Silencing PRDM14 expression by an innovative RNAi therapy inhibits stemness, tumorigenicity, and metastasis of breast cancer

Acute Myeloid Leukemia: New Multiomics Molecular Signatures and Implications for Systems Medicine Diagnostics and Therapeutics Innovation

Acute myeloid leukemia (AML) is a common, complex, and multifactorial malignancy of the hematopoietic system. AML diagnosis and treatment outcomes display marked heterogeneity and patient-to-patient variations. To date, AML-related biomarker discovery research has employed single omics inquiries. Multiomics analyses that reconcile and integrate the data streams from multiple levels of the cellular hierarchy, from genes to proteins to metabolites, offer much promise for innovation in AML diagnostics and therapeutics. We report, in this study, a systems medicine and multiomics approach to integrate the AML transcriptome data and reporter biomolecules at the RNA, protein, and metabolite levels using genome-scale biological networks. We utilized two independent transcriptome datasets (GSE5122, GSE8970) in the Gene Expression Omnibus database. We identified new multiomics molecular signatures of relevance to AML: miRNAs (e.g., mir-484 and miR-519d-3p), receptors (ACVR1 and PTPRG), transcription factors (PRDM14 and GATA3), and metabolites (in particular, amino acid derivatives). The differential expression profiles of all reporter biomolecules were crossvalidated in independent RNA-Seq and miRNA-Seq datasets. Notably, we found that PTPRG holds important prognostication potential as evaluated by Kaplan-Meier survival analyses. The multiomics relationships unraveled in this analysis point toward the genomic pathogenesis of AML. These multiomics molecular leads warrant further research and development as potential diagnostic and therapeutic targets.

Antitumoral RNA-targeted oligonucleotide therapeutics: the third pillar after small molecule inhibitors and antibodies

Oligonucleotide therapeutics, drugs consisting of 10–50 nucleotide‐long single‐ or double‐stranded DNA or RNA molecules that can bind to specific DNA or RNA sequences or proteins, include antisense oligonucleotides (ASOs), small interfering RNAs (siRNAs), microRNAs (miRNAs), aptamers, and decoys. These oligonucleotide therapeutics could potentially become the third pillar of drug development. In particular, ASOs and siRNAs are advanced tools that are widely used to silence gene expression. They are used in clinical trials, as they have high specificity for target mRNAs and non‐coding RNAs and limited toxicity. However, their clinical application remains challenging. Although chemotherapy has benefits, it has severe adverse effects in many patients. Therefore, new modalities for targeted molecular therapy against tumors, including oligonucleotide therapeutics, are required, and they should be compatible with diagnosis using next‐generation sequencing. This review provides an overview of the therapeutic uses of ASOs, siRNAs, and miRNAs in clinical studies on malignant tumors. Understanding previous research and development will help in developing novel oligonucleotide therapeutics against malignant tumors.

HOXA1, a breast cancer oncogene

More than 25 years ago, the first literature records mentioned HOXA1 expression in human breast cancer. A few years later, HOXA1 was confirmed as a proper oncogene in mammary tissue. In the following two decades, molecular data about the mode of action of the HOXA1 protein, the factors contributing to activate and maintain HOXA1 gene expression and the identity of its target genes have accumulated and provide a wider view on the association of this transcription factor to breast oncogenesis. Large-scale transcriptomic data gathered from wide cohorts of patients further allowed refining the relationship between breast cancer type and HOXA1 expression. Several recent reports have reviewed the connection between cancer hallmarks and the biology of HOX genes in general. Here we take HOXA1 as a paradigm and propose an extensive overview of the molecular data centered on this oncoprotein, from what its expression modulators, to the interactors contributing to its oncogenic activities, and to the pathways and genes it controls. The data converge to an intricate picture that answers questions on the multi-modality of its oncogene activities, point towards better understanding of breast cancer aetiology and thereby provides an appraisal for treatment opportunities.

