Tumor-initiating Cells Research Articles

Single-cell transcriptomic analysis uncovers the origin and intratumoral heterogeneity of parotid pleomorphic adenoma

Pleomorphic adenoma (PA) is the most common benign tumour in the salivary gland and has high morphological complexity. However, the origin and intratumoral heterogeneity of PA are largely unknown. Here, we constructed a comprehensive atlas of PA at single-cell resolution and showed that PA exhibited five tumour subpopulations, three recapitulating the epithelial states of the normal parotid gland, and two PA-specific epithelial cell (PASE) populations unique to tumours. Then, six subgroups of PASE cells were identified, which varied in epithelium, bone, immune, metabolism, stemness and cell cycle signatures. Moreover, we revealed that CD36+ myoepithelial cells were the tumour-initiating cells (TICs) in PA, and were dominated by the PI3K-AKT pathway. Targeting the PI3K-AKT pathway significantly inhibited CD36+ myoepithelial cell-derived tumour spheres and the growth of PA organoids. Our results provide new insights into the diversity and origin of PA, offering an important clinical implication for targeting the PI3K-AKT signalling pathway in PA treatment.

SND1, a novel co-activator of HIF1α, promotes tumor initiation in PyMT-induced breast tumor.

The multifunctional protein staphylococcal nuclease domain-containing protein 1 (SND1) is conserved and has been implicated in several aspects of tumor development, such as proliferation, epithelial-mesenchymal transition, and immune evasion. Despite this, the precise role of SND1 in the initiation and metastasis of mammary gland tumors remains largely unexplored. In this study, we utilized a mouse model of breast tumors induced by polyomavirus middle T antigen (PyMT) to demonstrate that the knockout of SND1 significantly delayed the onset of primary mammary tumor formation induced by PyMT. Histological staining and cytometric analysis were conducted to confirm the reduction of tumor-initiating cells and lung metastasis following depletion of SND1. Additionally, our findings demonstrate that enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2), a crucial epigenetic modifier implicated in PyMT-induced breast tumors, serves as an essential mediator of SND1-promoted primary mammary tumor formation. Mechanistic investigations revealed that SND1 functions as a transcriptional co-activator of hypoxia-inducible factor 1 subunit alpha (HIF1α), thereby regulating the downstream target gene EZH2 and promoting tumorigenesis. Overall, this study provides novel insights into the role of SND1 as a co-activator of HIF1α in the acceleration of PyMT-induced spontaneous breast tumor formation through the promotion of EZH2 transcription. The findings provide novel insights into the relationship between SND1 and the formation of tumor-initiating cells.

Linked CD4+/CD8+ T cell neoantigen vaccination overcomes immune checkpoint blockade resistance and enables tumor regression.

Therapeutic benefit to immune checkpoint blockade (ICB) is currently limited to the subset of cancers thought to possess a sufficient tumor mutational burden (TMB) to allow for the spontaneous recognition of neoantigens (NeoAg) by autologous T cells. We explored whether the response to ICB of an aggressive low-TMB squamous cell tumor could be improved through combination immunotherapy using functionally defined NeoAg as targets for endogenous CD4+ and CD8+ T cells. We found that, whereas vaccination with CD4+ or CD8+ NeoAg alone did not offer prophylactic or therapeutic immunity, vaccines containing NeoAg recognized by both subsets overcame ICB resistance and led to the eradication of large established tumors that contained a subset of PD-L1+ tumor-initiating cancer stem cells (tCSC), provided the relevant epitopes were physically linked. Therapeutic CD4+/CD8+ T cell NeoAg vaccination produced a modified tumor microenvironment (TME) with increased numbers of NeoAg-specific CD8+ T cells existing in progenitor and intermediate exhausted states enabled by combination ICB-mediated intermolecular epitope spreading. We believe that the concepts explored herein should be exploited for the development of more potent personalized cancer vaccines that can expand the range of tumors treatable with ICB.

