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1.  mTORC1 Is Essential for Early Steps during Schwann Cell Differentiation of Amniotic Fluid Stem Cells and Regulates Lipogenic Gene Expression 
PLoS ONE  2014;9(9):e107004.
Schwann cell development is hallmarked by the induction of a lipogenic profile. Here we used amniotic fluid stem (AFS) cells and focused on the mechanisms occurring during early steps of differentiation along the Schwann cell lineage. Therefore, we initiated Schwann cell differentiation in AFS cells and monitored as well as modulated the activity of the mechanistic target of rapamycin (mTOR) pathway, the major regulator of anabolic processes. Our results show that mTOR complex 1 (mTORC1) activity is essential for glial marker expression and expression of Sterol Regulatory Element-Binding Protein (SREBP) target genes. Moreover, SREBP target gene activation by statin treatment promoted lipogenic gene expression, induced mTORC1 activation and stimulated Schwann cell differentiation. To investigate mTORC1 downstream signaling we expressed a mutant S6K1, which subsequently induced the expression of the Schwann cell marker S100b, but did not affect lipogenic gene expression. This suggests that S6K1 dependent and independent pathways downstream of mTORC1 drive AFS cells to early Schwann cell differentiation and lipogenic gene expression. In conclusion our results propose that future strategies for peripheral nervous system regeneration will depend on ways to efficiently induce the mTORC1 pathway.
PMCID: PMC4164523  PMID: 25221943
2.  Phenotyping of Human Melanoma Cells Reveals a Unique Composition of Receptor Targets and a Subpopulation Co-Expressing ErbB4, EPO-R and NGF-R 
PLoS ONE  2014;9(1):e84417.
Malignant melanoma is a life-threatening skin cancer increasingly diagnosed in the western world. In advanced disease the prognosis is grave. Growth and metastasis formation in melanomas are regulated by a network of cytokines, cytokine-receptors, and adhesion molecules. However, little is known about surface antigens and target expression profiles in human melanomas. We examined the cell surface antigen profile of human skin melanoma cells by multicolor flow cytometry, and compared their phenotype with 4 melanoma cell lines (A375, 607B, Mel-Juso, SK-Mel28). Melanoma cells were defined as CD45−/CD31− cells co-expressing one or more melanoma-related antigens (CD63, CD146, CD166). In most patients, melanoma cells exhibited ErbB3/Her3, CD44/Pgp-1, ICAM-1/CD54 and IGF-1-R/CD221, but did not express CD20, ErbB2/Her2, KIT/CD117, AC133/CD133 or MDR-1/CD243. Melanoma cell lines were found to display a similar phenotype. In most patients, a distinct subpopulation of melanoma cells (4–40%) expressed the erythropoietin receptor (EPO-R) and ErbB4 together with PD-1 and NGF-R/CD271. Both the EPO-R+ and EPO-R− subpopulations produced melanoma lesions in NOD/SCID IL-2Rgammanull (NSG) mice in first and secondary recipients. Normal skin melanocytes did not express ErbB4 or EPO-R, but expressed a functional KIT receptor (CD117) as well as NGF-R, ErbB3/Her3, IGF-1-R and CD44. In conclusion, melanoma cells display a unique composition of surface target antigens and cytokine receptors. Malignant transformation of melanomas is accompanied by loss of KIT and acquisition of EPO-R and ErbB4, both of which are co-expressed with NGF-R and PD-1 in distinct subfractions of melanoma cells. However, expression of EPO-R/ErbB4/PD-1 is not indicative of a selective melanoma-initiating potential.
PMCID: PMC3906015  PMID: 24489649
3.  M6P/IGF2R modulates the invasiveness of liver cells via its capacity to bind mannose 6-phosphate residues 
Journal of Hepatology  2012;57(2):337-343.
