The roles of mitogen-activated protein kinase (MAPK) activation in immobilized Taxus cuspidata cells were investigated. Western blot analysis showed that the immobilized cultures enhanced the activation of extracellular signal-regulated kinase-like (ERK-like, approximately 46kDa) MAPK in T. cuspidata cells in their lag and stationary growth phases, but reduced the ERK-like MAPK activation of the cells in their exponential growth phase compared with the freely suspended cultures. From outer to central zone in the immobilization support matrices, the down regulation of the ERK-like MAPK activation in the 20-day-old immobilized cells was accompanied by marked decrease in mitotic index, increases in the amount of lignified cells and Taxol (paclitaxel) yield. The MEK-specific inhibitor (PD98059) inhibited cell growth, increased the amount of lignified cells and the total Taxol content when inhibiting the ERK-like MAPK activation of T. cuspidata cells. These results suggest that the ERK-like MAPK activation may play important roles in regulation of cell proliferation and differentiation of immobilized T. cuspidata cells, which seem to be related to the Taxol production of the immobilized T. cuspidata cells. (c) 2006 Elsevier Inc. All rights reserved.