Epidermal growth factor down-regulates the expression of human hepatic stimulator substance via CCAAT/enhancer-binding protein β in HepG2 cells

MASS (human hepatic stimulator substance), acting as a hepatotrophic growth factor, promotes liver regeneration However. the regulatory mechanisms for hHSS transcription are still poorly understood. In the present study, we investigated transcription of hHSS triggered by EGF (epidermal growth factor) and the role of C/EBP beta (CCAAT/enhancer-binding protein beta) as a potential core factor responsible for hHSS transcription in HepG2 cells. The results show that EGF. suppresses hHSS mRNA expression at early time. points. Using a promoter deletion assay, we identified a proximal region (-358/-212) that is required for EGF suppression. Overexpression of C/EBP beta enhances EGF suppression of hHSS, and mutation of the C/EBP beta-binding site at -292/-279 or siRNA (short interfering RNA) interference abolishes EGF suppression. Furthermore, using an electrophoretic mobility-shift assay and chromatin immunoprecipitation analysis, we found that C/EBP beta specifically binds to the -292/-279 site that is responsible for EGF Inhibition Moreover, using a knockin (overexpression) and knockdown strategy (siRNA). we confirmed that C/EBP beta is a key factor responsible for inhibition of hHSS mRNA expression. Pre-treatment with an inhibitor of JNK (c-Jun N-terminal kinase) or down-regula ion of JNK1 with specific siRNA reverses EGF-inhibited hHSS expression Our results provide a crucial regulatory mechanism for EGF in hHSS transcription within the promoter proximal region.