Protein kinase C regulates human pluripotent stem cell self-renewal.

BACKGROUND: The self-renewal of human pluripotent stem (hPS) cells including embryonic stem and induced pluripotent stem cells have been reported to be supported by various signal pathways. Among them, fibroblast growth factor-2 (FGF-2) appears indispensable to maintain self-renewal of hPS cells. However, downstream signaling of FGF-2 has not yet been clearly understood in hPS cells. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we screened a kinase inhibitor library using a high-throughput alkaline phosphatase (ALP) activity-based assay in a minimal growth factor-defined medium to understand FGF-2-related molecular mechanisms regulating self-renewal of hPS cells. We found that in the presence of FGF-2, an inhibitor of protein kinase C (PKC), GF109203X (GFX), increased ALP activity. GFX inhibited FGF-2-induced phosphorylation of glycogen synthase kinase-3ß (GSK-3ß), suggesting that FGF-2 induced PKC and then PKC inhibited the activity of GSK-3ß. Addition of activin A increased phosphorylation of GSK-3ß and extracellular signal-regulated kinase-1/2 (ERK-1/2) synergistically with FGF-2 whereas activin A alone did not. GFX negated differentiation of hPS cells induced by the PKC activator, phorbol 12-myristate 13-acetate whereas Gö6976, a selective inhibitor of PKCα, ß, and γ isoforms could not counteract the effect of PMA. Intriguingly, functional gene analysis by RNA interference revealed that the phosphorylation of GSK-3ß was reduced by siRNA of PKCδ, PKCε, and ζ, the phosphorylation of ERK-1/2 was reduced by siRNA of PKCε and ζ, and the phosphorylation of AKT was reduced by PKCε in hPS cells. CONCLUSIONS/SIGNIFICANCE: Our study suggested complicated cross-talk in hPS cells that FGF-2 induced the phosphorylation of phosphatidylinositol-3 kinase (PI3K)/AKT, mitogen-activated protein kinase/ERK-1/2 kinase (MEK), PKC/ERK-1/2 kinase, and PKC/GSK-3ß. Addition of GFX with a MEK inhibitor, U0126, in the presence of FGF-2 and activin A provided a long-term stable undifferentiated state of hPS cells even though hPS cells were dissociated into single cells for passage. This study untangles the cross-talk between molecular mechanisms regulating self-renewal and differentiation of hPS cells.

A novel antibody for human induced pluripotent stem cells and embryonic stem cells recognizes a type of keratan sulfate lacking oversulfated structures.

We have generated a monoclonal antibody (R-10G) specific to human induced pluripotent stem (hiPS)/embryonic stem (hES) cells by using hiPS cells (Tic) as an antigen, followed by differential screening of mouse hybridomas with hiPS and human embryonal carcinoma (hEC) cells. Upon western blotting with R-10G, hiPS/ES cell lysates gave a single but an unusually diffuse band at a position corresponding to >250 kDa. The antigen protein was isolated from the induced pluripotent stem (iPS) cell lysates with an affinity column of R-10G. The R-10G positive band was resistant to digestion with peptide N-glycanase F (PNGase F), neuraminidase, fucosidase, chondrotinase ABC and heparinase mix, but it disappeared almost completely on digestion with keratanase, keratanase II and endo-ß-galactosidase, indicating that the R-10G epitope is a keratan sulfate. The carrier protein of the R-10G epitope was identified as podocalyxin by liquid chromatography/mass spectrometry (LC/MS/MS) analysis of the R-10G positive-protein band material obtained on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The R-10G epitope is a type of keratan sulfate with some unique properties. (1) The epitope is expressed only on hiPS/ES cells, i.e. not on hEC cells, unlike those recognized by the conventional hiPS/ES marker antibodies. (2) The epitope is a type of keratan sulfate lacking oversulfated structures and is not immunologically cross-reactive with high-sulfated keratan sulfate. (3) The R-10G epitope is distributed heterogeneously on hiPS cells, suggesting that a single colony of undifferentiated hiPS cells consists of different cell subtypes. Thus, R-10G is a novel antibody recognizing hiPS/ES cells, and should be a new molecular probe for disclosing the roles of glycans on these cells.

The loss of endoglin promotes the invasion of extravillous trophoblasts.

Endoglin is a coreceptor for TGF-ß, which is expressed in syncytiotrophoblasts. The soluble form of endoglin (sEng) has been observed to increase in the serum of preeclamptic patients. Several studies have shown that endoglin is involved in cancer invasion. However, the role of endoglin in extravillous trophoblasts (EVT), which have an invasive phenotype, remains unknown. The present study was designed to investigate the expression and role of endoglin in human EVT. We found that endoglin was mainly expressed on cytotrophoblasts within the cell column during the first trimester and its expression decreased in the EVT by immunohistochemistry and immunocytochemistry. The expression of endoglin significantly increased after treatment with TGF-ß1 and TGF-ß3 in the human EVT cell line, HTR-8/SVneo, as detected by semiquantitative RT-PCR. To investigate the role of endoglin in EVT, the stable knockdown of endoglin was performed by lentiviral short hairpin RNA transfection into the HTR-8/SVneo cells. Although proliferation was not affected, the motility and invasiveness of the HTR-8/SVneo cells significantly increased by the knockdown of endoglin. Both the mRNA expression and secretion of urokinase-type plasminogen activator significantly increased in endoglin knockdown cells. The secretion of sEng was very low in HTR-8/SVneo, and the treatment of endoglin knockdown cells with 10 ng/ml sEng had no effect on their invasiveness. Therefore, the suppression of sEng was not involved in the increased invasiveness of endoglin knockdown cells. These results suggested that EVT increased their invasive function as a result of decreasing expression of transmembrane endoglin.