Advances in Molecular Perspectives of Tumor-Initiating Cells on Cancer Therapy

Advances in Molecular Perspectives of Tumor-Initiating Cells on Cancer Therapy

Immune evasion by cancer stem cells ensures tumor initiation and failure of immunotherapy

Cancer stem cells (CSCs) are a small subpopulation of cells that drive the formation and progression of tumors. However, during tumor initiation, how CSCs communicate with neighbouring immune cells to overcome the powerful immune surveillance barrier in order to form, spread, and maintain the tumor, remains poorly understood. It is, therefore, absolutely necessary to understand how a small number of tumor-initiating cells (TICs) survive immune attack during (a) the “elimination phase” of “tumor immune-editing”, (b) the establishment of regional or distant tumor after metastasis, and (c) recurrence after therapy. Mounting evidence suggests that CSCs suppress the immune system through a variety of distinct mechanisms that ensure the survival of not only CSCs but also non-stem cancer cells (NSCCs), which eventually form the tumor mass. In this review article, the mechanisms via which CSCs change the immune landscape of the tissue of origin, which contains macrophages, dendritic cells (DCs), myeloid-derived suppressor cells (MDSCs), natural killer (NK) cells, and tumor-infiltrating lymphocytes, in favour of tumorigenesis were discussed. The failure of cancer immunotherapy might also be explained by such interaction between CSCs and immune cells. This review will shed light on the critical role of CSCs in tumor immune evasion and emphasize the importance of CSC-targeted immunotherapy as a cutting-edge technique for battling cancer by restricting communication between immune cells and CSCs.

Netrin-1 blockade inhibits tumor associated Myeloid-derived suppressor cells, cancer stemness and alleviates resistance to chemotherapy and immune checkpoint inhibitor.

Drug resistance and cancer relapse represent significant therapeutic challenges after chemotherapy or immunotherapy, and a major limiting factor for long-term cancer survival. Netrin-1 was initially identified as a neuronal navigation cue but has more recently emerged as an interesting target for cancer therapy, which is currently clinically investigated. We show here that netrin-1 is an independent prognostic marker for clinical progression of breast and ovary cancers. Cancer stem cells (CSCs)/Tumor initiating cells (TICs) are hypothesized to be involved in clinical progression, tumor relapse and resistance. We found a significant correlation between netrin-1 expression and cancer stem cell (CSC) markers levels. We also show in different mice models of resistance to chemotherapies that netrin-1 interference using a therapeutic netrin-1 blocking antibody alleviates resistance to chemotherapy and triggers an efficient delay in tumor relapse and this effect is associated with CSCs loss. We also demonstrate that netrin-1 interference limits tumor resistance to immune checkpoint inhibitor and provide evidence linking this enhanced anti-tumor efficacy to a decreased recruitment of a subtype of myeloid-derived suppressor cells (MDSCs) called polymorphonuclear (PMN)-MDSCs. We have functionally demonstrated that these immune cells promote CSCsfeatures and, consequently, resistance to anti-cancer treatments. Together, these data support the view of both a direct and indirect contribution of netrin-1 to cancer stemness and we propose that this may lead to therapeutic opportunities by combining conventional chemotherapies and immunotherapies with netrin-1 interfering drugs.

Cancer-associated fibroblasts nurture LGR5 marked liver tumor-initiating cells and promote their tumor formation, growth, and metastasis.

