Identification of 130 kDa cell surface LDL-binding protein from smooth muscle cells as a partially processed T-cadherin precursor

Atypical cell surface lipoprotein-binding proteins of 105 kDa and 130 kDa a re present in membranes of vascular smooth muscle cells. We recently identi fied the 105 kDa protein from human aortic media as T-cadherin, an unusual glycosylphosphatidylinositol (GPI)-anchored member of the cadherin family o f cell adhesion proteins. The goal of the present study was to determine th e identity of 130 kDa lipoprotein-binding protein of smooth muscle cells. W e applied different approaches that included protein sequencing of purified protein from human aortic media, the use of human T-cadherin peptide-speci fic antisera, and enzymatic treatment of cultured cells with trypsin and CP I-specific phospholipase C. Our results indicate that the 130 kDa protein i s a partially processed form of T-cadherin which is attached to the membran e surface of smooth muscle cells via a GPI anchor and contains uncleaved N- terminal propeptide sequence. Our data disclose that, in contrast to classi cal cadherins, T-cadherin is expressed on the cell surface in both its prec ursor (130 kDa) and mature (105 kDa) forms. (C) 1999 Elsevier Science B.V. All rights reserved.