Metalloprotease-mediated cleavage-secretion of pulmonary angiotensin-converting enzyme by vascular endothelial and kidney epithelial cells. Ramchandran, Ramaswamy, Sriram Kasturi[acute]a, Janice G. Douglas[alpha] and Indira Sen[tilde]n. Department of Molecular Cardiology, Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio and the Department of Medicine, Case Western Reserve University, University Hospitals of Cleveland, Cleveland, Ohio 44195
APStracts 2:0557H, 1995.
The pulmonary isozyme of angiotensin converting enzyme (ACEP) is present in the body both as a cell-associated protein in endothelial, epithelial and monocytic cells and as a soluble protein in various body fluids including serum. The mechanism by which soluble ACEP is produced in vivo, is unknown. Using in vitro transfected cell culture systems, we have previously demonstrated that the rabbit testicular isozyme of ACE (ACET), which shares extensive homology with ACEP, is first synthesized as a plasma-membrane anchored ectoprotein and then secreted to the culture medium by cleavage-removal of its C-terminal membrane anchored tail. Here, using in vitro cultures of arterial endothelial cells and acutely isolated renal epithelial cells, we demonstrate that ACEP is also cleavage-secreted from their natural producer cells. Biochemical and immunological characterization of the in vitro secreted ACEP proteins revealed that it is missing the C -terminal membrane anchored region of the cell-associated ACEP. Similar analysis of ACEP proteins present in rabbit serum, lung and kidney established that ACEP secretion in vivo is also caused by the cleavage-removal of the C-terminal region of the cell-associated protein. To characterize the proteolytic enzyme responsible for secretion of ACEP, we employed rabbit renal proximal tubular epithelial cells and demonstrated significant inhibition of secretion by Compound 3, a hydroxamic acid-based inhibitor of specific metalloproteases. In contrast, the inhibitors of chymotrypsin, trypsin, serine, aspartate and cysteine proteases were ineffective. These results indicate that soluble ACEP production by vascular endothelial and renal epithelial cells, both in vitro and in vivo, is achieved by cleavage-removal of its membrane-anchoring C-terminal tail by a specific metalloprotease. 

Received 17 August 1995; accepted in final form 6 December 1995.
APS Manuscript Number H781-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 December 95