Analysis of ERK pathway in chronic and de novo infected GT1 cells. Approximately 20 μg of total proteins were resolved on 12% polyacrylamide gels to detect the levels of phosphorylated forms of ERK 1/2, MEK 1/2 and src family proteins. The total amount of the same proteins was determined as a control. Prions induced a general hyper-activation of ERK cascade in chronic infected GT1 cells (ScGT1) compared to uninfected cells (GT1). Levels of phospho-ERK and phospho-src proteins increased upon prion infection, whilst a decrease was found in levels of phospho-MEK (panel A). In de novo infected cells (iGT1) the levels of phospho-ERK and phospho-MEK were increased compared to mock-infected ones (cGT1), whilst a decrease of phospho-src was detected upon prion infection (panel B). Statistics were performed using Student's T-test on a set of three independent experiments; data were normalized on the total amount of proteins. * P < 0.05, ** P < 0.01 versus uninfected cells.