Early Growth Response-1-dependent Apoptosis Is Mediated by p53

Abstract

The early growth response-1 (EGR-1) protein is an anti-proliferative signal for certain tumor cells and is required for apoptosis induced by stimuli that elevate intracellular Ca 2؉. We present evidence that EGR-1 transactivates the promoter of the p53 gene and upregulates p53 RNA and protein levels. Inhibition of p53 function with dominant-negative p53 mutants abrogates EGR-1-dependent apoptosis. These findings establish a direct functional link between EGR-1 and the p53-mediated cell death pathway and suggest that mutant forms of p53 in tumor cells may provide resistance to the antiproliferative effects of EGR-1.Apoptosis, or programmed cell death, a genetic process of coordinated deletion of selective cells, is essential for metazoan development and homeostasis (1-4). The primordial forms of apoptosis in Caenorhabditis elegans and Drosophila have been recapitulated in mammalian cells, and striking similarities have been observed in the cell death programs of invertebrates and vertebrates (5-7). Apoptosis is characterized by cell membrane blebbing, chromatin condensation, changes in nuclear architecture, and oligonucleosome-length DNA fragmentation (8, 9). The apoptotic pathways consist of an early component that includes molecular events that are specific for an inducer or a group of inducers and of downstream effector components that are common to diverse apoptotic signals (10). The common components include a basal cell death machinery composed of initiator, amplifier, and effector proteases belonging to the interleukin-1 converting enzyme subfamily or an interleukin-1 converting enzyme-related family (10 -14). Downstream targets of these proteases include the interleukin-1 converting enzyme subfamily proteases themselves; the nuclear enzymes poly(ADP-ribose) polymerase and DNA-dependent protein kinase, which are involved in DNA repair; the nuclear protein U1 ribonucleoprotein and nuclear lamins; and cytoplasmic components such as protein kinase C␦ and cytoskeleton components such as actin (cited in Ref. 12).Intracellular calcium is a key second messenger implicated in the activation of the apoptotic program in diverse cell types and tissues (15-18). Intracellular calcium levels become elevated after the activation of T lymphocytes by anti-CD3 or that of B lymphocytes by anti-IgM antibodies; after withdrawal of survival factors, such as testosterone in the prostate gland; or after exposure to certain exogenous stimuli, such as calcium ionophores or thapsigargin (TG), 1 a potent inhibitor of the Ca 2ϩ

The transcription factor Egr1 is a direct regulator of multiple tumor suppressors including TGFβ1, PTEN, p53, and fibronectin

“…33 The stability of p53 is under extensive and complex regulation largely owing to intricate cytoplasmic and nuclear interactions, especially with Mdm2 and p14 ARF family members and related proteins (Figure 2) (reviewed in Nair et al 34 and Liu et al 35 ). Thus, significant regulation of p53 expression by the direct induction of transcription may be unusual.…”

“…Direct binding of the p53 promoter by Egr1 was first shown in human melanoma A375-C6 cells during thapsigargin-induced apoptosis. 34 Studies of the Egr1-null mouse system have revealed that Egr1 normally controls p53 expression leading to cell cycle arrest, senescence, and -for cells that survive 'crisis' -transformation. Freshly prepared primary fibroblasts (MEFs) from Egr1-null embryos exhibit a surprising phenotype characterized by rapid and apparent immortal growth, with no hint of replication-dependent growth arrest characteristic of MEFs from wild-type mice.…”

EGR-1 forms a complex with YAP-1 and upregulates Bax expression in irradiated prostate carcinoma cells

“…In this study, we selected the Egr-1 gene to understand its role in radiation resistance, because (a) upon orchiectomy Egr-1 was rapidly induced, leading to apoptosis of androgen-dependent prostate cells (Buttyan et al, 1988;Day et al, 1993); (b) IR upregulates EGR-1 expression (Datta et al, 1992); and (c) EGR-1 protein upregulates pro-apoptotic gene expression (Ahmed et al, 1997;Nair et al, 1997;Das et al, 2001).…”

“…EGR-1 protein upregulates p53 in response to thapsigargin-induced apoptotic stimuli (Nair et al, 1997). Expression of dominant-negative EGR-1 mutant (dnEGR-1) in melanoma cells (wt p53) caused radio resistance (Ahmed et al, 1996).…”

GTPase deficient mutant of Gα13 regulates the expression of Egr-1 through the small GTPase Rho

“…However, the Ga 13 -regulated cell type-speci®c signaling mechanism that activates these multiple pathways, has not been identi®ed. In this context, the ability of Ga 13 to activate the expression of early growth response factor-1 or Egr-1 (Vara Prasad et al, 1994) and the ability of Egr-1 to regulate cell proliferation, di erentiation and apoptosis in a cell-type speci®c manner are worth noting (Milbrant, 1987;Sukhatame et al, 1988;Cao et al, 1990;Nguyen et al, 1993;Nair et al, 1997). This interesting correlation suggests the possibility that the di erential e ects of Ga 13 on cell proliferation, di erentiation and apoptosis are functions of Egr-1 and/or the genes regulated by Egr-1.…”