Pathways of proliferation and antiapoptosis driven in breast cancer stem cells by stem cell protein piwil2

Potential roles of PIWI-interacting RNAs in breast cancer, a new therapeutic strategy

Breast cancer (BC) has been the focus of numerous studies aimed at identifying novel biological markers for its early detection. PIWI-interacting RNAs (piRNAs), a subset of small non-coding RNAs, have emerged as potential markers due to their aberrant expression in various cancers. PiRNAs have recently gained attention due to their aberrant expression in various cancers, including BC. PiRNAs, exhibit diverse biological activities, such as epigenetic regulation of gene and protein expression and their association with cell proliferation and metastasis has been well-established. As the field of non-coding RNAs rapidly evolves, there is great anticipation that therapies targeting piRNAs will advance swiftly. This review will delve into the various biological functions of piRNAs, such as gene suppression, transposon silencing, and epigenetic regulation of genes. The review will also highlight the role of piRNAs as either progenitors or suppressors in cancers, with a particular focus on BC. Lastly, it will touch upon the potential of piRNAs as biomarkers and therapeutic targets for BC.

Dexmedetomidine promotes colorectal cancer progression via Piwil2 signaling

PURPOSE

α2-adrenoceptor agonist dexmedetomidine (DEX) has been reported to promote tumorigenesis. Stem-cell protein Piwil2 is associated with cancer progression. Whether Piwil2 plays a role in tumor-promoting effects of DEX is unknown.

METHODS

We examined the expression of Piwil2 in human colorectal cancer (CRC) cell lines with/without DEX treatment. We also studied the roles of Piwil2 in proliferation, invasion, migration, as well as expressions of epithelial-mesenchymal transition (EMT)-related proteins in DEX-treated in vitro and in vivo CRC models. And the experiments with genetic and pharmacological treatments were conducted to investigate the underlying molecular mechanism.

RESULTS

RNA-sequencing (RNA-seq) analysis found Piwil2 is one of most upregulated genes upon DEX treatment in CRC cells. Furthermore, Piwil2 protein levels significantly increased in DEX-treated CRC cancer cells, which promoted proliferation, invasion, and migration in both CRC cell lines and human tumor xenografts model. Mechanistically, DEX increased nuclear factor E2-related factor 2 (Nrf2) expression, which enhanced Piwil2 transcription via binding to its promoter. Furthermore, in vitro experiments with Piwil2 knockdown or Siah2 inhibition indicated that DEX promoted EMT process and tumorigenesis through Siah2/PHD3/HIF1α pathway. The experiments with another α2-adrenoceptor agonist Brimonidine and antagonists yohimbine and atipamezole also suggested the role of Piwil2 signaling in tumor-promoting effects via an α2 adrenoceptor-dependent manner.

CONCLUSION

DEX promotes CRC progression may via activating α2 adrenoceptor-dependent Nrf2/Piwil2/Siah2 pathway and thus EMT process. Our work provides a novel insight into the mechanism underlying tumor-promoting effects of α2-adrenoceptor agonists.

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.

Expression of collagen-related piRNA is dysregulated in cultured dermal fibroblasts derived from patients with scleroderma

PIWI-interacting RNA (piRNA) is a class of recently discovered small non-coding RNAs. piRNAs derive from an initial transcript encompassing a piRNA cluster via a unique biosynthesis process, interact with PIWI proteins, bind to specific targets, and recruit chromatin modifiers to enable transcriptional repression. Abnormal expression of PIWI proteins and piRNAs has been reported in some human cancers, with participation of some PIWI/piRNAs complexes in tumorigenesis and association with cancer prognosis. Their expression in patients with systemic sclerosis (SSc) has not been widely elucidated. PIWI/piRNAs and their role in the pathogenesis of collagen accumulation in SSc was therefore investigated; no difference was found in the PIWIL1-4 levels between normal and cultured SSc dermal fibroblasts. Among piRNAs predicted to target SSc-related molecules, we first found significant piR-32364 up-regulation in SSc dermal fibroblasts, likely due to intrinsic TGF-β signaling. Forced piR-32364 overexpression in normal fibroblasts significantly reduced COL1A1 expression both at mRNA and protein levels, but not COL1A2. Thus, piR-32364 overexpression in SSc fibroblasts may be the negative feedback against collagen up-regulation, which could suggest the potential of piRNAs as a therapeutic target.

Single-Cell Transcriptomics for Unlocking Personalized Cancer Immunotherapy: Toward Targeting the Origin of Tumor Development Immunogenicity

Cancer immunotherapy is a promising approach for treating malignancies through the activation of anti-tumor immunity. However, the effectiveness and safety of immunotherapy can be limited by tumor complexity and heterogeneity, caused by the diverse molecular and cellular features of tumors and their microenvironments. Undifferentiated tumor cell niches, which we refer to as the "Origin of Tumor Development" (OTD) cellular population, are believed to be the source of these variations and cellular heterogeneity. From our perspective, the existence of distinct features within the OTD is expected to play a significant role in shaping the unique tumor characteristics observed in each patient. Single-cell transcriptomics is a high-resolution and high-throughput technique that provides insights into the genetic signatures of individual tumor cells, revealing mechanisms of tumor development, progression, and immune evasion. In this review, we explain how single-cell transcriptomics can be used to develop personalized cancer immunotherapy by identifying potential biomarkers and targets specific to each patient, such as immune checkpoint and tumor-infiltrating lymphocyte function, for targeting the OTD. Furthermore, in addition to offering a possible workflow, we discuss the future directions of, and perspectives on, single-cell transcriptomics, such as the development of powerful analytical tools and databases, that will aid in unlocking personalized cancer immunotherapy through the targeting of the patient's cellular OTD.

P-Element-Induced Wimpy Testis Proteins and P-Element-Induced Wimpy Testis-Interacting RNAs Expression in Ovarian Cancer Stem Cells

Background: P-element-induced wimpy testis (PIWI)-interacting RNAs (piRNAs) are a type of noncoding RNA and are predominantly expressed in germline cells. piRNAs function as gene regulators and potential biomarkers for the development of a number of malignancies. The biological importance of piRNAs in ovarian cancer is still unknown. In this study, we investigated the expression of piRNAs in ovarian cancer stem cells and compared it with that in adherent cells. Methods: To assess changes in the expression levels of PIWIL1/HIWI, PIWIL2/HILI, PIWIL3, and PIWIL4/HIWI2, we used quantitative reverse-transcription polymerase chain reaction (RT-qPCR) analysis. Changes in piRNA expression levels in ovarian cancer stem cells were analyzed using Arraystar piRNA microarray screening. Gene Ontology (GO) enrichment analysis was conducted to determine the potential functions of piRNAs. Results: Using microarray analysis, we identified a cohort of differentially expressed piRNAs. Fifteen piRNAs, including DQ570763 and DQ597396, were downregulated, and 58 piRNAs were upregulated when compared with those in adherent A2780 and SKOV3 cells (p > 0.05, >2.0, respectively). GO functions of the downregulated piRNAs (DQ570763 and DQ570797) suggest that their roles are commonly associated with the Golgi apparatus. In addition, A2780-SP and SKOV3-SP cells had higher PIWIL3 and PIWIL4 mRNA levels than adherent cells (A2780 and SKOV3). Moreover, we determined, using receiver operating characteristic plot, that the expression level of PIWIL4 was lower in responders than in nonresponders after treatment with platins in patients with ovarian cancer. Finally, in ovarian cancer, PIWIL4 expression was associated with somatic mutations of dynein axonemal heavy chain 2, signal induced proliferation associated 1 like 2, YTH N6-methyladenosine RNA-binding protein 1, TBC1 domain family member 8, and LPS responsive Beige-like anchor protein. Conclusion: Our study showed that PIWI proteins and piRNAs are potential diagnostic and prognostic biomarkers for ovarian cancer.

