Analysis and mapping of plastin phosphorylation

Area of Science:

• Cell Biology
• Biochemistry
• Signal Transduction

Background:

• Plastins (fimbrins) are actin-binding proteins involved in cytoskeletal dynamics.
• Leukocyte-specific L-plastin phosphorylation regulates leukocyte activation.
• The specific kinases and phosphorylation sites of L-plastin are not fully elucidated.

Purpose of the Study:

• To identify the specific phosphorylation sites and kinases involved in L-plastin regulation.
• To investigate the role of serine residues (Ser-5 and Ser-7) in L-plastin phosphorylation.
• To determine the kinase responsible for L-plastin phosphorylation in leukocytes and fibroblasts.

Main Methods:

• Site-directed mutagenesis to create L-plastin mutants (Ser-5 to Ala, Ser-7 to Ala).
• Expression of wildtype and mutant L-plastin in WI38VA13 fibroblasts and leukocytes.
• Two-dimensional gel electrophoresis to analyze protein phosphorylation.
• Treatment with phorbol myristate acetate and expression of casein kinase II alpha subunit.

Main Results:

• Mutating Ser-5 and Ser-7 to alanine abolished L-plastin phosphorylation in fibroblasts.
• Wildtype L-plastin was phosphorylated in fibroblasts, but less extensively than endogenous L-plastin in leukocytes.
• T-plastin was not phosphorylated in either cell type.
• Phorbol myristate acetate treatment induced L-plastin phosphorylation in both cell types, implicating protein kinase C.

Conclusions:

• Ser-5 and Ser-7 are critical sites for L-plastin phosphorylation.
• Protein kinase C is likely the primary kinase responsible for L-plastin phosphorylation.
• L-plastin phosphorylation is a conserved regulatory mechanism across different cell types.