Therapeutic siRNA targeting the cancer cell stemness regulator PRDI-BF1 and RIZ domain zinc finger protein 14

PRDI-BF1 and RIZ (PR) domain zinc finger protein 14 (PRDM14), first reported in 2007 to be overexpressed in breast cancer, plays an important role in breast cancer proliferation. Subsequent studies reported that PRDM14 is expressed in embryonic stem cells, primordial germ cells, and various cancers. PRDM14 was reported to confer stemness properties to cancer cells. These properties induce cancer initiation, cancer progression, therapeutic resistance, distant metastasis, and recurrence in refractory tumors. Therefore, PRDM14 may be an ideal therapeutic target for various types of tumors. Silencing PRDM14 expression using PRDM14-specific siRNA delivered through an innovative intravenous drug delivery system reduced the size of inoculated tumors, incidence of distant metastases, and increased overall survival in nude mice without causing adverse effects. Therapeutic siRNA targeting PRDM14 is now being evaluated in a human phase I clinical trial for patients with refractory breast cancer, including triple-negative breast cancer.

Histone 3 Lysine 27 Trimethylation Signature in Breast Cancer

Cancer development and progression rely on complicated genetic and also epigenetic changes which regulate gene expression without altering the DNA sequence. Epigenetic mechanisms such as DNA methylation, histone modifications, and regulation by lncRNAs alter protein expression by either promoting gene transcription or repressing it. The presence of so-called chromatin modification marks at various gene promoters and gene bodies is associated with normal cell development but also with tumorigenesis and progression of different types of cancer, including the most frequently diagnosed breast cancer. This review is focused on the significance of one of the abundant post-translational modifications of histone 3- trimethylation of lysine 27 (H3K27me3), which was shown to participate in tumour suppressor genes' silencing. Unlike other reviews in the field, here the overview of existing evidence linking H3K27me3 status with breast cancer biology and the tumour outcome is presented especially in the context of diverse breast cancer subtypes. Moreover, the potential of agents that target H3K27me3 for the treatment of this complex disease as well as H3K27 methylation in cross-talk with other chromatin modifications and lncRNAs are discussed.

Targeting Histone Modifications in Breast Cancer: A Precise Weapon on the Way

Histone modifications (HMs) contribute to maintaining genomic stability, transcription, DNA repair, and modulating chromatin in cancer cells. Furthermore, HMs are dynamic and reversible processes that involve interactions between numerous enzymes and molecular components. Aberrant HMs are strongly associated with tumorigenesis and progression of breast cancer (BC), although the specific mechanisms are not completely understood. Moreover, there is no comprehensive overview of abnormal HMs in BC, and BC therapies that target HMs are still in their infancy. Therefore, this review summarizes the existing evidence regarding HMs that are involved in BC and the potential mechanisms that are related to aberrant HMs. Moreover, this review examines the currently available agents and approved drugs that have been tested in pre-clinical and clinical studies to evaluate their effects on HMs. Finally, this review covers the barriers to the clinical application of therapies that target HMs, and possible strategies that could help overcome these barriers and accelerate the use of these therapies to cure patients.

Treatment of primary and metastatic breast and pancreatic tumors upon intravenous delivery of a PRDM14-specific chimeric siRNA/nanocarrier complex

PRDM14 is highly expressed in several cancers but is not detected in normal tissues. It confers cancer stem cell-like properties, including chemoresistance and distant metastasis, to cancer cells. Herein, we aimed to develop a highly effective therapy against advanced stage cancer based on intravenously delivered PRDM14-targeted siRNA. First, we examined PRDM14 expression and gene amplification in breast and pancreatic tumors and cell lines. PRDM14 was expressed in breast cancer, including the triple-negative subtype, and pancreatic cancer. PRDM14 was amplified in 23.8% of patients with PRDM14⁺ breast cancer. Next, we investigated the inoculated tumor growth and distant metastasis following PRDM14 depletion by administering mice with PRDM14-specific chimeric siRNA combined with a novel branched PEGylated poly-L-ornithine (PLO)-based intravenous drug delivery system, designated PRDM14 unit polyion complex (uPIC) (n = 6/group). Inhibition of PRDM14 expression with PRDM14 uPIC by systemic intravenous injection effectively reduced tumor size and metastasis in vivo, thereby improving survival. Finally, pharmacokinetic/toxicokinetic analyses were performed on PRDM14 uPIC, which was intravenously administered to rats (n = 10-15/group) and cynomolgus monkeys (n = 3-5/group), twice weekly for 4 weeks. This revealed that PRDM14 uPIC was relatively nontoxic and the siRNA exposure in serum was greater than that predicted by the administered dose ratio when delivered as a uPIC. Taken together, our study indicated that PRDM14 uPIC is highly effective in suppressing malignant features of solid cancers and does not cause severe toxicity, making it a promising therapeutic agent for cancer treatment.

