Lysine Metabolism is a New Tumor Suppressor Pathway in Breast Cancer that is Deregulated by Obesity
Session Number
C01
Advisor(s)
David Crowe, University of Illinois at Chicago
Location
B-116
Start Date
28-4-2016 10:40 AM
End Date
28-4-2016 11:05 AM
Abstract
Obesity (excess fat) is a cause of breast cancer, but reasons for this are not understood. Peroxisome proliferator- activated receptor gamma (PPARɣ) is responsible for fat cell differentiation and is activated by fatty acids stored in fat cells. PPARɣ prevents breast cancer in humans. We hypothesized that excess fatty acids may reverse PPARɣ function to tumor promotion. To test this hypothesis, we deleted the PPARɣ gene in mammary epithelium of normal and obese mice. Decreased PPARɣ expression in obese mice increases tumor latency and depletes tumorigenic progenitor cells. These cells slowly digest their mitochondria by the process of autophagy. To understand this, we determined changes in gene expression in obese PPARɣ null mammary tumors. Gene expression analysis showed a 16-fold increase in 2- aminoadipate semialdehyde synthase, an enzyme involved in lysine catabolism. PPARɣ suppressed expression of this enzyme, which may reduce cellular acetoacetate concentration (the end product of lysine catabolism). Human breast cancer lines that over expressed the synthase or were exposed to increased acetoacetate concentrations showed reduced proliferation and autophagy similar to that observed in mammary tumors. We conclude that obesity changes PPARɣ function from tumor suppressor to tumor promoter by inhibiting lysine catabolism, intracellular acetoacetate levels, and autophagy.
Lysine Metabolism is a New Tumor Suppressor Pathway in Breast Cancer that is Deregulated by Obesity
B-116
Obesity (excess fat) is a cause of breast cancer, but reasons for this are not understood. Peroxisome proliferator- activated receptor gamma (PPARɣ) is responsible for fat cell differentiation and is activated by fatty acids stored in fat cells. PPARɣ prevents breast cancer in humans. We hypothesized that excess fatty acids may reverse PPARɣ function to tumor promotion. To test this hypothesis, we deleted the PPARɣ gene in mammary epithelium of normal and obese mice. Decreased PPARɣ expression in obese mice increases tumor latency and depletes tumorigenic progenitor cells. These cells slowly digest their mitochondria by the process of autophagy. To understand this, we determined changes in gene expression in obese PPARɣ null mammary tumors. Gene expression analysis showed a 16-fold increase in 2- aminoadipate semialdehyde synthase, an enzyme involved in lysine catabolism. PPARɣ suppressed expression of this enzyme, which may reduce cellular acetoacetate concentration (the end product of lysine catabolism). Human breast cancer lines that over expressed the synthase or were exposed to increased acetoacetate concentrations showed reduced proliferation and autophagy similar to that observed in mammary tumors. We conclude that obesity changes PPARɣ function from tumor suppressor to tumor promoter by inhibiting lysine catabolism, intracellular acetoacetate levels, and autophagy.