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Research Objective The
objective of the Lab centers around the functional analysis of the family of
AP-2 transcription factors. In mice and men 5 different genes have been
described, named AP-2 alpha, beta, gamma, delta and epsilon. They all share a
unique helix-span-helix domain mediating DNA binding and, together with a
central, basic domain, dimerization of the Protein. AP-2 genes can be found
expressed in trophectodermal, neural, neural crest and basal cells of the skin
during embryogenesis (reviewed in Hilger-Eversheim et al., 2000 and Eckert et
al., 2005). So far, three out of five AP-2 genes have been knocked out by us and others (Werling and Schorle, 2002b, Schorle et al., 1996; Zhang et al., 1996, Moser et al., 1997). All knockout animals display lethal phenotypes, highlighting the importance of this transcription factor family for embryogenesis. Mice deficent for AP-2alpha develop cranio-abdominoschisis, AP-2beta deficient mice suffer from polycystic kidney failure and mice without AP-2gamma die early after implantation owing to a defect of the cells of the trophectoderm (TE) lineage. Recently, we showed, that forced epression of AP-2gamma in murine ES cells is sufficient for induction of trophectoderm-like fate in vitro (Kuckenberg et al, 2010). Hence we propose, that AP-2gamma (a.k.a. Tcfap2c, Tfap2c) is an important regulator of early lineage specification. The
TE-lineage is quite different from somatic lineages regarding gene expression,
methylation and imprinting. Early genetic programmes establish TE-fate in direct
competition to the pluripotent inner cell mass. These factors (Tead4, Cdx2,
Gata3) directly repress pluripotency genes like Oct3/4 and Nanog. We addressed
the question, whether it would be possible to convert cells from the TE-lineage
(Trophectoderm stem cells, TSC) into pluripotent somatic cells. Using the 'standard'
reprogramming factors Oct3/4, Sox2, c-Myc and Klf4, we demonstrated, that such 'lineage
conversion' or reprogramming is possible, indicating that the repressive role of
the TE-factors can be overcome (Kuckenberg, Mol. Cell. Biol, 2011).
Since overexpression of AP-2 genes can be detected in various human tumors, we addressed the question whether overexpression of AP-2gamma leads to hyperproliferation and thus to cancer (Jager et al., 2003).From these experiments we conclude, that overexpression of AP-2gamma might be involved in tumor progression rather than tumor initiation. Data from experiments using MMTV-neu/MMTV-AP-2gamma double transgenic mice support our hypothesis: Tumors of double transgenic mice display a more rapid progression towards malignancy compared to MMTV-neu single-transgenic controls (Jager et al., 2005).Using an 'in vitro' model, we showed that interference with AP-2 proteins renders mammary tumor cells more susceptible to irradiation and chemotherapeutic drugs (Thewes et al., 2010). In humans,
AP-2gamma has not only been detected in gonocytes during fetal development but
also in classical seminomas (Pauls et al., 2005). These data indicate, that
AP-2gamma might control genetic pathways important in gonocyte maintenance and
seminoma formation. Mice with conditional mutation of AP-2 genes have been
established and will help in further dissecting the cell type specific roles of
this gene family (Werling and Schorle, 2002a). Another line of experiments centers around germ cell tumors. Here we utilize the cell line TCam-2, a cell line which has been derived from a seminoma patient to address the functional consequences of loss and gain of genes which are implicated in the aetiology of this class of germ cell tumors (cKIT, AP-2gamma, NANOG, BLIMP1). Further, interference with global DNA methylation and/or histone modification in TCam-2 cells will bring insight in epigenetic control of pluripotency/differentiation programmes in these cells (Nettersheim, 2011).
References
(see Publications page)
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Questions, comments and reprint requests to: hubert.schorle@ukb.uni-bonn.de
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