Yoshimi Arima

Rb Depletion Results in Deregulation of E-Cadherin and Induction of Cellular Phenotypic Changes that Are Characteristic of the Epithelial-to-Mesenchymal Transition

The retinoblastoma tumor suppressor protein (Rb) is mutated or expressed at very low levels in several tumor types, including retinoblastoma and osteosarcoma, as well as small cell lung, colon, prostate, bladder, and breast carcinomas. Loss or reduction of Rb expression is seen most commonly in high-grade breast adenocarcinomas, suggesting that a relationship may exist between loss of Rb function and a less-differentiated state, increased proliferation, and high metastatic potential. In this study, we found that knockdown of Rb by small interfering RNA in MCF7 breast cancer cells disrupts cell-cell adhesion and induces a mesenchymal-like phenotype. The epithelial-to-mesenchymal transition (EMT), a key event in embryonic morphogenesis, is implicated in the metastasis of primary tumors. Additionally, Rb is decreased during growth factor- and cytokine-induced EMT and overexpression of Rb inhibits the EMT in MCF10A human mammary epithelial cells. Ectopic expression and knockdown of Rb resulted in increased or reduced expression of E-cadherin, which is specifically involved in epithelial cell-cell adhesion. Other EMT-related transcriptional factors, including Slug and Zeb-1, are also induced by Rb depletion. Furthermore, we confirmed that Rb binds to an E-cadherin promoter sequence in association with the transcription factor activator protein-2alpha. Finally, in breast cancer specimens, we observed a concurrent down-regulation of Rb and E-cadherin expression in mesenchymal-like invasive cancers. These findings suggest that Rb inactivation contributes to tumor progression due to not only loss of cell proliferation control but also conversion to an invasive phenotype and that the inhibition of EMT is a novel tumor suppressor function of Rb.

Breast cancer stem cells

Since the initial discovery of leukemia stem cells nearly a decade ago, a great deal of cancer research has focused on the identification of cancer stem cells (CSCs) in many types of solid tumors, including breast cancer. Through analysis of cell surface markers and xenotransplant models, a subpopulation of putative human breast cancer stem cells (BCSCs) that is CD24-negative/CD44-positive (CD24−/CD44+) and bears high aldehyde dehydrogenase 1 activity has been isolated in clinical samples of breast cancer tissues. Human BCSCs are considered to be derived from basal cells that reside in the basal membranes of alveolar units in human adult mammary glands. Furthermore, BCSCs have been shown to express higher levels of oxidative stress-responsive genes, which could confer part of their ability to resist anti-cancer therapy, than non-CSCs. The emerging picture of the biological properties of BCSCs would contribute for devising innovative therapies for breast cancer, targeting the intrinsic and extrinsic factors that maintain the BCSCs.

Induction of ZEB proteins by inactivation of RB protein is key determinant of mesenchymal phenotype of breast cancer.

Background: Inactivation of RB is a key event for induction of EMT in cancers. Results: ZEB proteins are markedly up-regulated through the reduction of miR-200 family of microRNAs in RB-inactive cancer cells. Conclusion: RB/ZEB pathway plays a pivotal role in mesenchymal and aggressive phenotype in breast cancers. Significance: Suppressing ZEB1 by cyclin-dependent kinase inhibitors provides a novel therapeutic strategy for RB-inactive breast cancers. We previously showed that depletion of the retinoblastoma protein (RB) induces down-regulation of the adhesion molecule E-cadherin and thereby triggers the epithelial-mesenchymal transition. To further characterize the effect of RB inactivation on the phenotype of cancer cells, we have now examined RB expression in human breast cancer cell lines and clinical specimens. We found that RB-inactive cells exhibit a mesenchymal-like morphology and are highly invasive. We also found that ZEB proteins, transcriptional repressors of the E-cadherin gene, are markedly up-regulated in these cells in a manner sensitive to the miR-200 family of microRNAs. Moreover, depletion of ZEB in RB-inactive cells suppressed cell invasiveness and proliferation and induced epithelial marker expression. These results implicate ZEB in induction of the epithelial-mesenchymal transition, as well as in maintenance of the mesenchymal phenotype in RB-inactive cells. We also developed a screening program for inhibitors of ZEB1 expression and thereby identified several cyclin-dependent kinase inhibitors that blocked both ZEB1 expression and RB phosphorylation. Together, our findings suggest that RB inactivation contributes to tumor progression not only through loss of cell cycle control but also through up-regulation of ZEB expression and induction of an invasive phenotype.

