PIWIL1 promotes gastric cancer via a piRNA-independent mechanism

piRNAs as emerging biomarkers and physiological regulatory molecules in cardiovascular disease

Cardiovascular diseases (CVD) represent one of the most considerable global health threats, owing to their high incidence and mortality rates. Despite the ongoing advancements in detection, prevention, treatment, and prognosis of CVD, which have resulted in a decline in both incidence and mortality rates, CVD remains a major public health concern. Therefore, novel diagnostic biomarkers and therapeutic interventions are imperative to minimise the risk of CVD. Non-coding RNAs (ncRNAs) have recently gained increasing attention, with PIWI-interacting RNAs (piRNAs) emerging as a class of small ncRNAs traditionally recognised for their role in silencing transposons within cells. Although the functional roles of PIWI proteins and piRNAs in human cells remain unclear, growing evidence suggests that these molecules are gradually becoming valuable biomarkers for the diagnosis and treatment of CVD. This review provides a comprehensive summary of the latest studies on piRNAs in CVD. This review discusses the roles of piRNAs in various cardiovascular subtypes, including myocardial hypertrophy, heart failure, myocardial infarction, and cardiac regeneration. The perceived insights may contribute novel perspectives for the diagnosis and treatment of CVD.

siRNA-based therapy for gastric adenocarcinoma: what's next step?

Gastric cancer continues to have a high death rate despite advancements in their diagnosis and treatment. Novel treatment techniques are thus desperately needed. This is where double-stranded RNA molecules known as small interfering RNA (siRNA), which may selectively target the mRNA of disease-causing genes, may find use in medicine. For siRNAs to function properly in the human body, they must be shielded from deterioration. Furthermore, in order to maintain organ function, they must only target the tumor and spare normal tissue. siRNAs have been designed using clever delivery mechanisms including polymers and lipids to achieve these objectives. Although siRNA protection is not hard to acquire, it is still challenging to target cancer cells with them. Here, we first discuss the basic characteristics of gastric cancer before describing the properties of siRNA and typical delivery methods created specifically for gastric tumors. Lastly, we provide a succinct overview of research using siRNAs to treat gastric tumors.

AVCAPIR: A Novel Procalcific PIWI-Interacting RNA in Calcific Aortic Valve Disease

BACKGROUND

Calcification of the aortic valve leads to increased leaflet stiffness and consequently results in the development of calcific aortic valve disease (CAVD). However, the underlying molecular and cellular mechanisms of calcification remain unclear. Here, we identified a novel aortic valve calcification-associated PIWI-interacting RNA (piRNA; AVCAPIR) that increases valvular calcification and promotes CAVD progression.

METHODS

Using piRNA sequencing, we identified piRNAs contributing to the pathogenesis of CAVD that we termed AVCAPIRs. High-cholesterol diet-fed ApoE-/- mice with AVCAPIR knockout were used to examine the role of AVCAPIR in aortic valve calcification (AVC). Gain- and loss-of-function assays were conducted to determine the role of AVCAPIR in the induced osteogenic differentiation of human valvular interstitial cells. To dissect the mechanisms underlying AVCAPIR-elicited procalcific effects, we performed various analyses, including an RNA pulldown assay followed by liquid chromatography-tandem mass spectrometry, methylated RNA immunoprecipitation sequencing, and RNA sequencing. RNA pulldown and RNA immunoprecipitation assays were used to study piRNA interactions with proteins.

RESULTS

We found that AVCAPIR was significantly upregulated during AVC and exhibited potential diagnostic value for CAVD. AVCAPIR deletion markedly ameliorated AVC in high-cholesterol diet-fed ApoE-/- mice, as shown by reduced thickness and calcium deposition in the aortic valve leaflets, improved echocardiographic parameters (decreased peak transvalvular jet velocity and mean transvalvular pressure gradient, as well as increased aortic valve area), and diminished levels of osteogenic markers (Runx2 and Osterix) in aortic valves. These results were confirmed in osteogenic medium-induced human valvular interstitial cells. Using unbiased protein-RNA screening and molecular validation, we found that AVCAPIR directly interacts with FTO (fat mass and obesity-associated protein), subsequently blocking its N6-methyladenosine demethylase activity. Further transcriptomic and N6-methyladenosine modification epitranscriptomic screening followed by molecular validation confirmed that AVCAPIR hindered FTO-mediated demethylation of CD36 mRNA transcripts, thus enhancing CD36 mRNA stability through the N6-methyladenosine reader IGF2BP1 (insulin-like growth factor 2 mRNA binding protein 1). In turn, the AVCAPIR-dependent increase in CD36 stabilizes its binding partner PCSK9 (proprotein convertase subtilisin/kexin type 9), a procalcific gene, at the protein level, which accelerates the progression of AVC.

CONCLUSIONS

We identified a novel piRNA that induced AVC through an RNA epigenetic mechanism and provide novel insights into piRNA-directed theranostics in CAVD.

The burgeoning importance of PIWI-interacting RNAs in cancer progression

PIWI-interacting RNAs (piRNAs) are a class of small noncoding RNA molecules that specifically bind to piwi protein family members to exert regulatory functions in germ cells. Recent studies have found that piRNAs, as tissue-specific molecules, both play oncogenic and tumor suppressive roles in cancer progression, including cancer cell proliferation, metastasis, chemoresistance and stemness. Additionally, the atypical manifestation of piRNAs and PIWI proteins in various malignancies presents a promising strategy for the identification of novel biomarkers and therapeutic targets in the diagnosis and management of tumors. Nonetheless, the precise functions of piRNAs in cancer progression and their underlying mechanisms have yet to be fully comprehended. This review aims to examine current research on the biogenesis and functions of piRNA and its burgeoning importance in cancer progression, thereby offering novel perspectives on the potential utilization of piRNAs and piwi proteins in the management and treatment of advanced cancer.

piRNA mmu_piR_037459 suppression alleviated the degeneration of chondrocyte and cartilage

OBJECTIVE

Osteoarthritis (OA) is a prevalent chronic degenerative joint ailment. Its primary pathological characteristics encompass degeneration of articular cartilage, inflammation of the synovium, and alterations in the subchondral bone proximate to the cartilage. Chondrocytes, as the sole cell type within articular cartilage, assume a crucial role in upholding the dynamic equilibrium between anabolic and catabolic processes within the extracellular matrix of articular cartilage. IL-1β stands as a pivotal inflammatory factor that instigates cartilage degeneration. piRNA, categorized as a subset of brief non-coding RNAs spanning nucleotide lengths of 26-31nt, assumes a significant regulatory role in cellular function.

