The cytoplasmic domain of the cell adhesion molecule L1 is not required for homophilic adhesion

L1 is a highly conserved cell adhesion molecule with complete homology of the cytoplasmic domain between the known mammalian protein sequences. Since the cytoplasmic domains of other adhesion molecules have been shown to influence adhesion, we have investigated the effects of deletion of the cytoplasmic domain on the ability of L1 to mediate hemophilic adhesion. Full length L1 and a truncated L1, lacking 95% of the cytoplasmic domain, were expressed in myeloma cells. Independent stable transfectants were assayed for the ability to form aggregates. Myelomas expressing L1 lacking the cytoplasmic domain were able to form cell aggregates as well as the myelomas expressing full length L1. Cell aggregate formation was correlated with the level of ii expression, and the aggregation could be blocked by anti-L1 Fabs. Similar results were obtained in adhesion assays of the myeloma cells to substrate-bound L1. These results indicate that the cytoplasmic domain of L1 is not required for homophilic interactions.