Knockdown of FUSE binding protein 1 enhances the sensitivity of epithelial ovarian cancer cells to carboplatin

FBP1 knockdown decreases ovarian cancer formation and cisplatin resistance through EZH2-mediated H3K27me3

Worldwide, ovarian cancer (OC) is the seventh common cancer and the second most common cause of cancer death in women. Due to high rates of relapse, there is an urgent need for the identification of new targets for OC treatment. The far-upstream element binding protein 1 (FBP1) and enhancer of zeste homolog 2 (EZH2) are emerging proto-oncogenes that regulate cell proliferation and metastasis. In the present study, Oncomine data analysis demonstrated that FBP1 was closely associated with the development of OC, and The Cancer Genome Atlas (TCGA) data analysis indicated that there was a positive correlation between FBP1 and EZH2 in ovarian tissues. Moreover, we found that FBP1 knockdown suppressed tumor formation in nude mice and cisplatin resistance of OC cells, but the role of FBP1 in the cisplatin resistance of OC cells remained unclear. In addition, we verified physical binding between FBP1 and EZH2 in OC cells, and we demonstrated that FBP1 knockdown enhanced cisplatin cytotoxicity in OC cells and down-regulated EZH2 expression and trimethylation of H3K27. These results suggested that FBP1 increases cisplatin resistance of OC cells by up-regulating EZH2/H3K27me3. Thus, FBP1 is a prospective novel target for the development of OC treatment.

MiR-124-3p.1 Sensitizes Ovarian Cancer Cells to Mitochondrial Apoptosis Induced by Carboplatin

Background

Carboplatin is a platinum-based chemotherapeutic drug that is commonly used as a treatment for ovarian cancer. However, high doses and repeated use of carboplatin usually reduce the sensitivity of cancer cells to the drug. There is an urgent need to develop strategies to increase the sensitivity of ovarian cancer cells to carboplatin.

Materials and Methods

Quantitative reverse-transcriptase real-time PCR was used to detect miR-124-3p.1 levels in ovarian cancer tissues and cell lines. Transfection with miR-124-3p.1 and caveolin-1 (CAV1) was used for gain-of-function experiments. Western blot and immunoprecipitation assays were performed to evaluate the expression and function of CAV1, AKT, Bad, and Bcl-xl. Flow cytometry analysis was used to measure the apoptosis rates of SKOV3 and A2780 cells.

Results

Expression levels of miR-124-3p.1 were decreased in ovarian cancer tissues and cell lines. Furthermore, overexpression of miR-124-3p.1 enhanced carboplatin-induced apoptotic cell death of ovarian cancer cell lines. Regarding the mechanism of this effect, we showed that CAV1 was the target of miR-124-3p.1 in ovarian cancer. Overexpression of miR-124-3p.1 suppressed the expression of CAV1, thereby reducing the activation of AKT and phosphorylation of Bad. As a result, the function of Bcl-xl was inhibited and carboplatin-induced mitochondrial apoptosis was enhanced.

Conclusion

miR-124-3p.1 sensitizes carboplatin-induced mitochondrial apoptosis through suppression of CAV1 in ovarian cancer. Increasing miR-124-3p.1 expression may represent a novel strategy to improve carboplatin sensitivity in ovarian cancer.

GSK343 induces programmed cell death through the inhibition of EZH2 and FBP1 in osteosarcoma cells

Enhancer of zeste homolog 2 (EZH2) is an important member of the epigenetic regulatory factor polycomb group proteins (PcG) and is abnormally expressed in a wide variety of tumors, including osteosarcoma. Scientists consider EZH2 as an attractive target for the treatment of osteosarcoma and have found many potential EZH inhibitors, such as GlaxoSmithKline 343 (GSK343). It has been reported that GSK343 can be used as an inhibitor in different types of cancer. This study demonstrated that GSK343 not only induced apoptosis by increasing cleaved Casp-3 and poly ADP-ribose polymerase (PARP) expression, but also induced autophagic cell death by inhibiting p62 expression. Apoptosis and autophagic cell death induced by GSK343 were confirmed by the high expression of cleaved caspase-3, LC3-II and transmission electron microscopy. GSK343 inhibited the expression of EZH2 and c-Myc. Additionally, GSK343 inhibited the expression of FUSE binding protein 1 (FBP1), which was identified by its regulatory effects on c-Myc expression. Since c-Myc is a common target of EZH2 and FBP1, and GSK343 inhibited the expression of these proliferation-promoting proteins, a mutual regulatory mechanism between EZH2 and FBP1 was proposed. The knockdown of EZH2 suppressed the expression of FBP1; similarly, the knockdown of FBP1 suppressed the expression of EZH2. These results suggest the mutual regulatory association between EZH2 and FBP1. The knockdown of either EZH2 or FBP1 accelerated the sensitivity of osteosarcoma cells to GSK343. Based on these results, this study clarified that GSK343, an EZH2 inhibitor, may have potential for use in the treatment of osteosarcoma. The underlying mechanisms of the effects of GSK343 are partly mediated by its inhibitory activity against c-Myc and its regulators (EZH2 and FBP1).

The master regulator FUBP1: its emerging role in normal cell function and malignant development

The human Far Upstream Element (FUSE) Binding Protein 1 (FUBP1) is a multifunctional DNA- and RNA-binding protein involved in diverse cellular processes. FUBP1 is a master regulator of transcription, translation, and RNA splicing. FUBP1 has been identified as a potent pro-proliferative and anti-apoptotic factor by modulation of complex networks. FUBP1 is also described either as an oncoprotein or a tumor suppressor. Especially, FUBP1 overexpression is observed in a growing number of cancer and leads to a deregulation of targets that includes the fine-tuned MYC oncogene. Moreover, recent loss-of-function analyses of FUBP1 establish its essential functions in hematopoietic stem cell maintenance and survival. Therefore, FUBP1 appears as an emerging suspect in hematologic disorders in addition to solid tumors. The scope of the present review is to describe the advances in our understanding of the molecular basis of FUBP1 functions in normal cells and carcinogenesis. We also delineate the recent progresses in the understanding of the master role of FUBP1 in normal and pathological hematopoiesis. We conclude that FUBP1 is not only worth studying biologically but is also of clinical relevance through its pivotal role in regulating multiple cellular processes and its involvement in oncogenesis.

FBP1 promotes ovarian cancer development through the acceleration of cell cycle transition and metastasis

Epithelial ovarian cancer (EOC) is the fifth most common malignancy in women, with a 5-year mortality of >70% in North America. As the symptoms are often not observed until the cancer has spread extensively, few women are diagnosed at an early stage of disease. Large-scale gene expression analyses have identified molecular subtypes within high-grade ovarian cancer with variable survival rates and drug resistance. The understanding of gene expression, the mechanisms underlying cancer processes and drug resistances have facilitated the development of targeted therapies. The far-upstream element (Fuse)-binding protein 1 (FBP1) is overexpressed in a number of malignancies such as hepatocellular carcinoma, and has been identified as an oncoprotein. In our early studies, FBP1 was demonstrated to physically interact with p53 and suppresses p53 transcription activity. In the present study, FBP1 expression increased as ovarian cancer developed. Among ovarian normal, adenoma and carcinoma tissues, the highest FBP1 expression was identified in carcinoma tissues. Furthermore FBP1 did not influence the apoptosis of ovarian carcinoma cells, yet enhanced cell cycle transition and metastasis. Therefore, it was hypothesized that FBP1 promotes ovarian cancer development through the acceleration of cell cycle transition and metastasis, and FBP1 is a novel potential biological marker for epithelial ovarian cancer diagnosis.