ABSTRACT
Objective To study the enzymatic progress of amyloid precursor protein (APP), and construct the recombinant eukaryotic expression plasmid encoding the double mutations of APP and 2 different types of fluorescent protein. Methods The last 300 bases of APP named as C99 containing APP717 mutation was amplified by polymerase chain reaction (PCR) with the template pcDNA3.0-APP.The cyan and yellow fluorescence sequences named as CFP and YFP respectively were obtained by PCR with the template of digestion of the plasmid pcDNA3.0-CFP-CaM-YFP.The 54 bases in the middle of APP named as 54 bp containingSwedish mutation were synthesized. The 4 fragments, CFP, YFP, C99 and 54 bp were inserted into the vector pcDNA3.0.By genetic engineering the recombinant plasmid pcDNA3.0-CFP-54bp-YFP-C99 and pcDNA3.0-CFP-54bp-YFP were constructed and finally identified by enzyme digestion, PCR and sequencing. Then the 2 constructs were transfected into SH-SY5Y cells respectively. The expression of the fusion gene was examined by multi-photon con-focal microscopy and the fluorescence resonance energy transfer (FRET) signal was collected. The amyloid beta (Aβ)deposition was detected by immunocytochemistry. Results (1) DNA sequencing showed that the sequence of the construct was correct.(2)The cyan and yellow fluorescence could be seen by the multi-photon con-focal fluorescence microscopy. The fusion gene could be correctly expressed.(3)FRET was present in the cells expressing CFP-54bp-YFP,but absent in the cells expressing CFP-54bp-YFP-C99.(4)A13 labeled by YFP was detected by multi-photon con-focal microscope and deposited in the cytoplasm, membrane and in the intercellular space.(5)It was shown that by immunocytochemistry, the CFP-54bp-YFP-C99 expressionproduct could generate Aβ. The Aβ deposition was detected in the cell membrane, cytoplasma and intercellular space. Conclusions (1) The fusion protein could generate Aβ peptide by β and γ proteolytic processing.(2)Aβ may be generated in the conrse of APP transportation from cell plasma to cell membrane.(3)C99 is very important for the correct cleavage of APP. Our test data strongly suggest that C99 may function as the signal-like peptide. It may guide and direct the APP to the right location for the cleavage.(4)Before the Aβ deposition is formed outside of the cell, Aβ intracellular accumulation results in the change of cell shape.