PIWIL2 Regulates the Proliferation, Apoptosis and Colony Formation of Colorectal Cancer Cell Line

Background

Tumor cells proliferation and apoptosis inhibition are the mechanisms through which the Colorectal Cancer (CRC) progression, metastasis and chemoresistance are promoted pathologically, offering clinical advantages for characterizing their molecular regulators.

Objectives

In this study, to unravel the role of PIWIL2 as a potential CRC oncogenic regulator, we examined the effect of its overexpression on proliferation, apoptosis and colony formation of SW480 colon cancer cell line.

Material and Methods

Established SW480-P (overexpression of PIWIL2) and SW480-control (SW480-empty vector) cell lines were cultured in DMEM containing 10% FBS with 1% penicillin-streptomycin. The total DNA and RNA was extracted for further experiments. Real-Time PCR and western blotting assay were performed to measure the differential expression of proliferation associated genes including the expression of cell cycle and anti-apoptotic genes as well as Ki-67 and PIWIL2 in both cell lines. Cell proliferation was determined using MTT assay, doubling time assay and the colony formation rate of transfected cells was measured with the 2D colony formation assay.

Results

At the molecular level, PIWIL2 overexpression was associated with significant up-regulation of cyclin D1, STAT3, BCL2-L1, BCL2-L2 and Ki-67 genes. MTT and doubling time assay showed that PIWIL2 expression induced time-related effects on proliferation rate of SW480 cells. Moreover, SW480-P cells had markedly greater capacity to form colonies.

Conclusions

PIWIL2 plays important roles to promote cancer cell proliferation and colonization via the cell cycle acceleration and inhibition of apoptosis, the mechanisms through which this gene seems to contribute to CRC development, metastasis and chemoresistance, hence potentially highlighting PIWIL2 targeted therapy as a valuable tool for CRC treatment.

Piwi-interacting RNAs (piRNAs) and Colorectal Carcinoma: Emerging Non-invasive diagnostic Biomarkers with Potential Therapeutic Target Based Clinical Implications

PIWI-interacting RNAs (piRNAs) constitute new small non-coding RNA molecules of around 24-31 nucleotides in length, mostly performing regulatory roles for the piwi protein family members. In recent times, developing evidence proposes that piRNAs are expressed in a tissue-specific way in various human tissues and act as moderate vital signalling pathways at the transcriptional or post-transcriptional level in addition to mammalian germline. Recent findings, however, show that the unusual expression of piRNAs is an exclusive and discrete feature in several diseases, including many human cancers. Recently, considerable evidence indicates that piRNAs could be dysregulated thus playing critical roles in tumorigenesis. The function and underlying mechanisms of piRNAs in cancer, particularly in colorectal carcinoma, are not fully understood to date. Abnormal expression of piRNAs is emerging as a critical player in cancer cell proliferation, apoptosis, invasion, and migration in vitro and in vivo. Functionally, piRNAs preserve genomic integrity and regulate the expression of downstream target genes through transcriptional or post-transcriptional mechanisms by repressing transposable elements' mobilization. However, little research has been done to check Piwi and piRNAs' potential role in cancer and preserve genome integrity by epigenetically silencing transposons via DNA methylation, especially in germline cancer stem cells. This review reveals emerging insights into piRNA functions in colorectal carcinoma, revealing novel findings behind various piRNA-mediated gene regulation mechanisms, biogenetic piRNA processes, and possible applications of piRNAs and piwi proteins in cancer diagnosis and their potential clinical significance in the treatment of colorectal carcinoma patients.

Attenuation of Piwil2 induced by hypoxic postconditioning prevents cerebral ischemic injury by inhibiting CREB2 promoter methylation

Epigenetic modification contributes to the pathogenesis of cerebral ischemia. Piwil2 belongs to the PIWI proteins subfamily and has a key role in the regulation of gene transcription through epigenetics. However, the roles of Piwil2 in cerebral ischemia have not been investigated. In this study, we aim to elucidate the roles and the underlying molecular mechanisms of Piwil2 in ischemic tolerance induced by hypoxic postconditioning (HPC) against transient global cerebral ischemia (tGCI). We found that the expression of Piwil2 in CA1 was downregulated by HPC after tGCI. Silencing Piwil2 with antisense oligodeoxynucleotide (AS-ODN) in CA1 after tGCI decreased the expression of apoptosis-related proteins and exerted neuroprotective effects. Opposite results were observed after overexpression of Piwil2 induced by administration of Piwil2-carried lentivirus. Furthermore, we revealed differentially expressed Piwil2-interacting piRNAs in CA1 between HPC and tGCI groups by RNA binding protein immunoprecipitation (RIP) assay. Moreover, downregulating Piwil2 induced by HPC or AS-ODN after tGCI caused a marked reduction of DNA methyltransferase 3A (DNMT3A), which in turn abolished the tGCI-induced increase in the DNA methylation of cyclic AMP response element-binding 2 (CREB2), thus increasing mRNA and protein of CREB2. Finally, downregulating Piwil2 restored dendritic complexity and length, prevented the loss of dentritic spines, thereby improving cognitive function after tGCI. These data firstly reveal that Piwil2 plays an important part in HPC-mediated neuroprotection against cerebral ischemia through epigenetic regulation of CREB2.

The function of novel small non-coding RNAs (piRNAs, tRFs) and PIWI protein in colorectal cancer

Although great research has been done to clarify the pathogenesis of colorectal cancer (CRC), it is still the third common cancer worldwide. Pathogenesis of CRC as a heterogeneous disease is correlated with mutations and epigenetic alterations that result in the inactivation of tumor-suppressive and activation of an oncogene. Small non-coding RNAs (sncRNAs), emerging as a key player in regulating the genes and protein expression, with a length less than 200 nucleotide (nt). In this review, we aimed to focus on the role and the biogenesis of PIWI-interacting RNA (piRNAs), and tRNA-derived small RNA (tRFs) and PIWI proteins in the initiation, progression, and metastasis of CRC and their molecular mechanisms to understand their function in cancers and to provide better therapeutic strategies for CRC.

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.

