FEN1 knockdown improves trastuzumab sensitivity in human epidermal growth factor 2-positive breast cancer cells

The endonuclease FEN1 mediates activation of STAT3 and facilitates proliferation and metastasis in breast cancer

BACKGROUND

The metastasis accounts for most deaths from breast cancer (BRCA). Understanding the molecular mechanisms of BRCA metastasis is urgently demanded. Flap Endonuclease 1 (FEN1), a pivotal factor in DNA metabolic pathways, contributes to tumor growth and drug resistance, however, little is known about the role of FEN1 in BRCA metastasis.

METHODS AND RESULTS

In this study, FEN1 expression and its clinical correlation in BRCA were investigated using bioinformatics, showing being upregulated in BRCA samples and significant relationships with tumor stage, node metastasis, and prognosis. Immunohistochemistry (IHC) staining of local BRCA cohort indicated that the ratio of high FEN1 expression in metastatic BRCA tissues rose over that in non-metastatic tissues. The assays of loss-of-function and gain-of-function showed that FEN1 enhanced BRCA cell proliferation, migration, invasion, xenograft growth as well as lung metastasis. It was further found that FEN1 promoted the aggressive behaviors of BRCA cells via Signal Transducer and Activator of Transcription 3 (STAT3) activation. Specifically, the STAT3 inhibitor Stattic thwarted the FEN1-induced enhancement of migration and invasion, while the activator IL-6 rescued the decreased migration and invasion caused by FEN1 knockdown. Additionally, overexpression of FEN1 rescued the inhibitory effect of nuclear factor-κB (NF-κB) inhibitor BAY117082 on phosphorylated STAT3. Simultaneously, the knockdown of FEN1 attenuated the phosphorylation of STAT3 promoted by the NF-κB activator tumor necrosis factor α (TNF-α).

CONCLUSIONS

These results indicate a novel mechanism that NF-κB-driven FEN1 contributes to promoting BRCA growth and metastasis by STAT3 activation.

A bibliometric analysis of researches on flap endonuclease 1 from 2005 to 2019

Background

Flap endonuclease 1 (FEN1) is a structure-specific nuclease that plays a role in a variety of DNA metabolism processes. FEN1 is important for maintaining genomic stability and regulating cell growth and development. It is associated with the occurrence and development of several diseases, especially cancers. There is a lack of systematic bibliometric analyses focusing on research trends and knowledge structures related to FEN1.

Purpose

To analyze hotspots, the current state and research frontiers performed for FEN1 over the past 15 years.

Methods

Publications were retrieved from the Web of Science Core Collection (WoSCC) database, analyzing publication dates ranging from 2005 to 2019. VOSviewer1.6.15 and Citespace5.7 R1 were used to perform a bibliometric analysis in terms of countries, institutions, authors, journals and research areas related to FEN1. A total of 421 publications were included in this analysis.

Results

Our findings indicated that FEN1 has received more attention and interest from researchers in the past 15 years. Institutes in the United States, specifically the Beckman Research Institute of City of Hope published the most research related to FEN1. Shen BH, Zheng L and Bambara Ra were the most active researchers investigating this endonuclease and most of this research was published in the Journal of Biological Chemistry. The main scientific areas of FEN1 were related to biochemistry, molecular biology, cell biology, genetics and oncology. Research hotspots included biological activities, DNA metabolism mechanisms, protein-protein interactions and gene mutations. Research frontiers included oxidative stress, phosphorylation and tumor progression and treatment.

Conclusion

This bibliometric study may aid researchers in the understanding of the knowledge base and research frontiers associated with FEN1. In addition, emerging hotspots for research can be used as the subjects of future studies.

