Induction of amphiregulin by p53 promotes apoptosis via control of microRNA biogenesis in response to DNA damage

Acquired vulnerability against EGF receptor inhibition in gastric cancer promoted by class I histone deacetylase inhibitor entinostat

INTRODUCTION

Histone deacetylase inhibitors (HDACi) have shown promising preclinical activity in gastric cancer cells; unfortunately, however, these could not be confirmed in clinical trials. This highlights the need for the identification of underlying reasons, which may also provide the basis for possible combination therapies. Here, we delineated the effects of HDACi on components of EGFR signalling in gastric cancer cells.

METHODS

We investigated entinostat effects on EGFR and amphiregulin (AREG) expression in various cell line- and primary patient tumor-based in vitro, ex vivo and in vivo models, on the mRNA and protein level. Based on these results, a combined entinostat plus EGFR inhibitor erlotinib treatment in vitro and in vivo was studied.

RESULTS

Proteomics analyses in gastric cancer cells treated with entinostat revealed a marked upregulation of EGFR in the majority of cell lines and an even more robust induction of the EGFR ligand AREG. This was confirmed in a panel of different cell lines in vitro, in tumor tissue-slice cultures ex vivo and in cell line- or patient-derived tumor xenografts in mice. Since previous studies in other tumor entities showed a downregulation of EGFR by HDACi, our findings thus indicate essential differences in the adaptive response of gastric carcinoma cells. Moreover, our results provided the basis for combined entinostat + EGFR inhibitor (erlotinib) treatment, and indeed we demonstrate synergistic effects in combination therapy studies.

CONCLUSION

Our findings establish the profound upregulation of the EGFR/AREG axis by entinostat as starting point for a rational combination therapy in gastric carcinoma.

Genome-Wide Analysis of p53 Targets Reveals SCN2A as a Novel Player in p53-Induced Cell Arrest in HPV-Positive Cells

The host transcription factor p53 is a critical tumor suppressor in HPV-induced carcinogenesis, regulating target genes involved in cell cycle arrest and apoptosis. However, the p53 targets have not been thoroughly analyzed in HPV-infected cells. In this study, p53 signaling in HPV16 and HPV18 cells was activated by depleting the viral oncoprotein E6. Subsequently, p53-regulated genes were identified by comparing them with genes altered in p53-silenced cells. True p53 targets were defined as genes with at least one overlapping p53 binding site and ChIP peak near their locus. Our analysis revealed that while some p53 targets were common to both the HPV16 and HPV18 cells, the majority of the targets differed between these two types, potentially contributing to the varying prevalence of HPV16 and HPV18 in cervical cancer. Additionally, we identified SCN2A as a novel p53 target involved in p53-induced cell cycle arrest in HPV-related carcinogenesis. This study provides new insights into the mechanisms by which p53 inhibits HPV-induced carcinogenesis.

Expanding Roles of the E2F-RB-p53 Pathway in Tumor Suppression

The transcription factor E2F links the RB pathway to the p53 pathway upon loss of function of pRB, thereby playing a pivotal role in the suppression of tumorigenesis. E2F fulfills a major role in cell proliferation by controlling a variety of growth-associated genes. The activity of E2F is controlled by the tumor suppressor pRB, which binds to E2F and actively suppresses target gene expression, thereby restraining cell proliferation. Signaling pathways originating from growth stimulative and growth suppressive signals converge on pRB (the RB pathway) to regulate E2F activity. In most cancers, the function of pRB is compromised by oncogenic mutations, and E2F activity is enhanced, thereby facilitating cell proliferation to promote tumorigenesis. Upon such events, E2F activates the Arf tumor suppressor gene, leading to activation of the tumor suppressor p53 to protect cells from tumorigenesis. ARF inactivates MDM2, which facilitates degradation of p53 through proteasome by ubiquitination (the p53 pathway). P53 suppresses tumorigenesis by inducing cellular senescence or apoptosis. Hence, in almost all cancers, the p53 pathway is also disabled. Here we will introduce the canonical functions of the RB-E2F-p53 pathway first and then the non-classical functions of each component, which may be relevant to cancer biology.

Single-cell transcriptomics reveals subtype-specific molecular profiles in Nrf2-deficient macrophages from murine atherosclerotic aortas