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.

piR-hsa-211106 Inhibits the Progression of Lung Adenocarcinoma Through Pyruvate Carboxylase and Enhances Chemotherapy Sensitivity

Although the importance of PIWI-interacting RNAs (piRNAs) in cancer has recently been recognized, studies on the role and functional mechanism of piRNAs in lung adenocarcinoma (LUAD) development and progression are limited. In this study, we identified 10 differently expressed piRNAs in LUAD tissues compared to normal tissues, among which, piR-hsa-211106 expression levels were downregulated in LUAD tissues and cell lines. Furthermore, the effects of piR-hsa-211106 on the malignant phenotypes and chemosensitivity of LUAD cells were detected by gain- and loss-of-function analyses in vitro and in vivo, which showed that piR-hsa-211106 inhibited LUAD cell proliferation, tumor growth, and migration, but promoted apoptosis. Moreover, our finding indicated that piR-hsa-211106 is a potential therapeutic target that synergistically imparts anticancer effects with a chemotherapeutic agent for LUAD-cisplatin. Further mechanistic investigation indicated that piR-hsa-211106 could bind to pyruvate carboxylase (PC) by RNA pull down and RNA immunoprecipitation assays and inhibited PC mRNA and protein expression. Our study demonstrates that piR-hsa-211106 inhibits LUAD progression by hindering the expression and function of PC and enhances chemotherapy sensitivity, suggesting that piR-hsa-211106 is a novel diagnostic and therapeutic target for LUAD.

Realization of Osteolysis, Angiogenesis, Immunosuppression, and Drug Resistance by Extracellular Vesicles: Roles of RNAs and Proteins in Their Cargoes and of Ectonucleotidases of the Immunosuppressive Adenosinergic Noncanonical Pathway in the Bone Marrow Niche of Multiple Myeloma

Simple Summary

Multiple myeloma (MM) is a disease that extensively involves bone, and angiogenesis and immunosuppression are important processes in the development of MM. Proteasome inhibitors and immunomodulatory drugs remarkably improve the survival of MM patients. However, MM is still an incurable disease that rapidly becomes resistant to these drugs. There is robust evidence that extracellular vesicles (EVs) contribute to cancer metastasis. Osteoclasts, in addition to immunosuppressive cells in the bone marrow (BM), are key players in osteolysis and immunosuppression. BM stromal cells and MM cells secrete EVs through which they communicate with each other: EVs, in fact, contain proteins, small RNAs, and long non-coding RNAs that mediate this communication and contribute to angiogenesis, osteolysis, and cancer dissemination and drug resistance. Ectoenzymes are expressed in myeloma cells, osteoclasts, and stromal cells and produce immunosuppressive adenosine. Recently, an antibody targeting CD38, an ectoenzyme, has been shown to improve the survival of patients with MM. Thus, understanding the properties of EV and ectoenzymes will help elucidate key processes of MM development.

Abstract

Angiogenesis and immunosuppression promote multiple myeloma (MM) development, and osteolysis is a primary feature of MM. Although immunomodulatory drugs and proteasome inhibitors (PIs) markedly improve the survival of patients with MM, this disease remains incurable. In the bone marrow niche, a chain of ectoenzymes, including CD38, produce immunosuppressive adenosine, inhibiting T cell proliferation as well as immunosuppressive cells. Therefore, anti-CD38 antibodies targeting myeloma cells have the potential to restore T cell responses to myeloma cells. Meanwhile extracellular vesicles (EVs) containing microRNAs, proteins such as cytokines and chemokines, long noncoding RNAs, and PIWI-interacting RNAs have been shown to act as communication tools in myeloma cell/microenvironment interactions. Via EVs, mesenchymal stem cells allow myeloma cell dissemination and confer PI resistance, whereas myeloma cells promote angiogenesis, myeloid-derived suppressor cell proliferation, and osteoclast differentiation and inhibit osteoblast differentiation. In this review, to understand key processes of MM development involving communication between myeloma cells and other cells in the tumor microenvironment, EV cargo and the non-canonical adenosinergic pathway are introduced, and ectoenzymes and EVs are discussed as potential druggable targets for the treatment of MM patients.

The debatable presence of PIWI-interacting RNAs in invasive breast cancer

Numerous factors influence breast cancer (BC) prognosis, thus complicating the prediction of outcome. By identifying biomarkers that would distinguish the cases with poorer response to therapy already at the time of diagnosis, the rate of survival could be improved. Lately, Piwi-interacting RNAs (piRNAs) have been introduced as potential cancer biomarkers, however, due to the recently raised challenges in piRNA annotations, further evaluation of piRNAs' involvement in cancer is required. We performed small RNA sequencing in 227 fresh-frozen breast tissue samples from the Eastern Finnish Kuopio Breast Cancer Project material to study the presence of piRNAs in BC and their associations with the clinicopathological features and outcome of BC patients. We observed the presence of three small RNAs annotated as piRNA database entries (DQ596932, DQ570994, and DQ571955) in our samples. The actual species of these RNAs however remain uncertain. All three small RNAs were upregulated in grade III tumors and DQ596932 additionally in estrogen receptor negative tumors. Furthermore, patients with estrogen receptor positive BC and higher DQ571955 had shorter relapse-free survival and poorer BC-specific survival, thus indicating DQ571955 as a candidate predictive marker for radiotherapy response in estrogen receptor positive BC. DQ596932 showed possible prognostic value in BC, whereas DQ570994 was identified as a candidate predictive marker for tamoxifen and chemotherapy response. These three small RNAs appear as candidate biomarkers for BC, which could after further investigation provide novel approaches for the treatment of therapy resistant BC. Overall, our results indicate that the prevalence of piRNAs in cancer is most likely not as comprehensive as has been previously thought.

Small Non-Coding-RNA in Gynecological Malignancies

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

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.

A Comprehensive Molecular and Clinical Analysis of the piRNA Pathway Genes in Ovarian Cancer

Simple Summary

Although ovarian cancer (OC) is one of the most lethal gynecological cancers, its development and progression remain poorly understood. The piRNA pathway is important for transposon defense and genome stability. piRNA maturation and function involve a number of genes known as the piRNA pathway genes. These genes have recently been implicated in cancer development and progression but information about their role in OC is limited. Our work aimed to provide a better understanding of the roles of piRNA pathway genes in OC. Through analyzing changes in the abundance of 10 piRNA pathway genes, we discovered gene expression differences in benign vs. cancer, chemosensitive vs. chemoresistant and post hormone treatment in OC samples and cells. Furthermore, we observed the differential effects of these genes on patient survival and OC cell invasion. Overall, this work supports a role of the piRNA pathway genes in OC progression and encourages further study of their clinical relevance.

