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Thyroid cancer is the most commonly diagnosed endocrine cancer. Anaplastic thyroid cancer (ATC) is the most aggressive type of thyroid cancer and has a poor prognosis. Loss of p53 function has been reported to lead to poorly differentiated thyroid tumors; therefore, mutant p53 protein can be considered a crucial therapeutic target in patients with ATC. Sorafenib, a multi-kinase inhibitor, has been approved for the treatment of metastatic and differentiated thyroid cancer. Combined targeted therapy, including sorafenib, may be clinically significant for patients with ATC harboring p53 mutations. In the present study, CP-31398, a p53-restoring agent, was used to improve the therapeutic efficacy of sorafenib in SW579 cells, an ATC cell line harboring p53 mutations. The molecular function of CP-31398 was evaluated using western blot analysis and a luciferase reporter assay. The decreased viability of SW579 cells, following CP-31398 treatment, was augmented by sorafenib, and CP-31398 enhanced the antimitogenic effect of sorafenib; thus, sorafenib and CP-31398 synergistically inhibited the growth of SW579 cells. These results indicate a potential clinical application of CP-31398 for patients with ATC harboring p53 abnormalities, since these individuals generally respond poorly to sorafenib alone.

INTRODUCTION: Mechanical force generated from the interstitial fluid flow inside and surrounding tissue has been known to play a significant role in cancer pathophysiology. In this study, we aimed to investigate the role of laminar shear stress (LSS) in modulating the cell cycle of human bladder transitional carcinoma (BFTC-905) cells which are frequently stimulated by not only the interstitial fluid flow, but also the urine flow transported from kidney to bladder in the urinary tract. METHODS: The BFTC-905 cells were subjected to 0–12 dynes cm(−2) LSS for 1, 4, 8, or 12 h, respectively, followed by cellular and molecular assays for investigations of cell cycle regulation protein expressions, cell growth rates, and the potential mechanism. RESULTS: The results showed that the LSS with ≥ 8 dynes cm(−2) for ≥ 8 h significantly increased protein expressions of cyclin B1, Wee1, p21, and p-CDK1((Tyr15)) (p < 0.05 for each), but conversely decreased protein expressions of cyclin A2, D1, E1, and CDK-1, -2, -4, and -6 (p < 0.05 for each) in the BFTC-905 cells, indicating that a G(2)/M cell cycle arrest was obtained after shearing stimulation. Furthermore, our data demonstrated that the LSS-induced G(2)/M arrest and the corresponding changes in cell cycle regulatory protein expressions were modulated by bone morphogenetic protein (BMP) receptor-Smad1/5 signaling pathway. CONCLUSIONS: Our findings provided evidences for the effect of mechanical microenvironment on urothelial cancer pathobiology and generated insights into mechanism of LSS-regulated bladder tumor cell cycle.

Purpose: To clarify the effects of cyclin E1 suppression on antitumor efficacy of sorafenib in hepatocellular carcinoma cells and to explore the potential of combining sorafenib with cyclin-dependent kinase (CDK) inhibition in therapy. Experimental Design: The effects of cyclin E1 suppression on sorafenib-induced apoptosis were tested in both sorafenib-sensitive (Huh-7 and HepG2, IC50 5–6 μmol/L) and sorafenib-resistant (Huh-7R and HepG2R, IC50 14–15 μmol/L) hepatocellular carcinoma cells. The activity of pertinent signaling pathways and the expression of cell cycle and apoptosis-related proteins were measured using Western blotting. Efficacy of sorafenib combined with the pan-CDK inhibitor flavopiridol was tested both in vitro and in xenograft experiments. The pertinent downstream mediators of antitumor efficacy were tested in transient transfection and RNA interference experiments. Results: Cyclin E1 mRNA and protein expressions were suppressed after sorafenib treatment in sorafenib-sensitive but not in sorafenib-resistant hepatocellular carcinoma cells. Changes in cyclin E2 or D1 were not correlated with sorafenib sensitivity. The knockdown of cyclin E1 expression reversed the resistance of hepatocellular carcinoma cells to sorafenib in terms of cell growth and apoptosis induction, whereas the overexpression of cyclin E1 increased the resistance to sorafenib. The growth-inhibitory and apoptosis-inducing effects of sorafenib were enhanced by flavopiridol, and Mcl-1 suppression was determined to play a critical role in mediating this enhancing effect. Conclusions: The cyclin E1 suppression in hepatocellular carcinoma cells may serve as a pharmacodynamic biomarker for predicting sorafenib efficacy. The combination of sorafenib and CDK inhibitors may improve the efficacy of sorafenib in hepatocellular carcinoma. Clin Cancer Res; 22(10); 2555–64. ©2015 AACR.

