Metformin Represses Self-Renewal of the Human Breast Carcinoma Stem Cells via Inhibition of Estrogen Receptor-Mediated OCT4 Expression

Abstract

Metformin, a Type II diabetic treatment drug, which inhibits transcription of gluconeogenesis genes, has recently been shown to lower the risk of some diabetes-related tumors, including breast cancer. Recently, “cancer stem cells” have been demonstrated to sustain the growth of tumors and are resistant to therapy. To test the hypothesis that metformin might be reducing the risk to breast cancers, the human breast carcinoma cell line, MCF-7, grown in 3-dimensional mammospheres which represent human breast cancer stem cell population, were treated with various known and suspected breast cancer chemicals with and without non-cytotoxic concentrations of metformin. Using OCT4 expression as a marker for the cancer stem cells, the number and size were measured in these cells. Results demonstrated that TCDD (100 nM) and bisphenol A (10 µM) increased the number and size of the mammospheres, as did estrogen (10 nM E2). By monitoring a cancer stem cell marker, OCT4, the stimulation by these chemicals was correlated with the increased expression of OCT4. On the other hand, metformin at 1 and 10 mM concentration dramatically reduced the size and number of mammospheres. Results also demonstrated the metformin reduced the expression of OCT4 in E2 & TCDD mammospheres but not in the bisphenol A mammospheres, suggesting different mechanisms of action of the bisphenol A on human breast carcinoma cells. In addition, these results support the use of 3-dimensional human breast cancer stem cells as a means to screen for potential human breast tumor promoters and breast chemopreventive and chemotherapeutic agents.

Metabolic control of cancer cell stemness: Lessons from iPS cells

“…AMPK activation impedes early reprogramming by preventing transcriptional activation of Oct4, the master regulator of the pluripotent state. [110][111][112] Moreover, AMPK activation facilitates the specific elimination of Oct4-positive teratoma-initiating pluripotent stem cells that are intermixed with non-tumorigenic iPS cell derivatives, strongly suggesting that an adequate functioning of the metabolic infrastructure might be an indispensable component of the CSC machinery. 111 Using an in vitro model of de novo generation of CSC-like states through nuclear reprogramming in an established breast cancer cell line, we have recently shown that the transcriptional suppression of mTOR repressors (i.e., PRKAA1, which codes for the catalytic a1 subunit of AMPK; DDIT4/REDD1, a stress response gene that operates as a negative regulator of mTOR; and DEPTOR, a naturally occurring endogenous inhibitor of mTOR activity) appears to be an intrinsic process that occurs during the acquisition of CSC-like properties by differentiated breast cancer cells.…”

“…Conversely, imposed barriers (dashes black lines) can occur via certain metabolic conditions that might inhibit and impair the epigenetic rewiring during reprogramming (e.g., AMPK activation hampers the reactivation of the stemness factor Oct4). [110][111][112] Indeed, CSC are not irreversibly locked in a tumorigenic state but instead amenable to metabolo-epigenetic reversion into a phenotypically non-CSC state.…”

Reprogramming of non-genomic estrogen signaling by the stemness factor SOX2 enhances the tumor-initiating capacity of breast cancer cells

“…Because it has been previously shown that ERα signaling can regulate breast CSC frequency, [11][12][13] with ERα stimulation resulting in increased numbers of CSCs, we investigated if the enhanced breast cancer-initiating capability of SOX2-overexpressing CSC-like MCF-7/Rep cells might be due to changes in E 2 signaling activation via non-genomic pathways. Serine phosphorylation is required for full activation of ERα, and phosphorylation of ERα on Ser118 activates the N-terminal transcriptional activation function (AF-1) that renders ERα hypersensitive to E 2 ; i.e., Ser118-ERα indicates an intact E 2 -dependent ERα pathway in primary breast tumors in vivo.…”

“…20 A bidirectional cross-talk interaction between the stem cell self-renewal regulator, SOX2, and the local and systemic ability of E 2 to increase breast CSC activity may have profound implications for the development of new CSC-directed strategies for breast cancer prevention and therapy. 13,[21][22][23] …”

Isolation and characterization of human breast cancer cells with SOX2 promoter activity

“…In our experiment, expression of ABCB1 was high in pSp-T + cells, but those of ABCG2 and ABCC1 did not differ between pSp-T + cells and pSp-T low/-cells. Many transcription factors such as Octamer-binding transcription factor 4 (OCT4), Kruppel-like factor 4 (KLF4), NANOG and C-MYC are known to be associated with induction or maintenace of stemness of CSCs [17][18][19]. In fact, pSp-T + cells highly expressed NANOG, C-MYC compared with pSp-T low/-cells or parent cells (Fig.…”