Regulation of CCN1 via the 3′-untranslated region

The 3′-untranslated region (UTR) is known to be a critical regulator of post-transcriptional events that determine the gene expression at the RNA level. The gene CCN1 is one of the classical members of the matricellular CCN family and is involved in a number of biological processes during mammalian development. In the present study, the 600-bp 3′-UTR of CCN1 was functionally characterized. Reporter gene analysis revealed that the entire 3′-UTR profoundly repressed gene expression in cis in different types of the cells, to which both the proximal and distal-halves of the 3′-UTR segments contributed almost equally. Deletion analysis of the 3′-UTR indicated a distinct functional element in the proximal half, whereas a putative target for microRNA-181s was predicted in silico in the distal half. Of note, the repressive RNA element in the proximal half was shown to be capable of forming a stable secondary structure. However, unexpectedly, a reporter construct with a tandem repeat of the predicted miR-181 targets failed to respond to miR-181a. In addition, the other major structured element predicted in the distal half was similarly characterized. To our surprise, the second element rather enhanced the reporter gene expression in cis. These results indicate the involvement of multiple regulatory elements in the CCN1 3′-UTR and suggest the complexity of the miRNA action as well as the 3′-UTR-mediated gene regulation.