piRNA-independent function of PIWIL1 as a co-activator for anaphase promoting complex/cyclosome to drive pancreatic cancer metastasis

Integration of multi-omics data to unveil the molecular landscape and role of piRNAs in early-onset colorectal cancer

BACKGROUND

The incidence of early-onset colorectal cancer (EOCRC) (< 50 years) has been steadily rising, with a parallel increase in metastatic and invasive cases. To elucidate the molecular mechanisms underlying this aggressive phenotype, we performed comprehensive multi-omics profiling to delineate the distinct features of EOCRC, with a focus on key drivers of metastatic and invasive potential.

METHODS

We initially characterized the genome, epigenome, and transcriptome of tumors from 515 (69 EOCRC and 446 late-onset CRC [LOCRC]) cases in The Cancer Genome Atlas. Key candidate molecules were further validated using RNA-seq and scRNA-seq data. Multi-omics profiling revealed PIWIL1/piRNA as a hallmark of EOCRC, with further validation through in vitro functional assays, transcriptomic profiling, and Kaplan-Meier survival analysis.

RESULTS

EOCRC demonstrated a mutational landscape similar to that of LOCRC, with comparable oncogenic driver mutations and somatic copy-number alterations. However, EOCRC exhibited a higher frequency of deletion in chromosomes 6, 15, and 19 regions, along with metabolic reprogramming favoring aerobic glycolysis and lipid metabolism. Integrative transcriptomic and DNA methylation analyses identified six EOCRC-specific molecules, including PIWIL1. Notably, PIWIL1 was mainly expressed in epithelial cells, with lower expression in EOCRC versus LOCRC. Its downstream piRNAs (FR019019, FR019089, and FR132045) were also downregulated in EOCRC. Functional experiments demonstrated that FR019089/FR019019 overexpression suppressed migration and invasion. Clinically, low FR019089 levels correlated with significantly shorter progression-free and overall survival in EOCRC patients. Additionally, downstream pathways of FR019089 and FR019019 overexpression were enriched in anti-cancer-related signaling pathways.

CONCLUSIONS

Our multi-omics approach yields novel insights into the molecular underpinnings of EOCRC and we characterize the role of PIWIL1-associated piRNAs in modulating EOCRC metastasis and invasion. FR019089 shows promise as a prognostic biomarker with potential clinical utility in the risk stratification and management of EOCRC patients.

Potentially diagnostic and prognostic roles of piRNAs/PIWIs in pancreatic cancer: A review

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy with limited early diagnostic methods and therapeutic options, contributing to its poor prognosis. Recent advances in high-throughput sequencing have highlighted the critical roles of noncoding RNAs (ncRNAs), particularly PIWI-interacting RNAs (piRNAs), in cancer biology. In this review, we systematically summarize the emerging roles of piRNAs and their associated PIWI proteins in PDAC pathogenesis, progression, and prognosis. We provide a comprehensive analysis of the molecular mechanisms by which piRNAs/PIWIs regulate gene expression and cellular signaling pathways in PDAC. Furthermore, we discuss their potential as novel biomarkers for early diagnosis and therapeutic targets. Importantly, this review identifies key piRNAs/PIWIs involved in PDAC and proposes innovative strategies for improving diagnosis and treatment outcomes. Our work not only consolidates current knowledge but also offers new perspectives for future research and clinical applications in PDAC management.

PIWI-interacting RNA biomarkers in gastrointestinal disease

Detection and diagnosis of neoplastic and inflammatory gastrointestinal (GI) diseases are typically based on endoscopic and pathologic examination. In GI neoplastic diseases, diagnosis can be delayed due to the expense and invasive nature of this approach. Recently, PIWI-interacting RNAs (piRNAs), a group of small non-coding RNA molecules containing 24-31 nucleotides, have been thought to serve as biomarkers in many disease processes. For example, piRNAs are differentially expressed in GI cancer but their biologic role remains unclear. Using next-generation sequencing and microarray analyses, researchers have suggested that monitoring piRNAs could facilitate diagnosis and prognosis in GI disease. Herein, we reviewed the use of piRNAs in neoplastic, inflammatory, functional, and other diseases of the digestive system, which could shed new light on cancer screening, early detection, and personalized treatment.

piRNA processing within non-membrane structures is governed by constituent proteins and their functional motifs

Discovered two decades ago, PIWI-interacting RNAs (piRNAs) are crucial for silencing transposable elements (TEs) in animal gonads, thereby protecting the germline genome from harmful transposition, and ensuring species continuity. Silencing of TEs is achieved through transcriptional and post-transcriptional suppression by piRNAs and the PIWI clade of Argonaute proteins within non-membrane structured organelle. These structures are composed of proteins involved in piRNA processing, including PIWIs and other proteins by distinct functional motifs such as the Tudor domain, LOTUS, and intrinsic disordered regions (IDRs). This review highlights recent advances in understanding the roles of these conserved proteins and structural motifs in piRNA biogenesis. We explore the molecular mechanisms of piRNA biogenesis, with a primary focus on Drosophila as a model organism, identifying common themes and species-specific variations. Additionally, we extend the discussion to the roles of these components in nongonadal tissues.

