The unknown alternative splicing generates a novel isoform of human angiotensin-converting enzyme as a soluble form

Abstract

Human angiotensin-converting enzyme (ACE) gene exists in the chromosome 17, and two kinds of molecules are produced from the same gene locus according to the alternative splicing as the somatic and testis form. It is said theACE activity in serum derives from proteolytic release of the somatic ACE located in endothelial cell surface. V~ report here, in human somaticACE mRNA, the unrecognized alternative splicing occurs in common, and as a result, a new isoform of ACE is generated. The samples were Jurkat cell (humanT cell leukemia line) and peripheral blood leukocytes obtained healthy subjects.The mRNA was extracted from these cells, and RT-PCR was executed with the primer set in the 15th exon and the 18th exon.The electroophoresis of the PCR product visualized two bands of DNA fragment; one was the expected band derived from somaticACE mRNA, and the other was the unexpected, 150bp-longer one. This longer DNA fragment was subcloned and sequenced. As a result, the structure of this fragment was revealed to be exon15-exon16-exon17-intronf7-exon18 of human ACE gene, and a novel alternative splicing was confirmed.This alternative splicing arose a new stop codon immediately after the 17th exon, and it was surmised that a novel isoform of ACE was £1enerated as a soluble form which deleted the transmembrane portion and C domain of two active centers of somaticACE. This isoform mRNAwas also detected in lung, kidney, aorta and pancreas, and not detected in brain, heart, liver, skeletal muscle, testis and placenta by screening the human cDNA library of each organ. In leukocytes and pancreas, the expression level was about 20 percent of somaticACE, and much lower in lung, kidney and aorta. The other research group have reported that the transgenic mouse of the equivalent artificial molecule had shown a similar phenotype of theACE-knockout mouse, therefore this spontaneously expressed molecule in human is also expected to have similar functions in vivo. Further, we have investigated the relationship between this alternative splicing and theACE Insertion/Deletion poiymorphism in the 16th intron. At this moment, any correlation have been found within both phenomena. The 2nd Annual Scientific Meeting • JHFS 67