METHODS

Small RNA sequencing and quantitative PCR (qPCR) were employed to investigate the impact of the inflammatory factor IL-1β on piRNA expression within chondrocytes. The regulation of mmu_piR_037459 expression in chondrocytes was achieved using piRNA mimics and inhibitors. Additionally, collagen II expression was assessed through both qPCR and Western blot analysis. Chondrocyte apoptosis was evaluated via flow cytometry and clonogenesis assays. To assess the influence of mmu_piR_037459 on osteoarthritis, a mouse model of anterior cruciate ligament transection (ACLT) was established. Furthermore, the regulatory effect of mmu_piR_037459 on USP7 was investigated using bioinformatics and a luciferase reporter gene assay.

RESULTS

mmu_piR_037459 inhibited the expression of collagen II in chondrocytes, inhibited the proliferation of chondrocytes, and promoted the apoptosis of chondrocytes. mmu_piR_037459 affected the function of chondrocytes by regulating the expression of USP7. Inhibition of mmu_piR_037459 expression could promote chondrocyte proliferation, inhibit chondrocyte apoptosis, and alleviate the degeneration of OA cartilage.

CONCLUSIONS

This study suggests that mmu_piR_037459 maybe a new therapeutic targets and strategies for the treatment of OA.

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.

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.

Novel roles of PIWI proteins and PIWI-interacting RNAs in human health and diseases

Non-coding RNA has aroused great research interest recently, they play a wide range of biological functions, such as regulating cell cycle, cell proliferation, and intracellular substance metabolism. Piwi-interacting RNAs (piRNAs) are emerging small non-coding RNAs that are 24-31 nucleotides in length. Previous studies on piRNAs were mainly limited to evaluating the binding to the PIWI protein family to play the biological role. However, recent studies have shed more lights on piRNA functions; aberrant piRNAs play unique roles in many human diseases, including diverse lethal cancers. Therefore, understanding the mechanism of piRNAs expression and the specific functional roles of piRNAs in human diseases is crucial for developing its clinical applications. Presently, research on piRNAs mainly focuses on their cancer-specific functions but lacks investigation of their expressions and epigenetic modifications. This review discusses piRNA's biogenesis and functional roles and the recent progress of functions of piRNA/PIWI protein complexes in human diseases. Video Abstract.

Relationship between PIWIL1 gene polymorphisms and epithelial ovarian cancer susceptibility among southern Chinese woman: a three-center case-control study

OBJECTIVE

To investigate the potential correlation between piwi-like RNA-mediated gene silencing 1 (PIWIL1) polymorphisms and susceptibility to epithelial ovarian cancer (EOC).

METHODS

A case-control study was conducted to evaluate the susceptibility of EOC using multinomial logistic regression analysis. The study analyzed the relationship between five functional single nucleotide polymorphisms (SNPs) in the PIWIL1 gene and EOC risk. Genotyping of 288 cases and 361 healthy samples from South China was identified using a TaqMan assay. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to estimate the relationship between the five selected SNPs and EOC susceptibility.

RESULTS

Among the five SNPs analyzed, the rs10848087 G > A and rs7957349 G > C variants significantly increased the susceptibility of EOC, rs10773771 C > T was associated with a decreased risk of EOC, while the rs35997018 and rs1106042 variants were not in Hardy-Weinberg equilibrium (p < 0.05). The rs10848087 G > A was significantly associated with increased risk of EOC in individuals with metastasis, FIGO stage I and III, low and high pathological grade, tumor numbers ≤ 3 and > 3, tumor size > 3 cm and ≤ 3 cm, pregnant more than 3 times, pre-menopausal status, and strong positive expression of ER (estrogen receptor), PR (progesterone receptor), PAX8 (paired-box 8), wild-type p53 (tumor protein 53), WT1 (Wilm's tumor gene), P16 (cyclin-dependent kinase inhibitor 2A). In addition, rs10848087 G > A enhanced the EOC risk of cases with negative/mild positive expression of wild p53 and Ki67, and with or without mutant p53 expression. The rs7957349 G > C variant was linked to an increased risk of EOC in subgroups with certain characteristics, including age equal or less than 53 years, metastasis, clinical stage I, low pathological grade, tumor number, tumor size, pregnant times, post-menopause, pre-menopause, and strong positive expression of wild p53 and Ki67 (Antigen identified by monoclonal antibody Ki-67), as well as without mutant p53 expression. The rs10773771 CT/TT alleles were identified to have a protective effect on EOC in women aged 53 years or older, as well as in cases with metastasis, advanced clinical stage, high pathological grade, multiple tumors, tumor size equal to or less than 3 cm, history of pregnancy, post-menopausal status, and strong positive expression of ER, PR, wild-type p53, PAX8, WT1, P16, and Ki67. Furthermore, rs10773771 CT/TT also showed a protective effect in patients with negative or mildly positive expression of PR, PAX8, wild-type p53, WT1, and P16, as well as positive expression of mutant p53. Compared to the reference haplotype GCG, individuals harboring haplotypes GTG were found to have a significantly decreased susceptibility to EOC. PIWIL1 was significantly expressed in the thyroid, pituitary, and adrenal glands with rs7957349 CC alleles.

CONCLUSIONS

PIWIL1 rs10848087 and rs7957349 were associated with increased risk of EOC, while rs10773771 may have a protective effect against EOC. These genetic variants may serve as potential biomarkers for EOC susceptibility in the South China population.

