might function as an oncogene in PCa by modulating the Hippo-YAP signaling pathway and serve as a candidate therapeutic target for PCa.

| S-EPMC6765676 | biostudies-literature

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