Characterization of the receptors for axon guidance factor netrin-4 and identification of the binding domains

Mol Cell Neurosci. 2007 Feb;34(2):243-50. doi: 10.1016/j.mcn.2006.11.002. Epub 2006 Dec 15.

Abstract

Netrins are a family of secreted protein related to laminin and act as tropic cues directing axon growth and cell migration during neural development. Netrin-4 is a novel member of netrin family recently identified in the vertebrate with neuritis elongation promoting activity; however, the receptors for netrin-4 are still unknown. To better understand the function and signal transduction pathway of netrin-4, the potential receptors for netrin-4 were studied in this paper. The netrin-4 protein was prepared by introducing a eukaryotic expression vector with a secretable alkaline phosphatase tag (AP4) into COS7 cells to allow the expression of AP4-netrin4 fusion protein. Axon guidance activity of netrin-4 was confirmed by using the cortical explants. After incubation with cultured primary cortical neurons, the neurons were distinctly labeled by the AP4-coupled netrin-4 ligands. In contrast, the binding activity of AP4-netrin4 to neurons could be completely competed by the exogenously expressed netrin-4 protein without AP4 tag, indicating specificity of netrin-4 binding to the potential receptors. Moreover, netrin-4 could also bind to CHO cells transfected with the plasmids expressing two known receptors for netrin-1, Deleted in Colorectal Cancer (DCC) and UNC5 homolog 1 (UNC5H1) respectively. As there are three domains in netrin-4, we further tried to narrow down the region containing binding sites with the receptors. Interestingly, only the N-terminal domain (LNT) could bind to DCC and UNC5H1. A further ligand-receptor binding analysis showed that both the N- and the C-terminal domain (NCT) but not the EGF-like (EGFL) domain of netrin-4 could bind to the surface of cultured primary neurons, indicating the existence of novel receptors for netrin-4. After competed by netrin-4, we confirmed that the binding of AP tagged netrin-4 domains to neurons were also netrin-4 dependent. The binding activity of the N-terminal domain of netrin-4 is about 3-fold higher than that for the C-terminal domain. In summary, our data here indicated that the two known receptors for netrin-1, DCC and UNC5H1, are also receptors for netrin-4, while only LNT but not EGFL and NCT is the key domain for specific binding. In addition, there are novel receptors for netrin-4, where both LNT and NCT but not EGFL are key domains for binding.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Alkaline Phosphatase / metabolism
  • Amino Acid Motifs / physiology
  • Animals
  • Animals, Newborn
  • Axons / physiology*
  • Binding Sites / physiology
  • Cells, Cultured
  • Cerebral Cortex / cytology
  • Cricetinae
  • Cricetulus
  • Models, Molecular
  • Nerve Growth Factors / physiology*
  • Netrin Receptors
  • Neurons / cytology*
  • Protein Binding / physiology
  • Protein Structure, Tertiary / physiology
  • Rats
  • Receptors, Cell Surface / physiology*
  • Recombinant Fusion Proteins / metabolism*

Substances

  • Nerve Growth Factors
  • Netrin Receptors
  • Receptors, Cell Surface
  • Recombinant Fusion Proteins
  • Alkaline Phosphatase