Mitotic Kinase Aurora Research Articles

Recruitment of PP1 to the centrosomal scaffold protein CEP192

Centrosomal protein of 192 kDa (CEP192) is a scaffolding protein that recruits the mitotic protein kinases Aurora A and PLK1 to the centrosome. Here we demonstrate that CEP192 also recruits the type one protein phosphatase (PP1) via a highly conserved KHVTF docking motif. The threonine of the KHVTF motif is phosphorylated during mitosis and protein kinase inhibition studies suggest this to be a PLK1-dependent process.

A water-mediated allosteric network governs activation of Aurora kinase A.

The catalytic activity of many protein kinases is controlled by conformational changes of a conserved Asp-Phe-Gly (DFG) motif. We used an infrared probe to track the DFG motif of the mitotic kinase Aurora A (AurA) and found that allosteric activation by the spindle-associated protein Tpx2 involves an equilibrium shift toward the active DFG-in state. Förster resonance energy transfer experiments show that the activation loop undergoes a nanometer-scale movement that is tightly coupled to the DFG equilibrium. Tpx2 further activates AurA by stabilizing a water-mediated allosteric network that links the C-helix to the active site through an unusual polar residue in the regulatory spine. The polar spine residue and water network of AurA are essential for phosphorylation-driven activation, but an alternative form of the water network found in related kinases can support Tpx2-driven activation, suggesting that variations in the water-mediated hydrogen bond network mediate regulatory diversification in protein kinases.

Functional Effects of AKT3 on Aurora Kinase Inhibitor-induced Aneuploidy

The suppression of mitotic Aurora kinases (AURKs) by AURK inhibitors frequently causes cytokinetic failure, leading to polyploidy or aneuploidy, indicating the critical role of AURK-mediated phosphorylation during cytokinesis. We demonstrate the deregulated expression of AKT3 in Aurora kinase inhibitor (AURKi)-resistant cells, which we established from human colorectal cancer HCT 116 cells. The AKT family, which includes AKT1, -2, and -3, plays multiple roles in antiapoptotic functions and drug resistance and is involved in cell growth and survival pathways. We found that an AKT inhibitor, AZD5363, showed synergistic effect with an AURKi, VX-680, on two AKT3-expressing AURKi-resistant cell lines, and AKT3 knockdown sensitized cells to VX-680. Consistent with these activities, AKT3 expression suppressed AURKi-induced apoptosis and conferred resistance to AURKi. Thus, AKT3 expression affects cell sensitivity to AURKi. Moreover, we found that AKT3 expression suppressed AURKi-induced aneuploidy, and inversely AKT3 knockdown enhanced it. In addition, partial co-localization of AKT3 with AURKB was observed during anaphase. Overall, this study suggests that AKT3 could repress the antiproliferative effects of AURKi, with a novel activity particularly suppressing the aneuploidy induction.

Nucleosome-Dependent Pathways That Control Mitotic Progression.

The majority of eukaryotic chromosomal DNA exists in the form of nucleosomes, where ∼147 bp DNA wraps around histone hetero-octamers, composed of histone H3, H4, H2A, and H2B. Despite their obvious importance in DNA compaction and accessibility, studying their specific roles, such as regulation of mitotic progression, in a physiological environment is associated with critical caveats because of their major contributions in transcriptional control. Through establishing a method to deplete endogenous histones H3 and H4 from frog egg extracts and complementing their functions using recombinant nucleosome arrays, we are now able to analyze their roles in mitotic progression without affecting overall transcriptomic profiles. Here we summarize advancements learned from this system, illustrating that microtubule and nuclear envelope assembly can be regulated by two major nucleosome-bound protein complexes, RCC1-Ran and the chromosomal passenger complex (CPC) containing the mitotic protein kinase Aurora B. We also discuss roles of the CPC on the proteomic composition of mitotic chromatin. The CPC promotes dissociation of a variety of nucleosome remodelers and DNA repair pathway proteins, suggesting its role in suppressing DNA processing activities on mitotic chromosomes. We speculate that this suppression particularly on chromosomes under microtubule tension may be important to preserve genome integrity.