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcriptional regulator of antioxidant and anti-inflammatory response in all cell types. It also activates the transcription of genes important for macrophage function. Nrf2 activity declines with age and has been closely linked to atherosclerosis, but its specific role in this vascular pathology is not clear. Atherosclerotic plaques contain several macrophage subsets with distinct, yet not completely understood, functions in the lesion development. The aim of this study was to analyze the transcriptome of diverse Nrf2-deficient macrophage subpopulations from murine atherosclerotic aortas. Mice with transcriptionally inactive Nrf2 in Cdh5-expressing cells (Nrf2 Cdh5tKO) were used in the experiments. These mice lack transcriptional Nrf2 activity in endothelial cells, but also in a proportion of leukocytes. We confirmed that the bone marrow-derived and tissue-resident macrophages isolated from Nrf2 Cdh5tKO mice exhibit a significant decline in Nrf2 activity. Atherosclerosis was induced in Nrf2 Cdh5tKO and appropriate control mice via adeno-associated viral vector (AAV)-mediated overexpression of murine proprotein convertase subtilisin/kexin type 9 (Pcsk9) in the liver and high-fat diet feeding. After 21 weeks, live aortic cells were sorted on FACS and single-cell RNA sequencing (scRNA-seq) was performed. Unsupervised clustering singled out 13 distinct aortic cell types. Among macrophages, 9 subclusters were identified. Differential gene expression analysis revealed cell subtype-specific expression patterns. A subset of inflammatory macrophages from atherosclerotic Nrf2 Cdh5tKO mice demonstrated downregulation of DNA replication genes (e.g. Mcm7, Lig1, Pola1) concomitant with upregulation of DNA damage sensor Atr gene. Atherosclerotic Nrf2 Cdh5tKO Lyve1+ resident macrophages showed strong upregulation of IFN-stimulated genes, as well as changes in the expression of death pathways-associated genes (Slc40a1, Bcl2a1). Furthermore, we observed subtype-specific expression of core ferroptosis genes (e.g. Cp, Hells, Slc40a1) in inflammatory versus tissue resident macrophages. This observation suggested a link between ferroptosis and inflammatory microenvironment appearing at a very early stage of atherogenesis. Our findings indicate that Nrf2 deficiency in aortic macrophages leads to subtype-specific transcriptomic changes associated with inflammation, iron homeostasis, cell injury or death pathways. This may help understanding the role of aging-associated decline of Nrf2 activity and the function of specific macrophage subtypes in atherosclerotic lesion development.

Role of the DEAD-box RNA helicase DDX5 (p68) in cancer DNA repair, immune suppression, cancer metabolic control, virus infection promotion, and human microbiome (microbiota) negative influence

There is increasing evidence indicating the significant role of DDX5 (also called p68), acting as a master regulator and a potential biomarker and target, in tumorigenesis, proliferation, metastasis and treatment resistance for cancer therapy. However, DDX5 has also been reported to act as an oncosuppressor. These seemingly contradictory observations can be reconciled by DDX5's role in DNA repair. This is because cancer cell apoptosis and malignant transformation can represent the two possible outcomes of a single process regulated by DDX5, reflecting different intensity of DNA damage. Thus, targeting DDX5 could potentially shift cancer cells from a growth-arrested state (necessary for DNA repair) to apoptosis and cell killing. In addition to the increasingly recognized role of DDX5 in global genome stability surveillance and DNA damage repair, DDX5 has been implicated in multiple oncogenic signaling pathways. DDX5 appears to utilize distinct signaling cascades via interactions with unique proteins in different types of tissues/cells to elicit opposing roles (e.g., smooth muscle cells versus cancer cells). Such unique features make DDX5 an intriguing therapeutic target for the treatment of human cancers, with limited low toxicity to normal tissues. In this review, we discuss the multifaceted functions of DDX5 in DNA repair in cancer, immune suppression, oncogenic metabolic rewiring, virus infection promotion, and negative impact on the human microbiome (microbiota). We also provide new data showing that FL118, a molecular glue DDX5 degrader, selectively works against current treatment-resistant prostate cancer organoids/cells. Altogether, current studies demonstrate that DDX5 may represent a unique oncotarget for effectively conquering cancer with minimal toxicity to normal tissues.

The role of amphiregulin in ovarian function and disease

Amphiregulin (AREG) is an epidermal growth factor (EGF)-like growth factor that binds exclusively to the EGF receptor (EGFR). Treatment with luteinizing hormone (LH) and/or human chorionic gonadotropin dramatically induces the expression of AREG in the granulosa cells of the preovulatory follicle. In addition, AREG is the most abundant EGFR ligand in human follicular fluid. Therefore, AREG is considered a predominant propagator that mediates LH surge-regulated ovarian functions in an autocrine and/or paracrine manner. In addition to the well-characterized stimulatory effect of LH on AREG expression, recent studies discovered that several local factors and epigenetic modifications participate in the regulation of ovarian AREG expression. Moreover, aberrant expression of AREG has recently been reported to contribute to the pathogenesis of several ovarian diseases, such as ovarian hyperstimulation syndrome, polycystic ovary syndrome, and epithelial ovarian cancer. Furthermore, increasing evidence has elucidated new applications of AREG in assisted reproductive technology. Collectively, these studies highlight the importance of AREG in female reproductive health and disease. Understanding the normal and pathological roles of AREG and elucidating the molecular and cellular mechanisms of AREG regulation of ovarian functions will inform innovative approaches for fertility regulation and the prevention and treatment of ovarian diseases. Therefore, this review summarizes the functional roles of AREG in ovarian function and disease.

Transcriptomic and Functional Evidence That miRNA193a-3p Inhibits Lymphatic Endothelial Cell (LEC) and LEC + MCF-7 Spheroid Growth Directly and by Altering MCF-7 Secretome

