LncRNA TUG1 promotes pulmonary fibrosis progression via up-regulating CDC27 and activating PI3K/Akt/mTOR pathway.

Idiopathic pulmonary fibrosis (IPF) is a fatal interstitial lung disease with an unclear pathogenesis. This study aimed to elucidate the function and potential mechanisms of TUG1 in IPF progression. Cell viability and migration were detected by CCK-8 and transwell assays. Autophagy, fibrosis, or EMT-related proteins were measured by Western blotting. Pro-inflammatory cytokine levels were assessed by ELISA kits. The subcellular localization of TUG1 was observed by FISH assay. RIP assay detected the interaction between TUG1 and CDC27. TUG1 and CDC27 was up-regulated in TGF-ß1-induced RLE-6TN cells. TUG1 depletion suppressed pulmonary fibrosis via attenuating inflammation, EMT, inducing autophagy and inactivating PI3K/Akt/mTOR pathway in vitro and in vivo. TUG1 knockdown prevented CDC27 expression. TUG1 silencing ameliorated pulmonary fibrosis by reducing CDC27 expression and inhibiting PI3K/Akt/mTOR pathway.

Nuclear-localized CTEN is a novel transcriptional regulator and promotes cancer cell migration through its downstream target CDC27

C-terminal tensin-like (CTEN) is a tensin family protein typically localized to the cytoplasmic side of focal adhesions, and primarily contributes to cell adhesion and migration. Elevated expression and nuclear accumulation of CTEN have been reported in several types of cancers and found to be associated with malignant behaviors. However, the function of nuclear CTEN remains elusive. In this study, we report for the first time that nuclear CTEN associates with chromatin DNA and occupies the region proximal to the transcription start site in several genes. The mRNA expression level of CTEN positively correlates with that of one of its putative target genes, cell division cycle protein 27 (CDC27), in a clinical colorectal cancer dataset, suggesting that CTEN may play a role in the regulation of CDC27 gene expression. Furthermore, we demonstrated that CTEN is recruited to the promoter region of the CDC27 gene and that the mRNA expression and promoter activity of CDC27 are both reduced when CTEN is downregulated. In addition, we found that enhanced nuclear accumulation of CTEN in HCT116 cells by overexpression of CTEN fused with nuclear localization signals increases CDC27 transcript levels and promoter activity. The increased nuclear-localized CTEN also significantly promotes cell migration, and the migratory ability is suppressed when CDC27 is knocked down. These results demonstrate that nuclear CTEN regulates CDC27 expression transcriptionally and promotes cell migration through CDC27. Our findings provide new insights into CTEN moonlighting in the nucleus as a DNA-associated protein and transcriptional regulator involved in modulating cancer cell migration. (AU)

Nuclear-localized CTEN is a novel transcriptional regulator and promotes cancer cell migration through its downstream target CDC27.

C-terminal tensin-like (CTEN) is a tensin family protein typically localized to the cytoplasmic side of focal adhesions, and primarily contributes to cell adhesion and migration. Elevated expression and nuclear accumulation of CTEN have been reported in several types of cancers and found to be associated with malignant behaviors. However, the function of nuclear CTEN remains elusive. In this study, we report for the first time that nuclear CTEN associates with chromatin DNA and occupies the region proximal to the transcription start site in several genes. The mRNA expression level of CTEN positively correlates with that of one of its putative target genes, cell division cycle protein 27 (CDC27), in a clinical colorectal cancer dataset, suggesting that CTEN may play a role in the regulation of CDC27 gene expression. Furthermore, we demonstrated that CTEN is recruited to the promoter region of the CDC27 gene and that the mRNA expression and promoter activity of CDC27 are both reduced when CTEN is downregulated. In addition, we found that enhanced nuclear accumulation of CTEN in HCT116 cells by overexpression of CTEN fused with nuclear localization signals increases CDC27 transcript levels and promoter activity. The increased nuclear-localized CTEN also significantly promotes cell migration, and the migratory ability is suppressed when CDC27 is knocked down. These results demonstrate that nuclear CTEN regulates CDC27 expression transcriptionally and promotes cell migration through CDC27. Our findings provide new insights into CTEN moonlighting in the nucleus as a DNA-associated protein and transcriptional regulator involved in modulating cancer cell migration.

Circ_0000775 promotes the migration, invasion and EMT of hepatic carcinoma cells by recruiting IGF2BP2 to stabilize CDC27.

