The Role of Fat in Tumor Formation

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Abstract Obesity is a world-wide public health concern. It has been estimated that 68% of American adults are overweight or obese, causing significant morbidity and mortality1. Recent research suggests that obesity can influence cancer risk. However, the molecular changes induced by obesity that actually enhance cancer development are poorly understood. Early research demonstrated that feeding a high fat diet to mice enhanced ultraviolet B (UVB)-induced skin cancer and that reducing parametrial fat (abdominal fat around the uterus) by either exercise or lipectomy attenuated UVB-induced skin tumor formation. This led us to establish a model to evaluate the role of fat in epidermal skin cell transformation as measured by JB6 P+ cell (an initiated mouse epidermal cell line) growth in soft agar. The JB6 P+ model is a well-characterized model for a neoplastic transformation response to tumor promoters such as 12-O-tetradecanoylphorbol-13-acetate and has a low background of spontaneous transformation. Preliminary data demonstrated that parametrial fat isolated from mice fed a high fat diet caused transformation of JB6 P+ cells. Significantly lower transforming activity was observed with parametrial fat from mice fed a low fat chow diet. Parametrial fat contains a number of adipokines that have the potential to stimulate proliferation, inhibit apoptosis and induce cells to produce reactive oxygen species (ROS) and reactive nitrogen species (RNS), which are hallmark characteristics of tumor promoters. A number of these adipokines that have the potential to stimulate transformation were identified in the parametrial fat pads of mice fed a high fat diet. These adipokines were either absent or present in lower abundance in the parametrial fat pads of mice fed a low fat diet and in other fat depots (inguinal, retroperitoneal, subcutaneous). It is our contention that fat in obesity is intrinsically different from fat from normal subjects in its profile of adipokine production. The central hypothesis of this application is that adipose tissue, specifically parametrial fat, can transform initiated epidermal cells and stimulate carcinogenesis through the release of Serpin E1, TIMP-1 and other adipokines that stimulate reactive oxygen/nitrogen species. The goals of this proposed research are to 1) further characterize a model of fat-stimulated neoplastic transformation 2) determine if the number of calories from fat and the duration of feeding a high fat diet will influence JB6 P+ and HaCaT cell transformation 3) determine the mechanisms of parametrial fat-stimulated transformation both in vitro and in an in vivo model of UVB-induced carcinogenesis and 4) determine if human adipose tissue isolated from obese and normal subjects will stimulate cell transformation. The studies within this proposal will help define the role of fat in skin tumor formation, identify molecular biomarkers of risk and pave the way for future mechanistic work.