The pluripotent factor OCT4A enhances the self-renewal of human dental pulp stem cells by targeting lncRNA FTX in an LPS-induced inflammatory microenvironment

BACKGROUND

Regulating the pluripotency of human dental pulp stem cells (hDPSCs) is key for the self-repair of injured dental pulp. We previously found that OCT4A promotes the proliferation and odontogenic differentiation of human dental pulp cells (hDPCs). Recent studies have shown the interaction between OCT4A and lncRNAs in pluripotency maintenance of various stem cells. The aim of this study was to explore the underlying roles and mechanisms of OCT4A and its related lncRNAs in the proliferation and multidirectional differentiation of hDPSCs in an inflammatory microenvironment.

METHODS

Human lncRNA microarrays were applied to screen out the differentially expressed lncRNAs in hDPSCs between the OCT4A-overexpressing and vector groups. Lipopolysaccharide (LPS) was used to simulate the inflammatory microenvironment. The effects of OCT4A and the lncRNA FTX on the proliferation and multidifferentiation of hDPSCs were observed by the CCK-8 assay, EdU staining, real-time PCR, western blotting, and Alizarin red and oil red O staining. Bioinformatics analysis and chromatin immunoprecipitation (ChIP) assays were performed to clarify the targeted mechanism of OCT4A on FTX. The regulation by FTX of the expression of OCT4A and its downstream pluripotent transcription factors SOX2 and c-MYC was further detected by real-time PCR and western blotting.

RESULTS

The microarray results showed that 978 lncRNAs (250 of which were upregulated and 728 downregulated) were potentially differentially expressed genes (fold change ≥ 2, P < 0.05). LPS stimulation attenuated the self-renewal of hDPSCs. OCT4A enhanced the cell proliferation and multidifferentiation capacities of hDPSCs in an inflammatory microenvironment, while FTX exhibited the opposite effects. OCT4A negatively regulated FTX function by binding to specific regions on the FTX promoter, thereby inhibiting the transcription of FTX. Moreover, overexpression of FTX downregulated the expression of OCT4A, SOX2 and c-MYC, whereas knockdown of FTX facilitated their expression.

CONCLUSIONS

OCT4A was found to be a crucial factor maintaining the self-renewal of hDPSCs by transcriptionally targeting FTX in an inflammatory microenvironment. Moreover, we proposed a novel function of FTX in negatively regulating the pluripotency and multilineage differentiation capacity of hDPSCs. The hierarchical organization between OCT4A and FTX expanded the understanding of the network between transcription factors and lncRNAs in fine-tuning the pluripotency/differentiation balance of adult stem cells, and provided prospective targets for optimizing dental-derived stem cell sources for regenerative endodontics.

Capsaicin inhibits the stemness of anaplastic thyroid carcinoma cells by triggering autophagy-lysosome mediated OCT4A degradation

Capsaicin (CAP) is a well-known anti-cancer agent. Recently, we reported capsaicin-induced apoptosis in anaplastic thyroid cancer (ATC) cells. It is well accepted that the generation of cancer stem cells (CSCs) is responsible for the dedifferentiation of ATC, the most lethal subtype of thyroid cancer with highly dedifferentiation status. Whether CAP inhibited the ATC growth through targeting CSCs needed further investigation. In the present study, CAP was found to induce autophagy in ATC cells through TRPV1 activation and subsequent calcium influx. Meanwhile, CAP dose-dependently decreased the sphere formation capacity of ATC cells. The stemness-inhibitory effect of CAP was further by extreme limiting dilution analysis (ELDA). CAP significantly decreased the protein level of OCT4A in both 8505C and FRO cells. Furthermore, CAP-induced OCT4A degradation was reversed by autophagy inhibitors 3-MA and chloroquine, BAPTA-AM and capsazepine, but not proteasome inhibitor MG132. Collectively, our study firstly showed CAP suppressed the stemness of ATC cells partially via calcium-dependent autophagic degradation of OCT4A. Our study lent credence to the feasible application of capsaicin in limiting ATC stemness.

