Undersulfation of Proteoheparan Sulfate Stimulates the Expression of Basic Fibroblast Growth Factor and Protein Synthesis but Suppresses Replication of Coronary Smooth Muscle Cells

Heparan sulfate proteoglycans are obligatory for receptor binding and mitogenic activity of the basic fibroblast growth factor (bFGF). In the present study the influence of undersulfated heparan sulfate on the expression of basic fibroblast growth factor and coronary smooth muscle cell (cSMC) proliferation was investigated. Chlorate, known to be an inhibitor of ATP-sulfurylase, was used as a tool to suppress sulfation of heparan sulfate. When cultured cSMC were treated with 10 mM sodium chlorate in sulfate-depleted medium, the cell number and [3H]thymidine incorporation decreased by 76% and 66% respectively, while the protein content per cell was doubled. At the same time the [35S]sulfate incorporation into cell-associated proteoglycans was reduced by 90%. The remaining minimal amount of available [35S]radioactivity was preferably incorporated into heparan sulfate. Under the same conditions the [6-(3)H]glucosamine incorporation into glycosaminoglycans was not impaired. The chlorate-induced increase of cell protein content includes an overexpression of bFGF, which increased from 6-8 ng to 18-22 ng/mg cell protein. However, no changes in the distribution of bFGF between the intracellular and pericellular compartment could be observed. Cell cycle analysis by FACS revealed a G1 arrest of the cell cycle with increase of the G1/S ratio from 2.9 (control) to 6.1 (chlorate) but the DNA content per cell corresponded to normal diploid cells both in control and chlorate-treated cells. The chlorate effect can be abolished by addition of 5 mM sodium sulfate to the cultures. Our results demonstrate an inverse association between the sulfation of heparan sulfate and the expression of bFGF. They suggest that chlorate blocks the cell cycle in the late G1-phage and that mitogenesis of cSMC requires fully sulfated cell-associated proteoheparan sulfate.