LSTM4piRNA: Efficient piRNA Detection in Large-Scale Genome Databases Using a Deep Learning-Based LSTM Network

Piwi-interacting RNAs (piRNAs) are a new class of small, non-coding RNAs, crucial in the regulation of gene expression. Recent research has revealed links between piRNAs, viral defense mechanisms, and certain human cancers. Due to their clinical potential, there is a great interest in identifying piRNAs from large genome databases through efficient computational methods. However, piRNAs lack conserved structure and sequence homology across species, which makes piRNA detection challenging. Current detection algorithms heavily rely on manually crafted features, which may overlook or improperly use certain features. Furthermore, there is a lack of suitable computational tools for analyzing large-scale databases and accurately identifying piRNAs. To address these issues, we propose LSTM4piRNA, a highly efficient deep learning-based method for predicting piRNAs in large-scale genome databases. LSTM4piRNA utilizes a compact LSTM network that can effectively analyze RNA sequences from extensive datasets to detect piRNAs. It can automatically learn the dependencies among RNA sequences, and regularization is further integrated to reduce the generalization error. Comprehensive performance evaluations based on piRNAs from the piRBase database demonstrate that LSTM4piRNA outperforms current advanced methods and is well-suited for analysis with large-scale databases.

Insights in piRNA targeting rules

PIWI-interacting RNAs (piRNAs) play an important role in the defense against transposons in the germline and stem cells of animals. To what extent other transcripts are also regulated by piRNAs is an ongoing topic of debate. The amount of sequence complementarity between piRNA and target that is required for effective downregulation of the targeted transcript is guiding in this discussion. Over the years, various methods have been applied to infer targeting requirements from the collections of piRNAs and potential target transcripts, and recent structural studies of the PIWI proteins have provided an additional perspective. In this review, I summarize the findings from these studies and propose a set of requirements that can be used to predict targets to the best of our current abilities. This article is categorized under: Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA-Based Catalysis > RNA-Mediated Cleavage.

PiRNA in Cardiovascular Disease: Focus on Cardiac Remodeling and Cardiac Protection

Cardiovascular diseases (CVDs) are common causes of death, which take about 18.6 million lives worldwide every year. Currently, exploring strategies that delay ventricular remodeling, reduce cardiomyocyte death, and promote cardiomyocyte regeneration has been the hotspot and difficulty of the ischemic heart disease (IHD) research field. Previous studies indicate that piwi-interacting RNA (piRNA) plays a vital role in the occurrence and development of cardiac remodeling and may offer novel therapeutic strategies for cardiac repair. The best-known biological function of piRNA is to silence transposons in cells. In the cardiovascular system, piRNA is known to participate in cardiac progenitor cell proliferation, AKT pathway regulation, and cardiac remodeling and decompensation. In this review, we systematically discuss the research progress on piRNA in CVDs, especially the mechanism of cardiac remodeling and the potential functions in cardiac protection, which provides new insights for the progress and treatment of cardiovascular diseases. Piwi-interacting RNA (piRNA) is one of the noncoding RNAs, with the best -known biological function to silence transposons in cells. Now piRNA is found to participate in cardiac progenitor cell proliferation, AKT pathway regulation, cardiac remodeling and decompensation, which implies the potential of piRNA in the diagnosis and treatment of cardiovascular diseases. Over expression of piRNA could promote cardiac apoptosis and cardiac hypertrophy, thus targeted therapy which inhibits expression of associated piRNA may reduce cardiac remodeling and reduce inflammation caused by necrotic cardiomyocytes. PiRNA is also speculated to participate in the proliferation of cardiac progenitor cells, implying the potential to induce cardiac regeneration th erapy, which provides new insights for treatment of cardiovascular diseases. At present, the treatment strategy of cardiac remodeling emphasizes the control of risk factors, prevention of disease progression and individualized treatment. With further studies in mechanism of piRNA, potential therapies above may come true and more therapies in cardiovascular diseases may be found.

Emerging roles of noncoding RNAs in human cancers

Studies have found that RNA encoding proteins only account for a small part of the total number, most RNA is non-coding RNA, and non-coding RNA may affect the occurrence and development of human cancers by affecting gene expression, therefore play an important role in human pathology. At present, ncRNAs studied include miRNA, circRNA, lncRNA, piRNA, and snoRNA, etc. After decades of research, the basic role of these ncRNAs in many cancers has been clear. As far as we know, the role of miRNAs in cancer is one of the hottest research directions, however, it is also found that the imbalance of ncRNAs will affect the occurrence of gastric cancer, breast cancer, lung cancer, meanwhile, it may also affect the prognosis of these cancers. Therefore, the study of ncRNAs in cancers may help to find new cancer diagnostic and treatment methods. Here, we reviewed the biosynthesis and characteristics of miRNA, cricRNA, and lncRNA etc., their roles in human cancers, as well as the mechanism through which these ncRNAs affect human cancers.

The Human Gastric Juice: A Promising Source for Gastric Cancer Biomarkers

Gastric cancer (GC) is a major public health problem worldwide, with high mortality rates due to late diagnosis and limited treatment options. Biomarker research is essential to improve the early detection of GC. Technological advances and research methodologies have improved diagnostic tools, identifying several potential biomarkers for GC, including microRNA, DNA methylation markers, and protein-based biomarkers. Although most studies have focused on identifying biomarkers in biofluids, the low specificity of these markers has limited their use in clinical practice. This is because many cancers share similar alterations and biomarkers, so obtaining them from the site of disease origin could yield more specific results. As a result, recent research efforts have shifted towards exploring gastric juice (GJ) as an alternative source for biomarker identification. Since GJ is a waste product during a gastroscopic examination, it could provide a "liquid biopsy" enriched with disease-specific biomarkers generated directly at the damaged site. Furthermore, as it contains secretions from the stomach lining, it could reflect changes associated with the developmental stage of GC. This narrative review describes some potential biomarkers for gastric cancer screening identified in gastric juice.

The epigenetic regulatory mechanism of PIWI/piRNAs in human cancers

PIWI proteins have a strong correlation with PIWI-interacting RNAs (piRNAs), which are significant in development and reproduction of organisms. Recently, emerging evidences have indicated that apart from the reproductive function, PIWI/piRNAs with abnormal expression, also involve greatly in varieties of human cancers. Moreover, human PIWI proteins are usually expressed only in germ cells and hardly in somatic cells, so the abnormal expression of PIWI proteins in different types of cancer offer a promising opportunity for precision medicine. In this review, we discussed current researches about the biogenesis of piRNA, its epigenetic regulatory mechanisms in human cancers, such as N6-methyladenosine (m⁶A) methylation, histone modifications, DNA methylation and RNA interference, providing novel insights into the markers for clinical diagnosis, treatment and prognosis in human cancers.