Role of Small GTPase RhoA in DNA Damage Response

Accumulating evidence has suggested a role of the small GTPase Ras homolog gene family member A (RhoA) in DNA damage response (DDR) in addition to its traditional function of regulating cell morphology. In DDR, 2 key components of DNA repair, ataxia telangiectasia-mutated (ATM) and flap structure-specific endonuclease 1 (FEN1), along with intracellular reactive oxygen species (ROS) have been shown to regulate RhoA activation. In addition, Rho-specific guanine exchange factors (GEFs), neuroepithelial transforming gene 1 (Net1) and epithelial cell transforming sequence 2 (Ect2), have specific functions in DDR, and they also participate in Ras-related C3 botulinum toxin substrate 1 (Rac1)/RhoA interaction, a process which is largely unappreciated yet possibly of significance in DDR. Downstream of RhoA, current evidence has highlighted its role in mediating cell cycle arrest, which is an important step in DNA repair. Unraveling the mechanism by which RhoA modulates DDR may provide more insight into DDR itself and may aid in the future development of cancer therapies.

FEN1 is a prognostic biomarker for ER+ breast cancer and associated with tamoxifen resistance through the ERα/cyclin D1/Rb axis

Background

Tamoxifen is an important choice in endocrine therapy for patients with oestrogen receptor-positive (ER+) breast cancer, and disease progression-associated resistance to tamoxifen therapy is still challenging. Flap endonuclease-1 (FEN1) is used as a prognostic biomarker and is considered to participate in proliferation, migration, and drug resistance in multiple cancers, especially breast cancer, but the prognostic function of FEN1 in ER+ breast cancer, and whether FEN1 is related to tamoxifen resistance or not, remain to be explored.

Methods

On-line database Kaplan-Meier (KM) plotter, GEO datasets, and immunohistochemistry were used to analyse the prognostic value of FEN1 in ER+ breast cancer from mRNA and protein levels. Cell viability assay and colony formation assays showed the response of tamoxifen in MCF-7 and T47D cells. Microarray data with FEN1 siRNA versus control group in MCF-7 cells were analysed by Gene Set Enrichment Analysis (GSEA). The protein levels downstream of FEN1 were detected by western blot assay.

Results

ER+ breast cancer patients who received tamoxifen for adjuvant endocrine therapy with poor prognosis showed a high expression of FEN1. MCF-7 and T47D appeared resistant to tamoxifen after FEN1 over-expression and increased sensitivity to tamoxifen after FEN1 knockdown. Importantly, FEN1 over-expression could activate tamoxifen resistance through the ERα/cyclin D1/Rb axis.

Conclusions

As a biomarker of tamoxifen effectiveness, FEN1 participates in tamoxifen resistance through ERα/cyclin D1/Rb axis. In the future, reversing tamoxifen resistance by knocking-down FEN1 or by way of action as a small molecular inhibitor of FEN1 warrants further investigation.

The inhibition of colorectal cancer growth by the natural product macrocarpal I

BACKGROUND

Presently, few small molecule compounds are used as targeted therapy drugs in the treatment of colorectal cancer (CRC). It is important to identify new small molecule compounds, which can be used in the treatment of CRC.

METHODS

In this study, we selected four protein molecules as drug targets: PRL-3 (Phosphatase of regenerating liver 3), CLIC4 (Chloride intracellular channel 4), THBS2 (Thrombospondin 2), and BGN (Biglycan). These protein molecules were associated with the growth and metastasis of CRC cells. Small molecular compounds were screened on the basis of their target structures. Thus, five small molecule compounds were screened from each target structure, and three small molecule compounds (macrocarpal I, sildenafil, and neoandrographolide) were found to bind with two drug targets at the same time. Further experiments revealed that the inhibition rate of macrocarpal I was the highest in CRC cells. Therefore, we determined the effects of macrocarpal I on proliferation, apoptosis, cytoskeleton of CRC cells, and subcutaneous tumorigenesis in nude mice. Furthermore, RNA-seq analysis was performed to determine the molecular mechanism through which macrocarpal I inhibited the progression of CRC.

RESULTS

We found that macrocarpal I could effectively inhibit proliferation, colony formation of CRC cells, and subcutaneous tumorigenesis in nude mice. Moreover, it also destroyed the cytoskeleton of CRC cells and promoted apoptosis. The effects on kinase activity, cytoskeleton, and DNA repair is the mechanism of macrocarpal I to inhibiting CRC growth.

