Regulatory Activities of the 5′- and 3′-Untranslated Regions and Promoter of the Human Aggrecan Gene

Identification and characterization of the regulatory elements of the human aggrecan gene are necessary first steps in addressing the molecular mechanisms through which the gene is regulated. Using luciferase reporter constructs driven by the human aggrecan promoter or the cytomegalovirus promoter, the 5′- and 3′-untranslated regions of the human aggrecan gene were found to regulate gene expression transcriptionally in a promoter- and/or cell type-specific manner. Independent of cell type, the 5′-untranslated region was inhibitory with respect to the cytomegalovirus promoter, but it was stimulatory to the human aggrecan promoter. The 5′-untranslated region inhibited the cytomegalovirus promoter by approximately 60% in both chondrocytes and NIH 3T3 cells, but it stimulated the activity of the human aggrecan promoter about 8-fold in chondrocytes and 40-fold in NIH 3T3 cells. In contrast, the 3′-untranslated region inhibited the activities of the human aggrecan promoter by 40–70% in both cell types, but it stimulated the cytomegalovirus promoter activities by 50–60% in NIH 3T3 cells and inhibited its activity by 70% in chondrocytes. The differential effects of the untranslated regions on the two types of promoters may be a reflection of differences in regulation of TATA-less promoters, such as the human aggrecan promoter, and TATA-containing promoters, such as the cytomegalovirus promoter.