MicroRNA 193a-3p (miR193a-3p) is a short non-coding RNA with tumor suppressor properties. Breast cancer (BC) progression is governed by active interaction between breast cancer cells, vascular (V)/lymphatic (L) endothelial cells (ECs), and BC secretome. We have recently shown that miR193a-3p, a tumor suppressor miRNA, inhibits MCF-7 BC cell-driven growth of VECs via direct antimitogenic actions and alters MCF-7 secretome. Since LEC-BC cross-talk plays a key role in BC progression, we investigated the effects of miR193a-3p on MCF-7 secretome and estradiol-mediated growth effects in LECs and LEC + MCF-7 spheroids, and delineated the underlying mechanisms. Transfection of LECs with miR193a-3p, as well as secretome from MCF-7 transfected cells, inhibited LEC growth, and these effects were mimicked in LEC + MCF-7 spheroids. Moreover, miR193a-3p inhibited ERK1/2 and Akt phosphorylation in LECs and LEC + MCF-7 spheroids, which are importantly involved in promoting cancer development and metastasis. Treatment of LECs and LEC + MCF-7 spheroids with estradiol (E2)-induced growth, as well as ERK1/2 and Akt phosphorylation, and was abrogated by miR193a-3p and secretome from MCF-7 transfected cells. Gene expression analysis (GEA) in LEC + MCF-7 spheroids transfected with miR193a-3p showed significant upregulation of 54 genes and downregulation of 73 genes. Pathway enrichment analysis of regulated genes showed significant modulation of several pathways, including interferon, interleukin/cytokine-mediated signaling, innate immune system, ERK1/2 cascade, apoptosis, and estrogen receptor signaling. Transcriptomic analysis showed downregulation in interferon and anti-apoptotic and pro-growth molecules, such as IFI6, IFIT1, OSA1/2, IFITM1, HLA-A/B, PSMB8/9, and PARP9, which are known to regulate BC progression. The cytokine proteome array of miR193a-3p transfected MCF secretome and confirmed the upregulation of several growth inhibitory cytokines, including IFNγ, Il-1a, IL-1ra, IL-32, IL-33, IL-24, IL-27, cystatin, C-reactive protein, Fas ligand, MIG, and sTIM3. Moreover, miR193a-3p alters factors in MCF-7 secretome, which represses ERK1/2 and Akt phosphorylation, induces pro-apoptotic protein and apoptosis in LECs, and downregulates interferon-associated proteins known to promote cancer growth and metastasis. In conclusion, miR193a-3p can potentially modify the tumor microenvironment by altering pro-growth BC secretome and inhibiting LEC growth, and may represent a therapeutic molecule to target breast tumors/cancer.

Recent findings on the role of microRNAs in genetic kidney diseases

BACKGROUND

MicroRNAs (miRNAs) are non-coding, endogenous, single-stranded, small (21-25 nucleotides) RNAs. Various target genes at the post-transcriptional stage are modulated by miRNAs that are involved in the regulation of a variety of biological processes such as embryonic development, differentiation, proliferation, apoptosis, inflammation, and metabolic homeostasis. Abnormal miRNA expression is strongly associated with the pathogenesis of multiple common human diseases including cardiovascular diseases, cancer, hepatitis, and metabolic diseases.

METHODS AND RESULTS

Various signaling pathways including transforming growth factor-β, apoptosis, and Wnt signaling pathways have also been characterized to play an essential role in kidney diseases. Most importantly, miRNA-targeted pharmaceutical manipulation has represented a promising new therapeutic approach against kidney diseases. Furthermore, miRNAs such as miR-30e-5p, miR-98-5p, miR-30d-5p, miR-30a-5p, miR-194-5p, and miR-192-5p may be potentially employed as biomarkers for various human kidney diseases.

CONCLUSIONS

A significant correlation has also been found between some miRNAs and the clinical markers of renal function like baseline estimated glomerular filtration rate (eGFR). Classification of miRNAs in different genetic renal disorders may promote discoveries in developing innovative therapeutic interventions and treatment tools. Herein, the recent advances in miRNAs associated with renal pathogenesis, emphasizing genetic kidney diseases and development, have been summarized.

PAK5 promotes RNA helicase DDX5 sumoylation and miRNA-10b processing in a kinase-dependent manner in breast cancer

P21-activated kinase 5 (PAK5) plays an important role in tumors. However, the functional role of PAK5 in mammary tumorigenesis in vivo remains unclear. Here, we show that PAK5 deficiency represses MMTV-PyVT-driven breast tumorigenesis. DEAD-box RNA helicase 5 (DDX5) is a substrate of PAK5, which is phosphorylated on threonine 69. PAK5-mediated DDX5 phosphorylation promotes breast cancer cell proliferation and metastasis. The increased expression levels of PAK5 and phospho-DDX5 threonine 69 are associated with metastasis and poor clinical outcomes of patients. PAK5 facilitates the phosphorylation-dependent sumoylation of DDX5 to stabilize DDX5. Both the phosphorylation and sumoylation of DDX5 enhance the formation of a DDX5/Drosha/DGCR8 complex, thus promoting microRNA-10b processing. Finally, we verify decreased expression of DDX5 phosphorylation and sumoylation and mature miR-10b in PAK5-/-/MMTV-PyVT transgenic mice. Our findings provide insights into the function of PAK5 in microRNA (miRNA) biogenesis, which might be a potential therapeutic target for breast cancer.

Mitochondrial glutamine metabolism regulates sensitivity of cancer cells after chemotherapy via amphiregulin

The DNA damage response is essential for sustaining genomic stability and preventing tumorigenesis. However, the fundamental question about the cellular metabolic response to DNA damage remains largely unknown, impeding the development of metabolic interventions that might prevent or treat cancer. Recently, it has been reported that there is a link between cell metabolism and DNA damage response, by repression of glutamine (Gln) entry into mitochondria to support cell cycle arrest and DNA repair. Here, we show that mitochondrial Gln metabolism is a crucial regulator of DNA damage-induced cell death. Mechanistically, inhibition of glutaminase (GLS), the first enzyme for Gln anaplerosis, sensitizes cancer cells to DNA damage by inducing amphiregulin (AREG) that promotes apoptotic cell death. GLS inhibition increases reactive oxygen species production, leading to transcriptional activation of AREG through Max-like protein X (MLX) transcription factor. Moreover, suppression of mitochondrial Gln metabolism results in markedly increased cell death after chemotherapy in vitro and in vivo. The essentiality of this molecular pathway in DNA damage-induced cell death may provide novel metabolic interventions for cancer therapy.

