Mechanisms involved in the HMGB1 modulation of tumor multidrug resistance (Review)

Tumor multidrug resistance (MDR) remains one of the most challenging barriers to successful cancer treatment. Several previous studies have suggested that high mobility group box 1 (HMGB1) may be a promising therapeutic target for overcoming cancer drug resistance. Emerging evidence has indicated that HMGB1 functions as a 'double‑edged sword' that plays both pro‑ and anti‑tumor roles in the development and progression of multiple types of cancer. HMGB1 has also been found to be a key regulator of several cell death and signaling pathways, and is involved in MDR by mediating cell autophagy and apoptosis, ferroptosis, pyroptosis and multiple signaling pathways. Additionally, HMGB1 is regulated by a variety of non‑coding RNAs (ncRNAs), such as microRNAs, long ncRNAs and circular RNAs that are involved in MDR. Thus far, studies have been conducted to identify strategies with which to overcome HMGB1‑mediated MDR by the targeted silencing of HMGB1 and the targeted interference of HMGB1 expression using drugs and ncRNAs. Therefore, HMGB1 is closely associated with tumor MDR and is a promising therapeutic target.

Role of non‑coding RNA intertwined with the Wnt/β‑catenin signaling pathway in endometrial cancer (Review)

Endometrial cancer (EC) ranks as the sixth most common malignancy in women around the world. Although low‑grade and early‑stage EC commonly have an excellent prognosis, ~20% of EC patients experience an unfavorable prognosis. Identifying the pathogenesis and novel therapeutic targets may help address this group of patients. Non‑coding (nc)RNAs, such as long non‑coding RNAs (lncRNAs), microRNAs and circular RNAs (circRNAs), have been associated with EC occurrence and development. In addition, the aberrant activation of the Wnt/β‑catenin signaling pathway can promote the proliferation, invasion, migration and epithelial‑to‑mesenchymal transition (EMT) of EC cells. The network of ncRNAs has also been demonstrated to inhibit or activate the Wnt/β‑catenin signaling pathway. In the present review, ncRNAs, the Wnt/β‑catenin signaling pathway, and their crosstalk in EC were summarized and highlighted. This information is expected to provide novel insights into improving the management of EC using RNA as therapeutics.

Modulating epigenetic modifications for cancer therapy (Review)

Cancer is a global public health concern. Alterations in epigenetic processes are among the earliest genomic aberrations occurring during cancer development and are closely related to progression. Unlike genetic mutations, aberrations in epigenetic processes are reversible, which opens the possibility for novel pharmacological treatments. Non‑coding RNAs (ncRNAs) represent an essential epigenetic mechanism, and emerging evidence links ncRNAs to carcinogenesis. Epigenetic drugs (epidrugs) are a group of promising target therapies for cancer treatment acting as coadjuvants to reverse drug resistance in cancer. The present review describes central epigenetic aberrations during malignant transformation and explains how epidrugs target DNA methylation, histone modifications and ncRNAs. Furthermore, clinical trials focused on evaluating the effect of these epidrugs alone or in combination with other anticancer therapies and other ncRNA‑based therapies are discussed. The use of epidrugs promises to be an effective tool for reversing drug resistance in some patients with cancer.

Epigenetic modification regulates tumor progression and metastasis through EMT (Review)

Epigenetics is the study of heritable molecular determinants that are independent of phenotypic features. The epigenetic features include DNA methylation, histone modifications, non‑coding RNAs, and chromatin remodeling. In multicellular organisms, the epigenetic state of a cell is critical in determining its differentiation status and its ability to perform its proper function. These processes are now well recognized as being a substantial factor in tumor progression and metastasis. The process through which epithelial cells acquire mesenchymal features is known as epithelial‑mesenchymal transition (EMT). EMT is associated with tumorigenesis, invasion, metastasis, and resistance to therapy in cancer. In the present review, we examine the recent studies that demonstrate the biological role of epigenetics, in particular, DNA methylation, histone modifications, non‑coding RNAs, and chromatin remodeling in tumor progression and metastasis by regulating EMT status, and we provide an overview of the current state of knowledge regarding the epigenetics involvement in tumor progression and metastasis. Because epigenetic changes can be reversed, learning more about their biological roles in EMT will not only help us better understand how cancer progresses and spreads, but it will also help us identify new ways to diagnose and treat human malignancy, which is currently lacking in the clinical setting.

