Glycosaminoglycan synthesis by proliferating and differentiated human keratinocytes in culture

Glycosaminoglycan (GAG) synthesis and compartmentalization were studied in populations of human neonatal keratinocytes under conditions of proliferation and terminal differentiation in vitro. Following isotopic labeling with the precursors [3H]glucosamine and [35S]sulfate, GAGs were extracted from the keratinocytes into several operationally created compartments associated with the cells and extracellular matrix. Chondroitin sulfate and heparan sulfate accounted for the majority of the incorporated label in all preparations. Although total sulfated GAGs per culture increased from proliferative to differentiated conditions, GAG content normalized to the DNA content of the cultures demonstrated the reverse trend. This was particularly evident for the chondroitin sulfates, which declined 60-70% in the differentiated cultures. Furthermore, label incorporation into chondroitin and heparan sulfates revealed a relative compartmental shift to a trypsin-accessible site upon keratinocyte differentiation. An analysis of heparan sulfate structure by characterization of the oligosaccharide products resulting from low pH nitrous acid deaminative degradation provided evidence that the parent material from differentiated keratinocytes contains a larger region of N-sulfated glucosamine residues unassociated with ester sulfate groups. The correlation of variations in GAG content and compartmentalization with the growth condition of human keratinocytes constitutes evidence that this heterogeneous group of cell surface-associated carbohydrates is involved in some aspect of cell function associated with growth control or differentiation. Furthermore, the apparent differences in heparan sulfate primary structure indicate that there is structure-function specificity to this association.