Ribosome Incorporation into Somatic Cells Promotes Lineage Transdifferentiation towards Multipotency

The epithelial-mesenchymal plasticity landscape: principles of design and mechanisms of regulation

Epithelial-mesenchymal plasticity (EMP) enables cells to interconvert between several states across the epithelial-mesenchymal landscape, thereby acquiring hybrid epithelial/mesenchymal phenotypic features. This plasticity is crucial for embryonic development and wound healing, but also underlies the acquisition of several malignant traits during cancer progression. Recent research using systems biology and single-cell profiling methods has provided novel insights into the main forces that shape EMP, which include the microenvironment, lineage specification and cell identity, and the genome. Additionally, key roles have emerged for hysteresis (cell memory) and cellular noise, which can drive stochastic transitions between cell states. Here, we review these forces and the distinct but interwoven layers of regulatory control that stabilize EMP states or facilitate epithelial-mesenchymal transitions (EMTs) and discuss the therapeutic potential of manipulating the EMP landscape.

Ribosomes and Ribosomal Proteins Promote Plasticity and Stemness Induction in Glioma Cells via Reprogramming

Glioblastoma multiforme (GBM) is a lethal tumor that develops in the adult brain. Despite advances in therapeutic strategies related to surgical resection and chemo-radiotherapy, the overall survival of patients with GBM remains unsatisfactory. Genetic research on mutation, amplification, and deletion in GBM cells is important for understanding the biological aggressiveness, diagnosis, and prognosis of GBM. However, the efficacy of drugs targeting the genetic abnormalities in GBM cells is limited. Investigating special microenvironments that induce chemo-radioresistance in GBM cells is critical to improving the survival and quality of life of patients with GBM. GBM cells acquire and maintain stem-cell-like characteristics via their intrinsic potential and extrinsic factors from their special microenvironments. The acquisition of stem-cell-like phenotypes and aggressiveness may be referred to as a reprogramming of GBM cells. In addition to protein synthesis, deregulation of ribosome biogenesis is linked to several diseases including cancer. Ribosomal proteins possess both tumor-promotive and -suppressive functions as extra-ribosomal functions. Incorporation of ribosomes and overexpression of ribosomal protein S6 reprogram and induce stem-cell-like phenotypes in GBM cells. Herein, we review recent literature and our published data on the acquisition of aggressiveness by GBM and discuss therapeutic options through reprogramming.

Ribosomal proteins induce stem cell-like characteristics in glioma cells as an "extra-ribosomal function"

The characteristic features of plasticity and heterogeneity in glioblastoma (GB) cells cause therapeutic difficulties. GB cells are exposed to various stimuli from the tumor microenvironment and acquire the potential to resist chemoradiotherapy. To investigate how GB cells acquire stem cell-like phenotypes, we focused on ribosomal proteins, because ribosome incorporation has been reported to induce stem cell-like phenotypes in somatic cells. Furthermore, dysregulation of ribosome biogenesis has been reported in several types of cancer. We focused on ribosomal protein S6, which promotes sphere-forming ability and stem cell marker expression in GB cells. We expect that investigation of dysregulation of ribosome biogenesis and extra-ribosomal function in GB will provide new insights about the plasticity, heterogeneity, and therapeutic resistance of GB cells, which can potentially lead to revolutionary therapeutic strategies.

Heterogeneity and dynamic of EMT through the plasticity of ribosome and mRNA translation

Growing evidence exposes translation and its translational machinery as key players in establishing and maintaining physiological and pathological biological processes. Examining translation may not only provide new biological insight but also identify novel innovative therapeutic targets in several fields of biology, including that of epithelial-to-mesenchymal transition (EMT). EMT is currently considered as a dynamic and reversible transdifferentiation process sustaining the transition from an epithelial to mesenchymal phenotype, known to be mainly driven by transcriptional reprogramming. However, it seems that the characterization of EMT plasticity is challenging, relying exclusively on transcriptomic and epigenetic approaches. Indeed, heterogeneity in EMT programs was reported to depend on the biological context. Here, by reviewing the involvement of translational control, translational machinery and ribosome biogenesis characterizing the different types of EMT, from embryonic and adult physiological to pathological contexts, we discuss the added value of integrating translational control and its machinery to depict the heterogeneity and dynamics of EMT programs.

