Transgenic overexpression of Tcfap2c/AP-2gamma results in liver failure and intestinal dysplasia.

BACKGROUND: The transcription factor Tcfap2c has been demonstrated to be essential for various processes during mammalian development. It has been found to be upregulated in various undifferentiated tumors and is implicated with poor prognosis. Tcfap2c is reported to impinge on cellular proliferation, differentiation and apoptosis. However, the physiological consequences of Tcfap2c-expression remain largely unknown. METHODOLOGY/PRINCIPAL FINDINGS: Therefore we established a gain of function model to analyze the role of Tcfap2c in development and disease. Induction of the transgene led to robust expression in all tissues (except brain and testis) and lead to rapid mortality within 3-7 days. In the liver cellular proliferation and apoptosis was detected. Accumulation of microvesicular lipid droplets and breakdown of major hepatic metabolism pathways resulted in steatosis. Serum analysis showed a dramatic increase of enzymes indicative for hepatic failure. After induction of Tcfap2c we identified a set of 447 common genes, which are deregulated in both liver and primary hepatocyte culture. Further analysis showed a prominent repression of the cytochrome p450 system, PPARA, Lipin1 and Lipin2. These data indicate that in the liver Tcfap2c represses pathways, which are responsible for fatty acid metabolism. In the intestine, Tcfap2c expression resulted in expansion of Sox9 positive and proliferative active epithelial progenitor cells resulting in dysplastic growth of mucosal crypt cells and loss of differentiated mucosa. CONCLUSIONS: The transgenic mice show that ectopic expression of Tcfap2c is not tolerated. Due to the phenotype observed, iTcfap2c-mice represent a model system to study liver failure. In intestine, Tcfap2c induced cellular hyperplasia and suppressed terminal differentiation indicating that Tcfap2c serves as a repressor of differentiation and inducer of proliferation. This might be achieved by the Tcfap2c mediated activation of Sox9 known to be expressed in intestinal and hepatic stem/progenitor cell populations.

The transcription factor TCFAP2C/AP-2gamma cooperates with CDX2 to maintain trophectoderm formation.

In mammals, cell lineage specification is established at the blastocyst stage. At this stage, transcription factor Cdx2 represses pluripotency genes, thus promoting extraembryonic trophoblast fate. Recently, transcription factor Gata3 was shown to act in a parallel pathway in promoting trophoblast cell fate, suggesting that there are more factors working in the trophoblast lineage. Here, we report that the transcription factor Tcfap2c is expressed at a high level in the trophectoderm and is able to induce trophoblast fate in embryonic stem cells. Trophoblast fate induced by Tcfap2c does not require Cdx2 and vice versa, suggesting that the molecules act in alternative pathways. However, both Tcfap2c and Cdx2 are required for the upregulation of Elf5, a marker of trophoblast stem cell maintenance, suggesting that both factors are required for stable trophoblast induction. Tcfap2c-induced trophoblast-like cells are stable in long-term culture, indicating that they are capable of self-renewal. Tcfap2c-controlled trophoblast maintenance involves the induction of Cdx2 and the repression of the pluripotency factor Nanog. Tcfap2c-induced trophoblast-like cells differentiate to trophoblast derivatives in vitro and contribute to the trophectoderm in blastocysts in vivo. Taken together, these observations suggest that Tcfap2c and Cdx2 cooperate to override the pluripotency program and establish the extraembryonic trophoblast maintenance program in murine embryos.