Epigenetic reversion of breast carcinoma phenotype is accompanied by changes in DNA sequestration as measured by AluI restriction enzyme

Tumor reversion: a dream or a reality

Reversion of tumor to a normal differentiated cell once considered a dream is now at the brink of becoming a reality. Different layers of molecules/events such as microRNAs, transcription factors, alternative RNA splicing, post-transcriptional, post-translational modifications, availability of proteomics, genomics editing tools, and chemical biology approaches gave hope to manipulation of cancer cells reversion to a normal cell phenotype as evidences are subtle but definitive. Regardless of the advancement, there is a long way to go, as customized techniques are required to be fine-tuned with precision to attain more insights into tumor reversion. Tumor regression models using available genome-editing methods, followed by in vitro and in vivo proteomics profiling techniques show early evidence. This review summarizes tumor reversion developments, present issues, and unaddressed challenges that remained in the uncharted territory to modulate cellular machinery for tumor reversion towards therapeutic purposes successfully. Ongoing research reaffirms the potential promises of understanding the mechanism of tumor reversion and required refinement that is warranted in vitro and in vivo models of tumor reversion, and the potential translation of these into cancer therapy. Furthermore, therapeutic compounds were reported to induce phenotypic changes in cancer cells into normal cells, which will contribute in understanding the mechanism of tumor reversion. Altogether, the efforts collectively suggest that tumor reversion will likely reveal a new wave of therapeutic discoveries that will significantly impact clinical practice in cancer therapy.

Cancer Stem Cells in Pheochromocytoma and Paraganglioma

Pheochromocytoma (PCC) and paraganglioma (PGL) are rare neuroendocrine tumors associated with high cardiovascular morbidity and variable risk of malignancy. The current therapy of choice is surgical resection. Nevertheless, PCCs/PGLs are associated with a lifelong risk of tumor persistence or recurrence. A high rate of germline or somatic mutations in numerous genes has been found in these tumors. For some, the tumorigenic processes are initiated during embryogenesis. Such tumors carry gene mutations leading to pseudohypoxic phenotypes and show more immature characteristics than other chromaffin cell tumors; they are also often multifocal or metastatic and occur at an early age, often during childhood. Cancer stem cells (CSCs) are cells with an inherent ability of self-renewal, de-differentiation, and capacity to initiate and maintain malignant tumor growth. Targeting CSCs to inhibit cancer progression has become an attractive anti-cancer therapeutic strategy. Despite progress for this strategy for solid tumors such as neuroblastoma, brain, breast, and colon cancers, no substantial advance has been made employing similar strategies in PCCs/PGLs. In the current review, we discuss findings related to the identification of normal chromaffin stem cells and CSCs, pathways involved in regulating the development of CSCs, and the importance of the stem cell niche in development and maintenance of CSCs in PCCs/PGLs. Additionally, we examine the development and feasibility of novel CSC-targeted therapeutic strategies aimed at eradicating especially recurrent and metastatic tumors.

Baicalein inhibits fibronectin-induced epithelial-mesenchymal transition by decreasing activation and upregulation of calpain-2

The extracellular matrix protein fibronectin (FN) facilitates tumorigenesis and the development of breast cancer. Inhibition of the FN-induced cellular response is a potential strategy for breast cancer treatment. In the present study, we investigated the effects of the flavonoid baicalein on FN-induced epithelial-mesenchymal transition (EMT) in MCF-10A breast epithelial cells and in a transgenic mouse MMTV-polyoma middle T antigen breast cancer model (MMTV-PyMT). Baicalein inhibited FN-induced migration, invasion, and F-actin remodeling. Baicalein also suppressed FN-induced downregulation of the epithelial markers E-cadherin and ZO-1 and upregulation of the mesenchymal markers N-cadherin, vimentin, and Snail. Further investigation revealed that calpain-2 was involved in baicalein suppression of FN-induced EMT. Baicalein significantly decreased FN-enhanced calpain-2 expression and activation by suppressing its plasma membrane localization, substrate cleavage, and degradation of its endogenous inhibitor calpastatin. Overexpression of calpain-2 in MCF-10A cells by gene transfection partially blocked the inhibitory effect of baicalein on FN-induced EMT changes. In addition, baicalein inhibited calpain-2 by decreasing FN-increased intracellular calcium ion levels and extracellular signal-regulated protein kinases activation. Baicalein significantly decreased tumor onset, growth, and pulmonary metastasis in a spontaneous breast cancer MMTV-PyMT mouse model. Baicalein also reduced the expression of FN, calpain-2, and vimentin, but increased E-cadherin expression in MMTV-PyMT mouse tumors. Overall, these results revealed that baicalein markedly inhibited FN-induced EMT by inhibiting calpain-2, thus providing novel insights into the pharmacological action and mechanism of baicalein. Baicalein may therefore possess therapeutic potential for the treatment of breast cancer though interfering with extracellular matrix-cancer cell interactions.