Glioma Cells Acquire Stem-like Characters by Extrinsic Ribosome Stimuli

Although glioblastoma (GBM) stem-like cells (GSCs), which retain chemo-radio resistance and recurrence, are key prognostic factors in GBM patients, the molecular mechanisms of GSC development are largely unknown. Recently, several studies revealed that extrinsic ribosome incorporation into somatic cells resulted in stem cell properties and served as a key trigger and factor for the cell reprogramming process. In this study, we aimed to investigate the mechanisms underlying GSCs development by focusing on extrinsic ribosome incorporation into GBM cells. Ribosome-induced cancer cell spheroid (RICCS) formation was significantly upregulated by ribosome incorporation. RICCS showed the stem-like cell characters (number of cell spheroid, stem cell markers, and ability for trans differentiation towards adipocytes and osteocytes). In RICCS, the phosphorylation and protein expression of ribosomal protein S6 (RPS6), an intrinsic ribosomal protein, and STAT3 phosphorylation were upregulated, and involved in the regulation of cell spheroid formation. Consistent with those results, glioma-derived extrinsic ribosome also promoted GBM-RICCS formation through intrinsic RPS6 phosphorylation. Moreover, in glioma patients, RPS6 phosphorylation was dominantly observed in high-grade glioma tissues, and predominantly upregulated in GSCs niches, such as the perinecrosis niche and perivascular niche. Those results indicate the potential biological and clinical significance of extrinsic ribosomal proteins in GSC development.

Coordinated regulation of the ribosome and proteasome by PRMT1 in the maintenance of neural stemness in cancer cells and neural stem cells

Previous studies suggested that cancer cells resemble neural stem/progenitor cells in regulatory network, tumorigenicity, and differentiation potential, and that neural stemness might represent the ground or basal state of differentiation and tumorigenicity. The neural ground state is reflected in the upregulation and enrichment of basic cell machineries and developmental programs, such as cell cycle, ribosomes, proteasomes, and epigenetic factors, in cancers and in embryonic neural or neural stem cells. However, how these machineries are concertedly regulated is unclear. Here, we show that loss of neural stemness in cancer or neural stem cells via muscle-like differentiation or neuronal differentiation, respectively, caused downregulation of ribosome and proteasome components and major epigenetic factors, including PRMT1, EZH2, and LSD1. Furthermore, inhibition of PRMT1, an oncoprotein that is enriched in neural cells during embryogenesis, caused neuronal-like differentiation, downregulation of a similar set of proteins downregulated by differentiation, and alteration of subcellular distribution of ribosome and proteasome components. By contrast, PRMT1 overexpression led to an upregulation of these proteins. PRMT1 interacted with these components and protected them from degradation via recruitment of the deubiquitinase USP7, also known to promote cancer and enriched in embryonic neural cells, thereby maintaining a high level of epigenetic factors that maintain neural stemness, such as EZH2 and LSD1. Taken together, our data indicate that PRMT1 inhibition resulted in repression of cell tumorigenicity. We conclude that PRMT1 coordinates ribosome and proteasome activity to match the needs for high production and homeostasis of proteins that maintain stemness in cancer and neural stem cells.

Ribosome-Induced Cellular Multipotency, an Emerging Avenue in Cell Fate Reversal

The ribosome, which is present in all three domains of life, plays a well-established, critical role in the translation process by decoding messenger RNA into protein. Ribosomal proteins, in contrast, appear to play non-translational roles in growth, differentiation, and disease. We recently discovered that ribosomes are involved in reverting cellular potency to a multipotent state. Ribosomal incorporation (the uptake of free ribosome by living cells) can direct the fate of both somatic and cancer cells into multipotency, allowing them to switch cell lineage. During this process, both types of cells experienced cell-cycle arrest and cellular stress while remaining multipotent. This review provides a molecular perspective on current insights into ribosome-induced multipotency and sheds light on how a common stress-associated mechanism may be involved. We also discuss the impact of this phenomenon on cancer cell reprogramming and its potential in cancer therapy.