In liver cancer, leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) compartment represents an important tumor-initiating cell (TIC) population and served as a potential therapeutic target. Cancer-associated fibroblasts (CAFs) is a critical part of the tumor microenvironment, heavily influenced TIC function and fate. However, deeply investigations have been hindered by the lack of accurate preclinical models to investigate the interaction between CAFs and TIC. Organoids model have achieved major advancements as a precious research model for recapitulating the morphological aspects of organs, and thus also serving as a candidate model to investigate the mutual interaction between different cell types. Consequently, this study aimed to construct a three-dimensional (3D) co-culture organoid model of primary LGR5-expressing tumor stem cells from primary murine liver tumors with CAFs to investigate the impact of CAFs on LGR5 marked TICs in liver cancer. First, both of the transgenic LGR5-diphtheria toxin receptor (DTR)-GFP knock-in mice and transgenic Rosa26-mT mice developed primary liver tumors by diethylnitrosamine (DEN) administration. Tumor organoids and CAFs were generated from those primary liver cancer separately. Second, LGR5-expressing TICs organoid with CAFs were established ex vivo based on cell-cell contact or trans-well co-culture system, and the mutual influence between those two types of cells was further investigated. Subsequently, immunodeficient mouse-based xenograft model was further adopted to evaluate the influence of CAFs to LGR5 tumor stem cell, tumor formation, and metastasis. The co-culture organoid model composed of murine liver tumor LGR5+ tumor-initiating cells and CAFs in 3D co-culture was successfully established, with the intention to investigate their mutual interaction. The existence of CAFs upon engrafting tumor organoids resulted in dramatic higher number of LGR5+ cells in the neoplasia when compared with engrafting tumor organoids alone. Furthermore, ex vivo culture of isolated LGR5+ cells from tumors of co-engrafted mice formed significantly larger size of organoids than mono-engrafted. Our results also indicated significantly larger size and number of formed organoids, when LGR5+ cells co-cultured with CAF in both cell-cell contact and paracrine signaling in vitro, comparing to LGR5+ cells alone. Furthermore, we found that specific knockout of LGR5 expressing cells suppressed CAF-mediated promotion of tumor formation, growth, and metastasis in the experimental mice model. Altogether, in a 3D co-culture type of murine liver LGR5+ cells and cancer-associated fibroblasts, we have demonstrated robust effects of CAFs in the promotion of LGR5 marked liver TICs. We also further revealed the influence of tumor microenvironment on stem cell-related therapy, suggesting the possibility of combing CAF-targeted and tumor stem cell targeted therapy in treating liver cancer.

Identification of Small Inhibitors for Human Metadherin, an Oncoprotein, through in silico Approach.

Cancer is a disease that takes lives of thousands of people each year. There are more than 100 different types of cancers known to man. This fatal disease is one of the leading causes of death today. Astrocyte elevated gene-1(AEG-1)/Metadherin (MTDH) activates multiple oncogenic signaling pathways and leads to different types of cancers. MTDH interacting with staphylococcal nuclease domain containing 1(SND1) supports the survival and growth of mammary epithelial cells under oncogenic conditions. Silencing MTDH or SND1 individually or disrupting their interaction compromises the tumorigenic potential of tumor-initiating cells. The aim of our present study was to investigate novel interactions of staphylococcal nuclease domain containing 1 (SND1) binding domain of AEG-1/MTDH with different lead compounds through molecular docking approach using MOE software. Molecular docking was done by docking the ChemBridge database against important residues of MTDH involved in interaction with SND1. After docking the whole ChemBridge database, the top 200 interactive compounds were selected based on docking scores. After applying Lipinski's rule, all the remaining chosen compounds were studied on the basis of binding affinity, binding energy, docking score and protein-ligand interactions. Finally, 10 compounds showing multiple interactions with different amino acid residues were selected as the top interacting compounds. Three compounds were selected for simulation studies after testing these compounds using topkat toxicity and ADMET studies. The simulation study indicated that compound 32538601 is a lead compound for inhibiting MTDH-SND1 complex formation. These novels, potent inhibitors of MTDH-SND1 complex can ultimately help us in controlling cancer up to some extent.

Cancer stem cells in brain tumors: From origin to clinical implications.

Malignant brain tumors are highly heterogeneous tumors with a poor prognosis and a high morbidity and mortality rate in both children and adults. The cancer stem cell (CSC, also named tumor-initiating cell) model states that tumor growth is driven by a subset of CSCs. This model explains some of the clinical observations of brain tumors, including the almost unavoidable tumor recurrence after initial successful chemotherapy and/or radiotherapy and treatment resistance. Over the past two decades, strategies for the identification and characterization of brain CSCs have improved significantly, supporting the design of new diagnostic and therapeutic strategies for brain tumors. Relevant studies have unveiled novel characteristics of CSCs in the brain, including their heterogeneity and distinctive immunobiology, which have provided opportunities for new research directions and potential therapeutic approaches. In this review, we summarize the current knowledge of CSCs markers and stemness regulators in brain tumors. We also comprehensively describe the influence of the CSCs niche and tumor microenvironment on brain tumor stemness, including interactions between CSCs and the immune system, and discuss the potential application of CSCs in brain-based therapies for the treatment of brain tumors.

