Samuel E. Gandy

Phosphorylation of Alzheimer amyloid precursor protein by protein kinase C

The beta/A4 amyloid precursor protein is a membrane protein with one transmembrane domain. The accumulation and deposition of beta/A4 amyloid protein in Alzheimers disease is thought to be brought about by altered processing of beta/A4 amyloid precursor protein. Activation of protein kinase C and/or inhibition of protein phosphatases 1 and 2A results in an increase in the proteolytic processing and secretion of beta/A4 amyloid precursor protein. These effects might result either from phosphorylation of beta/A4 amyloid precursor protein by protein kinase C or from phosphorylation of components of the beta/A4 amyloid precursor protein processing apparatus. We have previously reported phosphorylation by protein kinase C of a synthetic peptide corresponding to part of the cytoplasmic domain of beta/A4 amyloid precursor protein. However, it was not known whether beta/A4 amyloid precursor protein holoprotein was phosphorylated in its native conformation in the cell membrane. Using a PC12 (rat pheochromocytoma) semi-intact cell system, we now report that mature isoforms of beta/A4 amyloid precursor protein are phosphorylated by protein kinase C at Ser655. Five COOH-terminal fragments which are generated by processing of mature beta/A4 amyloid precursor protein were also phosphorylated by protein kinase C at Ser655. The results support the idea that the beta/A4 amyloid precursor protein haloprotein is a physiological substrate for protein kinase C. These observations should facilitate our understanding of the relationship between altered protein phosphorylation and beta/A4 amyloid production.

Protein Phosphorylation Regulates Relative Utilization of Processing Pathways for Alzheimer β/A4 Amyloid Precursor Proteina

The Alzheimer amyloid precursor protein (APP) is a phosphoprotein, and the phosphorylation state of APP at Ser655 can be regulated by protein kinase C, calcium/calmodulin‐dependent protein kinase II, and okadaic acid‐sensitive protein phosphatases. Other enzymes may also play a role at Ser655 of APP and, perhaps, at other residues.

The nature and metabolism of potentially amyloidogenic carboxyl-terminal fragments of the Alzheimer βA4-amyloid precursor protein: Some technical notes

The proteolytic processing and secretion of APP are regulated by protein phosphorylation, especially via protein kinase C and protein phosphatases 1 and/or 2A. Our studies of these regulatory mechanisms have led us to perform extensive experimentation on the metabolism of APP carboxyl-terminal fragments, using as our system either untransfected, undifferentiated rat pheochromocytoma (PC12) cells or APP-baculovirus infected Sf9 cells. We have not assayed APP fragments for biological activity in either system. However, we have made potentially relevant observations regarding APP carboxyl-terminal fragment trafficking. In this note, we review our published and unpublished data in relation to published reports from other laboratories using related systems.

Protein Phosphorylation Regulates the Cellular Trafficking and Processing of the Alzheimer Beta/A4 Amyloid Precursor Protein

Cerebral deposition of the beta/A4 amyloid peptide is an important feature of Alzheimer disease. The beta/A4 peptide is derived from the amyloid precursor protein (APP), a transmembrane glycoprotein whose function is unknown. Abnormal processing of APP has been causally linked to Alzheimer disease since mutations in the coding sequence of APP are associated with an inherited early-onset form of the disease. We have employed the rat neuroendocrine PC12 cell line to examine the normal cellular trafficking and proteolytic processing of APP and to investigate the role of protein phosphorylation in the regulation of normal and aberrant APP metabolism.