Ribosome induces transdifferentiation of A549 and H-111-TC cancer cell lines

Previously we reported that, lactic acid bacteria (LAB) can induce human dermal fibroblast (HDF) cells to form multipotent cell clusters which are able to transdifferentiate into three germ layer derived cell lineages. Later on, we confirmed that ribosome is responsible for the LAB-induced transdifferentiation and ribosomes from diverse organisms can mimic the LAB effect on HDF cells. In our present study we have shown that, upon incorporation of ribosomes, non-small cell lung cancer cell line A549 and gastric tubular adenocarcinoma cell line H-111-TC are transformed into spheroid like morphology those can be transdifferentiated into adipocytes and osteoblast. Our qPCR analysis has revealed that, during the formation of ribosome induced cancer cell spheroids, the expression of the cancer cell associated markers and cell cycle/proliferation markers were altered at different time point. Through our investigation, here we report a novel and a non-invasive approach for cancer cell reprogramming by incorporating ribosomes.

Ribosome Incorporation Induces EMT-like Phenomenon with Cell Cycle Arrest in Human Breast Cancer Cell

Although ribosomes are generally known to be a translational machinery, some ribosomal proteins also have accessory functions involving early development and differentiation. Previously, we reported that ribosome incorporation into human dermal fibroblasts generated embryoid body-like cell clusters, altered cellular fate, and differentiated into cells of all 3 germ layers. However, the molecular phenomena induced by ribosome incorporation in the cell remained unknown. Here, we demonstrate that ribosome incorporation into human breast cancer cell MCF7 leads to ribosome-induced cell clusters (RICs) formation accompanying with epithelial-mesenchymal transition (EMT)-like gene expression. Following ribosome incorporation, MCF7 cells cease proliferation, which is caused by inhibition of cell cycle transition from G0 to G1 phase. Further, MCF7 RICs show induced expression of EMT markers, TGF-β1 and Snail along with autophagy markers and tumor suppressor gene p53. These findings indicate that the incorporation of ribosome into cancer cells induces an EMT-like phenomenon and changes the cancer cell characteristics.

Ribosomes: An Exciting Avenue in Stem Cell Research

Stem cell research has focused on genomic studies. However, recent evidence has indicated the involvement of epigenetic regulation in determining the fate of stem cells. Ribosomes play a crucial role in epigenetic regulation, and thus, we focused on the role of ribosomes in stem cells. Majority of living organisms possess ribosomes that are involved in the translation of mRNA into proteins and promote cellular proliferation and differentiation. Ribosomes are stable molecular machines that play a role with changes in the levels of RNA during translation. Recent research suggests that specific ribosomes actively regulate gene expression in multiple cell types, such as stem cells. Stem cells have the potential for self-renewal and differentiation into multiple lineages and, thus, require high efficiency of translation. Ribosomes induce cellular transdifferentiation and reprogramming, and disrupted ribosome synthesis affects translation efficiency, thereby hindering stem cell function leading to cell death and differentiation. Stem cell function is regulated by ribosome-mediated control of stem cell-specific gene expression. In this review, we have presented a detailed discourse on the characteristics of ribosomes in stem cells. Understanding ribosome biology in stem cells will provide insights into the regulation of stem cell function and cellular reprogramming.

Ribosomal protein S6 promotes stem-like characters in glioma cells

Glioblastoma multiforme (GBM), a lethal brain tumor developing in the white matter of the adult brain, contains a small population of GBM stem cells (GSCs), which potentially cause chemotherapeutic resistance and tumor recurrence. However, the mechanisms underlying the pathogenesis and maintenance of GSCs remain largely unknown. A recent study reported that incorporation of ribosomes and ribosomal proteins into somatic cells promoted lineage trans-differentiation toward multipotency. This study aimed to investigate the mechanism underlying stemness acquisition in GBM cells by focusing on 40S ribosomal protein S6 (RPS6). RPS6 was significantly upregulated in high-grade glioma and localized at perivascular, perinecrotic, and border niches in GBM tissues. siRNA-mediated RPS6 knock-down significantly suppressed the characteristics of GSCs, including their tumorsphere potential and GSC marker expression; STAT3 was downregulated in GBM cells. RPS6 overexpression enhanced the tumorsphere potential of GSCs and these effects were attenuated by STAT3 inhibitor (AG490). Moreover, RPS6 expression was significantly correlated with SOX2 expression in different glioma grades. Immunohistochemistry data herein indicated that RPS6 was predominant in GSC niches, concurrent with the data from IVY GAP databases. Furthermore, RPS6 and other ribosomal proteins were upregulated in GSC-predominant areas in this database. The present results indicate that, in GSC niches, ribosomal proteins play crucial roles in the development and maintenance of GSCs and are clinically associated with chemoradioresistance and GBM recurrence.