Antitumor activity of TY-011 against gastric cancer by inhibiting Aurora A, Aurora B and VEGFR2 kinases

BackgroundOverexpression of Aurora A and B has been reported in a wide range of tumor types, including gastric cancer. Anti-angiogenesis has been considered as an important therapeutic modality in advanced gastric cancer. Here we identified a novel compound TY-011 with promising antitumor activity by targeting mitotic kinases (Aurora A and B) and angiogenic receptor tyrosine kinase (VEGFR2).MethodsHTRF® KinEASE™ assay was used to detect the effect of TY-011 against Aurora A, Aurora B and VEGFR2 activities. Docking simulation study was performed to predict the binding mode of TY-011 with Aurora A and B kinases. CCK-8 assay was used to test cell growth. Cell cycle and cell apoptosis was analyzed by flow cytometry. Gastric cancer cell xenograft mouse models were used for in vivo study. TUNEL kit was used to determine the apoptosis of tumor tissues. Immunohistochemistry analysis and HUVEC tube formation assay were performed to determine the anti-angiogenesis ability. Immunofluorescence and western blot were used to test protein expression.ResultsTY-011 was identified as a potential Aurora A and B inhibitor by HTRF® KinEASE™ assay. It effectively inhibited cellular Aurora A and B activities in a concentration-dependent manner. TY-011 occupied the ATP-binding site of both Aurora A and B kinases. TY-011 demonstrated prominent inhibitory effects on proliferation of gastric cancer cells. TY-011 treatment induced an obvious accumulation of cells at G2/M phase and a modest increase of cells with >4 N DNA content, which then underwent apoptosis. Meaningfully, orally administration of TY-011 demonstrated superior efficacy against the tumor growth in gastric cancer cell xenograft, with ~90% inhibition rate and 100% tumor regression at 9 mg/kg dose, and TY-011 did not affect the body weight of mice. Interestingly, we observed that TY-011 also antagonized tumor angiogenesis by targeting VEGFR2 kinase.ConclusionsThese results indicate that TY-011 is a well-tolerated, orally active compound that targets mitosis and angiogenesis in tumor growth, and provides strong preclinical support for use as a therapeutic for human gastric cancers.Electronic supplementary materialThe online version of this article (doi:10.1186/s13046-016-0464-2) contains supplementary material, which is available to authorized users.

The C-terminal domain of TPX2 is made of alpha-helical tandem repeats.

BackgroundTPX2 (Targeting Protein for Xklp2) is essential for spindle assembly, activation of the mitotic kinase Aurora A and for triggering microtubule nucleation. Homologs of TPX2 in Chordata and plants were previously identified. Currently, proteins of the TPX2 family have little structural information and only small parts are covered by defined protein domains.MethodsWe have used computational sequence analyses and structural predictions of proteins of the TPX2 family, supported with Circular Dichroism (CD) measurements.ResultsHere, we report our finding that the C-terminal domain of TPX2, which is responsible of its microtubule nucleation capacity and is conserved in all members of the family, is actually formed by tandem repeats, covering well above 2/3 of the protein. We propose that this region forms a flexible solenoid involved in protein-protein interactions. Structural prediction and molecular modeling, combined with Circular Dichroism (CD) measurements reveal a predominant alpha-helical content. Furthermore, we identify full length homologs in fungi and shorter homologs with a different domain organization in diptera (including a paralogous expansion in Drosophila).ConclusionsOur results, represent the first computational and biophysical analysis of the TPX2 proteins family and help understand the structure and evolution of this conserved protein family to direct future structural studies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12900-016-0070-8) contains supplementary material, which is available to authorized users.

The Unexpected Roles of Aurora A Kinase in Gliobastoma Recurrences.

The main obstacle for the cure of glioblastoma (GBM) is systematic tumor recurrence after treatment. More than 90% of GBM tumors are indeed recurrent within 5years after diagnosis and treatment. We urgently need new therapies to specifically address these deadly relapses. A major advance in the understanding of GBM recurrence is the identification of GBM-Initiating Cells (GIC), characterized by their abilities for self-renewal, multilineage differentiation, and proliferation. It appears that these features of GIC could be modulated by the mitotic kinase Aurora A (AurA). Indeed, besides its role in mitosis, AurA has recently been identified to regulate alternative functions like cell polarity, asymmetric cell division, and epithelial to mesenchymal transition. All these properties may help explain GBM therapeutic resistance and recurrence. In this review, we make the hypothesis that AurA could significantly contribute to GBM recurrences and we focus on the possible roles of AurA in GIC.

