OCT4: Less is more

KDM4 Demethylases: Structure, Function, and Inhibitors

KDM4 histone demethylases mainly catalyze the removal of methyl marks from H3K9 and H3K36 to epigenetically regulate chromatin structure and gene expression. KDM4 expression is strictly regulated to ensure proper function in a myriad of biological processes, including transcription, cellular proliferation and differentiation, DNA damage repair, immune response, and stem cell self-renewal. Aberrant expression of KDM4 demethylase has been documented in many types of blood and solid tumors, and thus, KDM4s represent promising therapeutic targets. In this chapter, we summarize the current knowledge of the structures and regulatory mechanisms of KDM4 proteins and our understanding of their alterations in human pathological processes with a focus on development and cancer. We also review the reported KDM4 inhibitors and discuss their potential as therapeutic agents.

Interspecies cell fusion between mouse embryonic stem cell and porcine pluripotent cell

In the area of stem cell research, fusion of somatic cells into pluripotent cells such as mouse embryonic stem (ES) cells induces reprogramming of the somatic nucleus and can be used to study the effect of trans-acting factors from the pluripotent cell on the pluripotent state of somatic nucleus. As many other groups, we previously established a porcine pluripotent cell line at a low potential. Therefore, here, we performed experiments to investigate if the fusion with mouse ES cell could improve the pluripotent state of porcine pluripotent cell. Our data showed that resultant mouse-porcine interspecies fused cells are AP positive, and could be passaged up to 20 passages. Different degrees of increases in expression of porcine pluripotent genes proved that pig-origin gene network can be programmed by mouse ES. Further differentiation study also confirmed these fused cells' potential to form three germ layers. However, unexpectedly, we found that chromosome loss and aberrant (especially in porcine chromosomes) is severe after the cell fusion, implying that interspecies cell fusion may be not suitable to study porcine pluripotency without additional supportive conditions for genome stabilization.

Chromatin-modifying agents convert fibroblasts to OCT4+ and VEGFR-2+ capillary tube-forming cells

RATIONALE

The human epigenome is plastic. The goal of this study was to address if fibroblast cells can be epigenetically modified to promote neovessel formation.

METHODS AND RESULTS

Here, we used highly abundant human adult dermal fibroblast cells (hADFCs) that were treated with the chromatin-modifying agents 5-aza-2'-deoxycytidine and trichostatin A, and subsequently subjected to differentiation by activating Wnt signaling. Our results show that these epigenetically modified hADFCs increasingly expressed β-catenin, pluripotency factor octamer-binding transcription factor-4 (OCT4, also known as POU5F1), and endothelial cell (EC) marker called vascular endothelial growth factor receptor-2 (VEGFR-2, also known as Fetal Liver Kinase-1). In microscopic analysis, β-catenin localized to cell-cell contact points, while OCT4 was found to be localized primarily to the nucleus of these cells. Furthermore, in a chromatin immunoprecipitation experiment, OCT4 bound to the VEGFR-2/FLK1 promoter. Finally, these modified hADFCs also transduced Wnt signaling. Importantly, on a two-dimensional (2D) gel substrate, a subset of the converted cells formed vascular network-like structures in the presence of VEGF.

CONCLUSION

Chromatin-modifying agents converted hADFCs to OCT4+ and VEGFR-2+ capillary tube-forming cells in a 2D matrix in VEGF-dependent manner.

DPF2 regulates OCT4 protein level and nuclear distribution

The amount of transcription factor OCT4 is strictly regulated. A tight regulation of OCT4 levels is crucial for mammalian embryonic development and oncogenesis. However, the mechanisms underlying regulation of OCT4 protein expression and nuclear distribution are largely unknown. Here, we report that DPF2, a plant homeodomain (PHD) finger protein, is upregulated during H9 cell differentiation induced by retinoic acid. Endogenous interaction between DPF2 and OCT4 in P19 cells was revealed by an immunoprecipitation assay. GST-pull down assay proved that OCT4 protein in H9 cells and recombinant OCT4 can precipitate with DPF2 in vitro. In vitro ubiquitination assay demonstrated DPF2 might serve as an E3 ligase. Knock down of dpf2 using siRNA increased OCT4 protein level and stability in P19 cells. DPF2 siRNAs also up-regulates OCT4 but not NANOG in H9 cells. However, RA fails to downregulates OCT4 protein level in cells infected by lenitviruses containing DPF2 siRNA. Moreover, overexpression of both DPF2 and OCT4 in 293 cells proved the DPF2-OCT4 interaction. DPF2 but not PHD2 mutant DPF2 enhanced ubiquitination and degradation of OCT4 in 293 cells co-expressed DPF2 and OCT4. Both wild type DPF2 and PHD2 mutant DPF2 redistributes nuclear OCT4 without affecting DPF2-OCT4 interaction. Further analysis indicated that DPF2 decreases monomeric and mono-ubiquitinated OCT4, assembles poly-ubiquitin chains on OCT4 mainly through Ub-K48 linkage. These findings contribute to an understanding of how OCT4 protein level and nuclear distribution is regulated by its associated protein.

