Eribulin Treatment Induces High Expression of miR-195 and Inactivates the Wnt/β - catenin Signaling Pathway in Triple-negative Breast Cancer

Triple-negative breast cancer （TNBC） accounts for 10-15％ of all breast cancer cases and shows a poor prognosis with 30％ distant metastasis. With few specific target molecules and ineffective hormonal and anti-HER2 treatment, an alternative therapeutic method for TNBC is urgently required. Recently, a non-taxane inhibitor of microtubule dynamics called eribulin was developed for breast cancer therapy. Eribulin induces irreversible mitotic mass formation in cancer cells during the G2-M phase, initiating apoptosis; however, the mechanism underlying this eribulin activity remains unclear. We reported previously that exposing non-basal-like （NBL） TNBC cells to eribulin increases miR-195 expression, which in turn decreases the expression of targeted Wnt3a. The present study sought to further clarify the mechanism of this antitumor effect by exploring how eribulin affects Wnt/β - catenin signaling based on miRNA expression changes in TNBC. In an NBL type of human breast cancer cell line （MDA-MB-231 cells）, we compared the expression levels of Wnt/β catenin signaling pathway proteins in cells exposed to an miR-195 mimic （cells transfected with miR-195 and in which Wnt3a expression was suppressed） and in cells exposed to eribulin. Expression levels of Wnt3a, β -catenin, and GSK-3β were measured by ELISA and observed by fluorescence immunostaining. Wnt3a and β -catenin expression was significantly lower and GSK-3β expression was significantly higher in the cells exposed to eribulin and transfected with miR-195 mimic than in the untreated controls, suggesting that eribulin inactivates the Wnt/β -catenin signaling pathway. Therefore, a novel antitumor mechanism of eribulin was determined, whereby eribulin induces high expression of miR-195 to inactivate the Wnt/β -catenin signaling pathway in NBL-type TNBC

Chk1 activation requires Rad9 S/TQ-site phosphorylation to promote association with C-terminal BRCT domains of Rad4TOPBP1

To gain insight into the function and organization of proteins assembled on the DNA in response to genotoxic insult we investigated the phosphorylation of the Schizosaccharomyces pombe PCNA-like checkpoint protein Rad9. C-terminal T412/S423 phosphorylation of Rad9 by Rad3ATR occurs in S phase without replication stress. Rad3ATR and Tel1ATM phosphorylate these same residues, plus additional ones, in response to DNA damage. In S phase and after damage, only Rad9 phosphorylated on T412/S423, but not unphosphorylated Rad9, associates with a two-BRCT-domain region of the essential Rad4TOPBP1 protein. Rad9¿Rad4TOPBP1 interaction is required to activate the Chk1 damage checkpoint but not the Cds1 replication checkpoint. When the Rad9-T412/S423 are phosphorylated, Rad4TOPBP1 coprecipitates with Rad3ATR, suggesting that phosphorylation coordinates formation of an active checkpoint complex

The CDK-PLK1 axis targets the DNA damage checkpoint sensor protein RAD9 to promote cell proliferation and tolerance to genotoxic stress

二刀流のがん増殖戦略. 京都大学プレスリリース. 2017-12-20.Genotoxic stress causes proliferating cells to activate the DNA damage checkpoint, to assist DNA damage recovery by slowing cell cycle progression. Thus, to drive proliferation, cells must tolerate DNA damage and suppress the checkpoint response. However, the mechanism underlying this negative regulation of checkpoint activation is still elusive. We show that human Cyclin-Dependent-Kinases (CDKs) target the RAD9 subunit of the 9-1-1 checkpoint clamp on Thr292, to modulate DNA damage checkpoint activation. Thr292 phosphorylation on RAD9 creates a binding site for Polo-Like-Kinase1 (PLK1), which phosphorylates RAD9 on Thr313. These CDK-PLK1-dependent phosphorylations of RAD9 suppress checkpoint activation, therefore maintaining high DNA synthesis rates during DNA replication stress. Our results suggest that CDK locally initiates a PLK1-dependent signaling response that antagonizes the ability of the DNA damage checkpoint to detect DNA damage. These findings provide a mechanism for the suppression of DNA damage checkpoint signaling, to promote cell proliferation under genotoxic stress conditions

Cancer stem-like cells have cisplatin resistance and miR-93 regulate p21 expression in breast cancer

Aim: This study aims to examine the role of microRNAs (miRNAs) in regulating the expression of p21, a cyclin-dependent kinase inhibitor, and in inducing resistance to cisplatin, an anticancer drug. Methods: Human breast cancer cell line MDA-MB231 cells were separated into two subpopulations, cancer stem-like cells (CSCs) and cancer cells, based on the expression of cell surface antigens CD44 and CD24. Results: p21 protein expression was higher in CSCs than in cancer cells. Exposure of MDA-MB-231 cells to cisplatin increased p21 protein expression. However, p21 expression was significantly lower in cisplatin-treated CSCs than in cisplatin-treated cancer cells, suggesting that p21-dependent cell cycle suppression was lower in CSCs than in cancer cells. Moreover, caspase-3 activity was significantly lower in cisplatin-treated CSCs than in cisplatin-treated cancer cells, indicating that CSCs were more resistant to cisplatin-induced apoptosis than cancer cells. Treatment with miR-93 inhibitors increased p21 expression in CSCs, suggesting that miR-93 suppressed p21 expression. Conclusion: The results of the present study indicate that CSCs contribute to cisplatin resistance of MDA-MB231 cells and suggest that miR-93 inhibits the expression of p21, a factor involved in drug resistance

