Opposing regulation of choline deficiency-induced apoptosis by p53 and nuclear factor kappaB.

Minnie Q Holmes-Mcnary,Steven H Zeisel,Albert S Baldwin

doi:10.1074/jbc.m010936200

Abstract

We have previously shown that fetal rat brain cells, preneuronal (PC12), and hepatocyte (CWSV-1) cells undergo apoptosis during choline deficiency (CD). The PC12 and epithelial cell culture models were used to determine the molecular mechanism by which CD induces apoptosis. Our data indicate that CD leads to both growth arrest and apoptosis in a subpopulation of cells, which correlate with the up-regulation of the tumor suppressor protein p53 and concurrent up-regulation of the cyclin-dependent kinase-inhibitor p21(WAF1/CIP1). Additionally, CD induced both a G1/S and a G2/M arrest. Transient transfection of a dominant negative p53 (p53DN) construct into PC12 cells, which inhibited endogenous p53 activation, significantly reduced the induction of apoptosis associated with CD. Interestingly, CD also induced the persistent activation of the transcription factor NF-kappaB. Activation of NF-kappaB has been shown to promote cell survival and proposed to antagonize p53. Consistent with this, expression of a super-repressor form of IkappaBalpha (SR-IkappaBalpha) that functions to strongly inhibit NF-kappaB activation, profoundly enhanced cell death during CD. In summary, these results suggest that the effects of CD on apoptosis and subsequent cell survival are mediated through two different signaling pathways, p53 and NF-kappaB, respectively. Taken together, our data demonstrates the induction of opposing mechanisms associated with nutrient deficiency that may provide a molecular mechanism by which CD promotes carcinogenesis.

Highlights

Choline is an essential nutrient required for normal function of all cells [1,2,3]
Cell-cycle Analysis of Choline-deficient Cells—choline deficiency (CD) has been shown previously to inhibit cell growth in PC12 cells [8, 15], the molecular mechanisms associated with this response have not been clearly determined
Our studies lead to several important conclusions regarding the relationship among CD, p53, and p21WAF1/CIP1 expression in growth arrest, apoptosis, and activation of the transcription factor, nuclear factor ␬B (NF-␬B)

Summary

Introduction

Choline is an essential nutrient required for normal function of all cells [1,2,3]. Choline is essential for DNA methylation and DNA synthesis in cells [1, 3]. Increased expression of p21WAF1/CIP1 by p53 transcription correlates with cell cycle control by the induction of a G1 and/or a G2/M arrest or apoptosis [19, 20] Another key transcription factor involved in the control of apoptosis is nuclear factor ␬B (NF-␬B) [23,24,25]. Following induction of nuclear translocation by exposure of cells to stimuli including inflammatory mediators, NF-␬B regulates the expression of genes encoding cytokines, cytokine receptors, and cell adhesion molecules [23,24,25] This control of inflammatory gene expression likely explains the association of NF-␬B activation with inflammatory diseases such as arthritis [26] and inflammatory bowel disease [27].

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