Recombinant, refolded tetrameric p53 and gonadotropin-releasing hormone-p53 slow proliferation and induce apoptosis in p53-deficient cancer cells

Molecular basis for SOX2-dependent regulation of super-enhancer activity

Pioneer transcription factors (TFs) like SOX2 are vital for stemness and cancer through enhancing gene expression within transcriptional condensates formed with coactivators, RNAs and mediators on super-enhancers (SEs). Despite their importance, how these factors work together for transcriptional condensation and activation remains unclear. SOX2, a pioneer TF found in SEs of pluripotent and cancer stem cells, initiates SE-mediated transcription by binding to nucleosomes, though the mechanism isn't fully understood. To address SOX2's role in SEs, we identified mSE078 as a model SOX2-enriched SE and p300 as a coactivator through bioinformatic analysis. In vitro and cell assays showed SOX2 forms condensates with p300 and SOX2-binding motifs in mSE078. We further proved that SOX2 condensation is highly correlated with mSE078's enhancer activity in cells. Moreover, we successfully demonstrated that p300 not only elevated transcriptional activity but also triggered chromatin acetylation via its direct interaction with SOX2 within these transcriptional condensates. Finally, our validation of SOX2-enriched SEs showcased their contribution to target gene expression in both stem cells and cancer cells. In its entirety, this study imparts valuable mechanistic insights into the collaborative interplay of SOX2 and its coactivator p300, shedding light on the regulation of transcriptional condensation and activation within SOX2-enriched SEs.

A general approach to protein folding using thermostable exoshells

In vitro protein folding is a complex process which often results in protein aggregation, low yields and low specific activity. Here we report the use of nanoscale exoshells (tES) to provide complementary nanoenvironments for the folding and release of 12 highly diverse protein substrates ranging from small protein toxins to human albumin, a dimeric protein (alkaline phosphatase), a trimeric ion channel (Omp2a) and the tetrameric tumor suppressor, p53. These proteins represent a unique diversity in size, volume, disulfide linkages, isoelectric point and multi versus monomeric nature of their functional units. Protein encapsulation within tES increased crude soluble yield (3-fold to >100-fold), functional yield (2-fold to >100-fold) and specific activity (3-fold to >100-fold) for all the proteins tested. The average soluble yield was 6.5 mg/100 mg of tES with charge complementation between the tES internal cavity and the protein substrate being the primary determinant of functional folding. Our results confirm the importance of nanoscale electrostatic effects and provide a solution for folding proteins in vitro.

Transcription factors: Time to deliver

Transcription factors (TFs) are at the center of the broad regulatory network orchestrating gene expression programs that elicit different biological responses. For a long time, TFs have been considered as potent drug targets due to their implications in the pathogenesis of a variety of diseases. At the same time, TFs, located at convergence points of cellular regulatory pathways, are powerful tools providing opportunities both for cell type change and for managing the state of cells. This task formulation requires the TF modulation problem to come to the fore. We review several ways to manage TF activity (small molecules, transfection, nanocarriers, protein-based approaches), analyzing their limitations and the possibilities to overcome them. Delivery of TFs could revolutionize the biomedical field. Whether this forecast comes true will depend on the ability to develop convenient technologies for targeted delivery of TFs.

High-efficiency generation of induced pluripotent mesenchymal stem cells from human dermal fibroblasts using recombinant proteins

Background

Induced pluripotent mesenchymal stem cells (iPMSCs) are novel candidates for drug screening, regenerative medicine, and cell therapy. However, introduction of transcription factor encoding genes for induced pluripotent stem cell (iPSC) generation which could be used to generate mesenchymal stem cells is accompanied by the risk of insertional mutations in the target cell genome.

Methods

We demonstrate a novel method using an inactivated viral particle to package and deliver four purified recombinant Yamanaka transcription factors (Sox2, Oct4, Klf4, and c-Myc) resulting in reprogramming of human primary fibroblasts. Whole genome bisulfite sequencing was used to analyze genome-wide CpG methylation of human iPMSCs. Western blot, quantitative PCR, immunofluorescence, and in-vitro differentiation were used to assess the pluripotency of iPMSCs.

Results

The resulting reprogrammed fibroblasts show high-level expression of stem cell markers. The human fibroblast-derived iPMSC genome showed gains in DNA methylation in low to medium methylated regions and concurrent loss of methylation in previously hypermethylated regions. Most of the differentially methylated regions are close to transcription start sites and many of these genes are pluripotent pathway associated. We found that DNA methylation of these genes is regulated by the four iPSC transcription factors, which functions as an epigenetic switch during somatic reprogramming as reported previously. These iPMSCs successfully differentiate into three embryonic germ layer cells, both in vitro and in vivo. Following multipotency induction in our study, the delivered transcription factors were degraded, leading to an improved efficiency of subsequent programmed differentiation.

