Effect of cAMP effectors on the maturation of wtβAPP751 in HEK293 cells, wtβAPP751-expressing HEK293 cells were cultured, metabolically labeled, and incubated in the absence (control) or presence of cAMP agonists as in Figure 1. Media were collected, diluted in 10× RIPA, and incubated overnight with FCA3542 antibodies then for 5 hr with protein-A Sepharose. Of the resulting supernatant, 500 µl was then exposed to the 207 antibody while the remainder was incubated with FCA3340 as described in Materials and Methods. After centrifugation, pellets were resuspended with the loading buffer and electrophoresed on a 16.5% Tris-tricine [Aβ40 (A) and Aβ42 (B)] or on a 8% Tris-glycine [APPα (D)]. Intracellular p10 (E) was measured after immunoprecipitation of cell lysates with B11.4 and 16.5% Tris-tricine electrophoresis as in Materials and Methods. Densitometric analysis of gel radioautographies of Aβs (C) and APPα/p10 (F) are expressed as the percent of control densitometry obtained in the absence of effector and are the means of three to four independent experiments.