BACKGROUND: Hepatic carcinoma (HC) is one of the leading causes of cancer-related death, and the incidence keeps high in the world. The vital role of circular RNAs (circRNAs) in HC development has been revealed to some extent. Circ_0000775, a novel circRNA, has never been thoroughly studied regarding HC. METHODS: Online datasets were utilized to obtain expression pattern of genes in tumor tissues. RT-qPCR and western blot examined the RNA and protein levels of indicated genes. ChIP, DNA pull down, RNA pull down, RIP and luciferase reporter assays were carried out to verify correlation between different factors. Supported by RT-qPCR and western blot analyses, transwell and wound healing assay were implemented for detecting cell migration and invasion and EMT. Additionally, cell EMT was also evaluated via cell morphology observation for calculation of spindle cell number. RESULTS: High expression of circ_0000775 in HC cells was induced by transcriptionally stimulation by TCF7L2. Circ_0000775 in cytoplasm recruited IGF2BP2 to enhance the mRNA stability of CDC27, thus positively modulating CDC27 expression. Circ_0000775 exacerbated HC cell migration, invasion and EMT through CDC27. CONCLUSION: TCF7L2 promoted the transcription of circ_0000775, and circ_0000775 recruited IGF2BP2 to maintain CDC27 mRNA stability, thereby facilitating HC cell migration, invasion and EMT.

A Novel Gene CDC27 Causes SLE and Is Associated With the Disease Activity.

Background: As genetic genetic factors are important in SLE, so screening causative genes is of great significance for the prediction and early prevention in people who may develop SLE. At present, it is very difficult to screen causative genes through pedigrees. The analytical method described herein can be used to screen causative genes for SLE and other complex diseases through pedigrees. Methods: For the first time, 24 lupus pedigrees were analyzed by combining whole exon sequencing and a variety of biological information tools including common-specific analysis, pVAAST (pedigree variant annotation, analysis and search tool), Exomiser (Combining phenotype and PPI associated analysis), and FARVAT (family based gene burden), and the causative genes of these families with lupus identified. Selected causative genes in peripheral-blood mononuclear cells (PBMCs) were evaluated by quantitative polymerase chain reaction (qPCR). Results: Cell division cycle 27 (CDC27) was screened out by common-specific analysis and Exomiser causative gene screening. FARVAT analysis on these families detected only CDC27 at the extremely significant level (false discovery rate <0.05) by three family-based burden analyses (BURDEN, CALPHA, and SKATO). QPCR was performed to detect for CDC27 in the PBMCs of the SLE family patients, sporadic lupus patients, and healthy people. Compared with the healthy control group, CDC27 expression was low in lupus patients (familial and sporadic patients) (P<0.05) and correlated with lupus activity indicators: negatively with C-reactive protein (CRP) (P<0.05) and erythrocyte sedimentation rate (P<0.05) and positively with complement C3 and C4 (P<0.05). The CDC27 expression was upregulated in PBMCs from SLE patients with reduced lupus activity after immunotherapy (P<0.05). Based on Receiver operating characteristic (ROC) curve analysis, the sensitivity and specificity of CDC27 in diagnosing SLE were 82.30% and 94.40%. Conclusion: The CDC27 gene, as found through WES combined with multiple analytical method may be a causative gene of lupus. CDC27 may serve as a marker for the diagnosis of SLE and is closely related to the lupus activity. We hope that the analytical method in this study will be used to screen causative genes for other diseases through small pedigrees, especially among non-close relatives.

Circular RNA circSLC8A1 inhibits the proliferation and invasion of glioma cells through targeting the miR-214-5p/CDC27 axis.

Circular RNA circSLC8A1 is one of the cancer-related circRNAs that is implicated in various cancers. However, studies focusing on the role of circSLC8A1 in glioma is rare. Here we attempted to evaluate the biological function of circSLC8A1 in glioma and explore the potential mechanism. The relative expression of circSLC8A1, miR-214-5p and CDC27 in tissues and cell lines was determined by qRT-PCR. Cell proliferation and invasion were respectively measured by CCK-8 and transwell assays. Protein level of CDC27 was analyzed by western blot. Luciferase reporter assay was performed to confirm the regulatory interaction of cirRNA-miRNA-mRNA. Lowly expressed circSLC8A1 was observed in both glioma tissues and cell lines. Further biological analyses showed that circSLC8A1 inhibits the cell proliferation and invasion of glioma cells. CircSLC8A1 directly sponged miR-214-5p and inhibited miR-214-5p expression in glioma cells. CDC27 was a direct target of miR-214-5p and could be regulated by miR-214-5p. Moreover, miR-214-5p mimics and CDC27 knockdown reversed the inhibitory effects of circSLC8A1 on cell proliferation and invasion. Taken together, our results demonstrated a tumor suppressive role of circSLC8A1 in glioma through regulation of glioma cells proliferation and invasion. The effects of circSLC8A1 were mediated by miR-214-5p/CDC27 axis. Our study provided a new understanding of the occurrence and development of glioma.

