Figure 2. 14-3-3ζ promotes PKA-catalyzed Ser²⁶² tau phosphorylation in PC12 and HEK-293 cells.

(A) NGF does not activate PKA in PC12 cells. PC12 cells were treated with forskolin, NGF, or vehicle for 24 hr. Treated cells were lysed and each lysate was assayed for PKA or Cdk5 activity using the respective peptide substrate. Values are the average of three determinations from three cultures, and are expressed as the fold change from vehicle-treated control cells. *p<0.005 with respect to vehicle treated cells. (B) Disruption of 14-3-3ζ function inhibits tau phosphorylation at Ser²⁶² in NGF-exposed PC12 cells. PC12 cells transfected with Myc-14-3-3ζ (K49N) or empty vector were exposed to NGF for 24 hr and then analyzed by Western blotting as in Figure 1. Values with standard error are the average of three determinations from three cultures. **p < 0.001 with respect to vector transfected and NGF-treated cells. (C) 14-3-3ζ promotes PKA-catalyzed tau Ser²⁶² phosphorylation in HEK293 cells. HEK293 cells co-transfected with Flag-tau and Myc-14-3-3ζ were analyzed by Western blotting. The relative amount of Ser²⁶² phosphorylated tau was determined by normalizing the Ser²⁶² band in each lane to the respective Flag-tau band. Values with standard error are the average of three determinations from three cultures. *p < 0.005 with respect to cells transfected with Flag-tau and Myc-PKAc.