Hiwi facilitates chemoresistance as a cancer stem cell marker in cervical cancer

The potential emerging role of piRNA/PIWI complex in virus infection

P-element-induced wimpy testis-interacting RNAs (piRNAs), a class of small noncoding RNAs with about 24-32 nucleotides, often interact with PIWI proteins to form a piRNA/PIWI complex that could influence spermiogenesis, transposon silencing, epigenetic regulation, etc. PIWI proteins have a highly conserved function in a variety of species and are usually expressed in germ cells. However, increasing evidence has revealed the important role of the piRNA/PIWI complex in the occurrence and prognosis of various human diseases and suggests its potential application in the diagnosis and treatment of related diseases, becoming a prominent marker for these human diseases. Recent studies have confirmed that piRNA/PIWI complexes or piRNAs are abnormally expressed in some viral infections, effecting disease progression and viral replication. In this study, we reviewed the association between the piRNA/PIWI complex and several human disease-associated viruses, including human papillomavirus, human immunodeficiency virus, human rhinovirus, severe acute respiratory syndrome coronavirus 2, respiratory syncytial virus, and herpes simplex virus type 1.

Critical appraisal of the piRNA-PIWI axis in cancer and cancer stem cells

Small noncoding RNAs play an important role in various disease states, including cancer. PIWI proteins, a subfamily of Argonaute proteins, and PIWI-interacting RNAs (piRNAs) were originally described as germline-specific molecules that inhibit the deleterious activity of transposable elements. However, several studies have suggested a role for the piRNA-PIWI axis in somatic cells, including somatic stem cells. Dysregulated expression of piRNAs and PIWI proteins in human tumors implies that, analogously to their roles in undifferentiated cells under physiological conditions, these molecules may be important for cancer stem cells and thus contribute to cancer progression. We provide an overview of piRNA biogenesis and critically review the evidence for the role of piRNA-PIWI axis in cancer stem cells. In addition, we examine the potential of piRNAs and PIWI proteins to become biomarkers in cancer.

Novel Perspectives for the Diagnosis and Treatment of Gynecological Cancers using Dysregulation of PIWI Protein and PiRNAs as Biomarkers

The term "gynecological cancer" is used for a group of cancers occurring in the female reproductive system. Some of these cancers are ranked as the leading causes of death in developed and developing countries. The lack of proper diagnostic strategies is one of the most important reasons that make them lethal. PIWI-interacting RNAs or piRNAs are a class of small non-coding RNAs, which contain 24-32 nucleotides. These RNAs take part in some cellular mechanisms, and their role in diverse kinds of cancer is confirmed by accumulative evidence. In this review, we gather some information on the roles of these RNAs and members of the PIWI protein family to provide new insight into accurate diagnostic biomarkers and more effective anti-cancer drugs with fewer side effects.

HPV16 E6/E7-mediated regulation of PiwiL1 expression induces tumorigenesis in cervical cancer cells

PURPOSE

PiwiL1 has been reported to be over-expressed in many cancers. However, the molecular mechanism by which these proteins contribute to tumorigenesis and their regulation in cancer cells is still unclear. We intend to understand the role of PiwiL1 in tumorigenesis and also its regulation in cervical cells.

METHODS

We studied the effect of loss of PiwiL1 function on tumor properties of cervical cancer cells in vitro and in vivo. Also we have looked into the effect of PiwiL1 overexpression in the malignant transformation of normal cells both in vitro and in vivo. Further RNA-seq and RIP-seq analyses were done to get insight of the direct and indirect targets of PiwiL1 in the cervical cancer cells.

RESULTS

Here, we report that PiwiL1 is not only over-expressed, but also play a major role in tumor induction and progression. Abolition of PiwiL1 in CaSki cells led to a decrease in the tumor-associated properties, whereas, its upregulation conferred malignant transformation of normal HaCaT cells. Our study delineates a new link between HPV oncogenes, E6 and E7 with PiwiL1. p53 and E2F1 directly bind and differentially regulate PiwiL1 promoter in a context-dependant manner. Further, RNA-seq together with RIP-RNA-seq suggested a strong and direct role for PiwiL1 in promoting metastasis in cervical cancer cells.

CONCLUSION

Our study demonstrates that PiwiL1 act as an oncogene in cervical cancer by inducing tumor-associated properties and EMT pathway. The finding that HPV oncogenes, E6/E7 can positively regulate PiwiL1 suggests a possible mechanism behind HPV-mediated tumorigenesis in cervical cancer.

PIWIL1 gene polymorphism and pediatric acute lymphoblastic leukemia relapse susceptibility among Chinese children: a five-center case-control study

Objective

PIWIL1 polymorphisms' role in pediatric acute lymphoblastic leukemia (ALL) relapse susceptibility remains undiscovered.

Methods

A case-control designed and multiple logistic regression model was performed to evaluate the overall risk of pediatric ALL and five single-nucleotide polymorphisms (SNPs) of PIWIL1 gene (rs35997018 C>T, rs1106042 A>G, rs7957349 C>G, rs10773771 C>T, and rs10848087 A>G) in 785 cases and 1,323 controls, which were genotyped by TaqMan assay. The odds ratio (OR) and its 95% confidence interval (CI) were used to estimate the relationship. Stratified analysis was used to investigate the correlation of rs1106042 and rs10773771 genotypes and pediatric ALL relapse susceptibility in terms of age, sex, number of white blood cells (WBC), immunophenotyping, gene fusion type, karyotype, primitive/naïve lymphocytes, and minimal residual disease (MRD) in bone marrow. Finally, the haplotype analysis was performed to appraise the relationship between inferred haplotypes of PIWIL1 and pediatric ALL risk.

Results

Among the five analyzed SNPs, rs1106042 A>G was related to increased ALL risk, and rs10773771 C>T was related to decreased ALL risk. Compared to the GG genotype, the rs1106042 GA/AA had a deleterious effect on children of age <120 months, who were female and male, had high or average number of WBC, pro-B ALL, pre-B ALL, T-ALL, low- and middle-risk ALL, E2A-PBX fusion gene, non-gene fusion, abnormal diploid, high hyperdiploid, hypodiploid, and normal diploid. Moreover, rs1106042 A>G harmfully affected primitive/naïve lymphocytes and MRD on days 15-19, day 33, and week 12. On the contrary, rs10773771 TC/CC exhibited a protective effect on ALL children with the TEL-AML fusion gene. Haplotype analysis demonstrated that haplotypes CAGT, TACC, TACT, and TAGT were significantly associated with increased pediatric ALL relapse susceptibility.

Conclusion

PIWIL1 rs1106042 A>G was related to increased ALL risk, and rs10773771 C>T was linked to decreased ALL risk in eastern Chinese children. Rs1106042 GA/AA may predict poor prognosis.

