Truncated trkB.T1 is dominant negative inhibitor of trkB.TK+-mediated cellsurvival

Truncated trkB.T1 (T1) neurotrophin receptor inhibits full-length trkB.TK(TK+) signaling. At least two possible mechanisms have been proposed for th is action: T1 could trap the ligand or function as a dominant negative rece ptor. To differentiate between these possibilities we have studied survival of serum-deprived PC12-trkB cells stably expressing TK+, PC12-trkB cells w ere observed to display constitutive trkB kinase activity which leads to su rvival of a cell subpopulation in the absence of added brain-derived neurot rophic factor (BDNF) and serum. Exogenous BDNF significantly increased cell survival, and this increase was inhibited by BDNF neutralizing antibody. T he antibody treatment had no effect on the constitutive TK+ activity. Trans fected T1 completely inhibited survival by BDNF or constitutive trkB kinase activity in PC12-trkB cells similarly to tyrosine kinase inhibitor K252a. In addition, T1 coimmunoprecipitated with TK+ and inhibited its autophospho rylation by BDNF, These data suggest that truncated T1 inhibits TK+ signali ng by dominant negative action. (C) 2001 Academic Press.