Abstract 1242: Combination of p21-activated kinase 1 (PAK1) inhibitor FRAX1036 and Aurora-A inhibitor alisertib is effective in hormone receptor-positive breast cancer

Abstract Estrogen receptor alpha (ERα) signaling plays a critical role in the development and progression of hormone receptor-positive (HR+) breast cancer. One mechanism of tumor progression of HR+ breast cancer is phosphorylation of ERα by non-receptor protein kinases, leading to ligand-independent activation of ERα. Mitotic kinases Aurora A (AURKA) and p21-activated kinase 1 (PAK1) are frequently overexpressed in breast cancer and can phosphorylate ERα on serine 305, increasing the ability of ERα to induce transcription of target genes implicated in tumorigenesis. In addition, PAK1 phosphorylates and activates AURKA and its functional partners, suggesting possible synergistic activity in tumors overexpressing both kinases. We tested the hypothesis that combined inhibition of AURKA and PAK1 would synergistically suppress tumor growth of HR+ breast cancer cells in vitro and in vivo. Treatment of T47D HR+ breast cancer cell line with the PAK1 inhibitor FRAX1036, combined with AURKA inhibitor alisertib, improved cell killing in comparison to single agents. FRAX1036 and alisertib were then evaluated in an orthotopic xenograft model using BT474 HR+ breast cancer cell line. Ten million BT474 cells were implanted into the mammary fat pads of 6-week old NSG mice simultaneously with implantation of estrogen pellets to facilitate growth of xenografts. Mice received 21 days of treatment with FRAX1036 20mg/kg daily and alisertib 10 or 15 mg/kg BID, alone or in combination. We observed exceptional inhibition of tumor growth in the combination treatment groups. Combination of FRAX1036 20mg/kg daily with alisertib 15mg/kg BID was the most effective, with partial or near-complete responses that continued through 21 days of treatment. This combination resulted in significantly better inhibition of tumor growth than alisertib 15mg/kg BID alone or FRAX1036 20mg/kg daily alone (p = 0.003 and p = 1.29e-6, respectively). Similarly, combination treatment of FRAX1036 20mg/kg daily with alisertib 10mg/kg BID was significantly better then alisertib alone or FRAX1036 alone in the corresponding doses (p = 0.002 and p = 3.52e-7, respectively). Analysis of H&E stained sections and Ki-67 proliferation index of BT474 xenograft tumors indicated a highly significant decrease in viable tumor cells and replacement by stroma after combination treatment compared to treatment with single agents or with control. Caspase-3 IHC analysis showed significantly greater proportion of apoptotic cells per tumor area in the group of mice treated with FRAX1036 and Alisertib 15mg/kg BID combination comparing to control (p = 0.008). We conclude that combining FRAX1036 and alisertib is a novel and promising approach in HR+ breast cancer. Citation Format: Elena Shagisultanova, Vladislav Korobeynikov, Anna Nikonova, Jonathan Chernoff, Virginia Borges, Erica Golemis. Combination of p21-activated kinase 1 (PAK1) inhibitor FRAX1036 and Aurora-A inhibitor alisertib is effective in hormone receptor-positive breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1242.

Mitotic noncoding RNA processing promotes kinetochore and spindle assembly in Xenopus.

Transcription at the centromere of chromosomes plays an important role in kinetochore assembly in many eukaryotes, and noncoding RNAs contribute to activation of the mitotic kinase Aurora B. However, little is known about how mitotic RNA processing contributes to spindle assembly. We found that inhibition of transcription initiation or RNA splicing, but not translation, leads to spindle defects in Xenopus egg extracts. Spliceosome inhibition resulted in the accumulation of high molecular weight centromeric transcripts, concomitant with decreased recruitment of the centromere and kinetochore proteins CENP-A, CENP-C, and NDC80 to mitotic chromosomes. In addition, blocking transcript synthesis or processing during mitosis caused accumulation of MCAK, a microtubule depolymerase, on the spindle, indicating misregulation of Aurora B. These findings suggest that co-transcriptional recruitment of the RNA processing machinery to nascent mitotic transcripts is an important step in kinetochore and spindle assembly and challenge the idea that RNA processing is globally repressed during mitosis.

Allosteric modulation of AURKA kinase activity by a small-molecule inhibitor of its protein-protein interaction with TPX2.

