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Major influence of cell differentiation status on characteristics of proteoglycans synthesized by cultured rabbit renal proximal tubule cells: Role of insulin and dexamethasone

To analyze the influence of epithelial cell differentiation and the effects of hormones on the characteristics of cell‐associated and secreted proteoglycans (PGs), we studied their distribution, synthesis, and biochemical features in a model of renal proximal tubule cells in primary culture in which cell differentiation could be controlled by medium composition. In cells cultured in serum‐free, hormonally defined medium supplemented with insulin and dexamethasone that exhibited a high degree of morphological and functional proximal differentiation (Ronco et al., 1990), cell‐associated PGs were similar to those extracted in vivo by their size estimated by Sepharose CL‐6B chromatography (Kav = 0.27, vs. 0.26), composition (heparan‐sulfate), and localization in a continuous basal layer of extra‐cellular matrix (ECM). In contrast, major quantitative and qualitative anomalies of cell‐associated PGs were observed in poorly differentiated cells grown in 1% fetal calf serum‐supplemented medium (FCS). PGs alterations included: (1) reduced and irregular expression of PGs at the cell basal pole, (2) a 2.8‐fold decrease in [35S]‐incorporation into cell‐associated PGs, (3) a 3.1‐fold increase in trypsin‐releasable PGs, and (4) the emergence of a high MW PG composed exclusively of chondroitin‐sulfate (CS) (Kav = 0.09 on Sepharose CL‐6B) as well as of putative free CS‐glycosaminoglycan (GAG) chains (Kav = 0.49 on Sepharose CL‐6B). The same alterations were identified in the basal defined medium devoid of hormones but were partially or totally abolished by addition of insulin and dexamethasone, respectively. At variance with cell‐associated PGs, production and biochemical features of secreted PGs were not influenced by cell differentiation status and medium composition. © 1993 Wiley‐Liss, Inc.