Alzheimer's disease-associated presenilin 1 in neuronal cells: evidence for localization to the endoplasmic...

The recently identified Alzheimer's disease-associated presenilin 1 and 2 (PS1 and PS2) genes encode two homologous multi membrane-spanning proteins. Rabbit antibodies to the N-terminal domain of PS1 detected PS1 in human neuroblastoma SH-SY5Y wild type and PS1 transfectants (SY5Y-PS1) as well as in mouse P19, in CHO-K1 and CHO-APP770 transfected cells, in rat cerebellar granule and hippocampal neurons, and astrocytes. Immunoblotting detected full-length protein of 50 kDa, and a major presumptive cleavage product of 30 kDa. The immunofluorescence pattern resembled labeling of the endoplasmic reticulum-Golgi intermediate compartment (ERGIC) marker protein ERGIC-53. PS1 distribution showed slight condensation after brefeldin A and more marked condensation after incubation of cells at 16 degrees C, characteristic of the ERGIC compartment. Double labeling showed colocalization of ERGIC-53 with PS1 in the SY5Y-PS1 cells. PS1 labeling of SY5Y-PS1 and P19 cells showed overlap of the cis-Golgi marker p210 and colocalization with p210 after brefeldin A which causes redistribution of p210 to the ERGIC. Expression of PS1 did not change in level or cellular distribution during development of neurons in culture. Double labeling for the amyloid precursor protein (APP) and PS1 on SY5Y-PS1 cells and CHO-APP770 cells showed some overlap under control conditions. These results indicate that PS1 is a resident protein of the ERGIC and could be involved in trafficking of proteins, including APP, between the ER and Golgi compartments.