The essential mitotic kinase Aurora A (AURKA) is controlled during cell cycle progression via two distinct mechanisms. Following activation loop autophosphorylation early in mitosis when it localizes to centrosomes, AURKA is allosterically activated on the mitotic spindle via binding to the microtubule-associated protein, TPX2. Here, we report the discovery of AurkinA, a novel chemical inhibitor of the AURKA-TPX2 interaction, which acts via an unexpected structural mechanism to inhibit AURKA activity and mitotic localization. In crystal structures, AurkinA binds to a hydrophobic pocket (the ‘Y pocket’) that normally accommodates a conserved Tyr-Ser-Tyr motif from TPX2, blocking the AURKA-TPX2 interaction. AurkinA binding to the Y- pocket induces structural changes in AURKA that inhibit catalytic activity in vitro and in cells, without affecting ATP binding to the active site, defining a novel mechanism of allosteric inhibition. Consistent with this mechanism, cells exposed to AurkinA mislocalise AURKA from mitotic spindle microtubules. Thus, our findings provide fresh insight into the catalytic mechanism of AURKA, and identify a key structural feature as the target for a new class of dual-mode AURKA inhibitors, with implications for the chemical biology and selective therapeutic targeting of structurally related kinases.

HP1-Assisted Aurora B Kinase Activity Prevents Chromosome Segregation Errors

Incorrect attachment of kinetochore microtubules is the leading cause of chromosome missegregation in cancers. The highly conserved chromosomal passenger complex (CPC), containing mitotic kinase Aurora B as a catalytic subunit, ensures faithful chromosome segregation through destabilizing incorrectmicrotubule attachments and promoting biorientation of chromosomes on the mitotic spindle. It is unknown whether CPC dysfunction affects chromosome segregation fidelity in cancers and, if so, how. Here, we show that heterochromatin protein 1 (HP1) is an essential CPC component required for full Aurora B activity. HP1 binding to the CPC becomes particularly important when Aurora B phosphorylates kinetochore targets to eliminate erroneous microtubule attachments. Remarkably, a reduced proportion of HP1 bound to CPC is widespread in cancers, which causes an impairment in Aurora B activity. These results indicate that HP1 is an essential modulator for CPC function and identify a molecular basis for chromosome segregation errors in cancer cells.

Aurora kinase targeting in lung cancer reduces KRAS-induced transformation.

BackgroundActivating mutations in KRAS are prevalent in lung cancer and have been causally linked to the oncogenic process. However, therapies targeted to oncogenic RAS have been ineffective to date and identification of KRAS targets that impinge on the oncogenic phenotype is warranted. Based on published studies showing that mitotic kinases Aurora A (AURKA) and B (AURKB) cooperate with oncogenic RAS to promote malignant transformation and that AURKA phosphorylates RAS effector pathway components, the aim of this study was to investigate whether AURKA and AURKB are KRAS targets in lung cancer and whether targeting these kinases might be therapeutically beneficial.MethodsIn order to determine whether oncogenic KRAS induces Aurora kinase expression, we used qPCR and western blotting in three different lung cell-based models of gain- or loss-of-function of KRAS. In order to determine the functional role of these kinases in KRAS-induced transformation, we generated KRAS-positive A549 and H358 cells with stable and inducible shRNA-mediated knockdown of AURKA or AURKB and evaluated transformation in vitro and tumor growth in vivo. In order to validate AURKA and/or AURKB as therapeutically relevant KRAS targets in lung cancer, we treated A549 and H358 cells, as well as two different lung cell based models of gain-of-function of KRAS with a dual Aurora kinase inhibitor and performed functional in vitro assays.ResultsWe determined that KRAS positively regulates AURKA and AURKB expression. Furthermore, in KRAS-positive H358 and A549 cell lines, inducible knockdown of AURKA or AURKB, as well as treatment with a dual AURKA/AURKB inhibitor, decreased growth, viability, proliferation, transformation, and induced apoptosis in vitro. In addition, inducible shRNA-mediated knockdown of AURKA in A549 cells decreased tumor growth in vivo. More importantly, dual pharmacological inhibiton of AURKA and AURKB reduced growth, viability, transformation, and induced apoptosis in vitro in an oncogenic KRAS-dependent manner, indicating that Aurora kinase inhibition therapy can specifically target KRAS-transformed cells.ConclusionsOur results support our hypothesis that Aurora kinases are important KRAS targets in lung cancer and suggest Aurora kinase inhibition as a novel approach for KRAS-induced lung cancer therapy.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-016-0494-6) contains supplementary material, which is available to authorized users.

