Structural analysis and tissue localization of human C4.4A: a protein homologue of the urokinase receptor

Biochem J. 2004 Jun 15;380(Pt 3):845-57. doi: 10.1042/BJ20031478.


C4.4A, a structural homologue of the urokinase-type plasminogen activator receptor (uPAR), was originally identified as a metastasis-associated membrane protein, but little is known about its structural and functional properties. Therefore, we expressed, purified and characterized a soluble truncated form of human C4.4A, and used this protein to produce specific polyclonal anti-C4.4A antibodies. By immunohistochemistry we observed a pronounced surface staining for C4.4A in suprabasal keratinocytes of chronic human wounds and found C4.4A expression markedly upregulated in migrating keratinocytes during re-epithelisation of incisional skin wounds. Phorbol-ester-induced hyperplasia of mouse skin is also accompanied by a significant induction of C4.4A expression in the multilayered, suprabasal keratinocytes. C4.4A contains two Ly-6 (leucocyte antigen 6)/uPAR/alpha-neurotoxin modules. Our recombinant human C4.4A is extensively modified by post-translational glycosylation, which include 5-6 N-linked carbohydrates primarily located in or close to its second Ly-6/uPAR/alpha-neurotoxin module and approximately 15 O-linked carbohydrates clustered in a Ser/Thr/Pro-rich region at the C-terminus. A highly protease-sensitive region (Tyr200-Arg204) is located between these two clusters of N- and O-linked carbohydrates. The natural, glycolipid-anchored C4.4A from amnion membranes of human term placenta exhibits similar properties. Using recombinant, soluble C4.4A or MCF 7 cells, which express significant amounts of GPI-anchored C4.4A, we find no evidence for an interaction between C4.4A and uPA, a property suggested previously for rat C4.4A. Collectively these data indicate that C4.4A, although being a structural homologue of uPAR, is unlikely to have a functional overlap with uPAR.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Breast Neoplasms / pathology
  • Cell Adhesion Molecules / biosynthesis
  • Cell Adhesion Molecules / chemistry*
  • Cell Adhesion Molecules / genetics
  • Cell Adhesion Molecules / metabolism*
  • Dermatologic Surgical Procedures
  • GPI-Linked Proteins
  • Humans
  • Hyperplasia / chemically induced
  • Hyperplasia / metabolism
  • Immunohistochemistry
  • Mice
  • Mice, Inbred C57BL
  • Molecular Sequence Data
  • Peptide Fragments / chemistry
  • Peptide Mapping / methods
  • Placenta / chemistry
  • Protein Interaction Mapping / methods
  • Protein Processing, Post-Translational / genetics
  • Receptors, Cell Surface / biosynthesis
  • Receptors, Cell Surface / chemistry*
  • Receptors, Cell Surface / genetics
  • Receptors, Cell Surface / metabolism
  • Receptors, Urokinase Plasminogen Activator
  • Recombinant Fusion Proteins / biosynthesis
  • Recombinant Fusion Proteins / genetics
  • Sequence Homology, Amino Acid
  • Skin / chemistry
  • Skin / pathology
  • Tetradecanoylphorbol Acetate / adverse effects
  • Tetradecanoylphorbol Acetate / analogs & derivatives*
  • Wound Healing


  • Cell Adhesion Molecules
  • GPI-Linked Proteins
  • LYPD3 protein, human
  • PLAUR protein, human
  • Peptide Fragments
  • Plaur protein, mouse
  • Plaur protein, rat
  • Receptors, Cell Surface
  • Receptors, Urokinase Plasminogen Activator
  • Recombinant Fusion Proteins
  • phorbolol myristate acetate
  • Tetradecanoylphorbol Acetate