The duality of PRDM proteins: epigenetic and structural perspectives

PRDF1 and RIZ1 homology domain containing (PRDMs) are a subfamily of Krüppel-like zinc finger proteins controlling key processes in metazoan development and in cancer. PRDMs exhibit unique dualities: (a) PR domain/ZNF arrays-their structure combines a SET-like domain known as a PR domain, typically found in methyltransferases, with a variable array of C2H2 zinc fingers (ZNF) characteristic of DNA-binding transcription factors; (b) transcriptional activators/repressors-their physiological function is context- and cell-dependent; mechanistically, some PRDMs have a PKMT activity and directly catalyze histone lysine methylation, while others are rather pseudomethyltransferases and act by recruiting transcriptional cofactors; (c) oncogenes/tumor suppressors-their pathological function depends on the specific PRDM isoform expressed during tumorigenesis. This duality is well known as the 'Yin and Yang' of PRDMs and involves a complex regulation of alternative splicing or alternative promoter usage, to generate full-length or PR-deficient isoforms with opposing functions in cancer. In conclusion, once their dualities are fully appreciated, PRDMs represent a promising class of targets in oncology by virtue of their widespread upregulation across multiple tumor types and their somatic dispensability, conferring a broad therapeutic window and limited toxic side effects. The recent discovery of a first-in-class compound able to inhibit PRDM9 activity has paved the way for the identification of further small molecular inhibitors able to counteract PRDM oncogenic activity.

Immune-related protein signature in serum stratify relapsed mantle cell lymphoma patients based on risk

Background

Response to modern treatment strategies, which combine cytotoxic compounds with immune stimulatory agents and targeted treatment is highly variable among MCL patients. Thus, providing prognostic and predictive markers for risk adapted therapy is warranted and molecular information that can help in patient stratification is a necessity. In relapsed MCL, biopsies are rarely available and molecular information from tumor tissue is often lacking. Today, the main tool to access risk is the MCL international prognostic index (MIPI), which does not include detailed biological information of relevance for different treatment options. To enable continuous monitoring of patients, non-invasive companion diagnostic tools are needed which can further reduce cost and patient distress and enable efficient measurements of biological markers.

Methods

We have assessed if serum-based protein profiling can identify immune related proteins that stratify relapsed MCL patients based on risk. Overall, 371 scFv targeting 158 proteins were assessed using an antibody microarray platform. We profiled patients (n = 44) who had been treated within the MCL6-Philemon trial combining targeted and immune-modulatory treatment.

Results

The downstream processing led to the identification of the relapsed immune signature (RIS) consisting of 11 proteins with potential to stratify patients with long and short overall survival (OS). Moreover, in this population, MIPI alone failed to separate high, intermediate and low risk patients, but a combined index based on MIPI together with RIS, MIPI_ris, showed improved performance and significantly stratified all three risk groups based on OS.

Conclusions

Our results show that addition of biological parameters to previous prognostic indices improves patient stratification among patients treated with BTK inhibitor triplet combination, particularly, in the identification of an extreme high risk group.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-020-07678-4.

Epithelial-Mesenchymal Transition Programs and Cancer Stem Cell Phenotypes: Mediators of Breast Cancer Therapy Resistance

Epithelial-mesenchymal transition (EMT) programs play essential functions in normal morphogenesis and organogenesis, including that occurring during mammary gland development and glandular regeneration. Historically, EMT programs were believed to reflect a loss of epithelial gene expression signatures and morphologies that give way to those associated with mesenchymal cells and their enhanced migratory and invasive behaviors. However, accumulating evidence now paints EMT programs as representing a spectrum of phenotypic behaviors that also serve to enhance cell survival, immune tolerance, and perhaps even metastatic dormancy. Equally important, the activation of EMT programs in transformed mammary epithelial cells not only enhances their acquisition of invasive and metastatic behaviors, but also expands their generation of chemoresistant breast cancer stem cells (BCSC). Importantly, the net effect of these events results in the appearance of recurrent metastatic lesions that remain refractory to the armamentarium of chemotherapies and targeted therapeutic agents deployed against advanced stage breast cancers. Here we review the molecular and cellular mechanisms that contribute to the pathophysiology of EMT programs in human breast cancers and how these events impact their "stemness" and acquisition of chemoresistant phenotypes.