Amphiregulin in cellular physiology, health, and disease: Potential use as a biomarker and therapeutic target

Amphiregulin (AREG), which acts as one of the ligands for epidermal receptor growth factor receptor (EGFR), plays a crucial role in tissue repair, inflammation, and immunity. AREG is synthesized as membrane-anchored pre-protein, and is excreted after proteolytic cleavage, and serves as an autocrine or paracrine factor. After engagement with the EGFR, AREG triggers a cascade of signaling events required for many cellular physiological processes including metabolism, cell cycle, and proliferation. Under different inflammatory and pathogenic conditions, AREG is expressed by various activated immune cells that orchestrate both tolerance and host resistance mechanisms. Several factors including xenobiotics, cytokines, and inflammatory lipids have been shown to trigger AREG gene expression and release. In this review, we discuss the structure, function, and regulation of AREG, its role in tissue repair, inflammation, and homeostasis as well as the potential of AREG as a biomarker and therapeutic target.

Gene expression changes with tumor disease and leech parasitism in the juvenile green sea turtle skin transcriptome

Emerging infectious diseases are a major threat to biodiversity in the 21st century. Fibropapillomatosis (FP) is an epithelial tumor disease that affects immature and adult marine turtles worldwide, particularly green turtles (Chelonia mydas). We know little about the host factors contributing to FP susceptibility, in part because transcriptomic studies that compare transcript expression in turtles with and without FP are lacking. Here, we performed RNA-Seq on healthy skin tissue from immature C. mydas in the Indian River Lagoon, Florida, USA, comparing turtles (1) with and without FP and (2) with and without leech parasites, a putative vector of FP. We assembled a de novo C. mydas skin transcriptome to identify transcripts with significant differential expression (DE) across FP and leech categories. Significant DE transcripts were found across FP and leech comparisons, including 10 of the same transcripts with DE across both comparisons. Leech-positive individuals significantly upregulated different immune and viral interaction transcripts than did leech-negative individuals, including viral interaction transcripts associated with herpesvirus interactions. This finding strengthens the role of marine leeches as mechanical vectors of Chelonid herpesvirus 5 (ChHV5) which has been implicated as a causative agent of FP. FP-positive turtles upregulated several tumor progression and suppression transcripts relative to FP-negative turtles, which had no significant DE tumor progression transcripts. FP-positive turtles also upregulated significantly more protein interaction transcripts than FP-negative turtles. DE transcripts across leech comparisons showed no functional enrichment, whereas DE transcripts across FP comparisons showed some GO terms were enriched in FP-positive and FP negative turtles. Notably, only FP-negative turtles were enriched for GO terms involved in acquired and inflammatory immune gene regulation. Overall, our DE transcripts included several candidate genes that may play important roles in C. mydas resistance to or recovery from FP, highlighting that transcriptomics provides a promising venue to understand this impactful disease. Continued investigation of C. mydas responses to FP and leech affliction is imperative for species persistence and the conservation of marine ecosystems worldwide due to the essential role of sea turtles in ecosystem function and stability.

Targeting autocrine amphiregulin robustly and reproducibly inhibits ovarian cancer in a syngeneic model: roles for wildtype p53

Ovarian cancer (OvCA) remains one of the most devastating malignancies, but treatment options are still limited. We report that amphiregulin (AREG) can serve as an effective and safe pharmacological target in a syngeneic murine model. AREG is highly abundant in abdominal fluids of patients with advanced OvCa. In immunocompetent animals, depletion or overexpression of AREG respectively prolonged or shortened animal survival. A new antibody we generated in AREG-knockout mice recognized murine AREG and reproducibly prolonged animal survival in the syngeneic model. The underlying mechanism likely involves binding of wildtype p53 to AREG's promoter and autocrine activation of the epidermal growth factor receptor (EGFR), a step blocked by the antibody. Accordingly, depletion of p53 downregulated AREG secretion and conferred tolerance, whereas blocking an adaptive process involving CXCL1, which transactivates EGFR, might increase therapeutic efficacy. Consistent with these observations, analysis of OvCa patients revealed that high AREG correlates with poor prognosis of patients expressing wildtype TP53. In conclusion, clinical tests of the novel antibody are warranted; high AREG, normal TP53, and reduced CXCL1 activity might identify patients with OvCa who may derive therapeutic benefit.

RNA helicase p68 inhibits the transcription and post-transcription of Pkd1 in ADPKD

Background: Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations of the PKD1 and PKD2 genes. Dysregulation of the expression of PKD genes, the abnormal activation of PKD associated signaling pathways, and the expression and maturation of miRNAs regulates cyst progression. However, the upstream factors regulating these abnormal processes in ADPKD remain elusive.

Methods: To investigate the roles of an RNA helicase, p68, in ADPKD, we performed Western blot and qRT-PCR analysis, immunostaining and ChIP assay in cystic renal epithelium cells and tissues.

