Altered gene expression in neurons during programmed cell death: identification of c-jun as necessary for neuronal apoptosis.

Abstract

Abstract. We have examined the hypothesis that neuronal programmed cell death requires a genetic program; we used a model wherein rat sympathetic neurons maintained in vitro are deprived of NGF and subsequently undergo apoptosis. To evaluate gene expression potentially necessary for this process, we used a PCR-based technique and in situ hybridization; patterns of general gene repression and selective gene induction were identified in NGF-deprived neurons. A temporal cascade of induced genes included "immediate early genes;' which were remarkable in that their induction occurred hours after the initial stimulus of NGF removal and the synthesis of some required ongoing protein synthesis. The cascade also included the cell cycle gene c-myb and the genes encoding the extracellular matrix proteases transin and collagenase. Concurrent in situ hybridization and nuclear staining revealed that while c-jun was induced in most neurons, c-fos induction was restricted to neurons undergoing chromatin condensation, a hallmark of apoptosis. To evaluate the functional role of the proteins encoded by these genes, neutralizing antibodies were injected into neurons. Antibodies specific for either c-Jun or the Fos family (c-Fos, Fos B, Fra-1, and Fra-2) protected NGF-deprived neurons from apoptosis, whereas antibodies specific for Jun B, Jun D, or three nonimmune antibody preparations had no protective effect. Because these induced genes encode proteins ranging from a transcription factor necessary for death to proteases likely involved in tissue remodeling concurrent with death, these data may outline a genetic program responsible for neuronal programmed cell death.

p21WAF1 induces permanent growth arrest and enhances differentiation, but does not alter apoptosis in PC12 cells

“…irradiation, heat shock (Davis, 1994;Zanke et al, 1996) and trophic factor withdrawal from PC12 cells (Xia et al, 1995). cJUN, the downstream target of JNK, was also shown to be critical for apoptosis in SCG cultures following NGF removal (Estus et al, 1994). In the current study, p21 did not inhibit death induced by trophic factor withdrawal, u.v.…”

Diverse functions of JNK signaling and c-Jun in stress response and apoptosis

“…Initial studies using PC12 cells and sympathetic neurons showed that inhibition of c-Jun activity, either by microinjection of antibodies against c-Jun or expression of dominant negative mutant forms of the protein protects the cells from nerve growth factor (NGF) withdrawal-induced apoptosis (Estus et al, 1994;Ham et al, 1995;Xia et al, 1995). Furthermore, ectopic expression of c-Jun is su cient to drive sympathetic neurons into apoptosis in the absence of external stimuli (Ham et al, 1995).…”

BH3-only proteins: key regulators of neuronal apoptosis

“…One of the first regulated genes to be identified was the basic/leucine zipper transcription factor c-Jun, a member of the AP-1 family. The level of the c-jun mRNA and c-Jun protein increases rapidly in sympathetic neurons after NGF withdrawal, and microinjection of neutralizing antibodies against c-Jun or expression of a c-Jun dominant-negative mutant protects sympathetic neurons against NGF withdrawal-induced death, 4,5 as does conditional knockout of the c-jun gene in sympathetic neurons isolated from mice with a floxed c-jun gene. 6 These observations supported the idea that NGF withdrawal-induced death involves the transcriptional induction of genes that activate the cell death programme.…”