The p53-PUMA axis suppresses iPSC generation

c-Myc alone is enough to reprogram fibroblasts into functional macrophages

BACKGROUND

Macrophage-based cell therapy is promising in solid tumors, but the efficient acquisition of macrophages remains a challenge. Induced pluripotent stem cell (iPSC)-induced macrophages are a valuable source, but time-consuming and costly. The application of reprogramming technologies allows for the generation of macrophages from somatic cells, thereby facilitating the advancement of cell-based therapies for numerous malignant diseases.

METHODS

The composition of CD45+ myeloid-like cell complex (MCC) and induced macrophage (iMac) were analyzed by flow cytometry and single-cell RNA sequencing. The engraftment capacity of CD45+ MCC was evaluated by two transplantation assays. Regulation of c-Myc on MafB was evaluated by ChIP-qPCR and promoter reporter and dual luciferase assays. The phenotype and phagocytosis of iMac were explored by flow cytometry and immunofluorescence. Leukemia, breast cancer, and patient-derived tumor xenograft models were used to explore the anti-tumor function of iMac.

RESULTS

Here we report on the establishment of a novel methodology allowing for reprogramming fibroblasts into functional macrophages with phagocytic activity by c-Myc overexpression. Fibroblasts with ectopic expression of c-Myc in iPSC medium rapidly generated CD45+ MCC intermediates with engraftment capacity as well as the repopulation of distinct hematopoietic compartments. MCC intermediates were stably maintained in iPSC medium and continuously generated functional and highly pure iMac just by M-CSF cytokine stimulation. Single-cell transcriptomic analysis of MCC intermediates revealed that c-Myc up-regulated the expression of MafB, a major regulator of macrophage differentiation, to promote macrophage differentiation. Characterization of the iMac activity showed NF-κB signaling activation and a pro-inflammatory phenotype. iMac cells displayed significantly increased in vivo persistence and inhibition of tumor progression in leukemia, breast cancer, and patient-derived tumor xenograft models.

CONCLUSIONS

Our findings demonstrate that c-Myc alone is enough to reprogram fibroblasts into functional macrophages, supporting that c-Myc reprogramming strategy of fibroblasts can help circumvent long-standing obstacles to gaining "off-the-shelf" macrophages for anti-cancer immunotherapy.

PRPS2 mutations drive acute lymphoblastic leukemia relapse through influencing PRPS1/2 hexamer stability

Tumor relapse is the major cause of treatment failure in childhood acute lymphoblastic leukemia (ALL), yet the underlying mechanisms are still elusive. Here, we demonstrate that phosphoribosyl pyrophosphate synthetase 2 (PRPS2) mutations drive ALL relapse through influencing PRPS1/2 hexamer stability. Ultra-deep sequencing was performed to identify PRPS2 mutations in ALL samples. The effects of PRPS2 mutations on cell survival, cell apoptosis, and drug resistance were evaluated. In vitro PRPS2 enzyme activity and ADP/GDP feedback inhibition of PRPS enzyme activity were assessed. Purine metabolites were analyzed by ultra-performance liquid-chromatography tandem mass spectrometry (UPLC-MS/MS). Integrating sequencing data with clinical information, we identified PRPS2 mutations only in relapsed childhood ALL with thiopurine therapy. Functional PRPS2 mutations mediated purine metabolism specifically on thiopurine treatment by influencing PRPS1/2 hexamer stability, leading to reduced nucleotide feedback inhibition of PRPS activity and enhanced thiopurine resistance. The 3-amino acid V103-G104-E105, the key difference between PRPS1 and PRPS2, insertion in PRPS2 caused severe steric clash to the interface of PRPS hexamer, leading to its low enzyme activity. In addition, we demonstrated that PRPS2 P173R increased thiopurine resistance in xenograft models. Our work describes a novel mechanism by which PRPS2 mutants drive childhood ALL relapse and highlights PRPS2 mutations as biomarkers for relapsed childhood ALL.

The cyclin-like protein SPY1 overrides reprogramming induced senescence through EZH2 mediated H3K27me3

Fully differentiated cells can be reprogrammed through ectopic expression of key transcription factors to create induced pluripotent stem cells. These cells share many characteristics of normal embryonic stem cells and have great promise in disease modeling and regenerative medicine. The process of remodeling has its limitations, including a very low efficiency due to the upregulation of many antiproliferative genes, including cyclin dependent kinase inhibitors CDKN1A and CDKN2A, which serve to protect the cell by inducing apoptotic and senescent programs. Our data reveals a unique cell cycle mechanism enabling mouse fibroblasts to repress cyclin dependent kinase inhibitors through the activation of the epigenetic regulator EZH2 by a cyclin-like protein SPY1. This data reveals that the SPY1 protein is required for reprogramming to a pluripotent state and is capable of increasing reprogramming efficiency.

Identification of functional cooperative mutations of GNAO1 in human acute lymphoblastic leukemia

Leukemogenesis is characterized by chromosomal rearrangements with additional molecular disruptions, yet the cooperative mechanisms are still unclear. Using whole-exome sequencing of a pair of monozygotic twins who were discordant for childhood acute lymphoblastic leukemia (ALL) with ETV6-RUNX1 (E/R) gene fusion successively after birth, we identified the R209C mutation of G protein subunit α o1 (GNAO1) as a new ALL risk loci. Moreover, GNAO1 missense mutations are recurrent in ALL patients and are associated with E/R fusion. Ectopic expression of the GNAO1 R209C mutant increased its GTPase activity and promoted cell proliferation and cell neoplastic transformation. Combined with the E/R fusion, the GNAO1 R209C mutation promoted leukemogenesis through activating PI3K/Akt/mTOR signaling. Reciprocally, activated mTORC1 phosphorylated p300 acetyltransferase, which acetylated E/R and thereby enhanced the E/R transcriptional activity of GNAO1 R209C. Thus, our study provides clinical evidence of the functional cooperation of GNAO1 mutations and E/R fusion, suggesting GNAO1 as a therapeutic target in human leukemia.

Generation of three iPSC lines from different types of pediatric acute leukemia patients

Leukemia is the most common malignant tumor in childhood. The pathogenesis of leukemia is still unclear. Therefore, it is imperative to establish effective disease models. In our study, we reprogrammed different types of pediatric acute leukemia cells into iPSCs using CytoTune®Sendai virus. All generated iPSCs maintained pluripotency and spontaneous in vivo differentiation capacity.

