Kyung-Soon Park

Direct Reprogramming of Rat Neural Precursor Cells and Fibroblasts into Pluripotent Stem Cells

Background Given the usefulness of rats as an experimental system, an efficient method for generating rat induced pluripotent stem (iPS) cells would provide researchers with a powerful tool for studying human physiology and disease. Here, we report direct reprogramming of rat neural precursor (NP) cells and rat embryonic fibroblasts (REF) into iPS cells by retroviral transduction using either three (Oct3/4, Sox2, and Klf4), four (Oct3/4, Sox2, Klf4, and c-Myc), or five (Oct3/4, Sox2, Klf4, c-Myc, and Nanog) genes. Methodology and Principal Findings iPS cells were generated from both NP and REF using only three (Oct3/4, Sox2, and Klf4) genes without c-Myc. Two factors were found to be critical for efficient derivation and maintenance of rat iPS cells: the use of rat instead of mouse feeders, and the use of small molecules specifically inhibiting mitogen-activated protein kinase and glycogen synthase kinase 3 pathways. In contrast, introduction of embryonic stem cell (ESC) extracts induced partial reprogramming, but failed to generate iPS cells. However, when combined with retroviral transduction, this method generated iPS cells with significantly higher efficiency. Morphology, gene expression, and epigenetic status confirmed that these rat iPS cells exhibited ESC-like properties, including the ability to differentiate into all three germ layers both in vitro and in teratomas. In particular, we found that these rat iPS cells could differentiate to midbrain-like dopamine neurons with a high efficiency. Conclusions/Significance Given the usefulness of rats as an experimental system, our optimized method would be useful for generating rat iPS cells from diverse tissues and provide researchers with a powerful tool for studying human physiology and disease.

PI3K/Akt and Stat3 signaling regulated by PTEN control of the cancer stem cell population, proliferation and senescence in a glioblastoma cell line.

Malignant gliomas are the most common primary brain tumor in adults. A number of genes have been implicated in glioblastoma including mutation and deletion of PTEN. PTEN is a regulator of PI3K-mediated Akt signaling pathways and has been recognized as a therapeutic target in glioblastoma. To achieve potent therapeutic inhibition of the PI3K-Akt pathway in glioblastoma, it is essential to understand the interplay between the regulators of its activation. Here, ectopic expression of PTEN in the U-87MG human glioblastoma-astrocytoma cell line is shown to result in the depletion of glioblastoma stem cells (GSCs) and to cause growth retardation and senescence. These effects are likely to be associated with PTEN-mediated cooperative perturbation of Akt and Stat3 signals. Using an in vivo rat model of glioblastoma, we showed that PTEN-overexpressing U-87MG cells failed to induce tumor formation, while untreated U-87MG cells did so. Furthermore, cells expressing the phosphorylated form of Stat3 were completely absent from the brain of rats implanted with PTEN-overexpressing U-87MG cells. Based on these results, PTEN appears to function as a crucial inhibitor of GSCs and as an inducer of senescence, suggesting that functional enhancement of the PTEN pathway will be useful to provide a therapeutic strategy for targeting glioblastoma.

Lefty1 and Lefty2 Control the Balance Between Self-Renewal and Pluripotent Differentiation of Mouse Embryonic Stem Cells

Lefty expression has been recognized as a stemness marker because Lefty is enriched both in undifferentiated embryonic stem cells (ESCs) and in blastocysts. Here, we examined the function of Lefty1 and Lefty2 in the maintenance of self-renewal and pluripotency of mouse ESCs (mESCs). Suppression of Lefty1 or Lefty2 expression in mESCs did not alter the self-renewal properties of mESCs under nondifferentiating conditions, but suppression of these genes did affect Smad2 phosphorylation and differentiation. Lefty1 knockdown mESCs showed enhanced phosphorylation of Smad2 and increased differentiation potential, whereas Lefty2 knockdown mESCs exhibited reduced phosphorylation of Smad2 and enhanced self-renewal in the presence of a differentiation signal. In vivo, teratomas developed from Lefty2 knockdown mESCs contained massive expansions of immature neuroepithelium, a marker of malignant teratomas. Taken together, these results suggest that optimal expression of Lefty1 and Lefty2 is critical for the balanced differentiation of mESCs into three germ layers.

Sprouty1 regulates neural and endothelial differentiation of mouse embryonic stem cells.

