Migration by haptotaxis of a Schwann cell tumor line to the basement membrane glycoprotein laminin

Laminin is a large (greater than 850-kdalton) glycoprotein that is localized within basement membranes. Recent work has indicated that this protein is present within the endoneurium of mouse sciatic nerve. Furthermore, it has been shown that a rat Schwannoma cell line, RN22F, produced laminin and that laminin promoted the attachment of these cells to bacterial plastic. This report presents evidence that RN22F cells migrate in vitro to laminin in a concentration-dependent fashion. Laminin was extracted from the mouse EHS tumor and purified by molecular sieve and heparin-agarose affinity chromatography. The migration of Schwannoma cells to laminin, as assessed in a microwell modified Boyden chamber, was inhibited in a dose-dependent manner by affinity-purified antilaminin antibody. Zigmond-Hirsch checkerboard analysis experiments indicated that laminin stimulated both random and directed movement of RN22F cells. Additionally, reversal of the laminin gradient in the chambers also stimulated RN22F migration in a concentration-dependent manner, suggesting that directed migration of RN22F cells was due to a substratum-bound laminin (haptotaxis) as opposed to cell movement in response to fluid-phase laminin (chemotaxis). Binding studies using [3H]laminin demonstrated that laminin bound to the filter surface under the assay conditions used, and support the contention that cells are migrating to substrate-bound material. Furthermore, RN22F cells were shown to migrate on filters coated with laminin in the absence of additional fluid-phase laminin. The magnitude of this response could be altered by changing the relative density of bound laminin. In contrast, fibronectin promoted only marginal migration of RN22F cells. Collectively, these observations indicate that haptotaxis may be a mechanism by which laminin may guide cells during development and raise the possibility that it may be involved in peripheral nervous system myelination.