Multifaceted Role of PRDM Proteins in Human Cancer

The PR/SET domain family (PRDM) comprise a family of genes whose protein products share a conserved N-terminal PR [PRDI-BF1 (positive regulatory domain I-binding factor 1) and RIZ1 (retinoblastoma protein-interacting zinc finger gene 1)] homologous domain structurally and functionally similar to the catalytic SET [Su(var)3-9, enhancer-of-zeste and trithorax] domain of histone methyltransferases (HMTs). These genes are involved in epigenetic regulation of gene expression through their intrinsic HMTase activity or via interactions with other chromatin modifying enzymes. In this way they control a broad spectrum of biological processes, including proliferation and differentiation control, cell cycle progression, and maintenance of immune cell homeostasis. In cancer, tumor-specific dysfunctions of PRDM genes alter their expression by genetic and/or epigenetic modifications. A common characteristic of most PRDM genes is to encode for two main molecular variants with or without the PR domain. They are generated by either alternative splicing or alternative use of different promoters and play opposite roles, particularly in cancer where their imbalance can be often observed. In this scenario, PRDM proteins are involved in cancer onset, invasion, and metastasis and their altered expression is related to poor prognosis and clinical outcome. These functions strongly suggest their potential use in cancer management as diagnostic or prognostic tools and as new targets of therapeutic intervention.

The genetic script of metastasis

Metastasis is a pivotal event that changes the course of cancers from benign and treatable to malignant and difficult to treat, resulting in the demise of patients. Understanding the genetic control of metastasis is thus crucial to develop efficient and sustainable targeted therapies. Here we discuss the alterations in epigenetic mechanisms, transcription, chromosomal instability, chromosome imprinting, non-coding RNAs, coding RNAs, mutant RNAs, enhancers, G-quadruplexes, and copy number variation to dissect the genetic control of metastasis. We conclude that the genetic control of metastasis is predominantly executed through epithelial to mesenchymal transition and evasion of cell death. We discuss how genetic regulatory mechanisms can be harnessed for therapeutic purposes to achieve sustainable control over cancer metastasis.

Targeting epigenetic regulators for cancer therapy: mechanisms and advances in clinical trials

Epigenetic alternations concern heritable yet reversible changes in histone or DNA modifications that regulate gene activity beyond the underlying sequence. Epigenetic dysregulation is often linked to human disease, notably cancer. With the development of various drugs targeting epigenetic regulators, epigenetic-targeted therapy has been applied in the treatment of hematological malignancies and has exhibited viable therapeutic potential for solid tumors in preclinical and clinical trials. In this review, we summarize the aberrant functions of enzymes in DNA methylation, histone acetylation and histone methylation during tumor progression and highlight the development of inhibitors of or drugs targeted at epigenetic enzymes.

Silencing PRDM14 via Oligonucleotide Therapeutics Suppresses Tumorigenicity and Metastasis of Breast Cancer

The PRDI-BF1 and RIZ (PR) domain zinc finger protein 14 (PRDM14) is upregulated in approximately 60% of breast cancers, some of which exhibit gene amplification. In contrast, PRDM14 is not expressed in normal, and differentiated tissues. PRDM14⁺ breast cancer cells are resistant to chemotherapy drugs, are tumorigenic, and metastasize to the lungs. It is commonly assumed that genes that are overexpressed in cancers, such as PRDM14, are effective targets for new therapies that specifically abrogate the expression of these genes. RNA interference of PRDM14, a gene expressed by breast cancer cells, reduced the size of tumors and lung metastases in nude mice. In this chapter, we introduce the concept and methods to develop and apply systematically injected small interfering RNA therapy for breast cancer models in vivo.

PRDM14 promotes malignant phenotype and correlates with poor prognosis in colorectal cancer

BACKGROUND

Emerging evidence suggests that stemness in cancer cells is a cause of drug resistance or metastasis and is an important therapeutic target. PR [positive regulatory domain I-binding factor 1 (PRDI-BF1) and retinoblastoma protein-interacting zinc finger gene (RIZ1)] domain containing 14 (PRDM14), that regulates pluripotency in primordial germ cell, has reported the overexpression and function of stemness in various malignancies, suggesting it as the possible therapeutic target. However, to our knowledge, there have been no reports on the expression and function of PRDM14 in colorectal cancer (CRC). Therefore, we investigated the expression and the role of PRDM14 in CRC.

