Downregulation of Histone H3.3 Induces p53-Dependent Cellular Senescence in Human Diploid Fibroblasts

Cellular senescence is an irreversible growth arrest that acts as a barrier to cancer initiation and progression. Histone alteration is one of the major events during replicative senescence. However, little is known about the function of H3.3 in cellular senescence. Here we found that the downregulation of H3.3 induced growth suppression with senescence-like phenotypes such as senescence-associated heterochromatin foci (SAHF) and β-galactosidase (SA-β-gal) activity. Furthermore, H3.3 depletion induced senescence-like phenotypes with the p53/p21-depedent pathway. In addition, we identified miR-22-3p, tumor suppressive miRNA, as an upstream regulator of the H3F3B (H3 histone, family 3B) gene which is the histone variant H3.3 and replaces conventional H3 in active genes. Therefore, our results reveal for the first time the molecular mechanisms for cellular senescence which are regulated by H3.3 abundance. Taken together, our studies suggest that H3.3 exerts functional roles in regulating cellular senescence and is a promising target for cancer therapy.

Leukocyte Telomeric G-Tail Length Shortening Is Associated with Esophageal Cancer Recurrence

Despite significant advances in therapeutics for esophageal cancer (ESC) in the past decade, it remains the sixth most fatal malignancy, with a poor 5-year survival rate (approximately 10%). There is an urgent need to improve the timely diagnosis to aid the prediction of the therapeutic response and prognosis of patients with ESC. The telomeric G-tail plays an important role in the chromosome protection. However, aging and age-related diseases lead to its shortening. Therefore, the G-tail length has been proposed as a novel potential biomarker. In the present study, to examine the possibility of G-tail shortening in patients with ESC, we measured the leukocyte telomere length (LTL) and the G-tail length using a hybridization protection assay in 147 patients with ESC and 170 age-matched healthy controls. We found that the G-tail length in patients with ESC was shorter than that in the healthy controls (p = 0.02), while the LTL shortening was not correlated with the ESC incidence and recurrence. Our results suggest that the G-tail length reflects the physiological status of patients with ESC and is a promising biomarker for the diagnosis and prognosis of ESC.

Identification of a Selective RelA Inhibitor Based on DSE-FRET Screening Methods

Nuclear factor-κB (NF-κB) is an important transcription factor involved in various biological functions, including tumorigenesis. Hence, NF-κB has attracted attention as a target factor for cancer treatment, leading to the development of several inhibitors. However, existing NF-κB inhibitors do not discriminate between its subunits, namely, RelA, RelB, cRel, p50, and p52. Conventional methods used to evaluate interactions between transcription factors and DNA, such as electrophoretic mobility shift assay and luciferase assays, are unsuitable for high-throughput screening (HTS) and cannot distinguish NF-κB subunits. We developed a HTS method named DNA strand exchange fluorescence resonance energy transfer (DSE-FRET). This assay is suitable for HTS and can discriminate a NF-κB subunit. Using DSE-FRET, we searched for RelA-specific inhibitors and verified RelA inhibition for 32,955 compounds. The compound A55 (2-(3-carbamoyl-6-hydroxy-4-methyl-2-oxopyridin-1(2H)-yl) acetic acid) selectively inhibited RelA–DNA binding. We propose that A55 is a seed compound for RelA-specific inhibition and could be used in clinical applications.

Abstract 1402: Preclinical evaluation of a novel senescence-associated miRNA miR-3140-3p for malignant pleural mesothelioma

Cellular senescence acts as a natural barrier against tumor progression Our previous study showed that selective induction of senescence using miR-22, one of senescence-associated microRNAs (SA-miRNAs), suppressed tumor progression (JCB 2011) In this study, we developed functional screening system using miRNA library to identify a potent SA-miRNA that suppress malignant tumor such as anti-cancer drug resistant and cancer stem cells.