Loss of p16 expression is associated with the stem cell characteristics of surface markers and therapeutic resistance in estrogen receptor-negative breast cancer

Triple‐negative breast cancer [TNBC, which is negative for the estrogen receptor (ER), progesterone receptor, and human epidermal growth factor receptor 2] is a high‐risk form of the disease without a specific therapy. DNA microarray and immunohistochemical analyses have shown that most TNBCs fall within the basal‐like histological subset of breast cancers, which frequently exhibit inactivation of the retinoblastoma tumor suppressor (Rb) and upregulation of the cyclin‐dependent kinase inhibitor p16INK4a (p16). However, downregulation of p16 expression has been observed in some basal‐like breast cancer cell lines, suggesting that such cells can be divided into two groups according to Rb and p16 status. We now show that cells that are CD44+ and CD24−, a phenotype associated with stem‐like breast cancer cells, are more abundant in ER−/p16− breast cancer cell lines than in ER−/p16+ lines. It was also found that p16 expression was downregulated in mammospheres from an ER‐negative breast cancer cell line. Depletion of p16 by RNA interference in ER‐negative breast cancer cells increased the percentage of CD44+/CD24− cells and increased the expression of mRNA of the ES‐like genes Nanog, Oct4, and Sox2 through an Rb‐independent pathway. Furthermore, such depletion of p16 reduced chemosensitivity. The loss of p16 expression may thus reduce the response of ER‐negative breast cancer cells to chemotherapy by conferring cancer stem cell‐like properties. Consistent with this conclusion, immunohistochemical analysis of the clinical samples suggests that low p16 expression in TNBC is associated with resistance to preoperative chemotherapy.

Maintenance of HCT116 colon cancer cell line conforms to a stochastic model but not a cancer stem cell model

The cancer stem cell (CSC) model, in which a small population of cells within a tumor possesses the ability to self‐renew and reconstitute the phenotype of primary tumor, has gained wide acceptance based on evidence over the past decade. It has also been reported that cancer cell lines contain a CSC subpopulation. However, phenotypic differences between CSCs and non‐CSCs in cancer cell lines are not better defined than in primary tumors. Furthermore, some cell lines do not have a CSC population, revealed as a side population and expression of CD133. Thus, the identification of CSCs in cancer cell lines remains elusive. Here, we investigated the CSC hierarchy within HCT116 colon cancer cells, which do not have a CD133‐positive subpopulation. We examined the expression of alternative CSC markers epithelial specific antigen (ESA) and CD44 in floating‐sphere‐derived cells, which are known to be the cells of enriching CSCs. Sphere‐derived HCT116 cells exhibited heterogeneous expression of ESA and CD44. The two major subpopulations of HCT116 sphere cells (ESAlowCD44−/low and ESAhighCD44high) exhibited a biological/proliferative hierarchy of sphere‐forming and soft agar colony‐forming activity. However, there was no difference between the two subpopulations in the incidence of xenograft tumors. When ESAlowCD44−/low cells were allowed to aggregate and re‐form floating‐spheres, the biological/proliferative hierarchy of parental HCT116 spheres was reconstituted, in terms of ESA and CD44 expression. Thus, HCT116 cells have plasticity when they are set in floating‐spheres, suggesting that maintenance of the HCT116 cell line conforms to a stochastic model, not a CSC model. (Cancer Sci 2009; 100: 2275–2282)

LATS1/WARTS phosphorylates MYPT1 to counteract PLK1 and regulate mammalian mitotic progression

Showing convergence with budding yeast mitotic exit network signaling, the LATS1/WARTS kinase phosphorylates the MYPT1 phosphatase to control PLK1 at the G2 DNA damage checkpoint.

