Energy balance, inflammation, and tumor progression : the role of NF-[kappa]B
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Obesity is an established risk and progression factor for many types of cancer, including pancreatic and colon cancer, and is characterized by abnormal metabolic hormone production and a chronic low-grade state of inflammation. However, the links between obesity, hormones, inflammation and tumorigenesis in colon and pancreatic tissue are poorly understood. Calorie restriction (CR), an anti-obesity dietary regimen with potent anticancer effects, reduces serum metabolic hormones and protumorigenic cytokines. Insulin-like growth factor (IGF)-1 is a metabolic hormone that activates NF-[kappa]B, a key regulator of inflammation. NF-[kappa]B is a transcription factor that mediates transcription of many cancer- and inflammation-related genes and is upregulated in both colon and pancreatic cancer. We hypothesized that CR inhibits colon and pancreatic tumor cell growth through modulation of hormone-stimulated NF-[kappa]B activation and protumorigenic gene expression. To test this hypothesis, we used CR and ad libitum feeding to generate a lean and overweight (control) phenotype, respectively; in C57BL/6 mice transplanted with MC38 colon cancer cells or Panc 02 pancreatic cancer cells, and analyzed the effect of diet on circulating hormone levels, markers of inflammation, and tumor growth. We also investigated the in vitro effects of IGF-1 on NF-[kappa]B activation and downstream protumorigenic gene expression in MC38 and Panc 02 cells. CR, relative to control diet, reduced body weight, circulating IGF-1 levels, and transplanted MC38 and Panc 02 tumor growth, as well as protumorigenic gene expression in the MC38 and Panc 02 tumor microenvironment. IGF-1 increased cell viability, NF-[kappa]B nuclear translocation and DNA binding, transcriptional activation, and downstream gene expression of inflammation and other protumorigenic genes in MC38 colon cancer cells and Panc 02 pancreatic cancer cells in vitro. Knockdown studies of NF-[kappa]B in Panc 02 cells using si-RNA established that the IGF-1-induced increase in protumorigenic gene expression is mediated, at least partially, through an NF-[kappa]B-dependent mechanism. In conclusion, these findings in models of pancreatic and colon cancer help clarify the links between obesity, IGF-1, NF-[kappa]B-mediated inflammation, and cancer. This work provides the underpinnings for several new molecular targets and strategies to test in model systems and translational studies for preventing or controlling obesity-related cancer.