We focused on microRNA inducing the senescent phenotype in normal human fibroblast cell After transfection of 2028 miRNA mimics library in normal human fibroblast TIG-3, we evaluate the senescence phenotypes such as cell growth arrest and size enlargement using high content analyzer, and found that 349 miRNAs induced cellular senescence More importantly, we identified miR-3140-3p as potent SA-miRNA that significantly suppressed tumor cell proliferation in several types of cancer cells including cancer stem cells and anti-cancer drug resistant cells.

We focused on malignant pleural mesothelioma (MPM) which is an aggressive tumor developed from the mesothelial lining cells of the pleura MPM is caused by direct asbestos exposure and is an incurable tumor type for the lack of effective treatment In addition, as Japan is one of the world's highest importers and users of asbestos, the cases of mesothelioma are expected to increase in the near future Therefore, we investigated the possibility of whether SA-miRNAs showed tumor suppressive effects against MPM cell lines Moreover, we tried to develop a new treatment or medicine for the MPM patients using SA-miRNA In vitro and in vivo analysis revealed that several SA-miRNAs drastically suppressed the tumor cell proliferation

Based on these findings, the modulation of SA-miRNA is a promising approach to improve the treatment of MPM patients In addition, we performed and completed pre-clinical trials and design first-in-human study in Japan.

Citation Format: Yuki Yamamoto, Ayaka Nishiura, Kimiyoshi Yano, Noriaki Matsuda, Ryou-u Takahashi, Yasuhiro Tsutani, Morihito Okada, Hidetoshi Tahara. Preclinical evaluation of a novel senescence-associated miRNA miR-3140-3p for malignant pleural mesothelioma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1402.

CD44s Induces miR-629-3p Expression in Association with Cisplatin Resistance in Head and Neck Cancer Cells

Cisplatin (cis-diamminedichloroplatinum II [CDDP] ) is a well-known chemotherapeutic drug that has been used for the treatment of various types of human cancers, including head and neck cancer. Cisplatin exerts anticancer effects by causing DNA damage, replication defects, transcriptional inhibition, cell cycle arrest, and the induction of apoptosis. However, drug resistance is one of the most serious problems with cancer chemotherapy, and it causes expected therapeutic effects to not always be achieved. Here, we analyzed global microRNA (miRNA) expression in CD44 standard form (CD44s)-expressing SAS cells, and we identified miR-629-3p as being responsible for acquiring anticancer drug resistance in head and neck cancer. The introduction of miR-629-3p expression inhibited apoptotic cell death under cisplatin treatment conditions, and it promoted cell migration. Among the computationally predicted target genes of miR-629-3p, we found that a number of gene expressions were suppressed by the transfection with miR-629-3p. Using a xenografting model, we showed that miR-629-3p conferred cisplatin resistance to SAS cells. Clinically, increased miR-629-3p expression tended to be associated with decreased survival in head and neck cancer patients. In conclusion, our data suggest that the increased expression of miR-629-3p provides a mechanism of cisplatin resistance in head and neck cancer and may serve as a therapeutic target to reverse chemotherapy resistance.

Abstract P3-04-01: Telomere G-tail length correlates with the presence of breast cancer

Background The telomere G-tail, located at the terminal 3’-end, plays an important role in the maintenance of chromosome stability. Telomere G-tail length has been shown to be related to the presence of various cancers; however, the association between telomere G-tail length and breast cancer has remained unclear. Methods We measured the length of the leukocyte telomere G-tail using the hybridization protection assay, which has the advantages of being simple to perform, accurate and highly sensitive for G-tails as short as 20 nucleotides. The association between telomere G-tail length and presence of breast cancer was estimated by comparing breast cancer patients (n=70) and cancer-free individuals (n=83). We recruited cStage I-III breast cancer patients who underwent surgery between November 2016 and December 2017 at Hiroshima University Hospital. Cancer-free individuals included age-matched female individuals with no previous or current history of any cancer. Results The median telomere G-tail length was significantly shorter in breast cancer patients (11,886.70 ± 2,008.74 RLU/μg DNA) than in cancer-free individuals (13,336.00 ± 2,072.31 RLU/μg DNA; p < 0.01). Shortening of the telomere G-tail length was observed in the phase of ductal carcinoma in situ, and this trend was observed with or without shortening of the total telomere length. Spearman’s rank correlation analysis showed that there was no significant association between telomere G-tail length and total telomere length in breast cancer patients (ρ = -0.09; p = 0.48). In contrast, a significant correlation was found between telomere G-tail length and total telomere length in cancer-free individuals (ρ = 0.29; p = 0.01). Conclusions Our study indicated that leukocyte telomere G-tail length may serve as a novel potential biomarker for detection of breast cancer.

