Polyamines are essential for growth and differentiation of eukaryotic cells. Aberrant regulation of ornithine decarboxylase (ODC), the rate limiting enzyme in polyamine biosynthesis, has been shown to play a causal role in tumorigenesis. ODC expression is tightly controlled in normal cells; its induction in response to mitogenic stimuli is generally rapid and transient. In contrast, ODC expression is altered in tumor cells, resulting in constitutively high levels of ODC enzyme and concomitant elevated levels of polyamines. The temporal correlation of polyamine biosynthesis with transcription of growth-related genes following mitogenic stimulation suggests that polyamines may contribute to the regulation of expression of genes associated with cell proliferation. Indeed, polyamines have been observed to enhance transcription of a number of genes, including protooncogenes. Gene activation is greatly influenced by the fine structure of nucleosomes bound to DNA. Dynamic changes in chromatin structure are modulated, at least in part, through acetylation of nucleosomal histones. Recently, several transcriptional co-factors have been identified as having histone acetyltransferase and deacetylase activities, suggesting a mechanism by which these chromatin remodeling activities may be directed to specific gene promoters, leading to activation or repression of transcription. Moreover, interference with normal function of these proteins is associated with cell transformation. The overall objective of this project is to determine how polyamines mediate changes in the chromatin environment, resulting in altered gene expression. Thus, the following specific aims are proposed:
Specific Aim #1 : A potential role for polyamines in altering gene transcription in vivo by exerting effects on histone acetyltransferase and deacetylase activities will be assessed. The overall degree and specificity of lysine acetylation of transcriptionally active nucleosomes in cells which have high basal levels of ODC will be compared to that in control cells. The modulation of enzymatic activity, phosphorylation status, protein level, and gene activation/repression ability of specific histone acetyltransferases and deacetylases promoted by polyamines will be examined.
Specific Aim #2 : The effect of elevated levels of polyamines on formation of protein complexes which recruit chromatin remodeling enzymes to gene promoters will be examined in vivo. Particular focus will be on complexes involving histone acetyltransferases and deacetylases which mediate nuclear receptor signaling and p53 regulation of cell proliferation. Polyamine-responsive domains of affected proteins will be characterized. These studies should enable us to better understand the normal role of polyamines in cell proliferation, as well as elucidate the mechanism(s) leading to inappropriate expression of genes implicated in neoplastic transformation.
| Hobbs, Cheryl A; Paul, Barry A; Gilmour, Susan K (2003) Elevated levels of polyamines alter chromatin in murine skin and tumors without global changes in nucleosome acetylation. Exp Cell Res 290:427-36 |
| Hobbs, Cheryl A; Paul, Barry A; Gilmour, Susan K (2002) Deregulation of polyamine biosynthesis alters intrinsic histone acetyltransferase and deacetylase activities in murine skin and tumors. Cancer Res 62:67-74 |
| Hobbs, C A; Gilmour, S K (2000) High levels of intracellular polyamines promote histone acetyltransferase activity resulting in chromatin hyperacetylation. J Cell Biochem 77:345-60 |
