Distinction between differentiation, cell cycle, and apoptosis signals in PC12 cells by the nerve growth factor mutant Delta 9/13, which is selectivefor the p75 neurotrophin receptor

The common neurotrophin receptor p75(NTR) (low affinity nerve growth factor receptor) participates in the high-affinity binding with the TrkA nerve gr owth factor (NGF) receptor, may mediate apoptosis, and may signal independe ntly in a cell-specific manner. The potential of p75NTR to signal independe ntly of TrkA was investigated with an NGF mutant protein (NGF Delta9/13) th at binds poorly to TrkA (Woo et al. [1995] J. Biol. Chem. 270: 6278-6285). The NGF Delta9/13 mutant does not activate TrkA autophosphorylation and fai ls to stimulate the normal NGF-induced growth arrest, demonstrating that Tr kA activation is required to arrest PC12 cells at the NGF-activated G1/S ce ll cycle checkpoint. However, apoptosis is successfully blocked and cell su rvival is promoted by the NGF Delta9/13 mutant in naive PC12 cells after se rum withdrawal, suggesting that p75(NTR) can signal for survival autonomous ly of TrkA. Annexin V binding, an indication of apoptotic plasma membrane d isruption, is inhibited by both NGF and the NGF Delta9/13 mutant after seru m deprivation. Both NGF and the NGF Delta9/13 mutant inhibit the rapid apop totic internucleosomal DNA cleavage of PC12 cells upon serum deprivation. F urthermore, the level of caspase3-like activity that is rapidly activated b y serum withdrawal from PC12 cells is reduced by both the NGF Delta9/13 pro tein and NGF. Finally, upon serum withdrawal, both NGF and the NGF Delta9/1 3 mutant activate nuclear translocation of the transcriptional factor NF-ka ppaB (nuclear factor kappaB), a process involved in cell survival. These re sults are consistent with p75NTR inhibition of caspase-mediated apoptosis i n PC12 cells. The different physiologic responses elicited by NGF Delta9/13 indicate the potential for individual signaling by the two NGF receptors a nd also demonstrate the utility of NGF mutants for receptor-selective signa l transduction. (C) 2001 Wiley-Liss, Inc.