Citation Format: Yumiko Koi, Yasuhiro Tsutani, Yukie Nishiyama, Shinsuke Sasada, Norio Masumoto, Takayuki Kadoya, Ryou-u Takahashi, Morihito Okada, Hidetoshi Tahara. Telomere G-tail length correlates with the presence of breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-04-01.

Identification and Characterization of CXCR4-Positive Gastric Cancer Stem Cells

Diffuse-type solid tumors are often composed of a high proportion of rarely proliferating (i.e., dormant) cancer cells, strongly indicating the involvement of cancer stem cells (CSCs) Although diffuse-type gastric cancer (GC) patients have a poor prognosis due to high-frequent development of peritoneal dissemination (PD), it is limited knowledge that the PD-associated CSCs and efficacy of CSC-targeting therapy in diffuse-type GC. In this study, we established highly metastatic GC cell lines by in vivo selection designed for the enrichment of PD-associated GC cells. By microarray analysis, we found C-X-C chemokine receptor type 4 (CXCR4) can be a novel marker for highly metastatic CSCs, since CXCR4-positive cells can grow anchorage-independently, initiate tumors in mice, be resistant to cytotoxic drug, and produce differentiated daughter cells. In clinical samples, these CXCR4-positive cells were found from not only late metastasis stage (accumulated ascites) but also earlier stage (peritoneal washings). Moreover, treatment with transforming growth factor-β enhanced the anti-cancer effect of docetaxel via induction of cell differentiation/asymmetric cell division of the CXCR4-positive gastric CSCs even in a dormant state. Therefore, differentiation inducers hold promise for obtaining the maximum therapeutic outcome from currently available anti-cancer drugs through re-cycling of CSCs.

Exosomes from bone marrow mesenchymal stem cells contain a microRNA that promotes dormancy in metastatic breast cancer cells

Breast cancer patients often develop metastatic disease years after resection of the primary tumor. The patients are asymptomatic because the disseminated cells appear to become dormant and are undetectable. Because the proliferation of these cells is slowed, dormant cells are often unresponsive to traditional chemotherapies that exploit the rapid cell cycling of most cancer cells. We generated a bone marrow-metastatic human breast cancer cell line (BM2) by tracking and isolating fluorescent-labeled MDA-MB-231 cells that disseminated to the bone marrow in mice. Coculturing BM2 cells with bone marrow mesenchymal stem cells (BM-MSCs) isolated from human donors revealed that BM-MSCs suppressed the proliferation of BM2 cells, decreased the abundance of stem cell-like surface markers, inhibited their invasion through Matrigel Transwells, and decreased their sensitivity to docetaxel, a common chemotherapy agent. Acquisition of these dormant phenotypes in BM2 cells was also observed by culturing the cells in BM-MSC-conditioned medium or with exosomes isolated from BM-MSC cultures, which were taken up by BM2 cells. Among various microRNAs (miRNAs) increased in BM-MSC-derived exosomes compared with those from adult fibroblasts, overexpression of miR-23b in BM2 cells induced dormant phenotypes through the suppression of a target gene, MARCKS, which encodes a protein that promotes cell cycling and motility. Metastatic breast cancer cells in patient bone marrow had increased miR-23b and decreased MARCKS expression. Together, these findings suggest that exosomal transfer of miRNAs from the bone marrow may promote breast cancer cell dormancy in a metastatic niche.