Role of noncoding RNAs with emphasis on long noncoding RNAs as cervical cancer biomarkers

Cervical cancer is a significant public health problem in developing countries, as most cases present at an advanced stage. This review aimed to analyze the role of noncoding RNAs as diagnostic and prognostic biomarkers in cervical cancers. Published studies on specific microRNA signatures in body fluids and cervical cancer tissues are highly heterogeneous, and there are no validated assays. The precision of the various immune-associated long noncoding (lncRNA) signatures should be assessed in clinical samples. Even though lncRNAs are tissue and cancer-specific, safe and appropriate methods for delivery to tumor tissues, toxicities and side effects are to be explored. Few studies have evaluated deregulated lncRNA expression levels with clinicopathological factors in a limited number of clinical samples. Prospective studies assessing the diagnostic and prognostic roles of circulating lncRNAs and P-Element-induced wimpy testis interacting PIWI RNAs (Piwil RNAs) in cervical cancer cases are essential. For the clinical application of lnc-RNA-based biomarkers, comprehensive research is needed as the impact of noncoding transcripts on molecular pathways is complex. The standardization and validation of deregulated ncRNAs in noninvasive samples of cervical cancer cases are needed.

Cervical cancer heterogeneity: a constant battle against viruses and drugs

Cervical cancer is the first identified human papillomavirus (HPV) associated cancer and the most promising malignancy to be eliminated. However, the ever-changing virus subtypes and acquired multiple drug resistance continue to induce failure of tumor prevention and treatment. The exploration of cervical cancer heterogeneity is the crucial way to achieve effective prevention and precise treatment. Tumor heterogeneity exists in various aspects including the immune clearance of viruses, tumorigenesis, neoplasm recurrence, metastasis and drug resistance. Tumor development and drug resistance are often driven by potential gene amplification and deletion, not only somatic genomic alterations, but also copy number amplifications, histone modification and DNA methylation. Genomic rearrangements may occur by selection effects from chemotherapy or radiotherapy which exhibits genetic intra-tumor heterogeneity in advanced cervical cancers. The combined application of cervical cancer therapeutic vaccine and immune checkpoint inhibitors has become an effective strategy to address the heterogeneity of treatment. In this review, we will integrate classic and recently updated epidemiological data on vaccination rates, screening rates, incidence and mortality of cervical cancer patients worldwide aiming to understand the current situation of disease prevention and control and identify the direction of urgent efforts. Additionally, we will focus on the tumor environment to summarize the conditions of immune clearance and gene integration after different HPV infections and to explore the genomic factors of tumor heterogeneity. Finally, we will make a thorough inquiry into completed and ongoing phase III clinical trials in cervical cancer and summarize molecular mechanisms of drug resistance among chemotherapy, radiotherapy, biotherapy, and immunotherapy.

Phytocompounds from the medicinal and dietary plants: Multi-target agents for cancer prevention and therapy

Cervical cancer is the fourth leading cause of cancer death among women worldwide. Due to cervical cancer's high incidence and mortality, there is an unmet demand for effective diagnostic, therapeutic, and preventive agents. At present, the preferred treatment strategies for advanced metastatic cervical cancer include surgery, radiotherapy, and chemotherapy. However, cervical cancer is gradually developing resistance to chemotherapy, thereby reducing its efficacy. Over the last several decades, phytochemicals, a general term for compounds produced from plants, have gained attention for their role in preventing cervical cancer. This role in cervical cancer prevention has garnered attention on the medicinal properties of fruits and vegetables. Phytochemicals are currently being evaluated for their ability to block proteins involved in carcinogenesis and chemoresistance against cervical cancer. Chemoresistance to cancer drugs like cisplatin, doxorubicin, and 5-fluorouracil has become a significant limitation of drug-based chemotherapy. However, the combination of cisplatin with other phytochemicals has been identified as a promising alternative to subjugate cisplatin resistance. Phytochemicals are promising chemo-preventive and chemotherapeutic agents as they possess antioxidant, anti-inflammatory, and anti-proliferative potential against many cancers, including cervical cancer. Furthermore, the ability of the phytochemicals to modulate cellular signaling pathways through up and down regulation of various proteins has been claimed for their therapeutic potential. Phytochemicals also display a wide range of biological functions, including cell cycle arrest, apoptosis induction, inhibition of invasion, and migration in cervical cancer cells. Numerous studies have revealed the critical role of different signaling proteins and their signaling pathways in the pathogenesis of cervical cancer. Here, we review the ability of several dietary phytochemicals to alter carcinogenesis by modulating various molecular targets.

PIWI-interacting RNA (piRNA): a narrative review of its biogenesis, function, and emerging role in lung cancer

Cancer remains elusive in many aspects, especially in its causes and control. After protein profiling, genetic screening, and mutation studies, scientists now have turned their attention to epigenetic modulation. This new arena has brought to light the world of noncoding RNA (ncRNA). Although very complicated and often confusing, ncRNA domains are now among the most attractive molecular markers for epigenetic control of cancer. Long ncRNA and microRNA (miRNA) have been studied best among the noncoding genome and huge data have accumulated regarding their inhibitory and promoting effects in cancer. Another sector of ncRNAs is the world of PIWI-interacting RNAs (piRNAs). Initially discovered with the asymmetric division of germline stem cells in the Drosophila ovary, piRNAs have a unique capability to associate with mammalian proteins analogous to P-element induced wimpy testis (PIWI) in Drosophila and are capable of silencing transposons. After a brief introduction to its discovery timelines, the present narrative review covers the biogenesis, function, and role of piRNAs in lung cancer. The effects on lung cancer are highlighted under sections of cell proliferation, stemness maintenance, metastasis, and overall survival, and the review concludes with a discussion of recent discoveries of another class of small ncRNAs, the piRNA-like RNAs (piR-Ls).

PIWIL1 Drives Chemoresistance in Multiple Myeloma by Modulating Mitophagy and the Myeloma Stem Cell Population

As an important member of the Argonaute protein family, PIWI-like protein 1 (PIWIL1) plays a key role in tumor cell viability. However, the exact function of PIWIL1 in multiple myeloma (MM) and the underlying mechanism remain unclear. Here, we revealed that PIWIL1 was highly expressed in myeloma cell lines and newly diagnosed MM patients, and that its expression was notably higher in refractory/relapsed MM patients. PIWIL1 promoted the proliferation of MM cells and conferred resistance to chemotherapeutic agents both in vitro and in vivo. More importantly, PIWIL1 enhanced the formation of autophagosomes, especially mitophagosomes, by disrupting mitochondrial calcium signaling and modulating mitophagy-related canonical PINK1/Parkin pathway protein components. Mitophagy/autophagy inhibitors overcome PIWIL1-induced chemoresistance. In addition, PIWIL1 overexpression increased the proportion of side population (SP) cells and upregulated the expression of the stem cell-associated genes Nanog, OCT4, and SOX2, while its inhibition resulted in opposite effects. Taken together, our findings demonstrated that PIWIL1 induced drug resistance by activating mitophagy and regulating the MM stem cell population. PIWIL1 depletion significantly overcame drug resistance and could be used as a novel therapeutic target for reversing resistance in MM patients.

