Increased expression of amyloid precursor protein and amyloid precursor-like protein 2 during trophic factor withdrawal-induced death of neuronal PC12 cells.

Programmed cell death (PCD) (apoptosis) is implicated in the neuronal cell death of Alzheimer's disease (AD). We investigated expression of amyloid precursor protein (APP) and amyloid precursor-like protein 2 (APLP2) during trophic factor deprivation-induced PCD of neuronally differentiated PC12 cells. Neuronal PC12 cells underwent PCD within two days following withdrawal of nerve growth factor (NGF) from the culture medium. Total APP mRNA levels increased gradually after 24 h, reaching levels 250% higher than those in control cells at 48 h after NGF withdrawal, and total APLP2 mRNA levels also increased similarly at 48 h. Analysis of the three major APP mRNA isoforms APP695, APP751, and APP770 by reverse transcription polymerase chain reaction showed a substantial increase in the proportion of APP770 at 48 h after NGF withdrawal. Basic fibroblast growth factor, which prevented the appearance of PCD after NGF withdrawal, inhibited the increases in APP and APLP2 mRNA levels as well as the increase in the proportion of APP770. Cellular holoprotein levels of total APP, APP containing the Kunitz protease inhibitor domain, and APLP2 also increased by approximately 60%, 100%, and 30%, respectively, at 48 h after NGF withdrawal. These data indicate that in neuronal PC12 cells undergoing PCD following trophic factor withdrawal, the syntheses of both APP and APLP2 are upregulated, and the alternative splicing of the APP gene is modified. This implies a linkage between APP and APLP2 expression and neuronal PCD.