Background & Aims
The mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF2R), a multifunctional protein, plays a central role in intracellular targeting of lysosomal enzymes and control of insulin-like growth factor II (IGF-II) bioactivity. Importantly, the gene encoding this receptor is frequently inactivated in a wide range of malignant tumors including hepatocellular carcinomas. Thus, M6P/IGF2R is considered a putative liver tumor suppressor. The aim of this study was to establish the impact of the receptor on the invasive properties of liver cells.
Reconstitution experiments were performed by expression of wild type and mutant M6P/IGF2R in receptor-deficient FRL14 fetal rat liver cells. RNA interference was used to induce M6P/IGF2R downregulation in receptor-positive MIM-1–4 mouse hepatocytes.
We show that the M6P/IGF2R status exerts a strong impact on the invasiveness of tumorigenic rodent liver cells. M6P/IGF2R-deficient fetal rat liver cells hypersecrete lysosomal cathepsins and penetrate extracellular matrix barriers in a cathepsin-dependent manner. Forced expression of M6P/IGF2R restores intracellular transport of cathepsins to lysosomes and concomitantly reduces the tumorigenicity and invasive potential of these cells. Conversely, M6P/IGF2R knock-down in receptor-positive mouse hepatocytes causes increased cathepsin secretion as well as enhanced cell motility and invasiveness. We also demonstrate that functional M6P-binding sites are important for the anti-invasive properties of M6P/IGF2R, whereas the capacity to bind IGF-II is dispensable for the anti-invasive activity of the receptor in liver cells.
M6P/IGF2R restricts liver cell invasion by preventing the pericellular action of M6P-modified proteins.
PMCID: PMC3401376  PMID: 22521359
BSA, bovine serum albumin; ECM, extracellular matrix; FBS, fetal bovine serum; HCC, hepatocellular carcinoma; HGF, hepatocyte growth factor; IGF-II, insulin-like growth factor II; M6P, mannose 6-phosphate; M6P/IGF2R, mannose 6-phosphate/insulin-like growth factor II receptor; MPR46, 46-kDa mannose 6-phosphate receptor; RNAi, RNA interference; shRNA, short hairpin RNA; siRNA, short interfering RNA; Cathepsin; Hepatocellular carcinoma; Lysosome; Matrix degradation; Cell invasion
4.  Amniotic fluid stem cell-based models to study the effects of gene mutations and toxicants on male germ cell formation 
Asian Journal of Andrology  2012;14(2):247-250.
Male infertility is a major public health issue predominantly caused by defects in germ cell development. In the past, studies on the genetic regulation of spermatogenesis as well as on negative environmental impacts have been hampered by the fact that human germ cell development is intractable to direct analysis in vivo. Compared with model organisms including mice, there are fundamental differences in the molecular processes of human germ cell development. Therefore, an in vitro model mimicking human sperm formation would be an extremely valuable research tool. In the recent past, both human embryonic stem (ES) cells and induced pluripotent stem (iPS) cells have been reported to harbour the potential to differentiate into primordial germ cells and gametes. We here discuss the possibility to use human amniotic fluid stem (AFS) cells as a biological model. Since their discovery in 2003, AFS cells have been characterized to differentiate into cells of all three germ layers, to be genomically stable, to have a high proliferative potential and to be non-tumourigenic. In addition, AFS cells are not subject of ethical concerns. In contrast to iPS cells, AFSs cells do not need ectopic induction of pluripotency, which is often associated with only imperfectly cleared epigenetic memory of the source cells. Since AFS cells can be derived from amniocentesis with disease-causing mutations and can be transfected with high efficiency, they could be used in probing gene functions for spermatogenesis and in screening for male reproductive toxicity.
PMCID: PMC3735087  PMID: 22231297
amniotic fluid; human genetics; infertility; primordial germ cells; reproduction; spermatogenesis; stem cells; toxicity
5.  Human amniotic fluid stem cells as a model for functional studies of genes involved in human genetic diseases or oncogenesis 
Oncotarget  2011;2(9):705-712.