A Bright Horizon of Intelligent Targeted-cancer Therapy: Nanoparticles Against Breast Cancer Stem Cells.

Breast cancer stem cells (BCSCs) are heterogeneous tumor-initiating cell subgroups of breast cancers that possess some stem cell markers and are sustained after chemotherapy. Due to BCSCs being sufficient for tumor relapse, and given that the biological behaviors of BCSCs are so complex, it is critical to figure out exactly how they work, learn more about their cell biology, and discover biomarkers and strategies for explicitly targeting and destructing cancer stem cells. In order to accomplish innovative treatment for breast cancer, it is also essential to target BCSCs. Despite the vast quantities of BCSC target chemicals, their therapeutic implementation is limited due to off-target behavior and bioavailability issues. Targeted drug delivery systems based on nanoparticles have advantages for transporting anti-BCSC materials, especially to targeted locations. Hence, breast cancer therapy using a nanoparticle-based BCSCs targeting system is a promising strategy. Such targeted drug delivery systems can resolve the biodistribution obstacles of nanosystems. Throughout this paper, we highlight various strategies for targeting BCSCs utilizing nano-based systems. In conclusion, issues about the inadequate stability of nanoparticles and the possibility of loaded drug leakage during delivery systems have yet to be answered. More fundamental and applied research, and proper methods such as coating or surface modification are required.

Role of SH3GLB1 in the regulation of CD133 expression in GBM cells

BackgroundGlioblastoma (GBM), a malignant brain tumor, has poor survival outcomes due to recurrence or drug resistance. We found that SH3GLB1 is a crucial factor for cells to evade temozolomide (TMZ) cytotoxicity through autophagy-mediated oxidative phosphorylation, which is associated with CD133 levels. Therefore, we propose that SH3GLB1 participate in the impact on tumor-initiating cells (TICs).MethodsThe parental, the derived resistant cell lines and their CD133+ cells were used, and the levels of the proteins were compared by western blotting. Then RNA interference was applied to observe the effects of the target protein on TIC-related features. Finally, in vitro transcription assays were used to validate the association between SH3GLB1 and CD133.ResultsThe CD133+ cells from resistant cells with enhanced SH3GLB1 levels more easily survived cytotoxic treatment than those from the parental cells. Inhibition of SH3GLB1 attenuated frequency and size of spheroid formation, and the levels of CD133 and histone 4 lysine 5 (H4K5) acetylation can be simultaneously regulated by SH3GLB1 modification. The H4K5 acetylation of the CD133 promoter was later suggested to be the mediating mechanism of SH3GLB1.ConclusionsThese data indicate that SH3GLB1 can regulate CD133 expression, suggesting that the protein plays a crucial role in TICs. Our findings on the effects of SH3GLB1 on the cells will help explain tumor resistance formation.

Loss of p53 enhances the tumor-initiating potential and drug resistance of clonogenic multiple myeloma cells.

Tumor relapse and drug resistance are major factors that limit the curability of multiple myeloma (MM). New regimens have improved overall MM survival rates, but patients with high-risk features continue to have inferior outcomes. Chromosome 17p13 deletion (del17p) that includes the loss of the TP53 gene is a high-risk cytogenetic abnormality and is associated with poor clinical outcomes owing to relatively short remissions and the development of pan-drug resistant disease. Increased relapse rates suggest that del17p enhances clonogenic growth, and we found that the loss of p53 increased both the frequency and drug resistance of tumor-initiating MM cells (TICs). Subsequent RNA sequencing (RNA-seq) studies demonstrated significant activation of the Notch signaling pathway and upregulation of inhibitor of DNA binding (ID1/ID2) genes in p53-knock out (p53-KO) cells. We found that the loss of ID1 or HES-1 expression or treatment with a gamma-secretase inhibitor (GSI) significantly decreased the clonogenic growth of p53-KO but not p53 wild-type cells. GSI treatment in a small set of MM specimens also reduced the clonogenic growth in del17p samples but not in non-del17p samples. This effect was specific as overexpression of the Notch intracellular domain (NICD) rescued the effects of GSI treatment. Our study demonstrates that the Notch signaling and ID1 expression are required for TIC expansion in p53-KO MM cells. These findings also suggest that GSI may be specifically active in patients with p53 mutant MM.