Abstract

Ovarian cancer (OC) is one of the most lethal gynecological malignancies, yet molecular mechanisms underlying its origin and progression remain poorly understood. With increasing reports of piRNA pathway deregulation in various cancers, we aimed to better understand its role in OC through a comprehensive analysis of key genes: PIWIL1-4, DDX4, HENMT1, MAEL, PLD6, TDRD1,9 and mutants of PIWIL1 (P1∆17) and PIWIL2 (PL2L60). High-throughput qRT-PCR (n = 45) and CSIOVDB (n = 3431) showed differential gene expression when comparing benign ovarian tumors, low grade OC and high grade serous OC (HGSOC). Significant correlation of disparate piRNA pathway gene expression levels with better progression free, post-progression free and overall survival suggests a complex role of this pathway in OC. We discovered PIWIL3 expression in chemosensitive but not chemoresistant primary HGSOC cells, providing a potential target against chemoresistant disease. As a first, we revealed that follicle stimulating hormone increased PIWIL2 expression in OV-90 cells. PIWIL1, P1∆17, PIWIL2, PL2L60 and MAEL overexpression in vitro and in vivo decreased motility and invasion of OVCAR-3 and OV-90 cells. Interestingly, P1∆17 and PL2L60, induced increased motility and invasion compared to PIWIL1 and PIWIL2. Our results in HGSOC highlight the intricate role piRNA pathway genes play in the development of malignant neoplasms.

CBP-mediated Wnt3a/β-catenin signaling promotes cervical oncogenesis initiated by Piwil2

Our previous work demonstrated that Piwil2 reactivated by the human papillomavirus oncoproteins E6 and E7 may reprogram somatic cells into tumor-initiating cells (TICs), which contribute to cervical neoplasia lesions. Maintaining the stemness of TICs is critical for the progression of cervical lesions. Here, we determined that canonical Wnt signaling was aberrantly activated in HaCaT cells transfected with lentivirus expressing Piwil2 and in cervical lesion specimens of low-grade squamous intraepithelial lesion, high-grade squamous intraepithelial lesion, and invasive carcinoma. Blocking the β-catenin and CREB binding protein interaction with ICG-001 significantly downregulated the reprogramming factors c-Myc, Nanog, Oct4, Sox2, and Klf4, thus leading to cell differentiation and preventing tumorigenicity in Piwil2-overexpressing HaCaT cells. Similarly, Piwil2 also critically regulated the canonical Wnt signaling pathway in cervical cancer. We further demonstrated that ICG-001 increased cisplatin sensitivity and significantly suppressed tumor growth of cervical cancer alone or in combination with cisplatin both in vitro and in vivo. The β-catenin/ CREB binding protein-mediated transcription activated by Piwil2 is essential for the maintenance of TICs, therefore contributing to the progression of cervical oncogenesis.

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.

Biological roles of piRNAs in colorectal cancer

Colorectal cancer (CRC) is one of the most common malignancies worldwide and a major cause of cancer-related deaths. Numerous studies have suggested that piwi-interacting RNAs (piRNAs), a new type of non-coding RNA (ncRNA), are closely related to the occurrence and development of cancer. piRNAs have been shown to regulate the occurrence of CRC by modulating multiple molecular signaling pathways. Here, the roles of piRNAs in CRC were reviewed to provide evidence for their potential as molecular targets for CRC.

Cyclin D1 promotes secretion of pro-oncogenic immuno-miRNAs and piRNAs

The molecular mechanisms governing the secretion of the non-coding genome are poorly understood. We show herein that cyclin D1, the regulatory subunit of the cyclin-dependent kinase that drives cell-cycle progression, governs the secretion and relative proportion of secreted non-coding RNA subtypes (miRNA, rRNA, tRNA, CDBox, scRNA, HAcaBox. scaRNA, piRNA) in human breast cancer. Cyclin D1 induced the secretion of miRNA governing the tumor immune response and oncogenic miRNAs. miR-21 and miR-93, which bind Toll-Like Receptor 8 to trigger a pro-metastatic inflammatory response, represented >85% of the cyclin D1-induced secreted miRNA transcripts. Furthermore, cyclin D1 regulated secretion of the P-element Induced WImpy testis (PIWI)-interacting RNAs (piRNAs) including piR-016658 and piR-016975 that governed stem cell expansion, and increased the abundance of the PIWI member of the Argonaute family, piwil2 in ERα positive breast cancer. The cyclin D1-mediated secretion of pro-tumorigenic immuno-miRs and piRNAs may contribute to tumor initiation and progression.

The Clinical Significance of PIWIL3 and PIWIL4 Expression in Pancreatic Cancer

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

PIWI-interacting RNAs: new biomarkers for diagnosis and treatment of breast cancer

Cancer is one of the most important reasons of mortality in the world. However, there are several therapeutic platforms to treat patients who suffering from cancer common treatments such as surgery, chemotherapy and etc. The current therapeutic approaches are related to some limitations. Hence, more understanding about molecular mechanisms that involved in cancer particularly in breast cancer pathogenesis, could contribute to provide better therapeutic platforms. Recently, non-coding RNAs such as microRNAs have attracted researchers' attention in the field of cancer due to their functions in gene expression's regulation and functional interactions with other molecules. Interestingly, great advances in next-generation sequencing lead to considering other roles for another non-coding RNAs subgroup called PIWI-interacting RNAs (piRNAs) in addition to their functions in the germline. Novel studies investigated the role of piRNAs in several cancers including lung cancer, hepatocellular carcinoma, gastric cancer, multiple myeloma and colorectal cancer. Hopefully, based on new findings, piRNAs may be a potential biomarker which can be used as a tool to diagnose or treat breast cancer. Thus, this review aimed to discuss the role of piRNAs in breast cancer progression and metastasis as well as its molecular mechanisms.

The emerging role of the piRNA/piwi complex in cancer

Piwi interacting RNAs (piRNAs) constitute novel small non-coding RNA molecules of approximately 24-31 nucleotides in length that often bind to members of the piwi protein family to play regulatory roles. Recently, emerging evidence suggests that in addition to the mammalian germline, piRNAs are also expressed in a tissue-specific manner in a variety of human tissues and modulate key signaling pathways at the transcriptional or post-transcriptional level. In addition, a growing number of studies have shown that piRNA and PIWI proteins, which are abnormally expressed in various cancers, may serve as novel biomarkers and therapeutic targets for tumor diagnostics and treatment. However, the functions of piRNAs in cancer and their underlying mechanisms remain incompletely understood. In this review, we discuss current findings regarding piRNA biogenetic processes, functions, and emerging roles in cancer, providing new insights regarding the potential applications of piRNAs and piwi proteins in cancer diagnosis and clinical treatment.

Multilayer network analysis of miRNA and protein expression profiles in breast cancer patients

MiRNAs and proteins play important roles in different stages of breast tumor development and serve as biomarkers for the early diagnosis of breast cancer. A new algorithm that combines machine learning algorithms and multilayer complex network analysis is hereby proposed to explore the potential diagnostic values of miRNAs and proteins. XGBoost and random forest algorithms were employed to screen the most important miRNAs and proteins. Maximal information coefficient was applied to assess intralayer and interlayer connection. A multilayer complex network was constructed to identify miRNAs and proteins that could serve as biomarkers for breast cancer. Proteins and miRNAs that are nodes in the network were subsequently categorized into two network layers considering their distinct functions. The betweenness centrality was used as the first measurement of the importance of the nodes within each single layer. The degree of the nodes was chosen as the second measurement to map their signalling pathways. By combining these two measurements into one score and comparing the difference of the same candidate between normal tissue and cancer tissue, this novel multilayer network analysis could be applied to successfully identify molecules associated with breast cancer.

