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J. Cell Biol.,
Volume 142, Number 4, August 24, 1998 1083-1093
Max-Delbrück-Centrum für Molekulare Medizin, D-13122 Berlin, Germany
Neurofascin is a member of the L1 subgroup
of the Ig superfamily that promotes axon outgrowth by
interactions with neuronal NgCAM-related cell adhesion
molecule (NrCAM). We used a combination of cellular
binding assays and neurite outgrowth experiments to investigate mechanisms that might modulate the interactions of neurofascin. In addition to NrCAM, we here
demonstrate that neurofascin also binds to the extracellular matrix glycoprotein tenascin-R (TN-R) and to the
Ig superfamily members axonin-1 and F11.
Isoforms of neurofascin that are generated by alternative splicing show different preferences in ligand
binding. While interactions of neurofascin with F11 are
only slightly modulated, binding to axonin-1 and TN-R
is strongly regulated by alternatively spliced stretches
located in the NH2-terminal half, and by the proline-alanine-threonine-rich segment.
In vitro neurite outgrowth and cell attachment assays
on a neurofascin-Fc substrate reveal a shift of cellular
receptor usage from NrCAM to axonin-1, F11, and at
least one additional protein in the presence of TN-R,
presumably due to competition of the neurofascin-
NrCAM interaction. Thereby, F11 binds to TN-R of the neurofascin/TN-R complex, but not to neurofascin,
whereas axonin-1 is not able to bind directly to the neurofascin/TN-R complex as shown by competition binding assays.
In conclusion, these investigations indicate that the
molecular interactions of neurofascin are regulated at
different levels, including alternative splicing and by
the presence of interacting proteins.
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