Growth of non-transformed mammalian cells in-vitro is characterized by the so-called density- dependent (or contact-dependent) inhibition of growth, i. e. they cease proferation after establishing cell-cell contacts by growing to a confluent monolayer.
We have isolated a glycoprotein referred to as contactinhibin which is responsible for density-dependent inhibition of growth of non-transformed fibroblasts.
It inhibits growth of non-transformed cells reversibly at picomole concentrations when added in immobilized form by binding to a specific receptor, CiR. The biologically active moiety, which is also the part of the molecule bound by the receptor CiR, is the N-glycans with terminal, á-glycosidically linked galactose residues.
Confluent cultures of diploid fibroblasts grown in the presence of anti - contactinhibin - antibodies have lost density-dependent inhibition of growth and show phenotypically transformed growth behaviour. Liposome-mediated loading of fibroblasts with anti -CiR - antibodies also results in loss of growth control in dense cultures.
Contactinhibin (60-70 kDa) is synthesized and stored intracellularily (appr. 90%) in highly sialylated, biologically inactive form. After cells have established contacts, plasma membrane localized contactinhibin is converted to low sialylated, biologically active forms by the activity of a trans-acting ectosialidase.
N-Glycanase digestion results in reduction of the app. molecular weight by appr. 20 kDa, while removal of O-glycans reduces molecular weight by appr. 10 kDa. In confluently grown cells sialylation is confined to O-glycans. Profile analysis of N-glycans by FACE revealed the presence of 5 distinct species. Structural analysis of the major form (performed by Oxford GlycoSystems) revealed the presence of a triantennary structure common to fetuin. Asialo-fetuin has been shown to be without growth inhibitory activity, as were several other glycoproteins. Since contactinhibin is the only plasma membrane glycoprotein which is recognized by CiR and which shows growth-inhibitory activity in a contact-dependent fashion, structural peculiarities of the biologically active N-glycan(s) have to be postulated.
This Abstract was presented during the
First Electronic Glycoscience Conference (EGC-1) in 1995
by
Wieser, R. J., Baumann, C. and Oesch, F.
Laboratory at the Institute of Toxicology, University of Mainz, D-55131 Mainz, Germany
HTMLized by: Christian Frosch
http://www.uni-mainz.de/~cfrosch
Institute of Toxicology
University of Mainz
Last update: 23.07.1997