Piwi maintains homeostasis in the Drosophila adult intestine

PIWI genes are well known for their germline but not somatic functions. Here, we report the function of the Drosophila piwi gene in the adult gut, where intestinal stem cells (ISCs) produce enteroendocrine cells and enteroblasts that generate enterocytes. We show that piwi is expressed in ISCs and enteroblasts. Piwi deficiency reduced ISC number, compromised enteroblasts maintenance, and induced apoptosis in enterocytes, but did not affect ISC proliferation and its differentiation to enteroendocrine cells. In addition, deficiency of zygotic but not maternal piwi mildly de-silenced several retrotransposons in the adult gut. Importantly, either piwi mutations or piwi knockdown specifically in ISCs and enteroblasts shortened the Drosophila lifespan, indicating that intestinal piwi contributes to longevity. Finally, our mRNA sequencing data implied that Piwi may achieve its intestinal function by regulating diverse molecular processes involved in metabolism and oxidation-reduction reaction.

Emerging roles and functional mechanisms of PIWI-interacting RNAs

PIWI-interacting RNAs (piRNAs) are a class of small non-coding RNAs that associate with proteins of the PIWI clade of the Argonaute family. First identified in animal germ line cells, piRNAs have essential roles in germ line development. The first function of PIWI-piRNA complexes to be described was the silencing of transposable elements, which is crucial for maintaining the integrity of the germ line genome. Later studies provided new insights into the functions of PIWI-piRNA complexes by demonstrating that they regulate protein-coding genes. Recent studies of piRNA biology, including in new model organisms such as golden hamsters, have deepened our understanding of both piRNA biogenesis and piRNA function. In this Review, we discuss the most recent advances in our understanding of piRNA biogenesis, the molecular mechanisms of piRNA function and the emerging roles of piRNAs in germ line development mainly in flies and mice, and in infertility, cancer and neurological diseases in humans.

Exosomal hsa-piR1089 promotes proliferation and migration in neuroblastoma via targeting KEAP1

Neuroblastoma (NB) is a sympathetic nervous system tumor and one of the most common pediatric, extra-cranial, solid tumors, especially in early childhood. Its expression is heterogeneous and shows a unique clinical and prognostic feature. Due to its insidious onset, most diagnoses are accompanied by metastasis, making patient prognoses extremely poor. Novel biomarkers are urgently needed for easy diagnosis, metastasis detection, and investigation of potential mechanisms regulating NB tumor progression. Recent research highlights that circulating tumor markers could be used to diagnose and monitor prognosis in various tumors. Among them, exosomal genetic material has attracted much attention because of its tumor-secreted specificity and unique mechanism of action. In this study, we used next-generation sequencing to study PIWI-interacting RNAs (piRNAs) in exosomes derived from NB patient plasma. We found higher human piRNA 1089 (hsa-piR-1089) levels in exosomes from NB patients than from normal controls. Our receiver operating characteristic (ROC) curve analyses showed that hsa-piR-1089 had high diagnostic sensitivity and specificity. We also found that high hsa-piR-1089 expression in NB tumor tissues was associated with a high-risk Children's Oncology Group classification and metastasis. Our in vitro experiments showed that exosomal hsa-piR-1089 promoted NB cell proliferation and migration by inhibiting Kelch-like ECH-associated protein 1 (KEAP1) expression. Moreover, low KEAP1 expression was associated with NB progression in clinical samples. In conclusion, our data indicate that blood-borne exosomal hsa-piR-1089 is a diagnostic marker for NB and assessing metastasis. Our study provides a quick, simple, and noninvasive diagnostic method for NB and contributes to developing new treatment strategies.

A combined miRNA-piRNA signature in the serum and urine of rabbits infected with Toxoplasma gondii oocysts

BACKGROUND

Increasing evidence has shown that non-coding RNA (ncRNA) molecules play fundamental roles in cells, and many are stable in body fluids as circulating RNAs. Study on these ncRNAs will provide insights into toxoplasmosis pathophysiology and/or help reveal diagnostic biomarkers.

METHODS

We performed a high-throughput RNA-Seq study to comprehensively profile the microRNAs (miRNAs) and PIWI-interacting RNAs (piRNAs) in rabbit serum and urine after infection with Toxoplasma gondii oocysts during the whole infection process.

RESULTS

Total RNA extracted from serum and urine samples of acutely infected [8 days post-infection (DPI)], chronically infected (70 DPI) and uninfected rabbits were subjected to genome-wide small RNA sequencing. We identified 2089 miRNAs and 2224 novel piRNAs from the rabbit sera associated with T. gondii infection. Meanwhile, a total of 518 miRNAs and 4182 novel piRNAs were identified in the rabbit urine associated with T. gondii infection. Of these identified small ncRNAs, 1178 and 1317 serum miRNAs and 311 and 294 urine miRNAs were identified as differentially expressed (DE) miRNAs in the acute and chronic stages of infections, respectively. A total of 1748 and 1814 serum piRNAs and 597 and 708 urine piRNAs were found in the acute and chronic infection stages, respectively. Of these dysregulated ncRNAs, a total of 88 common DE miRNAs and 120 DE novel piRNAs were found in both serum and urine samples of infected rabbits.

CONCLUSIONS

These findings provide valuable data for revealing the physiology of herbivore toxoplasmosis caused by oocyst infection. Circulating ncRNAs identified in this study are potential novel diagnostic biomarkers for the detection/diagnosis of toxoplasmosis in herbivorous animals.

