The selective estrogen receptor (ER) modulator tamoxifen inhibits ER signaling in breast cancer cells, and it is used for the treatment of ER-positive breast cancer. However, this type of cancer ...often acquires resistance to tamoxifen, and a better understanding of the molecular mechanisms underlying tamoxifen resistance is required. In this study, we established tamoxifen-resistant (TAM-R) breast cancer cells by long-term tamoxifen treatment of ER-positive breast cancer MCF7 cells. In TAM-R cells, expression of not only ERα, a major form of ER in breast cancer, but also its transcriptional partner forkhead box protein A1 (FOXA1) was found to be reduced. In contrast, activation of the transcription factor nuclear factor-κB (NF-κB) and expression of its target IL6 were increased in these cells. Stable expression of FOXA1, but not ERα, reduced the expression of IL6 in the FOXA1- and ERα-negative breast cancer MDA-MB-231 cells and TAM-R cells, without affecting the activation of the NF-κB signaling pathways. Conversely, FOXA1 knockdown induced IL6 expression in MCF7 cells. Chromatin immunoprecipitation assays revealed that FOXA1 bound to the promoter region of IL6 and repressed recruitment of the NF-κB complex to this region. TAM-R cells were found to have high mammosphere-forming activity, characteristics of cancer stem cells, and this activity was suppressed by NF-κB and IL6 signaling inhibitors. Taken together, these results suggest that FOXA1 suppresses expression of IL6 through inhibition of NF-κB recruitment to the IL6 promoter in an ERα-independent manner and that reduction in FOXA1 expression induces IL6 expression and contributes to cancer stem cell-like properties in TAM-R cells.
Background
Due to its tumor-specific metabolic pathway characteristics, 5-aminolevulinic acid (5-ALA) is a natural amino acid widely used in cancer treatment. The current study, demonstrated that ...5-ALA induced ferroptosis via glutathione peroxidase 4 (GPX4) and heme oxygenase 1 (HMOX1) and had an antitumor effect in esophageal squamous cell carcinoma (ESCC).
Methods
Expression of GPX4 and HMOX1 in pathologic specimens of 97 ESCC patients was examined, and prognostic analyses were performed. Real-time polymerase chain reaction (RT-PCR), RNA microarray, and Western blotting analyses were used to evaluate the role of 5-ALA in ferroptosis in vitro. In addition, this study used ferrostatin-1, a ferroptosis inhibitor, and a lipid peroxidation reagent against cell lines treated with 5-ALA. Finally, the role of 5-ALA was confirmed by its effect on an ESCC subcutaneous xenograft mouse model.
Results
The study showed that upregulation of GPX4 and downregulation of HMOX1 were poor prognostic factors in ESCC. In an RNA microarray analysis of KYSE30, ferroptosis was one of the most frequently induced pathways, with GPX4 suppressed and HMOX1 overexpressed by 5-ALA treatment. These findings were verified by RT-PCR and Western blotting. Furthermore, 5-ALA led to an increase in lipid peroxidation and exerted an antitumor effect in various cancer cell lines, which was inhibited by ferrostatin-1. In vivo, 5-ALA suppressed GPX4 and overexpressed HMOX1 in tumor tissues and led to a reduction in tumor size.
Conclusions
Modulation of GPX4 and HMOX1 by 5-ALA induced ferroptosis in ESCC. Thus, 5-ALA could be a promising new therapeutic agent for ESCC.
The cyclin B1-Cdk1 complex is a key regulator of mitotic entry. A large number of proteins are phosphorylated by the cyclin B1-Cdk1 complex prior to mitotic entry. Regulation of the mitotic events is ...linked to the control of the activity of the cyclin B1-Cdk1 complex to make cells enter mitosis, arrest at G2-phase, or skip mitosis. The roles of cyclin B1 levels in DNA damage are described. The ATM/ATR pathway acts as a molecular switch for regulating cell fates, flipping between cell death via progress into mitosis and polyploidization via sustained G2 arrest upon DNA damage, where cyclin B1 degradation is important for inducing polyploidization. The decrease in cyclin B1 levels that is induced by DNA damage leads to polyploidization in DNA damage-induced senescence. A useful method for monitoring the expression level of cyclin B1 throughout cell cycle progression in living cells is also presented.