Serum Circulating mRNA Panel for the Early Detection of Gastric Cancer: A Potential Biomarker Test

Circulating free messenger RNAs (cfmRNAs) in serum have emerged as potential noninvasive biomarkers for cancer diagnosis, including gastric cancer (GC). This study utilized RNA-sequencing data from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases to identify a training set of 100 differentially expressed genes (DEGs) specific to GC patients. Employing a support vector machine (SVM) classification, we narrowed down the candidate gene set to 23, which was further refined to 4 genes-DMBX1, EVX1, MAL, and PIWIL1-after validation through reverse transcription quantitative polymerase chain reaction (RT-qPCR). The diagnostic performance of mRNA panels, particularly the combinations of DMBX1 with EVX1 and EVX1 with PIWIL1, was exceptional, achieving area under the curve (AUC) values of 0.800, sensitivities of 90.0 %, and specificities of 80.0 %. The accuracy of these biomarkers was corroborated through various machine learning algorithms, underscoring their robust diagnostic potential. The findings of this study are poised to significantly influence clinical practice by providing robust tools for early GC detection. As these biomarkers undergo further investigation and validation, they hold promise to become integral to the diagnostic for GC.

PIWIL genes in hepatocellular carcinoma: a multi-omics approach uncovering dysregulated expression and ceRNA networks in mice

This multi-omics study delves into the expression patterns of PIWIL genes and their correlation with hepatocellular carcinoma (HCC) progression, utilizing whole transcriptome sequencing, bioinformatics, and reverse transcription quantitative polymerase chain reaction (RT-qPCR) in mice. We identified differential expression levels of PIWIL genes between HCC and control tissues and analyzed their roles within the competing endogenous RNA (ceRNA) network related to regulatory non-coding RNA-mediated gene silencing (RNGS). Our findings showed that Piwil1 and Piwil4 were overexpressed while Piwil2 is underexpressed. As ceRNAs, specific lncRNAs, including Pvt1, Gas5, and BGIGI10090_38749, might sponge up miR-351-5p and miR-31-5p, promoting Piwil1 and Piwil4 expression, while miR-133b-3p, lacking ceRNA sponge absorption, continues to inhibit Piwil2. Through their interactions with PPI proteins encoded by RNGS genes, especially Dhx9, Drosha, Mov10, and Tdrd1, PIWI family members might play a multifaceted role in regulating gene expression and metabolic processes, thereby involving the development and progression of HCC. These interactions within the PPI network could influence the stability and activity of PIWIL proteins and contribute to the overall regulation of gene expression and HCC progression. In the RNGS, a diverse array of miRNAs, genes, lncRNAs, circRNAs, and pseudogenes have been observed, which are suggested to intricately interplay, potentially weaving a complex ceRNA regulatory network. Abnormally expressed miRNA-targeted genes in RNGS are associated with key biological processes, such as lipid metabolism and immune responses, crucial for tumor cell survival, and processes supporting tumor growth and invasion, like translation and cytoskeleton organization. This regulation is reflected in distinct KEGG pathways for downregulated and upregulated targets, highlighting the dualistic role of PIWIL genes in modulating HCC progression. The study concludes that PIWI family members have a correlation with HCC progression and play divergent roles in the pathogenesis, with overexpression of the Piwil1 and Piwil4 potentially promoting HCC progression and underexpression of Piwil2 likely suppressing tumor development. The ceRNA mechanism and PPI network are crucial in regulating the expression and function of PIWIL genes, respectively. The intricate ceRNA network potentially regulates the expression of miRNA-targeted genes in RNGS, which might be crucial for tumor survival and promotion, with impacts on immune responses and cell growth based on enriching results of dysregulated miRNA-targeted genes in HCC. By shedding light on the molecular intricacies of HCC, this multi-omics study underscores the pivotal roles of epigenetic regulations, especially the influence of PIWI family genes with other genes and ncRNAs in the RNGS process in HCC pathology. The findings offer valuable insights into the molecular mechanisms underpinning HCC, which may inform future research into potential targets for therapeutic intervention. The future research could benefit from integrating a diverse range of methodologies to further elucidate the roles of PIWIL genes in HCC progression, building upon the findings presented here.

Mechanisms Behind the Impact of PIWI Proteins on Cancer Cells: Literature Review

The P-Element-induced wimpy testis (PIWI) group of proteins plays a key role in RNA interference, particularly in the regulation of small non-coding RNAs. However, in recent years, PIWIs have gained attention in several diseases, mainly cancer. Therefore, the aim of this review was to evaluate current knowledge about the impact of PIWI proteins on cancer cells. PIWIs alter a number of pathways within cells, resulting in significant changes in cell behavior. Basic processes of cancer cells have been shown to be altered by either overexpression or inhibition of PIWIs. Regulation of apoptosis, metastasis, invasion, or proliferation of cancerous cells by these proteins proves their involvement in the progression of the malignancy. It has been revealed that PIWIs are also connected with cancer stem cells (CSCs), which proves their ability to become a therapeutic target. However, research on this topic is still fairly limited, and with significant differences between cancer types, it is necessary to refrain from making any decisive conclusions.

