SUBTYPE-2 AND ATYPICAL ANGIOTENSIN RECEPTORS IN THE HUMAN HEART

Angiotensin receptors have been described in the human heart and are s uspected to play a central role in remodeling after myocardial infarct ion and in cardiac hypertrophy. Two subtypes, AT1 and AT2, have so far been described in humans, with AT2 being the dominant subtype in huma n atria. We have now determined subtype numbers and distribution by bi nding in ventricular myocardium from patients with end-stage heart fai lure. We found about 50 - 80 % of subtype AT2 in the right and left ve ntricles from patients with end-stage heart failure due to coronary ar tery disease and cardiomyopathy, indicating that AT2 is the dominant a ngiotensin receptor subtype in the whole human heart. To determine the cellular localization of angiotensin receptors in human myocardium in addition to the known localization on myocytes, smooth muscle cells a nd endothelial cells, we investigated cardiac fibroblasts. They expres s an angiotensin receptor with yet incompletely understood binding cha racteristics which is coupled to proliferation and DNA synthesis. As A T2 is the dominant angiotensin receptor subtype in human heart, we clo ned the complete mRNA sequence by a rapid amplification of cDNA ends ( RACE) procedure and thereafter the promoter sequence from a human geno mic library. Once the sequence of the mRNA and thus exon 1 was obtaine d by the RACE-PCR, a probe was constructed for the most 5' region of e r;on 1 and used for screening of a human genomic DNA bank. After cutti ng of the positive clones with EcoR1 and Not1, a 4000 bp fragment hybr idized with the probe and was further sequenced. A functional AT2 prom oter, with > 90 % homology with the mouse promoter and 35 % homology w ith the human AT1 promoter containing numerous cis-acting sequences fo r basal (TFIID) and inducible (AP-1, PEA-3, CBF) transcription factors in the first 1000 bp was identified.