Concise Review: Stem Cells and Epithelial‐Mesenchymal Transition in Cancer: Biological Implications and Therapeutic Targets

Cancer stem cells (CSCs) constitute a small subpopulation of cancer cells with stem‐like properties that are able to self‐renew, generate differentiated daughter cells, and give rise to heterogeneous tumor tissue. Tumor heterogeneity is a hallmark of cancer and underlies resistance to anticancer therapies and disease progression. The epithelial‐mesenchymal transition (EMT) is a reversible phenomenon that is mediated by EMT‐inducing transcription factors (EMT‐TFs) and plays an important role in normal organ development, wound healing, and the invasiveness of cancer cells. Recent evidence showing that overexpression of several EMT‐TFs is associated with stemness in cancer cells has suggested the existence of a link between EMT and CSCs. In this review, we focus on the roles of CSCs and EMT signaling in driving tumor heterogeneity. A better understanding of the dynamics of both CSCs and EMT‐TFs in the generation of tumor heterogeneity may provide a basis for the development of new treatment options for cancer patients. Stem Cells 2016;34:1997–2007

Stem Cells and Epithelial‐Mesenchymal Transition (EMT) in Cancer: Biological Implications and Therapeutic Targets

Cancer stem cells (CSCs) constitute a small subpopulation of cancer cells with stem‐like properties that are able to self‐renew, generate differentiated daughter cells, and give rise to heterogeneous tumor tissue. Tumor heterogeneity is a hallmark of cancer and underlies resistance to anticancer therapies and disease progression. The epithelial‐mesenchymal transition (EMT) is a reversible phenomenon that is mediated by EMT‐inducing transcription factors (EMT‐TFs) and plays an important role in normal organ development, wound healing, and the invasiveness of cancer cells. Recent evidence showing that overexpression of several EMT‐TFs is associated with stemness in cancer cells has suggested the existence of a link between EMT and CSCs. In this review, we focus on the roles of CSCs and EMT signaling in driving tumor heterogeneity. A better understanding of the dynamics of both CSCs and EMT‐TFs in the generation of tumor heterogeneity may provide a basis for the development of new treatment options for cancer patients. Stem Cells 2016;34:1997–2007

Expression of CD24 is associated with HER2 expression and supports HER2-Akt signaling in HER2-positive breast cancer cells.

Human epidermal growth factor receptor 2 (HER2)‐positive breast cancer is treated with HER2‐targeted agents, such as trastuzumab and lapatinib, that suppress signaling by phosphatidylinositol 3‐kinase (PI3K)‐Akt and MAPK pathways. However, resistance to HER2‐targeted therapy remains a major clinical problem. Overexpression of CD24 has been detected in many cancers and is associated with a poor prognosis in women with breast cancer. HER2‐positive breast tumors are predominantly positive for CD24, suggesting that the expression of the two molecules is related. To investigate the relation between HER2 and CD24, we overexpressed HER2 in breast cancer cells that were triple‐negative for the estrogen receptor, progesterone receptor and HER2. We found that expression of CD24 was increased by stable overexpression of HER2. Flow cytometry thus revealed that the percentage of CD24‐positive cells was markedly higher in the HER2‐positive fraction than in the HER2‐negative fraction. Knockdown of CD24 in breast cancer cells positive for endogenous HER2 downregulated HER2 expression, whereas knockdown of HER2 did not affect the expression of CD24. Knockdown of CD24 also suppressed the phosphorylation of Akt, which functions downstream of HER2 and PI3K to promote cell survival. Moreover, knockdown of CD24 increased the sensitivity of HER2‐positive breast cancer cells to lapatinib treatment. Our results thus indicate that CD24 supports both the expression of HER2 and the consequent activation of PI3K‐Akt signaling. Furthermore, CD24 may contribute to resistance to HER2‐targeted therapy and, therefore, is itself a potential therapeutic target in HER2‐positive breast cancer.

Decreased expression of neurofibromin contributes to epithelial-mesenchymal transition in neurofibromatosis type 1

Please cite this paper as: Decreased expression of neurofibromin contributes to epithelial–mesenchymal transition in neurofibromatosis type 1. Experimental Dermatology 2010; 19: e136–e141.