Further studies on the interaction of migrating keratinocytes with fibrinogen

If glass implants placed under one edge of a skin wound in the adult newt are coated with fibrinogen (FGN), keratinocytes from the wound periphery migrate onto the implant. To learn more about the site(s) in FGN that permits this migration, we exposed keratinocytes to implants coated with forms of FGN containing modifications or deletions in the 3 most commonly studied cell binding sites; the RGDF sequence at A alpha 95-98, RGDS at A alpha 572-575 and the carboxy terminal 12 amino acids in the gamma A chain. Recombinant FGN with either RGD sequence altered to RGE supported migration as well as unmodified FGN did. Replacement of the carboxy terminal 4 amino acids in the gamma A chain by a 20 amino acid sequence that disrupts the ability of the gamma terminus to mediate platelet aggregation (the gamma' variant) likewise had no effect. Nor did simultaneous antibody blockade of the RGDS, RGDF, and gamma A sites have any effect. At its best, Dhem1, a fragment containing the RGDS and gamma A sites, produced only about half as much migration as the maximum obtained on intact FGN. Dhem2, a fragment differing from Dhem1 only by having a gamma' variant in place of gamma A, was even less active. Two other D fragments, both of which were missing a large part of the A alpha chain, and one of which contained none of the three major binding sites, supported considerable migration, suggesting that loss of the A alpha chain COOH terminus reveals a site that was not exposed in Dhem1 and 2. A alpha chain fragments containing the RGDF or RGDS sequence were active, but a much larger fragment without RGD was inactive. A soluble peptide consisting of the sequence, RGDS, was a potent inhibitor of migration on FGN but RGDF and the gamma A pentapeptide, KQAGD, were minimally effective. Longer versions of these peptides decreased the effectiveness in all cases. These results suggest that under certain circumstances, newt keratinocytes may interact with each of the 3 major binding sites in FGN as well as a site outside these sequences.