Rad3-dependent phosphorylation of the checkpoint clamp regulates repair-pathway choice

When replication forks collapse, Rad3 phosphorylates the checkpoint-clamp protein Rad9 in a manner that depends on Thr 225, a residue within the PCNA-like domain. The physiological function of Thr 225-dependent Rad9 phosphorylation, however, remains elusive. Here, we show that Thr 225-dependent Rad9 phosphorylation by Rad3 regulates DNA repair pathways. A rad9T225C mutant induces a translesion synthesis (TLS)-dependent high spontaneous mutation rate and a hyper-recombination phenotype. Consistent with this, Rad9 coprecipitates with the post-replication repair protein Mms2. This interaction is dependent on Rad9 Thr 225 and is enhanced by DNA damage. Genetic analyses indicate that Thr 225-dependent Rad9 phosphorylation prevents inappropriate Rhp51-dependent recombination, potentially by redirecting the repair through a Pli1-mediated sumoylation pathway into the error-free branch of the Rhp6 repair pathway. Our findings reveal a new mechanism by which phosphorylation of Rad9 at Thr 225 regulates the choice of repair pathways for maintaining genomic integrity during the cell cycle

DDK Phosphorylates checkpoint clamp component Rad9 and promotes its release from damaged chromatin

When inappropriate DNA structures arise, they are sensed by DNA structure-dependent checkpoint pathways and subsequently repaired. Recruitment of checkpoint proteins to such structures precedes recruitment of proteins involved in DNA metabolism. Thus, checkpoints can regulate DNA metabolism. We show that fission yeast Rad9, a 9-1-1 heterotrimeric checkpoint-clamp component, is phosphorylated by Hsk1(Cdc7), the Schizosaccharomyces pombe Dbf4-dependent kinase (DDK) homolog, in response to replication-induced DNA damage. Phosphorylation of Rad9 disrupts its interaction with replication protein A (RPA) and is dependent on 9-1-1 chromatin loading, the Rad9-associated protein Rad4/Cut5(TopBP1), and prior phosphorylation by Rad3(ATR). rad9 mutants defective in DDK phosphorylation show wild-type checkpoint responses but abnormal DNA repair protein foci and decreased viability after replication stress. We propose that Rad9 phosphorylation by DDK releases Rad9 from DNA damage sites to facilitate DNA repair

Associations between Clinical Symptoms and Degree of Ossification in Patients with Cervical Ossification of the Posterior Longitudinal Ligament: A Prospective Multi-Institutional Cross-Sectional Study

This study aimed to clarify whether ossification predisposition influences clinical symptoms including pain, restriction of activities of daily living, and quality of life in patients with cervical ossification of the posterior longitudinal ligament (OPLL). Cervical ossification predisposition potentially causes neurologic dysfunction, but the relationship between clinical symptoms and radiologic severity of OPLL has not yet been investigated. Data were prospectively collected from 16 institutions across Japan. We enrolled 239 patients with cervical OPLL. The primary outcomes were patient-reported outcomes, including visual analog scale (VAS) pain scores and other questionnaires. Whole-spine computed tomography images were obtained, and correlations were investigated between clinical symptoms and radiologic findings, including the distribution of OPLL, the sum of the levels where OPLL was present (OP-index), and the canal narrowing ratio (CNR) grade. The cervical OP-index was Grade 1 in 113 patients, Grade 2 in 90, and Grade 3 in 36. No significant correlations were found between radiologic outcomes and VAS pain scores. The cervical OP-index was associated with lower extremity function, social dysfunction, and locomotive function. The CNR grade was not correlated with clinical symptoms, but Grade 4 was associated with lower extremity dysfunction. Thickness and extension of ossified lesions may be associated with lower extremity dysfunction in cervical OPLL

Associations between Clinical Findings and Severity of Diffuse Idiopathic Skeletal Hyperostosis in Patients with Ossification of the Posterior Longitudinal Ligament

Background: This study investigated how diffuse idiopathic skeletal hyperostosis (DISH) influences clinical characteristics in patients with cervical ossification of the posterior longitudinal ligament (OPLL). Although DISH is considered unlikely to promote neurologic dysfunction, this relationship remains unclear. Methods: Patient data were prospectively collected from 16 Japanese institutions. In total, 239 patients with cervical OPLL were enrolled who had whole-spine computed tomography images available. The primary outcomes were visual analog scale pain scores and the results of other self-reported clinical questionnaires. Correlations were sought between clinical symptoms and DISH using the following grading system: 1, DISH at T3-T10; 2, DISH at both T3–10 and C6–T2 and/or T11–L2; and 3, DISH beyond the C5 and/or L3 levels. Results: DISH was absent in 132 cases, grade 1 in 23, grade 2 in 65, and grade 3 in 19. There were no significant correlations between DISH grade and clinical scores. However, there was a significant difference in the prevalence of neck pain (but not in back pain or low back pain) among the three grades. Interestingly, DISH localized in the thoracic spine (grade 1) may create overload at the cervical spine and lead to neck pain in patients with cervical OPLL. Conclusion: This study is the first prospective multicenter cross-sectional comparison of subjective outcomes in patients with cervical OPLL according to the presence or absence of DISH. The severity of DISH was partially associated with the prevalence of neck pain