METHODS

We performed immunohistochemistry evaluations and assessed PRDM14 expression on 414 primary CRC specimens. Colon cancer cell lines were subjected to functional and stemness assays in vitro and in vivo.

RESULTS

We found that PRDM14 positive staining exhibited heterogeneity in the CRC primary tumor, especially at the tumor invasion front. The aberrant expression of PRDM14 at the invasion front was associated with lymph node metastasis and disease stage in patients with CRC. Furthermore, the multivariate analysis revealed high PRDM14 expression as an independent prognostic factor in the patients with Stage III CRC. Overexpression of PRDM14 enhanced the invasive, drug-resistant and stem-like properties in colon cancer cells in vitro and tumorigenicity in vivo.

CONCLUSION

Our findings suggest that PRDM14 is involved in progression and chemoresistance of CRC, and is a potential prognostic biomarker and therapeutic target in the CRC patients.

Off to a Bad Start: Cancer Initiation by Pluripotency Regulator PRDM14

Despite advances in chemotherapies that improve cancer survival, most patients who relapse succumb to the disease due to the presence of cancer stem cells (CSCs), which are highly chemoresistant. The pluripotency factor PR domain 14 (PRDM14) has a key role in initiating many types of cancer. Normally, PRDM14 uses epigenetic mechanisms to establish and maintain the pluripotency of embryonic cells, and its role in cancer is similar. This important link between cancer and induced pluripotency is a key revelation for how CSCs may form: pluripotency genes, such as PRDM14, can expand stem-like cells as they promote ongoing DNA damage. PRDM14 and its protein-binding partners, the ETO/CBFA2T family, are ideal candidates for eliminating CSCs from relevant cancers, preventing relapse and improving long-term survival.

The Pluripotency Regulator PRDM14 Requires Hematopoietic Regulator CBFA2T3 to Initiate Leukemia in Mice

PR domain-containing 14 (Prdm14) is a pluripotency regulator central to embryonic stem cell identity and primordial germ cell specification. Genomic regions containing PRDM14 are often amplified leading to misexpression in human cancer. Prdm14 expression in mouse hematopoietic stem cells (HSC) leads to progenitor cell expansion prior to the development of T-cell acute lymphoblastic leukemia (T-ALL), consistent with PRDM14's role in cancer initiation. Here, we demonstrate mechanistic insight into PRDM14-driven leukemias in vivo. Mass spectrometry revealed novel PRDM14-protein interactions including histone H1, RNA-binding proteins, and the master hematopoietic regulator CBFA2T3. In mouse leukemic cells, CBFA2T3 and PRDM14 associate independently of the related ETO family member CBFA2T2, PRDM14's primary protein partner in pluripotent cells. CBFA2T3 plays crucial roles in HSC self-renewal and lineage commitment, and participates in oncogenic translocations in acute myeloid leukemia. These results suggest a model whereby PRDM14 recruits CBFA2T3 to DNA, leading to gene misregulation causing progenitor cell expansion and lineage perturbations preceding T-ALL development. Strikingly, Prdm14-induced T-ALL does not occur in mice deficient for Cbfa2t3, demonstrating that Cbfa2t3 is required for leukemogenesis. Moreover, T-ALL develops in Cbfa2t3 heterozygotes with a significantly longer latency, suggesting that PRDM14-associated T-ALL is sensitive to Cbfa2t3 levels. Our study highlights how an oncogenic protein uses a native protein in progenitor cells to initiate leukemia, providing insight into PRDM14-driven oncogenesis in other cell types. IMPLICATIONS: The pluripotency regulator PRDM14 requires the master hematopoietic regulator CBFA2T3 to initiate leukemia in progenitor cells, demonstrating an oncogenic role for CBFA2T3 and providing an avenue for targeting cancer-initiating cells.

The Evolving Landscape of Cancer Stem Cells and Ways to Overcome Cancer Heterogeneity

Cancer stem cells (CSCs) with therapeutic resistance and plasticity can be found in various types of tumors and are recognized as attractive targets for treatments. As CSCs are derived from tissue stem or progenitor cells, and/or dedifferentiated mature cells, their signal transduction pathways are critical in the regulation of CSCs; chronic inflammation causes the accumulation of genetic mutations and aberrant epigenetic changes in these cells, potentially leading to the production of CSCs. However, the nature of CSCs appears to be stronger than the treatments of the past. To improve the treatments targeting CSCs, it is important to inhibit several molecules on the signaling cascades in CSCs simultaneously, and to overcome cancer heterogeneity caused by the plasticity. To select suitable target molecules for CSCs, we have to explore the landscape of CSCs from the perspective of cancer stemness and signaling systems, based on the curated databases of cancer-related genes. We have been studying the integration of a broad range of knowledge and experiences from cancer biology, and also from other interdisciplinary basic sciences. In this review, we have introduced the concept of developing novel strategies targeting CSCs.