PIWIL1 is recruited to centrosomes during mitosis in colorectal cancer cells and is linked to cell cycle progression

PIWI proteins, traditionally associated with germline development, have recently gained attention for their expression in various cancers, including colorectal cancer. However, the molecular mechanisms underlying their reactivation and impact on cancer initiation and progression remain elusive. Here, we found that PIWIL1 is expressed at relatively high levels in CRC-derived samples and cell lines, where it undergoes a dynamic relocalization to the centrosome during mitosis. Knockdown of PIWIL1 induces G2/M arrest associated with disruption of the mitotic spindle and aberrant metaphase events, highlighting its role in cell cycle progression. We also found that the expression of PIWIL1 is lost during the differentiation of Caco-2 cells into enterocytes and that PIWIL1 is expressed in cells at the base of the intestinal crypts in normal human colon tissue, where intestinal stem cells are known to reside. Thus, it is possible that the presence of PIWIL1 in cancer cells reflects a physiological role of this protein in stem cell maintenance, which would argue in favor of the proposed stem cell origin of CRC. Supporting this view, dedifferentiation of human fibroblasts into induced pluripotent stem cells (iPSCs) involves the reactivation of PIWIL2 expression, another member of the PIWI protein family. Overall, our findings suggest a role of PIWIL1 in mediating cell cycle dynamics, both in colorectal cancer cells and possibly also in intestinal stem cells. In a broader aspect, we provide evidence supporting an involvement of PIWI proteins in somatic stem cell maintenance, thus expanding the known non-gonadal functions of this protein family.

Sex differences in DNA methylation variations according to ART conception-evidence from the Norwegian mother, father, and child cohort study

Previous studies have shown cord-blood DNA methylation differences in newborns conceived using assisted reproductive technologies (ART) compared to those conceived naturally. However, whether these ART-related DNA methylation differences vary with children's sex is unknown. We hypothesize that the DNA methylation differences in cord blood between ART-conceived and naturally conceived newborns also varies by the sex of the child, with distinct patterns of differential methylation present in males and females. We investigated sex differences in cord-blood DNA methylation variation according to conception by ART using the Illumina MethylationEPIC platform, comparing 456 ART-conceived versus 507 naturally-conceived girls, and 503 ART-conceived and 473 naturally-conceived boys. We identified 37 differentially methylated CpGs according to ART-conception among girls, and 70 differentially methylated CpGs according to ART-conception among boys, when we used a 1% false discovery rate to account for multiple testing. Ten CpGs were differentially methylated according to conception by ART in both sexes. Among the genes that were associated with these CpGs, we found the BRCA1; NBR2 gene (two CpGs) was hypermethylated in girls while the APC2 (two CpGs) and NECAB3;ACTL10, (four CpGs) related to cellular signaling were hypomethylated in boys. These findings confirm the presence of sex-specific epigenetic differences, illustrating the nuanced impact of ART on the fetal epigenome. There is a need for further explorations into the implications for sex-specific developmental trajectories and health outcomes in ART-conceived children.

PIWI pathway: bridging acute myeloid leukemia stemness and cellular differentiation

PIWI proteins are stem cell-associated RNA-binding proteins crucial for survival of germ stem cells. In cancer, PIWI proteins are overexpressed. Specifically, PIWIL4 is highly expressed in multiple cancers with the highest levels found in acute myeloid leukemia (AML), an aggressive malignancy propagated by a population of leukemia stem cells (LSCs). Bamezai et al. (Blood Journal, blood, 2023, 142, 90-105) demonstrated that PIWIL4 supports AML blasts and LSCs but is not necessary for healthy human hematopoietic progenitor stem cells (HSPCs) function in vivo. PIWIL4 in AML acts by preventing the accumulation of R-loops in key genes for LSCs persistence implicated in: DNA damage, replicative stress, and transcription arrest. We report that PIWIL4 expression significantly decreases in THP-1 monocytes exposed to a differentiating agent, suggesting a potential role for PIWIL4 in maintaining the undifferentiated state of myeloid cells. PIWIL4 overexpression could lead to the emergence of LSCs, driving leukemia propagation and maintenance. Our findings correlate with the persistent overexpression of PIWIL4 in myeloid cancers as reported by Bamezai et al., and suggest that PIWIL4 may be involved in myeloid cell differentiation. In this perspective, we highlight recent findings on the implication of PIWI pathway in maintaining AML stemness. Additionally, we propose further investigation on the role of PIWI pathway in oncogenesis and cellular differentiation as a strategy to identify biomarkers and therapeutic targets for AML.

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 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.

Transcriptional co-activators: emerging roles in signaling pathways and potential therapeutic targets for diseases

Specific cell states in metazoans are established by the symphony of gene expression programs that necessitate intricate synergic interactions between transcription factors and the co-activators. Deregulation of these regulatory molecules is associated with cell state transitions, which in turn is accountable for diverse maladies, including developmental disorders, metabolic disorders, and most significantly, cancer. A decade back most transcription factors, the key enablers of disease development, were historically viewed as 'undruggable'; however, in the intervening years, a wealth of literature validated that they can be targeted indirectly through transcriptional co-activators, their confederates in various physiological and molecular processes. These co-activators, along with transcription factors, have the ability to initiate and modulate transcription of diverse genes necessary for normal physiological functions, whereby, deregulation of such interactions may foster tissue-specific disease phenotype. Hence, it is essential to analyze how these co-activators modulate specific multilateral processes in coordination with other factors. The proposed review attempts to elaborate an in-depth account of the transcription co-activators, their involvement in transcription regulation, and context-specific contributions to pathophysiological conditions. This review also addresses an issue that has not been dealt with in a comprehensive manner and hopes to direct attention towards future research that will encompass patient-friendly therapeutic strategies, where drugs targeting co-activators will have enhanced benefits and reduced side effects. Additional insights into currently available therapeutic interventions and the associated constraints will eventually reveal multitudes of advanced therapeutic targets aiming for disease amelioration and good patient prognosis.