Elevated P-Element-Induced Wimpy-Testis-Like Protein 1 Expression Predicts Unfavorable Prognosis for Patients with Various Cancers

Increasing evidence has shown that overexpression of P-element-induced wimpy-testis (PIWI)-like protein 1 (PIWIL1) was associated with unfavorable prognosis of patients with various types of cancers. Herein, we conducted this meta-analysis to identify the clinicopathological and prognostic value of the PIWIL1 expression in cancers. Three electronic databases (PubMed, Web of Science, and Embase) were comprehensively retrieved for relevant studies up to August 4^th, 2019. RevMan 5.3 and STATA 12.0 statistical software programs were used to explore the relationships between PIWIL1 expression and the prognosis and clinicopathological features in cancer patients. A total of 13 studies recruiting 2179 patients with 9 types of solid tumors were finally included in the meta-analysis. The results indicated that patients with high PIWIL1 expression tended to have a shorter survival, and additionally deeper tumor invasion, higher clinical stage, and more lymph node metastasis. PIWIL1 could serve as a biomarker for prognosis and clinicopathological characteristics in various cancers.

Infection by High-Risk Human Papillomaviruses, Epithelial-to-Mesenchymal Transition and Squamous Pre-Malignant or Malignant Lesions of the Uterine Cervix: A Series of Chained Events?

Wound healing requires static epithelial cells to gradually assume a mobile phenotype through a multi-step process termed epithelial-to-mesenchymal transition (EMT). Although it is inherently transient and reversible, EMT perdures and is abnormally activated when the epithelium is chronically exposed to pathogens: this event deeply alters the tissue and eventually contributes to the development of diseases. Among the many of them is uterine cervical squamous cell carcinoma (SCC), the most frequent malignancy of the female genital system. SCC, whose onset is associated with the persistent infection of the uterine cervix by high-risk human papillomaviruses (HR-HPVs), often relapses and/or metastasizes, being resistant to conventional chemo- or radiotherapy. Given that these fearsome clinical features may stem, at least in part, from the exacerbated and long-lasting EMT occurring in the HPV-infected cervix; here we have reviewed published studies concerning the impact that HPV oncoproteins, cellular tumor suppressors, regulators of gene expression, inflammatory cytokines or growth factors, and the interactions among these effectors have on EMT induction and cervical carcinogenesis. It is predictable and desirable that a broader comprehension of the role that EMT inducers play in SCC pathogenesis will provide indications to flourish new strategies directed against this aggressive tumor.

PIWI proteins and piRNAs in cervical cancer: a propitious dart in cancer stem cell-targeted therapy

Any form of cancer is a result of uncontrolled cell growth caused by mutations and/or epigenetic alterations, implying that a balance of chromatin remodeling activities and epigenetic regulators is crucial to prevent the transformation of a normal cell to a cancer cell. Many of the chromatin remodelers do not recognize any specific sites on their targets and require guiding molecules to reach the respective targets. PIWI proteins and their interacting small non-coding RNAs (piRNAs) have proved to act as a guiding signal for such molecules. While epigenetic alterations lead to tumorigenesis, the stemness of cancer cells contributes to recurrence and metastasis of cancer. Various studies have propounded that the PIWI-piRNA complex also promotes stemness of cancer cells, providing new doors for target-mediated anti-cancer therapies. Despite the progress in diagnosis and development of vaccines, cervical cancer remains to be the second most prevalent cancer among women, due to the lack of cost-effective and accessible diagnostic and prevention methods. With the emergence of liquid biopsy, there is a significant demand for the ideal biomarker in the diagnosis of cancer. PIWI and piRNAs have been recommended to serve as prognostic and diagnostic markers, to differentiate early and later stages of cancer, including cervical cancer. This review discusses how PIWIs and piRNAs are involved in disease progression as well as their potential role in diagnostics and therapeutics in cervical cancer.

Small Non-Coding-RNA in Gynecological Malignancies

Gynecologic malignancies, which include cancers of the cervix, ovary, uterus, vulva, vagina, and fallopian tube, are among the leading causes of female mortality worldwide, with the most prevalent being endometrial, ovarian, and cervical cancer. Gynecologic malignancies are complex, heterogeneous diseases, and despite extensive research efforts, the molecular mechanisms underlying their development and pathology remain largely unclear. Currently, mechanistic and therapeutic research in cancer is largely focused on protein targets that are encoded by about 1% of the human genome. Our current understanding of 99% of the genome, which includes noncoding RNA, is limited. The discovery of tens of thousands of noncoding RNAs (ncRNAs), possessing either structural or regulatory functions, has fundamentally altered our understanding of genetics, physiology, pathophysiology, and disease treatment as they relate to gynecologic malignancies. In recent years, it has become clear that ncRNAs are relatively stable, and can serve as biomarkers for cancer diagnosis and prognosis, as well as guide therapy choices. Here we discuss the role of small non-coding RNAs, i.e., microRNAs (miRs), P-Element induced wimpy testis interacting (PIWI) RNAs (piRNAs), and tRNA-derived small RNAs in gynecological malignancies, specifically focusing on ovarian, endometrial, and cervical cancer.

Critical Roles of PIWIL1 in Human Tumors: Expression, Functions, Mechanisms, and Potential Clinical Implications

P-element-induced wimpy testis (PIWI)-interacting RNAs (piRNAs) are a class of small non-coding RNA molecules that are 24-31 nucleotides in length. PiRNAs are thought to bind to PIWI proteins (PIWL1-4, a subfamily of Argonaute proteins), forming piRNA/PIWI complexes that influence gene expression at the transcriptional or post-transcriptional levels. However, it has been recently reported that the interaction of PIWI proteins with piRNAs does not encompass the entire function of PIWI proteins in human tumor cells. PIWIL1 (also called HIWI) is specifically expressed in the testis but not in other normal tissues. In tumor tissues, PIWIL1 is frequently overexpressed in tumor tissues compared with normal tissues. Its high expression is closely correlated with adverse clinicopathological features and shorter patient survival. Upregulation of PIWIL1 drastically induces tumor cell proliferation, epithelial-mesenchymal transition (EMT), invasion, cancer stem-like properties, tumorigenesis, metastasis and chemoresistance, probably via piRNA-independent mechanisms. In this article, we summarize the current existing literature on PIWIL1 in human tumors, including its expression, biological functions and regulatory mechanisms, providing new insights into how the dysregulation of PIWIL1 contributes to tumor initiation, development and chemoresistance through diverse signaling pathways. We also discuss the most recent findings on the potential clinical applications of PIWIL1 in cancer diagnosis and treatment.