Nuclear AURKA acquires kinase-independent transactivating function to enhance breast cancer stem cell phenotype

Centrosome-localized mitotic Aurora kinase A (AURKA) facilitates G2/M events. Here we show that AURKA translocates to the nucleus and causes distinct oncogenic properties in malignant cells by enhancing breast cancer stem cell (BCSC) phenotype. Unexpectedly, this function is independent of its kinase activity. Instead, AURKA preferentially interacts with heterogeneous nuclear ribonucleoprotein K (hnRNP K) in the nucleus and acts as a transcription factor in a complex that induces a shift in MYC promoter usage and activates the MYC promoter. Blocking AURKA nuclear localization inhibits this newly discovered transactivating function of AURKA, sensitizing resistant BCSC to kinase inhibition. These findings identify a previously unknown oncogenic property of the spatially deregulated AURKA in tumorigenesis and provide a potential therapeutic opportunity to overcome kinase inhibitor resistance.

Phosphorylation Regulates Interaction of 210-kDa Myosin Light Chain Kinase N-terminal Domain with Actin Cytoskeleton.

High molecular weight myosin light chain kinase (MLCK210) is a multifunctional protein involved in myosin II activation and integration of cytoskeletal components in cells. MLCK210 possesses actin-binding regions both in the central part of the molecule and in its N-terminal tail domain. In HeLa cells, mitotic protein kinase Aurora B was suggested to phosphorylate MLCK210 N-terminal tail at serine residues (Dulyaninova, N. G., and Bresnick, A. R. (2004) Exp. Cell Res., 299, 303-314), but the functional significance of the phosphorylation was not established. We report here that in vitro, the N-terminal actin-binding domain of MLCK210 is located within residues 27-157 (N27-157, avian MLCK210 sequence) and is phosphorylated by cAMP-dependent protein kinase (PKA) and Aurora B at serine residues 140/149 leading to a decrease in N27-157 binding to actin. The same residues are phosphorylated in a PKA-dependent manner in transfected HeLa cells. Further, in transfected cells, phosphomimetic mutants of N27-157 showed reduced association with the detergent-stable cytoskeleton, whereas in vitro, the single S149D mutation reduced N27-157 association with F-actin to a similar extent as that achieved by N27-157 phosphorylation. Altogether, our results indicate that phosphorylation of MLCK210 at distinct serine residues, mainly at S149, attenuates the interaction of MLCK210 N-terminus with the actin cytoskeleton and might serve to regulate MLCK210 microfilament cross-linking activity in cells.

Kinetochore function is controlled by a phospho-dependent coexpansion of inner and outer components.

It is widely accepted that the kinetochore is built on CENP-A-marked centromeric chromatin in a hierarchical order from inner to outer kinetochore. Recruitment of many kinetochore proteins depends on microtubule attachment status, but it remains unclear how their assembly/disassembly is orchestrated. Applying 3D structured illumination microscopy to Xenopus laevis egg extracts, here we reveal that in the absence of microtubule attachment, proteins responsible for lateral attachment and spindle checkpoint signaling expand to form micrometer-scale fibrous structures over CENP-A-free chromatin, whereas a core module responsible for end-on attachment (CENP-A, CENP-T, and Ndc80) does not. Both outer kinetochore proteins (Bub1, BubR1, Mad1, and CENP-E) and the inner kinetochore component CENP-C are integral components of the expandable module, whose assembly depends on multiple mitotic kinases (Aurora B, Mps1, and Plx1) and is suppressed by protein phosphatase 1. We propose that phospho-dependent coexpansion of CENP-C and outer kinetochore proteins promotes checkpoint signal amplification and lateral attachment, whereas their selective disassembly enables the transition to end-on attachment.

Inter-domain Cooperation in INCENP Promotes Aurora B Relocation from Centromeres to Microtubules.

The chromosomal passenger complex is essential for error-free chromosome segregation and proper execution of cytokinesis. To coordinate nuclear division with cytoplasmic division, its enzymatic subunit, Aurora B, relocalizes from centromeres in metaphase to the spindle midzone in anaphase. In budding yeast, this requires dephosphorylation of the microtubule-binding (MTB) domain of the INCENP analog Sli15. The mechanistic basis for this relocalization in metazoans is incompletely understood. We demonstrate that the putative coiled-coil domain within INCENP drives midzone localization of Aurora B via a direct, electrostatic interaction with microtubules. Furthermore, we provide evidence that the CPC multimerizes via INCENP's centromere-targeting domain (CEN box), which increases the MTB affinity of INCENP. In (pro)metaphase, the MTB affinity of INCENP is outcompeted by the affinity of its CEN box for centromeres, while at anaphase onset—when the histone mark H2AT120 is dephosphorylated—INCENP and Aurora B switch from centromere to microtubule localization.

