AMPKalpha2 Regulates Bladder Cancer Growth Through SKP2-mediated Degradation of p27.

AMP-activated protein kinase (AMPK) is the central metabolic regulator of the cell and controls energy consumption based upon nutrient availability. Due to its role in energy regulation, AMPK has been implicated as a barrier for cancer progression and is suppressed in multiple cancers. To examine whether AMPK regulates bladder cancer cell growth, HTB2 and HT1376 bladder cells were treated with an AMPK activator, 5-aminoimidazole-4carboxamide ribonucleotide (AICAR). AICAR treatment reduced proliferation and induced the expression of p27(Kip1) (CDKN1B), which was mediated through an mTOR-dependent mechanism. Interestingly, AMPK alpha 2 knockdown resulted in reduced p27 levels, whereas AMPK alpha 1 suppression did not. To further determine the exact mechanism by which AMPK alpha 2 regulates p27, HTB2 and HT1376 cells were transduced with an shRNA targeting AMPK alpha 2. Stable knockdown of AMPK alpha 2 resulted in increased proliferation and decreased p27 protein. The reduced p27 protein was determined to be dependent upon SKP2. Additionally, loss of AMPK alpha 2 in a xenograft and a chemical carcinogen model of bladder cancer resulted in larger tumors with less p27 protein and high SKP2 levels. Consistent with the regulation observed in the bladder cancer model systems, a comprehensive survey of human primary bladder cancer clinical specimens revealed low levels of AMPK alpha 2 and p27 and high levels of SKP2. (C) 2016 AACR.