Molecular landscape of recurrent cervical cancer

Cervical cancer (CC) is a major gynecological problem in developing and underdeveloped countries. Despite the significant advancement in early detection and treatment modalities, several patients recur. Moreover, the molecular mechanisms responsible for CC recurrence remains obscure. The patients with CC recurrence often show poor prognosis and significantly high mortality rates. The clinical management of recurrent CC depends on treatment history, site, and extent of the recurrence. Owing to poor prognosis and limited treatment options, recurrent CC often presents a challenge to the clinicians. Several in vitro, in vivo, and patient studies have led to the identification of the critical molecular changes responsible for CC recurrence. Both aberrant genetic and epigenetic modifications leading to altered cell signaling pathways have been reported to impact CC recurrence. Researchers are currently trying to dissect the molecular pathways in CC and translate these findings for better management of disease. This article attempts to review the existing knowledge of disease relapse, accompanying challenges, and associated molecular players in CC.

PIWI-Like 1 and PIWI-Like 2 Expression in Breast Cancer

Simple Summary

A family of proteins, the PIWI proteins, play a crucial role in the regulation of the development of germ cells and self-preservation of so-called stem cells. Former studies have shown that these proteins can be over- or underrepresented (over-/underexpressed) in some cancers and, in the case of abnormal expression, may be correlated with worse outcomes of tumor patients. In our study, we investigated the influence of the two PIWI proteins, PIWI-like 1 and PIWI-like 2, on the survival of breast cancer patients and their correlation with certain breast cancer subtypes. If a breast cancer showed a higher expression of PIWI-like 1 protein but less PIWI-like 2 protein than in non-tumorous tissue, the patient suffered from a more aggressive breast cancer subtype and had shorter survival. By analyzing these two proteins in breast cancer, we were able to predict tumor aggressiveness and prognosis.

Abstract

PIWI-like 1 and PIWI-like 2 play a role in stem cell self-renewal, and enhanced expression has been reported for several tumor entities. However, few studies have investigated PIWI-like 1 and PIWI-like 2 expressions in breast cancer subtypes regarding prognosis. Therefore, we examined protein expression in a large consecutive cohort of breast cancer patients and correlated it to breast cancer subtypes and survival outcome. PIWI-like 1 and PIWI-like 2 expressions were evaluated using immunohistochemistry in a cohort of 894 breast cancer patients, of whom 363 were eligible for further analysis. Percentage and intensity of stained tumor cells were analyzed and an immunoreactive score (IRS) was calculated. The interaction of PIWI-like 1 and PIWI-like 2 showed a prognostic effect on survival. For the combination of high PIWI-like 1 and low PIWI-like 2 expressions, adjusted hazard ratios (HRs) were significantly higher with regard to overall survival (OS) (HR 2.92; 95% confidence interval (CI) 1.24, 6.90), disease-free survival (DFS) (HR 3.27; 95% CI 1.48, 7.20), and distant disease-free survival (DDFS) (HR 7.64; 95% CI 2.35, 24.82). Both proteins were significantly associated with molecular-like and PAM50 subgroups. Combining high PIWI-like 1 and low PIWI-like 2 expressions predicted poorer prognosis and both markers were associated with aggressive molecular subtypes.

Recent advances in the contribution of noncoding RNAs to cisplatin resistance in cervical cancer

Cervical cancer (CC) remains a major disease burden on the female population worldwide. Chemotherapy with cisplatin (cis-diamminedichloroplatinum (II); CDDP) and related drugs are the main treatment option for CC; however, their efficacy is limited by the development of drug resistance. Noncoding RNAs (ncRNAs) have been found to play critical roles in numerous physiological and pathological cellular processes, including drug resistance of cancer cells. In this review, we describe some of the ncRNAs, including miRNAs, lncRNAs and circRNAs, that are involved in the sensitivity/resistance of CC to CDDP-based chemotherapy and discuss their mechanisms of action. We also describe some ncRNAs that could be therapeutic targets to improve the sensitivity of CC to CDDP-based chemotherapy.

Beyond MicroRNAs: Emerging Role of Other Non-Coding RNAs in HPV-Driven Cancers

Persistent infection with high-risk Human Papilloma Virus (HPV) leads to the development of several tumors, including cervical, oropharyngeal, and anogenital squamous cell carcinoma. In the last years, the use of high-throughput sequencing technologies has revealed a number of non-coding RNA (ncRNAs), distinct from micro RNAs (miRNAs), that are deregulated in HPV-driven cancers, thus suggesting that HPV infection may affect their expression. However, since the knowledge of ncRNAs is still limited, a better understanding of ncRNAs biology, biogenesis, and function may be challenging for improving the diagnosis of HPV infection or progression, and for monitoring the response to therapy of patients affected by HPV-driven tumors. In addition, to establish a ncRNAs expression profile may be instrumental for developing more effective therapeutic strategies for the treatment of HPV-associated lesions and cancers. Therefore, this review will address novel classes of ncRNAs that have recently started to draw increasing attention in HPV-driven tumors, with a particular focus on ncRNAs that have been identified as a direct target of HPV oncoproteins.

The Clinical Significance of PIWIL3 and PIWIL4 Expression in Pancreatic Cancer

P-element-induced wimpy testis (PIWI) proteins have been described in several cancers. PIWIL1 and PIWIL2 have been recently evaluated in pancreatic cancer, and elevated expression of PIWIL2 conferred longer survival to patients. However, PIWIL3’s and PIWIL4’s role in carcinogenesis is rather controversial, and their clinical implication in pancreatic cancer has not yet been investigated. In the present study, we evaluated PIWIL1, PIWIL2, PIWIL3 and PIWIL4 expression in pancreatic cancer-derived cell lines and in one non-tumor cell line as healthy control. Here, we show a differential expression in tumor and non-tumor cell lines of PIWIL3 and PIWIL4. Subsequently, functional experiments with PIWIL3 and/or PIWIL4 knockdown revealed a decrease in the motility ratio of tumor and non-tumor cell lines through downregulation of mesenchymal factors in pro of epithelial factors. We also observed that PIWIL3 and/or PIWIL4 silencing impaired undifferentiated phenotype and enhanced drug toxicity in both tumor- and non-tumor-derived cell lines. Finally, PIWIL3 and PIWIL4 evaluation in human pancreatic cancer samples showed that patients with low levels of PIWIL4 protein expression presented poor prognosis. Therefore, PIWIL3 and PIWIL4 proteins may play crucial roles to keep pancreatic cell homeostasis not only in tumors but also in healthy tissues.