Deep learning models for cancer stem cell detection: a brief review.

Cancer stem cells (CSCs), also known as tumor-initiating cells (TICs), are a subset of tumor cells that persist within tumors as a distinct population. They drive tumor initiation, relapse, and metastasis through self-renewal and differentiation into multiple cell types, similar to typical stem cell processes. Despite their importance, the morphological features of CSCs have been poorly understood. Recent advances in artificial intelligence (AI) technology have provided automated recognition of biological images of various stem cells, including CSCs, leading to a surge in deep learning research in this field. This mini-review explores the emerging trend of deep learning research in the field of CSCs. It introduces diverse convolutional neural network (CNN)-based deep learning models for stem cell research and discusses the application of deep learning for CSC research. Finally, it provides perspectives and limitations in the field of deep learning-based stem cell research.

Deciphering Common Traits of Breast and Ovarian Cancer Stem Cells and Possible Therapeutic Approaches.

Breast cancer (BC) and ovarian cancer (OC) are among the most common and deadly cancers affecting women worldwide. Both are complex diseases with marked heterogeneity. Despite the induction of screening programs that increase the frequency of earlier diagnosis of BC, at a stage when the cancer is more likely to respond to therapy, which does not exist for OC, more than 50% of both cancers are diagnosed at an advanced stage. Initial therapy can put the cancer into remission. However, recurrences occur frequently in both BC and OC, which are highly cancer-subtype dependent. Therapy resistance is mainly attributed to a rare subpopulation of cells, named cancer stem cells (CSC) or tumor-initiating cells, as they are capable of self-renewal, tumor initiation, and regrowth of tumor bulk. In this review, we will discuss the distinctive markers and signaling pathways that characterize CSC, their interactions with the tumor microenvironment, and the strategies they employ to evade immune surveillance. Our focus will be on identifying the common features of breast cancer stem cells (BCSC) and ovarian cancer stem cells (OCSC) and suggesting potential therapeutic approaches.

Control of SOX2 protein stability and tumorigenic activity by E3 ligase CHIP in esophageal cancer cells.

SOX2 is highly expressed and controls tumor initiation and cancer stem cell function in various squamous cell carcinomas including esophageal squamous cancer. However, the molecular mechanism leading to SOX2 overexpression in cancer is incompletely understood. Here, we identified CHIP, a chaperone-associated ubiquitin E3 ligase, as a novel negative regulator of SOX2 protein stability and tumorigenic activity in esophageal squamous carcinoma cells. We showed that CHIP interacted with SOX2 primarily via chaperone HSP70, together they catalyzed SOX2 ubiquitination and degradation via proteasome. In contrast, HSP90 promoted SOX2 stability and inhibition of HSP90 activity induced SOX2 ubiquitination and degradation. Notably, unlike the case in normal esophageal tissues where CHIP was detected in both the cytoplasm and nucleus, CHIP in clinical esophageal tumor specimens was predominantly localized in the cytoplasm. Consistent with this observation, we observed increased expression of exportin-1/CRM-1 in clinical esophageal tumor specimens. We further demonstrated that CHIP catalyzed SOX2 ubiquitination and degradation primarily in the nuclear compartment. Taken together, our study has identified CHIP as a key suppressor of SOX2 protein stability and tumorigenic activity and revealed CHIP nuclear exclusion as a potential mechanism for aberrant SOX2 overexpression in esophageal cancer. Our study also suggests HSP90 inhibitors as potential therapeutic agents for SOX2-positive cancers.

Visualization of Metastatic Lung Cancer with TiNIR.

The development of efficient biomarkers and probes for monitoring and treating cancer, specifically metastatic cancer, is a critical research area that can have a significant impact on both patient outcomes and drug discovery. In this context, TiNIR has been developed to detect tumor-initiating cells (TICs), with heme oxygenase 2 (HO2) as a promising therapeutic biomarker for tumor-initiating cells. In this study, TiNIR has demonstrated its effectiveness as an in vivo metastatic lung cancer tracker, highlighting its potential as a valuable tool in cancer research and therapy. The development of innovative approaches that selectively target metastatic cancers represents a promising avenue for improving survival rates and enhancing the quality of life of cancer patients.

