MAPK inhibitors differently modulate TGF-β/Smad signaling in HepG2 cells.

The aim of this study was to investigate the mitogen-activated protein kinase (MAPK) pathway, which crosstalk with TGF-β/Smad signaling via linker phosphorylation of Smad2/3 to promote hepatocarcinogenesis. After DEN-induced hepatocellular carcinoma (HCC) in rats showed increased phosphorylation of JNK1/2, p38, and ERK1/2, we next antagonized TGF-β1-induced phosphorylation of JNK1/2, p38, ERK1/2, Smad2/3 signaling in HepG2 cells using SP600125, SB203580, and PD98059, respectively. Cell proliferation and invasion were assessed by MTT assay and transwell invasion chambers, respectively. Smad2/3, Smad4, and Smad7 expressions and PAI-1 messenger RNA (mRNA) transcription were measured by using immuno-precipitation/immuno-blotting and real-time RT-PCR, respectively. All the MAPK-specific inhibitors suppressed cell invasion, while all but PD98059 suppressed cell proliferation. Both SP600125 and SB203580 blocked pSmad2C/L and oncogenic pSmad3L. PD98059 blocked pSmad2L but had no effect on elevated pSmad2C and oncogenic pSmad3L. All but PD98059 blocked Smad2/3/4 complex formation and restored Smad7 expression, while all the three MAPK-Specific inhibitors repressed PAI-1 mRNA transcription. Both SP600125 and SB203580 inhibited HepG2 cells' proliferation and invasion by blocking oncogenic pSmad3L and Smad2/3/4 complex formation. PD98059 repressed PAI-1 mRNA by an unknown mechanism.