Cdk7 functions as a cdk5 activating kinase in brain.

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Cyclin-dependent kinase 5 (Cdk5) activity is vital for central nervous system (CNS) development.
• Cdk5 requires association with regulatory subunits like p35 or p39 for its function.
• The precise mechanisms regulating Cdk5 activation, particularly phosphorylation events, remain incompletely understood.

Purpose of the Study:

• To identify the kinase responsible for phosphorylating Cdk5 at Serine 159.
• To elucidate the role of this kinase in modulating Cdk5 activity.
• To investigate the physiological relevance of this Cdk5 activation mechanism in brain development.

Main Methods:

• Partial purification of a bovine brain enzyme capable of phosphorylating Cdk5 peptides.
• Characterization of the purified enzyme's components (Cdk7, cyclin H, Mat1).
• In vitro kinase assays using wild-type and mutant Cdk5, and Cdk7 immunoprecipitates from mouse brain.
• Assessment of Cdk5/p25 activity modulation by the identified kinase.
• Correlation of Cdk5 and Cdk7 activity in developing mouse brain.

Main Results:

• A bovine brain enzyme containing Cdk7, cyclin H, and Mat1 was identified.
• This enzyme specifically phosphorylates Serine 159 of Cdk5, enhancing Cdk5/p25 activity.
• The identified kinase activates wild-type Cdk5 but not a Ser159Ala mutant.
• Cdk7 or cyclin H immunoprecipitates from mouse brain also phosphorylate and activate Cdk5.
• Cdk7 activity in developing mouse brain correlates with elevated Cdk5 activity.

Conclusions:

• Cdk7 functions as a Cdk5 activating kinase in the brain.
• Phosphorylation of Cdk5 at Serine 159 by Cdk7 is a key regulatory mechanism for Cdk5 activity.
• This regulatory pathway is active during CNS development.