Polyploid (2n, 3n, and 4n) genomes are known to be unstable in Saccharomyces cerevisiae. Here, we attempted construction of super-polypoid strains (defined as having higher ploidy than tetraploidy) ...up to 32n by using the matα2-PBT method that we newly developed and investigated their genomic stability. It is known that cell size increases as ploidy increases up to tetraploid. However, unexpectedly, there was no change in the average cell size of the super-polyploid strains compared with tetraploid or pentaploid strains. Smaller sized cells were observed at a rather higher frequency in super-polyploid cell populations compared with those of diploid, triploid and tetraploid strains, suggesting that ploidy reduction in super-polyploid strains occurs quickly at a relatively high frequency. Assuming that ploidy reduction occurs through chromosome loss (or non-disjunction) during mitotic growth, we also estimated the frequency of chromosome loss (or non-disjunction) in various polyploid strains. Our results indicated that the frequency of chromosome loss (or non-disjunction) is drastically increased (10−2–10−3/cells plated) in super-polyploid strains compared with that (10−4–10−5/cells plated) of conventional polyploid (2n–4n) strains. This is the first attempt of construction of super-polyploid strains and investigation of their genomic stability in S. cerevisiae. We believe that the matα2-PBT method will be an invaluable tool for investigating a variety of interesting issues regarding polyploidy and their genomic characterization in eukaryotes.
The nucleolus is a non-membranous structure in the nucleus and forms around ribosomal DNA repeats. It plays a major role in ribosomal biogenesis through the transcription of ribosomal DNA and ...regulates mRNA translation in response to cellular stress including DNA damage. Rad17 is one of the proteins that initiate and maintain the activation of the ATR pathway, one of the major DNA damage checkpoints. We have recently reported that the central basic domain of Rad17 contains a nuclear localization signal and that the nuclear translocation of Rad17 promotes its proteasomal degradation. Here, we show that the central basic domain contains the nucleolar localization signal as well as the nuclear localization signal. The nucleolar localization signal overlaps with the nuclear localization signal and is capable of transporting an exogenous protein into the nucleolus. Phosphomimetic mutations of the central basic domain inhibit nucleolar accumulation, suggesting that the post-translational modification sites regulate the nucleolar localization. Nucleolar accumulation of Rad17 is promoted by proteasome inhibition and UV irradiation. Our data show the nucleolar localization of Rad17 and suggest a possible role of Rad17 in the nucleolus upon UV irradiation.
Accumulating evidence has indicated that immune regulatory cells are involved in the establishment of tumoral immune evasion. However, the role of regulatory B cells (Bregs) in this remains unclear. ...Here, we identified a role for Bregs in immune evasion in gastric cancer (GC) patients. The frequency of peripheral Bregs was significantly higher in GC patients than in healthy controls (P = 0.0023). Moreover, the frequency of CD19
CD24
CD27
B cells in GC tissue was significantly higher than in peripheral blood and healthy gastric tissue. Carboxyfluorescein succinimidyl ester labeling revealed that CD19
CD24
CD27
B cells could suppress the proliferation of autologous CD4
T cells. Moreover, CD19
CD24
CD27
B cells inhibited the production of interferon-gamma by CD4
T cells. Double staining immunohistochemistry of interleukin-10 and CD19 revealed 5-year overall survival rates of 65.4% and 13.3% in Breg
and Breg
groups, respectively (P < 0.0001). Multivariate analysis indicated that the frequency of Bregs was an independent prognostic indicator in GC patients. Taken together, our results show the existence of Bregs in GC tissue, and indicate that they are significantly correlated with the prognosis of GC patients.
