摘要 : The signaling pathway involved in low density lipoprotein (LDL) receptor gene expression induced by tile phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) was investigated in the human hepatoma HepG2 cell line. Treatment of... 展开 The signaling pathway involved in low density lipoprotein (LDL) receptor gene expression induced by tile phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) was investigated in the human hepatoma HepG2 cell line. Treatment of HepG2 cells with 100 nM TPX resulted in an approximately 20-fold increase in LDL receptor MRNA level, as determined by RT-PCR, which peaked at 2-4 of treatment and subsequently declined. Tile protein kinase C (PRC) inhibitors calphostin C and staurosporine prevented TPX-mediated LDL receptor mRNA induction. In contrast, TPA did not affect squalene synthase mRNA expression, Immunoblotting of cell extracts with isozyme-specific PKC antibodies revealed that HepG2 cells expressed PKC alpha, which was mainly cytosolic, and PKC beta, PK epsilon, and PKC zeta, all of which were present in both the cytosolic and particulate fractions. Treatment of HepG2 cells with 100 nM TPA resulted in translocation of cytosolic PKC alpha to the particulate fraction, with a maximum at SO min-2 h of treatment, but was without effect on tile subcellular distribution of the other isozymes. TPX treatment also led to activation of the mitogen-activated protein kinase (MAPK) ERK cascade. The specific MAPK pathway inhibitor PD98059 blocked TPA-induced ERK activation. Furthermore, pretreatment of cells with PD98059 inhibited TPA-induced LDL receptor mRNA induction. Mat-cover, pretreatment of cells with calphostin C inhibited TPA-mediated ERK activation and LDL receptor-mRNA induction in a dose-dependent fashion LDL Based on a close kinetic correlation between PKC alpha translocation and ERR activation, and the erects of specific inhibitors, these findings suggest that translocation/activation of PRC(x. and subsequent activation of the Raf-1/MEK/ERK MAPK cascade, represent kev events in the transcriptional induction of LDL receptor-gene by TPA in HepG2 cells. [References: 46] 收起