the invention relates to a use of an urushiol compound in preparation of pharmaceutical compositions for inhibiting smad3 phosphorylation . we verify that gq - 5 inhibited the interaction of smad3 with tgf - β type i receptor , inhibited subsequent phosphorylation of smad3 , reduced nuclear translocation of smads complex , and suppressed the transcription of major fibrotic genes such as α - smooth muscle actin , collagen i and fibronectin . therefore , gq - 5 could be a potent and selective inhibitor of tgf - β1 - induced smad3 phosphorylation , and be used to prepare pharmaceutical compositions for inhibiting smad3 phosphorylation .