Integrated Analysis of Genetic Abnormalities of the Histone Lysine Methyltransferases in Prostate Cancer

Background

The histone methyltransferase (HMT) family includes histone lysine methyltransferases (HKMTs) and histone/protein arginine methyltransferases (PRMTs). The role of HMT gene variants in prostate cancer remains unknown. Therefore, this study aimed to evaluate HMT gene variants in the pathogenesis and prognosis of human prostate cancer, using in vitro cell studies and bioinformatics analysis.

Material/Methods

Integrative bioinformatics analysis of the expression of 51 HMT genes in human prostate cancer was based on datasets from the Cancer Genome Atlas (TCGA). Correlation and regression analysis were used to identify critical HMTs in prostate cancer. Kaplan-Meier and the area under the receiver operating characteristics curve (AUROC) were performed to evaluate the function of the HMTs on prognosis. Gene expression and function of 22Rv1 human prostate carcinoma cells were studied.

Results

The HMT genes identified to have a role in the pathogenesis of prostate cancer included the EZH2, SETD5, PRDM12, NSD1, SETD6, SMYD1, and the WHSC1L1 gene. The EZH2, SETD5, and SMYD1 genes were selected as a prognostic panel, with the SUV420H2 HMT gene. SETD2, NSD1, and ASH1L were identified as critical genes in the development of castration-resistant prostate cancer (CRPC), similar to mixed-lineage leukemia (MLL) complex family members. Knockdown of the SETD5 gene in 22Rv1 prostate carcinoma cells in vitro inhibited cancer cell growth and migration.

Conclusions

HMT gene variants may have a role in the pathogenesis of prostate cancer. Future studies may determine the role of HMT genes as prognostic biomarkers in patients with prostate cancer.

Targeted DamID reveals differential binding of mammalian pluripotency factors

The precise control of gene expression by transcription factor networks is crucial to organismal development. The predominant approach for mapping transcription factor-chromatin interactions has been chromatin immunoprecipitation (ChIP). However, ChIP requires a large number of homogeneous cells and antisera with high specificity. A second approach, DamID, has the drawback that high levels of Dam methylase are toxic. Here, we modify our targeted DamID approach (TaDa) to enable cell type-specific expression in mammalian systems, generating an inducible system (mammalian TaDa or MaTaDa) to identify genome-wide protein/DNA interactions in 100 to 1000 times fewer cells than ChIP-based approaches. We mapped the binding sites of two key pluripotency factors, OCT4 and PRDM14, in mouse embryonic stem cells, epiblast-like cells and primordial germ cell-like cells (PGCLCs). PGCLCs are an important system for elucidating primordial germ cell development in mice. We monitored PRDM14 binding during the specification of PGCLCs, identifying direct targets of PRDM14 that are key to understanding its crucial role in PGCLC development. We show that MaTaDa is a sensitive and accurate method for assessing cell type-specific transcription factor binding in limited numbers of cells.

PRDM14 is overexpressed in chronic pancreatitis prior to pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive and lethal cancer that is typically diagnosed at a later stage with metastases and is difficult to treat. Therefore, investigating the mechanism of PDAC initiation is important to aid early‐stage cancer detection. PRDM14 is a transcription factor that maintains pluripotency in embryonic stem cells and is overexpressed in several cancers. We previously reported that PRDM14 is overexpressed and regulates cancer stem‐like phenotypes in PDAC, and herein, we assess whether PRDM14 expression increases prior to tumorigenesis. Through immunohistochemistry analyses of clinical tissues, we detected PRDM14‐positive cells in precursor pancreatic intraepithelial neoplasia and chronic pancreatitis, which is a risk factor for PDAC, lesions. PRDM14 staining in chronic pancreatitis was as high as that in PDAC and cancer adjacent tissues. We induced pancreatitis in mouse models by cerulein injection, and observed that PRDM14 expression increased in chronic pancreatitis models but not in control or acute pancreatitis mice. Moreover, cerulein treatment increased PRDM14 expression in PK‐1 and AsPC‐1 pancreatic cancer cell lines. Our results suggest that inflammation increases the expression of PRDM14, which regulates cancer stem‐like phenotypes, and this occurs prior to PDAC initiation and progression.

