Journal of Neuroscience, Vol 5, 2662-2671, Copyright © 1985 by Society for Neuroscience
Isolation and characterization of rat schwannoma neurite-promoting factor: evidence that the factor contains laminin
GE Davis, M Manthorpe, E Engvall and S Varon
Rat RN22 schwannoma cells in vitro release into their growth medium a
macromolecular factor that, when bound to polyornithine-coated culture
substrata, will stimulate neuritic regeneration from axotomized peripheral
and central neurons. During the purification of this factor, the
neurite-promoting activity co-purifies with laminin immunoreactivity as
measured by an enzyme-linked immunoadsorbent assay. The purified factor has
an immunoreactivity per milligram of protein similar to that of purified
rat yolk sac tumor laminin. After sodium dodecyl sulfate-polyacrylamide gel
electrophoresis (SDS-PAGE) under reducing conditions, the purified factor
exhibits a major band at 200 kilodaltons (kD) and two minor ones at about
130 and 35 kD. The 200-kD band comigrates with the 200-kD band of purified
rat laminin. After SDS- PAGE under non-reducing conditions, the rat
schwannoma factor and rat laminin both exhibit a band in the 900-kD range
with the schwannoma factor band migrating slightly faster than the laminin
one. The 200-kD (reducing conditions) and 900-kD (non-reducing conditions)
bands of both the schwannoma factor and laminin are stained by
immunoblotting with antisera raised against rat and human laminin and
against a partially purified preparation of the schwannoma factor. On
immunoblots the 400-kD band of laminin (a band not seen in the schwannoma
factor preparation) also stains with all three antisera. When the
antibodies from each of the three antisera are immobilized on protein
A-agarose beads, the beads will completely remove from solution the
neurite- promoting activities of both the schwannoma factor and laminin.
Antibodies raised against rat laminin fail to block the neurite- promoting
activity of the purified schwannoma factor but totally block that of rat
laminin. In contrast, antibodies raised against the schwannoma factor will
block the neurite-promoting activities of both the schwannoma factor and
laminin. By rotary shadowing electron microscopy the schwannoma factor
preparation exhibits cross-shaped images similar but not identical to those
previously reported for rat and mouse laminin. In addition, the schwannoma
factor preparation contains images resembling proteoglycans.