Modeling leukemia with pediatric acute leukemia patient-derived iPSCs

OBJECTIVE

ediatric acute leukemia (AL) is the most common hematological malignancy in childhood. However, the limitation of clinical specimens hindered the progress of research. Therefore, new research platforms are urgently needed to establish and clarify the pathogenesis of pediatric AL, and it is necessary to try to find novel targeted therapies for the clinical use. Here, the induced pluripotent stem cells (iPSCs) derived from AL provide a reliable model for basic research.

METHODS

eukemia cells were sorted by flow cytometry and then reprogrammed into iPSCs by Sendai virus. Cell cycle assay was used to analyze cell proliferation.

RESULTS

iPS cell lines from T cell acute lymphoblastic leukemia (T-ALL) and acute myeloid leukemia (AML) cells were successfully established. The reprogramming efficiency of AML cells was much higher than that of ALL cells. Disease iPS cells switched off the expression of the disease marker genes at iPS and HPC stage. When different subtypes of AML-iPSCs were differentiated into hematopoietic progenitor cells, iPS derived from acute megakaryocytic leukemia was more readily differentiated into megakaryocyte-erythroid progenitors. Whereas, the differentiation of multipotent lymphoid progenitor (MLP) and granulocyte macrophage progenitor (GMP) were blocked. The iPS derived from acute monocyte leukemia (AMCL) also showed the differentiation of common myeloid progenitors (CMP), GMP and monocytes significantly increased but MLP differentiation was inhibited. The AML-iPSC could form teratomas and we could obverse three germ layers in vivo, indicating that the AML-iPSCs have full pluripotency. However, there were not enough blood cells in teratoma to identify the leukemia.

CONCLUSIONS

Our results provide a novel platform for AL research and critical insight into the difference of hematopoietic differentiation between ALL and AML.

Fas/FasL mediates NF-κBp65/PUMA-modulated hepatocytes apoptosis via autophagy to drive liver fibrosis

Fas/Fas ligand (FasL)-mediated cell apoptosis involves a variety of physiological and pathological processes including chronic hepatic diseases, and hepatocytes apoptosis contributes to the development of liver fibrosis following various causes. However, the mechanism of the Fas/FasL signaling and hepatocytes apoptosis in liver fibrogenesis remains unclear. The Fas/FasL signaling and hepatocytes apoptosis in liver samples from both human sections and mouse models were investigated. NF-κBp65 wild-type mice (p65^f/f), hepatocytes specific NF-κBp65 deletion mice (p65Δhepa), p53-upregulated modulator of apoptosis (PUMA) wild-type (PUMA-WT) and PUMA knockout (PUMA-KO) littermate models, and primary hepatic stellate cells (HSCs) were also used. The mechanism underlying Fas/FasL-regulated hepatocytes apoptosis to drive HSCs activation in fibrosis was further analyzed. We found Fas/FasL promoted PUMA-mediated hepatocytes apoptosis via regulating autophagy signaling and NF-κBp65 phosphorylation, while inhibition of autophagy or PUMA deficiency attenuated Fas/FasL-modulated hepatocytes apoptosis and liver fibrosis. Furthermore, NF-κBp65 in hepatocytes repressed PUMA-mediated hepatocytes apoptosis via regulating the Bcl-2 family, while NF-κBp65 deficiency in hepatocytes promoted PUMA-mediated hepatocytes apoptosis and enhanced apoptosis-linked inflammatory response, which contributed to the activation of HSCs and liver fibrogenesis. These results suggest that Fas/FasL contributes to NF-κBp65/PUMA-modulated hepatocytes apoptosis via autophagy to enhance liver fibrogenesis, and this network could be a potential therapeutic target for liver fibrosis.

Design and linkage optimization of ursane-thalidomide-based PROTACs and identification of their targeted-degradation properties to MDM2 protein

Ursolic acid (UA) is an accessible triterpenoid, widely applied in the design and synthesis of antitumor compounds. However, the mechanism of its anti-tumor effect is still unclear. To verify the molecular mechanism of its biological activity, based on the bifunctional activity of ubiquitination and subsequent proteasomal degradation of the target protein of the proteolysis-targeting chimeras (PROTACs) strategy, here we report the design, synthesis and cellular activity of six UA PROTAC hydrochloride compounds 1A-1F, in which UA acts as the binding ligand of the PROTAC and is linked to thalidomide (E3 ligand) through a series of synthetic linkers. The results revealed that compound 1B, connected with a POE-3 (3-Polyoxyether) possessed remarkable in vitro antitumor activity (with the IC₅₀ value of 0.23 ~ 0.39 μM against A549, Huh7, HepG2). WB results demonstrated that the administration of compound 1B induced significant degradation of MDM2 (only 25% to that of SM1), and promoted the expression of P21 and PUMA proteins, and thus inhibited the proliferation (77.67% of 1B vs 60.37% of CON in G1 phase) and promoted the apoptosis (26.74% of 1B vs 3.35% of CON) of A549 cells. This work demonstrated proof of designing the efficient target protein degradation by UA PROTACs with the POE linkers. In addition, we confirmed that UA possess the characteristic of targeted-binding the protein of murine double minute-2 protein (MDM2). This will lay a foundation for the comprehensive utilization of forest natural compound UA.

PUMA facilitates EMI1-promoted cytoplasmic Rad51 ubiquitination and inhibits DNA repair in stem and progenitor cells

Maintenance of genetic stability via proper DNA repair in stem and progenitor cells is essential for the tissue repair and regeneration, while preventing cell transformation after damage. Loss of PUMA dramatically increases the survival of mice after exposure to a lethal dose of ionizing radiation (IR), while without promoting tumorigenesis in the long-term survivors. This finding suggests that PUMA (p53 upregulated modulator of apoptosis) may have a function other than regulates apoptosis. Here, we identify a novel role of PUMA in regulation of DNA repair in embryonic or induced pluripotent stem cells (PSCs) and immortalized hematopoietic progenitor cells (HPCs) after IR. We found that PUMA-deficient PSCs and HPCs exhibited a significant higher double-strand break (DSB) DNA repair activity via Rad51-mediated homologous recombination (HR). This is because PUMA can be associated with early mitotic inhibitor 1 (EMI1) and Rad51 in the cytoplasm to facilitate EMI1-mediated cytoplasmic Rad51 ubiquitination and degradation, thereby inhibiting Rad51 nuclear translocation and HR DNA repair. Our data demonstrate that PUMA acts as a repressor for DSB DNA repair and thus offers a new rationale for therapeutic targeting of PUMA in regenerative cells in the context of DNA damage.