PRDM14, a putative histone methyl-transferase, interacts with and decreases the stability and activity of the HOXA1 transcription factor

Understanding how the activity of transcription factors like HOX proteins is regulated remains a widely open question. In a recent screen for proteins interacting with HOXA1, we identified a PRDM protein family member, PRDM14, which is known to be transiently co-expressed with HOXA1 in epiblast cells before their specification towards somatic versus germ cell fate. Here, we confirm PRDM14 is an interactor of HOXA1 and we identify the homeodomain of HOXA1 as well as the PR domain and Zinc fingers of PRDM14 to be required for the interaction. An 11-His repeat of HOXA1 previously highlighted to contribute to HOXA1-mediated protein-protein interactions is also involved. At a functional level, we provide evidence that HOXA1 displays an unexpectedly long half-life and demonstrate that PRDM14 can reduce the stability and affect the transcriptional activity of HOXA1.

PRDM14, a Zinc Finger Protein, Regulates Cancer Stemness

PRDI-BF1 and RIZ homology (PR) domain zinc finger protein 14 (PRDM14) contains a PR domain related to the SET methyltransferase domain and zinc finger motifs. PRDM14 maintains stemness in embryonic stem cells and primordial germ cells via epigenetic mechanisms. PRDM14, however, is not expressed in normal differentiated tissues. We and other groups previously reported that PRDM14 expression is markedly higher in some types of cancers compared to the corresponding normal tissues. PRDM14 confers stem cell-like characteristics upon cancer cells, such as sphere formation, dye efflux, chemotherapy resistance, proliferation, and distant metastasis. Cancer stem cells (CSCs) are thought to be responsible for tumor initiation, drug and radiation resistance, invasive growth, metastasis, and tumor relapse, which are the primary causes of cancer-related deaths. Because CSCs are also thought to be resistant to conventional therapies, an effective and novel therapeutic approach for CSCs is imperative.RNAi silencing of PRDM14 expressed by breast and pancreatic cancer cells reduced tumor size and distant metastasis of these cells in nude mice. Inhibition of PRDM14 expression by cancer cells may be an effective and radical therapy for solid cancers. In this chapter, we discuss methods for studying CSC-like properties in cancer cells and describe the use of siRNA with a drug delivery system by systemic injection in vivo.

PRDM14 directly interacts with heat shock proteins HSP90α and glucose-regulated protein 78

PRDM14 is overexpressed in various cancers and can regulate cancer phenotype under certain conditions. Inhibiting PRDM14 expression in breast and pancreatic cancers has been reported to reduce cancer stem‐like phenotypes, which are associated with aggressive tumor properties. Therefore, PRDM14 is considered a promising target for cancer therapy. To develop a pharmaceutical treatment, the mechanism and interacting partners of PRDM14 need to be clarified. Here, we identified the proteins interacting with PRDM14 in triple‐negative breast cancer (TNBC) cells, which do not express the three most common types of receptor (estrogen receptors, progesterone receptors, and HER2). We obtained 13 candidates that were pulled down with PRDM14 in TNBC HCC1937 cells and identified them by mass spectrometry. Two candidates—glucose‐regulated protein 78 (GRP78) and heat shock protein 90‐α (HSP90α)—were confirmed in immunoprecipitation assay in two TNBC cell lines (HCC1937 and MDA‐MB231). Surface plasmon resonance analysis using GST‐PRDM14 showed that these two proteins directly interacted with PRDM14 and that the interactions required the C‐terminal region of PRDM14, which includes zinc finger motifs. We also confirmed the interactions in living cells by NanoLuc luciferase‐based bioluminescence resonance energy transfer (NanoBRET) assay. Moreover, HSP90 inhibitors (17DMAG and HSP990) significantly decreased breast cancer stem‐like CD24⁻ CD44⁺ and side population (SP) cells in HCC1937 cells, but not in PRDM14 knockdown HCC1937 cells. The combination of the GRP78 inhibitor HA15 and PRDM14 knockdown significantly decreased cell proliferation and SP cell number in HCC1937 cells. These results suggest that HSP90α and GRP78 interact with PRDM14 and participate in cancer regulation.