The CDC4 gene of Saccharomyces cerevisiae encodes an essential function that is required for G1-S and G2-M transitions during mitosis and at various stages during meiosis. We have isolated a functional homologue of CDC4 (CaCDC4) from the pathogenic yeast Candida albicans by complementing the S. cerevisiae cdc4-3 mutation with CaCDC4 expressed from its own promoter on a single-copy vector. The predicted product of CaCDC4 has 37% overall identity to the S. cerevisiae Cdc4 protein, although this identity is biased towards the C-terminal region of the two proteins which contains eight copies of the degenerate WD-40 motif, an element found in proteins that regulate diverse biological processes and an F-box domain proximal to the first iteration of the WD-40 motif. Both the F-box domain and WD-40 motifs appear necessary for the mitotic functions of Cdc4 in both yeasts. In contrast to its conserved role in mitosis, C. albicans CDC4 is unable to rescue the meiotic deficiency in a S. cerevisiae cdc4 homozygous diploid under restrictive conditions, even when expressed from an efficient S. cerevisiae promoter. In opposition to S. cerevisiae CDC4 being essential, C. albicans CDC4 appears to be nonessential and in its absence is critical for filamentous growth in C. albicans.

Human Mps1 (hMps1) is a mitotic checkpoint kinase responsible for sensing the unattached and tensionless kinetochore. Despite its importance in safeguarding proper chromosome segregation, how hMps1 is recruited to the kinetochore remains incompletely understood. Here, we demonstrate that phosphorylation at Thr-288 by the cell cycle checkpoint kinase CHK2 is involved in this process. We discovered that the phosphorylation-deficient T288A mutant has an impaired ability to localize to the kinetochore and cannot reestablish the mitotic checkpoint in hMps1-depleted cells. In support, we found that nocodazole induced hMps1 phosphorylation at the previously identified CHK2 site Thr-288 and that this could be detected at the kinetochore in a CHK2-dependent manner. Mechanistically, phosphorylation at Thr-288 promoted the interaction with the KMN (KNL1-Mis12-Ndc80 network) protein HEC1. Forced kinetochore localization corrected the defects associated with the T288A mutant. Our results provide evidence of a newly identified hMps1 phosphorylation site that is involved in the mitotic checkpoint and that CHK2 contributes to chromosomal stability through hMps1.

B-cell translocation gene 3 ( BTG3 ) is a member of the antiproliferative BTG / Transducer of ErbB2 gene family and is induced by genotoxic stress in a p53- and Checkpoint kinase 1 (CHK1)-dependent manner. Down-regulation of BTG3 has been observed in human cancers, suggesting that it plays an important role in tumor suppression, although the underlying mechanisms are unclear. Here, we report that BTG3 interacts with CHK1, a key effector kinase in the cell cycle checkpoint response, and regulates its phosphorylation and activation. Upon interaction, BTG3 mediates K63-linked ubiquitination of CHK1 at Lys132 through the cullin-RING ligase 4 Cdt2 E3 complex, thus facilitating CHK1 chromatin association. We show that BTG3-depleted cells phenocopy those CHK1-deficient cells, exhibiting increased cell death after replication block and impaired chromosome alignment and segregation. These defects could be corrected by wild-type BTG3 but not by a mutant impaired in CHK1 interaction. We propose that BTG3-dependent CHK1 ubiquitination contributes to its chromatin localization and activation and that a defect in this regulation may increase genome instability and promote tumorigenesis.