Linc-ROR has a Potential ceRNA Activity for OCT4A by Sequestering miR-335-5p in the HEK293T Cell Line

Linc-ROR has a regulatory role in reprogramming, and the core stem cell transcription factors, OCT4, SOX2, and NANOG, regulate its expression. MicroRNAs (miRNAs) are also a critical constituent of pivotal posttranscriptional regulatory pathways. One of such interactions is a competing endogenous RNA interaction that connects small and long non-coding RNAs with coding transcripts. Here, we aimed to investigate the existence of such associations between OCT4A, Linc-ROR, hsa-miR-335-5p, and hsa-miR-544. Bioinformatic analysis was performed to evaluate the expression status of OCT4A, Linc-ROR, miR-335, and miR-544 throughout differentiation as well as in various differentiated cells. The complete lengths of OCT4A and Linc-ROR, and OCT4A 3'-UTR were cloned in the luciferase reporter vector, and the precursors of miR-335 and miR-544 were cloned in expression vectors. Following the overexpression of miR-335 and miR-544 in the 5637 cell line, the endogenous expression of OCT4A and Linc-ROR was evaluated. Afterward, the expression vectors of miRNAs and the reporter vectors of OCT4A/Linc-ROR were co-transfected in the HEK293T cell line. Via the Dual-Luciferase assay, the effect of the overexpression of miRNAs on their two possible targets (Linc-ROR and OCT4A) was investigated. The bioinformatic analysis demonstrated a relatively similar expression pattern for OCT4A and Linc-ROR, while miR-335 showed a different expression status. Both miR-335 and miR-544 inhibited the endogenous expression of OCT4A. The Dual-Luciferase assay likewise confirmed the inhibitory effect of miR-335 and miR-544 on OCT4A expression. In contrast, the miR-335 inhibitory effect was reversed in the presence of Linc-ROR, resulting in the upregulation of OCT4A. Such evidence suggests that Linc-ROR may compete with OCT4A to interact with miR-335.

Novel Variant of OCT4, Named OCT4B5, is Highly Expressed in Human Pluripotent Cells

Alternative promoter and alternative splicing are two important mechanisms of gene regulation and protein diversity in different physiological contexts of eukaryotes, especially in stem cells and developmental stages. Pou5f1 gene which codes the stemness marker OCT4, utilizes alternative splicing and promoter mechanisms, which result in generation of multiple spliced variants and subsequently multiple protein isoforms. By far, nine variants of OCT4 (OCT4A, OCT4B, OCT4B1, OCT4B2, OCT4B3, OCT4B4, OCT4C, OCT4C1, and OCT4D) have been introduced. It has been well established that OCT4A plays essential roles in early developmental stages as well as maintenance of stemness in embryonic stem cells (ESCs). However, the roles and functions of other variants and isoforms of OCT4 in biological systems are less appreciated. In this study, we report a new OCT4 variant, designated as OCT4B5. RT-PCR assay on different human cell lines including pluripotent, normal and cancer cells showed that OCT4B5 is expressed at variable level in different cell lines. By semi-quantifying of OCT4B5 expression in pluripotent and differentiated states of NT2 cell lines, we reveal that this variant of OCT4 is highly expressed in undifferentiated state and its expression is down-regulated upon differentiation. Compared to OCT4A which is sharply down-regulated in retinoic acid induced differentiation of NT2 cell line, the expression of OCT4B5 remains at low level in differentiated state. Overall, this study emphasizes the complexity of OCT4 gene expression and regulation in different states of stem cells and physiological contexts. Graphical Abstract.

Cellular context- and protein level-dependent interaction of pluripotency factor OCT4A with multiple octamer motifs of the same target gene

AIMS

To compare how OCT4A proteins interact with and regulate multiple OCT4A-octamer motifs (OMs) in different regions of the FOS gene expressed in somatic cancer cells versus pluripotent stem cells.

MATERIALS AND METHODS

Two FOS reporter gene systems harboring predicted OMs or their mutational counterparts were introduced into HeLa and NCCIT cells with varying OCT4A protein levels. The transcription of dsGFP reflecting FOS expression was quantitated by RT-qPCR, the OCT4A-OMs binding and the correlation between OCT4A and FOS transcription was determined by ChIP-PCR and RNA-Seq, respectively.

KEY FINDINGS

In NCCIT cells, abundant OCT4A proteins bound to and inhibited OM1 and OM2 at the promoter of the FOS gene. RA-induced OCT4A down-regulation transiently increased FOS transcription. In contrast, in HeLa cells that contain much lower levels of endogenous OCT4A proteins, OCT4A primarily bound to and activate OM1 thereby promoting FOS transcription. OCT4A KO significantly reduced FOS expression. Ectopically introduced OCT4A, at its leaked or induced expression level, promoted FOS transcription by binding to OM2/OM3 or OM1/OM3, respectively. Thus, the interaction of OCT4A proteins with different OMs is cellular context- and protein level-dependent, and such complicated OCT4A binding mode can only be reflected by a dsGFP-based reporter harboring the full-length FOS gene but not by that merely having the FOS promoter.

