Overexpression of the 3'-phosphoadenosine 5'-phosphosulfate (PAPS) transporter 1 increases sulfation of chondroitin sulfate in the apical pathway of MDCK II cells

The canine 3'-phosphoadenosine 5'-phosphosulfate (PAPS) transporter1 fused to GFP was stably expressed with a typical Golgi localizationin MDCK II cells (MDCK II-PAPST1). The capacity for PAPS uptakeinto Golgi vesicles was enhanced to almost three times thatof Golgi vesicles isolated from untransfected cells. We havepreviously shown that chondroitin sulfate proteoglycans (CSPGs)are several times more intensely sulfated in the basolateralthan the apical secretory pathway in MDCK II cells (Tveit H,Dick G, Skibeli V, Prydz K. 2005. A proteoglycan undergoes differentmodifications en route to the apical and basolateral surfacesof Madin-Darby canine kidney cells. J Biol Chem. 280:29596–29603).Here we demonstrate that increased availability of PAPS in theGolgi lumen enhances the sulfation of CSPG in the apical pathwayseveral times, while sulfation of CSPGs in the basolateral pathwayshows minor changes. Sulfation of heparan sulfate proteoglycansis essentially unchanged. Our data indicate that CSPG sulfationin the apical pathway of MDCK II cells occurs at suboptimalconditions, either because the sulfotransferases involved havehigh K_m values, or there is a lower PAPS concentration in thelumen of the apical secretory route than in the basolateralcounterpart.