Cyclic AMP-dependent protein phosphorylation in isolated neuronal growth cones from developing rat forebrain

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• Neuronal growth cones possess adenylate cyclase activity, producing cyclic AMP.
• Cyclic AMP can be stimulated by neurotransmitters and forskolin.
• Understanding cyclic AMP-mediated mechanisms is crucial for neuronal development.

Purpose of the Study:

• To investigate cyclic AMP-dependent protein phosphorylation in isolated neuronal growth cones.
• To identify specific phosphoproteins regulated by cyclic AMP.
• To elucidate the role of these proteins in growth cone function.

Main Methods:

• One-dimensional and two-dimensional gel electrophoresis.
• Analysis of 32P incorporation into phosphoproteins.
• Isoelectric focusing and nonequilibrium electrophoresis.
• Immunoprecipitation and peptide digest experiments.

Main Results:

• Cyclic AMP analogs increased 32P incorporation into phosphoproteins (50-58 kDa and 76-82 kDa), notably 82, 76, and 51 kDa.
• Two-dimensional electrophoresis identified phosphorylated alpha- and beta-tubulin, actin, a 93 kDa acidic protein, and two proteins (x and x') near beta-tubulin.
• Proteins x and x' were highly enriched in growth cones and showed enhanced phosphorylation, distinct from beta-tubulin.
• Nonequilibrium electrophoresis revealed enhanced phosphorylation of 79/75 kDa doublet, 74 kDa, and 58 kDa doublet proteins.

Conclusions:

• Cyclic AMP significantly influences protein phosphorylation in neuronal growth cones.
• Specific phosphoproteins, including tubulin and novel proteins x and x', are key targets of cyclic AMP signaling.
• These findings provide insights into the molecular mechanisms underlying neuronal growth cone function and development.