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BASIC BIOLOGY

Identification of a Novel Alternatively Spliced Variant Endothelin Converting Enzyme-1 Lacking a Transmembrane Domain

Eyal Klipper^*, Nitzan Levy^*, Tamar Gilboa^*, Laurent Muller and Rina Meidan^*,1

^* Department of Animal Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot 76100, Israel; and INSERM U 36 College de France Paris, 75005 Paris, France

To whom requests for reprints should be addressed at ¹ Department of Animal Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot 76100, Israel. E-mail: rina.meidan{at}huji.ac.il

Abstract

Endothelin-converting enzyme (ECE)-1 cleaves big endothelins, as well as bradykinin and ß-amyloid peptide. Several isoforms of ECE-1 (ECE-1a, 1b, 1c, and 1d) have been identified to date, they differ only in their amino terminus and share the catalytic domain located in the C-terminal end. In addition to full-length ECE-1 forms, we identified novel, alternatively spliced messenger RNAs (mRNAs) of ECE-1b, 1c, and 1d. These splice variants (SVs) lack exon 3', which codes for the transmembrane (TM) region and is present in full-length forms. SV mRNAs were highly expressed in endothelial cells (EC) derived from macrovascular and microvascular beds. Analyses of ECE-1d and its SV forms in stably transfected human embryonic kidney (HEK)-293 cells revealed that both proteins were recognized by antibodies to C-terminal ECE-1, but an antibody to the N-terminal only bound ECE-1d. The novel protein, designated ECE-1sv, has an apparent molecular weight of 75 kDa. ECE-1sv lacks the TM sequence (or signal peptide) and, therefore, is expected to remain cytosolic. Presence of ECE-1sv in different cellular compartments than the full-length forms of the ECE-1 may suggest a distinct physiologic role for these proteins.

Key Words: endothelial cells • steroidogenic cells • protein translation • enzymatic activity