Telomerase expression and cell proliferation in ovarian cancer cells induced by histone deacetylase inhibitors

Butyrate as a Potential Modulator in Gynecological Disease Progression

This review investigates the therapeutic potential of butyrate, a short-chain fatty acid (SCFA) produced by gut microbiota, in the prevention and treatment of various gynecological diseases, including polycystic ovary syndrome (PCOS), endometriosis, and gynecologic cancers like cervical and ovarian cancer. These conditions often pose treatment challenges, with conventional therapies offering limited and temporary relief, significant side effects, and a risk of recurrence. Emerging evidence highlights butyrate's unique biological activities, particularly its role as a histone deacetylase (HDAC) inhibitor, which allows it to modulate gene expression, immune responses, and inflammation. In PCOS, butyrate aids in restoring hormonal balance, enhancing insulin sensitivity, and reducing chronic inflammation. For endometriosis, butyrate appears to suppress immune dysregulation and minimize lesion proliferation. Additionally, in cervical and ovarian cancers, butyrate demonstrates anticancer effects through mechanisms such as cell cycle arrest, apoptosis induction, and suppression of tumor progression. Dietary interventions, particularly high-fiber and Mediterranean diets, that increase butyrate production are proposed as complementary approaches, supporting natural microbiota modulation to enhance therapeutic outcomes. However, butyrate's short half-life limits its clinical application, spurring interest in butyrate analogs and probiotics to maintain stable levels and extend its benefits. This review consolidates current findings on butyrate's multifaceted impact across gynecological health, highlighting the potential for microbiota-centered therapies in advancing treatment strategies and improving women's reproductive health.

Telomerase Regulation: A Role for Epigenetics

Simple Summary

Maintenance of telomeres is a fundamental step in human carcinogenesis and is primarily regulated by telomerase and the human telomerase reverse transcriptase gene (TERT). Improved understanding of the transcriptional control of this gene may provide potential therapeutic targets. Epigenetic modifications are a prominent mechanism to control telomerase activity and regulation of the TERT gene. TERT-targeting miRNAs have been widely studied and their function explained through pre-clinical in vivo model-based validation studies. Further, histone deacetylase inhibitors are now in pre and early clinical trials with significant clinical success. Importantly, TERT downregulation through epigenetic modifications including TERT promoter methylation, histone deacetylase inhibitors, and miRNA activity might contribute to clinical study design. This review provides an overview of the epigenetic mechanisms involved in the regulation of TERT expression and telomerase activity.

Abstract

Telomerase was first described by Greider and Blackburn in 1984, a discovery ultimately recognized by the Nobel Prize committee in 2009. The three decades following on from its discovery have been accompanied by an increased understanding of the fundamental mechanisms of telomerase activity, and its role in telomere biology. Telomerase has a clearly defined role in telomere length maintenance and an established influence on DNA replication, differentiation, survival, development, apoptosis, tumorigenesis, and a further role in therapeutic resistance in human stem and cancer cells including those of breast and cervical origin. TERT encodes the catalytic subunit and rate-limiting factor for telomerase enzyme activity. The mechanisms of activation or silencing of TERT remain open to debate across somatic, cancer, and stem cells. Promoter mutations upstream of TERT may promote dysregulated telomerase activation in tumour cells but additional factors including epigenetic, transcriptional and posttranscriptional modifications also have a role to play. Previous systematic analysis indicated methylation and mutation of the TERT promoter in 53% and 31%, respectively, of TERT expressing cancer cell lines supporting the concept of a key role for epigenetic alteration associated with TERT dysregulation and cellular transformation. Epigenetic regulators including DNA methylation, histone modification, and non-coding RNAs are now emerging as drivers in the regulation of telomeres and telomerase activity. Epigenetic regulation may be responsible for reversible silencing of TERT in several biological processes including development and differentiation, and increased TERT expression in cancers. Understanding the epigenetic mechanisms behind telomerase regulation holds important prospects for cancer treatment, diagnosis and prognosis. This review will focus on the role of epigenetics in telomerase regulation.

Synergistic activity of the histone deacetylase inhibitor trichostatin A and the proteasome inhibitor PS-341 against taxane-resistant ovarian cancer cell lines

Although a combination of platinum- and taxane-based chemotherapy is recommended for at least 70% patients with ovarian cancer as treatment subsequent to surgery, the initial response to the chemotherapy is not durable and tumors become resistant. Histone deacetylase and proteasome inhibitors are novel therapeutic agents. However, the moderate antitumoral effect of the inhibitors has restricted their clinical use when used as single agents. The aim of the present study was to investigate the synergistic activity of trichostatin A (TSA) and PS-341 in ovarian cancer cells, along with the investigation of the molecular mechanisms of taxane resistance. The taxane-sensitive ovarian cancer A2780 cell line and its resistant variant, A2780T, were treated with taxane, TSA and PS-341 at various concentrations. An Annexin V assay was performed to determine the levels of cell viability and apoptosis, while flow cytometry and immunofluorescence staining for the mitotic phase-specific protein phosphorylated-histone H3 (Ser10) were used for cell cycle detection. The effects of combined TSA and PS-341 on cell cycle-associated proteins were tested by western blot analysis. Furthermore, the present study examined the apoptosis and cell cycle arrest induced by the 3 agents subsequent to overexpression or downregulation of cyclin B1 in A2780 and A2780T cells, respectively. It was found that TSA interacted synergistically with PS-341, resulting in a marked increase in apoptosis and the rate of G₂/M arrest in A2780T cells. A lower basal level of cyclin B1 expression and the incompetence of the upregulation of the cyclin may explain the taxane resistance found in A2780T cells. Collectively, the combination of TSA and PS-341 increased cyclin B1 expression level regardless of the basal expression level, resulting in the proliferation inhibition and apoptosis in A2780 and A2780T cells, which raised the possibility that a combination of the two drugs may represent a novel strategy for the treatment of ovarian cancer, particularly in taxane-resistant ovarian cancer.