Fibroblast growth factor (FGF) signaling is implicated in the control of pluripotency and lineage differentiation of both human and mouse embryonic stem cells (mESCs). FGF4 dependent stimulation of ERK1/2 signaling triggers transition of pluripotent ESCs from self-renewal and lineage commitment. In this study, Sprouty 1 (Spry1) expression was observed in undifferentiated mESCs, where it modulated ERK1/2 activity. Spry1 was confirmed as dispensable for the maintenance of self-renewal. However, suppression of Spry1 expression and subsequent activation of ERK1/2 signaling promoted neural differentiation and inhibited endothelial differentiation of mESCs. Moreover, evidence is presented which indicates that SHP2, a major determinant of balance between mESC self-renewal and differentiation, directly regulates Spry1 activity to modulate ERK1/2 signaling and lineage-specific differentiation in mESCs. Our results show that Spry1 has an essential role in the lineage specific differentiation of mESCs.

Zap70 functions to maintain stemness of mouse embryonic stem cells by negatively regulating Jak1/Stat3/c-Myc signaling

Zeta‐chain‐associated protein kinase‐70 (Zap70), a Syk family tyrosine kinase, has been reported to be present exclusively in normal T‐cells, natural killer cells, and B cells, serving as a pivotal regulator of antigen‐mediated receptor signaling and development. In this study, we report that Zap70 is expressed in undifferentiated mouse embryonic stem cells (mESCs) and may critically regulate self‐renewal and pluripotency in mESCs. We found that Zap70 knocked‐down mESCs (Zap70KD) show sustained self‐renewal and defective differentiation. In addition, we present evidence that the sustained self‐renewal in Zap70KD is associated with enhanced Jak/Stat3 signaling and c‐Myc induction. These altered signaling appears to result from upregulated leukemia inhibitory factor receptor and downregulated src homology region 2 domain containing phosphatase 1 (SHP‐1) phosphatase activity. On the basis of these results, we propose that in undifferentiated mESCs, Zap70 plays important roles in modulating the balance between self‐renewal capacity and pluripotent differentiation ability as a key regulator of the Jak/Stat3/c‐Myc signaling pathway. Stem Cells 2010; 28:1476–1486.

Obox4 critically regulates cAMP-dependent meiotic arrest and MI-MII transition in oocytes.

Extra follicular oocytes spontaneously resume meiosis in vitro, but the intact germinal vesicle (GV) is retained if the oocytes are cultured in medium containing phosphodiesterase (PDE) inhibitors or cAMP analogues. On the basis of our finding that Obox4 is prominently expressed in oocytes, the present study was conducted to determine the functional role of the homeodomain‐containing factor Obox4 during in vitro oocyte maturation. After microinjection of Obox4 dsRNA into the cytoplasm of GV oocytes cultured in M16 medium, oocytes were arrested at metaphase I (MI, 77.7%) and metaphase II (MII, 22.3%). Surprisingly, however, 89% of Obox4 RNAitreated oocytes resumed meiosis and developed to MI and MII when cultured in medium containing 0.2 mM 3‐isobutyl‐1‐metyl‐xanthine (IBMX), in which untreated oocytes maintain intact GVs. Spindles were aberrant, and chromosomes were severely aggregated with decreased MPF and MAP kinase activities in arrested MI oocytes after exposure to Obox4 RNAi. Oocytes overexpressing Obox4 retained intact GVs when cultured in M16 medium. Taken together, for the first time to our knowledge, these findings indicate that Obox4 plays a key role in the cAMP‐dependent signaling cascades that maintain GV arrest. Oocytes not expressing Obox4 failed to maintain intact GVs in IBMX‐supplemented medium, while GVs remained intact when oocytes were kept in plain medium and overexpressing Obox4, suggesting that Obox4 plays a critical role in cAMP‐dependent cascade for maintaining intact GVs.—Lee, H.‐S., Kim, E.‐Y., Kim, K‐H., Moon, J., Park, K‐S., Kim, K‐S., Lee, K‐A. Obox4 critically regulates cAMP‐dependent meiotic arrest and MI‐MII transition in oocytes. FASEB J. 24, 2314–2324 (2010). www.fasebj.org

Ell3 stimulates proliferation, drug resistance, and cancer stem cell properties of breast cancer cells via a MEK/ERK-dependent signaling pathway