PIWIL-2 and piRNAs are regularly expressed in epithelia of the skin and their expression is related to differentiation

PIWI proteins play multiple roles in germline stem cell maintenance and self-renewal. PIWI-interacting RNAs (piRNAs) associate with PIWI proteins, form effector complexes and maintain genome integrity and function in the regulation of gene expression by epigenetic modifications. Both are involved in cancer development. In this study, we investigated the expression of PIWIL-2 and piRNAs in normal human skin and epithelial tumors and its regulation during keratinocyte (KC) differentiation. Immunohistochemistry showed that PIWIL-2 was regularly expressed in the epidermis and adnexal tissue with strongest expression in sebaceous glands. Cell culture studies revealed an association of PIWIL-2 expression with the state of differentiated KC. In contrast, the PIWIL-2 expression pattern did not correlate with stem cell compartments or malignancy. piRNAs were consistently detected in KC in vitro by next-generation sequencing and the expression levels of numerous piRNAs were regulated during KC differentiation. Epidermal piRNAs were predominantly derived from processed snoRNAs (C/D-box snoRNAs), tRNAs and protein coding genes. Our data indicate that components of the PIWIL-2-piRNA pathway are present in epithelial cells of the skin and are regulated in the context of KC differentiation, suggesting a role of somatic gene regulation. However, putative roles in the maintenance of stem cell compartments or the development of malignancy in the skin were not supported by this study.

The Non-Coding RNA Landscape of Plasma Cell Dyscrasias

Despite substantial advancements have been done in the understanding of the pathogenesis of plasma cell (PC) disorders, these malignancies remain hard-to-treat. The discovery and subsequent characterization of non-coding transcripts, which include several members with diverse length and mode of action, has unraveled novel mechanisms of gene expression regulation often malfunctioning in cancer. Increasing evidence indicates that such non-coding molecules also feature in the pathobiology of PC dyscrasias, where they are endowed with strong therapeutic and/or prognostic potential. In this review, we aim to summarize the most relevant findings on the biological and clinical features of the non-coding RNA landscape of malignant PCs, with major focus on multiple myeloma. The most relevant classes of non-coding RNAs will be examined, along with the mechanisms accounting for their dysregulation and the recent strategies used for their targeting in PC dyscrasias. It is hoped these insights may lead to clinical applications of non-coding RNA molecules as biomarkers or therapeutic targets/agents in the near future.

Epigenetic roles of PIWI proteins and piRNAs in lung cancer

Lung cancer is one of very important malignancies which are related to high mobility and mortality in the world. Despite several efforts for improving diagnosis and treatment strategies of lung cancer, finding and developing new and effective therapeutic and diagnostic are needed. A variety of internal and external factors could be involved in lung cancer pathogenesis. Among internal factors, epigenetic mechanisms have been emerged as very important players in the lung cancer. Non-coding RNAs is known as one of epigenetic regulators which exert their effects on a sequence of cellular and molecular mechanisms. P-element induced wimpy testis (PIWI)-interacting RNAs (piRNAs or piR) is one of small non-coding RNAs that the deregulation of these molecules is associated with initiation and progression of different cancers such as lung cancer. Several activities are related to PIWI/piRNA pathway such as suppression of transposons and mobile genetic elements. In vitro and in vivo studies demonstrated the upregulation or downregulation of PIWI proteins and piRNAs could lead to the increasing of cell proliferation, apoptosis reduction and promoting tumor growth in the lung cancer. Hence, PIWI proteins and piRNA could be introduced as new diagnostic and therapeutic biomarkers in the lung cancer therapy. Herein, we have focused on PIWI proteins and piRNA functions and their impact on the progression of lung cancer.

Molecular and Functional Characterization of the Somatic PIWIL1/piRNA Pathway in Colorectal Cancer Cells

PIWI-like (PIWIL) proteins and small non-coding piRNAs, involved in genome regulation in germline cells, are found aberrantly expressed in human tumors. Gene expression data from The Cancer Genome Atlas (TCGA), the Genotype-Tissue Expression (GTEx) project, and the European Genome-Phenome Archive (EGA) indicate that the PIWIL1 gene is ectopically activated in a significant fraction of colorectal cancers (CRCs), where this is accompanied by promoter demethylation, together with germline factors required for piRNA production. Starting from this observation, the PIWIL/piRNA pathway was studied in detail in COLO 205 CRC cells, which express significant levels of this protein, to investigate role and significance of ectopic PIWIL1 expression in human tumors. RNA sequencing and cell and computational biology led to the demonstration that PIWIL1 localizes in a nuage-like structure located in the perinuclear region of the cell and that a significant fraction of the piRNAs expressed in these cells are methylated, and, therefore, present in an active form. This was further supported by RNA immunoprecipitation, which revealed how several piRNAs can be found loaded into PIWIL1 to form complexes also comprising their target mRNAs. The mature transcripts associated with the PIWIL-piRNA complex encode key regulatory proteins involved in the molecular mechanisms sustaining colorectal carcinogenesis, suggesting that the PIWI/piRNA pathway may actively contribute to the establishment and/or maintenance of clinico-pathological features of CRCs.

α-Actinin-4 regulates cancer stem cell properties and chemoresistance in cervical cancer

Cancer stem cells (CSCs) initiate tumors and possess the properties of self-renewal and differentiation. Since they are responsible for chemoresistance, CSCs are known to be a key factor in cancer recurrence. α-Actinin-4 (ACTN4) is an actin-binding protein that is involved in muscle differentiation and cancer metastasis. It promotes epithelial to mesenchymal transition and cell cycle progression via β-catenin stabilization in cervical cancer. In the present study, we investigated the role of ACTN4 in regulating cancer cell stemness and chemoresistance in cervical cancer. Results from the gene expression database analysis showed that ACTN4 mRNA expression was elevated in cancerous cervices when compared with normal cervices. Furthermore, ACTN4 knockdown suppressed sphere formation and CSC proliferation. It also decreased CSC size and CD44high/CD24low cell population. ACTN4-knockdown CSCs were sensitive to anticancer drugs, which was observed by down-regulation of the ATP-binding cassette family G2 involved in drug resistance. Finally, ACTN4-knockdown CSCs formed reduced tumors in vivo when compared with control CSCs. Overall, these findings suggest that ACTN4 regulates CSC properties and contributes to chemoresistance in cervical cancer.

