A timetable of events during programmed cell death induced by trophic factor withdrawal from neuronal PC12 cells

Abstract

We describe a timetable of events during programmed cell death (PCD) in neuronal PC12 cells, specifically, Ras signaling, immediate-early gene (IEG) expression, DNA fragmentation and commitment to PCD. Commitment occurs over a period from 10-20 hr after NGF withdrawal. Ras signaling declines rapidly after NGF removal, reaching minimal levels within 2-4 hr, well before the onset of commitment. DNA fragmentation, detected by TUNEL reaction, begins about 24 hr after NGF withdrawal, well after all cells are committed, but coincident with the onset of cell dissolution previously determined by trypan blue exclusion (Mesner et al., 1992). Among the IEGs studied here, c-jun and TIS21 are expressed within 6 hr after NGF withdrawal. Expression of c-fos, egr-1, and TIS11 does not begin until 20 hr after NGF withdrawal. IEG expression generally ends by 24 hr after NGF withdrawal. The IEGs TIS7 and nur77 are not expressed during PCD, yielding a pattern distinct from that following other stimuli. An identical pattern of IEG expression occurs in non-neuronal PC12 cells deprived of serum, although expression begins at 10-14 hr after serum withdrawal. A similar IEG expression pattern was observed in Rat-1 fibroblasts, with various genes expressed 6-18 hr after serum withdrawal. In none of these cell types did expression of the stress-related gene Hsp70 change following trophic factor withdrawal. The distinctive pattern of IEG expression described here should facilitate identification of intracellular regulatory signals active during PCD.

Mechanisms of Cell Death Induced by the Mitochondrial Toxin 3-Nitropropionic Acid: Acute Excitotoxic Necrosis and Delayed Apoptosis

“…No morphologically normal nuclei were TUNEL-positive, indicating that DNA damage at detectable levels is a late event in both apoptosis and necrosis. This is in agreement with previous studies (Oberhammer et al, 1993;Mesner et al, 1995).…”

Cytoplasmic Localization of Tristetraprolin Involves 14-3-3-dependent and -independent Mechanisms

“…In mice, TTP is expressed in developing oocytes and regenerating small intestine and liver, in addition to hematopoietic tissues (10, 24 -26). Like some other immediate early proteins, in certain contexts TTP is also expressed during induction of apoptosis (27)(28)(29)(30). Consistent with the model that TTP/TIS11 proteins influence growth, survival, or apoptotic signals, we have determined that their constitutive expression at modest levels induces apoptosis through the mitochondrial pathway (31).…”

MyD genes in negative growth control

“…Evidence has been obtained that Egr-1 also trans-activates the p53 promoter, where inhibition of p53 function abrogated Egr-1-dependent apoptosis. Additional evidence for a role for Egr-1 in apoptosis has been obtained in other cell systems as well, including B cell receptor-induced apoptosis in immature B cells (Muthukkuma et al, 1997;Dinkel et al, 1997), apoptosis induced by Ca 2+ ionophor in melanoma cells (Muthukkuma et al, 1995), and stress or growth factor induced apoptosis of neuronal cells (Goodenough et al, 1997;Mesner et al, 1995). The mechanisms by which Egr-1 mediates apoptosis in di erent cell types, including cells of hematopoietic origin, remain to be elucidated.…”