Latent transforming growth factor β-binding protein-3 and fibulin-1C interact with the extracellular domain of the heparin-binding EGF-like growth factor precursor

From ≈ 3 × 106 screened monkey cDNA clones, cDNA clones were recovered that contained nucleotide sequences encoding domains of the monkey latent transforming growth factor-β binding protein-3 (MkLTBP-3) and fibulin-1C protein. The amino acid sequence derived from the MkLTBP-3 gene shared 98.6% identity with human LTBP-3 and 86.7% identity with mouse LTBP-3 amino acid sequences. The amino acid sequence derived from the monkey fibulin-1C gene shared 97.2% identity with human fibulin-1C. Yeast two-hybrid screens indicate that LTBP-3 and fibulin-1C interact with proHB-EGF through their calcium-binding EGF-like modules.The interactions of the extracellular domain of proHB-EGF with LTBP-3 and fibulin-1C suggest novel functions for HB-EGF between cell and tissue surfaces.The precursor of heparin-binding EGF-like growth factor (proHB-EGF) is found on a wide variety of cell surfaces and is present in numerous tissue types [1]. Previously in our laboratory, we cloned the cDNA encoding proHB-EGF from monkey Vero cells and identified this cell-surface molecule as a receptor for diphtheria toxin (DT) [2]. The predicted amino acid sequence was shown to be identical to that of the cell surface-expressed precursor of human heparin-binding EGF-like growth factor (proHB-EGF) [3,4]. The derived amino acid sequence revealed a signal sequence (residues 1–23), an extracellular domain (residues 24–159), a transmembrane domain (residues 160–184), and a carboxyl terminal cytoplasmic domain (residues 185–208) [2]. Proteolytic processing of the proHB-EGF occurs on the cell surface and results in the release of mature HB-EGF (mHB-EGF) (residues 63–148) [5]. The mature/soluble HB-EGF is a member of the EGF family of growth factors that includes amphiregulin, epidermal growth factor, and transforming growth factor a [6]. Mature HB-EGF released from the cell surface is mitogenic and is able to bind to the EGF receptor [3]. Membrane-bound proHB-EGF has juxtacrine growth factor activity [7] and als