The antiproliferative effects of enzymatic deglycosylation and metabolic undersulfation of proteoglycans from the cell surface.
Enzymatic deglycosylation of plasma membrane proteoglycans and metabolic inhibition of glycosaminoglycan sulfation were employed as complementary methods to evaluate the effects of reduced cell surface content of functionally intact proteoglycans on the proliferative potential of cells. A Flavobacter heparinum extract, possessing multiple glycosaminoglycan substrate specificities, markedly inhibited the time-dependent expansion of BALB/c 3T3 fibroblast and human squamous cell carcinoma monolayers in culture and concurrently reduced the proportion of subconfluent cell populations in S-cell cycle phase by DNA flow-cytometry analysis. This antiproliferative effect was partially reproduced by lyases with heparan sulfate or chondroitin sulfate monospecificity, alone and in combination. The observed lability of heparan sulfate lyases I and II in serum-containing medium possibly hampered full reproduction of the effects of the multifunctional reagent. Growth inhibition of comparable magnitude was observed when glycosaminoglycan sulfation was metabolically blocked with sodium chlorate. The chlorate anion had its expected effect of substantially reducing sulfated glycosaminoglycan synthesis by the cells. Following release from serum deprivation, analysis of the progression of synchronized cell populations past the G1 restriction point suggested that in situ digestion with the glycosaminoglycan lyases limited, but did not delay, the numbers of cells entering S phase. These data support the hypothesis that plasma membrane proteoglycans mediate some of the cell-growth-promoting effects of serum factors via their glycosaminoglycan side chains.