Besides their putative usage for therapies, stem cells are a promising tool for functional studies of genes involved in human genetic diseases or oncogenesis. For this purpose induced pluripotent stem (iPS) cells can be derived from patients harbouring specific mutations. In contrast to adult stem cells, iPS cells are pluripotent and can efficiently be grown in culture. However, iPS cells are modulated due to the ectopic induction of pluripotency, harbour other somatic mutations accumulated during the life span of the source cells, exhibit only imperfectly cleared epigenetic memory of the source cell, and are often genomically instable. In addition, iPS cells from patients only allow the investigation of mutations, which are not prenatally lethal. Embryonic stem (ES) cells have a high proliferation and differentiation potential, but raise ethical issues. Human embryos, which are not transferred in the course of in vitro fertilization, because of preimplantation genetic diagnosis of a genetic defect, are still rarely donated for the establishment of ES cell lines. In addition, their usage for studies on gene functions for oncogenesis is hampered by the fact the ES cells are already tumorigenic per se. In 2003 amniotic fluid stem (AFS) cells have been discovered, which meanwhile have been demonstrated to harbour the potential to differentiate into cells of all three germ layers. Monoclonal human AFS cell lines derived from amniocenteses have a high proliferative potential, are genomically stable and are not associated with ethical controversies. Worldwide amniocenteses are performed for routine human genetic diagnosis. We here discuss how generation and banking of monoclonal human AFS cell lines with specific chromosomal aberrations or monogenic disease mutations would allow to study the functional consequences of disease causing mutations. In addition, recently a protocol for efficient and highly reproducible siRNA-mediated long-term knockdown of endogenous gene functions in AFS cells was established. Since AFS cells are not tumorigenic, gene modulations not only allow to investigate the role of endogenous genes involved in human genetic diseases but also may help to reveal putative oncogenic gene functions in different biological models, both in vitro and in vivo. This concept is discussed and a “proof of principle”, already obtained via modulating genes involved in the mammalian target of rapamycin (mTOR) pathway in AFS cells, is presented.
PMCID: PMC3248217  PMID: 21926447
stem cells; human genetics; oncogenesis; amniocentesis; RNA interference; mTOR
6.  Mutations in TMEM216 perturb ciliogenesis and cause Joubert, Meckel and related syndromes 
Nature genetics  2010;42(7):619-625.
Joubert syndrome (JBTS), related disorders (JSRD) and Meckel syndrome (MKS) are ciliopathies. We now report that MKS2 and JBTS2 loci are allelic and due to mutations in TMEM216, encoding an uncharacterized tetraspan transmembrane protein. JBTS2 patients displayed frequent nephronophthisis and polydactytly, and two cases conformed to the Oro-Facio-Digital type VI phenotype, whereas skeletal dysplasia was common in MKS fetuses. A single p.R73L mutation was identified in all patients of Ashkenazi Jewish descent (n=10). TMEM216 localized to the base of primary cilia, and loss of TMEM216 in patient fibroblasts or following siRNA knockdown caused defective ciliogenesis and centrosomal docking, with concomitant hyperactivation of RhoA and Dishevelled. TMEM216 complexed with Meckelin, encoded by a gene also mutated in JSRD and MKS. Abrogation of tmem216 expression in zebrafish led to gastrulation defects that overlap with other ciliary morphants. The data implicate a new family of proteins in the ciliopathies, and further support allelism between ciliopathy disorders.
PMCID: PMC2894012  PMID: 20512146
7.  Nuclear β-Catenin Induces an Early Liver Progenitor Phenotype in Hepatocellular Carcinoma and Promotes Tumor Recurrence 
The American journal of pathology  2009;176(1):472-481.
