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Amyloid beta peptide specifically promotes phosphorylation and nuclear translocation of the extracellular signal-regulated kinase in cultured rat cortical astrocytes.

To explore cellular signaling molecules that respond to amyloid beta protein (A beta), we investigated the effect of A beta on tyrosine phosphorylation of cellular proteins in cultured rat cortical astrocytes. Western blotting with the phosphotyrosine-specific monoclonal antibody 4G10 demonstrated that exposure of cultured rat cortical astrocytes to 20 microM A beta 1-40 or A beta 25-35 for 24 h resulted in a prominent increase in the phosphotyrosine content of 44-kDa protein. The A beta-induced increase in tyrosine phosphorylation of 44-kDa protein was blocked by U0126, a specific inhibitor of the extracellular signal-regulated kinase (ERK) kinase MEK. Western blotting with anti-phospho-ERK1/2 antibody and anti-ERK1/2 antibody demonstrated that A beta 1-40 or A beta 25-35 induced an increase in the dually (tyrosine and threonine) phosphorylated form of ERK1 and ERK2, with no change in total ERK1/2 level. In addition, immunofluorescent staining with anti-ERK1/2 antibody revealed that A beta induced a significant increase in the number of cells expressing ERK1/2 mainly in the nucleus. These results suggest that A beta specifically promotes tyrosine phosphorylation and nuclear translocation of ERK in astrocytes.