Epigenetic modifications in acute myeloid leukemia: The emerging role of circular RNAs (Review)

Canonical epigenetic modifications, which include histone modification, chromatin remodeling and DNA methylation, play key roles in numerous cellular processes. Epigenetics underlies how cells that posses DNA with similar sequences develop into different cell types with different functions in an organism. Earlier epigenetic research has primarily been focused at the chromatin level. However, the number of studies on epigenetic modifications of RNA, such as N1‑methyladenosine, 2'‑O‑ribosemethylation, inosine, 5‑methylcytidine, N6‑methyladenosine (m6A) and pseudouridine, has seen an increase. Circular RNAs (circRNAs), a type of RNA species that lacks a 5' cap or 3' poly(A) tail, are abundantly expressed in acute myeloid leukemia (AML) and may regulate disease progression. circRNAs possess various functions, including microRNA sponging, gene transcription regulation and RNA‑binding protein interaction. Furthermore, circRNAs are m6A methylated in other types of cancer, such as colorectal and hypopharyngeal squamous cell cancers. Therefore, the critical roles of circRNA epigenetic modifications, particularly m6A, and their possible involvement in AML are discussed in the present review. Epigenetic modification of circRNAs may become a diagnostic and therapeutic target for AML in the future.

Histone deacetylase‑2: A potential regulator and therapeutic target in liver disease (Review)

Histone acetyltransferases are responsible for histone acetylation, while histone deacetylases (HDACs) counteract histone acetylation. An unbalanced dynamic between histone acetylation and deacetylation may lead to aberrant chromatin landscape and chromosomal function. HDAC2, a member of class I HDAC family, serves a crucial role in the modulation of cell signaling, immune response and gene expression. HDAC2 has emerged as a promising therapeutic target for liver disease by regulating gene transcription, chromatin remodeling, signal transduction and nuclear reprogramming, thus receiving attention from researchers and clinicians. The present review introduces biological information of HDAC2 and its physiological and biochemical functions. Secondly, the functional roles of HDAC2 in liver disease are discussed in terms of hepatocyte apoptosis and proliferation, liver regeneration, hepatocellular carcinoma, liver fibrosis and non-alcoholic steatohepatitis. Moreover, abnormal expression of HDAC2 may be involved in the pathogenesis of liver disease, and its expression levels and pharmacological activity may represent potential biomarkers of liver disease. Finally, research on selective HDAC2 inhibitors and non-coding RNAs relevant to HDAC2 expression in liver disease is also reviewed. The aim of the present review was to improve understanding of the multifunctional role and potential regulatory mechanism of HDAC2 in liver disease.

Upregulated long non‑coding RNA LincIN promotes tumor progression via the regulation of nuclear factor 90/microRNA‑7/HOXB13 in esophageal squamous cell carcinoma

Long non-coding RNA LincIN has been reported to be overexpressed and to be involved in the metastasis of breast cancer. However, the expression and role of LincIN in esophageal squamous cell carcinoma (ESCC) remain unsolved. In the present study, LincIN expression was examined in ESCC by RT-qPCR, and the roles of LincIN in ESCC were determined using cell growth, migration and invasion assays. In addition, the effects of LincIN on nuclear factor 90 (NF90) and microRNA/miR (miR)-7 were examined by RNA immunoprecipitation assay, RT-qPCR, dual-luciferase reporter assay and western blot analysis. The results revealed that LincIN expression was significantly increased in ESCC tissues and cell lines. The increased expression of LincIN was positively associated with invasion depth, lymph node metastasis, TNM stage and a poor prognosis. Functional assays revealed that the overexpression of LincIN promoted ESCC cell growth, migration and invasion. Mechanistic analysis revealed that LincIN physically bound to NF90, enhanced the binding between NF90 and primary miR-7 (pri-miR-7), and further enhanced the inhibitory effects of NF90 on miR-7 biogenesis. Therefore, LincIN downregulated miR-7 expression in ESCC. The expression of miR-7 inversely correlated with that of LincIN in ESCC tissues. By downregulating miR-7, LincIN increased the expression of HOXB13, a target of miR-7. The overexpression of miR-7 or the depletion of HOXB13 both attenuated the tumor-promoting roles of LincIN in ESCC cell growth, migration and invasion. On the whole, the findings of the present study suggest that LincIN is overexpressed and plays an oncogenic role in ESCC via the regulation of the NF90/miR-7/HOXB13 axis. Thus, LincIN may prove to be a promising prognostic biomarker and therapeutic target for ESCC.