The role of 17β‑estradiol‑induced upregulation of Piwi‑like 4 in modulating gene expression and motility in breast cancer cells

A majority of breast cancer cases are positive for the estrogen receptor (ER), which means that they can respond to the estrogen hormone to achieve growth. Hence, the ER signaling pathway has been extensively targeted in pharmaceutical research and development in order to suppress tumor growth. However, prevalent hormone therapy and targeted therapy often become ineffective as cancer cells ultimately develop resistance, suggesting that there could be unidentified signaling molecules and events that regulate breast cancer growth. Notably, recent studies have uncovered that Piwi-like (Piwil) proteins, which were initially found in germline cells, are expressed in a wide spectrum of human cancers, including breast cancers. Although Piwil proteins have been well established to silence retrotransposons and to promote heterochromatin formation in germline cells, their somatic functions in cancer cells remain largely unknown. In the present study, we profiled the expression of four Piwi homologs in an ER-positive breast cancer cell line, MCF-7, and found that only Piwil4 was upregulated by 17β-estradiol treatment. Notably, Piwil4 upregulation was not observed in an ER-positive but non-tumorigenic breast cancer cell line, MCF-12A. In addition, the induced expression of Piwil4 was dependent on estrogen/ERα signaling. To explore the biological significance of Piwil4 in breast cancer growth, we knocked down Piwil4 with multiple siRNAs and observed the suppressed expression of some canonical targets of ER. The knockdown of Piwil4 expression also decreased the migration and invasion capabilities of MCF-7 cells. Furthermore, the loss-of-function of Piwil4 reduced the motility of MCF-7 cells in wound-healing assays, which could be associated to decreased expression of vimentin and N-cadherin. Collectively, these findings revealed that Piwil4 is a novel regulator of ER signaling that could be targeted to inhibit breast cancer growth and migration.

An unusual intragenic promoter of PIWIL2 contributes to aberrant activation of oncogenic PL2L60

PIWIL2-like (PL2L) protein 60 (PL2L60), a product of aberrantly activated PIWIL2 gene, is widely expressed in various types of tumors and may promote tumorigenesis. However, the mechanisms underlying the activation of expression of PL2L60 remain unknown. In this study, an intragenic promoter responsible for the activation of PL2L60 within the human PIWIL2 gene has been identified, cloned and characterized. The promoter of PL2L60 is located in the intron 10 of the host gene PIWIL2. Bioinformatic and mutagenic analysis reveals that this intragenic promoter within the sequence of 50 nucleotides contains two closely arranged cis-acting elements specific for the hepatic leukemia factor (HLF) in the positive strand and signal transducer and activator of transcription 3 (STAT3) in the negative strand. Chromatin immunoprecipitation analysis demonstrates that both the HLF and polymerase II (Pol II), a hallmark of active promoters, directly bind to the sequence, although STAT3 does not. Knockdown of HLF and STAT3 alone or both by RNA interference significantly reduced both promoter activity and the PL2L60 protein expression, although there is no additive effect. The expression of PL2L60 proteins was enhanced when host gene Piwil2 was genetically disrupted in a murine cell model. Taken together, we have identified a PL2L60-specific intragenic promoter in the host gene of PIWIL2, which is interdependently activated by HLF and STAT3 through steric interaction. This activation is dependent on cellular milieu rather than the integrity of host gene PIWIL2, highlighting a novel, important mechanism for a cancer-causing gene to be activated during tumorigenesis.

PIWIL2 suppresses Siah2-mediated degradation of HDAC3 and facilitates CK2α-mediated HDAC3 phosphorylation

HDAC3 is involved in deacetylation of histone and non-histone proteins, having a key role in the regulation of gene transcription and also in the process of tumorgenesis. However, how HDAC3 is regulated in cancer remains largely unclear. Here, we showed that PIWIL2 can interact with HDAC3, leading to stabilization of HDAC3 from ubiquitin-mediated degradation by competitive association with E3 ubiquitin ligase Siah2. Furthermore, we found that expression of PIWIL2 enhanced HDAC3 activity via CK2α. PIWIL2 facilitated the interaction between HDAC3 and CK2α, thus exhibiting a promotion on the HDAC3 phosphorylation by CK2α. Further work showed that PIWIL2 could promote cell proliferation and suppress cell apoptosis via regulating HDAC3. Our present study firstly revealed that PIWIL2 can play a role in HDAC3-mediated epigenetic regulation on cancer cell proliferation and apoptosis. These findings provide a novel insight into the roles of PIWIL2 in tumorigenesis.

Piwil2 is reactivated by HPV oncoproteins and initiates cell reprogramming via epigenetic regulation during cervical cancer tumorigenesis

The human papillomavirus (HPV) oncoproteins E6 and E7 are risk factors that are primarily responsible for the initiation and progression of cervical cancer, and they play a key role in immortalization and transformation by reprogramming differentiating host epithelial cells. It is unclear how cervical epithelial cells transform into tumor-initiating cells (TICs). Here, we observed that the germ stem cell protein Piwil2 is expressed in pre-cancerous and malignant lesions of the cervix and cervical cancer cell lines with the exception of the non-HPV-infected C33a cell line. Knockdown of Piwil2 by shRNA led to a marked reduction in proliferation and colony formation, in vivo tumorigenicity, chemo-resistance, and the proportion of cancer stem-like cells. In contrast, Piwil2 overexpression induced malignant transformation of HaCaT cells and the acquisition of tumor-initiating capabilities. Gene-set enrichment analysis revealed embryonic stem cell (ESC) identity, malignant biological behavior, and specifically, activation targets of the cell reprogramming factors c-Myc, Klf4, Nanog, Oct4, and Sox2 in Piwil2-overexpressing HaCaT cells. We further confirmed that E6 and E7 reactivated Piwil2 and that E6 and E7 overexpression resulted in a similar gene-set enrichment pattern as Piwil2 overexpression in HaCaT cells. Moreover, Piwil2 overexpression or E6 and E7 activation induced H3K9 acetylation but reduced H3K9 trimethylation, which contributed to the epigenetic reprogramming and ESC signature maintenance, as predicted previously. Our study demonstrates that Piwil2, reactivated by the HPV oncoproteins E6 and E7, plays an essential role in the transformation of cervical epithelial cells to TICs via epigenetics-based cell reprogramming.