The Prognosis Value of PIWIL1 and PIWIL2 Expression in Pancreatic Cancer

Pancreatic cancer is a highly aggressive manifestation of cancer, and currently presents poor clinical outcome due to its late diagnosis with metastasic disease. Surgery is the only approach with a curative intend; however, the survival rates seen in this type of patient are still low. After surgery, there is a lack of predictive prognosis biomarkers to predict treatment response and survival to establish a personalized medicine. Human P-element-induced wimpy testis 1 (PIWIL1) and P-element-induced wimpy testis 2 (PIWIL2) proteins act as protectors of germline, and their aberrant expression has been described in several types of tumors. In this study, we aimed to assess an association between PIWIL1 and PIWIL2 expression and the prognosis of biliopancreatic cancer patients. For this, we analyzed protein expression in complete resected tumor samples, and found a significant association between PIWIL2 expression and both progression-free and overall survival (p = 0.036 and p = 0.012, respectively). However, PIWIL2 expression was significantly associated with progression-free survival (p = 0.029), and overall survival (p = 0.025) of such tumors originated in the pancreas, but not in the bile duct or ampulla of Vater. Further analysis revealed that PIWIL1 and PIWIL2, at both mRNA and protein expression levels, correlated positively with factors associated to the progenitor molecular subtype of pancreatic cancer. Based on these findings, PIWIL1 and PIWIL2 expression may be considered a potential prognostic biomarker for resectable pancreatic cancer and may serve to guide subsequent adjuvant treatment decisions.

Piwi-interacting RNAs (piRNAs) and cancer: Emerging biological concepts and potential clinical implications

Piwi-interacting RNAs (piRNAs) are a very recently discovered class of small non-coding RNAs (ncRNAs), with approximately 20,000 piRNA genes already identified within the human genome. These short RNAs were originally described as key functional regulators for the germline maintenance and transposon silencing. However, due to our limited knowledge regarding their function, piRNAs were for a long time assumed to be the "dark matter" of ncRNAs in our genome. However, recent evidence has now changed our viewpoint of their biological and clinical significance in various diseases, as newly emerging data reveals that aberrant expression of piRNAs is a unique and distinct feature in many diseases, including multiple human cancers. Furthermore, their altered expression in cancer patients has been significantly associated with clinical outcomes, highlighting their important biological functional role in disease progression. Functionally, piRNAs maintain genomic integrity by silencing transposable elements, and are capable of regulating the expression of specific downstream target genes in a post-transcriptional manner. Moreover, accumulating evidences demonstrates that analogous to other small ncRNAs (e.g. miRNAs) piRNAs have both oncogenic and tumor suppressive roles in cancer development. In this article, we discuss emerging insights into roles of piRNAs in a variety of cancers, reveal new findings underpinning various mechanisms of piRNAs-mediated gene regulation, and highlight their potential clinical significance in the management of cancer patients.

Role of DDX53 in taxol-resistance of cervix cancer cells in vitro

Cancer/Testis antigen DDX53 shows high expression level in various tumors and is involved in anti-cancer drug resistance. However, the functional study of DDX53 in cervix cancer remains unknown. In this study, the role of DDX53 in taxol-resistance of cervix cancer cells was investigated. In taxol-resistant Hela^TR cells, DDX53 was significantly increased as compared to the parental HeLa cells. Hela^TR cells also showed upregulation of multidrug resistant gene MDR1, invasive characteristics and decreased apoptosis. In addition, increased autophagy level was observed in Hela^TR cells. Overexpression of DDX53 in HeLa and SiHa markedly led to greater resistance to taxol and cisplatin, whereas knockdown of DDX53 in Hela^TR cells restored sensitivity, demonstrating that DDX53 regulated taxol resistance in cervix cancer cells. DDX53 overexpression in HeLa and SiHa cells enhanced invasion, migration and anchorage independent growth, DDX53 knockdown showed inverse effects in HeLa^TR cells. When DDX53 expression was suppressed by siRNA, autophagic flux and drug resistance of Hela^TR cells were decreased. In addition, DDX53 was upregulated in cervix cancer tissues from patient with a glassy cell carcinoma of cervix. Taken together, these results suggest that DDX53 plays a critical role in taxol-resistance by activating autophagy and a potential therapeutic target for the treatment of taxol-resistant cervix cancer.

Suppression of Hiwi inhibits the growth and epithelial-mesenchymal transition of cervical cancer cells

Cervical cancer is a common gynecological malignancy. Hiwi exhibits a high level of expression in cervical cancer cells. However, the effects of Hiwi expression in cervical cancer cells remain unresolved. In the present study, the effects of Hiwi downregulation on the growth and epithelial-mesenchymal transition of cervical cancer cells were investigated. The results of the present study revealed that the suppression of Hiwi was able to inhibit the proliferation of cervical cancer cells and arrest cell cycle at G1 phase. The downregulation of Hiwi was also revealed to inhibit the epithelial-mesenchymal transition process of cervical cancer cells by regulating the expression of E-cadherin, N-cadherin, vimentin, and snail. The present study demonstrated that the suppression of Hiwi was able to inhibit the growth and epithelial-mesenchymal transition of cervical cancer cells. Therefore, the results suggest that Hiwi may function as an oncogene in cervical cancer cells and may become a potential target for cervical cancer therapy.

Hiwi overexpression does not affect proliferation, migration or apoptosis of liver cancer cells in vitro or in vivo

Piwi like RNA-mediated gene silencing 1 (Hiwi) is a human homolog of the Piwi gene family that has been reported to be upregulated in hepatocellular carcinoma (HCC). The present study aimed to investigate the role of Hiwi in the initiation and development of HCC in vitro and in vivo. Adenovirus-mediated Hiwi overexpression was established in primary murine hepatocytes and SMMC7721 HCC cells. Cell viability and proliferation were assessed using MTT and EdU assays, respectively. Cell migration was measured using a scratch migration assay. The cell cycle was assessed using flow cytometry, and the expression of genes associated with the epithelial mesenchymal transition (EMT) was assessed using reverse transcription-quantitative polymerase chain reaction. SMMC7721 cells that stably express Hiwi were also generated and injected subcutaneously into the nude mice, and tumor growth was examined. Recombinant adenovirus encoding green fluorescent protein or Hiwi was delivered by injection into the tail vein, and its effect on murine hepatocyte gene expression was studied. The present study revealed that the overexpression of Hiwi did not affect the proliferation or migration of liver cancer cells and failed to suppress perifosine- or doxorubicin-induced apoptosis in vitro. The tumors of mice that were injected with Hiwi-expressing SMMC7721 cells were not significantly larger compared with mice that were injected with control SMMC7721 cells. Hiwi overexpression did not noticeably alter the expression of genes involved in EMT, either in vitro or in vivo. The results of the present study indicate that although expression of Hiwi is associated with HCC development and progression in the clinic, it does not act as an oncogene in liver cancer cells.

