Expression of reprogramming factors in breast cancer cell lines and the regulation by activated Stat3

Abstract Distinct gene expression patterns, accompanied by particular epigenetic states, provide the basis for different stages of cellular differentiation. The programming of cells usually proceeds from stem cells to progenitor cells to differentiated progeny. The process, however, is not irreversible, and pluripotency can be reestablished in terminally differentiated cells through the expression of the reprogramming factors (RFs) octamer-binding transcription factor 3/4 (Oct4), sex-determining region Y box 2 (Sox2), Krüppel-like factor 4 (Klf4), and c-Myc. Tumor cell formation is characterized by partial differentiation, epigenetic alterations, and drastic changes in the transcriptional program. As the RF can cause pluripotency through cellular dedifferentiation and epigenetic alterations, it is possible that the activation of their genes might contribute to cellular transformation. The shared capacity for self-renewal between pluripotent stem cells and cancer stem cells is in line with this assumption. The deregulation of RF has been observed in poorly differentiated, high-grade breast cancer and is associated with unfavorable prognosis. Signal transducer and activator of transcription 3 (Stat3) mediates a wide variety of cellular functions including survival, proliferation, and differentiation and is constitutively activated in tumor cells of diverse origins. Stat3 is also accelerates somatic cell reprogramming. We investigated the connection between Stat3 activation and the expression of RF in the breast cancer cell lines MCF-7, SK-BR-3, MDA-MB-231, and MDA-MB-468 and the normal mammary epithelial cell line MCF-10A by real-time quantitative PCR and immunoblot analyses. We detected strong expression of Sox2 and Klf4 messenger RNA (mRNA) in MCF-7 cells and the expression of Oct4 mRNA in all the four cell lines. Immunoblot analyses revealed the strong protein expression of homeobox protein Nanog (Nanog), Oct4, and Sox2 in MCF-7 cells. This cell line only contains a low level of phosphorylated Stat3. We also examined the effect of the Stat3 inhibitor Stattic on the expression of RF and observed that it suppressed mRNA and protein expression of RF in MCF-7 cells. The expression levels of reprogramming proteins can strongly differ from their mRNA expression levels and do not necessarily correspond with the extent of Stat3 activation in the cell lines compared.