A novel long non-coding RNA RP11-286H15.1 represses hepatocellular carcinoma progression by promoting ubiquitination of PABPC4.

Hepatocellular carcinoma (HCC) is a malignancy found at high frequency around the world. Unfortunately, the scarcity of effective early diagnostic methods invariably results in poor outcomes. Long noncoding RNAs (lncRNAs) are known to regulate the progression of hepatocellular carcinoma (HCC). A novel lncRNA RP11-286H15.1(OTTHUMG00000186042) has been identified and associated with HCC; however, the potential role of RP11-286H15.1 in HCC remains undefined. The transcript abundance of RP11-286H15.1 in 80 pairs of HCC samples and cell lines was evaluated by qRT-PCR analysis. The functional role of RP11-286H15.1 in HCC was tested in vivo and in vitro. The mechanisms underlying the role of RP11-286H15.1 in HCC were explored by RNA pulldown, transcriptome sequencing, and RNA immunoprecipitation (RIP), ubiquitination and fluorescence in situ hybridization (FISH) assays as well as Western blot analysis. The qRT-PCR and FISH assays revealed that RP11-286H15.1 was significantly decreased in HCC, and implied a shorter survival time. RP11-286H15.1 overexpression inhibited HCC cell proliferation and metastasis in vitro and in vivo, whereas RP11-286H15.1 knockdown produced the opposite results. Furthermore, we confirmed that RP11-286H15.1 (620-750 nucleotides) binds to poly(A) binding protein 4 (PABPC4) and promotes its ubiquitination, thus, reducing the stability of TRIM37 and CDC27 mRNAs. Our study demonstrates that a novel lncRNA, RP11-286H15.1, represses HCC progression by promoting PABPC4 ubiquitination. These findings highlight potential therapeutic targets for HCC.

Cyclin B3 activates the Anaphase-Promoting Complex/Cyclosome in meiosis and mitosis.

In mitosis and meiosis, chromosome segregation is triggered by the Anaphase-Promoting Complex/Cyclosome (APC/C), a multi-subunit ubiquitin ligase that targets proteins for degradation, leading to the separation of chromatids. APC/C activation requires phosphorylation of its APC3 and APC1 subunits, which allows the APC/C to bind its co-activator Cdc20. The identity of the kinase(s) responsible for APC/C activation in vivo is unclear. Cyclin B3 (CycB3) is an activator of the Cyclin-Dependent Kinase 1 (Cdk1) that is required for meiotic anaphase in flies, worms and vertebrates. It has been hypothesized that CycB3-Cdk1 may be responsible for APC/C activation in meiosis but this remains to be determined. Using Drosophila, we found that mutations in CycB3 genetically enhance mutations in tws, which encodes the B55 regulatory subunit of Protein Phosphatase 2A (PP2A) known to promote mitotic exit. Females heterozygous for CycB3 and tws loss-of-function alleles lay embryos that arrest in mitotic metaphase in a maternal effect, indicating that CycB3 promotes anaphase in mitosis in addition to meiosis. This metaphase arrest is not due to the Spindle Assembly Checkpoint (SAC) because mutation of mad2 that inactivates the SAC does not rescue the development of embryos from CycB3-/+, tws-/+ females. Moreover, we found that CycB3 promotes APC/C activity and anaphase in cells in culture. We show that CycB3 physically associates with the APC/C, is required for phosphorylation of APC3, and promotes APC/C association with its Cdc20 co-activators Fizzy and Cortex. Our results strongly suggest that CycB3-Cdk1 directly activates the APC/C to promote anaphase in both meiosis and mitosis.

Hsa_circ_0044226 knockdown attenuates progression of pulmonary fibrosis by inhibiting CDC27.

