Cell-contact mediated modulation of the sialylation of contactinhibin.

Contactinhibin was found to be involved in contact-dependent inhibition of growth. The growth inhibitory activity of contactinhibin is mediated by N-linked oligosaccharides with desialylated beta-glycosidically linked, terminal galactose residues. Here we show that in sparse human fibroblasts contactinhibin was expressed in a biologically inactive, highly sialylated form both on the plasma membrane and intracellularly, while in confluent cells plasma membrane localized contactinhibin was present in a biologically active, low sialylated form. Plasma membranes were shown to contain a glycoprotein sialidase which is suggested to be engaged in the activation of contactinhibin in a cell contact-dependent manner.