Differential activation of CREB by Akt1 and Akt2

Area of Science:

• Molecular Biology
• Cell Signaling
• Biochemistry

Background:

• The Akt family of protein kinases are crucial for diverse cellular functions.
• Despite high conservation, Akt isoforms (Akt1, Akt2, Akt3) exhibit distinct in vivo roles.
• Understanding isoform-specific functions is key to deciphering complex cellular signaling pathways.

Purpose of the Study:

• To investigate and compare the abilities of Akt1 and Akt2 to activate CREB (cAMP response element-binding protein).
• To identify the molecular determinants responsible for potential differences in Akt1 and Akt2 substrate specificity.
• To elucidate the role of the regulatory domain in conferring functional specificity to Akt isoforms.

Main Methods:

• In vivo studies examining CREB phosphorylation at Ser-133.
• Analysis of CREB target gene expression.
• Investigation of FoxO1 mediated gene expression.
• Site-directed mutagenesis to substitute regulatory domains between Akt1 and Akt2.

Main Results:

• Akt1, but not Akt2, induced CREB phosphorylation at Ser-133 and subsequent target gene expression in vivo.
• Both Akt1 and Akt2 effectively inhibited FoxO1 mediated gene expression, indicating CREB specificity.
• Substitution of the Akt1 regulatory domain with that of Akt2 abolished Akt1's ability to activate CREB.
• Conversely, substitution of the Akt2 regulatory domain with that of Akt1 conferred CREB activation ability.

Conclusions:

• The regulatory domain of Akt proteins is a critical determinant of substrate specificity, particularly for CREB activation.
• Functional divergence between Akt1 and Akt2 in CREB signaling is mediated by their respective regulatory domains.
• These findings highlight the importance of isoform-specific regulatory mechanisms in Akt-mediated cellular processes.