Turnover of Functional Basic Fibroblast Growth Factor Receptors on the Surface of BHK and NIH 3T3 Cells

Abstract

The recovery of functional cell-surface bFGF receptors after trypsin treatment was studied in BHK cells and NIH 3T3 cells. Restoration of functional bFGF receptors occurred at an approximately linear rate with 50% of the high-affinity binding capacity restored after 4 hr. Restoration of functional receptors required protein synthesis but not RNA synthesis. Upon exposure of BHK cells to bFGF, cell-surface receptors were rapidly lost, with only 25% remaining after 1 hr. When the bFGF was removed, down-regulated BHK and NIH 3T3 cells recovered cell-surface receptors at about the same rate observed in trypsin-treated cells. The recovery of receptors after down-regulation was inhibited by protein synthesis inhibitors. Addition of the protein synthesis inhibitor cycloheximide to unperturbed cultures of BHK or NIH 3T3 cells resulted in a time-dependent loss of cell-surface bFGF receptors, demonstrating that the receptors turn over constantly in the absence of ligand. These results suggest that bFGF receptors do not recycle and must be continuously synthesized.

Key Words:

• Receptor synthesis
• receptor down-regulation
• receptor degradation