PRPS1-mediated purine biosynthesis is critical for pluripotent stem cell survival and stemness

Pluripotent stem cells (PSCs) have a unique energetic and biosynthetic metabolism compared with typically differentiated cells. However, the metabolism profiling of PSCs and its underlying mechanism are still unclear. Here, we report PSCs metabolism profiling and identify the purine synthesis enzymes, phosphoribosyl pyrophosphate synthetase 1/2 (PRPS1/2), are critical for PSCs stemness and survival. Ultra-high performance liquid chromatography/mass spectroscopy (UHPLC-MS) analysis revealed that purine synthesis intermediate metabolite levels in PSCs are higher than that in somatic cells. Ectopic expression of PRPS1/2 did not improve purine biosynthesis, drug resistance, or stemness in PSCs. However, knockout of PRPS1 caused PSCs DNA damage and apoptosis. Depletion of PRPS2 attenuated PSCs stemness and assisted PSCs differentiation. Our finding demonstrates that PRPS1/2-mediated purine biosynthesis is critical for pluripotent stem cell stemness and survival.

Cancer Stemness: p53 at the Wheel

The tumor suppressor p53 maintains an equilibrium between self-renewal and differentiation to sustain a limited repertoire of stem cells for proper development and maintenance of tissue homeostasis. Inactivation of p53 disrupts this balance and promotes pluripotency and somatic cell reprogramming. A few reports in recent years have indicated that prevalent TP53 oncogenic gain-of-function (GOF) mutations further boosts the stemness properties of cancer cells. In this review, we discuss the role of wild type p53 in regulating pluripotency of normal stem cells and various mechanisms that control the balance between self-renewal and differentiation in embryonic and adult stem cells. We also highlight how inactivating and GOF mutations in p53 stimulate stemness in cancer cells. Further, we have explored the various mechanisms of mutant p53-driven cancer stemness, particularly emphasizing on the non-coding RNA mediated epigenetic regulation. We have also analyzed the association of cancer stemness with other crucial gain-of-function properties of mutant p53 such as epithelial to mesenchymal transition phenotypes and chemoresistance to understand how activation of one affects the other. Given the critical role of cancer stem-like cells in tumor maintenance, cancer progression, and therapy resistance of mutant p53 tumors, targeting them might improve therapeutic efficacy in human cancers with TP53 mutations.

The function of a heterozygous p53 mutation in a Li-Fraumeni syndrome patient

p53 is one of the most extensively studied proteins in cancer research. Mutations in p53 generally abolish normal p53 function, and some mutants can gain new oncogenic functions. However, the mechanisms underlying p53 mutation-driven cancer remains to be elucidated. Our study investigated the function of a heterozygous p53 mutation (p.Asn268Glufs*4) in a Li-Fraumeni syndrome (LFS) patient. We used episomal technology to perform somatic reprogramming, and used molecular and cell biology methods to determine the p53 mutation levels in patient-originated induced pluripotent stem (iPS) cells at the RNA and protein levels. We found that p53 protein expression was not increased in this patient’s somatic cells compared with those of a healthy control. p53 mutation facilitates the proliferation of tumor cells by inhibiting apoptosis and promoting cell division. It can inhibit the efficiency of somatic reprogramming by inhibiting OCT4 expression during reprogramming stage. Moreover, not all p53 mutant iPS cell lines have mutant p53 RNA sequences. A small percentage of mutant p53 mRNA is present in the somatic cells from the patient and his mother. In summary, this p53 mutation can promote tumor cell proliferation, inhibit somatic reprogramming, and exhibit random p53 allelic expression of heterozygous mutations in the patient and iPS cells which may be one of the reasons why the people with p53 mutations develop cancer at random. This finding suggested that mutant p53 allelic expression should be added to the risk forecasting of cancer.

Cell fate, metabolic reprogramming and lncRNA of tumor-initiating stem-like cells induced by alcohol

Alcoholism synergizes the development of the hepatocellular carcinoma (HCC) in patients infected with hepatitis B or C virus (HBV or HCV). Tumor-initiating stem-like cells (TICs) are refractory to therapy and have expression of stemness transcription factors. Leaky-gut-derived endotoxin stimulates TLR4-NANOG pathway that skews asymmetric cell division and that metabolically reprograms hepatocytes/liver progenitor cells, leading to self-renewal. TICs isolated from mouse HCC models or human HCCs are tumorigenic and have p53 degradation via phosphorylation of the protective protein NUMB and its dissociation from p53 by the oncofetal protein TBC1D15. Furthermore, dysregulation of lncRNA promotes genesis of TICs, leading to HCC development. This review describes roles of cell fate decision, metabolic reprogramming and lncRNA for TIC genesis and liver oncogenesis. This project was supported by NIH grants 1R01AA018857-01, 5R21AA025470, P50AA11999 (Animal Core, Morphology Core, and Pilot Project Program), R24AA012885 (Non-Parenchymal Liver Cell Core) and pilot project funding (5P30DK048522-13).

A connection in life and death: The BCL-2 family coordinates mitochondrial network dynamics and stem cell fate

The B cell CLL/lymphoma-2 (BCL-2) family of proteins control the mitochondrial pathway of apoptosis, also known as intrinsic apoptosis. Direct binding between members of the BCL-2 family regulates mitochondrial outer membrane permeabilization (MOMP) after an apoptotic insult. The ability of the cell to sense stress and translate it into a death signal has been a major theme of research for nearly three decades; however, other mechanisms by which the BCL-2 family coordinates cellular homeostasis beyond its role in initiating apoptosis are emerging. One developing area of research is understanding how the BCL-2 family of proteins regulate development using pluripotent stem cells as a model system. Understanding BCL-2 family-mediated regulation of mitochondrial homeostasis in cell death and beyond would uncover new facets of stem cell maintenance and differentiation potential.

Targeting of apoptosis gene loci by reprogramming factors leads to selective eradication of leukemia cells

Applying somatic cell reprogramming strategies in cancer cell biology is a powerful approach to analyze mechanisms of malignancy and develop new therapeutics. Here, we test whether leukemia cells can be reprogrammed in vivo using the canonical reprogramming transcription factors-Oct4, Sox2, Klf4, and c-Myc (termed as OSKM). Unexpectedly, we discover that OSKM can eradicate leukemia cells and dramatically improve survival of leukemia-bearing mice. By contrast, OSKM minimally impact normal hematopoietic cells. Using ATAC-seq, we find OSKM induce chromatin accessibility near genes encoding apoptotic regulators in leukemia cells. Moreover, this selective effect also involves downregulation of H3K9me3 as an early event. Dissection of the functional effects of OSKM shows that Klf4 and Sox2 play dominant roles compared to c-Myc and Oct4 in elimination of leukemia cells. These results reveal an intriguing paradigm by which OSKM-initiated reprogramming induction can be leveraged and diverged to develop novel anti-cancer strategies.

