The fibronectin domains of the neural adhesion molecule TAX-1 are necessary and sufficient for homophilic binding.
Cell adhesion molecules belonging to the immunoglobulin superfamily promote cell aggregation and neurite outgrowth. These proteins are multidomain molecules comprising a number of distinct modules, notably Ig domains of the C2 class and fibronectin type III repeats. A subgroup of these neural adhesion molecules are linked to the membrane with a glycosylphosphatidylinositol anchor and show a more restricted pattern of expression in the embryo. Among them, the human homologue of the transient axonal glycoprotein, named TAX-1, shares a great degree of similarity at the protein level with rodent TAG-1. In the present study we set out to determine which domains of TAX-1 are involved in promoting the homophilic, adhesive properties of the molecule. We established stable Schneider-2 cell lines expressing the intact molecule, the fibronectin, or the immunoglobulin domains. The fibronectin domains were necessary and sufficient to mediate homophilic binding and induce cell aggregation, a response also observed with cells expressing the intact TAX-1 molecule. Aggregation was inhibited by the secreted form of the TAG-1 protein. On the other hand, the immunoglobulin domains by themselves were not able to induce cell aggregation. In addition, TAX-1 was localized in areas of cell contact among aggregating cells, justifying its role as an adhesion molecule.
Tsiotra
P C
PC
Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology, Heraklion 71110, Crete, Greece. karagogeos@nefeli.imbb.forth.gr
Theodorakis
K
K
Papamatheakis
J
J
Karagogeos
D
D
D015816:Cell Adhesion Molecules, Neuronal / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D058969:Contactin 2; D018076:DNA, Complementary; D005353:Fibronectins / Q000378:metabolism*; D006133:Growth Substances / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007136:Immunoglobulins / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D011485:Protein Binding
C548674:CNTN2 protein, human; D015816:Cell Adhesion Molecules, Neuronal; D058969:Contactin 2; D018076:DNA, Complementary; D005353:Fibronectins; D006133:Growth Substances; D007136:Immunoglobulins; D008562:Membrane Glycoproteins; D010727:Phosphoric Diester Hydrolases; D043265:Phosphatidylinositol Diacylglycerol-Lyase