Transcriptional regulation of the human transferrin gene by GADD153 in hepatoma cells

The transcription factor CHOP/GADD153 is reportedly induced by cellular stresses such as UV light, genotoxic agents, and protein misfolding in the endoplasmic reticulum. However, the mechanism whereby induction of the GADD153 gene is linked to a downstream pathway is still unclear. Previously, we observed that a synthetic retinoid N-(4-hydroxyphenyl)retinamide (4HPR) effectively impaired cell growth and survival (induction of growth arrest and apoptosis) in human hepatoma cells, which was accompanied by over expression of GADD153. Furthermore, GADD153-transfected Hep 3B cells were growth arrested and were sensitized to drug-induced apoptosis. Thus, in this study, we used suppression subtractive hybridization (SSH) to identify GADD153 target genes that were up-regulated or down-regulated in the GADD153 transfectants. We screened 614 sequence-verified clones by Northern blotting, of which 42 genes were scored as over expressed and 17 genes as under expressed in GADD153 transfectants compared with control vector transfectants. Of those genes, 49 corresponded to known genes in public databases. Among them, we further verified that the expression of transferrin (Tf), which is a negative acute-phase protein and is essential to cell survival as a growth factor, was highly modulated by drug-induced GADD153 over expression or by in vitro transfection. GADD153 significantly antagonized the C/EBP (C/EBP-alpha, -beta, and -delta)-mediated transcriptional activation of the Tf gene. In conclusion, Tf and other target genes identified may play a functional role in the downstream pathway of GADD153.