The secretion of soluble amyloid beta precursor protein (AβPPS)by chick neurons in serum-free primary culture is not regulated by protein kinase C

The metabolism of amyloid precursor protein (A beta PP) in chick neurons cultured in serum-free medium is described. A beta PP immunoreactivity, detected with the 22C11 antibody, was seen at similar to 135 and similar to 120 kDa. A beta PPs (similar to 120 kDa) was released from the cells and could be detected in the culture medium without the need of a purification step. The content of A beta PPs increased with time after medium change, but was not affected by either carbachol (100 mu M), glutamate (50 mu M), veratrine (20 mu M), oleic acid (200 mu M), A23187 (5 mu M), phorbol 12,13-dibutyrate (PDBu, 1 mu M), staurosporine (1 mu M), Go 6976(1 mu M) or okadaic acid (50 nM) although the combination of PDBu and okadaic acid reduced the secretion. Addition of the muscarinic receptor agonist carbachol to the neurons increased the rate of phosphoinositide breakdown. In Western blot experiments using antibodies to the alpha, beta II and epsilon isoforms of protein kinase C and conditions whereby robust signals could be seen with rat brain lysates, no immunoreactive bands that could be inhibited by appropriate positive control peptides were seen. It is concluded A beta PPs production by chick neurons in culture is mainly constitutive in nature.