The expression level of human granurocytes macrophage colony stimulating factor (hGM-CSF) mRNA in Chinese hamster ovary (CHO) DR1000L4N cells increased by 24% with pressurization. Treatment of cells with chelerythrine chloride (10 nM, 15 min), an inhibitor of protein kinase C (PKC), did not suppress the pressure-induced (0.9 MPa) expression of hGM-CSF mRNA, while it decreased the hGM-CSF gene expression level at normal pressure (0.1 MPa). Treatment with U0126 (20 muM, 60 min), a specific inhibitor of extracellular signal-related kinase (ERK1/2), decreased the expression level of hGM-CSF mRNA at 0.1 MPa to 80% of that without U0126 treatment. Similarly, treatment with U0126 decreased the pressure-induced (0.9 MPa) expression level of hGM-CSF mRNA to 79% of the control expression level at 0.1 MPa without treatment. The amount of intracellular phosphorylated ERK1/2 increased with pressurization (0.9 MPa). These results suggest that the pressure-induced expression of hGM-CSF mRNA in CHO DR1000L4N cells depends not on PKC but on the ERK1/2 signaling cascade.