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive lung disorder. Here, we performed a bioinformatics analysis using the GSE102660 dataset from the Gene Expression Omnibus database to identify differentially expressed circRNAs (DEcircRNAs) in tissues from IPF patients and healthy controls. The results identified 45 DEcircRNAs, among which expression of hsa_circ_0044226 was markedly higher in lung tissues from IPF patients than from healthy controls. Knocking down hsa_circ_0044226 expression using a targeted shRNA inhibited TGF-ß1-induced fibrosis in RLE-6TN cells and in a bleomycin-induced mouse model of IPA. The diminished TGF-ß1-induced fibrosis was associated with upregulated expression of E-cadherin and downregulated expression of α-SMA, collagen III and fibronectin 1, as well as with reduced expression of CDC27, suggesting inhibition of epithelial-to-mesenchymal transition (EMT). All of those effects were reversed by overexpression of CDC27. This suggests CDC27 overexpression abolishes the antifibrotic effect of hsa_circ_0044226 knockdown through activation of EMT. Furthermore, hsa_circ_0044226 knockdown decreased the expression of CDC27 in BLM-induced pulmonary fibrosis mouse model. Collectively then, these findings indicate that downregulation of hsa_circ_0044226 attenuates pulmonary fibrosis in vitro and in vivo by inhibiting CDC27, which in turn suppresses EMT. This suggests hsa_circ_0044226 may be a useful therapeutic target for the treatment of IPF.

CDC27 Facilitates Gastric Cancer Cell Proliferation, Invasion and Metastasis via Twist-Induced Epithelial-Mesenchymal Transition.

BACKGROUND/AIMS: Lymph node metastasis is the primary cause of cancer-related death among patients with gastric cancer (GC), and cell division cycle 27 (CDC27) promotes the metastasis and epithelial-mesenchymal transition in many cancers. Till now, the mechanisms underlying CDC27-induced the epithelial-mesenchymal transition (EMT) of GC are still unclear. METHODS: We analyzed the expression levels of CDC27 and EMT-related biomarkers using immunohistochemistry and Western blot in 60 cases of GC tissues, and then GC cells with CDC27 shRNAs or plasmids were subjected to in vitro and in vivo assays, including CCK-8, wound healing and transwell assays. RESULTS: The CDC27 expression was obviously increased in GC tissues, and significantly correlates with EMT-related biomarkers, lymph node metastasis and poor 5-year overall survival. Additionally, in vitro and in vivo assays demonstrated that silencing of CDC27 expression effectively inhibited GC cell proliferation, invasion and metastasis. Conversely, CDC27 overexpression led to the opposite results. Finally, we demonstrated that Twist shRNA inhibited CDC27-meditated invasion and EMT of GC cells. CONCLUSION: CDC27 facilitates gastric cancer cell proliferation, invasion and metastasis via Twist-induced EMT; thus, this study offered a new therapy method for GC patients.

Germline and somatic variations influence the somatic mutational signatures of esophageal squamous cell carcinomas in a Chinese population.

BACKGROUND: Esophageal squamous cell carcinomas (ESCC) is the fourth most lethal cancer in China. Previous studies reveal several highly conserved mutational processes in ESCC. However, it remains unclear what are the true regulators of the mutational processes. RESULTS: We analyzed the somatic mutational signatures in 302 paired whole-exome sequencing data of ESCC in a Chinese population for potential regulators of the mutational processes. We identified three conserved subtypes based on the mutational signatures with significantly different clinical outcomes. Our results show that patients of different subpopulations of Chinese differ significantly in the activity of the "NpCpG" signature (FDR = 0.00188). In addition, we report ZNF750 and CDC27, of which the somatic statuses and the genetic burdens consistently influence the activities of specific mutational signatures in ESCC: the somatic ZNF750 status is associated with the AID/APOBEC-related mutational process (FDR = 0.0637); the somatic CDC27 copy-number is associated with the "NpCpG" (FDR = 0.00615) and the AID/APOBEC-related mutational processes (FDR = 8.69 × 10- 4). The burdens of germline variants in the two genes also significantly influence the activities of the same somatic mutational signatures (FDR < 0.1). CONCLUSIONS: We report multiple factors that influence the mutational processes in ESCC including: the subpopulations of Chinese; the germline and somatic statuses of ZNF750 and CDC27 and exposure to alcohol and tobacco. Our findings based on the evidences from both germline and somatic levels reveal potential genetic regulators of the somatic mutational processes and provide insights into the biology of esophageal carcinogenesis.

