Reprogramming into Cancer Stem Cell Figure 4. Activity of CPM modules in human somatic cells and pluripotent stem cells. Properties of self-renewal and pluripotency are linked with transient or continuous up-regulation of the Core and Myc modules, but not PRC module. C, Core module; P, PRC module; M, Myc module. doi:10.1371/journal.pone.0048699.g004 especially polycomb repressive complex 2 containing Ezh2, Eed, and Suz12, are crucial repressors of genes in association with H3K27me3 [16]. In order to reset the somatic memory of genes with a homeodomain in iESCs and iCSCs and over-write the ES cell-like epigenetic signature in the reprogrammed nuclei of iESCs, the activity of the PRC module should be reduced continuously or transiently. Relatively reduced activity of the PRC module may be a key event for reprogramming somatic cells to iPSCs. It is speculated that lack of H3K27me3 plays important roles in promoting reprogramming from pre-iPSCs to iPSCs in the late phase of reprogramming [17]. The fate of somatic cells, whether they are reprogrammed to iCSCs or iPSCs, could be determined by activity of the PRC module, after acquiring the capability of self-renewal and pluripotency (Fig. 4). Supporting Information Figure S1 Spontaneous differentiation of iESCs and conversion into iPSCs. (A) Differentiation of iESCs after long-term culture. (B) Conventional iPSCs (right panel) were generated from a small colony (yellow circle in left panel) appearing in iESC culture at high cell density. (TIF) References 1. Nguyen LV, Vanner R, Dirks P, Eaves CJ (2012) Cancer stem cells: an evolving concept. Nat Rev Cancer 12: 133–143. 2. Clarke MF, Dick JE, Dirks PB, Eaves CJ, Jamieson CHM, et al. (2006) Cancer Stem Cells-Perspectives on Current Status and Future Directions: AACR Workshop onCancer Stem Cells. Cancer Res 66: 9339–9344. 3. Kang J, Shakya A, Tantin D (2009) Stem cells, stress, metabolism and cancer: a drama in two Octs. Trends Biochem Sci 34: 491–499. Figure S2 Global gene expression analysis of iESCs and iCSCs. Comparative analysis of global gene expression profile in iPSC, human embryonic stem (ES) cell, iESC, 1st iCSC, and TIG1 lines by gene expression microarray assay. (TIF) Figure S3 Expression of pluripotent marker proteins in iESCs and iCSCs. Expression of marker cell surface proteins, CDH1, SSEA4, and TRA-1-60 was detected as green fluorescence, while cell nuclei were as blue with DAPI. (TIF) Figure S4 Average gene expression values (log2) of CPM modules in in somatic cells and pluripotent stem cells. (TIF) Table S1 (DOC) Primers for RT-PCR analyses. Author Contributions Conceived and designed the experiments: TT. Performed the experiments: SN KH MK LTS TT. Analyzed the data: SN KH MK LTS TT. Wrote the paper: SN TT. 4. Schoenhals M, Kassambara A, De Vos J, Hose D, Moreaux J, et al. (2009) Embryonic stem cell markers expression in cancers. Biochem Biophys Res Commun 383: 157–162. 5. Cole MD, Henriksson M (2006) 25 years of the c-Myc oncogene. Semin Cancer Biol 16: 241. PLOS ONE | www.plosone.org 6 November 2012 | Volume 7 | Issue 11 | e48699