Cdk5 targets active Src for ubiquitin-dependent degradation by phosphorylating Src(S75).

Area of Science:

• Molecular Biology
• Cell Signaling
• Biochemistry

Background:

• The non-receptor tyrosine kinase Src regulates crucial cellular processes like cytoskeletal contraction, adhesion, and migration.
• Src activity is normally controlled by Csk-dependent phosphorylation (Src Y530) and Cullin-5-dependent ubiquitinylation of active Src (pY419), targeting it for proteasomal degradation.
• Previous studies indicated Cyclin-dependent kinase 5 (Cdk5) limits Src activity by phosphorylating Src at S75.

Purpose of the Study:

• To investigate the role of Cdk5-dependent phosphorylation of Src at S75 in regulating Src activity and stability.
• To elucidate the mechanism by which Cdk5 influences Src degradation and cellular localization.

Main Methods:

• In vivo studies using epithelial cells to assess Src(S75) phosphorylation.
• Site-specific mutation (S75A) of Src to prevent Cdk5 phosphorylation.
• Cdk5 inhibition and suppression experiments.
• Analysis of Src phosphorylation (Y419), kinase activity, ubiquitinylation, and half-life.

Main Results:

• Cdk5-dependent phosphorylation of Src(S75) promotes ubiquitin-dependent degradation of Src, restricting active Src availability.
• Src(S75) phosphorylation occurs in vivo in epithelial cells and is associated with active Src.
• Inhibition or mutation of Cdk5 phosphorylation sites increased Src(Y419) phosphorylation, kinase activity, and Src stability, leading to cytoskeletal changes.

Conclusions:

• Cdk5-dependent phosphorylation of Src(S75) is a significant physiological mechanism for regulating intracellular Src activity.
• This pathway acts in concert with other regulatory mechanisms to control Src kinase function.
• Understanding this regulation provides insights into cellular processes controlled by Src.