Oligomeric β‐amyloid(1‐42) induces the expression of Alzheimer disease‐relevant proteins in cholinergic SN56.B5.G4 cells as revealed by proteomic analysis

Alzheimer's disease (AD) is characterized by cholinergic dysfunction and progressive basal forebrain cell loss which has been hypothesized to be associated with extensive accumulation of β‐amyloid (Aβ). To reveal whether oligomeric Aβ displays a particular toxicity for cholinergic neurons, the cholinergic cell line SN56.B5.G4 (SN56) was used as a model. Recently performed microarray analyses demonstrated that genes affected by exposure of SN56 cells with 50 μM oligomeric Aβ(1‐42) for 24 h were involved in protein modification and degradation [Heinitz, K., Beck, M., Schliebs, R., Perez‐Polo, J.R., 2006. Toxicity mediated by soluble oligomers of beta‐amyloid(1‐42) on cholinergic SN56.B5.G4 cells. J. Neurochem. 98, 1930–1945]. Using a proteomic approach, we compared the levels of proteins and specially of phosphorylated proteins in cytosolic fractions of cell lysates from cholinergic SN56 cells exposed to 50 μM Aβ(1‐42) for 24 h to those in control incubations. We show here that the levels of calreticulin, and mitogen‐activated protein kinase (MAPK) kinase 6c were up‐regulated in cholinergic SN56 cells exposed to Aβ(1‐42), while γ‐actin appeared down‐regulated. Aβ(1‐42) exposure of cholinergic SN56 cells led to decreased phosphorylation of phosphoproteins, such as the Rho GDP dissociation inhibitor, the ubiquitin carboxyl terminal hydrolase‐1, and the tubulin α‐chain isotype Mα6, as compared to untreated control lysates. The proteins identified have also been reported to be affected in brains of AD patients, suggesting a potential role of Aβ in influencing the integrity and functioning of the proteome in AD.