Mutations in the
diastrophic dysplasia sulfate transporter (DTDST) gene constitute a family of recessively inherited
osteochondrodysplasias including
achondrogenesis type 1B,
atelosteogenesis type II, and
diastrophic dysplasia. However, the functional properties of the gene product have yet to be elucidated. We cloned rat DTDST
cDNA from rat UMR-106 osteoblastic cells. Northern blot analysis suggested that cartilage and intestine were the major expression sites for DTDST
mRNA. Analysis of the genomic sequence revealed that the rat DTDST gene was composed of at least five exons. Two distinct transcripts were expressed in chondrocytes due to alternative utilization of the third exon, corresponding to an internal portion of the 5'-untranslated region of the
cDNA. Injection of rat and human DTDST
cRNA into Xenopus laevis oocytes induced Na+-independent
sulfate transport. Transport activity of the expressed DTDST was markedly inhibited by extracellular
chloride and
bicarbonate. In contrast, canalicular Na+-independent
sulfate transporter Sat-1 required the presence of extracellular
chloride in the
cRNA-injected oocytes. The activity profile of
sulfate transport in growth plate chondrocytes was studied in the extracellular presence of various
anions and found substantially identical to DTDST expressed in oocytes. Thus,
sulfate transport of chondrocytes is dominantly dependent on the DTDST system. Finally, we demonstrate that undersulfation of
proteoglycans by the
chlorate treatment of chondrocytes significantly impaired growth response of the cells to
fibroblast growth factor, suggesting a role for DTDST in endochondral bone formation.