UBE2S associated with OSCC proliferation by promotion of P21 degradation via the ubiquitin-proteasome system.

Ubiquitin-conjugating enzyme E2S (UBE2S), a family of E2 protein in the ubiquitin-proteasome system, is highly expressed in several types of cancers; however, its roles in oral squamous cell carcinoma (OSCC) have not yet been well elucidated. The purpose of this study was to clarify the functional activities of UBE2S in OSCCs. We analyzed the expression levels of UBE2S in nine OSCC cell lines and primary OSCC tissues by quantitative reverse transcriptase-polymerase chain reaction, Western blotting, and immunohistochemistry (IHC). The correlations between UBE2S expression and clinical classifications of OSCCs were analyzed using the IHC scoring system. We also used UBE2S knockdown OSCC cells for functional assays (proliferation assay, flow cytometry, and Western blotting). UBE2S was overexpressed in OSCCs in vitro and in vivo and was correlated significantly (P < 0.05) with the primary tumoral size. The cellular growth was decreased and the cell-cycle was arrested in the G2/M phase in the UBE2S knockdown (shUBE2S) cells. The expression level of P21, a target of the ubiquitin-proteasome system, was increased in the shUBE2S cells because of lower anaphase activity that promotes complex subunit 3 (APC3), an E3 ubiquitin ligase, compared with shMock cells. These findings might promote the understanding of the relationship between UBE2S overexpression and oral cancer proliferation, indicating that UBE2S would be a potential biomarker of and therapeutic target in OSCCs.

APC/C Dysfunction Limits Excessive Cancer Chromosomal Instability.

Intercellular heterogeneity, exacerbated by chromosomal instability (CIN), fosters tumor heterogeneity and drug resistance. However, extreme CIN correlates with improved cancer outcome, suggesting that karyotypic diversity required to adapt to selection pressures might be balanced in tumors against the risk of excessive instability. Here, we used a functional genomics screen, genome editing, and pharmacologic approaches to identify CIN-survival factors in diploid cells. We find partial anaphase-promoting complex/cyclosome (APC/C) dysfunction lengthens mitosis, suppresses pharmacologically induced chromosome segregation errors, and reduces naturally occurring lagging chromosomes in cancer cell lines or following tetraploidization. APC/C impairment caused adaptation to MPS1 inhibitors, revealing a likely resistance mechanism to therapies targeting the spindle assembly checkpoint. Finally, CRISPR-mediated introduction of cancer somatic mutations in the APC/C subunit cancer driver gene CDC27 reduces chromosome segregation errors, whereas reversal of an APC/C subunit nonsense mutation increases CIN. Subtle variations in mitotic duration, determined by APC/C activity, influence the extent of CIN, allowing cancer cells to dynamically optimize fitness during tumor evolution. SIGNIFICANCE: We report a mechanism whereby cancers balance the evolutionary advantages associated with CIN against the fitness costs caused by excessive genome instability, providing insight into the consequence of CDC27 APC/C subunit driver mutations in cancer. Lengthening of mitosis through APC/C modulation may be a common mechanism of resistance to cancer therapeutics that increase chromosome segregation errors. Cancer Discov; 7(2); 218-33. ©2017 AACR.See related commentary by Burkard and Weaver, p. 134This article is highlighted in the In This Issue feature, p. 115.

mir-218-2 promotes glioblastomas growth, invasion and drug resistance by targeting CDC27.

Glioma has become a significant global health problem with substantial morbidity and mortality, underscoring the importance of elucidating its underlying molecular mechanisms. Recent studies have identified mir-218 as an anti-oncogene; however, the specific functions of mir-218-1 and mir-218-2 remain unknown, especially the latter. The objective of this study was to further investigate the role of mir-218-2 in glioma. Our results indicated that mir-218-2 is highly overexpressed in glioma. Furthermore, we showed that mir-218-2 is positively correlated with the growth, invasion, migration, and drug susceptibility (to ß-lapachone) of glioma cells. In vitro, the overexpression of mir-218-2 promoted glioma cell proliferation, invasion, and migration. In addition, the overexpression of mir-218-2 in vivo was found to increase glioma tumor growth. Accordingly, the inhibition of mir-218-2 resulted in the opposite effects. Cell division cycle 27 (CDC27), the downstream target of mir-218-2, is involved in the regulation of glioma cells. Our results indicate that the overexpression of CDC27 counteracted the function of mir-218-2 in glioma cells. These novel findings provide new insight in the application of mir-218-2 as a potential glioma treatment.