Ribophorin II regulates breast tumor initiation and metastasis through the functional suppression of GSK3β

Mutant p53 (mtp53) gain of function (GOF) contributes to various aspects of tumor progression including cancer stem cell (CSC) property acquisition. A key factor of GOF is stabilization and accumulation of mtp53. However, the precise molecular mechanism of the mtp53 oncogenic activity remains unclear. Here, we show that ribophorin II (RPN2) regulates CSC properties through the stabilization of mtp53 (R280K and del126-133) in breast cancer. RPN2 stabilized mtp53 by inactivation of glycogen synthase kinase-3β (GSK3β) which suppresses Snail, a master regulator of epithelial to mesenchymal transition. RPN2 knockdown promoted GSK3β-mediated suppression of heat shock proteins that are essential for mtp53 stabilization. Furthermore, our study reveals that high expression of RPN2 and concomitant accumulation of mtp53 were associated with cancer tissues in a small cohort of metastatic breast cancer patients. These findings elucidate a molecular mechanism for mtp53 stabilization and suggest that RPN2 could be a promising target for anti-CSC therapy.

Genome-wide analysis of DNA methylation and expression of microRNAs in breast cancer cells

DNA methylation of promoters is linked to transcriptional silencing of protein-coding genes, and its alteration plays important roles in cancer formation. For example, hypermethylation of tumor suppressor genes has been seen in some cancers. Alteration of methylation in the promoters of microRNAs (miRNAs) has also been linked to transcriptional changes in cancers; however, no systematic studies of methylation and transcription of miRNAs have been reported. In the present study, to clarify the relation between DNA methylation and transcription of miRNAs, next-generation sequencing and microarrays were used to analyze the methylation and expression of miRNAs, protein-coding genes, other non-coding RNAs (ncRNAs), and pseudogenes in the human breast cancer cell lines MCF7 and the adriamycin (ADR) resistant cell line MCF7/ADR. DNA methylation in the proximal promoter of miRNAs is tightly linked to transcriptional silencing, as it is with protein-coding genes. In protein-coding genes, highly expressed genes have CpG-rich proximal promoters whereas weakly expressed genes do not. This is only rarely observed in other gene categories, including miRNAs. The present study highlights the epigenetic similarities and differences between miRNA and protein-coding genes.

[Role of microRNA in cancer development: biology and clinical applications]

The role of RNA, as commonly understood, is to carry the genetic code for protein from the DNA to the sites of protein production. Over the years, however, new forms of RNA were discovered, such as microRNA (miRNA) and large intergenic noncoding RNA, and the range of RNA function was extended, miRNA constitutes a large family of small, approximately 20-nucleotide-long, noncoding RNA which controls the expression of target genes at the posttranscriptional level. Recent studies have indicated that miRNA plays an essential role in cancer biology by affecting cell growth, differentiation, and apoptosis as well as the cell cycle. This review summarizes the newly determined role of miRNA in cancer development, discusses some controversies regarding different functions of miRNA, and highlights the prospects for clinical applications of miRNA, such as therapeutic targets and diagnostic markers.

An integrative genomic analysis revealed the relevance of microRNA and gene expression for drug-resistance in human breast cancer cells

Background

Acquisition of drug-resistance in cancer has led to treatment failure, however, their mechanisms have not been clarified yet. Recent observations indicated that aberrant expressed microRNA (miRNA) caused by chromosomal alterations play a critical role in the initiation and progression of cancer. Here, we performed an integrated genomic analysis combined with array-based comparative hybridization, miRNA, and gene expression microarray to elucidate the mechanism of drug-resistance.

Results

Through genomic approaches in MCF7-ADR; a drug-resistant breast cancer cell line, our results reflect the unique features of drug-resistance, including MDR1 overexpression via genomic amplification and miRNA-mediated TP53INP1 down-regulation. Using a gain of function study with 12 miRNAs whose expressions were down-regulated and genome regions were deleted, we show that miR-505 is a novel tumor suppressive miRNA and inhibits cell proliferation by inducing apoptosis. We also find that Akt3, correlate inversely with miR-505, modulates drug sensitivity in MCF7-ADR.

