Abstract 310: Role of AMPKalpha isoforms in bladder tumorigenesis.
Authors: Kopsiaftis Stavros , Phoenix Kathryn N. , Sullivan Katie L. , Hegde Poornima , Taylor John A. , Claffey Kevin P. 
Published: August 2014

Bladder cancer is the fifth most diagnosed cancer and currently is one of the most expensive cancers to treat due to lifelong surveillance. Bladder cancer is marked by two distinct pathways that result in either noninvasive low grade or invasive high grade cancer. Although low and high grade bladder cancers are defined by driver mutations, similarities such as mTORC1 pathway activation exist. Along these lines rapamycin treatment, an mTORC1 inhibitor, has been shown to suppress tumorigenesis in a mouse model of bladder cancer. These data suggest that mTORC1 activation may be an early tumorigenic event in the bladder.

In order to elucidate the mechanism by which the mTORC1 signaling is increased, AMPK (AMP-activated protein kinase), a critical negative regulator of the pathway, was further investigated. AMPK governs a cell's response to metabolic stressors by suppressing anabolic pathways and inhibiting cell growth. Furthermore, it has been observed that AMPK activation is diminished in primary breast cancer. In order to determine whether AMPK activation and/or levels are altered in bladder cancer, a pilot cohort of human samples was obtained and the expression of both AMPKa catalytic isoforms was assessed. Both AMPKa1 and AMPKa2 were significantly suppressed in bladder cancer. AMPKa isoform levels in adjacent non-tumor bladder epithelium and bladder cancer were evaluated in matched patient samples and this revealed cancer-specific AMPKa suppression does indeed exist. Additionally, AMPKa1 protein levels were partially suppressed in low grade cancer and further suppressed in high grade cancer. In contrast, AMPKa2 levels were uniformly suppressed in both high and low grade of cancer. Interestingly, it was observed that AMPKa1 is localized predominantly to the cytoplasm while AMPKa2 was present in cytoplasmic and nuclear compartments. This data suggests that the AMPKa isoforms may have distinct roles in the bladder.

To test whether loss of AMPKa2 function promoted bladder tumorigenesis, wild-type and AMPKa2-/- mice received 0.05% BBN [n-butyl-n-(4 hydroxybutyl)] nitrosamine, a rodent bladder carcinogen, in drinking water over the course of 20 weeks. Significant tumors were observed at 20 weeks in both wild-type and AMPKa2-/- mice and bladder weights were significantly higher in AMPKa2-/- mice correlating with larger bladder tumor mass. Additionally, there was a significant increase in the amount of proliferating tumor cells as assessed by Ki67 in the AMPKa2-/- mice. This study suggests that AMPKa isoforms are suppressed in bladder cancer and that AMPKa may play a critical role in bladder cancer progression by loss of expression and tumor suppressive function.

Citation Format: Stavros Kopsiaftis, Kathryn N. Phoenix, Katie L. Sullivan, Poornima Hegde, John A. Taylor, Kevin P. Claffey. Role of AMPKalpha isoforms in bladder tumorigenesis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 310. doi:10.1158/1538-7445.AM2013-310