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.

PIWI interacting RNA-13643 contributes to papillary thyroid cancer development through acting as a novel oncogene by facilitating PRMT1 mediated GLI1 methylation

BACKGROUND

Recently, aberrant expression of PIWI-interacting RNAs (piRNAs) has been discovered in a variety of cancer cells. However, the roles of PIWI proteins and piRNAs in papillary thyroid carcinoma (PTC) are still elusive.

METHODS

RT-qPCR and Northern blotting were used to evaluate piR-13643 levels in PTC and para-carcinoma tissues, as well as in PTC cell lines. piR-13643 mimic and piR-13643 inhibitor were transfected into K-1 and B-CPAP cells. CCK-8, Transwell, annexin V-FITC/PI, flow cytometry and Western blot assays were performed to measure cell proliferation, invasion, apoptosis, cell cycle and E-cadherin and Vimentin proteins, respectively. Total RNA from B-CPAP cells was pulled down with PIWIL1, PIWIL2, or PIWIL3 specific antibodies or IgG as a control, respectively, followed by detection of piR-13643 expression with RT-qPCR. Immunoblotting of PRMT1 was detected in piR-13643 / PIWIL1 complex immune-precipitates by Co-IP assay. Subsequently, PRMT1 protein expression was detected by stably transfection of Flag tagged GLI1 (Flag-GLI1) into B-CPAP cells. Methylation assay with PRMT1 and wild-type or R597 lysine (R597K)-mutant GLI1. Then rescue experiments were applied to explore effects of piR-13643 and GLI1 on the malignant behavior of PTC cells. B-CPAP cells transfected with piR-13643 inhibitor were subcutaneously injected into nude mice to evaluate the effect of piR-13643 knockdown on the xenograft tumor growth of PTC.

RESULTS

piR-13643 was elevated in PTC patient specimens and cell lines. piR-13643 overexpression facilitated cell proliferation, invasion and Vimentin level, and restrained apoptosis and E-cadherin expression, whereas piR-13643 knockdown showed the opposite results. Mechanically, piR-13643 could bind to PIWIL1 to form the PIWIL1/piR-13643 complex, and PRMT1 enhanced GLI1 transcription by methylating GLI1 at R597. Further, PIWIL1/piR-13643 promoted PRMT1-mediated GLI1 methylation. GLI1 knockdown countered the effects of piR-13643 mimic on cell malignant behaviors. piR-13643 knockdown preeminently prevented the xenograft tumor growth of PTC in vivo.

CONCLUSIONS

This study confirmed that piR-13643 facilitates PTC malignant behaviors in vitro and in vivo by promoting PRMT1-mediated GLI1 methylation via forming a complex with PIWIL1, which may provide a novel insight for PTC treatment.

Emerging roles of interactions between ncRNAs and other epigenetic modifications in breast cancer

Up till the present moment, breast cancer is still the leading cause of cancer-related death in women worldwide. Although the treatment methods and protocols for breast cancer are constantly improving, the long-term prognosis of patients is still not optimistic due to the complex heterogeneity of the disease, multi-organ metastasis, chemotherapy and radiotherapy resistance. As a newly discovered class of non-coding RNAs, ncRNAs play an important role in various cancers. Especially in breast cancer, lncRNAs have received extensive attention and have been confirmed to regulate cancer progression through a variety of pathways. Meanwhile, the study of epigenetic modification, including DNA methylation, RNA methylation and histone modification, has developed rapidly in recent years, which has greatly promoted the attention to the important role of non-coding RNAs in breast cancer. In this review, we carefully and comprehensively describe the interactions between several major classes of epigenetic modifications and ncRNAs, as well as their different subsequent biological effects, and discuss their potential for practical clinical applications.

Non-gonadal somatic piRNA pathways ensure sexual differentiation, larval growth, and wing development in silkworms

PIWI-interacting RNAs (piRNAs) guide PIWI proteins to target transposons in germline cells, thereby suppressing transposon activity to preserve genome integrity in metazoans' gonadal tissues. Piwi, one of three Drosophila PIWI proteins, is expressed in the nucleus and suppresses transposon activity by forming heterochromatin in an RNA cleavage-independent manner. Recently, Piwi was reported to control cell metabolism in Drosophila fat body, providing an example of piRNAs acting in non-gonadal somatic tissues. However, mutant flies of the other two PIWI proteins, Aubergine (Aub) and Argonaute3 (Ago3), show no apparent phenotype except for infertility, blurring the importance of the piRNA pathway in non-gonadal somatic tissues. The silkworm, Bombyx mori, possesses two PIWI proteins, Siwi (Aub homolog) and BmAgo3 (Ago3 homolog), whereas B. mori does not have a Piwi homolog. Siwi and BmAgo3 are mainly expressed in gonadal tissues and play a role in repressing transposon activity by cleaving transposon RNA in the cytoplasm. Here, we generated Siwi and BmAgo3 loss-of-function mutants of B. mori and found that they both showed delayed larval growth and failed to become adult moths. They also exhibited defects in wing development and sexual differentiation. Transcriptome analysis revealed that loss of somatic piRNA biogenesis pathways results in abnormal expression of not only transposons but also host genes, presumably causing severe growth defects. Our results highlight the roles of non-gonadal somatic piRNAs in B. mori development.