Results: We found that p68 was upregulated in cystic renal epithelial cells and tissues. p68 represses Pkd1 gene expression via transcriptional and posttranscriptional mechanisms in renal epithelial cells, in that 1) p68 binds to the promoter of the Pkd1 gene together with p53 to repress transcription; and 2) p68 promotes the expression and maturation of miR-17, miR-200c and miR-182 and via these miRNAs, post-transcriptionally regulates the expression of Pkd1 mRNA. Drosha is involved in this process by forming a complex with p68. p68 also regulates the phosphorylation and activation of PKD proliferation associated signaling and the expression of fibrotic markers in Pkd1 mutant renal epithelial cells. Silence of p68 delays cyst formation in collecting duct cell mediated 3D cultures. In addition, the expression of p68 is induced by H₂O₂-dependent oxidative stress and DNA damage which causes downregulation of Pkd1 transcription in cystic renal epithelial cells and tissues.

Conclusions: p68 plays a critical role in negatively regulating the expression of the PKD1 gene along with positively regulating the expression and maturation of miRNAs and activation of PKD associated signaling pathways to cause renal cyst progression and fibrosis in ADPKD.

The roles of RNA in DNA double-strand break repair

Effective DNA repair is essential for cell survival: a failure to correctly repair damage leads to the accumulation of mutations and is the driving force for carcinogenesis. Multiple pathways have evolved to protect against both intrinsic and extrinsic genotoxic events, and recent developments have highlighted an unforeseen critical role for RNA in ensuring genome stability. It is currently unclear exactly how RNA molecules participate in the repair pathways, although many models have been proposed and it is possible that RNA acts in diverse ways to facilitate DNA repair. A number of well-documented DNA repair factors have been described to have RNA-binding capacities and, moreover, screens investigating DNA-damage repair mechanisms have identified RNA-binding proteins as a major group of novel factors involved in DNA repair. In this review, we integrate some of these datasets to identify commonalities that might highlight novel and interesting factors for future investigations. This emerging role for RNA opens up a new dimension in the field of DNA repair; we discuss its impact on our current understanding of DNA repair processes and consider how it might influence cancer progression.

Wnt3a promotes pro-angiogenic features in macrophages in vitro: Implications for stroke pathology

Wnt3a is implicated in several key cellular processes and its expression has been reported in different cell types. Here, we report a novel function for Wnt3a in macrophages, whose exposure to this ligand shifts them towards a pro-angiogenic phenotype capable, under oxygen and glucose deprivation, of inducing in vitro tubular pattern structures in endothelial cells resembling capillary-like vasculature. These newly acquired angiogenetic features also include increased proliferation and migration and surprisingly, an increase in cell death. This work provides a new link between Wnt3a and macrophage-mediated angiogenesis under glucose and oxygen deprivation in vitro, which are worth further investigation in pathological conditions including stroke, where the stimulation of the angiogenic process might help to recovery after tissue injury Impact statement This work provides a new link between Wnt3a and macrophage-mediated angiogenesis under glucose and oxygen deprivation in vitro. Our results reveal how Wnt3a shifts macrophages towards a pro-angiogenic phenotype, which is able-in absence of both glucose and oxygen-of inducing angiogenesis in vitro, thus pointing to a synergy between the activation of the pathway and the hypoxia scenario. This work also demonstrates that modulation of cell death is key in order to explain the observed angiogenic effects. We consider all these findings of significant importance, since no connection between Wnt3a, macrophages, and angiogenesis has been established so far. Furthermore, we do believe that this work provides new and interesting results, with Wnt signaling pathway emerging as an interesting target mediating beneficial outcomes during the inflammatory response undoubtedly linked to stroke pathology, where angiogenesis has been already proposed as a potential mechanism to promote recovery after the injury.

miRNA-34c-5p inhibits amphiregulin-induced ovarian cancer stemness and drug resistance via downregulation of the AREG-EGFR-ERK pathway

Epithelial ovarian cancer is the most lethal gynecological cancer mainly due to late diagnosis, easy spreading and rapid development of chemoresistance. Cancer stem cells are considered to be one of the main mechanisms for chemoresistance, as well as metastasis and recurrent disease. To explore the stemness characteristics of ovarian cancer stem cells, we successfully enriched ovarian cancer stem-like cells from an established ovarian cancer cell line (SKOV-I6) and a fresh ovarian tumor-derived cell line (OVS1). These ovarian cancer stem-like cells possess important cancer stemness characteristics including sphere-forming and self-renewing abilities, expressing important ovarian cancer stem cell and epithelial–mesenchymal transition markers, as well as increased drug resistance and potent tumorigenicity. Microarray analysis of OVS1-derived sphere cells revealed increased expression of amphiregulin (AREG) and decreased expression of its conserved regulatory microRNA, miR-34c-5p, when compared with the OVS1 parental cells. Overexpression of AREG and decreased miR-34c-5p expression in SKOV-I6 and OVS1 sphere cells were confirmed by quantitative real-time PCR analysis. Luciferase reporter assay and mutant analysis confirmed that AREG is a direct target of miR-34c-5p. Furthermore, AREG-mediated increase of sphere formation, drug resistance toward docetaxel and carboplatin, as well as tumorigenicity of SKOV-I6 and OVS1 cells could be abrogated by miR-34c-5p. We further demonstrated that miR-34c-5p inhibited ovarian cancer stemness through downregulation of the AREG-EGFR-ERK pathway. Overexpression of AREG was found to be correlated with advanced ovarian cancer stages and poor prognosis. Taken together, our data suggest that AREG promotes ovarian cancer stemness and drug resistance via the AREG-EGFR-ERK pathway and this is inhibited by miR-34c-5p. Targeting AREG, miR-34c-5p could be a potential strategy for anti-cancer-stem cell therapy in ovarian cancer.