Inhibition of Anaphase-Promoting Complex by Silence APC/CCdh1 to Enhance Radiosensitivity of Nasopharyngeal Carcinoma Cells.

The aim of this study was to investigate the possibility of APC/CCdh1 as a potential therapeutic target in the radiosensitivity of nasopharyngeal carcinoma (NPC) cell CNE-1, and explain the role of APC subunits after silence of Cdh1 combined with radiotherapy. Transfection with Cdh1 shRNA significantly increased the radiosensitivity of CNE-1 cells and the radiation enhancement ratio (RER) of sh-Cdh1 cells was 1.76. Knockdown of Cdh1 in CNE-1 cells increased irradiation induced apoptosis and G2/M phase cell cycle arrest. The levels of CDC20 and CylinB1 increased and the levels of Ku70 and APC3 decreased after irradiation. APC/CCdh1 is involved in regulation of radiosensitivity in human NPC CNE-1 cells. Our study may provide a promising therapeutic strategy for NPC by targeting Cdh1. J. Cell. Biochem. 118: 3150-3157, 2017. © 2016 Wiley Periodicals, Inc.

PCBP1/HNRNP E1 Protects Chromosomal Integrity by Translational Regulation of CDC27.

UNLABELLED: CDC27 is a core component of the anaphase-promoting complex/cyclosome (APC/C), a multisubunit E3 ubiquitin ligase, whose oscillatory activity is responsible for the metaphase-to-anaphase transition and mitotic exit. Here, in normal murine mammary gland epithelial cells (NMuMG), CDC27 expression is controlled posttranscriptionally through the RNA binding protein poly(rC) binding protein 1 (PCBP1)/heterogeneous nuclear ribonucleoprotein E1 (HNRNP E1). shRNA-mediated knockdown of HNRNP E1 abrogates translational silencing of the Cdc27 transcript, resulting in constitutive expression of CDC27. Dysregulated expression of CDC27 leads to premature activation of the G2-M-APC/C-CDC20 complex, resulting in the aberrant degradation of FZR1/CDH1, a cofactor of the G1 and late G2-M-APC/C and a substrate normally reserved for the SCF-ßTRCP ligase. Loss of CDH1 expression and of APC/C-CDH1 activity, upon constitutive expression of CDC27, results in mitotic aberrations and aneuploidy in NMuMG cells. Furthermore, tissue microarray of breast cancer patient tumor samples reveals high CDC27 levels compared with nonneoplastic breast tissue and a significant correlation between disease recurrence and CDC27 expression. These results suggest that dysregulation of HNRNP E1-mediated translational regulation of Cdc27 leads to chromosomal instability and aneuploidy and that CDC27 expression represents a significant predictor of breast cancer recurrence. IMPLICATIONS: The RNA-binding protein HNRNP E1 mediates translational regulation of the cell-cycle regulator CDC27 and that dysregulation of CDC27 leads to aneuploidy. In addition, high CDC27 expression in breast cancer patient tumor specimens significantly predicts disease recurrence, suggesting a novel role for CDC27 as a predictor of relapse. Mol Cancer Res; 14(7); 634-46. ©2016 AACR.

Molecular mechanism of APC/C activation by mitotic phosphorylation.

In eukaryotes, the anaphase-promoting complex (APC/C, also known as the cyclosome) regulates the ubiquitin-dependent proteolysis of specific cell-cycle proteins to coordinate chromosome segregation in mitosis and entry into the G1 phase. The catalytic activity of the APC/C and its ability to specify the destruction of particular proteins at different phases of the cell cycle are controlled by its interaction with two structurally related coactivator subunits, Cdc20 and Cdh1. Coactivators recognize substrate degrons, and enhance the affinity of the APC/C for its cognate E2 (refs 4-6). During mitosis, cyclin-dependent kinase (Cdk) and polo-like kinase (Plk) control Cdc20- and Cdh1-mediated activation of the APC/C. Hyperphosphorylation of APC/C subunits, notably Apc1 and Apc3, is required for Cdc20 to activate the APC/C, whereas phosphorylation of Cdh1 prevents its association with the APC/C. Since both coactivators associate with the APC/C through their common C-box and Ile-Arg tail motifs, the mechanism underlying this differential regulation is unclear, as is the role of specific APC/C phosphorylation sites. Here, using cryo-electron microscopy and biochemical analysis, we define the molecular basis of how phosphorylation of human APC/C allows for its control by Cdc20. An auto-inhibitory segment of Apc1 acts as a molecular switch that in apo unphosphorylated APC/C interacts with the C-box binding site and obstructs engagement of Cdc20. Phosphorylation of the auto-inhibitory segment displaces it from the C-box-binding site. Efficient phosphorylation of the auto-inhibitory segment, and thus relief of auto-inhibition, requires the recruitment of Cdk-cyclin in complex with a Cdk regulatory subunit (Cks) to a hyperphosphorylated loop of Apc3. We also find that the small-molecule inhibitor, tosyl-l-arginine methyl ester, preferentially suppresses APC/C(Cdc20) rather than APC/C(Cdh1), and interacts with the binding sites of both the C-box and Ile-Arg tail motifs. Our results reveal the mechanism for the regulation of mitotic APC/C by phosphorylation and provide a rationale for the development of selective inhibitors of this state.