Ell3 is a RNA polymerase II transcription elongation factor that is enriched in testis. The C-terminal domain of Ell3 shows strong similarities to that of Ell (eleven-nineteen lysine-rich leukemia gene), which acts as a negative regulator of p53 and regulates cell proliferation and survival. Recent studies in our laboratory showed that Ell3 induces the differentiation of mouse embryonic stem cells by protecting differentiating cells from apoptosis via the promotion of p53 degradation. In this study, we evaluated the function of Ell3 in breast cancer cell lines. MCF-7 cell lines overexpressing Ell3 were used to examine cell proliferation and cancer stem cell properties. Ectopic expression of Ell3 in breast cancer cell lines induces proliferation and 5-FU resistance. In addition, Ell3 expression increases the cancer stem cell population, which is characterized by CD44 (+) or ALDH1 (+) cells. Mammosphere-forming potential and migration ability were also increased upon Ell3 expression in breast cancer cell lines. Through biochemical and molecular biological analyses, we showed that Ell3 regulates proliferation, cancer stem cell properties and drug resistance in breast cancer cell lines partly through the MEK-extracellular signal-regulated kinase signaling pathway. Murine xenograft experiments showed that Ell3 expression promotes tumorigenesis in vivo. These results suggest that Ell3 may play a critical role in promoting oncogenesis in breast cancer by regulating cell proliferation and cancer stem cell properties via the ERK1/2 signaling pathway.

Ell3 enhances differentiation of mouse embryonic stem cells by regulating epithelial-mesenchymal transition and apoptosis.

Ell3 is a testis-specific RNA polymerase II elongation factor whose cellular function is not clear. The present study shows that Ell3 is activated during the differentiation of mouse embryonic stem cells (mESCs). Furthermore, Ell3 plays a critical role in stimulating lineage differentiation of mESCs by promoting epithelial-mesenchymal transition (EMT) and suppressing apoptosis. Mouse ESCs engineered to stably express Ell3 were rapidly differentiated compared with control cells either under spontaneous differentiation or neural lineage-specific differentiation conditions. Gene expression profile and quantitative RT-PCR analysis showed that the expression of EMT markers, such as Zeb1 and Zeb2, two major genes that regulate EMT, was upregulated in Ell3-overexpressing mESCs. Remarkably, knockdown of Zeb1 attenuated the enhanced differentiation capacity of Ell3-overexpressing mESCs, which indicates that Ell3 plays a role in the induction of mESC differentiation by inducing EMT. In contrast to Ell3-overexpressing mESCs, Ell3-knock down mESCs could not differentiate under differentiation conditions and, instead, underwent caspase-dependent apoptosis. In addition, apoptosis of differentiating Ell3-knock out mESCs was associated with enhanced expression of p53. The present results suggest that Ell3 promotes the differentiation of mESCs by activating the expression of EMT-related genes and by suppressing p53 expression.

TCEA3 binds to TGF-beta receptor I and induces Smad-independent, JNK-dependent apoptosis in ovarian cancer cells

TFIIS is a transcription elongation factor conserved in frog, mouse and human. Recently, knockdown of TCEA1, the most well-characterized isoform of TFIIS, by RNA silencing was reported to inhibit cancer cell proliferation and induce apoptosis in breast, lung and pancreatic cancer cell lines through activation of p53 (Hubbard et al., 2008 [1]). However, the functions of other TFIIS isoforms are poorly defined. The present study shows that TCEA3, an isoform of TFIIS, can trigger ovarian cancer-specific cell death by activating the JNK signaling pathway. TCEA3 expression is low in ovarian cancer cell lines compared to noncancerous ovarian epithelial cells. Suppression of TCEA3 in noncancerous ovarian epithelial cells promotes cell growth whereas ectopic expression of TCEA3 in ovarian cancer cell lines induces the caspase-dependent mitochondrial cell death pathway. Molecular and chemical inhibition assays show that the interaction of TCEA3 with TGFβ receptor I induces cell death in ovarian cancer cell through Smad-independent activation of the JNK pathway. These results reveal that TCEA3 induces a novel apoptotic mechanism in OEC, which provides TCEA3 as a novel target to develop therapeutics of ovarian cancer.

SHP2 is a downstream target of ZAP70 to regulate JAK1/STAT3 and ERK signaling pathways in mouse embryonic stem cells

Previous research indicated that ZAP70, a Syk family tyrosine kinase, is expressed in mouse embryonic stem cells (mESCs) and regulates the Janus kinase 1 (JAK1)/signal transducer and activator of transcription 3 (STAT3) signaling through consolidating SHP1 enzymatic activity. In this study, we report that SHP2 is another downstream target of ZAP70 in mESCs. We found that SHP2 phosphorylation and enzymatic activity are affected by Zap70 expression. In addition, we present evidence that ERK pathways activated by ZAP70 and SHP2 reduce the protein level of leukemia inhibitory factor (LIF) receptor. Based on these results, we propose that SHP2 is an essential mediator of the ZAP70 signal to regulate JAK1/STAT3 and ERK pathways in undifferentiated mESCs.