Amphiregulin impairs apoptosis-stimulating protein 2 of p53 overexpression-induced apoptosis in hepatoma cells

Overexpression of apoptosis-stimulating protein 2 of p53 (ASPP2) induces apoptotic cell death in hepatoma cells (e.g. HepG2 cells) by enhancing the transactivation activity of p53, but long-term ASPP2 overexpression fails to induce more apoptosis since activation of the epidermal growth factor/epidermal growth factor receptor/SOS1 pathway impairs the pro-apoptotic role of ASPP2. In this study, in recombinant adenovirus-ASPP2-infected HepG2 cells, ASPP2 overexpression induces amphiregulin expression in a p53-dependent manner. Although amphiregulin initially contributes to ASPP2-induced apoptosis, it eventually impairs the pro-apoptotic function of ASPP2 by activating the epidermal growth factor/epidermal growth factor receptor/SOS1 pathway, leading to apoptosis resistance. Moreover, blocking soluble amphiregulin with a neutralizing antibody also significantly increased apoptotic cell death of HepG2 cells due to treatment with methyl methanesulfonate, cisplatin, or a recombinant p53 adenovirus, suggesting that the function of amphiregulin involved in inhibiting apoptosis may be a common mechanism by which hepatoma cells escape from stimulus-induced apoptosis. Thus, our data elucidate an apoptosis-evasion mechanism in hepatocellular carcinoma and have potential implications for hepatocellular carcinoma therapy.

Impairment of DYRK2 augments stem-like traits by promoting KLF4 expression in breast cancer

Whereas accumulating studies have supported the cancer stem cell theory, a specific therapy targeting a cancer stem cell subpopulation has not been established. Here, we show that dual-specificity tyrosine phosphorylation-kinase 2 (DYRK2) is a novel negative regulator for formation of breast cancer stem cells. Downregulation of DYRK2 promotes cancer stem-like traits in vitro, tumourigenesis in vivo and the proportion of the cancer stem cell population in human breast cancer tissues. We found that Krupple-like factor 4 (KLF4) serves as a key mediator of DYRK2's control over the cancer stem phenotype. Reduced DYRK2 expression increases KLF4 expression, which induces cancer stem-like properties. We identified androgen receptor (AR) as a transcription factor binding to the KLF4 promoter region; this process is dependent on DYRK2 kinase activity. Our findings delineate a mechanism of cancer stem cell regulation by the DYRK2-AR-KLF4 axis in breast cancer. Targeting of this pathway may be a promising strategy against breast cancer stem cells.

Interaction between RNF8 and DYRK2 is required for the recruitment of DNA repair molecules to DNA double-strand breaks

The genome of eukaryotic cells is frequently exposed to damage by various genotoxins. Phosphorylation of histone H2AX at Serine 139 (γ-H2AX) is a hallmark of DNA damage. RNF8 monoubiquitinates γ-H2AX with the Lys63-linked ubiquitin chain to tether DNA repair molecules at DNA lesions. A high-throughput screening identified RNF8 as a binding partner of dual-specificity tyrosine phosphorylation-regulated kinase 2 (DYRK2). Notably, DNA damage-induced monoubiquitination of γ-H2AX is impaired in DYRK2-depleted cells. The foci formation of p53-binding protein 1 at DNA double-strand break sites is suppressed in DYRK2 knockdown cells, which fail to repair the DNA damage. A homologous recombination assay showed decreased repair efficiency in DYRK2-depleted cells. Our findings indicate direct interaction of DYRK2 with RNF8 in regulating response to DNA damage.

Transcriptomic Analysis Implicates the p53 Signaling Pathway in the Establishment of HIV-1 Latency in Central Memory CD4 T Cells in an In Vitro Model

The search for an HIV-1 cure has been greatly hindered by the presence of a viral reservoir that persists despite antiretroviral therapy (ART). Studies of HIV-1 latency in vivo are also complicated by the low proportion of latently infected cells in HIV-1 infected individuals. A number of models of HIV-1 latency have been developed to examine the signaling pathways and viral determinants of latency and reactivation. A primary cell model of HIV-1 latency, which incorporates the generation of primary central memory CD4 T cells (TCM), full-length virus infection (HIVNL4-3) and ART to suppress virus replication, was used to investigate the establishment of HIV latency using RNA-Seq. Initially, an investigation of host and viral gene expression in the resting and activated states of this model indicated that the resting condition was reflective of a latent state. Then, a comparison of the host transcriptome between the uninfected and latently infected conditions of this model identified 826 differentially expressed genes, many of which were related to p53 signaling. Inhibition of the transcriptional activity of p53 by pifithrin-α during HIV-1 infection reduced the ability of HIV-1 to be reactivated from its latent state by an unknown mechanism. In conclusion, this model may be used to screen latency reversing agents utilized in shock and kill approaches to cure HIV, to search for cellular markers of latency, and to understand the mechanisms by which HIV-1 establishes latency.

