Examination of Ornithine Decarboxylase Antizyme RNA Structure and Function from Various Organisms for the Development of Antibiological Agents

Creighton University, Omaha NE

Investigators

Abstract

PROJECT SUMMARY Nearly all organisms possess the capability to synthesize the natural polyamines - putrescine, spermidine and spermine - which are essential for cell growth and differentiation. Due to the ability of polyamines to interact with nearly every biomolecule - DNA, RNA, phospholipids, proteins and ATP, to name a few - they play many roles within the cell in order to support cell growth. It has been well documented that polyamine levels in mammalian cells correlate with the rate of cell growth, high polyamine concentrations have been observed in rapidly proliferating cells and low concentrations have been measured in slow-growing or quiescent cells. Not surprisingly, the transport and metabolism of polyamines are highly regulated by complex feedback mechanisms. Ornithine decarboxylase (ODC) is the key regulatory enzyme in polyamine biosynthesis. ODC homeostasis affects cell growth and cancer development. ODC over-expression has been observed in many tumor types, including prostate, breast, and skin cancers. Both ODC and cellular uptake of polyamines is inhibited by Ornithine Decarboxylase Antizyme (OAZ). The making of Antizyme protein from OAZ mRNA requires translational frameshifting at a highly conserved site to bypass premature termination. Mammalian OAZ mRNAs further possess a pseudoknot (PK) RNA 3¢ to the frameshift site that stimulates +1 frameshifting. Moreover, frameshifting is stimulated by polyamines, thus providing a feedback mechanism whereby the accumulation of metabolic products inhibits biosynthesis. Although the role of the OAZ pseudoknot RNA element (further designated OAZ-PK) in polyamine-dependent frameshifting has been investigated, it has not been examined as a distinct polyamine “sensor”. Riboswitches are elements within noncoding regions of mRNAs that directly bind to cellular metabolites and modulate gene expression. Many riboswitches provide a mechanism of feedback regulation for gene products within the biosynthetic pathway of the cognate metabolite. Riboswitches are widespread among bacteria, and one class further resides in fungi and plants, but no riboswitches have been found in animals. It is proposed that the OAZ-PK RNA functions as a riboswitch, and herein evidence is provided that this noncoding RNA is a polyamine sensor. This RNA element is highly conserved among vertebrate genes required for spermine biosynthesis. Development of drugs that target putative spermine riboswitches from different organisms might therefore be used for wide-ranging purposes such as anticancer agents, antifungal agents, or pesticides. This proposal will examine the structure and function of the OAZ-PK RNA from various organisms, including those of biomedical relevance – human, pathogenic fungi and disease harboring insects - with the following specific aims: (1) examine the specificity and affinity of polyamine binding to OAZ RNAs from various organisms, (2) investigate the three-dimensional structure of OAZ RNAs, and (3) explore the role of Antizyme OAZ RNAs from various organisms in control of gene expression.