SIGNIFICANCE

Our findings unravel an additional layer of regulatory mechanisms that account for the cellular context- and dose-related versatile functions of OCT4A protein, and further underscore the importance of precise modulation of OCT4A in the regenerative medicine and anticancer therapies.

Proteome and miRNome profiling of microvesicles derived from medulloblastoma cell lines with stem-like properties reveals biomarkers of poor prognosis

Primary central nervous system (CNS) tumors are the most common deadly childhood cancer. Several patients with medulloblastoma experience local or metastatic recurrences after standard treatment, a condition associated with very poor prognosis. Current neuroimaging techniques do not accurately detect residual stem-like medulloblastoma cells promoting tumor relapses. In attempt to identify candidate tumor markers that could be circulating in blood or cerebrospinal (CSF) fluid of patients, we evaluated the proteome and miRNome content of extracellular microvesicles (MVs) released by highly-aggressive stem-like medulloblastoma cells overexpressing the pluripotent factor OCT4A. These cells display enhanced tumor initiating capability and resistance to chemotherapeutic agents. A common set of 464 proteins and 10 microRNAs were exclusively detected in MVs of OCT4A-overexpressing cells from four distinct medulloblastoma cell lines, DAOY, CHLA-01-MED, D283-MED, and USP13-MED. The interactome mapping of these exclusive proteins and miRNAs revealed ERK, PI3K/AKT/mTOR, EGF/EGFR, and stem cell self-renewal as the main oncogenic signaling pathways altered in these aggressive medulloblastoma cells. Of these MV cargos, four proteins (UBE2M, HNRNPCL2, HNRNPCL3, HNRNPCL4) and five miRNAs (miR-4449, miR-500b, miR-3648, miR-1291, miR-3607) have not been previously reported in MVs from normal tissues and in CSF. These proteins and miRNAs carried within MVs might serve as biomarkers of aggressive stem-like medulloblastoma cells to improve clinical benefit by helping refining diagnosis, patient stratification, and early detection of relapsed disease.

A Potential Application of Triangular Microwells to Entrap Single Cancer Cells: A Canine Cutaneous Mast Cell Tumor Model

Cellular heterogeneity is a major hindrance, leading to the misunderstanding of dynamic cell biology. However, single cell analysis (SCA) has been used as a practical means to overcome this drawback. Many contemporary methodologies are available for single cell analysis; among these, microfluidics is the most attractive and effective technology, due to its advantages of low-volume specimen consumption, label-free evaluation, and real-time monitoring, among others. In this paper, a conceptual application for microfluidic single cell analysis for veterinary research is presented. A microfluidic device is fabricated with an elastomer substrate, polydimethylsiloxane (PDMS), under standard soft lithography. The performance of the microdevice is high-throughput, sensitive, and user-friendly. A total of 53.1% of the triangular microwells were able to trap single canine cutaneous mast cell tumor (MCT) cells. Of these, 38.82% were single cell entrapments, while 14.34% were multiple cell entrapments. The ratio of single-to-multiple cell trapping was high, at 2.7:1. In addition, 80.5% of the trapped cells were viable, indicating that the system was non-lethal. OCT4A-immunofluorescence combined with the proposed system can assess OCT4A expression in trapped single cells more precisely than OCT4A-immunohistochemistry. Therefore, the results suggest that microfluidic single cell analysis could potentially reduce the impact of cellular heterogeneity.

miR-367 as a therapeutic target in stem-like cells from embryonal central nervous system tumors

Aberrant expression of the pluripotency factor OCT4A in embryonal tumors of the central nervous system (CNS) is a key factor that contributes to tumor aggressiveness and correlates with poor patient survival. OCT4A overexpression has been shown to up-regulate miR-367, a microRNA (miRNA) that regulates pluripotency in embryonic stem cells and stem-like aggressive traits in cancer cells. Here, we show that (a) miR-367 is carried in microvesicles derived from embryonal CNS tumor cells expressing OCT4A; and (b) inhibition of miR-367 in these cells attenuates their aggressive traits. miR-367 silencing in OCT4A-overexpressing tumor cells significantly reduced their proliferative and invasive behavior, clonogenic activity, and tumorsphere generation capability. In vivo, targeting of miR-367 through direct injections of a specific inhibitor into the cerebrospinal fluid of Balb/C nude mice bearing OCT4A-overexpressing tumor xenografts inhibited tumor development and improved overall survival. miR-367 was also shown to target SUZ12, one of the core components of the polycomb repressive complex 2 known to be involved in epigenetic silencing of pluripotency-related genes, including POU5F1, which encodes OCT4A. Our findings reveal possible clinical applications of a cancer stemness pathway, highlighting miR-367 as a putative liquid biopsy biomarker that could be further explored to improve early diagnosis and prognosis prediction, and potentially serve as a therapeutic target in aggressive embryonal CNS tumors.