Abdominal Computed Tomography Enhanced Image Features under an Automatic Segmentation Algorithm in Identification of Gastric Cancer and Gastric Lymphoma

To analyze the application value of CT-enhanced scanning based on artificial intelligence algorithm in the diagnosis of gastric cancer and gastric lymphoma, the CT images of 80 patients with Borrmann type IV gastric cancer or primary gastric lymphoma diagnosed by endoscopic pathology were retrospectively collected. Meanwhile, a lymph node recognition algorithm based on OTSU threshold segmentation was proposed for CT image processing. The results showed that the missed diagnosis rate of suspected lymph nodes and the missed lymph node detection rate of this algorithm were substantially lower than those of other algorithms (P < 0.05). The probability of gastric wall motility disappearance, perigastric fat infiltration, and type A enhancement pattern in the Borrmann type IV gastric cancer group was higher than that in the gastric lymphoma group, with remarkable differences (P < 0.05). There was no remarkable difference between the Borrmann type IV gastric cancer group and the gastric lymphoma group in the probability of swollen lymph nodes under the renal hilum (P > 0.05). In addition, 5the sensitivity (83.17%), specificity (95.52%), and accuracy (93.08%) of the combined detection of the three CT signs (stomach wall motility, perigastric fat infiltration, and enhancement mode) were substantially improved compared with those of a single sign (P < 0.05). To sum up, the lymph node recognition algorithm based on OTSU threshold segmentation had better performance in detecting gastric lymph nodes than traditional algorithms. The CT image characteristics of gastric wall motility, perigastric fat infiltration, and enhancement pattern based on artificial intelligence algorithms were effective indicators for distinguishing gastric cancer and gastric lymphoma.

MiR-762 regulates the activation of PI3K/AKT and Hippo pathways involved in the development of gastric cancer by targeting LZTS1

OBJECTIVE

MiR-762 has been confirmed as a tumor promoter in multiple tumors, while few reports illustrate its role in gastric cancer (GC). Thus, this research aimed to investigate whether miR-762 is involved in GC development.

METHODS

MiR-762 expression in the tumor tissues from GC patients and GC cell lines was analyzed by qRT-PCR. The assays including CCK-8, transwell, and flow cytometry were performed to reveal the functions of miR-762 in GC. The target genes of miR-762 were searched by online databases, and then were verified by dual-luciferase reporter assay. Western blot was performed to investigate the activation of PI3K/AKT and Hippo pathways in GC.

RESULTS

MiR-762 was aberrantly upregulated in the tumor tissues and cell lines, and miR-762 silencing could effectively reduce the viability and promote apoptosis of GC cell lines. The study identified LZTS1 as a target gene of miR-762. It was also found that the effects of miR-762 on GC cells could be reversed by LZTS1, and miR-762 could upregulate the activation of the PI3K/AKT pathway but inhibit the Hippo pathway by targeting LZTS1.

CONCLUSION

MiR-762 activates PI3K/AKT and suppresses Hippo pathways to boost GC proliferation and invasion by targeting LZTS1.

PIWI-interacting RNAs in human diseases: databases and computational models

PIWI-interacting RNAs (piRNAs) are short 21-35 nucleotide molecules that comprise the largest class of non-coding RNAs and found in a large diversity of species including yeast, worms, flies, plants and mammals including humans. The most well-understood function of piRNAs is to monitor and protect the genome from transposons particularly in germline cells. Recent data suggest that piRNAs may have additional functions in somatic cells although they are expressed there in far lower abundance. Compared with microRNAs (miRNAs), piRNAs have more limited bioinformatics resources available. This review collates 39 piRNA specific and non-specific databases and bioinformatics resources, describes and compares their utility and attributes and provides an overview of their place in the field. In addition, we review 33 computational models based upon function: piRNA prediction, transposon element and mRNA-related piRNA prediction, cluster prediction, signature detection, target prediction and disease association. Based on the collection of databases and computational models, we identify trends and potential gaps in tool development. We further analyze the breadth and depth of piRNA data available in public sources, their contribution to specific human diseases, particularly in cancer and neurodegenerative conditions, and highlight a few specific piRNAs that appear to be associated with these diseases. This briefing presents the most recent and comprehensive mapping of piRNA bioinformatics resources including databases, models and tools for disease associations to date. Such a mapping should facilitate and stimulate further research on piRNAs.

Novel piRNA Regulates PIWIL1 to Modulate the Behavior of Placental Trophoblast Cells and Participates in Preeclampsia

Objectives

This study is aimed at investigating the role of PIWIL1/piRNA in the development of preeclampsia.

Methods

High-throughput sequencing was performed in 5 preeclampsia and 5 normal placentas to get a piRNA expression profile. WGCNA network was constructed to find hub piRNAs. Through target gene prediction and protein interaction network analysis, we found the potential relationship between the key genes and PIWIL1. Subsequently, we detected the expression of PIWIL1 in 35 preeclampsia and 29 normal placental tissues. Overexpression and inhibition of PIWIL1 in HTR-8/SVneo trophoblast cells were achieved by transfecting an overexpression vector and siRNAs, respectively. Cell proliferation, apoptosis, and invasion were assessed using CCK-8, flow cytometric, and transwell assays, respectively.

Results

It was found that a total of three piRNAs were upregulated in preeclampsia (pir-hsa-1256314, uniq_271431, and uniq_277797). And two target genes with the highest connectivity (FXR1 and DDX6) both pointed to PIWIL1. PIWIL1 expression was significantly lower in preeclampsia. In vitro studies linked PIWIL1 expression to trophoblast overgrowth. Overexpression of PIWIL1 remarkably promoted cell proliferation and invasion and inhibited apoptosis of HTR-8/SVneo cells and vice versa.

Conclusions

PIWIL1/piRNA may be involved in the pathogenesis of preeclampsia by inhibiting the proliferation and invasion and promoting the apoptosis of placental trophoblasts. This study was registered with the China Clinical Trials Registry (http://www.clinicaltrials.gov): registration number ChiCTR1900027479.

Noncanonical Functions of PIWIL1/piRNAs in animal male germ cells and human diseases

PIWI proteins and PIWI-interacting RNAs (piRNAs) are specifically expressed in animal germlines and play essential roles during gametogenesis in animals. The primary function of PIWI/piRNAs is known to silence transposable elements for protecting genome integrity in animal germlines, while their roles beyond silencing transposons are also documented by us and others. In particular, we show that mouse PIWIL1 (MIWI)/piRNAs play a dual role in regulating protein-coding genes in mouse spermatids through interacting with different protein factors in a developmental stage-dependent manner, including translationally activating a subset of ARE-containing mRNAs in round spermatids and inducing massive mRNA degradation in late spermatids. We further show that MIWI is eliminated through the ubiquitin-26S proteasome pathway during late spermiogenesis. By exploring the biological function of MIWI ubiquitination by APC/C, we identified ubiquitination-deficient mutations in human PIWIL1 of infertile men and further established their causative role in male infertility in mouse model, supporting PIWIL1 as a human male infertility-relevant gene. Additionally, we reported that PIWIL1, aberrantly induced in human tumors, functions as an oncoprotein in a piRNA-independent manner in cancer cells. In the current review, we summarize our latest findings regarding the roles and mechanisms of PIWIL1 and piRNAs in mouse spermatids and human diseases, and discuss the related works in the field.

