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Published on: October 24, 2015
Metformin Regulates the Expression of CD133 Through the AMPK-CEBPβ Pathway in Hepatocellular Carcinoma Cell Lines
Osamu Maehara1, Shunsuke Ohnishi2, Ayaka Asano1
1Department of Pathophysiology and Therapeutics, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
Abstract:
CD133 is a cellular surface protein, which has been reported to be a cancer stem cell marker, and thus is considered a potential target for cancer treatment. Metformin, one of the biguanides used for the treatment of diabetes, is also known to reduce the risk of cancer development and cancer stem-like cells (CSCs), including the expression of CD133. However, the mechanism underlying the reduction of the expression of CD133 by metformin is not yet understood. This study shows that metformin suppressed CD133 expression mainly by affecting the CD133 P1 promoter via adenosine monophosphate (AMP)-activated protein kinase (AMPK) signaling but not the mammalian target of rapamycin (mTOR). AMPK inhibition rescued the reduction of CD133 by metformin. Further experiments demonstrated that CCAAT/enhancer-binding protein beta (CEBPβ) was upregulated by metformin and that two isoforms of CEBPβ reciprocally regulated the expression of CD133. Specifically, the liver-enriched activator protein (LAP) isoform increased the expression of CD133 by directly binding to the P1 promoter region, whereas the liver-enriched inhibitory protein (LIP) isoform suppressed the expression of CD133. Consistent with these findings, a three dimensional (3D) culture assay and drug sensitivity assay demonstrated that LAP-overexpressing cells formed large spheroids and were more resistant to 5-fluorouracil (5-FU) treatment, whereas LIP-overexpressing cells were more sensitive to 5-FU and showed combined effects with metformin. Our results indicated that metformin-AMPK-CEBPβ signaling plays a crucial role in regulating the gene expression of CD133. Additionally, regulating the ratio of LAP/LIP may be a novel strategy for targeting CSCs for the treatment of cancer.
Insights
Metformin reduces cancer stem cell marker CD133 by activating AMPK signaling, which influences CEBPβ isoforms. This pathway offers a new strategy for targeting cancer stem cells (CSCs) and improving treatments.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- CD133 is a cancer stem cell marker targeted for cancer therapy.
- Metformin, an anti-diabetic drug, reduces cancer risk and cancer stem-like cells (CSCs), including CD133 expression.
- The mechanism by which metformin reduces CD133 expression remains unclear.
Purpose of the Study:
- To elucidate the molecular mechanism by which metformin suppresses CD133 expression.
- To investigate the role of adenosine monophosphate (AMP)-activated protein kinase (AMPK) and CCAAT/enhancer-binding protein beta (CEBPβ) in metformin's effect on CD133.
Main Methods:
- Investigated metformin's effect on CD133 promoter activity via AMPK and mammalian target of rapamycin (mTOR) signaling.
- Analyzed the role of CEBPβ isoforms (LAP and LIP) in regulating CD133 expression.
- Utilized 3D culture and drug sensitivity assays to assess the functional impact of CEBPβ isoforms and metformin treatment.
Main Results:
- Metformin suppressed CD133 expression primarily through the CD133 P1 promoter via AMPK signaling.
- AMPK inhibition reversed the metformin-induced reduction in CD133.
- Metformin upregulated CEBPβ, with the LAP isoform increasing CD133 expression and the LIP isoform suppressing it.
- LAP-overexpressing cells showed increased spheroid formation and 5-fluorouracil (5-FU) resistance, while LIP-overexpressing cells were more sensitive to 5-FU and showed synergistic effects with metformin.
Conclusions:
- Metformin-AMPK-CEBPβ signaling is critical for regulating CD133 gene expression.
- Modulating the LAP/LIP ratio presents a potential novel therapeutic strategy for targeting CSCs in cancer treatment.
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