Anti‐β1 integrin antibody inhibits schwann cell meylination

Abstract

Schwann cells (SCs) co-cultured with sensory neurons require ascorbate supplementation for basal lamina assembly and differentiation into myelinating cells. The ascorbate requirement can be bypassed by adding a purified basal lamina component, laminin, to SC/neuron co-cultures. We have examined the role of laminin receptors, namely, the beta 1 subfamily of integrins, in the process of myelination. We demonstrate by immunostaining or immunoprecipitation that undifferentiated SCs in contact with axons express large amounts of the beta 1 subunit in association with the alpha 1 or alpha 6 subunit. In co-cultures of myelinating SCs, alpha 1 beta 1 is no longer present, alpha 6 beta 1 is still present but at reduced levels, and alpha 6 beta 4 is expressed at much higher levels than in co-cultures of undifferentiated SCs. Immunogold labelling at the electron microscope level suggested that beta 1 integrins are randomly distributed on undifferentiated SCs, become localized to the SC surface contacting basal lamina in differentiating SCs before the onset of myelination, and are not detected on myelinating SCs. Fab fragments of beta 1 function-blocking antibody block both attachment of isolated SCs to laminin and formation of myelin sheaths by SCs co-cultured with neurons in ascorbate-supplemented medium. SCs unable to myelinate in the presence of the anti-beta 1 antibody assemble patchy basal lamina that is only loosely attached to the cell surface and in some cases appears to be detaching from the membrane. In contrast, an alpha 1 beta 1 function-blocking antibody only partially blocks attachment of isolated SCs to laminin but has no inhibitory effect on SC myelination. These results are consistent with the hypothesis that a member of the beta 1 subfamily of integrins other than alpha 1 beta 1 binds laminin present in basal lamina to the SC surface and transduces signals that are critical for initiation of SC differentiation into a myelinating cell.

Neuregulin and laminin stimulate phosphorylation of the NF2 tumor suppressor in Schwann cells by distinct protein kinase A and p21-activated kinase-dependent pathways

“…Laminin-1 is present in the endoneurium of nerves in perinatal mice, and promotes strong in vitro adhesion, migration and proliferation of SCs (Milner et al, 1997;Dubovy et al, 1999). Previously we demonstrated that a6b1 integrin is the predominant laminin-1-binding integrin present in SCs at this stage of development (Fernandez-Valle et al, 1994). Our new findings indicate that laminin-1 binding to a6b1 integrin promotes Sch-S518 phosphorylation by Pak.…”

“…As the SCs were grown on laminin-1, a ligand for b1 integrin that mediates SC adhesion (Fernandez-Valle et al, 1994), we tested whether a 30 min exposure to soluble laminin-1 stimulated Sch phosphorylation in subconfluent and serum-starved SCs grown on poly-Llysine (PLL). Laminin-1 promoted a strong increase in the fluorescence intensity of phosphorylated Sch and Pak compared to starved SCs (Figure 2c).…”

Ruffling membrane, stress fiber, cell spreading and proliferation abnormalities in human Schwannoma cells

“…Our data are consistent with a requirement for integrin-dependent signaling pathways in the induction of schwannoma phenotypes. Schwann cells express speci®c matrix-binding integrins that are required for establishment of Schwann cell polarity and myelination (Einhaber et al, 1993;Feltri et al, 1994;Fernandez-Valle et al, 1994Jaakkola et al, 1993). We predict, therefore, that schwannoma cells should abnormally ensheath axons and should fail to establish polarity.…”

Cellular transformation by a FERM domain mutant of the Nf2 tumor suppressor gene

“…Studying the consequence of such an interaction may be important to uncovering the role of merlin in cell adhesion. b1 integrins, like merlin, have been shown to suppress anchorage-independent growth (Giancotti and Ruoslahti, 1990;Tikoo et al, 1994), and, most interestingly, b1 integrin interactions with the extracellular matrix and cytoskeleton have been implicated as part of a signal transduction complex necessary for Schwann cell myelination (Fernandez-Valle et al, 1994). Perhaps loss of merlin expression leads to aberrant signaling downstream of b1 integrins resulting in abnormal growth/proliferation of Schwann cells.…”