Episomal Induced Pluripotent Stem Cells: Functional and Potential Therapeutic Applications

The term episomal induced pluripotent stem cells (EiPSCs) refers to somatic cells that are reprogrammed into induced pluripotent stem cells (iPSCs) using non-integrative episomal vector methods. This reprogramming process has a better safety profile compared with integrative methods using viruses. There is a current trend toward using episomal plasmid reprogramming to generate iPSCs because of the improved safety profile. Clinical reports of potential human cell sources that have been successfully reprogrammed into EiPSCs are increasing, but no review or summary has been published. The functional applications of EiPSCs and their potential uses in various conditions have been described, and these may be applicable to clinical scenarios. This review summarizes the current direction of EiPSC research and the properties of these cells with the aim of explaining their potential role in clinical applications and functional restoration.

Zinc-finger protein p52-ZER6 accelerates colorectal cancer cell proliferation and tumour progression through promoting p53 ubiquitination

Background

Aberrant expression of p53 and its downstream gene p21 is closely related to alterations in cell cycle and cell proliferation, and is common among cancer patients. However, the underlying molecular mechanism has not been fully unravelled. ZER6 is a zinc-finger protein with two isoforms possessing different amino termini (N-termini) in their proteins, p52-ZER6 and p71-ZER6. The biological function of ZER6 isoforms, as well as their potential involvement in tumourigenesis and the regulation of p53 remain elusive.

Methods

The effect of ZER6 isoforms on p53 and p21 was determined using specific knockdown and overexpression. p52-ZER6 expression in tumours was analysed using clinical specimens, while gene modulation was used to explore p52-ZER6 roles in regulating cell proliferation and tumourigenesis. The mechanism of p52-ZER6 regulation on the p53/p21 axis was studied using molecular biology and biochemical methods.

Findings

p52-ZER6 was highly expressed in tumour tissues, and was closely related with tumour progression. Mechanistically, p52-ZER6 bound to p53 through a truncated KRAB (tKRAB) domain in its N-terminus and enhanced MDM2/p53 complex integrity, leading to increased p53 ubiquitination and degradation. p52-ZER6-silencing induced G₀-G₁ phase arrest, and subsequently reduced cell proliferation and tumourigenesis. Intriguingly, this regulation on p53 was specific to p52-ZER6, whereas p71-ZER6 did not affect p53 stability, most likely due to the presence of a HUB-1 domain.

Interpretation

We identified p52-ZER6 as a novel oncogene that enhances MDM2/p53 complex integrity, and might be a potential target for anti-cancer therapy.

Induced pluripotent stem cell generation from bovine somatic cells indicates unmet needs for pluripotency sustenance

Mechanisms that direct reprogramming of differentiated somatic cells to induced pluripotent stem cells (iPSCs), albeit incomplete in understanding, are highly conserved across all mammalian species studied. Equally, proof of principle that iPSCs can be derived from domestic cattle has been reported in several publications. In our efforts to derive and study bovine iPSCs, we encountered inadequacy of methods to generate, sustain, and characterize these cells. Our results suggest that iPSC protocols optimized for mouse and human somatic cells do not effectively translate to bovine somatic cells, which show some refractoriness to reprogramming that also affects sustenance. Moreover, methods that enhance reprogramming efficiency in mouse and human cells had no effect on improving bovine cell reprogramming. Although use of retroviral vectors coding for bovine OCT4, SOX2, KLF4, cMYC, and NANOG appeared to produce consistent iPSC-like cells from both fibroblasts and cells from the Wharton's jelly, these colonies could not be sustained. Use of bovine genes could successfully reprogram both mouse and human cells. These findings indicated either incomplete reprogramming and/or discordant/inadequate culture conditions for bovine pluripotent stem cells. Therefore, additional studies that advance core knowledge of bovine pluripotency are necessary before any anticipated iPSC-driven bovine technologies can be realized.

NANOG-Dependent Metabolic Reprogramming and Symmetric Division in Tumor-Initiating Stem-like Cells

Alcohol abuse synergistically heightens the development of the third most deadliest cancer hepatocellular carcinoma (HCC) in patients infected with hepatitis C virus (HCV). Ectopically expressed TLR4 promotes liver tumorigenesis in alcohol-fed HCV Ns5a or Core transgenic mice. CD133+/CD49f + tumor-initiating stem cell-like cells (TICs) isolated from these models are tumorigenic have p53 degradation via phosphorylation of the protective protein NUMB and its dissociation from p53 by the oncoprotein TBC1D15. Nutrient deprivation reduces overexpressed TBC1D15 in TICs via autophagy-mediated degradation, suggesting a possible role of this oncoprotein in linking metabolic reprogramming and self-renewal.

Remodeling of mitochondrial morphology and function: an emerging hallmark of cellular reprogramming

Research in the stem cell field has traditionally focused on understanding key transcriptional factors that provide pluripotent cell identity. However, much less is known about other critical non-transcriptional signaling networks that govern stem cell identity. Although we continue to gain critical insights into the mechanisms underlying mitochondrial morphology and function during cellular reprogramming – the process of reverting the fate of a differentiated cell into a stem cell, many uncertainties remain. Recent studies suggest an emerging landscape in which mitochondrial morphology and function have an active role in maintaining and regulating changes in cell identity. In this review, we will focus on these emerging concepts as crucial modulators of cellular reprogramming. Recognition of the widespread applicability of these concepts will increase our understanding of the mitochondrial mechanisms involved in cell identity, cell fate and disease.

Cell Reprogramming in Tumorigenesis and Its Therapeutic Implications for Breast Cancer

Breast cancer is the most common malignancy in women worldwide and can be categorized into several subtypes according to histopathological parameters or genomic signatures. Such heterogeneity of breast cancer can arise from the reactivation of mammary stem cells in situ during tumorigenesis. Moreover, different breast cancer subtypes exhibit varieties of cancer incidence, therapeutic response, and patient prognosis, suggesting that a specific therapeutic protocol is required for each breast cancer subtype. Recent studies using molecular and cellular assays identified a link between specific genetic/epigenetic alterations and distinct cells of origin of breast cancer subtypes. These alterations include oncogenes, tumor suppressor genes, and cell-lineage determinants, which can induce cell reprogramming (dedifferentiation and transdifferentiation) among two lineage-committed mammary epithelial cells, namely basal and luminal cells. The interconversion of cell states through cell reprogramming into the intermediates of mammary stem cells can give rise to heterogeneous breast cancers that complicate effective therapies of breast cancer. A better understanding of mechanisms underlying cell reprogramming in breast cancer can help in not only elucidating tumorigenesis but also developing therapeutics for breast cancer. This review introduces recent findings on cancer gene-mediated cell reprogramming in breast cancer and discusses the therapeutic potential of targeting cell reprogramming.