Morphine Attenuated the Cytotoxicity Induced by Arsenic Trioxide in H9c2 Cardiomyocytes

Arsenic trioxide (ATO) is an efficient drug for the treatment of the patients with acute promyelocytic leukemia (APL). Inhibition of proliferation as well as apoptosis, attenuation of migration, and induction of differentiation in tumor cells are the main mechanisms through which ATO acts against APL. Despite advantages of ATO in treatment of some malignancies, certain harmful side effects, such as cardiotoxicity, have been reported. It has been well documented that morphine has antioxidant, anti-apoptotic, and cytoprotective properties and is able to attenuate cytotoxicity. Therefore, in this study, we aimed to investigate the protective effects of morphine against ATO toxicity in H9c2 myocytes using multi-parametric assay including thiazolyl blue tetrazolium bromide (MTT) assay, reactive oxygen species (ROS) generation, caspase 3 activity, nuclear factor kappa B (NF-κB) phosphorylation assay, and expression of apoptotic markers. Our results showed that morphine (1 μM) attenuated cytotoxicity induced by ATO in H9c2 cells. Results of this study suggest that morphine may have protective properties in management of cardiac toxicity in patients who receive ATO as an anti-cancer treatment.

The DNA damage-induced cell death response: a roadmap to kill cancer cells

Upon massive DNA damage cells fail to undergo productive DNA repair and trigger the cell death response. Resistance to cell death is linked to cellular transformation and carcinogenesis as well as radio- and chemoresistance, making the underlying signaling pathways a promising target for therapeutic intervention. Diverse DNA damage-induced cell death pathways are operative in mammalian cells and finally culminate in the induction of programmed cell death via activation of apoptosis or necroptosis. These signaling routes affect nuclear, mitochondria- and plasma membrane-associated key molecules to activate the apoptotic or necroptotic response. In this review, we highlight the main signaling pathways, molecular players and mechanisms guiding the DNA damage-induced cell death response.

Nuclear EGFR impairs ASPP2-p53 complex-induced apoptosis by inducing SOS1 expression in hepatocellular carcinoma

ASPP2 can bind to p53 and enhance the apoptotic capabilities of p53 by guiding it to the promoters of pro-apoptotic genes. Here, ASPP2 overexpression for 24 hours transiently induced apoptosis in hepatoma cells by enhancing the transactivation of p53 on pro-apoptotic gene promoters. However, long-term ASPP2 overexpression (more than 48 hours) failed to induce apoptosis because p53 was released from the pro-apoptotic gene promoters. In non-apoptotic cells, nuclear EGFR induced SOS1 expression by directly binding to the SOS1 promoter. SOS1 activated the HRAS/PI3K/AKT pathway and resulted in nuclear translocation of p-AKT and Bcl-2. The interaction between p-AKT and ASPP2 facilitates Bcl-2 binding to p53, which releases p53 from the pro-apoptotic gene promoters. The in vivo assay demonstrated that EGFR/SOS1-promoted growth of nuclear p-AKT⁺, Bcl-2⁺ cells results in the resistance of hepatoma cells to ASPP2-p53 complex-induced apoptosis and that blocking nuclear translocation of EGFR dramatically improves and enhances the pro-apoptotic function of ASPP2. Finally, the activation of the HRAS/PI3K/AKT pathway by EGFR-induced SOS1 also inhibits cisplatin-induced apoptosis, suggesting a common apoptosis-evasion mechanism in hepatoma cells. Because evasion of apoptosis contributes to treatment resistance in hepatoma, our results also support further investigation of combined therapeutic blockade of EGFR and SOS1.

Current View of microRNA Processing

Small evolutionarily conserved noncoding RNAs, microRNAs (miRNAs), regulate gene expression either by translational repression or by mRNA degradation in mammals. miRNAs play functional roles in diverse physiological and pathological processes. miRNA processing is accurately regulated through multifarious factors. The canonical miRNA processing pathway consists of four sequential steps: (a) miRNA gene is transcribed into primary miRNA (pri-miRNA) mainly by RNA polymerase II; (b) pri-miRNA is processed into precursor miRNA (pre-miRNA) through microprocessor complex; (c) pre-miRNA is exported from the nucleus to the cytoplasm with the assistance of Exportin 5 (EXP5/XP05) protein; and (d) pre-miRNA is further processed into mature miRNA via Dicer. Emerging evidence has also demonstrated that some miRNAs undergo alternative processing pathways. Dysregulation of miRNA processing is closely related to tumorigenesis. Here, we review the current advances in the knowledge of miRNA processing and briefly discuss its impact on human cancers.

Cell death decision by p53 via control of the mitochondrial membrane

The tumor suppressor p53 is mutated in more than half of human cancers. Recent evidence has revealed that p53 not only regulates apoptosis but also regulates necrotic/necroptotic cell death via the mitochondria. The regulation of apoptosis by p53 is tightly connected to the mitochondrial outer membrane permeabilization and the induction of and interaction with Bcl-2 family members. Interestingly, p53-mediated regulation of necrosis/necroptosis is correlated with mitochondrial permeabilization pore opening via interactions with CypD and Drp1. This review discusses the p53-regulating molecules that induce apoptosis or necrosis/necroptosis via the mitochondria.

