Background: Human xylosyltransferase-I (XT-I) catalyzes the rate-limiting step in proteoglycan glycosylation. An increase in XYLT1 mRNA expression and serum XT activity is associated with diseases characterized by abnormal extracellular matrix accumulation like, for instance, fibrosis. Nevertheless, physiological and pathological mechanisms of transcriptional XT regulation remain elusive.
Results: To elucidate whether promoter variations might affect the naturally occurring variability in serum XT activity, a complete sequence analysis of the XYLT1 promoter was performed in genomic DNA of healthy blood donors. Based on promoter amplification by a specialized PCR technique, sequence analysis revealed a fragment of 238 bp, termed XYLT1 238*, which has never been described in the human XYLT1 reference sequence so far. In silico characterization of this unconsidered fragment depicted an evolutionary conservation between sequences of Homo sapiens and Pan troglodytes (chimpanzee) or Mus musculus (mouse), respectively. Promoter activity studies indicated that XYLT1 238* harbors various transcription factor binding sites affecting basal XYLT1 expression and inducibility by transforming growth factor-β1, the key fibrotic mediator. A microsatellite and two single nucleotide variants (SNV), c.-403C>T and c.-1088C>A, were identified and genotyped in 100 healthy blood donors. Construct associated changes in XYLT1 promoter activity were detected for several sequence variants, whereas serum XT activity was only marginally affected.
Conclusions: Our findings describe for the first time the entire XYLT1 promoter sequence and provide new insights into transcriptional regulation of XT-I. Future studies should analyze the impact of regulatory XYLT1 promoter variations on XT-associated diseases.