Absence of cyclin-dependent kinase inhibitor p27 or p18 increases efficiency of iPSC generation without induction of iPSC genomic instability

Mechanisms underlying the generation of induced pluripotent stem cells (iPSC) and keeping iPSC stability remain to be further defined. Accumulated evidences showed that iPSC reprogramming may be controlled by the cell-division-rate-dependent model. Here we reported effects of absence of mouse p27 or p18 on iPSC generation efficiency and genomic stability. Expression levels of cyclin-dependent kinases inhibitors (CDKIs), p21, p27, and p18 decreased during iPSC reprogramming. Like p21 loss, p27 or p18 deficiency significantly promoted efficiency of iPSC generation, whereas ectopic expression of p27, p18, or treatment with CDK2 or CDK4 inhibitors repressed the reprogramming rate, suggesting that CDKIs-regulated iPSC reprogramming is directly related with their functions as CDK inhibitors. However, unlike p21 deletion, absence of p27 or p18 did not increase DNA damage or chromosomal aberrations during iPSC reprogramming and at iPSC stage. Our data not only support that cell cycle regulation is critical for iPSC reprogramming, but also reveal the distinction of CDKIs in somatic cell reprogramming.

A Novel Small Molecule p53 Stabilizer for Brain Cell Differentiation

Brain tumor, as any type of cancer, is assumed to be sustained by a small subpopulation of stem-like cells with distinctive properties that allow them to survive conventional therapies and drive tumor recurrence. Thus, the identification of new molecules capable of controlling stemness properties may be key in developing effective therapeutic strategies for cancer by inducing stem-like cells differentiation. Spiropyrazoline oxindoles have previously been shown to induce apoptosis and cell cycle arrest, as well as upregulate p53 steady-state levels, while decreasing its main inhibitor MDM2 in the HCT116 human colorectal carcinoma cell line. In this study, we made modifications in this scaffold by including combinations of different substituents in the pyrazoline ring in order to obtain novel small molecules that could modulate p53 activity and act as differentiation inducer agents. The antiproliferative activity of the synthesized compounds was assessed using the isogenic pair of HCT116 cell lines differing in the presence or absence of the p53 gene. Among the tested spirooxindoles, spiropyrazoline oxindole 1a was selective against the cancer cell line expressing wild-type p53 and presented low cytotoxicity. This small molecule induced neural stem cell (NSC) differentiation through reduced SOX2 (marker of multipotency) and increased βIII-tubulin (marker of neural differentiation) which suggests a great potential as a non-toxic inducer of cell differentiation. More importantly, in glioma cancer cells (GL-261), compound 1a reduced stemness, by decreasing SOX2 protein levels, while also promoting chemotherapy sensitization. These results highlight the potential of p53 modulators for brain cell differentiation, with spirooxindole 1a representing a promising lead molecule for the development of new brain antitumor drugs.

Receptor interacting protein kinase 3 (RIP3) regulates iPSCs generation through modulating cell cycle progression genes

The molecular mechanisms involved in induced pluripotent stem cells (iPSCs) generation are poorly understood. The cell death machinery of apoptosis-inducing caspases have been shown to facilitate the process of iPSCs reprogramming. However, the effect of other cell death processes, such as programmed necrosis (necroptosis), on iPSCs induction has not been studied. In this study, we investigated the role of receptor-interacting protein kinase 3 (RIP3), an essential regulator of necroptosis, in reprogramming mouse embryonic fibroblast cells (MEFs) into iPSCs. RIP3 was found to be upregulated in iPSCs compared to MEFs. Deletion of RIP3 dramatically suppressed the reprogramming of iPSCs (~82%). RNA-seq analysis and qRT-PCR showed that RIP3 KO MEFs expressed lower levels of genes that control cell cycle progression and cell division and higher levels of extracellular matrix-regulating genes. The growth rate of RIP3 KO MEFs was significantly slower than WT MEFs. These findings can partially explain the inhibitory effects of RIP3 deletion on iPSCs generation and show for the first time that the necroptosis kinase RIP3 plays an important role in iPSC reprogramming. In contrast to RIP3, the kinase and scaffolding functions of RIPK1 appeared to have distinct effects on reprogramming.

Optimizing the method for generation of integration-free induced pluripotent stem cells from human peripheral blood

Background

Generation of induced pluripotent stem cells (iPSCs) from human peripheral blood provides a convenient and low-invasive way to obtain patient-specific iPSCs. The episomal vector is one of the best approaches for reprogramming somatic cells to pluripotent status because of its simplicity and affordability. However, the efficiency of episomal vector reprogramming of adult peripheral blood cells is relatively low compared with cord blood and bone marrow cells.

Methods

In the present study, integration-free human iPSCs derived from peripheral blood were established via episomal technology. We optimized mononuclear cell isolation and cultivation, episomal vector promoters, and a combination of transcriptional factors to improve reprogramming efficiency.

Results

Here, we improved the generation efficiency of integration-free iPSCs from human peripheral blood mononuclear cells by optimizing the method of isolating mononuclear cells from peripheral blood, by modifying the integration of culture medium, and by adjusting the duration of culture time and the combination of different episomal vectors.

Conclusions

With this optimized protocol, a valuable asset for banking patient-specific iPSCs has been established.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0908-z) contains supplementary material, which is available to authorized users.

Cellular Pliancy and the Multistep Process of Tumorigenesis

Completion of early stages of tumorigenesis relies on the dynamic interplay between the initiating oncogenic event and the cellular context. Here, we review recent findings indicating that each differentiation stage within a defined cellular lineage is associated with a unique susceptibility to malignant transformation when subjected to a specific oncogenic insult. This emerging notion, named cellular pliancy, provides a rationale for the short delay in the development of pediatric cancers of prenatal origin. It also highlights the critical role of cellular reprogramming in early steps of malignant transformation of adult differentiated cells and its impact on the natural history of tumorigenesis.