Mio depletion links mTOR regulation to Aurora A and Plk1 activation at mitotic centrosomes.

Coordination of cell growth and proliferation in response to nutrient supply is mediated by mammalian target of rapamycin (mTOR) signaling. In this study, we report that Mio, a highly conserved member of the SEACAT/GATOR2 complex necessary for the activation of mTORC1 kinase, plays a critical role in mitotic spindle formation and subsequent chromosome segregation by regulating the proper concentration of active key mitotic kinases Plk1 and Aurora A at centrosomes and spindle poles. Mio-depleted cells showed reduced activation of Plk1 and Aurora A kinase at spindle poles and an impaired localization of MCAK and HURP, two key regulators of mitotic spindle formation and known substrates of Aurora A kinase, resulting in spindle assembly and cytokinesis defects. Our results indicate that a major function of Mio in mitosis is to regulate the activation/deactivation of Plk1 and Aurora A, possibly by linking them to mTOR signaling in a pathway to promote faithful mitotic progression.

Fluorescent photoaffinity probes for mitotic protein kinase Aurora A.

We combined the advantages of the selective inhibitor VX689, the bisubstrate-analogue conjugate approach, and photoreactive amino acids to develop 8 photoaffinity probes for Aurora A. The most efficient compounds possessed one-digit nanomolar KD values in the equilibrium binding assay, inhibited Aurora A at elevated concentrations of ATP in the phosphorylation assay in the presence of TPX2, and formed covalent complexes with the recombinant kinase or Aurora A in HeLa cells upon UV-irradiation. The recognition of the correct target by the probes during formation of the covalent complex in the biochemical assay and in situ was demonstrated by competition experiments using the non-labelled inhibitors VX689 and MLN8237.

Aurora B-dependent phosphorylation of Ataxin-10 promotes the interaction between Ataxin-10 and Plk1 in cytokinesis.

Spinocerebellar ataxia type 10 (SCA10) is an autosomal dominant neurologic disorder caused by ATTCT expansion in the ATXN10 gene. Previous investigations have identified that depletion of Ataxin-10, the gene product, leads to cellular apoptosis and cytokinesis failure. Herein we identify the mitotic kinase Aurora B as an Ataxin-10 interacting partner. Aurora B interacts with and phosphorylates Ataxin-10 at S12, as evidenced by in vitro kinase and mass spectrometry analysis. Both endogenous and S12-phosphorylated Ataxin-10 localizes to the midbody during cytokinesis, and cytokinetic defects induced by inhibition of ATXN10 expression is not rescued by the S12A mutant. Inhibition of Aurora B or expression of the S12A mutant renders reduced interaction between Ataxin-10 and polo-like kinase 1 (Plk1), a kinase previously identified to regulate Ataxin-10 in cytokinesis. Taken together, we propose a model that Aurora B phosphorylates Ataxin-10 at S12 to promote the interaction between Ataxin-10 and Plk1 in cytokinesis. These findings identify an Aurora B-dependent mechanism that implicates Ataxin-10 in cytokinesis.

CSN6 deregulation impairs genome integrity in a COP1-dependent pathway.

Understanding genome integrity and DNA damage response are critical to cancer treatment. In this study, we identify CSN6's biological function in regulating genome integrity. Constitutive photomorphogenic 1 (COP1), an E3 ubiquitin ligase regulated by CSN6, is downregulated by DNA damage, but the biological consequences of this phenomenon are poorly understood. p27(Kip1) is a critical CDK inhibitor involved in cell cycle regulation, but its response to DNA damage remains unclear. Here, we report that p27(Kip1) levels are elevated after DNA damage, with concurrent reduction of COP1 levels. Mechanistic studies showed that during DNA damage response COP1's function as an E3 ligase of p27 is compromised, thereby reducing the ubiquitin-mediated degradation of p27(Kip1). Also, COP1 overexpression leads to downregulation of p27(Kip1), thereby promoting the expression of mitotic kinase Aurora A. Overexpression of Aurora A correlates with poor survival. These findings provide new insight into CSN6-COP1-p27(Kip1)-Aurora A axis in DNA damage repair and tumorigenesis.