Quantitation of glycogen synthase kinase-3 sensitive proteins in neuronal membrane rafts.

We report a quantitative proteomic study to investigate the changes induced in membrane rafts by the inhibition of glycogen synthase kinase-3. Sensitive quantitation of membrane raft proteins using isobaric tagging chemistries was enabled by a novel hybrid proteomic method to isolate low-microgram (10-30 microg) membrane raft protein preparations as unresolved bands in a low-density acrylamide gel. Samples were in-gel digested, differentially tagged and combined for 2-D LC and quantitative MS. Analysis of hippocampal membrane preparations using this approach resulted in a sixfold increase in sensitivity and a threefold increase in the number of quantifiable proteins compared with parallel processing using a traditional in-solution method. Quantitative analysis of membrane raft preparations from a human neuronal cell line treated with glycogen synthase kinase-3 inhibitors SB415286 or lithium chloride, that have been reported to modulate processing of the Alzheimer amyloid precursor protein, identified several protein changes. These included decreases in lamin B1 and lamin B receptor, as well as increases in several endosome regulating rab proteins, rab5, rab7 and rab11 that have been implicated in processing of the amyloid precursor protein in Alzheimer's disease.