BAK/BAX-Mediated Apoptosis Is a Myc-Induced Roadblock to Reprogramming

Despite intensive efforts to optimize the process, reprogramming differentiated cells to induced pluripotent stem cells (iPSCs) remains inefficient. The most common combination of transcription factors employed comprises OCT4, KLF4, SOX2, and MYC (OKSM). If MYC is omitted (OKS), reprogramming efficiency is reduced further. Cells must overcome several obstacles to reach the pluripotent state, one of which is apoptosis. To directly determine how extensively apoptosis limits reprogramming, we exploited mouse embryonic fibroblasts (MEFs) lacking the two essential mediators of apoptosis, BAK and BAX. Our results show that reprogramming is enhanced in MEFs deficient in BAK and BAX, but only when MYC is part of the reprogramming cocktail. Thus, the propensity for Myc overexpression to elicit apoptosis creates a significant roadblock to reprogramming under OKSM conditions. Our results suggest that blocking apoptosis during reprogramming may enhance the derivation of iPSCs for research and therapeutic purposes.

Identification of XBP1-u as a novel regulator of the MDM2/p53 axis using an shRNA library

Cell cycle progression is a tightly controlled fundamental process in living cells, with any defects being closely linked to various abnormalities. The tumor suppressor p53/p21 axis is a core pathway controlling cell cycle progression; however, its regulatory mechanism has not been fully elucidated. In an effort to unravel this crucial network, we screened a short hairpin RNA expression vector library and identified unspliced X-box binding protein 1 (XBP1-u) as a novel and critical regulator of the p53/p21 axis. Specifically, XBP1-u negatively regulates the p53/p21 axis by enhancing p53 ubiquitination, which in turn down-regulates p21 expression. We show that XBP1-u suppression induces G₀-G₁ phase arrest and represses cell proliferation. We further report that the carboxyl terminus of XBP1-u, which differs from that of its spliced form (XBP1-s) due to a codon shift, binds and stabilizes mouse double minute homolog 2 (MDM2) protein, a negative regulator of p53, by inhibiting its self-ubiquitination. Concomitantly, XBP-u overexpression enhances tumorigenesis by positively regulating MDM2. Together, our findings suggest that XBP1-u functions far beyond being merely a precursor of XBP1-s and, instead, is involved in fundamental biological processes. Furthermore, this study provides new insights regarding the regulation of the MDM2/p53/p21 axis.

Transcription factor Yin Yang 2 is a novel regulator of the p53/p21 axis

Yin Yang 2 (YY2) is a multifunctional zinc-finger transcription factor that belongs to YY family. Unlike the well-characterized YY1, our understanding regarding the biological functions of YY2 is still very limited. Here we found for the first time that in contrast to YY1, which had been reported to be oncogenic, the expression level of YY2 in tumor cells and/or tissues was downregulated compared with its expression level in the normal ones. We also demonstrated that YY2 exerts biological function contrary to YY1 in cell proliferation. We elucidated that YY2 positively enhances p21 expression, and concomitantly, its silencing promotes cells to enter G2/M phase and enhances cell proliferation. Furthermore, we found that YY2 regulation on p21 occurs p53-dependently. Finally, we identified a novel YY2 binding site in the promoter region of tumor suppressor p53. We found that YY2 binds to the p53 promoter and activates its transcriptional activity, and subsequently, regulates cell cycle progression via p53/p21 axis. Taken together, our study not only identifies YY2 as a novel tumor suppressor gene that plays a pivotal role in cell cycle regulation, but also provides new insights regarding the regulatory mechanism of the conventional p53/p21 axis.

Transdifferentiation and reprogramming: Overview of the processes, their similarities and differences

Reprogramming, or generation of induced pluripotent stem (iPS) cells (functionally similar to embryonic stem cells or ES cells) by the use of transcription factors (typically: Oct3/4, Sox2, c-Myc, Klf4) called "Yamanaka factors" (OSKM), has revolutionized regenerative medicine. However, factors used to induce stemness are also overexpressed in cancer. Both, ES cells and iPS cells cause teratoma formation when injected to tissues. This raises a safety concern for therapies based on iPS derivates. Transdifferentiation (lineage reprogramming, or -conversion), is a process in which one mature, specialized cell type changes into another without entering a pluripotent state. This process involves an ectopic expression of transcription factors and/or other stimuli. Unlike in the case of reprogramming, tissues obtained by this method do not carry the risk of subsequent teratomagenesis.

Generation of Integration-free Induced Pluripotent Stem Cells from Human Peripheral Blood Mononuclear Cells Using Episomal Vectors

Induced Pluripotent Stem Cells (iPSCs) hold great promise for disease modeling and regenerative therapies. We previously reported the use of Episomal Vectors (EV) to generate integration-free iPSCs from peripheral blood mononuclear cells (PB MNCs). The episomal vectors used are DNA plasmids incorporated with oriP and EBNA1 elements from the Epstein-Barr (EB) virus, which allow for replication and long-term retainment of plasmids in mammalian cells, respectively. With further optimization, thousands of iPSC colonies can be obtained from 1 mL of peripheral blood. Two critical factors for achieving high reprogramming efficiencies are: 1) the use of a 2A "self-cleavage" peptide to link OCT4 and SOX2, thus achieving equimolar expression of the two factors; 2) the use of two vectors to express MYC and KLF4 individually. Here we describe a step-by-step protocol for generating integration-free iPSCs from adult peripheral blood samples. The generated iPSCs are integration-free as residual episomal plasmids are undetectable after five passages. Although the reprogramming efficiency is comparable to that of Sendai Virus (SV) vectors, EV plasmids are considerably more economical than the commercially available SV vectors. This affordable EV reprogramming system holds potential for clinical applications in regenerative medicine and provides an approach for the direct reprogramming of PB MNCs to integration-free mesenchymal stem cells, neural stem cells, etc.

Integrating Gene Correction in the Reprogramming and Transdifferentiation Processes: A One-Step Strategy to Overcome Stem Cell-Based Gene Therapy Limitations

The recent advent of induced pluripotent stem cells (iPSCs) and gene therapy tools has raised the possibility of autologous cell therapy for rare genetic diseases. However, cellular reprogramming is inefficient in certain diseases such as ataxia telangiectasia, Fanconi anemia, LIG4 syndrome, and fibrodysplasia ossificans progressiva syndrome, owing to interference of the disease-related genes. To overcome these therapeutic limitations, it is necessary to fundamentally correct the abnormal gene during or prior to the reprogramming process. In addition, as genetic etiology of Parkinson's disease, it has been well known that induced neural stem cells (iNSCs) were progressively depleted by LRRK2 gene mutation, LRRK2 (G2019S). Thus, to maintain the induced NSCs directly derived from PD patient cells harboring LRRK2 (G2019S), it would be ideal to simultaneously treat the LRRK2 (G2019S) fibroblast during the process of TD. Therefore, simultaneous reprogramming (or TD) and gene therapy would provide the solution for therapeutic limitation caused by vulnerability of reprogramming or TD, in addition to being suitable for general application to the generation of autologous cell-therapy products for patients with genetic defects, thereby obviating the need for the arduous processes currently required.

