Platelet-derived growth factor. II. Specific binding to cultured cells

Area of Science:

• Molecular Biology
• Cell Signaling
• Biochemistry

Background:

• Platelet-derived growth factor (PDGF) is a potent mitogen involved in cell growth and proliferation.
• Understanding PDGF receptor binding is crucial for elucidating its biological functions and therapeutic potential.

Purpose of the Study:

• To characterize the binding kinetics and specificity of radioiodinated PDGF (125I-PDGF) to target cells.
• To investigate the relationship between PDGF binding and its mitogenic activity.

Main Methods:

• Preparation of biologically active radioiodinated PDGF (125I-PDGF).
• Saturation binding assays using Swiss 3T3 cells, fibroblasts, and arterial smooth muscle cells.
• Competition assays with unlabeled PDGF and other growth factors.
• Analysis of binding under varying temperatures, pH, and salt conditions.
• Assessment of receptor-mediated internalization and degradation.

Main Results:

• 125I-PDGF binding is saturable, specific, and exhibits high affinity (Kd = 10(-11) M) to responsive cells.
• Binding capacity varies significantly among cell types, correlating with mitogenic response.
• Cells selected for reduced mitogenic response show drastically decreased 125I-PDGF binding.
• Internalization and degradation of 125I-PDGF are observed at physiological temperatures.

Conclusions:

• Specific, high-affinity binding of PDGF to its receptor is essential for its mitogenic activity.
• The number of PDGF binding sites on cells dictates their responsiveness to the growth factor.
• PDGF receptor interaction involves internalization and degradation, indicating a dynamic regulatory mechanism.