DNA (cytosine-5) methylation represents one of the most widely used mechanisms of enduring cellular memory. Stable patterns of DNA methylation are established during development, resulting in creation of persisting cellular phenotypes. There is growing evidence that the nervous system has co-opted a number of cellular mechanisms used during development to subserve the formation of long term memory. In this study, we examined the role DNA (cytosine-5) methyltransferase (DNMT) activity might play in regulating the induction of synaptic plasticity. We found that the DNA within promoters for reelin and brain-derived neurotrophic factor, genes implicated in the induction of synaptic plasticity in the adult hippocampus, exhibited rapid and dramatic changes in cytosine methylation when DNMT activity was inhibited. Moreover, zebularine and 5-aza-2-deoxycytidine, inhibitors of DNMT activity, blocked the induction of long term potentiation at Schaffer collateral synapses. Activation of protein kinase C in the hippocampus decreased reelin promoter methylation and increased DNMT3A gene expression. Interestingly, DNMT activity is required for protein kinase C-induced increases in histone H3 acetylation. Considered together, these results suggest that DNMT activity is dynamically regulated in the adult nervous system and that DNMT may play a role in regulating the induction of synaptic plasticity in the mature CNS. DNA (cytosine-5) methyltransferases (DNMTs)5 are a family of enzymes that catalyze the methylation of cytosine residues (1-5). Many biological processes, including imprinting, differentiation, X-chromosome inactivation, and long term transcriptional regulation, involve cytosine methylation, a covalent modification of DNA (6, 7). Tissue-specific patterns of DNA methylation are established early during development as a consequence of cellular differentiation (8, 9). Expression and activity of DNMT is generally restricted to dividing cells and is very high during early development (5, 10 -13). In most cell types, DNMT expression diminishes greatly once terminal differentiation occurs (5, 10 -14).The mammalian brain consists primarily of postmitotic neurons and glial cells that possess relatively low proliferative potential. In addition, there are small populations of stem cells in various regions of the brain that have the potential to develop into new neurons (15). Therefore, reports that the adult central nervous system (CNS) possesses relatively high levels of DNMT mRNA and enzyme activity were surprising (5, 13, 16). Early studies into the function of DNMT in the brain suggested that this enzyme might be involved in DNA repair and neurodegeneration (16 -19). Important recent studies also have implicated misregulation of DNMT specifically or DNA methylation in general in such cognitive disorders as schizophrenia, Rett syndrome, and Fragile X mental retardation (20 -22).Epigenetics refers to a set of self-perpetuating post-translational modifications of DNA and nuclear proteins that produce lasting alterations in ch...

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Risk of pancreatic cancer, the fourth deadliest cancer in the U.S., is increased by obesity. Calorie restriction (CR) prevents obesity, suppresses carcinogenesis in many models, and reduces serum levels of insulin-like growth factor (IGF)-1. In the present study, we examined the impact of CR on a model of inflammation-associated pancreatitis and pancreatic dysplasia, with a focus on the mechanistic contribution of systemic IGF-1. Administration of a 30% CR diet for 14 weeks decreased serum IGF-1 and hindered pancreatic ductal lesion formation and dysplastic severity, relative to a higher calorie control diet, in transgenic mice overexpressing cyclooxygenase (COX)-2 (BK5.COX-2). These findings in CR mice correlated with reductions in Ki-67-positive cells, vascular luminal size, vascular endothelial growth factor expression, and phosphorylation and total expression of downstream mediators of the IGF-1 pathway. Cell lines derived from BK5.COX-2 ductal lesions (JC101cells) formed pancreatic tumors in wild-type FVB mice that were significantly reduced in size by a 14-week CR regimen, relative to the control diet. To further understand the impact of circulating levels of IGF-1 on tumor growth in this model, we orthotopically injected JC101 cells into liver-specific IGF-1-deficient (LID) mice. The ~65% reduction of serum IGF-1 in LID mice resulted in significantly decreased burden of JC101 tumors, despite modestly elevated levels of circulating insulin and leptin. These data show that CR prevents development of dysplasia and growth of pancreatic cancer through alterations in IGF-1, suggesting that modulation of this pathway with dietary and/or pharmacologic interventions is a promising pancreatic cancer prevention strategy.