Genetic and epigenetic trends in telomere research: a novel way in immunoepigenetics

Telomeres are protective heterochromatic structures that cap the end of linear chromosomes and play a key role in preserving genomic stability. Telomere length represents a balance between processes that shorten telomeres during cell divisions with incomplete DNA replication and the ones that lengthen telomeres by the action of telomerase, an RNA-protein complex with reverse transcriptase activity which adds telomeric repeats to DNA molecule ends. Telomerase activity and telomere length have a crucial role in cellular ageing and in the pathobiology of several human diseases attracting intense research. The last few decades have witnessed remarkable advances in our understanding about telomeres, telomere-associated proteins, and the biogenesis and regulation of the telomerase holoenzyme complex, as well as about telomerase activation and the telomere-independent functions of telomerase. Emerging data have revealed that telomere length can be modified by genetic and epigenetic factors, sex hormones, reactive oxygen species and inflammatory reactions. It has become clear that, in order to find out more about the factors influencing the rate of telomere attrition in vivo, it is crucial to explore both genetic and epigenetic mechanisms. Since the telomere/telomerase assembly is under the control of multiple epigenetic influences, the unique design of twin studies could help disentangle genetic and environmental factors in the functioning of the telomere/telomerase system. It is surprising that the literature on twin studies investigating this topic is rather scarce. This review aims to provide an overview of some important immune response- and epigenetics-related aspects of the telomere/telomerase system demanding more research, while presenting the available twin data published in connection with telomere research so far. By emphasising what we know and what we still do not know in these areas, another purpose of this review is to urge more twin studies in telomere research.

Epigenetic regulation of the human telomerase reverse transciptase gene: A potential therapeutic target for the treatment of leukemia (Review)

Telomerase activation is a critical step in human carcinogenesis through the maintenance of telomeres. Telomerase activity is primarily regulated by the human telomerase reverse transcriptase gene (hTERT), thus, an improved understanding of the transcriptional control of hTERT may provide potential therapeutic targets for the treatment of leukemia and other forms of cancer. Epigenetic modulation, a significant regulatory process in cell biology, has recently been shown to be involved in the regulation of the hTERT gene. Moreover, several epigenetic modifiers, including DNA methyltransferase (DNMT) and histone deacetylase (HDAC) inhibitors, are now in pre- and early clinical trials of leukemia as monotherapies or in combination with other drugs, and have achieved significant clinical success. In the present review, the epigenetic mechanisms associated with telomerase activity in leukemia, and the therapeutic potential of an antitelomerase strategy that combines epigenetic modifiers with telomerase hTR subunit small molecule inhibitors are discussed.

Valproic acid increases susceptibility to endotoxin shock through enhanced release of high-mobility group box 1

High-mobility group box 1 (HMGB1) is a nuclear factor and a secreted protein. During inflammation, HMGB1 is secreted into the extracellular space where it can interact with the receptor for advanced glycation end products and trigger proinflammatory signals. Extracellular HMGB1 plays a critical role in several inflammatory diseases such as sepsis and rheumatoid arthritis. Valproic acid (VPA) is one of the most frequently prescribed antiepileptic drugs. The present study was undertaken to investigate the effect of VPA on secretion of HMGB1 in systemic inflammatory responses induced by lipopolysaccharide. Pretreatment with VPA increased the susceptibility of mice to lipopolysaccharide in endotoxemia. Valproic acid induced HMGB1 release and nuclear factor κB activation in RAW-blue cells. Valproic acid promoted the phosphorylation of ERK1/2 but not that of p38 or JNK. The MEK1/2 inhibitor PD98059 also suppressed HMGB1 release and activation of nuclear factor κB induced by VPA. Valproic acid induced expression of γ-aminobutyric acid receptors in macrophages, and picrotoxin, a γ-aminobutyric acid A receptor antagonist, inhibited the VPA-activated phosphorylation of ERK and VPA-induced HMGB1 release. These results suggest that VPA may exacerbate innate immune responses to endotoxin through enhanced release of HMGB1.

Synergistic efficacy in human ovarian cancer cells by histone deacetylase inhibitor TSA and proteasome inhibitor PS-341

Histone deacetylase inhibitors and proteasome inhibitor are all emerging as new classes of anticancer agents. We chose TSA and PS-341 to identify whether they have a synergistic efficacy on human ovarian cancer cells. After incubated with 500 nM TSA or/and 40 nM PS-341, we found that combined groups resulted in a striking increase of apoptosis and G2/M blocking rates, no matter in A2780, cisplatin-sensitive ovarian cancer cell line OV2008 or its resistant variant C13*. This demonstrated that TSA interacted synergistically with PS-341, which raised the possibility that combined the two drugs may represent a novel strategy in ovarian cancer.