PUMA mediates the combinational therapy of 5-FU and NVP-BEZ235 in colon cancer

Colon cancer is the third most common cancer in humans which has a high mortality rate, and 5-Fluorouracil (5-FU) is one of the most widely used drugs in colon cancer therapy. However, acquired chemoresistance is becoming the major challenges for patients, and the molecular mechanism underlying the development of 5-FU resistance is still poorly understood. In this study, a newly designed therapy in combination with 5-FU and NVP-BEZ235 in colon cancer cells (HCT-116 and RKO) was established, to investigate the mechanism of 5-FU resistance and optimize drug therapy to improve outcome for patients. Our results show 5-FU induced cell apoptosis through p53/PUMA pathway, with aberrant Akt activation, which may well explain the mechanism of 5-FU resistance. NVP-BEZ235 effectively up-regulated PUMA expression, mainly through inactivation of PI3K/Akt and activation of FOXO3a, leading to cell apoptosis even in the p53^−/− HCT-116 cells. Combination treatment of 5-FU and NVP-BEZ235 further increased cell apoptosis in a PUMA/Bax dependent manner. Moreover, significantly enhanced anti-tumor effects were observed in combination treatment in vivo. Together, these results demonstrated that the combination treatment of 5-FU and NVP-BEZ235 caused PUMA-dependent tumor suppression both in vitro and in vivo, which may promise a more effective strategy for colon cancer therapy.

Concise Review: Pluripotent Stem Cell-Derived Cardiac Cells, A Promising Cell Source for Therapy of Heart Failure: Where Do We Stand?

Heart failure is still a major cause of hospitalization and mortality in developed countries. Many clinical trials have tested the use of multipotent stem cells as a cardiac regenerative medicine. The benefit for the patients of this therapeutic intervention has remained limited. Herein, we review the pluripotent stem cells as a cell source for cardiac regeneration. We more specifically address the various challenges of this cell therapy approach. We question the cell delivery systems, the immune tolerance of allogenic cells, the potential proarrhythmic effects, various drug mediated interventions to facilitate cell grafting and, finally, we describe the pathological conditions that may benefit from such an innovative approach. As members of a transatlantic consortium of excellence of basic science researchers and clinicians, we propose some guidelines to be applied to cell types and modes of delivery in order to translate pluripotent stem cell cardiac derivatives into safe and effective clinical trials.

NUMB phosphorylation destabilizes p53 and promotes self-renewal of tumor-initiating cells by a NANOG-dependent mechanism in liver cancer

Stem cell populations are maintained through self-renewing divisions in which one daughter cell commits to a particular fate whereas the other retains the multipotent characteristics of its parent. The NUMB, a tumor suppressor, in conjunction with another tumor-suppressor protein, p53, preserves this property and acts as a barrier against deregulated expansion of tumor-associated stem cells. In this context, NUMB-p53 interaction plays a crucial role to maintain the proper homeostasis of both stem cells, as well as differentiated cells. Because the molecular mechanism governing the assembly and stability of the NUMB-p53 interaction/complex are poorly understood, we tried to identify the molecule(s) that govern this process. Using cancer cell lines, tumor-initiating cells (TICs) of liver, the mouse model, and clinical samples, we identified that phosphorylations of NUMB destabilize p53 and promote self-renewal of TICs in a pluripotency-associated transcription factor NANOG-dependent manner. NANOG phosphorylates NUMB by atypical protein kinase C zeta (aPKCζ), through the direct induction of Aurora A kinase (AURKA) and the repression of an aPKCζ inhibitor, lethal (2) giant larvae. By radioactivity-based kinase activity assays, we showed that NANOG enhances kinase activities of both AURKA and aPKCζ, an important upstream process for NUMB phosphorylation. Phosphorylation of NUMB by aPKCζ destabilizes the NUMB-p53 interaction and p53 proteolysis and deregulates self-renewal in TICs.

CONCLUSION

Post-translational modification of NUMB by the NANOG-AURKA-aPKCζ pathway is an important event in TIC self-renewal and tumorigenesis. Hence, the NANOG-NUMB-p53 signaling axis is an important regulatory pathway for TIC events in TIC self-renewal and liver tumorigenesis, suggesting a therapeutic strategy by targeting NUMB phosphorylation. Further in-depth in vivo and clinical studies are warranted to verify this suggestion.

Genome-editing tools for stem cell biology

Human pluripotent stem cells provide a versatile platform for regenerative studies, drug testing and disease modeling. That the expression of only four transcription factors, Oct4, Klf4, Sox2 and c-Myc (OKSM), is sufficient for generation of induced pluripotent stem cells (iPSCs) from differentiated somatic cells has revolutionized the field and also highlighted the importance of OKSM as targets for genome editing. A number of novel genome-editing systems have been developed recently. In this review, we focus on successful applications of several such systems for generation of iPSCs. In particular, we discuss genome-editing systems based on zinc-finger fusion proteins (ZFs), transcription activator-like effectors (TALEs) and an RNA-guided DNA-specific nuclease, Cas9, derived from the bacterial defense system against viruses that utilizes clustered regularly interspaced short palindromic repeats (CRISPR).

Netrin-1 regulates somatic cell reprogramming and pluripotency maintenance

The generation of induced pluripotent stem (iPS) cells holds great promise in regenerative medicine. The use of the transcription factors Oct4, Sox2, Klf4 and c-Myc for reprogramming is extensively documented, but comparatively little is known about soluble molecules promoting reprogramming. Here we identify the secreted cue Netrin-1 and its receptor DCC, described for their respective survival/death functions in normal and oncogenic contexts, as reprogramming modulators. In various somatic cells, we found that reprogramming is accompanied by a transient transcriptional repression of Netrin-1 mediated by an Mbd3/Mta1/Chd4-containing NuRD complex. Mechanistically, Netrin-1 imbalance induces apoptosis mediated by the receptor DCC in a p53-independent manner. Correction of the Netrin-1/DCC equilibrium constrains apoptosis and improves reprogramming efficiency. Our work also sheds light on Netrin-1's function in protecting embryonic stem cells from apoptosis mediated by its receptor UNC5b, and shows that the treatment with recombinant Netrin-1 improves the generation of mouse and human iPS cells.

