Phosphorylation-dependent degradation of transgenic CREB protein initiated by heterodimerization

Area of Science:

• Neuroscience
• Molecular Biology
• Gene Therapy

Background:

• CREB (cyclic AMP response element binding protein) is crucial for brain functions and a potential gene therapy target.
• The stability and expression of exogenous CREB in cells are not well understood.
• Understanding CREB regulation is key for developing effective gene therapies for neurological disorders.

Purpose of the Study:

• To investigate the factors influencing the stability of exogenously expressed CREB.
• To determine the role of CREB heterodimerization and phosphorylation in its protein stability.
• To assess the in vivo expression and stability of transgenic CREB in the rat brain.

Main Methods:

• Transient expression assays in 293 human embryonic kidney cells using CREB mutants (A-CREB, ICER) and protein kinase A activation.
• Somatic gene transfer into the rat brain using adeno-associated virus vectors with the NSE promoter.
• Analysis of CREB mRNA and protein levels in hippocampal dentate granule cells following tetanization.

Main Results:

• A-CREB and ICER expression decreased co-expressed CREB levels in HEK293 cells, an effect reversed by protein kinase A activation.
• A-CREB did not affect the expression of a CREB mutant lacking the leucine zipper domain, indicating a specific effect of heterodimerization.
• In vivo, transgenic CREB mRNA was robustly expressed, but protein levels remained low until tetanization induced CREB phosphorylation, which increased transgenic CREB protein levels.

Conclusions:

• Heterodimerization of unphosphorylated CREB with A-CREB or ICER leads to CREB protein degradation.
• CREB phosphorylation prevents degradation, stabilizing the protein both in vitro and in vivo.
• These findings provide critical insights into CREB regulation, essential for its therapeutic applications.