PIWI-RNAs Small Noncoding RNAs with Smart Functions: Potential Theranostic Applications in Cancer

P-element-induced wimpy testis (PIWI)-interacting RNAs (piRNAs) are a new class of small noncoding RNAs (ncRNAs) that bind components of the PIWI protein family. piRNAs are specifically expressed in different human tissues and regulate important signaling pathways. Aberrant expressions of piRNAs and PIWI proteins have been associated with tumorigenesis and cancer progression. Recent studies reported that piRNAs are contained in extracellular vesicles (EVs), nanosized lipid particles, with key roles in cell-cell communication. EVs contain several bioactive molecules, such as proteins, lipids, and nucleic acids, including emerging ncRNAs. EVs are one of the components of liquid biopsy (LB) a non-invasive method for detecting specific molecular biomarkers in liquid samples. LB could become a crucial tool for cancer diagnosis with piRNAs as biomarkers in a precision oncology approach. This review summarizes the current findings on the roles of piRNAs in different cancer types, focusing on potential theranostic applications of piRNAs contained in EVs (EV-piRNAs). Their roles as non-invasive diagnostic and prognostic biomarkers and as new therapeutic options have been also discussed.

piRNA-1742 promotes renal cell carcinoma malignancy by regulating USP8 stability through binding to hnRNPU and thereby inhibiting MUC12 ubiquitination

Accumulating studies have confirmed that PIWI-interacting RNAs (piRNAs) are considered epigenetic effectors in cancer. We performed piRNA microarray expression analysis on renal cell carcinoma (RCC) tumor tissues and paired normal tissues and performed a series of in vivo and in vitro experiments to explore piRNAs associated with RCC progression and investigate their functional mechanisms. We found that piR-1742 was highly expressed in RCC tumors and that patients with high piR-1742 expression had a poor prognosis. Inhibition of piR-1742 significantly reduced tumor growth in RCC xenograft and organoid models. Mechanistically, piRNA-1742 regulates the stability of USP8 mRNA by binding directly to hnRNPU, which acts as a deubiquitinating enzyme that inhibits the ubiquitination of MUC12 and promotes the development of malignant RCC. Subsequently, nanotherapeutic systems loaded with piRNA-1742 inhibitors were found to effectively inhibit the metastasis and growth of RCC in vivo. Therefore, this study highlights the functional importance of piRNA-related ubiquitination in RCC and demonstrates the development of a related nanotherapeutic system, possibly contributing to the development of therapeutic approaches for RCC.

A novel microRNA-182/Interleukin-8 regulatory axis controls osteolytic bone metastasis of lung cancer

Bone metastasis is one of the main complications of lung cancer and most important factors that lead to poor life quality and low survival rate in lung cancer patients. However, the regulatory mechanisms underlying lung cancer bone metastasis are still poor understood. Here, we report that microRNA-182 (miR-182) plays a critical role in regulating osteoclastic metastasis of lung cancer cells. We found that miR-182 was significantly upregulated in both bone-metastatic human non-small cell lung cancer (NSCLC) cell line and tumor specimens. We further demonstrated that miR-182 markedly enhanced the ability of NSCLC cells for osteolytic bone metastasis in nude mice. Mechanistically, miR-182 promotes NSCLC cells to secrete Interleukin-8 (IL-8) and in turn facilitates osteoclastogenesis via activating STAT3 signaling in osteoclast progenitor cells. Importantly, systemically delivered IL-8 neutralizing antibody inhibits NSCLC bone metastasis in nude mice. Collectively, our findings identify the miR-182/IL-8/STAT3 axis as a key regulatory pathway in controlling lung cancer cell-induced osteolytic bone metastasis and suggest a promising therapeutic strategy that targets this regulatory axis to interrupt lung cancer bone metastasis.

PIWI-interacting RNAs: Critical roles and therapeutic targets in cancer

P-element-induced wimpy testis (PIWI)-interacting RNAs (piRNAs) are a novel class of small regulatory RNAs (approximately 24-31 nucleotides in length) that often bind to members of the PIWI protein family. piRNAs regulate transposons in animal germ cells; piRNAs are also specifically expressed in many human tissues and regulate pivotal signaling pathways. Additionally, the abnormal expression of piRNAs and PIWI proteins has been associated with various malignant tumours, and multiple mechanisms of piRNA-mediated target gene dysregulation are involved in tumourigenesis and progression, suggesting that they have the potential to serve as new biomarkers and therapeutic targets for tumours. However, the functions and potential mechanisms of action of piRNAs in cancer have not yet been elucidated. This review summarises the current findings on the biogenesis, function, and mechanisms of piRNAs and PIWI proteins in cancer. We also discuss the clinical significance of piRNAs as diagnostic or prognostic biomarkers and therapeutic tools for cancer. Finally, we present some critical questions regarding piRNA research that need to be addressed to provide insight into the future development of the field.

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.