Conclusion

Recombinant transcription factor based reprogramming and derivatization of iPMSC offers a novel high-efficiency approach for regenerative medicine from patient-derived cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0358-4) contains supplementary material, which is available to authorized users.

Transduction of Recombinant M3-p53-R12 Protein Enhances Human Leukemia Cell Apoptosis

Tumor suppressor protein p53 plays important roles in initiating cell cycle arrest and promoting tumor cell apoptosis. Previous studies have shown that p53 is either mutated or defective in approximately 50% of human cancers; therefore restoring normal p53 activity in cancer cells might be an effective anticancer therapeutic approach. Herein, we designed a chimeric p53 protein flanked with the MyoD N-terminal transcriptional activation domain (amino acids 1-62, called M3) and a poly-arginine (R12) cell penetrating signal in its N-and C-termini respectively. This chimeric protein, M3-p53-R12, can be expressed in E. coli and purified using immobilized metal ion chromatography followed by serial refolding dialysis. The purified M3-p53-R12 protein retains DNA-binding activity and gains of cell penetrating ability. Using MTT assay, we demonstrated that M3-p53-R12 inhibited the growth of K562, Jurkat as well as HL-60 leukemia cells carrying mutant p53 genes. Results from FACS analysis also demonstrated that transduction of M3-p53-R12 protein induced cell cycle arrest of these leukemia cells. Of special note, M3-p53-R12 has no apoptotic effect on normal mesenchymal stem cells (MSC) and leukocytes, highlighting its differential effects on normal and tumor cells. To sum up, our results reveal that purified recombinant M3-p53-R12 protein has functions of suppressing the leukemia cell lines' proliferation and launching cell apoptosis, suggesting the feasibility of using M3-p53-R12 protein as an anticancer drug. In the future we will test whether this chimeric protein can preferentially trigger the death of malignant cancer cells without affecting normal cells in animals carrying endogenous or xenographic tumors.

A Compendium of Preparation and Application of Stem Cells in Parkinson's Disease: Current Status and Future Prospects

Parkinson's Disease (PD) is a progressively neurodegenerative disorder, implicitly characterized by a stepwise loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) and explicitly marked by bradykinesia, rigidity, resting tremor and postural instability. Currently, therapeutic approaches available are mainly palliative strategies, including L-3,4-dihydroxy-phenylalanine (L-DOPA) replacement therapy, DA receptor agonist and deep brain stimulation (DBS) procedures. As the disease proceeds, however, the pharmacotherapeutic efficacy is inevitably worn off, worse still, implicated by side effects of motor response oscillations as well as L-DOPA induced dyskinesia (LID). Therefore, the frustrating status above has propeled the shift to cell replacement therapy (CRT), a promising restorative therapy intending to secure a long-lasting relief of patients' symptoms. By far, stem cell lines of multifarious origins have been established, which can be further categorized into embryonic stem cells (ESCs), neural stem cells (NSCs), induced neural stem cells (iNSCs), mesenchymal stem cells (MSCs), and induced pluripotent stem cells (iPSCs). In this review, we intend to present a compendium of preparation and application of multifarious stem cells, especially in relation to PD research and therapy. In addition, the current status, potential challenges and future prospects for practical CRT in PD patients will be elaborated as well.

Generation of pluripotent stem cells without the use of genetic material

Induced pluripotent stem cells (iPSCs) provide a platform to obtain patient-specific cells for use as a cell source in regenerative medicine. Although iPSCs do not have the ethical concerns of embryonic stem cells, iPSCs have not been widely used in clinical applications, as they are generated by gene transduction. Recently, iPSCs have been generated without the use of genetic material. For example, protein-induced PSCs and chemically induced PSCs have been generated by the use of small and large (protein) molecules. Several epigenetic characteristics are important for cell differentiation; therefore, several small-molecule inhibitors of epigenetic-modifying enzymes, such as DNA methyltransferases, histone deacetylases, histone methyltransferases, and histone demethylases, are potential candidates for the reprogramming of somatic cells into iPSCs. In this review, we discuss what types of small chemical or large (protein) molecules could be used to replace the viral transduction of genes and/or genetic reprogramming to obtain human iPSCs.

Current techniques in reprogramming cell potency

The first successful attempt to reprogram somatic cell into embryonic-like stem cell was achieved on 2006. Since then, it had sparked a race against time to bring this wonderful invention from bench to bedside but it is not easily achieved due to severe problems in term of epigenetic and genomic. With each problem arise, new technique and protocol will be constructed to try to overcome it. This review addresses the various techniques made available to create iPSC with problems hogging down the technique.

