Cycloheximide Protects HepG2 Cells from Serum Withdrawal-Induced Apoptosis by Decreasing p53 and Phosphorylated p53 Levels

Abstract

Cycloheximide (CHX), an inhibitor of protein synthesis, has been reported to prevent cell death in a wide variety of cell types and produced by different apoptotic stimuli. However, the mechanisms by which CHX protects cells from apoptosis are still unclear. In this study, we investigated whether p53 plays a role in the protection by CHX against serum withdrawalinduced apoptosis. Deprivation of serum from the culture medium causes apoptosis in HepG2 cells, and CHX dramatically protects cells from death. p53, p21, and Bax protein levels were elevated, and cell cycle arrest was produced after serum withdrawal. CHX abolished this elevation of p53, p21, and Bax as well as the cell cycle arrest induced by serum deprivation. The p53 inhibitor pifithrin-␣ protects HepG2 cells against apoptosis induced by serum withdrawal. HepG2 cells expressing a dominant negative form of mutant p53 and Hep3B cells lacking p53 were resistant to serum withdrawal-induced apoptosis. Lowering of p53 by small interfering RNA protects HepG2 cells from serum withdrawal-induced apoptosis. p53 phosphorylation was induced by serum withdrawal and other chemotherapeutic reagents such as actinomycin D, doxorubicin, and etoposide. CHX decreases the levels of phosphorylated p53 (pp53) even in the presence of a proteasome inhibitor, which maintains the total p53 levels, whereas it does not affect the dephosphorylation of pp53. These results suggest the possibility that kinases that phosphorylate p53 might be affected by CHX administration. In summary, CHX protects HepG2 cells from serum withdrawal-induced apoptosis through inhibiting the synthesis of p53 and the phosphorylation of p53.

Hdm2 is regulated by K-Ras and mediates p53-independent functions in pancreatic cancer cells

“…The expression of hdm2 in cell lines other than HPDE-E6E7 and Panc-1 cells appeared mostly constitutive and independent of serum factors ( Figure 1a). As reported earlier for other cell types (Shaulian et al, 1997;Bai and Cederbaum, 2006), an inverse relationship between the expression of p53 and hdm2 was observed but only in HPDE-E6E7 cells (Figure 1a). These results suggest that hdm2 is expressed in pancreatic cancer cells that contain inactivating p53 mutations and constitutively active K-Ras.…”

Inhibition of apoptosis by 2,3,7,8-tetrachlorodibenzo-p-dioxin depends on protein biosynthesis

“…This might be due to the inhibition of the translation of proapoptotic proteins by CHX. This has also been shown for HepG2 cells, where co-treatment with pro-apoptotic stimuli and CHX led to a partial reduction of apoptosis (Bai and Cederbaum 2006). Treatment of irradiated cells with both CHX and TCDD did not further inhibit apoptosis indicating that either anti-apoptotic proteins induced by TCDD are not translated anymore or that pro-apoptotic proteins induced by UV-irradiation which are normally affected by TCDD, are not translated anymore.…”

Anti-tumor effect of emodin on gynecological cancer cells

“…The mechanism of cell cycle regulation is closely related to tumorigenesis. Many tumor suppressors, such as p53, RB, BRCA1, p16 and p15, as well as their downstream regulators, such as p21 and Gadd45, are important components of cell cycle checkpoints [29][30][31][32]. Interactions between cell cycleassociated proteins, i.e., cyclins (Cyclin D1 and Cyclin E1) and cyclin-dependent kinases (CDKs; CDK4 and CDK2) regulate progression through the G1 phase.…”