OCT4B2, a novel alternative spliced variant of OCT4, is significantly upregulated under heat-stress condition and downregulated in differentiated cells

OCT4 is a crucial transcription factor that maintains self-renewal and pluripotency of embryonic stem and embryonic carcinoma cells. The human OCT4 gene can generate at least three variants (OCT4A, OCT4B, and OCTB1) via alternative splicing and alternative promoters. It has been previously reported that OCT4A is the main isoform, retaining stemness state in embryonic stem and embryonic carcinoma cells. There are several reports on the expression of OCT4A, OCT4B, and OCT4B1 in some cancers and tumor cells. The expression of OCT4 in cancer tissues and cell lines appeared to be highly controversial since it was believed that OCT4 is exclusively expressed in embryonic stem/embryonic carcinoma cells. Here, we are reporting the detection of a novel alternatively spliced variant of OCT4, OCT4B2, in several pluripotent and tumor cell lines. Moreover, the expression pattern of OCT4B2 in the course of neural differentiation of NT2 and NCCIT, embryonic carcinoma cells, was similar to that of OCT4A. OCT4B2 was highly expressed in undifferentiated cells; however, its expression was sharply downregulated upon induction of differentiation. Overexpression of OCT4B2 did not affect the distribution of cells in different cell-cycle phases of transfected cells, compared to the mock transfected cells. Interestingly, the expression of OCT4B2 transcript was elevated under the heat-shock induction. In conclusion, we are reporting a new variant of OCT4, which is expressed under different physiological conditions. The finding shed more light on complexity of OCT4 expression and functions.

High OCT4A levels drive tumorigenicity and metastatic potential of medulloblastoma cells

Medulloblastoma is a highly aggressive pediatric brain tumor, in which sporadic expression of the pluripotency factor OCT4 has been recently correlated with poor patient survival. However the contribution of specific OCT4 isoforms to tumor aggressiveness is still poorly understood. Here, we report that medulloblastoma cells stably overexpressing the OCT4A isoform displayed enhanced clonogenic, tumorsphere generation, and invasion capabilities. Moreover, in an orthotopic metastatic model of medulloblastoma, OCT4A overexpressing cells generated more developed, aggressive and infiltrative tumors, with tumor-bearing mice attaining advanced metastatic disease and shorter survival rates. Pro-oncogenic OCT4A effects were expression-level dependent and accompanied by distinct chromosomal aberrations. OCT4A overexpression in medulloblastoma cells also induced a marked differential expression of non-coding RNAs, including poorly characterized long non-coding RNAs and small nucleolar RNAs. Altogether, our findings support the relevance of pluripotency-related factors in the aggravation of medulloblastoma traits classically associated with poor clinical outcome, and underscore the prognostic and therapeutic value of OCT4A in this challenging type of pediatric brain cancer.

PD-L1 promotes OCT4 and Nanog expression in breast cancer stem cells by sustaining PI3K/AKT pathway activation

The expression of PD‐L1 in breast cancer is associated with estrogen receptor negativity, chemoresistance and epithelial‐to‐mesenchymal transition (EMT), all of which are common features of a highly tumorigenic subpopulation of cancer cells termed cancer stem cells (CSCs). Hitherto, the expression and intrinsic role of PD‐L1 in the dynamics of breast CSCs has not been investigated. To address this issue, we used transcriptomic datasets, proteomics and several in vitro and in vivo assays. Expression profiling of a large breast cancer dataset (530 patients) showed statistically significant correlation (p < 0.0001, r = 0.36) between PD‐L1 expression and stemness score of breast cancer. Specific knockdown of PD‐L1 using ShRNA revealed its critical role in the expression of the embryonic stem cell transcriptional factors: OCT‐4A, Nanog and the stemness factor, BMI1. Conversely, these factors could be induced upon PD‐L1 ectopic expression in cells that are normally PD‐L1 negative. Global proteomic analysis hinted for the central role of AKT in the biology of PD‐L1 expressing cells. Indeed, PD‐L1 positive effect on OCT‐4A and Nanog was dependent on AKT activation. Most importantly, downregulation of PD‐L1 compromised the self‐renewal capability of breast CSCs in vitro and in vivo as shown by tumorsphere formation assay and extreme limiting dilution assay, respectively. This study demonstrates a novel role for PD‐L1 in sustaining stemness of breast cancer cells and identifies the subpopulation and its associated molecular pathways that would be targeted upon anti‐PD‐L1 therapy.

