Intron 16 insertion of the angiotensin converting enzyme gene and transcriptional regulation

The insertion/deletion (I/D) polymorphism in intron 16 of angiotensin converting enzyme (ACE) is associated with circulating and tissue enzymatic levels, around two-fold higher in homozygous D than homozygous I individuals. The mechanism underlying this quantitative difference is unknown and the hypothesis that the deletion removes a transcriptional silencer located within the intron has been proposed.

We have set up an assay based on constructs carrying fragments of intron 16, either in the I or in the D form, fused to the Herpes simplex virus thymidine kinase heterologous promoter driving the expression of the CAT reporter gene. These constructs have been used in transfection experiments in ACE expressing cells.

Plasmids containing either intronic fragments from I and D subjects or an artificial D fragment derived from an I intron did not show significant difference between I and D in affecting the heterologous promoter activity. The finding of a yet undescribed polymorphism in intron 16 is also reported.

The above results suggest that the intron 16 deletion by itself has no effect in regulating transcription in our assay system.