Cyclin-dependent kinase 1-dependent activation of APC/C ubiquitin ligase.

Error-free genome duplication and segregation are ensured through the timely activation of ubiquitylation enzymes. The anaphase-promoting complex or cyclosome (APC/C), a multisubunit E3 ubiquitin ligase, is regulated by phosphorylation. However, the mechanism remains elusive. Using systematic reconstitution and analysis of vertebrate APC/Cs under physiological conditions, we show how cyclin-dependent kinase 1 (CDK1) activates the APC/C through coordinated phosphorylation between Apc3 and Apc1. Phosphorylation of the loop domains by CDK1 in complex with p9/Cks2 (a CDK regulatory subunit) controlled loading of coactivator Cdc20 onto APC/C. A phosphomimetic mutation introduced into Apc1 allowed Cdc20 to increase APC/C activity in interphase. These results define a previously unrecognized subunit-subunit communication over a distance and the functional consequences of CDK phosphorylation. Cdc20 is a potential therapeutic target, and our findings may facilitate the development of specific inhibitors.

Identification of a novel protein interaction between Elmo1 and Cdc27.

Elmo has no intrinsic catalytic activity but coordinate multiple cellular processes via their interactions with other proteins. Studies thus have been focused on identifying Elmo binding partners, but the number of characterized Elmo-interacting proteins remains limited. Here, we report Cdc27 as a novel Elmo1-interacting protein. In yeast and mammalian cells, Cdc27 specifically interacted with the C-terminal region of Elmo1 essential for Dock1 association and function. The interaction of Elmo1 with Dock1 abrogated binding between Elmo1 and Cdc27, but the Dock1-Elmo1 interaction was unaffected by Cdc27. Similarly, cellular phagocytotic functions mediated by the Elmo1-Dock1-Rac module were unaffected by Cdc27 levels. In summary, a novel binding partner, Cdc27, was identified for Elmo1 and they appear to be independent of Elmo-Dock1-Rac-mediated processes.

Downregulation of CDC27 inhibits the proliferation of colorectal cancer cells via the accumulation of p21Cip1/Waf1.

Dysregulated cell cycle progression has a critical role in tumorigenesis. Cell division cycle 27 (CDC27) is a core subunit of the anaphase-promoting complex/cyclosome, although the specific role of CDC27 in cancer remains unknown. In our study, we explored the biological and clinical significance of CDC27 in colorectal cancer (CRC) growth and progression and investigated the underlying molecular mechanisms. Results showed that CDC27 expression is significantly correlated with tumor progression and poor patient survival. Functional assays demonstrated that overexpression of CDC27 promoted proliferation in DLD1 cells, whereas knockdown of CDC27 in HCT116 cells inhibited proliferation both in vitro and in vivo. Further mechanistic investigation showed that CDC27 downregulation resulted in G1/S phase transition arrest via the significant accumulation of p21 in HCT116 cells, and the upregulation of CDC27 promoted G1/S phase transition via the attenuation of p21 in DLD1 cells. Furthermore, we also demonstrated that CDC27 regulated inhibitor of DNA binding 1 (ID1) protein expression in DLD1 and HCT116 cells, and rescue assays revealed that CDC27 regulated p21 expression through modulating ID1 expression. Taken together, our results indicate that CDC27 contributes to CRC cell proliferation via the modulation of ID1-mediated p21 regulation, which offers a novel approach to the inhibition of tumor growth. Indeed, these findings provide new perspectives for the future study of CDC27 as a target for CRC treatment.