Alternative RNA splicing affects function of encoded platelet-derived growth factor A chain

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Platelet-derived growth factor (PDGF) is a mitogenic protein crucial for cell growth.
• PDGF consists of A and B polypeptide chains, with the B-chain encoded by the c-sis gene.
• Alternative splicing of PDGF A-chain transcripts occurs in transformed cells.

Purpose of the Study:

• To investigate the functional differences between normal and tumor-derived PDGF A-chain variants.
• To determine the impact of alternative RNA splicing on PDGF secretion and mitogenic activity.

Main Methods:

• Isolation and sequencing of PDGF A-chain cDNA from endothelial cells and glioma cells.
• Transfection of monkey kidney cells (COS) with different PDGF A-chain cDNA constructs.
• Measurement of mitogenic activity in cell culture media.

Main Results:

• Normal human umbilical vein endothelial cell (EC) A-chain precursor lacks specific C-terminal amino acids found in tumor cell cDNA.
• Culture media from COS cells transfected with endothelial cDNA showed significantly lower mitogenic activity compared to those transfected with tumor cell cDNA.
• Inefficient assembly or secretion of the endothelial-type growth factor likely accounts for the reduced activity.

Conclusions:

• Alternative RNA splicing of PDGF A-chain in transformed cells can alter growth factor properties.
• Tumor cells may utilize alternative splicing to enhance the efficiency of growth factor assembly and secretion.
• This mechanism could contribute to uncontrolled cell proliferation in cancer.