Interdependent fibroblast growth factor and activin A signaling promotes the expression of endodermal genes in differentiating mouse embryonic stem cells expressing Src Homology 2-domain inactive Shb.

The mechanisms controlling endodermal development during stem cell differentiation have been only partly elucidated, although previous studies have suggested the participation of fibroblast growth factor (FGF) and activin A in these processes. Shb is a Src homology 2 (SH2) domain-containing adapter protein that has been implicated in FGF receptor 1 (FGFR1) signaling. To study the putative crosstalk between activin A and Shb-dependent FGF signaling in the differentiation of endoderm from embryonic stem (ES) cells, embryoid bodies (EBs) derived from mouse ES cells overexpressing wild-type Shb or Shb with a mutated SH2 domain (R522K-Shb) were cultured in the presence of activin A. We show that expression of R522K-Shb results in up-regulation of FGFR1 and FGF2 in EBs. Addition of activin A to the cultures enhances the expression of endodermal genes primarily in EBs expressing mutant Shb. Inhibition of FGF signaling by the addition of the FGFR1 inhibitor SU5402 completely counteracts the synergistic effects of R522K-Shb and activin A. In conclusion, the present results suggest that expression of R522K-Shb enhances certain signaling pathways downstream of FGF and that an interplay between FGF and activin A participates in ES cell differentiation to endoderm.

Expression of liver-enriched nuclear factors and their isoforms in alpha-fetoprotein-producing gastric carcinoma cells.

Alpha-fetoprotein (AFP)-producing gastric cancer (AFP-GC) is a highly malignant variant of adenocarcinoma with aberrant hepatocellular phenotype. A detailed understanding of the regulation of its liver phenotype is lacking. Liver-enriched nuclear factors (LENFs) are implicated in the transcriptional regulation of AFP in the fetal liver. To investigate the regulatory role of LENFs in AFP-GCs, the expression of LENFs including CCAAT/enhancer binding protein (C/EBP)-beta, C/EBP-alpha, hepatocyte nuclear factor (HNF)-1alpha, HNF-1beta and HNF-4alpha was investigated in 3 cell lines of AFP-GC and 7 cell lines of control GC. The liver activating protein (LAP), an activating isoform of C/EBP-beta, was predominantly expressed in AFP-GCs, whereas the liver inhibitory protein (LIP), an inhibitory isoform of C/EBP-beta, predominated in the control GCs. HNF-1alpha was relatively suppressed in AFP-GCs. HNF-4alpha was expressed in one of three AFP-GC cell lines. C/EBP-alpha and HNF-1beta were expressed at the same levels in both cell types of GC. AFP-GCs expressed a set of hepatocyte-related proteins (e.g., transferrin and albumin) while they still retained the several glandular cell-related proteins (e.g., MUC2). The induction of LIP reduced transferrin expression and induced CEA expression in an AFP-GC line. Collecting these results, it was suggested that the contribution of LENFs, especially isoforms of C/EBP-beta, is possibly important in phenotypic regulation of AFP-GCs.