RGS16, a novel p53 and pRb cross-talk candidate inhibits migration and invasion of pancreatic cancer cells

Data collected since the discovery of p53 and pRb/RB1 suggests these tumor suppressors cooperate to inhibit tumor progression. Patients who have mutations in both p53 and RB1 genes have increased tumor reoccurrence and decreased survival compared to patients with only one tumor suppressor gene inactivated. It remains unclear how p53 and pRb cooperate toward inhibiting tumorigenesis. Using RNA expression profiling we identified 179 p53 and pRb cross-talk candidates in normal lung fibroblasts (WI38) cells exogenously coexpressing p53 and pRb. Regulator of G protein signaling 16 (RGS16) was among the p53 and pRb cross-talk candidates and has been implicated in inhibiting activation of several oncogenic pathways associated with proliferation, migration, and invasion of cancer cells. RGS16 has been found to be downregulated in pancreatic cancer patients with metastases compared to patients without metastasis. Expression of RGS16 mRNA was decreased in the pancreatic cancer cell lines tested compared to control. Expression of RGS16 inhibited migration of the BxPC-3 and AsPC-1 but not PANC-1 cells and inhibited invasion of BxPC-3 and AsPC-1 cells with no impact on cell viability. We have identified for the first time p53 and pRb cross-talk candidates and a role for RGS16 to inhibit pancreatic cancer migration and invasion.

Engagement of DYRK2 in proper control for cell division

Dysregulation of cell cycle machinery causes abnormal cell division, leading to cancer development. To drive cell cycle properly, expression levels of cell cycle regulators are tightly regulated through the cell cycle. Dual specificity tyrosine phosphorylation-regulated kinase 2 (DYRK2) is a Ser/Thr kinase, and its intracellular functions had not been elucidated for decades. Recent studies have shown that DYRK2 down-regulates key molecules on cell cycle control. This review mainly highlights the DYRK2 function during cell division. In addition, we summarize tumor suppressive role of DYRK2 in cancer cells and discuss future research directions for DYRK2 toward the novel cancer therapies.

PARP-1 inhibitor sensitizes arsenic trioxide in hepatocellular carcinoma cells via abrogation of G2/M checkpoint and suppression of DNA damage repair

Arsenic trioxide (ATO) is successfully used to treat hematological malignancies. However, the clinical application of the agent in solid tumors is largely limited by its dose-dependent toxicity which results from the high intrinsic resistance of the cancer cells. In this study, we firstly identified a series of sensitization effects of 4AN, a PARP-1 inhibitor, on human hepatocellular carcinoma cell line HepG2 to ATO treatment. We showed that treatment of HepG2 cells with 4AN promoted ATO-induced cell death in a synergistic manner. The ATO-sensitization by 4AN was associated with its effect on abrogation of ATO-induced G2/M checkpoint which impairs DNA damage repair and promotes cell apoptosis. Further analysis demonstrated that the ATO-induced G2/M checkpoint was closely related to a decrease in cyclin B1, a key G2/M mediator; whereas 4AN up-regulated the expression of cyclin B1 in ATO-treated cells, which may be at least partly responsible for its effect on abrogation of ATO-induced G2/M checkpoint. This was further supported by the result showing that down-regulation of cyclin B1 using siRNA could restore the G2/M checkpoint in cells co-treated with ATO and 4AN, thereby improving DNA damage repair and decreasing apoptosis. Our study indicates that the abrogation of G2/M checkpoint and the suppression of DNA damage repair contribute to ATO-sensitization by PARP-1 inhibitor in HepG2 cells, which provides a novel insight into the chemo-sensitization mechanism of PARP-1 inhibitor.

miR-205 acts as a tumour radiosensitizer by targeting ZEB1 and Ubc13

Tumor cells associated with therapy resistance (radioresistance and drug resistance) are likely to give rise to local recurrence and distant metastatic relapse. Recent studies revealed microRNA (miRNA)-mediated regulation of metastasis and epithelial-mesenchymal transition; however, whether specific miRNAs regulate tumor radioresistance and can be exploited as radiosensitizing agents remains unclear. Here we find that miR-205 promotes radiosensitivity and is downregulated in radioresistant subpopulations of breast cancer cells, and that loss of miR-205 is highly associated with poor distant relapse-free survival in breast cancer patients. Notably, therapeutic delivery of miR-205 mimics via nanoliposomes can sensitize the tumor to radiation in a xenograft model. Mechanistically, radiation suppresses miR-205 expression through ataxia telangiectasia mutated (ATM) and zinc finger E-box binding homeobox 1 (ZEB1). Moreover, miR-205 inhibits DNA damage repair by targeting ZEB1 and the ubiquitin-conjugating enzyme Ubc13. These findings identify miR-205 as a radiosensitizing miRNA and reveal a new therapeutic strategy for radioresistant tumors.

Amphiregulin

Amphiregulin (AREG) is a ligand of the epidermal growth factor receptor (EGFR), a widely expressed transmembrane tyrosine kinase. AREG is synthesized as a membrane-anchored precursor protein that can engage in juxtacrine signaling on adjacent cells. Alternatively, after proteolytic processing by cell membrane proteases, mainly TACE/ADAM17, AREG is secreted and behaves as an autocrine or paracrine factor. AREG gene expression and release is induced by a plethora of stimuli including inflammatory lipids, cytokines, hormones, growth factors and xenobiotics. Through EGFR binding AREG activates major intracellular signaling cascades governing cell survival, proliferation and motility. Physiologically, AREG plays an important role in the development and maturation of mammary glands, bone tissue and oocytes. Chronic elevation of AREG expression is increasingly associated with different pathological conditions, mostly of inflammatory and/or neoplastic nature. Here we review the essential aspects of AREG structure, function and regulation, discuss the basis for its differential role within the EGFR family of ligands, and identify emerging aspects in AREG research with translational potential.