Tumors are often heterogeneous, being composed of multiple cell types with different phenotypic and molecular properties. Cancer stem-like cells (CSCs) are a highly tumorigenic cell type found in developmentally diverse tumors or cancer cell lines, and they are often resistant to standard chemotherapeutic drugs. The origins of CSCs and their relationships to nonstem cancer cells (NSCCs) are poorly understood. In an inducible breast oncogenesis model, CSCs are generated from nontransformed cells at a specific time during the transformation process, but CSC formation is not required for transformation. MicroRNA profiles indicate that CSCs and NSCCs are related, but different cell types arising from a common nontransformed population. Interestingly, medium from the transformed population stimulates NSCCs to become CSCs, and conversion of NSCCs to CSCs occurs in mouse xenografts. Furthermore, IL6 is sufficient to convert NSCCs to CSCs in genetically different breast cell lines, human breast tumors, and a prostate cell line. Thus, breast and prostate CSCs and NSCCs do not represent distinct epigenetic states, and these CSCs do not behave as or arise from classic stem cells. Instead, tumor heterogeneity involves a dynamic equilibrium between CSCs and NSCCs mediated by IL6 and activation of the inflammatory feedback loop required for oncogenesis. This dynamic equilibrium provides an additional rationale for combining conventional chemotherapy with metformin, which selectively inhibits CSCs. cellular transformation | inflammation | cancer stem cells equilibrium

with HKL 24 or XDS 25 . Crystals belong to space group P2 1 2 1 2 1 with unit cell dimensions a ¼ 56.7 Å , b ¼ 67.7 Å and c ¼ 135.6 Å , and contain three molecules per asymmetric unit. Structure determinationSelenium sites were located with SnB 26 . MAD phases were calculated with SHARP 27 and improved by density modification. A CID model was built with O 28 and refined with CNS 29 . The refined model has excellent stereochemical quality and a free R-factor of 25.2%. A difference Fourier for the peptide-soaked crystal was calculated with phases from the CID model and identified strong density for the CTD peptide bound to one CID molecule (chain B). The two other CID molecules pack against each other, burying their peptide-binding sites. After peptide building, the CID-CTD model was refined to a free R-factor of 25.7%. Peptide binding does not result in significant conformational changes in the CID domain. Soaking experiments with phosphoserine did not reveal any additional electron density. D 54, 799-804 (1998). 27. Terwilliger, T. C. Automated structure solution, density modification and model building. Acta. Crystallogr. 58, 1937Crystallogr. 58, -1940Crystallogr. 58, (2002 Competing interests statement The authors declare that they have no competing financial interests.Correspondence and requests for materials should be addressed to P.C.(cramer@lmb.uni-muenchen.de). Atomic coordinates and structure factors for the Pcf11 CID domain and the CTD-CID complex have been deposited in the Protein Data Bank under accession numbers 1SZ9 and 1SZA, respectively.

EZH2 (the Enhancer of Zeste Homolog 2), as a key epigenetic regulator and EMT inducer, participates in a variety of cancer metastasis. EZH2 stability is regulated by several types of post-translational modifications (PTMs).The long non-coding RNAs (lncRNA) have been implicated to have critical roles in multiple carcinogenesis through a wide range of mechanisms, including modulating the stability of proteins. To date, whether the stability of EZH2 protein is regulated by lncRNAs remains unexplored. Here we report the discovery of ANCR modulating the stability of EZH2, and hence in the invasion and metastasis of breast cancer cells. We determined that ANCR potentiated the CDK1-EZH2 interaction, which then increased the intensity of phosphorylation at Thr-345 and Thr-487 sites of EZH2, facilitating EZH2 ubiquitination and hence its degradation. Moreover, we also uncover ANCR is an important player in breast cancer progression and metastasis mainly through decreasing EZH2 stability. More specifically, we initially found that ANCR level was lower in breast cancer tissues and breast cancer cell lines, in contrast to their normal counterparts. We then demonstrated that knockdown of ANCR induced an EMT program and promoted cell migration and invasion in MCF10A (epithelial cells), whereas ectopic expression of ANCR repressed breast cancer cells migration and invasion. Furthermore, we validated in a nude mouse model that overexpression of ANCR in highly malignant and invasive MDA-MB-231 breast cancer cells significantly reduced the ability of the cells to form tumors and prevented the lung metastasis in vivo. Based on these data, our findings define a new mechanism underlying modulation of EZH2 stability by linking ANCR interaction with EZH2 to promote its phosphorylation that facilitates EZH2 degradation and suppresses breast cancer progression.

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