PUMILIO proteins promote colorectal cancer growth via suppressing p21

PUMILIO (PUM) proteins belong to the highly conserved PUF family post-transcriptional regulators involved in diverse biological processes. However, their function in carcinogenesis remains under-explored. Here, we report that Pum1 and Pum2 display increased expression in human colorectal cancer (CRC). Intestine-specific knockout of Pum1 and Pum2 in mice significantly inhibits the progression of colitis-associated cancer in the AOM/DSS model. Knockout or knockdown of Pum1 and/or Pum2 in human CRC cells result in a significant decrease in the tumorigenicity and delayed G1/S transition. We identify p21/Cdkn1a as a direct target of PUM1. Abrogation of the PUM1 binding site in the p21 mRNA also results in decreased cancer cell growth and delayed G1/S transition. Furthermore, intravenous injection of nanoparticle-encapsulated anti-Pum1 and Pum2 siRNAs reduces colorectal tumor growth in murine orthotopic colon cancer models. These findings reveal the requirement of PUM proteins for CRC progression and their potential as therapeutic targets.

RNA binding proteins can contribute to colorectal cancer (CRC) initiation and development. Here the authors show that PUMILIO proteins, PUM1 and PUM2 contribute to CRC growth by inhibiting p21 expression.

piRNAs and PIWI Proteins as Diagnostic and Prognostic Markers of Genitourinary Cancers

piRNAs (PIWI-interacting RNAs) are small non-coding RNAs capable of regulation of transposon and gene expression. piRNAs utilise multiple mechanisms to affect gene expression, which makes them potentially more powerful regulators than microRNAs. The mechanisms by which piRNAs regulate transposon and gene expression include DNA methylation, histone modifications, and mRNA degradation. Genitourinary cancers (GC) are a large group of neoplasms that differ by their incidence, clinical course, biology, and prognosis for patients. Regardless of the GC type, metastatic disease remains a key therapeutic challenge, largely affecting patients’ survival rates. Recent studies indicate that piRNAs could serve as potentially useful biomarkers allowing for early cancer detection and therapeutic interventions at the stage of non-advanced tumour, improving patient’s outcomes. Furthermore, studies in prostate cancer show that piRNAs contribute to cancer progression by affecting key oncogenic pathways such as PI3K/AKT. Here, we discuss recent findings on biogenesis, mechanisms of action and the role of piRNAs and the associated PIWI proteins in GC. We also present tools that may be useful for studies on the functioning of piRNAs in cancers.

HIWI2 induces G2/M cell cycle arrest and apoptosis in human fibrosarcoma via the ROS/DNA damage/p53 axis

AIMS

Piwi, like RNA-mediated gene silencing 4 (PIWIL4) or HIWI2, are seen deregulated in human cancers and possibly play critical roles in tumorigenesis. It is unknown what role HIWI2 plays in the regulation of fibrosarcoma, an early metastatic lethal type of soft tissue sarcoma (STS). The present study aimed to investigate the role of HIWI2 in the tumorigenesis of fibrosarcoma.

MAIN METHODS

The expression of HIWI2 in HT1080 fibrosarcoma cells was determined by qRT-PCR and western blotting. The MTT assay, colony formation assay, cell cycle, and PE-AnnexinV/7AAD apoptosis assay using flow cytometry, DNA laddering assay, comet assay, and γH2AX accumulation assay were performed to study the effect of HIWI2 overexpression in HT1080 cells. Further, the effect of silencing of HIWI2 was determined by cell viability assay, transwell migration, and invasion assay.

KEY FINDINGS

HIWI2 is under-expressed in STS cell lines and tissues, which is associated with poor disease-free survival, disease-specific survival, and progression-free survival of the patients. Overexpression of HIWI2 in HT1080 cells causes DNA damage by increasing intracellular ROS by inhibiting the expression of antioxidant genes (SOD1, SOD2, GPX1, GPX4, and CAT). Furthermore, an increase in H2AX phosphorylation was observed, which activates p53 that promotes p21 expression and caspase-3 activation, leading to G2/M phase cell cycle arrest and apoptosis. HIWI2 silencing, on the contrary, promotes cell growth, migration, and invasion by activating MMP2 and MMP9.

SIGNIFICANCE

These results are the first to show that HIWI2 acts as a tumor suppressor in fibrosarcoma by modulating the ROS/DNA damage/p53 pathway.

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.

Characterization of novel CTNNB1 mutation in Craniopharyngioma by whole-genome sequencing

Background

Craniopharyngioma (CP) is rare histologically benign but clinically challenging tumor because of its intimate relationship with the critical structure in the central brain. CP can be divided into two major histologic subtypes: adamantinomatous-type CP (ACP) and papillary-type CP (PCP). Although some genetic aberrations for both categories have been revealed in previous studies, the complete spectrum of genetic changes of this tumor remains unknown.

Methods

In this study, we conducted whole genome sequencing (WGS) on twenty-six CPs including 16 ACPs and 10 PCPs together with their matched blood samples. Somatic variants (SNVs, InDels, SVs and CNVs) were identified and mutational signatures were characterized for each patient. We investigated the impact of a novel CTNNB1 mutant on its protein stability, ubiquitination and Wnt pathway activity. Cell proliferation ability of the CTNNB1 mutant in ACP primary cells was additionally analyzed by CCK8 and colony formation assays.

Results

We found that CPs had showed less complexity with fewer somatic mutations compared with malignant tumors. Moreover, mutations in CTNNB1 (68.75% of ACP) and BRAF V600E (70.00% of PCP) are mutually exclusive in ACP and PCP, consolidating that the driving roles of these two genes in ACP and PCP, respectively. A novel mutation in the exon 3 of CTNNB1 which compromised both a transversion and in-frame deletion was identified in ACP. This mutation was experimentally validated to confer β-catenin increased stability by inhibiting its ubiquitination, thus activating Wnt-signaling pathway and promoting cell proliferation.

