Characterization of promoter elements of the human HYAL-2 gene.

The regulated catabolism of hyaluronan is critical to the function of many connective tissues. In cartilage, hyaluronan catabolism occurs locally by resident chondrocytes. To determine whether the expression of lysosomal hyaluronidases contributes to this regulation, the promoter elements associated with HYAL-2 gene expression were characterized. Human articular chondrocytes were found to express all three lysosomal hyaluronidases, HYAL-1, HYAL-2, and HYAL-3. HYAL-2 was the predominant gene product. Using 5' RACE (rapid amplification of cDNA ends) analysis, multiple transcription initiation sites were identified including a novel initiation site located within intron 1 of the gene expressed by human articular chondrocytes. The presence of multiple transcriptional initiation sites is a typical feature of TATA-less promoter regions, such as those of HYAL-2. Approximately 4000 bp of 5' flanking sequence of the HYAL-2 gene was characterized. Transient transfection of C-28/I2 cells with various 5' deletion constructs indicated that the region between +959 to +1158 (within intron 1) contains the basal promoter for HYAL-2 in chondrocytes. In addition, the region +224 to +958 contained a negative modulator that could control the basal expression level of HYAL-2. Treatment of human articular chondrocytes or C-28/I2 cells with various catabolic cytokines did not alter HYAL-2 mRNA expression, luciferase promoter expression, or hyaluronidase enzymatic activity. Thus, in chondrocytes HYAL-2 appears to be constitutively expressed and not inducibly regulated by catabolic agents. As such, it appears that the expression of lysosomal hyaluronidase participates little in the overall regulation of hyaluronan catabolism.