Differential expression of PIWIL2 in papillary thyroid cancers

Thyroid cancer is the most common type of endocrine malignancy and a leading cause of death among endocrine organ-related cancers. Similar to other types of cancers, early diagnosis of thyroid cancer is important to increase the survival and treatment of this disease. Several immunohistochemical markers are used in the differential diagnosis of thyroid papillary carcinoma. Also, increasing evidence indicates that P-element induced wimpy testis like 2 (PIWIL2) is an RNA-binding protein involved in the induction and progression of numerous types of human malignancies such as lung, breast, colon, prostate and cervix cancers. However, the role of PIWIL2 was poorly investigated in thyroid cancers. Accordingly, aim of the present study was to elucidate the relationship between PIWIL2 and thyroid cancers. The expression level of PIWIL2 was determined by analyzing both protein and mRNA levels in papillary and micropapillary carcinoma tissues by using immunohistochemistry and real-time PCR methods, respectively. Immunohistochemical analysis of HBME-1, galectin-3 and CK-19 was also performed. Similar to other immune markers of HBME-1, galectin-3 and CK-19, protein expression levels of PIWIL2 was significantly up-regulated in both papillary and micropapillary thyroid cancers (p < 0.01). Moreover, consistent with protein expression levels, mRNA expression levels of PIWIL2 was elevated in both papillary and micropapillary thyroid cancer tissues. Yet, mRNA expression changes were statistically insignificant. In conclusion, results of the current study suggest that PIWIL2 can be involved in thyroid cancer tumorigenesis and can be used as a novel predictive biomarker and/or therapeutic target.

NSD1 inactivation defines an immune cold, DNA hypomethylated subtype in squamous cell carcinoma

Chromatin modifying enzymes are frequently mutated in cancer, resulting in widespread epigenetic deregulation. Recent reports indicate that inactivating mutations in the histone methyltransferase NSD1 define an intrinsic subtype of head and neck squamous cell carcinoma (HNSC) that features pronounced DNA hypomethylation. Here, we describe a similar hypomethylated subtype of lung squamous cell carcinoma (LUSC) that is enriched for both inactivating mutations and deletions in NSD1. The ‘NSD1 subtypes’ of HNSC and LUSC are highly correlated at the DNA methylation and gene expression levels, featuring ectopic expression of developmental transcription factors and genes that are also hypomethylated in Sotos syndrome, a congenital disorder caused by germline NSD1 mutations. Further, the NSD1 subtype of HNSC displays an ‘immune cold’ phenotype characterized by low infiltration of tumor-associated leukocytes, particularly macrophages and CD8⁺ T cells, as well as low expression of genes encoding the immunotherapy target PD-1 immune checkpoint receptor and its ligands. Using an in vivo model, we demonstrate that NSD1 inactivation results in reduced T cell infiltration into the tumor microenvironment, implicating NSD1 as a tumor cell-intrinsic driver of an immune cold phenotype. NSD1 inactivation therefore causes epigenetic deregulation across cancer sites, and has implications for immunotherapy.

Piwil2-transfected human fibroblasts are cancer stem cell-like and genetically unstable

Uncontrolled cell proliferation and inhibition of apoptosis are considered to be vital for cancer initiation, maintenance, infiltration, metastasis and recurrence after anti-cancer therapy. Here we report the generation of a novel cell line by reprogramming child foreskin fibroblast with the full length apoptosis inhibitor gene PIWIL2. The fibroblasts transfected with PIWIL2 expressed the stem cell markers OCT-4, NANOG, SOX-2, KLF-4 and C-MYC; endoderm marker AFP and GATA6; mesoderm markers ACTA2 and BRACHYURY; and ectoderm markers NESTIN and TUBB3. The karyotype was found to be hyperdiploid. The PIWIL2 transfected fibroblast cells grew into tumorous masses within 5 weeks of subcutaneous injection into adult nude mice. Although the injected cell expressed markers for all three germlines, ectoderm, mesoderm, and endoderm, they did not form teratomas in vivo. This study indicates that the PIWIL2 gene could play a key role in cancer induction and maintenance. This method for generating induced tumorigenic cells (ITGC) provides a new research tool to study oncogenesis that in turn may lead to a better understanding of cancer etiology and the development of novel anti-cancer therapies.

Cbp80 is needed for the expression of piRNA components and piRNAs

Cap binding protein 80 (Cbp80) is the larger subunit of the nuclear cap-binding complex (nCBC), which is known to play important roles in nuclear mRNA processing, export, stability and quality control events. Reducing Cbp80 mRNA levels in the female germline revealed that Cbp80 is also involved in defending the germline against transposable elements. Combining such knockdown experiments with large scale sequencing of small RNAs further showed that Cbp80 is involved in the initial biogenesis of piRNAs as well as in the secondary biogenesis pathway, the ping-pong amplification cycle. We further found that Cbp80 knockdown not only led to the upregulation of transposons, but also to delocalization of Piwi, Aub and Ago3, key factors in the piRNA biosynthesis pathway. Furthermore, compared to controls, levels of Piwi and Aub were also reduced upon knock down of Cbp80. On the other hand, with the same treatment we could not detect significant changes in levels or subcellular distribution (nuage localization) of piRNA precursor transcripts. This shows that Cbp80 plays an important role in the production and localization of the protein components of the piRNA pathway and it seems to be less important for the production and export of the piRNA precursor transcripts.

High expression of PIWIL2 promotes tumor cell proliferation, migration and predicts a poor prognosis in glioma

Piwi-like RNA-mediated gene silencing 2 (PIWIL2), has been reported as an oncogene tightly associated with the genesis and progression of various malignancies. Nevertheless, the function of the PIWIL2 protein in human gliomas has not yet been clarified. In this study, we sought to investigate the clinical significance of PIWIL2 expression and reveal its function in the pathological process of gliomas. Through western blot and immunohistochemical analyses we found that PIWIL2 was overexpressed in glioma tissues. Moreover, the expression level of PIWIL2 was also significantly correlated with the WHO grades of human gliomas and Ki-67 expression. Kaplan‑Meier curves indicated that PIWIL2 was a prognostic factor for the survival of glioma patients and a high expression of PIWIL2 was correlated with a poor prognosis. In vitro, knockdown of PIWIL2 in glioma cells was shown to induce cell cycle arrest and increase apoptosis. Furthermore, silencing of PIWIL2 expression also obviously suppressed the migration of glioma cells. All the results demonstrated that PIWIL2 plays a significant role in the pathogenesis of human gliomas and may be used as a potential diagnostic marker and a therapeutic target of glioma in the future.

HILI destabilizes microtubules by suppressing phosphorylation and Gigaxonin-mediated degradation of TBCB

Human PIWIL2, aka HILI, is a member of PIWI protein family and overexpresses in various tumors. However, the underlying mechanisms of HILI in tumorigenesis remain largely unknown. TBCB has a critical role in regulating microtubule dynamics and is overexpressed in many cancers. Here we report that HILI inhibits Gigaxonin-mediated TBCB ubiquitination and degradation by interacting with TBCB, promoting the binding between HSP90 and TBCB, and suppressing the interaction between Gigaxonin and TBCB. Meanwhile, HILI can also reduce phosphorylation level of TBCB induced by PAK1. Our results showed that HILI suppresses microtubule polymerization and promotes cell proliferation, migration and invasion via TBCB for the first time, revealing a novel mechanism for HILI in tumorigenesis.

