DEGRADATION OF CELL-SURFACE HEPARAN SULFATES DECREASES THE HIGH-AFFINITY BINDING OF BASIC FGF TO ENDOTHELIAL-CELLS, BUT NOT TO FRTL-5 RAT-THYROID CELLS

The role of cell surface heparan sulfate proteoglycans in the effect o f basic fibroblast growth factor (bFGF) on FRTL-5 rat thyroid cells wa s investigated and compared with that of endothelial cells, FRTL-5 cel ls were incubated for 2 h with heparitinase (0.5-5.0 mU/mL), which spe cifically degrades heparan sulfate proteolgycans, and then stimulated by bFGF, The mitogenic effect of bFGF was estimated by measuring [H-3] thymidine incorporation. Although cell surface heparan sulfates have b een believed to be necessary for bFGF binding to its high affinity rec eptors, the heparitinase treatment had no significant effect on the DN A synthesis of FRTL-5 cells stimulated by bFGF, The binding study reve aled that heparitinase treatment decreased low affinity bindings of [I -125]bFGF to FRTL-5 cells by only 50% and did not attenuate the high a ffinity binding, while the same treatment abolished the high and low a ffinity binding to bovine pulmonary artery endothelial (CPAE) cells. A nalysis of trypsin accessible cell surface (SO4)-S-35-labeled material s by Q-sepharose anion-exchange column chromatography showed that hepa ran sulfate proteoglycans, peaked at 0.55 M NaCl elution, disappeared from the surface of FRTL-5 cells after treatment with 2.0 mU/mL of hep aritinase, indicating that the heparitinase resistant low-affinity bin ding sites are not heparan sulfates, These results demonstrate that ce ll surface heparan sulfates are not required for the high affinity bin ding of bFGF to FRTL-5 rat thyroid cells, while proteoglycans are nece ssary for binding to endothelial cells, and suggest that the mechanism of the action of bFGF is different in rat thyroid cells compared with endothelial cells.