CONCLUSION

Macrocarpal I is a small molecule compound that can effectively inhibit the progression of CRC. Thus, macrocarpal I is a therapeutic compound that shows promising results in the treatment of advanced CRC.

Biological and clinical significance of flap endonuclease‑1 in triple‑negative breast cancer: Support of metastasis and a poor prognosis

Flap endonuclease‑1 (FEN1), a structure‑specific nuclease participating in DNA replication and repair processes, has been confirmed to promote the proliferation and drug resistance of tumor cells. However, the biological functions of FEN1 in cancer cell migration and invasion have not been defined. In the present study, using online database analysis and immunohistochemistry of the specimens, it was found that FEN1 expression was associated with a highly invasive triple‑negative breast cancer (TNBC) subtype in both breast cancer samples from the Oncomine database and from patients recruited into the study. Furthermore, FEN1 was an important biomarker of lymph node metastasis and poor prognosis in patients with TNBC. FEN1 promoted migration of TNBC cell lines and FEN1 knockdown reduced the number of spontaneous lung metastasis in vivo. Ingenuity Pathway Analysis of FEN1‑related transcripts in 198 patients with TNBC demonstrated that the polo‑like kinase family may be the downstream target of FEN1. PLK4 was further identified as a critical target of FEN1 mediating TNBC cell migration, by regulating actin cytoskeleton rearrangement. The results of the present study validate FEN1 as a therapeutic target in patients with TNBC and revealed a new role for FEN1 in regulating TNBC invasion and metastasis.

Transcriptome Analysis of FEN1 Knockdown HEK293T Cell Strain Reveals Alteration in Nucleic Acid Metabolism, Virus Infection, Cell Morphogenesis and Cancer Development

AIM AND OBJECTIVE

Flap endonuclease-1 (FEN1) plays a central role in DNA replication and DNA damage repair process. In mammals, FEN1 functional sites variation is related to cancer and chronic inflammation, and supports the role of FEN1 as a tumor suppressor. However, FEN1 is overexpressed in multiple types of cancer cells and is associated with drug resistance, supporting its role as an oncogene. Hence, it is vital to explore the multi-functions of FEN1 in normal cell metabolic process. This study was undertaken to examine how the gene expression profile changes when FEN1 is downregulated in 293T cells.

MATERIALS AND METHODS

Using the RNA sequencing and real-time PCR approaches, the transcript expression profile of FEN1 knockdown HEK293T cells have been detected for the next step evaluation, analyzation, and validation.

RESULTS

Our results confirmed that FEN1 is important for cell viability. We showed that when FEN1 downregulation led to the interruption of nucleic acids related metabolisms, cell cycle related metabolisms are significantly interrupted. FEN1 may also participate in non-coding RNA processing, ribosome RNA processing, transfer RNA processing, ribosome biogenesis, virus infection and cell morphogenesis.

CONCLUSION

These findings provide insight into how FEN1 nuclease might regulate a wide variety of biological processes, and laid the foundation for understanding the role of other RAD2 family nucleases in cell growth and metabolism.

Innovative Strategies: Targeting Subtypes in Metastatic Breast Cancer

Metastatic breast cancer continues to be a life-threatening diagnosis that impacts hundreds of thousands of patients around the world. Targeted therapies are usually associated with less toxicity compared with cytotoxic chemotherapies and often induce response or durable disease control in estrogen receptor (ER) and/or HER2+ breast cancers. Drugs that target CDK 4/6 either alone or in combination with endocrine therapy have demonstrated substantial improvements in progression-free survival (PFS) compared with endocrine monotherapy. Most recently, PARP inhibitors have shown longer PFS compared with physician's choice of chemotherapy in BRCA-associated cancers, leading to the first U.S. Food and Drug Administration (FDA) approval of a targeted therapy with the potential to benefit a subgroup of patients with triple-negative breast cancer (TNBC). Finally, newer drug delivery strategies using antibody drug conjugates have also allowed a "targeted approach" to deliver moderate to extremely potent cytotoxins directly to sites of metastatic disease, with less toxicity.