The amyloid-β precursor-like protein APLP2 and its relative APP are differentially regulated during neuroendocrine cell activation

The amyloid-β precursor-like protein APLP2 is structurally and functionally related to the amyloid-β precursor protein APP, the protein generally accepted to be involved in Alzheimer's disease. Since we previously observed that the levels of APP mRNA and protein were up-regulated threefold in the active intermediate pituitary melanotrope cells of black-adapted Xenopus laevis, we now decided to study the regulation of APLP2 in these physiologically inducible neuroendocrine cells. Interestingly, both the mRNA and protein levels of Xenopus APLP2 were similar in the melanotrope cells of black and white frogs. Newly synthesized APLP2 became glycosylated and sulfated, chondroitin sulfate glycosaminoglycan chains were added, and eventually the protein was proteolytically cleaved. Unlike for APP, no phosphorylated APLP2 was observed. Our results show that, although APP and APLP2 are thought to be functionally related, their responses to neuroendocrine cell activation differ, suggesting distinct roles for these proteins.