Efficient delivery of p53 and cytochrome c by supramolecular assembly of a dendritic multi-domain delivery system

Versatile nanocarrier systems facilitating uptake of exogenous proteins are highly alluring in evaluating these proteins for therapeutic applications. The self-assembly of an efficient nano-sized protein transporter consisting of three different entities is presented: A streptavidin protein core functioning as an adapter, second generation polyamidoamine dendrons for facilitating cell uptake as well as two different therapeutic proteins (tumor suppressor p53 or pro-apoptotic cytochrome c as cargo). Well-defined dendrons containing a biotin core are prepared and display no cytotoxic behavior upon conjugation to streptavidin. The integration of biotinylated human recombinant p53 (B-p53) into the three component system allows excellent internalization into HeLa, A549 and SaOS osteosarcoma cells monitored via confocal microscopy, immunoblot analysis and co-localization studies. In addition, the conjugation of B-p53 to dendronized streptavidin preserves its specific DNA-binding in vitro, and its delivery into SaOS cells impairs cell viability with concomitant activation of caspases 3 and 7. The versatility of this system is further exhibited by the significant enhancement of the pro-apoptotic effects of internalized cytochrome c which is analyzed by flow cytometry and cell viability assays. These results demonstrate that the "bio-click" self-assembly of biotinylated dendrons and proteins on a streptavidin adapter yields a stable supramolecular complex. This efficient bionanotransporter provides an attractive platform for mediating the delivery of functional proteins of interest into living mammalian cells in a facile and rapid way.

A cell-permeable fusion protein based on Clostridium botulinum C2 toxin for delivery of p53 tumorsuppressor into cancer cells

Genetically engineered bacterial protein toxins are attractive systems for delivery of exogenous proteins into the cytosol of mammalian cells. The binary C2 toxin from C. botulinum has emerged as powerful delivery vehicle, which rests on its binding/translocation component C2IIa and the genetically modified adaptor domain C2IN that act in concert to trigger cell uptake. The p53 tumor suppressor protein has a crucial function in suppressing carcinogenesis and is frequently inactivated by diverse mechanisms in human tumor cells. Therefore, we constructed a C2IN-p53 fusion protein, which is internalized into cancer cells by C2IIa. To this end, the C2IN-p53 fusion construct was overexpressed in E. coli with good solubility, purified by heparin affinity chromatography and protein identity was confirmed by immunoblotting. We demonstrated that the fusion protein is capable of binding to the p53 consensus-DNA with high affinity in a p53-specific manner in vitro. Next, the internalization of C2IN-p53 was monitored in HeLa cells by cell fractionation and immunoblot analysis, which revealed a C2IIa-mediated translocation of the fusion protein into the cytosol. The uptake was also shown in A549 and Saos-2 cells with similar efficiency. These findings were further corroborated by confocal immunofluorescence analyses of C2IN-p53/C2IIa-treated HeLa and A549 cells, displaying predominantly cytoplasmic localization of the fusion construct.

C2-streptavidin mediates the delivery of biotin-conjugated tumor suppressor protein p53 into tumor cells

We have previously generated a recombinant C2-streptavidin fusion protein for the delivery of biotin-labeled molecules of low molecular weight into the cytosol of mammalian cells. A nontoxic moiety of Clostridium botulinum C2 toxin mediates the cellular uptake, whereas the streptavidin unit serves as a binding platform for biotin-labeled cargo molecules. In the present study, we used the C2-streptavidin transporter to introduce biotin-conjugated p53 protein into various mammalian cell lines. The p53 tumor suppressor protein is inactivated in many human cancers by multiple mechanisms and therefore the restoration of its activity in tumor cells is of great therapeutic interest. Recombinant p53 was expressed in insect cells and biotin-labeled. Biotin-p53 retained its specific high-affinity DNA-binding as revealed by gel-shift analysis. Successful conjugation of biotin-p53 to the C2-streptavidin transporter was monitored by an overlay blot technique and confirmed by real-time surface plasmon resonance, providing a KD-value in the low nM range. C2-streptavidin significantly enhanced the uptake of biotin-p53 into African Green Monkey (Vero) epithelial cells as shown by flow cytometry. Using cell fractionation, the cytosolic translocation of biotin-p53 was detected in Vero cells as well as in HeLa cervix carcinoma cells. In line with this finding, confocal microscopy displayed cytoplasmic staining of biotin-p53 in HeLa and HL60 leukemia cells. Internalized biotin-p53 partially colocalized with early endosomes, as confirmed by confocal microscopy. In conclusion, our results demonstrate the successful conjugation of biotin-p53 to C2-streptavidin and its subsequent receptor-mediated endocytosis into different human tumor cell lines.