The interaction between F3 immunoglobulin domains and protein tyrosine phosphatases zeta/beta triggers bidirectional signalling between neurons and glial cells

F3, a mouse glycosyl-phosphatidylinositol anchored molecule of the immunogl obulin superfamily, is known to influence axonal growth and fasciculation v ia multiple interactions of its modular immunoglobulin-like domains. We pre pared an Fc chimeric molecule (F3IgFc) to identify molecules interacting wi th these domains and characterize the functional impact of the interactions . We affinity-isolated tenascin-C and isoforms of the proteoglycan-type pro tein tyrosine phosphatases zeta/beta (PTP zeta/RPTP beta) from extracts of developing mouse brain. We showed that both PTP zeta/RPTP beta and tenascin -C can bind directly to F3, possibly in an exclusive manner, with the highe st affinity for the F3-PTP zeta/RPTP beta interaction. We observed a strong binding of F3IgFc-coated fluorospheres to astrocytes in neural primary cul tures and to C6 astrocytoma cells, and demonstrated, in antibody perturbati on experiments, that F3-Ig binding on astrocytes depends on its interaction with PTP zeta/RPTP beta. We also found by confocal analysis that tenascin- C and PTP zeta/RPTP beta were colocalized on astrocytes which suggests a co mplex interplay of interactions between PTP zeta/RPTP beta, tenascin-C and F3. We showed that the interaction between PTP zeta/RPTP beta and F3-Ig-lik e domains can trigger bidirectional signalling. C6 glia-expressed PTP zeta/ RPTP beta stimulated neurite outgrowth by cortical and cerebellar neurons, whereas preclustered F3IgFc specifically modified the distribution of phosp hotyrosine labelling in these glial cells. Both effects could be prevented and/or mimicked by anti-F3 and anti-6B4PG antibodies. These results identif y F3 and PTP zeta/RPTP beta as potential mediators of a reciprocal exchange of information between glia and neurons.