Analysis of the human lumican gene promoter

The human lumican gene was shown to possess one major transcription start site, resulting in exon 1 of the gene giving rise to the first 74 base pairs (bp) of the 5'-untranslated region. About 1.6 kilobase pairs of upstream promoter sequence were sequenced and analyzed to identify elements responsible for gene expression. No typical TATAA sequence was identified in the vacinity of the transcription start site, but an atypical TATCA sequence residing 41 bp upstream was shown to be necessary for transcription, although it was incapable of supporting transcription by itself. A GC box residing 74 bp upstream of the transcription start site also was essential for the initiation of transcription. Sp3 was identified as the transcriptional activator binding to the GC box. No additional elements that significantly modulated transcription were noted in the promoter sequence analyzed, when using human adult chondrocytes as the cell source for transfection in reporter assays. In contrast, reporter assays carried out in human fetal lung fibroblasts, where lumican expression is deplete, revealed the presence of a repressor element located between 384 and 598 bp upstream of the transcription start site. A GATA-binding site located between bp -386 and -391 was identified as being necessary for repression of transcription. The mouse lumican promoter does not possess an equivalent site, and this may explain why the lumican gene is expressed in fetal murine cartilage but not in fetal human cartilage.