Etiologic factors for pancreatic cancer, the fourth deadliest malignant neoplasm in the United States, include obesity and abnormal glucose metabolism. Calorie restriction (CR) and rapamycin each affect energy metabolism and cell survival pathways via inhibition of mammalian target of rapamycin (mTOR) signaling. Using a Panc02 murine pancreatic cancer cell transplant model in 45 male C57BL/6 mice, we tested the hypothesis that rapamycin mimics the effects of CR on pancreatic tumor growth. A chronic regimen of CR, relative to an ad libitum-fed control diet, produced global metabolic effects such as reduced body weight (20.6±1.6g vs. 29.3±2.3g; p<0.0001), improved glucose responsiveness, and decreased circulating levels of insulin-like growth factor (IGF)-1 (126±8ng/mL vs. 199±11ng/mL; p=0.0006) and leptin (1.14±0.2 ng/mL vs. 5.05±1.2 ng/mL; p=0.01). In contrast, rapamycin treatment (2.5mg/kg i.p. every other day, initiated in mice following 20 weeks of ad libitum control diet consumption), relative to control diet, produced no significant change in body weight, IGF-1 or leptin levels, but decreased glucose responsiveness. Pancreatic tumor volume was significantly reduced in the CR group (221±107mm3; p<0.001) and, to a lesser extent, the rapamycin group (374±206mm3; p=0.04) relative to controls (550±147mm3), and this differential inhibition correlated with expression of the proliferation marker Ki-67. Both CR and rapamycin decreased phosphorylation of mTOR, p70/S6K and S6 ribosomal protein, but only CR decreased phosphorylation of Akt, GSK-3β, ERK/MAPK, and STAT-3TYR705. These findings suggest rapamycin partially mimics the anticancer effects of calorie restriction on tumor growth in a murine model of pancreatic cancer.

Pancreatic cancer is the 4th deadliest cancer in the U.S. Obesity has emerged as a significant and modifiable risk factor for pancreatic cancer. Calorie restriction (CR) is an anti-obesity intervention that has been shown in many model systems to have potent anticancer effects. Levels of bioavailable insulin-like growth factor (IGF)-1, an established mitogen in a variety of cancer cell lines, increase in response to positive energy balance and decrease with CR. We hypothesized that the genetic reduction of circulating IGF-1 levels seen in liver-specific IGF-1-deficient (LID) mice would diminish the tumor burden of orthotopically transplanted pancreatic cancer cells, similar to CR, while administration of exogenous IGF-1 would restore the tumor burden. To test this hypothesis, mouse pancreatic cancer cells (JC101, derived from our BK5-COX-2 transgenic mouse model of spontaneous pancreatic cancer) were orthotopically transplanted in LID and littermate control (LC) mice. LID mice were also randomized to receive Alzet miniature osmotic pumps (implanted subcutaneously) continuously infusing either vehicle (n=8) or 1 µg/hr of recombinant human IGF-1 (Increlex®, Tercica, Inc., Brisbane, CA; n=8). LC mice were infused with vehicle (n=8). Mice were killed 28 days after injection, blood was collected by cardiac puncture and serum samples were stored at −80°C, and tumors were weighed and fixed in 10% normal buffered formalin for histological and immunohistochemical (IHC) analysis. IHC staining was performed on paraffin-embedded tissues using antibodies against Ki67 and cyclin D1 to assess proliferation. LID mice exhibited significantly smaller tumors (0.20 ± 0.02 g) than LC mice (0.45 ± 0.11 g, p&lt;0.05) or LID + IGF-1 mice (0.57 ± 0.14 g, p&lt;0.01). Serum IGF-1 levels were reduced approximately 60% in the LID mice relative to the LC mice (p&lt;0.01), while infusion of human IGF-1 resulted in total serum IGF-1 levels (murine plus human IGF-1) exceeding either LC or LID mice (p&lt;0.01). In contrast, insulin and leptin levels in LID mice were significantly higher than those seen in LC (p&lt;0.05) or LID+IGF-1 (p&lt;0.01) mice. Consistent with tumor burden data, LID tumors, relative to LC and LID + IGF-1, displayed less expression of proliferative markers. These findings suggest that genetic reduction of circulating IGF-1 levels decreases transplanted pancreatic tumor growth despite increased levels of insulin and leptin, underscoring the importance of the IGF-1 pathway as a pancreatic cancer prevention target. Citation Information: Cancer Prev Res 2010;3(1 Suppl):A102.