A bryostatin-sensitive protein kinase C required for nerve growth factor activity

Area of Science:

• Cell Biology
• Molecular Biology
• Neuroscience

Background:

• Nerve growth factor (NGF) induces neuronal differentiation in PC12 cells, characterized by neurite extensions.
• Protein kinase C (PKC) plays a role in signal transduction pathways regulating cellular processes.
• Phorbol 12-myristate 13-acetate (PMA) and bryostatin are known activators of PKC.

Purpose of the Study:

• To investigate the role of bryostatin-activated protein kinase C in NGF-induced neuronal differentiation of PC12 cells.
• To determine if bryostatin affects the induction of protooncogenes c-fos and c-jun during NGF stimulation.
• To characterize the specific PKC signaling pathway involved in neurite outgrowth.

Main Methods:

• PC12 cells were treated with NGF, PMA, and bryostatin under various time courses (acute and chronic).
• Neurite outgrowth was assessed morphologically.
• Protein kinase C activity was measured in cytosolic, membrane, and nuclear fractions.
• Expression of c-fos and c-jun protooncogenes was analyzed.

Main Results:

• Chronic bryostatin treatment inhibited NGF- or bFGF-induced neurite outgrowth, unlike PMA which causes downregulation.
• Bryostatin did not block NGF-induced c-fos or c-jun expression.
• Chronic bryostatin treatment reduced PKC activity in all cellular fractions, while acute treatment increased cytosolic and nuclear PKC activity.
• Bryostatin alone or with PMA did not induce neurite outgrowth.

Conclusions:

• A specific bryostatin-sensitive protein kinase C is necessary, but not sufficient, for NGF-induced neurite outgrowth in PC12 cells.
• This PKC pathway appears to act in the nucleus and is independent of c-fos and c-jun transcription.
• Bryostatin provides a distinct tool to study PKC signaling in neuronal differentiation, separate from PMA-sensitive pathways.