Conclusions

Whole genome landscape for CP was revealed by WGS analysis, and a novel mutation in the exon 3 of CTNNB1 was identified. This novel mutation activates Wnt-signaling pathway through increasing the stability of β-catenin. Our findings provided us with more comprehensive insight into the spectrum of genetic alterations in CP.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-021-01468-7.

PIWI interacting RNAs perspectives: a new avenues in future cancer investigations

As a currently identified small non-coding RNAs (ncRNAs) category, the PIWI-interacting RNAs (piRNAs) are crucial mediators of cell biology. The human genome comprises over 30.000 piRNA genes. Although considered a new field in cancer research, the piRNA pathway is shown by the existing evidence as an active pathway in a variety of different types of cancers with critical impacts on main aspects of cancer progression. Among the regulatory molecules that contribute to maintaining the dynamics of cancer cells, the P-element Induced WImpy testis (PIWI) proteins and piRNAs, as new players, have not been broadly studied so far. Therefore, the identification of cancer-related piRNAs and the assessment of target genes of piRNAs may lead to better cancer prevention and therapy strategies. This review articleaimed to highlight the role and function of piRNAs based on existing data. Understanding the role of piRNA in cancer may provide perspectives on their applications as particular biomarker signature in diagnosis in early stage, prognosis and therapeutic strategies.

Transposable elements and Piwi‑interacting RNAs in hemato‑oncology with a focus on myelodysplastic syndrome (Review)

Our current understanding of hematopoietic stem cell differentiation and the abnormalities that lead to leukemogenesis originates from the accumulation of knowledge regarding protein‑coding genes. However, the possible impact of transposable element (TE) mobilization and the expression of P‑element‑induced WImpy testis‑interacting RNAs (piRNAs) on leukemogenesis has been beyond the scope of scientific interest to date. The expression profiles of these molecules and their importance for human health have only been characterized recently due to the rapid progress of high‑throughput sequencing technology development. In the present review, current knowledge on the expression profile and function of TEs and piRNAs was summarized, with specific focus on their reported involvement in leukemogenesis and pathogenesis of myelodysplastic syndrome.

Segmentation of Gastric Computerized Tomography Images under Intelligent Algorithms in Evaluation of Efficacy of Decitabine Combined with Paclitaxel in Treatment of Gastric Cancer

To analyze the evaluation of artificial intelligence algorithm combined with gastric computed tomography (CT) image in clinical chemotherapy for advanced gastric cancer, 112 patients with advanced gastric cancer were selected as the research object. Among which, 56 patients in the experimental group received paclitaxel (PTX) combined with decitabine sequential decitabine maintenance therapy. Fifty-six patients in the control group received first-line treatment with decitabine combined with cisplatin. The image segmentation algorithm based on fast interactive dictionary selection was used to process gastric CT images. Complete response (CR), partial response (PR), stable disease (SD), progressive disease (PD), response rate (RR), disease control rate (DCR), and overall survival (OS) after treatment were recorded. The true-positive rate (TPR) and coincidence ratio (CR) of the proposed algorithm for image segmentation were significantly higher than those of the mean shift algorithm and the iCoseg algorithm. The mean edge distance (MED) and edge distance variance (EDV) were significantly lower than the mean shift algorithm and the iCoseg algorithm, and the differences were considerable (P < 0.05). The number of CR (5 cases), PR (13 cases), RR (18 cases), and DCR (44 cases) in the experimental group was significantly higher than that in the control group, while the number of PD (12 cases) was significantly lower than that in the control group (P < 0.05). The number of patients complicated with hematological toxicity, leucopenia, thrombocytopenia, and digestive tract reaction in the experimental group was less than that in the control group (P < 0.05). From the comparison of long-term efficacy, the survival rate of patients in both groups showed a decreasing trend within 24 months, but the decreasing trend of survival rate of patients in the experimental group was better than that in the control group. In short, the proposed algorithm had better segmentation performance than traditional algorithms. Compared with first-line treatment with decitabine and cisplatin, PTX in combination with decitabine sequential citabine maintenance regimens had better disease control rates, lower toxicity, and more effective improvements in patient quality of life and longer survival in patients with advanced gastric cancer.

An essential role for the piRNA pathway in regulating the ribosomal RNA pool in C. elegans

Piwi-interacting RNAs (piRNAs) are RNA effectors with key roles in maintaining genome integrity and promoting fertility in metazoans. In Caenorhabditis elegans loss of piRNAs leads to a transgenerational sterility phenotype. The plethora of piRNAs and their ability to silence transcripts with imperfect complementarity have raised several (non-exclusive) models for the underlying drivers of sterility. Here, we report the extranuclear and transferable nature of the sterility driver, its suppression via mutations disrupting the endogenous RNAi and poly-uridylation machinery, and copy-number amplification at the ribosomal DNA locus. In piRNA-deficient animals, several small interfering RNA (siRNA) populations become increasingly overabundant in the generations preceding loss of germline function, including ribosomal siRNAs (risiRNAs). A concomitant increase in uridylated sense rRNA fragments suggests that poly-uridylation may potentiate RNAi-mediated gene silencing of rRNAs. We conclude that loss of the piRNA machinery allows for unchecked amplification of siRNA populations, originating from abundant highly structured RNAs, to deleterious levels.

The Regulation and Role of piRNAs and PIWI Proteins in Cancer

P-element-induced wimpy testis (PIWI)-interacting RNAs (piRNAs) are regulatory small non-coding RNAs that participate in transposon inactivation, chromatin regulation, and endogenous gene regulation. Numerous genetic and epigenetic factors regulate cell proliferation and tumor metastasis. PIWI proteins and piRNAs have been revealed to function in regulating upstream or downstream of oncogenes or tumor-suppressor genes in cancer tissues. In the present review, we summarize major recent findings in uncovering the regulation and role of PIWI proteins and piRNAs in tumorigenesis and highlight some of the promising applications of specific piRNAs in cancer therapeutics and as cancer biomarkers.

