Abstract
BackgroundAngiotensin-converting enzyme (ACE; Kininase II; CD143) hydrolyzes small peptides such as angiotensin I, bradykinin, substance P, LH-RH and several others and thus plays a key role in blood pressure regulation and vascular remodeling. Complete absence of ACE in humans leads to renal tubular dysgenesis (RTD), a severe disorder of renal tubule development characterized by persistent fetal anuria and perinatal death.Methodology/Principal FindingsPatient with RTD in Lisbon, Portugal, maintained by peritoneal dialysis since birth, was found to have a homozygous substitution of Arg for Glu at position 1069 in the C-terminal domain of ACE (Q1069R) resulting in absence of plasma ACE activity; both parents and a brother who are heterozygous carriers of this mutation had exactly half-normal plasma ACE activity compared to healthy individuals. We hypothesized that the Q1069R substitution impaired ACE trafficking to the cell surface and led to accumulation of catalytically inactive ACE in the cell cytoplasm. CHO cells expressing wild-type (WT) vs. Q1069R-ACE demonstrated the mutant accumulates intracellularly and also that it is significantly degraded by intracellular proteases. Q1069R-ACE retained catalytic and immunological characteristics of WT-ACE N domain whereas it had 10–20% of the nativity of the WT-ACE C domain. A combination of chemical (sodium butyrate) or pharmacological (ACE inhibitor) chaperones with proteasome inhibitors (MG 132 or bortezomib) significantly restored trafficking of Q1069R-ACE to the cell surface and increased ACE activity in the cell culture media 4-fold.Conclusions/SignificanceHomozygous Q1069R substitution results in an ACE trafficking and processing defect which can be rescued, at least in cell culture, by a combination of chaperones and proteasome inhibitors. Further studies are required to determine whether similar treatment of individuals with this ACE mutation would provide therapeutic benefits such as concentration of primary urine.
Highlights
Angiotensin I-converting enzyme (ACE, CD143) is a Zn2+ carboxydipeptidase which plays a key role in the regulation of blood pressure and in the development of vascular pathologies and tissue remodeling [1,2,3,4]
Angiotensin-converting enzyme (ACE) is expressed as two isoforms: somatic ACE, which is responsible for its hypertensive properties, and a smaller isoform, which is expressed solely in germinal cells. sACE is highly expressed in endothelial [5,6], epithelial, neuroepithelial [7,8], and immune cells [9,10] as a membrane-bound protein and has recently been designated as CD143 [11,12]
Human fetuses exposed to ACE inhibitors during the second and third trimesters of gestation are at risk of developing a fetopathy characterized by anuriaoligohydramnios, hypotension, growth restriction, renal tubular dysgenesis and hypocalvaria [22]
Summary
Angiotensin I-converting enzyme (ACE, CD143) is a Zn2+ carboxydipeptidase which plays a key role in the regulation of blood pressure and in the development of vascular pathologies and tissue remodeling [1,2,3,4]. We demonstrate in a CHO cell expression model that a combination of chemical (sodium butyrate) or pharmacological (ACE inhibitor) chaperones with proteasome inhibitors (MG 132 or bortezomib) significantly restored trafficking of mutant ACE to the cell surface.
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