Tumour-derived exosomal piR-25783 promotes omental metastasis of ovarian carcinoma by inducing the fibroblast to myofibroblast transition

Ovarian carcinoma inherently possesses a distinct metastatic organotropism for the adipose-rich omentum, contributing to disease progression. Although the premetastatic microenvironment (PMM) has been known to often play a prometastatic role during the process, incomplete mechanistic insight into PMM formation has prevented its therapeutic targeting. Omental fibroblasts can be activated by tumour cells to differentiate into myofibroblasts, termed the fibroblast-to-myofibroblast transition (FMT), which, in turn, enhances cancer aggressiveness. Here, we report crosstalk between cancer cells and omental fibroblasts through exosomal piR-25783, which fuels tumour metastasis. Tumour cell-secreted exosomal piR-25783 activates the TGF-β/SMAD2/SMAD3 pathway in fibroblasts and promotes the FMT in the omentum along with the secretion of various cytokines and elevation of proliferative, migratory, and invasive properties, contributing to the formation of PMMs. Furthermore, piR-25783-induced myofibroblasts promote tumour implantation and growth in the omentum. In addition, the overexpression of piR-25783 in ovarian carcinoma is associated with unfavourable clinicopathological characteristics and shorter survival. In this study, we provide molecular, functional, and translational evidence suggesting that exosomal piR-25783 plays an important role in the formation of PMMs and the development of metastatic diseases in vitro and in vivo and may serve as a potential therapeutic target for ovarian carcinoma with metastasis.

Potential roles of PIWI-interacting RNAs in lung cancer

Lung cancer is a malignant tumor with high morbidity and mortality in the world today. Emerging evidence suggests that PIWI-interacting RNAs (piRNAs) are aberrantly expressed in various human cancers, including lung cancer. Despite of the poorly understood mechanism, piRNAs may work as carcinogenic roles or tumor suppressors by engaging in a variety of cancer-associated signaling pathways. Therefore, they might serve as potential therapeutic targets, diagnostic indicators, or prognostic indicators in lung cancer. This review will discuss the new findings of piRNAs, including their biosynthetic processes, mechanisms of gene suppression, and the significance of these piRNAs tested in lung cancer samples to determine their involvement in cancer progression.

Emerging roles of PIWI-interacting RNAs (piRNAs) and PIWI proteins in head and neck cancer and their potential clinical implications

Head and neck squamous cell carcinoma (HNSCC) are among the well-known neoplasms originating in the oral cavity, pharynx, and larynx. Despite advancements in chemotherapy, radiotherapy, and surgery, the survival rates of the patients are low, which has posed a major therapeutic challenge. A growing number of non-coding RNAs (ncRNAs), for instance, microRNAs, have been identified whose abnormal expression patterns have been implicated in HNSCC. However, more recently, several seminal research has shown that piwi-interacting RNAs (piRNAs), a promising and young class of small ncRNA, are linked to the emergence and progression of cancer. They can regulate transposable elements (TE) and gene expression through multiple mechanisms, making them potentially more powerful regulators than miRNAs. Hence, they can be more promising ncRNAs candidates for cancer therapeutic intervention. Here, we surveyed the roles and clinical implications of piRNAs and their PIWI proteins partners in tumorigenesis and associated molecular processes of cancer, with a particular focus on HNSCC, to offer a new avenue for diagnosis, prognosis, and therapeutic interventions for the malignancy, improving patient's outcomes.

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.

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.

Butorphanol Suppresses the Proliferation and Migration of Osteosarcoma by Promoting the Expression of piRNA hsa_piR_006613

Butorphanol, a partial agonist of opioid receptor κ 1 receptor, can and is widely used as an analgesic drug to relieve moderate and severe pain in clinic. Osteosarcoma is one of the most common malignant bone tumor in adolescents under the age of 20. To our knowledge no study has investigated the effect of butorphanol on the proliferation of osteosarcoma cells. In this study, The proliferation of osteosarcoma cells was measured by CCK-8 and colony formation assays, and the migration of osteosarcoma cells were detected by scratch and transwell assays. The expression of piRNA was detected by RNA sequencing and real-time PCR. PiRNA mimics or inhibitors have been used to upregulate or inhibit piRNA expression in osteosarcoma cells, respectively. We found that butorphanol, at the concentration of 10ug/ml or higher, could significantly inhibit the proliferation and migration of osteosarcoma cells. Our resuslts indicated that butorphanol promoted the expression of piRNA hsa_piR_006613 and overexpression of piRNA hsa_piR_006613 inhibited the proliferation and migration of osteosarcoma cells. our study also showed that inhibition of the expression of piRNA hsa_piR_006613 could promote the proliferation and migration of osteosarcoma cells. Butorphanol played the regulatory role on osteosarcoma cells in dependent of piRNA hsa_piR_006613. Butorphanol was found to inhibit the proliferation and migration of osteosarcoma cells by promoting piRNA hsa_piR_006613 expression. Bioinformatics analysis showed that hsa_piR_006613 downregulated FN1 protein expression by binding with 3’-UTR of FN1 mRNA. In all, the present research indicated that butorphanol suppresses the proliferation of osteosarcoma by promoting the expression of piRNA hsa_piR_006613, which downregulated the expression of FN1. Has_piR_006613 may become a new therapeutic target for osteosarcoma.

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.

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.

