Antibodies to the retina N‐acetylgalactosaminylphosphotransferase inhibit neurite outgrowth

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Abstract
The neural retina N‐acetylgalactosaminylphospho‐transferase (GalNAcPTase) is a cell surface molecule (Balsamo and Lilien, 1980, 1983; Balsamo et al., 1986a) that is tightly associated with, and glycosy‐lates, the calcium‐dependent, cell‐cell adhesion molecule, N‐cadherin (Balsamo and Lilien, 1990). N‐cad‐herin has been implicated in neuronal attachment and neurite outgrowth when at the surface of cels (Bixby et al., 1987, 1988; Matsunaga et al., 1988; Neugebauer et al., 1988; Tomaselli et al., 1988). The intimate association of the GalNAcPTase and N‐cadherin prompted us to test the possibility that the GalNAcPTase is also involved in the process of neurite outgrowth. We tested the effect of one polyclonal and two monoclonal anti‐GalNAcPTase antibodies in cultures of chick neural retina cells extending neurites on substrates requiring N‐cadherin, beta inte‐grin receptors, or the chicken homologue of L1, G4. The length and number of neurites produced were dramatically reduced on all of these substrates by the polyclonal and one of the monoclonal anti‐GalNAcPTase antibodies. The second monoclonal antibody bound to the cell surface but was not inhibitory, indicating that it reacts with a different epitope. The mechanism through which the retina cell surface GalNAcPTase may modulate neurite outgrowth on many substrates is discussed.