Enhancer of zeste homolog 2 (EZH2) is enzymatic catalytic subunit of polycomb repressive complex 2 (PRC2) that can alter downstream target genes expression by trimethylation of Lys-27 in histone 3 (H3K27me3). EZH2 could also regulate gene expression in ways besides H3K27me3. Functions of EZH2 in cells proliferation, apoptosis, and senescence have been identified. Its important roles in the pathophysiology of cancer are now widely concerned. Therefore, targeting EZH2 for cancer therapy is a hot research topic now and different types of EZH2 inhibitors have been developed. In this review, we summarize the structure and action modes of EZH2, focusing on up-to-date findings regarding the role of EZH2 in cancer initiation, progression, metastasis, metabolism, drug resistance, and immunity regulation. Furtherly, we highlight the advance of targeting EZH2 therapies in experiments and clinical studies.

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EZH2: a novel target for cancer treatment.

Given that the PI3K/AKT pathway has manifested its compelling influence on multiple cellular process, we further review the roles of hyperactivation of PI3K/AKT pathway in various human cancers. We state the abnormalities of PI3K/AKT pathway in different cancers, which are closely related with tumorigenesis, proliferation, growth, apoptosis, invasion, metastasis, epithelial-mesenchymal transition, stem-like phenotype, immune microenvironment and drug resistance of cancer cells. In addition, we investigated the current clinical trials of inhibitors against PI3K/AKT pathway in cancers and found that the clinical efficacy of these inhibitors as monotherapy has so far been limited despite of the promising preclinical activity, which means combinations of targeted therapy may achieve better efficacies in cancers. In short, we hope to feature PI3K/AKT pathway in cancers to the clinic and bring the new promising to patients for targeted therapies.

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Role of PI3K/AKT pathway in cancer: the framework of malignant behavior.

Growth/differentiation factor-15 (GDF-15), also named macrophage inhibitory cytokine-1, is a divergent member of the transforming growth factor β superfamily. While physiological expression is barely detectable in most somatic tissues in humans, GDF-15 is abundant in placenta. Elsewhere, GDF-15 is often induced under stress conditions, seemingly to maintain cell and tissue homeostasis; however, a moderate increase in GDF-15 blood levels is observed with age. Highly elevated GDF-15 levels are mostly linked to pathological conditions including inflammation, myocardial ischemia, and notably cancer. GDF-15 has thus been widely explored as a biomarker for disease prognosis. Mechanistically, induction of anorexia via the brainstem-restricted GDF-15 receptor GFRAL (glial cell-derived neurotrophic factor [GDNF] family receptor α-like) is well-documented. GDF-15 and GFRAL have thus become attractive targets for metabolic intervention. Still, several GDF-15 mediated effects (including its physiological role in pregnancy) are difficult to explain via the described pathway. Hence, there is a clear need to better understand non-metabolic effects of GDF-15. With particular emphasis on its immunomodulatory potential this review discusses the roles of GDF-15 in pregnancy and in pathological conditions including myocardial infarction, autoimmune disease, and specifically cancer. Importantly, the strong predictive value of GDF-15 as biomarker may plausibly be linked to its immune-regulatory function. The described associations and mechanistic data support the hypothesis that GDF-15 acts as immune checkpoint and is thus an emerging target for cancer immunotherapy.

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Growth/Differentiation Factor-15 (GDF-15): From Biomarker to Novel Targetable Immune Checkpoint.

Chemoresistance, whether intrinsic or acquired, is a major obstacle in the treatment of cancer. The resistance of cancer cells to chemotherapeutic drugs can result from various mechanisms. Over the last decade, it has been reported that 1ong noncoding RNAs (lncRNAs) can mediate carcinogenesis and drug resistance/sensitivity in cancer cells. This article reviews, in detail, recent studies regarding the roles of lncRNAs in mediating drug resistance.

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Long non-coding RNAs regulate drug resistance in cancer

Growth differentiation factor 15 (GDF15): A survival protein with therapeutic potential in metabolic diseases

Gefitinib, a tyrosine kinase inhibitor of epidermal growth factor receptor, has been used as the first choice of treatment for advanced non-small-cell lung cancer. However, during the course of treatment, cancer cells often develop resistance to gefitinib without fully understood mechanisms. In this study, we aimed to elucidate an important role of long intergenic non-coding RNA 00665 in developing resistance to gefitinib in non-small-cell lung cancer. We showed that long intergenic non-coding RNA 00665 expression was significantly upregulated in lung cancer tissues and cells with acquired gefitinib resistance. Long intergenic non-coding RNA 00665 knockdown restored gefitinib sensitivity both in vitro and in vivo by suppressing cell proliferation and inducing apoptosis. Moreover, knockdown of long intergenic non-coding RNA 00665 markedly reduced activation of EGFR and its downstream event protein kinase B (AKT). Moreover, LINC00665 could interact with EZH2 and regulate the phosphatidylinositol 3-kinase (PI3K)/AKT pathway. Thus, our study suggests that long intergenic non-coding RNA 00665 is important for non-small-cell lung cancer to develop drug resistance and might be a potential biomarker for drug resistance and a therapeutic target for non-small-cell lung cancer.

LINC00665 Induces Acquired Resistance to Gefitinib through Recruiting EZH2 and Activating PI3K/AKT Pathway in NSCLC.

Growth differentiation factor 15 (GDF15), a member of the TGF-β superfamily of cytokines, has been reported to exert very heterogeneous functions in various tumors. However, its expression and roles in mediating non-small-cell lung cancer (NSCLC) progression remain unknown. In this study, we found that GDF15 is downregulated in paired NSCLC tissues and correlated with poor clinical outcomes in NSCLC. A functional experiment demonstrated that overexpression of GDF15 significantly repressed NSCLC proliferation both in vitro and in vivo. Mechanistic studies reveal that inhibition of EZH2 expression prevented its binding to the GDF15 promoter region and reduced the trimethylation modification pattern of H3K27. Together, our data uncover that GDF15 is a direct target of EZH2 and, as a regulator of proliferation, might serve as a candidate prognostic biomarker and target for new therapies in human NSCLC.

Kun Xu

Papers

LINC00665 Induces Acquired Resistance to Gefitinib through Recruiting EZH2 and Activating PI3K/AKT Pathway in NSCLC.

EZH2-Mediated Epigenetic Suppression of GDF15 Predicts a Poor Prognosis and Regulates Cell Proliferation in Non-Small-Cell Lung Cancer