RARE-06. DISSECTING CELLULAR DIFFERENTIATION HETEROGENEITY IN CHOROID PLEXUS CARCINOMA PATHOGENESIS

Abstract Choroid plexus (CP) neoplasms are rare, predominantly pediatric, brain tumors ranging from benign CP papilloma to aggressive CP carcinoma (CPC) associated with poor survival. Survivors often experience devastating side effects from current treatment strategies. There is an urgent need for safer, more effective therapies for CPC. A subset of human CPC exhibits abnormal NOTCH activity, whereas mutations of tumor suppressor gene TP53 are detected in >50% of CPC and are associated with increased genetic tumor instability and worse prognosis. CPC is one hallmark of Li-Fraumeni syndrome (LFS), a rare genetic disorder associated with germline TP53 mutations. Human CP tumors also frequently display aberrant expression of transcriptional regulators of roof plate/CP differentiation, including LIM homeodomain transcription factors LMX1A, and SRY-Box Transcription Factor 2 (SOX2). To investigate the role of transcriptional regulation in CP tumorigenesis, animal models were developed driven by molecular defects commonly found in CP tumors in humans. Accordingly, sustained NOTCH and Sonic Hedgehog (SHH) activation or combined deletion of Rb1 and Trp53 tumor suppressors led to malignant CP tumors with characteristics of CPC in humans. NOTCH-driven CP tumors arose from monociliated roof plate progenitors and exhibited increased levels of Lmx1a, Lmx1b, and Sox2. In contrast, their expression was significantly reduced, while OTX2 levels were markedly increased in Rb1/Trp53-deficient CPC. Consistently, single-cell transcriptomics data show a proliferative Otx2+ tumor bulk and a small Lmx1a+/Sox2+ population in Rb1/Trp53-deficient CPC. Importantly, deletion of Sox2 in Lmx1a+ progenitors blocked NOTCH-driven CP tumor and reduced Lmx1a/b expression. Thus, LMX1A and SOX2 expression marks tumor-initiating cells, while OTX2 labels differentiated tumor cells in CPC. Together, our studies revealed intra- and inter-tumoral heterogeneity in CPC driven by distinct oncogenic signals. Knowledge of the molecular and cellular basis of heterogeneity in CP tumor development may facilitate the development of innovative diagnostic and therapeutic strategies in CPC.

LGG-13. GANGLIOGLIOMA DEEP TRANSCRIPTOMICS REVEALS A CD34+ PRIMITIVE NEUROECTODERM NEURAL PRECURSOR-LIKE POPULATION

Abstract Gangliogliomas are glioneuronal brain tumors that typically present in childhood or early adulthood. Though most often low-grade, new insights are needed to refine glioneuronal tumor classification and to identify therapeutic approaches, particularly for unresectable, high-grade, and/or recurrent disease. Gangliogliomas often possess a rare population of immature astrocyte-appearing CD34+ cells. CD34 is expressed in neuroectoderm neural precursor cells during embryogenesis. Neural cell CD34 expression is usually lost prior to birth. We hypothesized that CD34+ ganglioglioma cells represent tumor precursor/stem cells and closely resemble ganglioglioma cells of origin. To test this, we evaluated five gangliogliomas with single nucleus RNA-seq, cellular indexing of transcriptomes and epitopes by sequencing, and/or spatially-resolved RNA-seq. Developmental trajectory analyses uncovered a neoplastic cellular hierarchy, with CD34+PAX6+SOX2+MSI1+PECAM1-VWF-DCN-COL1A2- cells being the most primordial and precursor to neuron-like and macroglia-like neoplastic cell states. Gene regulatory network inference of CD34+ ganglioglioma cells indicated TCF7L2/MEIS1-PAX6 and SOX2-mediated transcriptional programming, similar to that found during neuroectodermal/neural development in utero. Spatially-resolved transcriptomics revealed a neuroectoderm neural precursor-like tumor cell niche relatively devoid of vascular and immune cells. We used these high-resolution results to deconvolute clinically-annotated transcriptomic data, confirming that CD34+ neural precursor-like cell-associated gene programs associate with gangliogliomas compared to other brain tumors. Together, these deep transcriptomic approaches characterized a ganglioglioma cellular hierarchy - identifying CD34+ neuroectoderm neural precursor-like tumor-initiating cells, corresponding regulatory transcriptional programs, cell signaling pathways, and associated immune cell states. These findings may facilitate improved ganglioglioma tumor classification, diagnosis, and therapeutic investigations.