Identifying Protein Complexes With Clear Module Structure Using Pairwise Constraints in Protein Interaction Networks

The protein-protein interaction (PPI) networks can be regarded as powerful platforms to elucidate the principle and mechanism of cellular organization. Uncovering protein complexes from PPI networks will lead to a better understanding of the science of biological function in cellular systems. In recent decades, numerous computational algorithms have been developed to identify protein complexes. However, the majority of them primarily concern the topological structure of PPI networks and lack of the consideration for the native organized structure among protein complexes. The PPI networks generated by high-throughput technology include a fraction of false protein interactions which make it difficult to identify protein complexes efficiently. To tackle these challenges, we propose a novel semi-supervised protein complex detection model based on non-negative matrix tri-factorization, which not only considers topological structure of a PPI network but also makes full use of available high quality known protein pairs with must-link constraints. We propose non-overlapping (NSSNMTF) and overlapping (OSSNMTF) protein complex detection algorithms to identify the significant protein complexes with clear module structures from PPI networks. In addition, the proposed two protein complex detection algorithms outperform a diverse range of state-of-the-art protein complex identification algorithms on both synthetic networks and human related PPI networks.

PIWI-interacting RNAs: Mitochondria-based biogenesis and functions in cancer

PIWI-interacting RNA (piRNAs), once thought to be mainly functioning in germlines, are now known to play an essential role in somatic and cancerous tissues. Ping-pong cycle initiation and mitochondria-based phased production constitute the core of the piRNA biogenesis and these two processes are well conserved in mammals, including humans. By being involved in DNA methylation, histone marker deposition, mRNA degradation, and protein modification, piRNAs also contribute to carcinogenesis partly due to oncogenic stress-induced piRNA dysregulation. Also, piRNAs play important roles in cancer stemness, drug resistance, and tumor immunology. Results from liquid biopsy analysis of piRNA can be used in both cancer diagnoses and cancer prognoses. A combination of targeting piRNA with other therapeutic strategies could be groundbreaking cancer treatment.

Identification and characterization of Piwi-interacting RNAs in human placentas of preeclampsia

Preeclampsia is a common disease of pregnancy that poses a serious threat to the safety of pregnant women and the fetus; however, the etiology of preeclampsia is inconclusive. Piwi-interacting RNAs (piRNAs) are novel non-coding RNAs that are present at high levels in germ cells and are associated with spermatogenesis. Emerging evidence demonstrated that piRNA is expressed in a variety of human tissues and is closely associated with tumorigenesis. However, changes in the piRNA expression profile in the placenta have not been investigated. In this study, we used small RNA sequencing to evaluate the differences in piRNA expression profiles between preeclampsia and control patients and potential functions. Differential expression analysis found 41 up-regulated and 36 down-regulated piRNAs in preeclamptic samples. In addition, the functional enrichment analysis of piRNAs target genes indicated that they were related to the extracellular matrix (ECM) formation and tissue-specific. Finally, we examined the expression pattern of the PIWL family proteins in the placenta, and PIWL3 and PIWIL4 were the primary subtypes in the human placenta. In summary, this study first summarized the changes in the expression pattern of piRNA in preeclampsia and provided new clues for the regulatory role of piRNA in the human placenta.

PIWI‑interacting RNA in cancer: Molecular mechanisms and possible clinical implications (Review)

PIWI‑interacting RNA is a class of non‑coding small RNA that is ~30 nt long and is primarily found in mammalian germ cells from mice and humans. In cooperation with the members of PIWI protein family, this macromolecule participates in germ cell development, inhibits DNA self‑-replication and maintains genomic stability. Increasing evidence has demonstrated that PIWI‑interacting RNA (piRNAs) are abnormally expressed in various human cancers, such as liver cancer, stomach cancer, colorectal cancer, osteosarcoma, breast cancer, lung cancer, prostate cancer, etc. piRNAs abnormal expression is also associated with the occurrence and development of human cancers, such as liver cancer, stomach cancer, colorectal cancer, etc. Despite their unclear molecular mechanisms, piRNAs may act as oncogenes or tumor suppressors by interacting with multiple cancer‑related signal pathways including STAT3/Bcl‑xl or coding genes, such as heat shock transcription factor‑1. Hence, piRNAs may be potential markers and targets and provide new opportunities for cancer diagnosis, treatment or prognosis monitoring. The current review mainly aims to highlight the latest research progress made in the biological functions and regulation of piRNAs in mammals, their involvement in various cancer forms and their potential clinical applications.

Knockout Gene-Based Evidence for PIWI-Interacting RNA Pathway in Mammals

The PIWI-interacting RNA (piRNA) pathway mainly consists of evolutionarily conserved protein factors. Intriguingly, many mutations of piRNA pathway factors lead to meiotic arrest during spermatogenesis. The majority of piRNA factor-knockout animals show arrested meiosis in spermatogenesis, and only a few show post-meiosis male germ cell arrest. It is still unclear whether the majority of piRNA factors expressed in spermatids are involved in long interspersed nuclear element-1 repression after meiosis, but future conditional knockout research is expected to resolve this. In addition, recent hamster knockout studies showed that a piRNA factor is necessary for oocytes-in complete contrast to the findings in mice. This species discrepancy allows researchers to reexamine the function of piRNA in female germ cells. This mini-review focuses on the current knowledge of protein factors derived from mammalian knockout studies and summarizes their roles in the biogenesis and function of piRNAs.

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.

