Altered synthesis and intracellular transport of proteoglycans by cyst-derived cells from human polycystic kidneys

Employing in vitro pulse-chase techniques, we investigated the de novo synthesis and the kinetics of intracellular transport and extracellular matrix incorporation of proteoglycans (PG) by normal human renal epithelial cell and by epithelial cells isolated from cysts of autosomal dominant kidneys (ADPKD). Cell monolayers were pulsed either with (³H)leucine for 15 min and chased for seven intervals between 15 and 270 min or with (³⁵S)sulfate for 150 min and chased for a single interval of 120 min. Total proteins and PG were isolated from cell, media, and matrix fractions and characterized by Sepharose CL-6B and DEAE-Sephacel chromatographies. ADPKD and NK cells synthesized comparable amounts of total proteins; however, the de novo synthesis of PG by ADPKD cells was significantly reduced. ADPKD versus NK cells exhibited a substantial delay in the cellular transport and extracellular release of de novo synthesized PG, indicating an impairment at the level of the Golgi complex and/or secretory vacuoles. PG synthesized by ADPKD versus NK cells had decreased charge density characteristics, probably due to a posttranslational defect in the sulfation of the PG glycosaminoglycan chains. ADPKD versus NK cells synthesized PG of higher molecular weight and had an increased proportion of chondroitin sulfate PG versus heparan sulfate PG. Collectively, these findings suggest a defect in the synthesis and intracellular transport of sulfated PG in human ADPKD cells.