Salinomycin may inhibit the cancer stem-like populations with increased chemoradioresistance that nasopharyngeal cancer tumorspheres contain

Tumor recurrence and metastasis of nasopharyngeal cancer (NPC) often result in the failure of treatment due to chemoradioresistance. Cancer stem cells (CSCs) have been observed to drive tumor initiation and tumor chemoradioresistance. Therefore, the poor prognosis of advanced NPC is likely to result from the failure to kill CSCs. Sphere formation may be used as an experimental method to enrich potential CSC subpopulations. At present, there are few reports on NPC tumorspheres. The present study focused on examining the cancer stem-like properties of NPC tumorspheres from NPC cell lines. Western blot analysis revealed that NPC tumorspheres had a higher expression of stem cell markers Nanog homeobox and SRY-box 2, compared with parental cells. It was additionally verified that NPC tumorspheres contained a high aldehyde dehydrogenase (ALDH) enzymatic activity compared with parental cells. ALDH+ cells were amplified by 9- to 10-fold in tumorspheres, compared with parental cells (1.8 vs. 16.9%). The tumorsphere cells exhibited an increased half maximal inhibitory concentration value of >10-fold with cisplatin compared with the control parental cells. Compared with the parental cells, the percentage of side population cells in the tumorsphere cell population increased significantly (10.3 vs. 2.3%; P<0.05). NPC tumorsphere cells demonstrated enhanced resistance to radiation. Further investigation verified that salinomycin inhibited NPC CSCs by selectively targeting its stem cells. Altogether, the data revealed that NPC tumorspheres contain cancer stem-like populations with increased chemoradioresistance. It was suggested that the serum-free culture of NPC cells may provide an appropriate model for researching the sensitivity of CSCs to therapeutic agents. It was additionally revealed that salinomycin is an efficient inhibitor of NPC CSCs, supporting the hypothesis that salinomycin may eliminate CSCs and imply a need for further clinical evaluation.

RNAi‑mediated downregulation of asparaginase‑like protein 1 inhibits growth and promotes apoptosis of human cervical cancer line SiHa

Asparaginase like 1 (ASRGL1) protein belongs to the N-terminal nucleophile group, cleaving the isoaspartyl-dipeptides and L-asparagine by adding water. It tends to be overexpressed in cancerous tumors including ovarian cancer and breast tumors. The present study assessed the potential ability of ASRGL1 as a molecular target in gene-based cervical cancer treatment. The protein expression level of ASRGL1 was determined in paraffin-embedded tumor specimen by immunohistochemistry. Additionally, in order to assess the activity of ASRGL1 during the process of cervical cancer cell multiplication, ASRGL1-short hairpin (sh) RNA-expressing lentivirus was established, which was used to infect SiHa cells. The Cellomics ArrayScan VT1 Reader identified the influence of downregulation on SiHa caused by RNA interference-intervened ASRGL1. Flow cytometric analysis was also performed to evaluate the influence. The cyclin dependent kinase (CDK2), cyclin A2, B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X protein (Bax) expression levels were assessed by western blot analysis. ASRGL1 was observed to be overexpressed in cervical cancer tissues when compared with the adjacent normal tissues. The knockdown of ASRGL1 in SiHa by ASRGL1-shRNA lentivirus infection significantly inhibited cell growth and enhanced cellular apoptosis; the cells were also captured during the S phase. The knockdown of ASRGL1 expression led to the increased expression of Bax and decreased expression of Bcl-2, CDK2 and cyclin A2. In conclusion, ASRGL1 was closely associated with growth and apoptosis in cervical cancer. Therefore, ASRGL1 may be a novel, potentially effective anti-cervical cancer therapy.

Next-generation sequencing reveals differentially expressed small noncoding RNAs in uterine leiomyoma

OBJECTIVE

To determine the expression profile of small noncoding RNAs (sncRNAs) in leiomyoma, which has not been investigated to date.

DESIGN

Laboratory-based investigation.

SETTING

Academic center.

PATIENT(S)

Women undergoing hysterectomy for benign indications.

INTERVENTION(S)

Next-generation sequencing and screening of an sncRNA database with confirmatory analysis by quantitative reverse-transcription polymerase chain reaction (qRT-PCR).

MAIN OUTCOME MEASURE(S)

Expression profile of sncRNAs in leiomyoma and matched myometrium.

RESULT(S)

Screening our previously determined RNA sequencing data with the sncRNA database resulted in identification of 15 small nuclear (sn) RNAs, 284 small nucleolar (sno) RNAs, 98 Piwi-interacting (pi) RNAs, 152 transfer (t) RNAs, and 45 ribosomal (r) RNAs, of which 15 snoRNAs, 24 piRNAs, 7 tRNAs, and 6 rRNAs were differentially expressed at a 1.5-fold change cutoff in leiomyoma compared with myometrium. We selected 5 snoRNAs, 4 piRNAs, 1 tRNA, and 1 rRNA that were differentially expressed and confirmed their expression in paired tissues (n = 20) from both phases of the menstrual cycle with the use of qRT-PCR. The results indicated up-regulation of the snoRNAs (SNORD30, SNORD27, SNORA16A, SNORD46, and SNORD56) and down-regulation of the piRNAs (piR-1311, piR-16677, piR-20365, piR-4153), tRNA (TRG-GCC5-1), and rRNA (RNA5SP202) expression in leiomyoma compared with myometrium (P<.05). The pattern of expression of these sncRNAs was similar to RNA sequencing analysis, with no menstrual cycle-dependent differences detected except for SNORD30. Because Argonaute 2 (AGO2) is required for sncRNA-mediated gene silencing, we determined its expression and found greater abundance in leiomyoma.

CONCLUSION(S)

Our results provide the first evidence for the differential expression of additional classes of sncRNAs and AGO2 in leiomyoma, implicating their roles as a gene regulatory mechanism.

TAK1 inhibitor 5Z-7-oxozeaenol sensitizes cervical cancer to doxorubicin-induced apoptosis

Aberrant activation of nuclear factor-κB (NF-κB) allows cancer cells to escape chemotherapy-induced cell death and acts as one of the major mechanisms of acquired chemoresistance in cervical cancer. TAK1, a crucial mediator that upregulates NF-κB activation in response to cellular genotoxic stress, is required for tumor cell viability and survival. Herein, we examined whether TAK1 inhibition is a potential therapeutic strategy for treating cervical cancer. We found that TAK1 inhibitor 5Z-7-oxozeaenol significantly augmented the cytotoxic effects of Dox in a panel of cervical cancer cell lines. Treatment with 5Z-7-oxozeaenol hindered Dox-induced NF-κB activation and promoted Dox-induced apoptosis in cervical cancer cells. Moreover, 5Z-7-oxozeaenol showed similar effects in both positive and negative human papillomavirus-infected cervical cancer cells. Taken together, our results provide evidence that TAK1 inhibition significantly sensitizes cervical cancer cells to chemotherapy-induced cell death and supports the use of TAK1 inhibitor with current chemotherapies in the clinic for patients with refractory cervical cancer.