Transforming growth factor-β cooperates with oncogenic Ras to activate nuclear β-catenin during the epithelial to mesenchymal transition of hepatocytes, a process relevant in the progression of hepatocellular carcinoma (HCC). In this study we investigated the role of β-catenin in the differentiation of murine, oncogene-targeted hepatocytes and in 133 human HCC patients scheduled for orthotopic liver transplantation. Transforming growth factor-β caused dissociation of plasma membrane E-cadherin/β-catenin complexes and accumulation of nuclear β-catenin in Ras-transformed, but otherwise normal hepatocytes in p19ARF−/− mice. Both processes were inhibited by Smad7-mediated disruption of transforming growth factor-β signaling. Overexpression of constitutively active β-catenin resulted in high levels of CK19 and M2-PK, whereas ablation of β-catenin by axin overexpression caused strong expression of CK8 and CK18. Therefore, nuclear β-catenin resulted in dedifferentiation of neoplastic hepatocytes to immature progenitor cells, whereas loss of nuclear β-catenin led to a differentiated HCC phenotype. Poorly differentiated human HCC showed cytoplasmic redistribution or even loss of E-cadherin, suggesting epithelial to mesenchymal transition. Analysis of 133 HCC patient samples revealed that 58.6% of human HCC exhibited strong nuclear β-catenin accumulation, which correlated with clinical features such as vascular invasion and recurrence of disease after orthotopic liver transplantation. These data suggest that activation of β-catenin signaling causes dedifferentiation to malignant, immature hepatocyte progenitors and facilitates recurrence of human HCC after orthotopic liver transplantation.
PMCID: PMC2797905  PMID: 20008139
8.  Crucial function of histone deacetylase 1 for differentiation of teratomas in mice and humans 
The EMBO Journal  2010;29(23):3992-4007.
Crucial function of histone deacetylase 1 for differentiation of teratomas in mice and humans
Although histone deacetylases are generally known as pro-tumourigenic factors, loss of HDAC1 is here shown to promote proliferation and inhibit differentiation in a mouse teratoma model, at least partly via regulation of the transcription factor SNAIL1.
Histone deacetylase (HDAC) inhibitors induce cell cycle arrest, differentiation or apoptosis in tumour cells and are, therefore, promising anti-cancer reagents. However, the specific HDAC isoforms that mediate these effects are not yet identified. To explore the role of HDAC1 in tumourigenesis and tumour proliferation, we established an experimental teratoma model using wild-type and HDAC1-deficient embryonic stem cells. HDAC1-deficient teratomas showed no significant difference in size compared with wild-type teratomas. Surprisingly, loss of HDAC1 was not only linked to increased apoptosis, but also to significantly enhanced proliferation. Epithelial structures showed reduced differentiation as monitored by Oct3/4 expression and changed E-cadherin localization and displayed up-regulated expression of SNAIL1, a regulator of epithelial cell plasticity. Increased levels of the transcriptional regulator SNAIL1 are crucial for enhanced proliferation and reduced differentiation of HDAC1-deficient teratoma. Importantly, the analysis of human teratomas revealed a similar link between loss of HDAC1 and enhanced tumour malignancy. These findings reveal a novel role for HDAC1 in the control of tumour proliferation and identify HDAC1 as potential marker for benign teratomas.
PMCID: PMC3020644  PMID: 20967026
cancer treatment; chromatin; epigenetics; HDAC inhibitors; histone modifications
9.  The transcription factor ZEB1 (δEF1) represses Plakophilin 3 during human cancer progression 
FEBS letters  2007;581(8):1617-1624.
Plakophilin 3 (PKP3) belongs to the p120ctn family of armadillo-related proteins predominantly functioning in desmosome formation. Here we report that PKP3 is transcriptionally repressed by the E-cadherin repressor ZEB1 in metastatic cancer cells. ZEB1 physically associates with two conserved E-box elements in the PKP3 promoter and partially represses the activity of corresponding human and mouse PKP3 promoter fragments in reporter gene assays. In human tumours ZEB1 is upregulated in invasive cancer cells at the tumour–host interface, which is accompanied by downregulation of PKP3 expression levels. Hence, the transcriptional repression of PKP3 by ZEB1 contributes to ZEB1-mediated disintegration of intercellular adhesion and epithelial to mesenchymal transition.
PMCID: PMC2938730  PMID: 17391671
Epithelial to mesenchymal transition; Invasion; Transcription; Desmosomes; Cell adhesion

Results 1-9 (9)