Mitotic progression requires the precise formation of spindle microtubules based on mature centrosomes. During the G2/M transition, centrosome maturation progresses, and associated microtubules ...bundle to form mitotic spindle fibers and capture the chromosomes for alignment at the cell equator. Mitotic kinases-induced phosphorylation signaling is necessary for these processes. Here, we identified SH2 domain-containing protein 4A (SH2D4A/PPP1R38) as a new mitotic regulator. SH2D4A knockdown delays mitotic progression. The time-lapse imaging analysis showed that SH2D4A specifically contributes to the alignment of chromosomes. The cold treatment assay and microtubule regrowth assay indicated that SH2D4A promotes microtubule nucleation to support kinetochore-microtubule attachment. This may be due to the centrosome maturation by SH2D4A via centrosomal recruitment of pericentriolar material (PCM) such as cep192, γ-tubulin, and PLK1. SH2D4A was found to be a negative regulator of PP1 phosphatase. Consistently, treatment with a PP1 inhibitor rescues SH2D4A-knockdown-induced phenotypes, including the microtubule nucleation and centrosomal recruitment of active PLK1. These results suggest that SH2D4A is involved in PCM recruitment to centrosomes and centrosome maturation through attenuation of PP1 phosphatases, accelerating the spindle formation and supporting mitotic progression.
ABSTRACT
Heat shock causes proteotoxic stress that induces various cellular responses, including delayed mitotic progression and the generation of an aberrant number of chromosomes. In this study, ...heat shock delayed the onset of anaphase by increasing the number of misoriented cells, accompanied by the kinetochore localization of budding uninhibited by benzimidazole–related (BubR)1 in a monopolar spindle (Mps)l‐dependent manner. The mitotic delay was canceled by knockdown of mitotic arrest defect (Mad)2. Knockdown of heat shock protein (Hsp)105 partially abrogated the mitotic delay with the loss of the kinetochore localization of BubR1 under heat shock conditions and accelerated mitotic progression under nonstressed conditions. Consistent with this result, Hsp105 knockdown increased the number of anaphase cells with lagging chromosomes, through mitotic slippage, and decreased taxol sensitivity more than Mad2 knockdown. Hsp105 was coprecipitated with cell division cycle (Cdc)20 in an Mps1‐dependent manner; however, its knockdown did not affect coprecipitation of Mad2 and BubR1 with Cdc20. We propose that heat shock delays the onset of anaphase via the activation of the spindle assembly checkpoint (SAC). Hsp105 prevents abnormal cell division by contributing to SAC activation under heat shock and nonstressed conditions by interacting with Cdc20 but not affecting formation of the mitotic checkpoint complex.—Kakihana, A., Oto, Y., Saito, Y., Nakayama, Y. Heat shock‐induced mitotic arrest requires heat shock protein 105 for the activation of spindle assembly checkpoint. FASEB J. 33, 3936–3953 (2019). www.fasebj.org
Microtubule poisons inhibit spindle function, leading to activation of spindle assembly checkpoint (SAC) and mitotic arrest. Cell death occurring in prolonged mitosis is the first target of ...microtubule poisons in cancer therapies. However, even in the presence of microtubule poisons, SAC and mitotic arrest are not permanent, and the surviving cells exit the mitosis without cytokinesis (mitotic slippage), becoming tetraploid. Another target of microtubule poisons-based cancer therapy is antiproliferative fate after mitotic slippage. The ultimate goal of both the microtubule poisons-based cancer therapies involves the induction of a mechanism defined as mitotic catastrophe, which is a bona fide intrinsic oncosuppressive mechanism that senses mitotic failure and responds by driving a cell to an irreversible antiproliferative fate of death or senescence. This mechanism of antiproliferative fate after mitotic slippage is not as well understood. We provide an overview of mitotic catastrophe, and explain new insights underscoring a causal association between basal autophagy levels and antiproliferative fate after mitotic slippage, and propose possible improved strategies. Additionally, we discuss nuclear alterations characterizing the mitotic catastrophe (micronuclei, multinuclei) after mitotic slippage, and a possible new type of nuclear alteration (clustered micronuclei).
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