The role and regulation of Pnn in proliferative and non-dividing cells: Form embryogenesis to pathogenesis

Pnn, a multiple functional protein, plays roles in embryonic development, cellular differentiation, tumorigenesis, and metastasis. In the past two decades, the functions of Pnn in regulating RNA alternative splicing, gene regulation, and cell-cell connection have been revealed. Although Pnn is originally identified as a desmosome-associated protein for linking desmosome and intermediated filament, emerging evidence implies that Pnn not only is a desmosome protein but also plays critical roles in the nucleus. To date, through cell biology investigation and the generation of animal models with genetic manipulation, the physiological role of Pnn has been characterized in the research fields of developmental biology, tumor biology, and neuroscience. Through proteomic and molecular biology studies, transcription regulators, splicing regulators, and cytoskeletal proteins were found to interact with Pnn. In addition, histopathological and biochemical evidence has pointed to an association of Pnn expression level with tumorigenesis and metastasis. A previous clinical study also demonstrated a correlation between a reduced expression of Pnn and human dementia. Besides, experimental studies showed a protective role of Pnn against ischemic stress in astrocytes. All indicated a variety of roles of Pnn in different cell types. In this review article, we introduced the role of Pnn in embryogenesis and pathogenesis as well as discussed its potential clinical application.

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.

Non-Coding RNAs in Cancer Diagnosis and Therapy: Focus on Lung Cancer

Over the last several decades, clinical evaluation and treatment of lung cancers have largely improved with the classification of genetic drivers of the disease, such as EGFR, ALK, and ROS1. There are numerous regulatory factors that exert cellular control over key oncogenic pathways involved in lung cancers. In particular, non-coding RNAs (ncRNAs) have a diversity of regulatory roles in lung cancers such that they have been shown to be involved in inducing proliferation, suppressing apoptotic pathways, increasing metastatic potential of cancer cells, and acquiring drug resistance. The dysregulation of various ncRNAs in human cancers has prompted preclinical studies examining the therapeutic potential of restoring and/or inhibiting these ncRNAs. Furthermore, ncRNAs demonstrate tissue-specific expression in addition to high stability within biological fluids. This makes them excellent candidates as cancer biomarkers. This review aims to discuss the relevance of ncRNAs in cancer pathology, diagnosis, and therapy, with a focus on lung 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.

Piwil1 Regulates Glioma Stem Cell Maintenance and Glioblastoma Progression

Piwi proteins are a subfamily of Argonaute proteins that maintain germ cells in eukaryotes. However, the role of their human homologs in cancer stem cells, and more broadly in cancer, is poorly understood. Here, we report that Piwi-like family members are overexpressed in glioblastoma (GBM), with Piwil1 (Hiwi) most frequently overexpressed (88%). Piwil1 is enriched in glioma stem-like cells (GSCs) to maintain self-renewal. Silencing Piwil1 in GSCs leads to global changes in gene expression resulting in cell-cycle arrest, senescence, or apoptosis. Piwil1 knockdown increases expression of the transcriptional co-regulator BTG2 and the E3-ubiquitin ligase FBXW7, leading to reduced c-Myc expression, as well as loss of expression of stem cell factors Olig2 and Nestin. Piwil1 regulates mRNA stability of BTG2, FBXW7, and CDKN1B. In animal models of GBM, Piwil1 knockdown suppresses tumor growth and promotes mouse survival. These findings support a role of Piwil1 in GSC maintenance and glioblastoma progression.

Huang et al. find that Piwil1 protein is overexpressed in glioblastoma and glioma stem cells (GSCs). Piwil1 maintains GSC self-renewal and survival by regulating gene expression. Targeting Piwil1 extends survival in mouse models of glioblastoma. Piwil1 represents a therapeutic vulnerability.

Expression and Distribution Pattern of Pnn in Ischemic Cerebral Cortex and Cultured Neural Cells Exposed to Oxygen-Glucose Deprivation

Pinin (Pnn), a multifunctional protein, participates in embryonic development as well as in cellular apoptosis, proliferation, and migration through regulating mRNA alternative splicing and gene transcription. Previous studies have shown that Pnn plays important roles in neural system development and the expression level of Pnn in astrocytes is altered by ischemic stress and associated with cellular apoptosis. In the present study, we further utilized primary cultured rat neurons and astrocytes with oxygen-glucose deprivation (OGD) and a mouse model with middle cerebral artery occlusion (MCAO)-induced ischemic stroke to examine the effect of ischemic stress on Pnn expression and distribution in different types of neural cells. Under normoxia, Pnn is mainly localized in the nuclear speckle of primary cultured neurons. The expression level of Pnn was increased after the OGD treatment and then decreased in the reoxygenation period. Moreover, the cytoplasmic expression of Pnn was observed in neurons with OGD and reoxygenation (OGD/R). Unlike that in neurons, the Pnn expression in astrocytes was decreased after OGD treatment and then gradually increased during the reoxygenation period. Of interest, the nuclear–cytoplasmic translocation of Pnn was not observed in astrocytes with OGD/R. In the MCAO mouse model, the neuronal expression of Pnn in the peri-ischemic region was reduced by three days post induction of ischemic stroke. However, the Pnn expression in astrocytes was not altered. Moreover, the nuclear speckle distribution of Pnn in neurons was also diminished following ischemic stroke. In conclusion, the Pnn expression and distribution after OGD and during reoxygenation showed distinct manners in neurons and astrocytes, implying that Pnn may play different roles in different types of neural cells in the stress response to ischemic injury.