Epithelial mechenchymal transition (EMT) has recently been linked to stem cell phenotype1, 2. However, the molecular mechanism involving regulation of EMT and stemness remains elusive. Here, using genomic approaches, we discovered that tumor suppressor p53 plays a role in regulating both EMT and EMT-associated stem cell properties through transcriptional activation of miR-200c. p53 transactivates miR-200c through direct binding to the miR-200c promoter. Loss of p53 in mammary epithelial cells leads to decreased expression of miR-200c and activates EMT program, accompanied by increased mammary stem cell population. Re-expressing miR-200c suppresses genes that mediate EMT and stemness properties3, 4 and thereby reverts mesenchymal and stem cell-like phenotype caused by loss of p53 to differentiated epithelial cell phenotype. Furthermore, loss of p53 negatively correlates with miR-200c level but positively with increased expression of EMT and stemness markers as well as high tumor grade in a cohort of breast tumors. Together, this study elucidates a role of p53 in regulating EMT-MET (mechenchymal epithelial transition) and stemness or differentiation plasticity and reveals a potential therapeutic implication to suppress EMT associated-cancer stem cells through activation of p53-miR-200c pathway.

Summary It has been proposed that an aggressive secondary cancer stem cell population arises from a primary cancer stem cell population through acquisition of additional genetic mutations and drives cancer progression. Overexpression of Polycomb protein EZH2, essential in stem cell self-renewal, has been linked to breast cancer progression. However, critical mechanism linking increased EZH2 expression to BTIC (breast tumor initiating cell) regulation and cancer progression remains unclear. Here, we identify a mechanism in which EZH2 expression-mediated downregulation of DNA damage repair leads to accumulation of recurrent RAF1 gene amplification in BTICs, which activates p-ERK-β-catenin signaling to promote BTIC expansion. We further reveal that AZD6244, a clinical trial drug that inhibits RAF1-ERK signaling, could prevent breast cancer progression by eliminating BTICs.

Accumulated evidence shows that EZH2 is deregulated in a wide range of cancer types, and it has a crucial role in stem cell maintenance and tumour development. Therefore, blocking EZH2 expression or activity may represent a promising strategy for anticancer treatment. In this review, we address the current understanding of the mechanisms underlying EZH2 regulation alongside the function of EZH2 gene targets that are involved in cancer progression. Finally, we will describe cancer therapies that target EZH2 or its downstream cascades, which could potentially reverse the oncogenic and stemness properties of the tumour cells to suppress cancer progression and recurrence.

Cancer stem cells, which share many common properties and regulatory machineries with normal stem cells, have recently been proposed to be responsible for tumorigenesis and to contribute to cancer resistance 1 . The main challenges in cancer biology are to identify cancer stem cells and to define the molecular events required for transforming normal cells to cancer stem cells. Here we show that Pten deletion in mouse haematopoietic stem cells leads to a myeloproliferative disorder, followed by acute T-lymphoblastic leukaemia (T-ALL). Self-renewable leukaemia stem cells (LSCs) are enriched in the c-Kit mid CD3 + Lin − compartment, where unphosphorylated β-catenin is significantly increased. Conditional ablation of one allele of the β-catenin gene substantially decreases the incidence and delays the occurrence of T-ALL caused by Pten loss, indicating that activation of the β-catenin pathway may contribute to the formation or expansion of the LSC population. Moreover, a recurring chromosomal translocation, T(14;15), results in aberrant overexpression of the c-myc oncogene in c-Kit mid CD3 + Lin − LSCs and CD3 + leukaemic blasts,

We demonstrate that PTEN loss causes reduced NKX3.1 expression in both murine and human prostate cancers. Restoration of Nkx3.1 expression in vivo in Pten null epithelium leads to decreased cell proliferation, increased cell death, and prevention of tumor initiation. Whereas androgen receptor (AR) positively regulates NKX3.1 expression, NKX3.1 negatively modulates AR transcription and consequently the AR-associated signaling events. Consistent with its tumor suppressor functions, NKX3.1 engages cell cycle and cell death machinery via association with HDAC1, leading to increased p53 acetylation and half-life through MDM2-dependent mechanisms. Importantly, overexpression of Nkx3.1 has little effect on Pten wild-type epithelium, suggesting that PTEN plays a predominant role in PTEN-NKX3.1 interplay. Manipulating NKX3.1 expression may serve as a therapeutic strategy for treating PTEN-deficient prostate cancers.