Conclusion

These findings indicate that various genes and miRNAs orchestrate to temper the drug-resistance in cancer cells, and thus acquisition of drug-resistance is intricately controlled by genomic status, gene and miRNA expression changes.

Cancer stem cells in breast cancer

The cancer stem cell (CSC) theory is generally acknowledged as an important field of cancer research, not only as an academic matter but also as a crucial aspect of clinical practice. CSCs share a variety of biological properties with normal somatic stem cells in self-renewal, the propagation of differentiated progeny, the expression of specific cell markers and stem cell genes, and the utilization of common signaling pathways and the stem cell niche. However, CSCs differ from normal stem cells in their chemoresistance and their tumorigenic and metastatic activities. In this review, we focus on recent reports regarding the identification of CSC markers and the molecular mechanism of CSC phenotypes to understand the basic properties and molecular target of CSCs. In addition, we especially focus on the CSCs of breast cancer since the use of neoadjuvant chemotherapy can lead to the enrichment of CSCs in patients with that disease. The identification of CSC markers and an improved understanding of the molecular mechanism of CSC phenotypes should lead to progress in cancer therapy and improved prognoses for patients with cancer.

Mutational analysis of the carboxyl-terminal region of the SV40 major capsid protein VP1

Virus-like particles (VLPs), a promising next-generation drug delivery vehicle, can be formed in vitro using a recombinant viral capsid protein VP1 from SV40. Seventy-two VP1 pentamers interconnect to form the T = 7d lattice of SV40 capsids, through three types of C-terminal interactions, alpha-alpha'-alpha'', beta-beta' and gamma-gamma. These appear to require VP1 conformational switch, which involve in particular the region from amino acids 301-312 (herein Region I). Here we show that progressive deletions from the C-terminus of VP1, up to 34 amino acids, cause size and shape variations in the resulting VLPs, including tubular formation, whereas deletions beyond 34 amino acids simply blocked VP1 self-assembly. Mutants carrying in Region I point mutations predicted to disrupt alpha-alpha'-alpha''-type and/or beta-beta'-type interactions formed small VLPs resembling T = 1 symmetry. Chimeric VP1, in which Region I of SV40 VP1 was substituted with the homologous region from VP1 of other polyomaviruses, assembled only into small VLPs. Together, our results show the importance of the integrity of VP1 C-terminal region and the specific amino acid sequences within Region I in the assembly of normal VLPs. By understanding how to alter VLP sizes and shapes contributes to the development of drug delivery systems using VLPs.

The VP2/VP3 Minor Capsid Protein of Simian Virus 40 Promotes the in Vitro Assembly of the Major Capsid Protein VP1 into Particles

The SV40 capsid is composed primarily of 72 pentamers of the VP1 major capsid protein. Although the capsid also contains the minor capsid protein VP2 and its amino-terminally truncated form VP3, their roles in capsid assembly remain unknown. An in vitro assembly system was used to investigate the role of VP2 in the assembly of recombinant VP1 pentamers. Under physiological salt and pH conditions, VP1 alone remained dissociated, and at pH 5.0, it assembled into tubular structures. A stoichiometric amount of VP2 allowed the assembly of VP1 pentamers into spherical particles in a pH range of 7.0 to 4.0. Electron microscopy observation, sucrose gradient sedimentation analysis, and antibody accessibility tests showed that VP2 is incorporated into VP1 particles. The functional domains of VP2 important for VP1 binding and for enhancing VP1 assembly were further explored with a series of VP2 deletion mutants. VP3 also enhanced VP1 assembly, and a region common to VP2 and VP3 (amino acids 119-272) was required to promote VP1 pentamer assembly. These results are relevant for controlling recombinant capsid formation in vitro, which is potentially useful for the in vitro development of SV40 virus vectors.