Abstract 4209: AMPK suppression in bladder tumorigenesis

Bladder cancer is the fifth most diagnosed cancer in the US. In 2013 there were approximately 72,570 newly diagnosed cases and 15,210 deaths attributing to this disease where the average age of onset for this disease is 65 and remains one of the most expensive cancers to treat due to lifelong surveillance and invasive procedures. Bladder cancer is defined by two distinct pathways which result in either low grade non-invasive or high grade invasive cancer. Although these are marked by distinct mutations, it has been observed that both display mTORC1 activation. This suggests that activated mTORC1 may be an early contributing factor in bladder tumorigenesis. Additionally, rapamycin, an inhibitor of mTORC1, inhibited tumorigenesis in a mouse model of bladder cancer further implicating mTORC1 as an essential pathway in tumorigenesis. To elucidate the mechanism of mTORC1 activation in bladder cancer, AMP-activated protein kinase (AMPK), a negative regulator of mTORC1, was investigated. AMPK is a critical metabolic regulator that suppresses cellular growth in response to metabolic stress. Additionally it has been observed that AMPK activation is suppressed in breast and hepatocellular carcinoma and the AMPKα2 isoform is suppressed in breast and gastric cancer. To investigate whether levels or activation of AMPK are altered in bladder cancer a pilot cohort of adjacent non-tumor and bladder tumor human samples was obtained as was a human bladder cancer tissue array. In both the pilot cohort and the array, the levels of AMPKα1 and AMPKα2 were suppressed at statistically significant levels in low and high grade bladder cancer when compared to adjacent non-tumor tissue. Messenger RNA expression for both isoforms in bladder tumors revealed that AMPKα2 may be selectively suppressed at the mRNA level. However AMPKα1 suppression appeared to be due to translational or post translational regulatory mechanisms. It was also observed that AMPKα1 was located predominately in the cytoplasm while AMPKα2 was located in both the nuclear and cytoplasmic compartments. This suggests that AMPKα isoforms may have distinct roles in the bladder and may be suppressed by different mechanisms. To test the relevance of AMPK in bladder tumorigenesis the mouse BBN bladder carcinogenesis model was employed. BBN was supplemented in the drinking water of wild-type and AMPKα2-/- mice at a concentration of .05% over the course of 20 weeks. AMPKα2-/- mice displayed a significant increase in bladder weight indicating the presence of larger tumors. There was also an increase in KI67 positive cells in the tumors of AMPKα2-/- mice indicating increased proliferation with no appreciable apoptosis observed in any tumors. Ongoing studies in which BBN is supplemented for 16 weeks and then removed for the duration aim to validate the role of AMPKα2 in bladder tumor initiation and/or progression. In summary, loss of AMPK activity, especially AMPKα2, can promote bladder tumorigenesis through increased proliferation via mTORC1 activity. Citation Format: Stavros Kopsiaftis, Kathryn N. Phoenix, Katie L. Sullivan, John A. Taylor, Kevin P. Claffey. AMPK suppression in bladder tumorigenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4209. doi:10.1158/1538-7445.AM2014-4209