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AMPKα Is Suppressed in Bladder Cancer through Macrophage-Mediated Mechanisms
Stavros Kopsiaftis1, Poornima Hegde2, John A Taylor3
1Center for Vascular Biology, University of Connecticut Health Center, Farmington, CT, USA; Department of Cell Biology, University of Connecticut Health Center, Farmington, CT, USA.
Abstract:
Bladder cancer presents as either low- or high-grade disease, each with distinct mutational profiles; however, both display prominent mTORC1 activation. One major negative regulator of mTORC1 is AMPK, which is a critical metabolic regulator that suppresses cellular growth in response to metabolic stress by negatively regulating mTORC1. Alterations in the activation and protein levels of AMPK have been reported in breast, gastric, and hepatocellular carcinoma. To investigate whether AMPK suppression is responsible for mTOR activation in bladder cancer, the levels of AMPKα were quantified in a cohort of primary human bladder cancers and adjacent nontumor tissues. The levels of p-AMPKα, AMPKα1, AMPKα2, and total AMPKα were significantly suppressed in both low- and high-grade disease when compared with nontumor tissue. To elucidate the AMPKα suppression mechanism, we focused on inflammation, particularly tumor-infiltrating macrophages, due to their reported role in regulating AMPK expression. Treatment of HTB2 cancer cells with varying doses of differentiated U937 macrophage conditioned medium (CM) demonstrated a dose-dependent reduction of AMPKα protein. Additionally, macrophage CM treatment of HTB2 and HT1376 bladder cells for various times also reduced AMPKα protein but not mRNA levels. Direct TNFα treatment also suppressed AMPKα at the protein but not RNA level. Finally, staining of the human cohort for CD68, a macrophage marker, revealed that CD68+ cell counts correlated with reduced AMPKα levels. In summary, these data demonstrate the potential role for inflammation and inflammatory cytokines in regulating the levels of AMPKα and promoting mTORC1 activation in bladder cancer.
Insights
AMP-activated protein kinase (AMPK) is suppressed in bladder cancer, leading to mTORC1 activation. Inflammation, particularly from macrophages, contributes to this AMPK suppression, suggesting a new therapeutic target for bladder cancer.
Area of Science:
- Oncology
- Molecular Biology
- Cell Metabolism
Background:
- Bladder cancer exhibits distinct grades but shares mTORC1 activation.
- AMP-activated protein kinase (AMPK) is a key negative regulator of mTORC1 and cellular growth.
- AMPK alterations are implicated in various cancers, including breast, gastric, and hepatocellular carcinoma.
Purpose of the Study:
- To investigate AMPK suppression as a driver of mTOR activation in bladder cancer.
- To quantify AMPKα levels in human bladder cancer tissues.
- To explore the role of inflammation and macrophages in AMPK suppression.
Main Methods:
- Quantification of AMPKα, p-AMPKα, AMPKα1, and AMPKα2 in human bladder cancer and adjacent nontumor tissues.
- In vitro studies using macrophage-conditioned medium (CM) to treat bladder cancer cells (HTB2, HT1376).
- Analysis of TNFα effects on bladder cancer cells and correlation of CD68+ macrophage counts with AMPKα levels in human tissues.
Main Results:
- Significantly suppressed levels of p-AMPKα, AMPKα1, AMPKα2, and total AMPKα were observed in both low- and high-grade bladder cancers compared to nontumor tissues.
- Macrophage CM induced a dose- and time-dependent reduction in AMPKα protein levels in bladder cancer cells, without affecting mRNA levels.
- TNFα treatment suppressed AMPKα protein but not mRNA, and CD68+ macrophage counts correlated with reduced AMPKα levels in human bladder cancers.
Conclusions:
- AMPKα is suppressed in human bladder cancer, potentially contributing to mTORC1 activation.
- Inflammation, specifically via tumor-infiltrating macrophages and cytokines like TNFα, plays a role in suppressing AMPKα protein levels.
- Targeting inflammation may represent a therapeutic strategy to restore AMPK activity and inhibit mTORC1 in bladder cancer.