Piwi-Interacting RNAs: A New Class of Regulator in Human Breast Cancer

P-element-induced wimpy testis (Piwi)-interacting RNAs (piRNAs) are a class of germline-enriched small non-coding RNA that associate with Piwi family proteins and mostly induce transposon silencing and epigenetic regulation. Emerging evidence indicated the aberrant expression of Piwil proteins and associated piRNAs in multiple types of human cancer including breast cancer. Although the majority of piRNAs in breast cancer remains unclear of the function mainly due to the variety of regulatory mechanisms, the potential of piRNAs serving as biomarkers for cancer diagnosis and prognosis or therapeutic targets for cancer treatment has been demonstrated by in vitro and in vivo studies. Herein we summarized the research progress of oncogenic or tumor suppressing piRNAs and their regulatory mechanisms in regulating human breast cancer, including piR-021285, piR-823, piR-932, piR-36712, piR-016658, piR-016975 and piR-4987. The challenges and perspectives of piRNAs in the field of human cancer were discussed.

The biogenesis and biological function of PIWI-interacting RNA in cancer

Small non-coding RNAs (ncRNAs) are vital regulators of biological activities, and aberrant levels of small ncRNAs are commonly found in precancerous lesions and cancer. PIWI-interacting RNAs (piRNAs) are a novel type of small ncRNA initially discovered in germ cells that have a specific length (24-31 nucleotides), bind to PIWI proteins, and show 2'-O-methyl modification at the 3'-end. Numerous studies have revealed that piRNAs can play important roles in tumorigenesis via multiple biological regulatory mechanisms, including silencing transcriptional and posttranscriptional gene processes and accelerating multiprotein interactions. piRNAs are emerging players in the malignant transformation of normal cells and participate in the regulation of cancer hallmarks. Most of the specific cancer hallmarks regulated by piRNAs are involved in sustaining proliferative signaling, resistance to cell death or apoptosis, and activation of invasion and metastasis. Additionally, piRNAs have been used as biomarkers for cancer diagnosis and prognosis and have great potential for clinical utility. However, research on the underlying mechanisms of piRNAs in cancer is limited. Here, we systematically reviewed recent advances in the biogenesis and biological functions of piRNAs and relevant bioinformatics databases with the aim of providing insights into cancer diagnosis and clinical applications. We also focused on some cancer hallmarks rarely reported to be related to piRNAs, which can promote in-depth research of piRNAs in molecular biology and facilitate their clinical translation into cancer treatment.

Circulating SNORD57 rather than piR-54265 is a promising biomarker for colorectal cancer: common pitfalls in the study of somatic piRNAs in cancer

There is increasing interest among cancer researchers in the study of Piwi-interacting RNAs (piRNAs), a group of small RNAs important for maintaining genome stability in the germline. Aberrant expression of piRNAs in cancer could imply an involvement of these regulatory RNAs in neoplastic transformation. On top of that, it could enable early cancer diagnosis based on RNA analysis in liquid biopsies, as piRNAs are not expected to widely circulate in the bloodstream of healthy individuals. Indeed, it has recently been shown that serum piR-54265 allows for excellent discrimination between colorectal cancer patients and healthy controls. However, we have also shown that most somatic piRNAs reported to date in mammals are actually fragments of other noncoding RNAs. Herein, we show that reports positioning piR-54265 as a noninvasive biomarker for colorectal cancer were actually measuring variations in the levels of a full-length (72 nt) small nucleolar RNA in serum. This should place a cautionary note for future research in somatic and cancer-specific piRNAs. We deeply encourage this line of research but discuss proper ways to identify somatic piRNAs without the interference of erroneous entries contained in piRNA databases. We also introduce the concept of miscellaneous-piRNAs (m-piRNAs) to distinguish between canonical piRNAs and other small RNAs circumstantially associated with PIWI proteins in somatic cells.

Hamster PIWI proteins bind to piRNAs with stage-specific size variations during oocyte maturation

In animal gonads, transposable elements are actively repressed to preserve genome integrity through the PIWI-interacting RNA (piRNA) pathway. In mice, piRNAs are abundantly expressed in male germ cells, and form effector complexes with three distinct PIWIs. The depletion of individual Piwi genes causes male-specific sterility with no discernible phenotype in female mice. Unlike mice, most other mammals have four PIWI genes, some of which are expressed in the ovary. Here, purification of PIWI complexes from oocytes of the golden hamster revealed that the size of the PIWIL1-associated piRNAs changed during oocyte maturation. In contrast, PIWIL3, an ovary-specific PIWI in most mammals, associates with short piRNAs only in metaphase II oocytes, which coincides with intense phosphorylation of the protein. An improved high-quality genome assembly and annotation revealed that PIWIL1- and PIWIL3-associated piRNAs appear to share the 5′-ends of common piRNA precursors and are mostly derived from unannotated sequences with a diminished contribution from TE-derived sequences, most of which correspond to endogenous retroviruses. Our findings show the complex and dynamic nature of biogenesis of piRNAs in hamster oocytes, and together with the new genome sequence generated, serve as the foundation for developing useful models to study the piRNA pathway in mammalian oocytes.

piRNAs as Modulators of Disease Pathogenesis

Advances in understanding disease pathogenesis correlates to modifications in gene expression within different tissues and organ systems. In depth knowledge about the dysregulation of gene expression profiles is fundamental to fully uncover mechanisms in disease development and changes in host homeostasis. The body of knowledge surrounding mammalian regulatory elements, specifically regulators of chromatin structure, transcriptional and translational activation, has considerably surged within the past decade. A set of key regulators whose function still needs to be fully elucidated are small non-coding RNAs (sncRNAs). Due to their broad range of unfolding functions in the regulation of gene expression during transcription and translation, sncRNAs are becoming vital to many cellular processes. Within the past decade, a novel class of sncRNAs called PIWI-interacting RNAs (piRNAs) have been implicated in various diseases, and understanding their complete function is of vital importance. Historically, piRNAs have been shown to be indispensable in germline integrity and stem cell development. Accumulating research evidence continue to reveal the many arms of piRNA function. Although piRNA function and biogenesis has been extensively studied in Drosophila, it is thought that they play similar roles in vertebrate species, including humans. Compounding evidence suggests that piRNAs encompass a wider functional range than small interfering RNAs (siRNAs) and microRNAs (miRNAs), which have been studied more in terms of cellular homeostasis and disease. This review aims to summarize contemporary knowledge regarding biogenesis, and homeostatic function of piRNAs and their emerging roles in the development of pathologies related to cardiomyopathies, cancer, and infectious diseases.

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.