Induced cancer stem cells generated by radiochemotherapy and their therapeutic implications

Local and distant recurrence of malignant tumors following radio- and/or chemotherapy correlates with poor prognosis of patients. Among the reasons for cancer recurrence, preexisting cancer stem cells (CSCs) are considered the most likely cause due to their properties of self-renewal, pluripotency, plasticity and tumorigenicity. It has been demonstrated that preexisting cancer stem cells derive from normal stem cells and differentiated somatic cells that undergo transformation and dedifferentiation respectively under certain conditions. However, recent studies have revealed that cancer stem cells can also be induced from non-stem cancer cells by radiochemotherapy, constituting the subpopulation of induced cancer stem cells (iCSCs). These findings suggest that radiochemotherapy has the side effect of directly transforming non-stem cancer cells into induced cancer stem cells, possibly contributing to tumor recurrence and metastasis. Therefore, drugs targeting cancer stem cells or preventing dedifferentiation of non-stem cancer cells can be combined with radiochemotherapy to improve its antitumor efficacy. The current review is to investigate the mechanisms by which induced cancer stem cells are generated by radiochemotherapy and hence provide new strategies for cancer treatment.

The meaning of PIWI proteins in cancer development

Cancer is a histologically and genetically heterogeneous population of tumor cells that exhibits distinct molecular profiles determined by epigenetic alterations. P-element-induced wimpy testis (PIWI) proteins in complex with PIWI-interacting RNA (piRNA) have been previously demonstrated to be involved in epigenetic regulation in germline cells. Recently, reactivation of PIWI expression, primarily PIWI-like protein 1 and 2, through aberrant DNA methylation resulting in genomic silencing has been identified in various types of tumors. It has been suggested that the PIWI-piRNA complex contributes to cancer development and progression by promoting a stem-like state of cancer cells, or cancer stem cells (CSCs). It has been identified that CSCs represent the cells that have undergone epithelial-mesenchymal transition (EMT) and acquired metastatic capacities. However, the molecular association between the EMT process and the stem-cell state remains unclear. Further extensive characterization of CSCs in individual types of tumors is required to identify specific markers for the heterogeneous population of CSCs and therefore selectively target CSCs. Previous studies indicate a reciprocal regulation between PIWI proteins and a complex signaling network linking markers characterized for CSCs and transcription factors involved in EMT. In the present review, studies of PIWI function are summarized, and the potential involvement of PIWI proteins in cancer development and progression is discussed.

Overexpression of Hiwi Inhibits the Growth and Migration of Chronic Myeloid Leukemia Cells

Chronic myeloid leukemia (CML) is a hematopoietic malignancy characterized by dysregulated growth and proliferation of hematopoietic stem/progenitor cells in bone marrow and excessive expansion of hematopoietic compartments in peripheral blood. Expression deletion of Hiwi, a human Piwi homolog, has been reported to be implicated in leukemogenesis. We here explored Hiwi's role in CML pathogenesis by determining how and whether its forced overexpression could affect CML cell growth and migration. The present results showed that lentivirus-mediated overexpression of Hiwi significantly suppressed cell proliferation and induced obvious apoptosis in K562 cells, a CML line cell line. Tumors in BALB/c nude mice generated by the K562 cells expressing Hiwi were much smaller than those formed by the control cells. Like in vitro, Hiwi upregulation induced cell apoptosis in the tumor tissues in vivo. Additionally, Hiwi elevation suppressed K562 cell migration and inhibited the activity and expression of matrix metalloproteinase-2 and -9. In summary, our study demonstrates that Hiwi overexpression inhibits CML cell growth and migration, providing insights into its role in CML pathogenesis.

Argonaute and Argonaute-Bound Small RNAs in Stem Cells

Small RNAs are essential for a variety of cellular functions. Argonaute (AGO) proteins are associated with all of the different classes of small RNAs, and are indispensable in small RNA-mediated regulatory pathways. AGO proteins have been identified in various types of stem cells in diverse species from plants and animals. This review article highlights recent progress on how AGO proteins and AGO-bound small RNAs regulate the self-renewal and differentiation of distinct stem cell types, including pluripotent, germline, somatic, and cancer stem cells.

Hiwi Promotes the Proliferation of Colorectal Cancer Cells via Upregulating Global DNA Methylation

Hiwi is well known for its role in stem cell renewal, maintaining the resting stage, and downregulating cell cycle of stem cells via RNA silencing. And Hiwi overexpression has been recognized in several types of cancers. In the present study, we examined the Hiwi expression in colorectal cancer (CRC) specimens in both mRNA and protein levels via real-time quantitative PCR, western blot assay, and immunohistochemical staining. Then we explored the role of Hiwi in the cancer cell proliferation and in the DNA methylation in human CRC Caro-2 and HT-29 cell lines. Results demonstrated that both mRNA and protein levels of Hiwi were significantly higher in 38 CRC tissues than in 38 peritumor tissues. Moreover, the Hiwi overexpression with an adenovirus vector significantly promoted the proliferation of Caro-2 and HT-29 cells, associated with significant increase in the global DNA methylation levels. And the chemical inhibition of DNA methylation significantly restrained such proliferation promotion. In summary, we confirmed that Hiwi was overexpressed in CRC tissues and that the forced Hiwi overexpression promoted the proliferation and global DNA methylation of CRC cell lines. Our results imply for the first time that Hiwi promotes the proliferation of CRC cells via promoting global DNA methylation.

Emerging roles for PIWI proteins in cancer

It is generally accepted that PIWI proteins are predominately expressed in the germline but absent in somatic tissues. Their best-characterized role is to suppress transposon expression, which ensures genomic stability in the germline. However, increasing evidence has suggested that PIWI proteins are linked to the hallmarks of cancer defined by Weinberg and Hanahan, such as cell proliferation, anti-apoptosis, genomic instability, invasion and metastasis. This provides new possibilities for anticancer therapies through the targeting of PIWI proteins, which may have fewer side effects due to their potential classification as a CTA (cancer/testis antigen). Furthermore, PIWI has been proposed to act as a diagnostic and prognostic marker for many types of cancer, and even to differentiate early- and late-stage cancers. We herein summarize the latest progress in this exciting field, hoping to encourage new investigations of PIWIs in cancer biology that will help to develop new therapeutics for clinical application.