The meaning of PIWI proteins in cancer development

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

Rare germline alterations in cancer-related genes associated with the risk of multiple primary tumor development

Multiple primary tumors (MPT) have been described in carriers of inherited cancer predisposition genes. However, the genetic etiology of a large proportion of MPT cases remains unclear. We reviewed 267 patients with hereditary cancer predisposition syndromes (HCPS) that underwent genetic counseling and selected 22 patients with MPT to perform genomic analysis (CytoScan HD Array, Affymetrix) aiming to identify new alterations related to a high risk of developing MPT. Twenty patients had a positive family history of cancer and 11 met phenotypic criteria for HCPS. Genetic testing for each of the genes associated with these syndromes revealed negative results for pathogenic mutations. Seventeen rare germline copy number variations (CNVs) covering 40 genes were identified in 11 patients, including an EPCAM/MSH2 deletion in one Lynch syndrome patient. An enrichment analysis revealed a significant number of genes (where the CNVs are mapped) associated with carcinogenesis and/or related to functions implicated with tumor development, such as proliferation and cell survival. An interaction network analysis highlighted the importance of TP53 pathway in cancer emergence. A high number of germline copy-neutral loss of heterozygosity (cnLOH) was identified in nine cases, particularly in two patients. Eighteen genes were covered by both rare CNVs and cnLOH, including 14 related to tumorigenesis and seven genes (ABCC1, KDM4C, KIAA0430, MYH11, NDE1, PIWIL2, and ULK2) specifically associated with cellular growth and proliferation. Overall, we identified 14 cases with rare CNVs and/or cnLOH that may contribute to the risk of MPT development.

KEY MESSAGE

CNVs may explain the risk of hereditary cancer syndromes in MPT patients. CNVs affecting genes related to cancer are candidates to be involved in MPT risk. EPCAM/MSH2 deletions should be investigated in patients suspected to have LS. Gene enrichment related to the TP53 network is associated with MPT development. cnLOH and CNVs contribute to the risk of MPT development.

Enrichment and Detection of Circulating Tumor Cells and Other Rare Cell Populations by Microfluidic Filtration

The current standard methods for isolating circulating tumor cells (CTCs) from blood involve EPCAM-based immunomagnetic approaches. A major disadvantage of these strategies is that CTCs with low EPCAM expression will be missed. Isolation by size using filter membranes circumvents the reliance on this cell surface marker, and can facilitate the capture not only of EPCAM-negative CTCs but other rare cells as well. These cells that are trapped on the filter membrane can be characterized by immunocytochemistry (ICC) , enumerated and profiled to elucidate their clinical significance. In this chapter, we discuss advances in filtration systems to capture rare cells as well as downstream ICC methods to detect and identify these cells. We highlight our recent clinical study demonstrating the feasibility of using a novel method consisting of automated microfluidic filtration and sequential ICC for detection and enumeration of CTCs, as well as circulating mesenchymal cells (CMCs), circulating endothelial cells (CECs), and putative circulating stem cells (CSCs). We hypothesize that simultaneous analysis of circulating rare cells in blood of cancer patients may lead to a better understanding of disease progression and development of resistance to therapy.

Upregulation of MEK5 by Stat3 promotes breast cancer cell invasion and metastasis

Mitogen extracellular-signal-regulated kinase kinase 5 (MEK5) plays an important role in promoting cell proliferation and tumorigenesis. The aberrant expression of MEK5 has been reported in various malignant diseases including cancers of breast, prostate, lung, colorectal and brain. However, the function and regulation of MEK5 signaling pathway are ambiguous and remain elusive with respect to its oncogenic roles in various cancers, especially in the regulation of the initiation and progression of cancer invasion and metastasis. Ectopic expression of MEK5 or knockdown of MEK5 by shRNA with in vitro cell based models demonstrated the role of MEK5 in regulation of epithelial mesenchymal transition (EMT) and breast cancer invasion and metastasis. Here, we show that MEK5 upregulated by Stat3 promotes breast cancer cell invasion through EMT. Further study demonstrated that Stat3 could bind to promoter region of MEK5 and enhanced MEK5 transcription and expression. In addition, the phosphorylation of MEK5 significantly increased in breast cancer cells corresponding to metastatic capability of breast cancer cells. The depletion of MEK5 by shRNA significantly decreased breast cancer invasion. Ectopic expression of MEK5 could confer non-invasive breast cancer cells to become invasion capable cells. Moreover, the phosphorylation of Erk5, a MEK5-regulated downstream kinase, was also upregulated consistent with the increased level of active MEK5. Our studies provide insights into a molecular mechanism by which MEK5 transcriptionally upregulated by Stat3 augments breast cancer cell EMT, which subsequently enhances cancer cell invasion and metastasis. This finding may suggest that Stat3 and MEK5/Erk5 pathways could be an effective therapeutic target for inhibition of breast cancer invasion and metastasis.

Genetic variants in the PIWI-piRNA pathway gene DCP1A predict melanoma disease-specific survival

The Piwi-piRNA pathway is important for germ cell maintenance, genome integrity, DNA methylation and retrotransposon control and thus may be involved in cancer development. In this study, we comprehensively analyzed prognostic roles of 3,116 common SNPs in PIWI-piRNA pathway genes in melanoma disease-specific survival. A published genome-wide association study (GWAS) by The University of Texas M.D. Anderson Cancer Center was used to identify associated SNPs, which were later validated by another GWAS from the Harvard Nurses' Health Study and Health Professionals Follow-up Study. After multiple testing correction, we found that there were 27 common SNPs in two genes (PIWIL4 and DCP1A) with false discovery rate < 0.2 in the discovery dataset. Three tagSNPs (i.e., rs7933369 and rs508485 in PIWIL4; rs11551405 in DCP1A) were replicated. The rs11551405 A allele, located at the 3' UTR microRNA binding site of DCP1A, was associated with an increased risk of melanoma disease-specific death in both discovery dataset [adjusted Hazards ratio (HR) = 1.66, 95% confidence interval (CI) = 1.21-2.27, p =1.50 × 10^-3 ] and validation dataset (HR = 1.55, 95% CI = 1.03-2.34, p = 0.038), compared with the C allele, and their meta-analysis showed an HR of 1.62 (95% CI, 1.26-2.08, p =1.55 × 10^-4 ). Using RNA-seq data from the 1000 Genomes Project, we found that DCP1A mRNA expression levels increased significantly with the A allele number of rs11551405. Additional large, prospective studies are needed to validate these findings.

The Role of PIWIL4, an Argonaute Family Protein, in Breast Cancer

P-element-induced wimpy testis (PIWI) proteins bind to PIWI-interacting RNAs and play key roles in the biogenesis and functions of PIWI-interacting RNAs. It has been reported that PIWI proteins are essential for stem cell self-renewal and germline development in diverse organisms and that they are ectopically expressed in multiple forms of cancer. However, the role of PIWI in cancer remains elusive. Here we report that one of the four PIWI proteins in humans, PIWIL4, is highly expressed in both breast cancer tissues and the cytoplasm of MDA-MB-231 cells derived from breast cancer. Reducing PIWIL4 expression drastically impairs the migration ability of MDA-MB-231 cells, significantly increases their apoptosis, and mildly affects their proliferation. Our transcriptome and proteome analysis reveal that these functions are at least partially achieved via the PIWIL4 regulation of TGF-β and FGF signaling pathways and MHC class II proteins. These findings suggest that PIWIL4 may serve as a potential therapeutic target for breast cancer.