Reprogramming holds great promise for regenerative medicine but the molecular mechanisms governing the generation of induced pluripotent stem cells remain unclear. Here, the authors reveal functions for the axonal guidance cue Netrin-1 in constraining apoptosis at the early stage of reprogramming and in established pluripotent cells.

Key points of basic theories and clinical practice in rAd-p53 ( Gendicine ™) gene therapy for solid malignant tumors

INTRODUCTION

Wild-type p53 gene is an essential cancer suppressor gene which plays an important role in carcinogenesis and malignant progressions. The p53 gene family participates in almost all the key procedures of cancer biology, such as programmed cell death, angiogenesis, metabolism and epithelial-mesenchymal transition. The mutation or functional defects of the p53 gene family are detected in most of the solid malignant tumors, and the restoration of the p53 gene by adenovirus-mediated gene therapy becomes a promising treatment for cancer patients now.

AREAS COVERED

In the present review, the potential therapeutic effects of recombinant adenovirus p53 rAd-p53 ( Gendicine ™) were reviewed to explore the biological mechanism underlying the adenovirus-mediated p53 gene therapy. Then, the key points of the drug administration were discussed, including the routes of administration, dosage calculation and treatment cycles, based on findings of the preclinical and clinical trials in order to establish a standard treatment for the p53 gene therapy.

EXPERT OPINION

As an important part of the combined therapy for the cancer patients, the adenovirus-mediated p53 gene therapy was blossomed to be a promising treatment strategy. A new evaluation criteria and guideline for the gene therapy is urgently needed for the further clinical practice.

Cancer: pathological nuclear reprogramming?

The ability of stem cells to self-renew and generate different lineages during development and organogenesis is a fundamental, tightly controlled, and generally unidirectional process, whereas the 'immortality' of cancer cells could be regarded as pathological self-renewal. The molecular mechanisms that underpin the generation of induced pluripotent stem cells are remarkably similar to those that are deregulated in cancer - so much so that aberrant reprogramming is tumorigenic. The similarities also suggest that mutations in genes implicated in DNA methylation dynamics might represent a hallmark of cancers with a stem cell origin, and they highlight an alternative view of cancer that may be of clinical benefit.

Cell reprogramming. Histone chaperone ASF1A is required for maintenance of pluripotency and cellular reprogramming

Unfertilized oocytes have the intrinsic capacity to remodel sperm and the nuclei of somatic cells. The discoveries that cells can change their phenotype from differentiated to embryonic state using oocytes or specific transcription factors have been recognized as two major breakthroughs in the biomedical field. Here, we show that ASF1A, a histone-remodeling chaperone specifically enriched in the metaphase II human oocyte, is necessary for reprogramming of human adult dermal fibroblasts (hADFs) into undifferentiated induced pluripotent stem cell. We also show that overexpression of just ASF1A and OCT4 in hADFs exposed to the oocyte-specific paracrine growth factor GDF9 can reprogram hADFs into pluripotent cells. Our Report underscores the importance of studying the unfertilized MII oocyte as a means to understand the molecular pathways governing somatic cell reprogramming.

Notch inhibition allows oncogene-independent generation of iPS cells

The reprogramming of somatic cells to pluripotency using defined transcription factors holds great promise for biomedicine. However, human reprogramming remains inefficient and relies either on the use of the potentially dangerous oncogenes KLF4 and CMYC or the genetic inhibition of the tumor suppressor gene p53. We hypothesized that inhibition of signal transduction pathways that promote differentiation of the target somatic cells during development might relieve the requirement for non-core pluripotency factors during iPSC reprogramming. Here, we show that inhibition of Notch significantly improves the efficiency of iPSC generation from mouse and human keratinocytes by suppressing p21 in a p53-independent manner and thereby enriching for undifferentiated cells capable of long-term self-renewal. Pharmacological inhibition of Notch enabled routine production of human iPSCs without KLF4 and CMYC while leaving p53 activity intact. Thus, restricting the development of somatic cells by altering intercellular communication enables the production of safer human iPSCs.

p53: the barrier to cancer stem cell formation

The role of p53 as the "guardian of the genome" in differentiated somatic cells, triggering various biological processes, is well established. Recent studies in the stem cell field have highlighted a profound role of p53 in stem cell biology as well. These studies, combined with basic data obtained 20 years ago, provide insight into how p53 governs the quantity and quality of various stem cells, ensuring a sufficient repertoire of normal stem cells to enable proper development, tissue regeneration and a cancer free life. In this review we address the role of p53 in genomically stable embryonic stem cells, a unique predisposed cancer stem cell model and adult stem cells, its role in the generation of induced pluripotent stem cells, as well as its role as the barrier to cancer stem cell formation.

Induced multipotency in adult keratinocytes through down-regulation of ΔNp63 or DGCR8

The roles of microRNAs (miRNAs) and the miRNA processing machinery in the regulation of stem cell biology are not well understood. Here, we show that the p53 family member and p63 isoform, ΔNp63, is a transcriptional activator of a cofactor critical for miRNA processing (DGCR8). This regulation gives rise to a unique miRNA signature resulting in reprogramming cells to multipotency. Strikingly, ΔNp63(-/-) epidermal cells display profound defects in terminal differentiation and express a subset of markers and miRNAs present in embryonic stem cells and fibroblasts induced to pluripotency using Yamanaka factors. Moreover, ΔNp63(-/-) epidermal cells transduced with an inducible DGCR8 plasmid can differentiate into multiple cell fates in vitro and in vivo. We found that human primary keratinocytes depleted of ΔNp63 or DGCR8 can be reprogrammed in 6 d and express a unique miRNA and gene expression signature that is similar but not identical to human induced pluripotent stem cells. Our data reveal a role for ΔNp63 in the transcriptional regulation of DGCR8 to reprogram adult somatic cells into multipotent stem cells.

Cellular reprogramming of human peripheral blood cells

Breakthroughs in cell fate conversion have made it possible to generate large quantities of patient-specific cells for regenerative medicine. Due to multiple advantages of peripheral blood cells over fibroblasts from skin biopsy, the use of blood mononuclear cells (MNCs) instead of skin fibroblasts will expedite reprogramming research and broaden the application of reprogramming technology. This review discusses current progress and challenges of generating induced pluripotent stem cells (iPSCs) from peripheral blood MNCs and of in vitro and in vivo conversion of blood cells into cells of therapeutic value, such as mesenchymal stem cells, neural cells and hepatocytes. An optimized design of lentiviral vectors is necessary to achieve high reprogramming efficiency of peripheral blood cells. More recently, non-integrating vectors such as Sendai virus and episomal vectors have been successfully employed in generating integration-free iPSCs and somatic stem cells.