Covalent linkage between nucleotides and platelet-derived endothelial cell growth factor

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Signaling

Background:

• Platelet-derived endothelial cell growth factor (PD-ECGF) is a mitogen found in platelets and placenta.
• PD-ECGF is produced by various cultured cell lines and plays a role in endothelial cell growth.
• The post-translational modification of PD-ECGF was investigated to understand its biochemical properties.

Purpose of the Study:

• To investigate the in vivo and in vitro phosphorylation of PD-ECGF.
• To identify the specific residues involved in phosphorylation and the nature of the modification.
• To explore the potential role of nucleotides in PD-ECGF modification.

Main Methods:

• Metabolic labeling of A431 cells with [32P]orthophosphate followed by immunoprecipitation of PD-ECGF.
• Phosphoamino acid analysis to identify phosphorylated residues.
• In vitro labeling of purified PD-ECGF with radiolabeled ATP and GTP under various conditions.
• Enzymatic (snake venom phosphodiesterase) and chemical (piperidine) treatments to analyze nucleotide linkage.

Main Results:

• In vivo and in vitro phosphorylation of PD-ECGF was confirmed, primarily on serine residues.
• Forskolin, phorbol ester, and epidermal growth factor did not affect in vivo PD-ECGF phosphorylation.
• ATP and GTP were preferred nucleotide substrates for in vitro labeling.
• Analysis revealed covalent linkage of phosphate groups from nucleotides to serine residues, forming a nucleotidylated protein.

Conclusions:

• PD-ECGF can be modified by nucleotidylation, a post-translational modification involving serine residues.
• This nucleotidylation links phosphate groups from nucleotides to the protein.
• The functional significance of this PD-ECGF nucleotidylation requires further investigation.