Reversible lineage-specific priming of human embryonic stem cells can be exploited to optimize the yield of differentiated cells

The clinical use of human embryonic stem cells (hESCs) requires efficient cellular expansion that must be paired with an ability to generate specialized progeny through differentiation. Self-renewal and differentiation are deemed inherent hallmarks of hESCs and a growing body of evidence suggests that initial culture conditions dictate these two aspects of hESC behavior. Here, we reveal that defined culture conditions using commercial mTeSR1 media augment the expansion of hESCs and enhance their capacity for neural differentiation at the expense of hematopoietic lineage competency without affecting pluripotency. This culture-induced modification was shown to be reversible, as culture in mouse embryonic fibroblast-conditioned media (MEF-CM) in subsequent passages allowed mTeSR1-expanded hESCs to re-establish hematopoietic differentiation potential. Optimal yield of hematopoietic cells can be achieved by expansion in mTeSR1 followed by a recovery period in MEF-CM. Furthermore, the lineage propensity to hematopoietic and neural cell types could be predicted via analysis of surrogate markers expressed by hESCs cultured in mTeSR1 versus MEF-CM, thereby circumventing laborious in vitro differentiation assays. Our study reveals that hESCs exist in a range of functional states and balance expansion with differentiation potential, which can be modulated by culture conditions in a predictive and quantitative manner.

A piece of the pi(e): The diverse roles of animal piRNAs and their PIWI partners

Small non-coding RNAs are indispensable to many biological processes. A class of endogenous small RNAs, termed PIWI-interacting RNAs (piRNAs) because of their association with PIWI proteins, has known roles in safeguarding the genome against inordinate transposon mobilization, embryonic development, and stem cell regulation, among others. This review discusses the biogenesis of animal piRNAs and their diverse functions together with their PIWI protein partners, both in the germline and in somatic cells, and highlights the evolutionarily conserved aspects of these molecular players in animal biology.

A Novel Strategy for Detection and Enumeration of Circulating Rare Cell Populations in Metastatic Cancer Patients Using Automated Microfluidic Filtration and Multiplex Immunoassay

Size selection via filtration offers an antigen-independent approach for the enrichment of rare cell populations in blood of cancer patients. We evaluated the performance of a novel approach for multiplex rare cell detection in blood samples from metastatic breast (n = 19) and lung cancer patients (n = 21), and healthy controls (n = 30) using an automated microfluidic filtration and multiplex immunoassay strategy. Captured cells were enumerated after sequential staining for specific markers to identify circulating tumor cells (CTCs), circulating mesenchymal cells (CMCs), putative circulating stem cells (CSCs), and circulating endothelial cells (CECs). Preclinical validation experiments using cancer cells spiked into healthy blood demonstrated high recovery rate (mean = 85%) and reproducibility of the assay. In clinical studies, CTCs and CMCs were detected in 35% and 58% of cancer patients, respectively, and were largely absent from healthy controls (3%, p = 0.001). Mean levels of CTCs were significantly higher in breast than in lung cancer patients (p = 0.03). Fifty-three percent (53%) of cancer patients harbored putative CSCs, while none were detectable in healthy controls (p<0.0001). In contrast, CECs were observed in both cancer and control groups. Direct comparison of CellSearch^® vs. our microfluidic filter method revealed moderate correlation (R² = 0.46, kappa = 0.47). Serial blood analysis in breast cancer patients demonstrated the feasibility of monitoring circulating rare cell populations over time. Simultaneous assessment of CTCs, CMCs, CSCs and CECs may provide new tools to study mechanisms of disease progression and treatment response/resistance.

Epigenome-wide analysis of piRNAs in gene-specific DNA methylation

PIWI-interacting RNAs (piRNAs) have long been associated with the silencing of transposable elements (TEs). However, over 20,000 unique species of piRNAs mapped to the human genome are more than the relatively few presumably required to regulate the known human transposon classes. Here, we present the results of the first genome-wide effort to study the effects of piRNAs on gene specific DNA methylation. We found that exon-derived piRNAs consist almost universally of species with 10 or fewer genomic copies, whereas piRNAs existing in high copies originate predominately from intronic and intergenic regions. Genome-wide methylation profiling following transfection of human somatic cells with piRNA mimics revealed methylation changes at numerous genic loci in single copy piRNA-transfected cells. Moreover, genomic regions directly adjacent to differentially methylated CpG sites were enriched for sequence matches to the transfected piRNAs. These findings suggest that a subset of single copy piRNAs may be able to induce DNA methylation at non-TE genic loci, a process that may be mediated in part by direct binding to either genomic DNA or nascent mRNA near target CpG sites.

PIWIL2 promotes progression of non-small cell lung cancer by inducing CDK2 and Cyclin A expression

Background

PIWI proteins have important roles in tumorigenesis due to their interaction with piRNAs. Recent studies suggest that PIWI proteins affect prognosis of various cancers.

Methods

In the present study, PIWI genes expression was assayed in non-small cell lung cancer (NSCLC). To determine the effects of PIWIL2 on NSCLC cells, overexpression and interference assays were performed using the A549 and H460 cell lines. The tumor formation model was performed to demonstrate the effects of PIWIL2 on tumor formation in vivo.

Results

PIWIL2 was increased both at the RNA and protein level in malignant cancer tissues compared with adjacent normal tissue. Moreover, increased PIWIL2 gene expression was negatively correlated with prognosis in NSCLC patients. Overexpression and interference of PIWIL2 promoted and depressed cell proliferation, respectively. Meanwhile, PIWIL2 interference arrested cells at the G2/M stage. In addition, we found that CDK2 and Cyclin A expression were correlated with PIWIL2 expression. Moreover, transfection of PIWIL2 promoted tumor growth in nude mice.

Conclusion

Our findings shed light on the function of PIWIL2 in NSCLC and suggest potential prognostic and therapeutic value.

PIWIL2 induces c-Myc expression by interacting with NME2 and regulates c-Myc-mediated tumor cell proliferation

c-Myc serves as a crucial regulator in multiple cellular events. Cumulative evidences demonstrate that anomalous c-Myc overexpression correlates with proliferation, invasion and metastasis in various human tumors. However, the transcriptionally activating mechanisms responsible for c-Myc overexpression are complex and continue to be intangible. Here we showed that Piwi-Like RNA-Mediated Gene Silencing 2 (PIWIL2) can upregulate c-Myc via binding with NME/NM23 nucleoside diphosphate kinase 2 (NME2). PIWIL2 promotes c-Myc transcription by interacting with and facilitating NME2 to bind to G4-motif region within c-Myc promoter. Interestingly, in a c-Myc-mediated manner, PIWIL2 upregulates RhoA, which in turn induces filamentary F-actin. Deficiency of PIWIL2 results in obstacle for c-Myc expression, cell cycle progress and cell proliferation. Taken together, our present work demonstrates that PIWIL2 modulates tumor cell proliferation and F-actin filaments via promoting c-Myc expression.