Simvastatin induced HCT116 colorectal cancer cell apoptosis through p38MAPK-p53-survivin signaling cascade

Background

Statins, the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors with cholesterol-lowering properties, were recently shown to exhibit anti-cancer effects. However, the molecular mechanism underlying statin-induced cancer cell death remains to be elucidated. Elevated level of survivin is often found over-expressed in human cancers and has been implicated in the progression of tumorigenesis. Given its central role in cell division and action as an apoptosis suppressor, survivin represents a potential molecular target in cancer management.

Methods

In this study, we explored the underlying mechanisms in simvastatin-induced HCT116 colorectal cancer cell apoptosis.

Results

Simvastatin decreased cell viability and induced cell apoptosis in HCT116 cells. These results are associated with the modulation of p21^cip/Waf1 and survivin. Survivin knockdown using survivin siRNAs also decreased cell viability and induced cell apoptosis. Simvastatin's actions on p21^cip/Waf1, survivin and apoptosis were reduced in p53 null HCT116 cells. Simvastatin caused an increase in p53 phosphorylation and acetylation. In addition, simvastatin activated p38 mitogen-activated protein kinase (p38MAPK), whereas an inhibitor of p38MAPK signaling abrogated simvastatin's effects of increasing p53 and p21^cip/Waf1 promoter luciferase activity. Cell viability and survivin promoter luciferase activity in the presence of simvastatin were also restored by p38MAPK inhibitor. Furthermore, Sp1 binding to the survivin promoter region decreased while p53 and p63 binding to the promoter region increased after simvastatin exposure.

Conclusions

Simvastatin activates the p38MAPK-p53-survivin cascade to cause HCT116 colorectal cancer cell apoptosis.

General significance

This study delineates, in part, the underlying mechanisms of simvastatin in decreasing survivin and subsequent colorectal cancer cell apoptosis.     

Histone deacetylase inhibitor BL1521 induces a G1-phase arrest in neuroblastoma cells through altered expression of cell cycle proteins

Histone deacetylase inhibitors (HDACi) have been discovered as potential drugs for cancer treatment. The effect of BL1521, a novel HDACi, on the cell cycle distribution and the induction of apoptosis was investigated in a panel of MYCN single copy and MYCN amplified neuroblastoma cell lines. BL1521 arrested neuroblastoma cells in the G1 phase and induced up to 30% apoptosis. Downregulation of CDK4, upregulation of p21(WAF1/CIP1) and an increase of hypophosphorylated retinoblastoma protein were observed, indicating a possible mechanism for the cell-cycle arrest. BL1521 also induced downregulation of p27, which may underlie the observed induction of apoptosis.     

Estrogen regulation of trefoil factor 1 expression by estrogen receptor alpha and Sp proteins

Estrogen-responsive genes in human breast cancer cells often have an estrogen response element (ERE) positioned next to an Sp1 binding site. In chromatin immunoprecipitation (ChIP) assays, we investigated the binding of estrogen receptor alpha (ER), Sp1, and Sp3 to the episomal and native estrogen-responsive trefoil factor 1 (TFF1; formerly pS2) promoter in MCF-7 breast cancer cells. Mutation of the Sp site upstream of the ERE reduced estrogen responsiveness and prevented binding of Sp1 and Sp3, but not ER to the episomal promoter. In the absence of estradiol (E2), Sp1, Sp3, histone deacetylase 1 (HDAC), and HDAC2, and low levels of acetylated H3 and H4 are associated with the native promoter, with the histones being engaged in dynamic reversible acetylation. Following E2 addition, levels of ER and acetylated H3 and H4 bound to the native promoter increases. There is clearance of Sp1, but not of Sp3, from the promoter while HDAC1 and HDAC2 remain bound. These data are consistent with a model in which Sp1 or Sp3 aid in recruitment of HDACs and histone acetyltransferases (HATs) to mediate dynamic acetylation of histones associated with the TFF1 promoter, which is in a state of readiness to respond to events occurring following the addition of estrogen.     

Differential AMPK phosphorylation by glucagon and metformin regulates insulin signaling in human hepatic cells

Insulin and glucagon signaling in the liver are major contributors to glucose homeostasis. Patients with Type 1 and Type 2 diabetes have impaired glycemic control due, in part, to dysregulation of the opposing actions of these hormones. While hyperglucagonemia is a common feature in diabetes, its precise role in insulin resistance is not well understood. Recently, metformin, an AMPK activator, was shown to regulate hepatic glucose output via inhibition of glucagon-induced cAMP/PKA signaling; however, the mechanism for how PKA inhibition leads to AMPK activation in human hepatic cells is not known. Here we show that glucagon impairs insulin-mediated AKT phosphorylation in human hepatic cell line Huh7. This impairment of AKT activation by glucagon is due to PKA-mediated inhibition of AMPK via increased inhibitory phosphorylation of AMPK^Ser173 and reduced activating phosphorylation of AMPK^Thr172. In contrast, metformin decreases PKA activity, leading to decreased pAMPK^Ser173 and increased pAMPK^Thr172. These data support a novel mechanism involving PKA-dependent AMPK phosphorylation that provides new insight into how glucagon and metformin modulate hepatic insulin resistance.     

Acidic domain is indispensable for MDM2 to negatively regulate the acetylation of p53

MDM2 is the most important negative regulator of tumor suppressor p53. Both RING finger domain and acidic domain of MDM2 contribute to the ubiquitination of p53. The crosstalk between ubiquitination and acetylation of p53 prompts us to examine whether acidic domain is essential for MDM2 to regulate the acetylation of p53. We find that the acidic domain of MDM2 is necessary to inhibit p300-mediated acetylation of p53 as well as to mediate the deacetylation of p53. Our results indicate that acidic domain of MDM2 provides essential information for acetyltransferase p300 and deacetylase HDAC1 and is indispensable for MDM2 to negatively regulate the acetylation of p53.     

Molecular mechanisms for inhibition of colon cancer cells by combined epigenetic-modulating epigallocatechin gallate and sodium butyrate

Bioactive compounds are considered safe and have been shown to alter genetic and epigenetic profiles of tumor cells. However, many of these changes have been reported at molecular concentrations higher than physiologically achievable levels. We investigated the role of the combinatorial effects of epigallocatechin gallate (EGCG), a predominant polyphenol in green tea, and sodium butyrate (NaB), a dietary microbial fermentation product of fiber, in the regulation of survivin, which is an overexpressed anti-apoptotic protein in colon cancer cells. For the first time, our study showed that the combination treatment induced apoptosis and cell cycle arrest in RKO, HCT-116 and HT-29 colorectal cancer cells. This was found to be regulated by the decrease in HDAC1, DNMT1, survivin and HDAC activity in all three cell lines. A G2/M arrest was observed for RKO and HCT-116 cells, and G1 arrest for HT-29 colorectal cancer cells for combinatorial treatment. Further experimentation of the molecular mechanisms in RKO colorectal cancer (CRC) cells revealed a p53-dependent induction of p21 and an increase in nuclear factor kappa B (NF-κB)-p65. An increase in double strand breaks as determined by gamma-H2A histone family member X (γ-H2AX) protein levels and induction of histone H3 hyperacetylation was also observed with the combination treatment. Further, we observed a decrease in global CpG methylation. Taken together, these findings suggest that at low and physiologically achievable concentrations, combinatorial EGCG and NaB are effective in promoting apoptosis, inducing cell cycle arrest and DNA-damage in CRC cells.