What's new?

Cancer cells that express the T‐cell inhibitory molecule programmed death‐ligand 1 (PD‐L1) readily escape immune attack. In addition, PD‐L1 expression contributes to chemoresistance and is associated with epithelial‐to‐mesenchymal transition, a process that generates cancer stem cells (CSCs). This study shows that in breast cancer, PD‐L1 expression further plays a direct part in maintaining CSC stemness. In breast cancer cells, PD‐L1 expression sustained stemness factors OCT‐4A and Nanog, via a PI3K/AKT‐dependent pathway, and promoted expression of the stemness controlling factor BMI1, independent of PI3K/AKT. Targeting PD‐L1 could help advance breast cancer therapy, owing to impacts on the pool of breast CSCs.

Induced overexpression of OCT4A in human embryonic stem cells increases cloning efficiency

Our knowledge of the molecular mechanisms underlying human embryonic stem cell (hESC) self-renewal and differentiation is incomplete. The level of octamer-binding transcription factor 4 (Oct4), a critical regulator of pluripotency, is precisely controlled in mouse embryonic stem cells. However, studies of human OCT4 are often confounded by the presence of three isoforms and six expressed pseudogenes, which has complicated the interpretation of results. Using an inducible lentiviral overexpression and knockdown system to manipulate OCT4A above or below physiological levels, we specifically examine the functional role of the OCT4A isoform in hESC. (We also designed and generated a comparable series of vectors, which were not functional, for the overexpression and knockdown of OCT4B.) We show that specific knockdown of OCT4A results in hESC differentiation, as indicated by morphology changes, cell surface antigen expression, and upregulation of ectodermal genes. In contrast, inducible overexpression of OCT4A in hESC leads to a transient instability of the hESC phenotype, as indicated by changes in morphology, cell surface antigen expression, and transcriptional profile, that returns to baseline within 5 days. Interestingly, sustained expression of OCT4A past 5 days enhances hESC cloning efficiency, suggesting that higher levels of OCT4A can support self-renewal. Overall, our results indicate that high levels of OCT4A increase hESC cloning efficiency and do not induce differentiation (whereas OCT4B expression cannot be induced in hESC), highlighting the importance of isoform-specific studies in a stable and inducible expression system for human OCT4. Additionally, we demonstrate the utility of an efficient method for conditional gene expression in hESC.

TRA-1-60+, SSEA-4+, POU5F1+, SOX2+, NANOG+ Clones of Pluripotent Stem Cells in the Embryonal Carcinomas of the Testes

INTRODUCTION

Cancer of the testes is currently the most frequent neoplasm and a leading cause of morbidity in men 15-35 years of age. Its incidence is increasing. Embryonal carcinoma is its most malignant form, which either may be resistant or may develop resistance to therapies, which results in relapses. Cancer stem cells are hypothesized to be drivers of these phenomena.

SPECIFIC AIM

The specific aim of this work was identification and isolation of spectra of single, living cancer stem cells, which were acquired directly from the patients' biopsies, followed by testing of their pluripotency.

PATIENTS METHODS

Biopsies were obtained from the patients with the clinical and histological diagnoses of the primary, pure embryonal carcinomas of the testes. The magnetic and fluorescent antibodies were genetically engineered. The SSEA-4 and TRA-1-60 cell surface display was analyzed by multiphoton fluorescence spectroscopy (MPFS), flow cytometry (FCM), immunoblotting (IB), nuclear magnetic resonance spectroscopy (NMRS), energy dispersive x-ray spectroscopy (EDXS), and total reflection x-ray spectroscopy (TRXFS). The single, living cells were isolated by magnetic or fluorescent sorting followed by their clonal expansion. The OCT4A, SOX2, and NANOG genes' transcripts were analyzed by qRTPCR and the products by IB and MPFS.

RESULTS

The clones of cells, with the strong surface display of TRA-1-60 and SSEA-4, were identified and isolated directly from the biopsies acquired from the patients diagnosed with the pure embryonal carcinomas of the testes. These cells demonstrated high levels of transcription and translation of the pluripotency genes: OCT4A, SOX2, and NANOG. They formed embryoid bodies, which differentiated into ectoderm, mesoderm, and endoderm.

CONCLUSION

In the pure embryonal carcinomas of the testes, acquired directly from the patients, we identified, isolated with high viability and selectivity, and profiled the clones of the pluripotent stem cells. These results may help in explaining therapy-resistance and relapses of these neoplasms, as well as, in designing targeted, personalized therapy.