The tumor suppressor gene PTEN (phosphatase and tensin homologue deleted on chromosome 10) is frequently mutated or deleted in various human cancers. PTEN localizes predominantly to the cytoplasm and functions as a lipid phosphatase, thereby negatively regulating the phosphatidylinositol 3-kinase-AKT signaling pathway. PTEN can also localize to the nucleus, where it binds and regulates p53 protein level and transcription activity. However, the precise function of nuclear PTEN and the factors that control PTEN nuclear localization are still largely unknown. In this study, we identified oxidative stress as one of the physiological stimuli that regulate the accumulation of nuclear PTEN. Specifically, oxidative stress inhibits PTEN nuclear export, a process depending on phosphorylation of its amino acid residue Ser-380. Nuclear PTEN, independent of its phosphatase activity, leads to p53-mediated G 1 growth arrest, cell death, and reduction of reactive oxygen species production. Using xenografts propagated from human prostate cancer cell lines, we reveal that nuclear PTEN is sufficient to reduce tumor progression in vivo in a p53-dependent manner. The data outlined in this study suggest a unique role of nuclear PTEN to arrest and protect cells upon oxidative damage and to regulate tumorigenesis. Since tumor cells are constantly exposed to oxidative stress, our study elucidates the cooperative roles of nuclear PTEN with p53 in tumor suppression.The PTEN (phosphatase and tensin homologue deleted on chromosome 10) tumor suppressor gene is mutated at high frequency in many primary human cancers and several cancer predisposition disorders (2). PTEN encodes a dually specific phosphatase that recognizes both lipid and peptide substrates (23), including phosphatidylinositol (3,4,5)-trisphosphate (PIP3), a product of phosphatidylinositol 3-kinase (PI3K). PTEN protein contains an N-terminal catalytic phosphatase domain (18, 32), a calcium-independent C2 domain (16), two PEST motifs, and a C-terminal PDZ binding domain (1). Several critical phosphorylation sites have been found in the PTEN C2 domain, including Ser-380, Thr-382, Thr-383, and Ser-385. Importantly, phosphorylation of these residues has been implicated to increase PTEN stability but decrease PTEN catalytic activity (36, 37).Although PTEN is localized mainly to the cytoplasm, it preferentially resides in the nucleus of differentiated or resting cells (15) as exemplified in MCF-7 cells (14), in which nuclear PTEN peaks in the G 1 phase and reaches a nadir in the S phase. Interestingly, changes in nuclear PTEN expression have also been observed in the endometrium during hormonal cycles (27). These data suggest that nuclear localization of PTEN is a dynamic process, associated with cell cycle, cell differentiation, and cellular functions. Decreased nuclear PTEN has been correlated with progressing thyroid carcinoma and melanoma (40), suggesting a functional role of nuclear PTEN in regulating tumorigenesis.Several studies have shown that PTEN nuclear localization depend...

MDM2 is an oncoprotein that controls tumorigenesis through both p53-dependent and -independent mechanisms. Mdm2 mRNA level is transcriptionally regulated by p53 in response to stress such as DNA damage, and its protein level and subcellular localization are post-translationally modulated by the AKT serine/threonine kinase. Previous studies showed that PTEN, a dual specificity phosphatase that antagonizes phosphatidylinositol 3-kinase/AKT signaling, is capable of blocking MDM2 nuclear translocation and destabilizing the MDM2 protein. Results from our current study demonstrate an additional role for PTEN in regulating MDM2 functions; PTEN modulates Mdm2 transcription and isoform selection by negatively regulating its P1 promoter. In Pten-null cell lines and prostate cancer tissues, Mdm2 P1 promoter activity is up-regulated, resulting in increased L-Mdm2 expression and enhanced p90 MDM2 isoform production. Furthermore, PTEN controls Mdm2 P1 promoter activity through its lipid phosphatase activity, independent of p53. Thus, our results provide a novel mechanism for PTEN in controlling MDM2 oncoprotein functions.The murine double minute 2 (Mdm2) was originally cloned as an amplified gene present on double minute chromosomes in the tumorigenic 3T3DM murine cell line (1). The human homolog, HDM2, mapping to human chromosome 12q13-14, is overexpressed in over 30% of soft tissue sarcomas due to amplification (2, 3). HDM2 expression is controlled by two different promoters (6 -8), leading to alternatively spliced transcripts that differ in their 5Ј-untranslated regions. Transcription from the first promoter P1 is independent of p53 and yields mRNA (L-HDM2) with exon 2 spliced out. Conversely, transcription from the second promoter P2 is p53-dependent. p53 binds to the two p53-responsive elements in the intron 1 and gives rise to a transcript (S-HDM2) lacking exon 1 but containing exon 2. Multiple gene products of MDM2 have been identified in mammalian cells. The full-length p90 MDM2oncoprotein binds to and inactivates the p53 tumor suppressor protein whereas a short p76 MDM2 isoform that lacks the first 49 amino acids of p90 MDM2 cannot bind p53 (4). A recent study suggests that the ratio of the two MDM2 protein products, p90 MDM2 to p76 MDM2 , is determined by the relative abundance of L-Mdm2 mRNA. The L-Mdm2 predominantly gives rise to p90 MDM2 whereas p76 MDM2 appears to be the product of translational initiation at codon 50 (AUG) in exon 4 (5).One of the major biological functions of MDM2 is to regulate p53 level and activity. The p53 tumor suppressor is a shortlived and non-abundant protein in normal cells (9, 10). p53 functions as a transcription factor that up-regulates gene products necessary for cell cycle arrest and apoptosis in response to cell stress such as DNA damage (9). MDM2 regulates p53 activity by at least two mechanisms; MDM2 protein binds p53 in the nucleus and inhibits its transcriptional activity (11-13), and the MDM2-p53 complex shuttles from the nucleus to the cytoplasm (14 -16) where MDM2 serves ...

SUMMARY Breast cancer initiating cells (BCICs), which can fully recapitulate the tumor origin and are often resistant to chemo- and radiotherapy, are currently considered as a major obstacle for breast cancer treatment. Here, we show that BIKDD, a constitutively active mutant form of proapoptotic gene, BIK, effectively induces apoptosis of breast cancer cells and synergizes with lapatinib. Most importantly, BikDD significantly reduced BCICs through co-antagonism of its binding partners Bcl-2, Bcl-xL and Mcl-1, suggesting a potential therapeutic strategy targeting BCICs. Furthermore, we developed a cancer-specific targeting approach for breast cancer that selectively expresses BikDD in breast cancer cells including BCICs, and demonstrated its potent antitumor activity and synergism with lapatinib in vitro and in vivo.