Polycomb repressive complex 2 binds and stabilizes NANOG to suppress differentiation-related genes to promote self-renewal

The synergistic effect of alcohol and HCV mediated through TLR4 signaling transactivates NANOG, a pluripotency transcription factor important for the stemness of tumor-initiating stem-like cells (TICs). NANOG together with the PRC2 complex suppresses expression of oxidative phosphorylation (OXPHOS) genes to generate TICs. The phosphodegron sequence PEST domain of NANOG binds EED to stabilize NANOG protein by blocking E3 ligase recruitment and proteasome-dependent degradation, while the tryptophan-rich domain of NANOG binds EZH2 and SUZ12. Human ARID1A gene loss results in the resistance to combined FAO and PRC2 inhibition therapies due to reduction of mitochondrial ROS levels. CRISPR-Cas9-mediated ARID1A knockout and/or constitutively active CTNNB1 driver mutations promoted tumor development in humanized FRG HCC mouse models, in which use of an interface inhibitor antagonizing PRC2-NANOG binding and/or FAO inhibitor blocked tumor growth. Together, the PRC2-NANOG interaction becomes a new drug target for HCC via inducing differentiation-related genes, destabilizing NANOG protein, and suppressing NANOG activity.

PUF: A potential repressor of oncogenes.

e15095 Background: RNA-binding proteins (RBPs) play a crucial role in orchestrating the function of RNAs. The regulation of RBPs is critical in various biological processes, including tumorigenesis. The PUF (Pumilio/FBF) RBPs are of particular interest due to their function in stem cells and tumor-initiating cells. Its has been shown that PUF proteins inhibit the translation of target genes by binding to a regulatory element (PBE) in the 3’ untranslated regions (3’UTRs) of their target mRNA. PUF proteins are required to maintain normal stem cells and potentially inhibit the formation of tumor-initiating cells by repressing the expression of oncogenes. Bioinformatics analysis has identified many oncogenes as potential targets of PUF, and pilot studies have confirmed that ERK, p38, JAK2, RUNX2, and RET mRNAs specifically interact with PUF protein. The objective of this study is to investigate the function of human PUF proteins in the initiation and progression of cancer cells. Methods: In worms (C. elegans), 100 % PUF mutants form tumors. Bioinformatics were performed to identify PUF target genes, it specifically binds UGUAnAUA sequences on target mRNA 3'UTRs. Yeast three-hybrid assay were performed to test the physical interaction between PUF protein and its target mRNA. The novel function of human PUF proteins in the initiation and progression of cancer cells was investigated using CRISPR/Cas9 knockout cancer cell lines and western Blot/IHC was done to determine their expression. Results: The results of the study showed that PUF proteins play a crucial role in inhibiting the formation of tumor-initiating cells. Loss of PUF function and activation of ERK signaling were found to promote the formation of these cells. Bioinformatics analysis revealed that many oncogenes are potential targets for PUF repression. The study also demonstrated that PUF represses the expression of ERK and p38 mRNAs via their 3’UTRs. These findings suggest that PUF may have therapeutic potential as a target for cancer treatment. Conclusions: In worms and human cells, normal PUF proteins promote the cell proliferation of stem cells, however, stem cells begin to differentiate, PUF proteins are required to complete differentiation. Therefore, in the differentiating cells, PUF mutation cannot complete differentiation, instead, return to undifferentiating cells, resulting in tumors. Bioinformatics and biochemical analyses revealed that many PUF repressing targets (~ > 30%) are oncogene and some labs including us found that PUF knockdown enhanced oncogene expression. PUF can be a potential biomarker, as low PUF expression may initiate tumors. Therapeutically, conditional PUF expression in tumor-initiating cells may suppress tumor progression by suppressing oncogene.