Effect of MAPK/Erk and PI3K/Akt pathway inhibitors on MMP secretion. HME cell lines expressing different levels of HER receptors were preincubated with one of the following inhibitors (20 μg/ml LY 294002, 200 nM wortmannin, 25 µM PD 98059 or 10 µM U0126) for 1 h, followed by the treatment with 12 ng/ml EGF for 8 h. DMSO concentration was 0.1% in all the different cell culture media except those marked as "ctrl" runs, which lacked any DMSO. CM was collected and concentration of accumulated A) MMP1, B) MMP2 and C) MMP9 in CM were detected from samples of parental HER1 cell line, HER2 and HER3 cell lines. Each ligand concentrations was normalized with respect to its concentration in the parental HER1 cells that had been treated with 12 ng/ml EGF for 8 h. Error bars represent one standard deviation from the mean of five biological replicates. The asterisks denote statistically significant differences between treated samples and ctrl runs with EGF in each cell line by both analysis of variance and Fisher's protected least significant difference analysis.