Conversion of human fibroblasts into multipotent cells by cell-penetrating peptides

The potential application of human induced pluripotent stem cells (hiPSCs) brings great expectations to regenerative medicine. However, several safety concerns, such as oncogenic transformation, remain. A number of methods have been developed to produce hiPSCs with potentially reduced risks. Cell-penetrating peptides (CPPs) are expected to improve the efficiency of nonviral reprogramming by delivering biologically active molecules into cells. Here, we show that the transfection of CPPs alone into normal adult human fibroblasts generated embryonic body (EB)-like cell clusters in the absence of reprogramming factors. The CPP-generated cell clusters were positive for a set of multipotency markers and differentiated into endodermal, ectodermal, and mesodermal cells in vitro. These results suggest that CPPs converted normal human adult somatic cells into multipotent cells. Moreover, we show that CPPs dissociated histone deacetylase 1 and lysine-specific demethylase 1 from the promoter/enhancer regions of reprogramming factors to reactivate their expression. This is the first report of an easy and quick method for somatic cell reprogramming by CPPs and a novel mechanism of reprogramming. The potential application of CPP-generated multipotent cells resolves several concerns, especially safety issues, in regenerative medicine.

Experimental and Computational Approaches to Direct Cell Reprogramming: Recent Advancement and Future Challenges

The process of direct cell reprogramming, also named transdifferentiation, permits for the conversion of one mature cell type directly into another, without returning to a dedifferentiated state. This makes direct reprogramming a promising approach for the development of several cellular and tissue engineering therapies. To achieve the change in the cell identity, direct reprogramming requires an arsenal of tools that combine experimental and computational techniques. In the recent years, several methods of transdifferentiation have been developed. In this review, we will introduce the concept of direct cell reprogramming and its background, and cover the recent developments in the experimental and computational prediction techniques with their applications. We also discuss the challenges of translating this technology to clinical setting, accompanied with potential solutions.

Dynamic organelle localization and cytoskeletal reorganization during preimplantation mouse embryo development revealed by live imaging of genetically encoded fluorescent fusion proteins

Live imaging is one of the most powerful technologies for studying the behaviors of cells and molecules in living embryos. Previously, we established a series of reporter mouse lines in which specific organelles are labeled with various fluorescent proteins. In this study, we examined the localizations of fluorescent signals during preimplantation development of these mouse lines, as well as a newly established one, by time‐lapse imaging. Each organelle was specifically marked with fluorescent fusion proteins; fluorescent signals were clearly visible during the whole period of time‐lapse observation, and the expression of the reporters did not affect embryonic development. We found that some organelles dramatically change their sub‐cellular distributions during preimplantation stages. In addition, by crossing mouse lines carrying reporters of two distinct colors, we could simultaneously visualize two types of organelles. These results confirm that our reporter mouse lines can be valuable genetic tools for live imaging of embryonic development.

Transdifferentiation of human somatic cells by ribosome

Ribosomes are intracellular organelles ubiquitous in all organisms, which translate information from mRNAs to synthesize proteins. They are complex macromolecules composed of dozens of proteins and ribosomal RNAs. Other than translation, some ribosomal proteins also have side-jobs called "Moonlighting" function. The majority of these moonlighting functions influence cancer progression, early development and differentiation. Recently, we discovered that ribosome is involved in the regulation of cellular transdifferentiation of human dermal fibroblasts (HDFs). In vitro incorporation of ribosomes into HDFs arrests cell proliferation and induces the formation of cell clusters, that differentiate into three germ layer derived cells upon induction by differentiation mediums. The discovery of ribosome induced transdifferentiation, that is not based on genetic modification, find new possibilities for the treatment of cancer and congenital diseases, as well as to understand early development and cellular lineage differentiation.