Minireview: the diverse roles of nuclear receptors in the regulation of embryonic stem cell pluripotency

Extensive research has been devoted to the goal of understanding how a single cell of embryonic origin can give rise to every somatic cell type and the germ cell lineage, a hallmark defined as "pluripotency." The aggregate of this work supports fundamentally important roles for the gene transcription networks inherent to the pluripotent cell. Transcription networks have been identified that are both required for pluripotency, as well as sufficient to reprogram somatic cells to a naive pluripotent state. Several members of the nuclear receptor (NR) superfamily of transcription factors have been identified to play diverse roles in the regulation of pluripotency. The ligand-responsive nature of NRs coupled with the abundance of genetic models available has led to a significant advance in the understanding of NR roles in embryonic stem cell pluripotency. Furthermore, the presence of a ligand-binding domain may lead to development of small molecules for a wide range of therapeutic and research applications, even in cases of NRs that are not known to respond to physiologic ligands. Presented here is an overview of NR regulation of pluripotency with a focus on the transcriptional, proteomic, and epigenetic mechanisms by which they promote or suppress the pluripotent state.

The oncogenic potential of Jumonji D2 (JMJD2/KDM4) histone demethylase overexpression

The Jumonji D2 proteins (JMJD2/KDM4) function to demethylate di- and trimethylated (me2/3) histone 3 lysine 9 (H3K9me2/3) and H3K36me3. Knockout mouse models for Kdm4b and Kdm4d have not resulted in gross abnormalities, while mouse models for Kdm4a and Kdm4c have not been reported. However, the KDM4 subfamily of demethylases are overexpressed in several tumor types. Overexpression of KDM4 proteins alters transcription and chromatin remodeling, driving cellular proliferation, anchorage-independent growth, invasion, and migration. Increased proliferation occurs through KDM4-mediated modification of cell cycle timing, as well as through increased numbers of replication forks. Recent evidence also suggests that KDM4C overexpression contributes to the maintenance of a pluripotent state. Together these data suggest that overexpression of KDM4 proteins induces numerous oncogenic effects.

Expression analysis of pluripotency-associated genes in human fetal cortical and striatal neural stem cells during differentiation

In the field of developmental biology, there is compelling evidence for a network of activity of pluripotency and stem-associated genes comprising of Oct4, Nanog and nestin. During neurogenesis, the choice between enhancement versus suppression of transcriptional modulation of these identified genes determines the balance between self-renewal neural stem cells (NSC) and immature neuronal phenotypes. By using immunocytochemistry and RT-PCR techniques, our study aims to address the question whether and to what extent mRNA and protein profiles are expressed in human fetal neurospheres obtained from cortical and striatal brain regions, both in expansion (undifferentiated cells) and differentiation conditions monitored after 1 and 4 weeks in vitro culturing. Our results clearly demonstrate the sustained presence of opposite signals: strong downregulation of Oct4 and Nanog genes in cortical differentiating cells and significant up-regulation for nestin gene both in cortical and striatal differentiating cells. Notably, by immunostaining techniques, Oct4 and Nanog protein expression have indicated the presence of both nuclear and cytoplasmic content followed by their rapid turnover (immediately after 1 week). Moreover, during the differentiation process, dissociated neurospheres displayed unexpected number of nestin positive cells accompanied by a constant level of staining intensity. In conclusion, the present study provides new insights into brain region related features in terms of Oct4, Nanog and nestin expression both at cellular and molecular level.

Dynamic methylation and expression of Oct4 in early neural stem cells

Neural stem cells are a multipotent population of tissue-specific stem cells with a broad but limited differentiation potential. However, recent studies have shown that over-expression of the pluripotency gene, Oct4, alone is sufficient to initiate a process by which these can form 'induced pluripotent stem cells' (iPS cells) with the same broad potential as embryonic stem cells. This led us to examine the expression of Oct4 in endogenous neural stem cells, as data regarding its expression in neural stem cells in vivo are contradictory and incomplete. In this study we have therefore analysed the expression of Oct4 and other genes associated with pluripotency throughout development of the mouse CNS and in neural stem cells grown in vitro. We find that Oct4 is still expressed in the CNS by E8.5, but that this expression declines rapidly until it is undetectable by E15.5. This decline is coincident with the gradual methylation of the Oct4 promoter and proximal enhancer. Immunostaining suggests that the Oct4 protein is predominantly cytoplasmic in location. We also found that neural stem cells from all ages expressed the pluripotency associated genes, Sox2, c-Myc, Klf4 and Nanog. These data provide an explanation for the varying behaviour of cells from the early neuroepithelium at different stages of development. The expression of these genes also provides an indication of why Oct4 alone is sufficient to induce iPS formation in neural stem cells at later stages.