Abstract 1138: AMPK promotes survival of breast cancer cells by modulating metabolic stress

Breast cancer cells can respond to microenvironmental stressors by becoming dormant, that is inhibiting cell proliferation until the environment becomes growth-permissive. One of the survival pathways implicated in dormant cancer cells is the p38MAPK pathway. Modulation of signaling to combat metabolic stressors could provide survival benefits to dormant breast cancer cells. AMPK (AMP-activated protein kinase) is the central metabolic regulator of the cell, and its expression is altered in breast cancer. Moreover, there are two isoforms of the catalytic subunit (α1 and α2), and differential functionality of these isoforms has been reported. Using estrogen-receptor positive human breast cancer cell lines, we investigated the effect of differential AMPKα isoform expression on breast cancer survival. We found that over-expression of AMPKα2 in MCF-7 cells resulted in stronger p38MAPK activation in response to chemical AMPK activation or metabolic stress. Moreover, the same signaling was observed in HCC1500 cells, which endogenously express AMPKα2. Additionally, we cultured our cell lines as spheroids in order to mimic a tumor microenvironment. MCF-7 AMPKα2 cells formed larger, more viable spheres than control cells. In addition, the expression of AMPKα2 facilitated spheroid survival under hypoxic conditions. Finally, activation of p38MAPK was seen most abundantly in the MCF-7 AMPKα2 spheres. Our in vitro studies indicate an AMPKα2-dependent regulation of p38MAPK in response to metabolic stress in order to promote cancer cell survival. To evaluate cancer dormancy in vivo, MCF-7 cells expressing either GFP or AMPKα2 were injected into athymic nude mice previously implanted with slow-release estradiol pellets. After one week, the estradiol pellets were removed to induce cellular dormancy for thirty days. Analysis of tumors at this time indicated that more of the AMPKα2 expressing cells survived estradiol deprivation than did the control cells. Analysis of proliferation by Ki67 staining indicated that the GFP cells maintained proliferation during deprivation, while AMPKα2 cells were largely negative for proliferation. ApoTag staining revealed a similar trend for apoptotic cells. This suggests an inability to control cell cycle resulted in a decreased survival of the GFP cells under estradiol deprivation. Consistent with our observed in vitro cell signaling, AMPKα2 expressing tumors expressed higher levels of phospho-p38MAPK than GFP expressing tumors. Following th