Energy metabolism and protein phosphorylation during apoptosis: a phosphorylation study of tau and high-molecular-weight tau in differentiated PC12 cells

Apoptosis has been characterized as a regulated, energy-dependent process. Specific protein-phosphorylation events have been demonstrated previously t o occur during apoptosis and may play an important role in the regulation o f this death process. In this study, energy metabolism and protein phosphor ylation during apoptosis of neuronal PC 12 cells induced by nerve growth fa ctor and serum deprivation was examined using [P-32]P-i-labelling technique s. Although ATP levels were maintained at control levels during apoptosis, [32P]P-i incorporation into ATP was decreased significantly, coinciding wit h an almost identical decrease in Na+-dependent phosphate uptake. During ne uronal PC 12-cell apoptosis, increased phosphorylation of tau and high-mole cular-weight (HMW) tau was observed within the epitope of Tau-l, a phosphat e-dependent tau antibody that only recognizes the unphosphorylated form of its epitope. In addition, based on two-dimensional phosphopeptide mapping, [P-32]P-i incorporation into a phosphopeptide of tau and HMW tau from apopt otic cells increased. Whereas [32P]P-i incorporation into total protein dec reased to 23% of the control during apoptosis, [P-32]P-i incorporation into tau and HMW tau was significantly higher, indicating a preferential phosph orylation of specific proteins during the apoptotic process. This study pro vides novel information about phosphate uptake, incorporation of [32P]P-i i nto ATP, and protein phosphorylation events during apoptosis.