p53 and Egr-1 additively suppress transformed growth in HT1080 cells but Egr-1 counteracts p53-dependent apoptosis

Abstract

The human ®brosarcoma cell line, HT1080, clone H4, was used to determine if the transformation suppressive functions of p53 and Egr-1 have the same underlying mechanism. This cell line expresses only mutant p53 and no detectable Egr-1. H4 clones stably expressing Egr-1 are less transformed in proportion to the level of Egr-1 expressed, acting through the induction of the TGFb1 gene. Here, H4 cells and the highest Egr-1 expressing clone were transfected with a vector expressing normal human p53 to derive stable clones expressing p53. The expression of p53 in H4 cells inhibited transformed growth and reduced tumorigenicity. The eect of coexpression of both p53 and Egr-1 was additive, producing cell lines with 30% of normal growth rate and sevenfold reduced tumorigenicity compared with control lines. These results indicated that each factor may act independently by dierent pathways, although each additively increased the level of p21 WAF1 cell cycle inhibitor. However, exposure of the H4-derived cells to UV-C irradiation produced contrasting eects. Cell cycle analyses showed that the presence of p53 was associated with loss of the G1 and S cells to apoptosis after irradiation. In contrast, the expression of Egr-1 increased entry into S/G2 phase of the cell cycle with little apoptosis via a mechanism involving elevated FAK and low caspase activities. Apoptosis was observed only in the cell lines that expressed no Egr-1, especially those expressing wt-p53, and was preceded by high caspase activity. In summary, Egr-1 suppressed transformation and counteracted apoptosis by the coordinated activation of TGFb1, FN, p21 and FAK, leading to enhanced cell attachment and reduced caspase activity. In the doubly expressing cell line, the survival eect of Egr-1 was dominant over the apoptotic eect of p53.

Iron deficiency upregulates Egr1 expression

“…Egr1 is implicated in cell proliferation and death, depending on the context (Shaulian and Karin 2001). Some studies reported that upregulation of Egr1 prevents cell cycle progression in tumor cells, and others reported that Egr1 activation increases tumor growth (de Belle et al 1999;Scharnhorst et al 2000;Akutagawa et al 2008). Our data for mouse Hepa1c1c7 cells treated with 100 lM DFO for 24 h showed significant decreases in viability and increases in caspase 3/7 activities, suggesting that DFO induced apoptotic cell death.…”

Gene program for cardiac cell survival induced by transient ischemia in conscious pigs

“…Because serpins inhibit caspase activation by serine proteinases (35), they may play a central role in the control of apoptosis. The expression of EGR-1 promotes growth and inhibits apoptosis in different cell types (16)(17)(18), including the heart (19,20). Its antiapoptotic effect includes the down-regulation of the Fas͞Apo-1 promoter (36) and the transcriptional stimulation of PAI-1 (37).…”

“…The plasminogen activator inhibitors PAI-1 and -2 are serine proteinase inhibitors with antiapoptotic potential (12)(13)(14)(15). The expression of EGR-1 promotes growth and inhibits apoptosis (16)(17)(18)(19)(20). The IAP blocks the activation of several caspases (21).…”

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

“…18 As described earlier, expression of Egr1 in HT1080 human fibrosarcoma cells results in increased secretion of functional fibronectin 7,13 and activation of FAK. 45 Activated Akt is a major modulator of apoptosis at several levels (reviewed in Ruoslahti 18 and Kishimoto et al 47 ) (Figure 1). It phosphorylates and inactivates the proapoptotic factors BAD and Caspase 8.…”