ITIH5 mediates epigenetic reprogramming of breast cancer cells

Background

Extracellular matrix (ECM) is known to maintain epithelial integrity. In carcinogenesis ECM degradation triggers metastasis by controlling migration and differentiation including cancer stem cell (CSC) characteristics. The ECM-modulator inter- α-trypsin inhibitor heavy chain family member five (ITIH5) was recently identified as tumor suppressor potentially involved in impairing breast cancer progression but molecular mechanisms underlying its function are still elusive.

Methods

ITIH5 expression was analyzed using the public TCGA portal. ITIH5-overexpressing single-cell clones were established based on T47D and MDA-MB-231 cell lines. Colony formation, growth, apoptosis, migration, matrix adhesion, traction force analyses and polarization of tumor cells were studied in vitro. Tumor-initiating characteristics were analyzed by generating a metastasis mouse model. To identify ITIH5-affected pathways we utilized genome wide gene expression and DNA methylation profiles. RNA-interference targeting the ITIH5-downstream regulated gene DAPK1 was used to confirm functional involvement.

Results

ITIH5 loss was pronounced in breast cancer subtypes with unfavorable prognosis like basal-type tumors. Functionally, cell and colony formation was impaired after ITIH5 re-expression in both cell lines. In a metastasis mouse model, ITIH5 expressing MDA-MB-231 cells almost completely failed to initiate lung metastases. In these metastatic cells ITIH5 modulated cell-matrix adhesion dynamics and altered biomechanical cues. The profile of integrin receptors was shifted towards β1-integrin accompanied by decreased Rac1 and increased RhoA activity in ITIH5-expressing clones while cell polarization and single-cell migration was impaired. Instead ITIH5 expression triggered the formation of epithelial-like cell clusters that underwent an epigenetic reprogramming. 214 promoter regions potentially marked with either H3K4 and /or H3K27 methylation showed a hyper- or hypomethylated DNA configuration due to ITIH5 expression finally leading to re-expression of the tumor suppressor DAPK1. In turn, RNAi-mediated knockdown of DAPK1 in ITIH5-expressing MDA-MB-231 single-cell clones clearly restored cell motility.

Conclusions

Our results provide evidence that ITIH5 triggers a reprogramming of breast cancer cells with known stem CSC properties towards an epithelial-like phenotype through global epigenetic changes effecting known tumor suppressor genes like DAPK1. Therewith, ITIH5 may represent an ECM modulator in epithelial breast tissue mediating suppression of tumor initiating cancer cell characteristics which are thought being responsible for the metastasis of breast cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-017-0610-2) contains supplementary material, which is available to authorized users.

Cancer stem cells: progress and challenges in lung cancer

The identification of a subpopulation of tumor cells with stem cell-like characteristics first in hematological malignancies and later in solid tumors has emerged into a novel field of cancer research. It has been proposed that this aberrant population of cells now called "cancer stem cells" (CSCs) drives tumor initiation, progression, metastasis, recurrence, and drug resistance. CSCs have been shown to have the capacity of self-renewal and multipotency. Adopting strategies from the field of stem cell research has aided in identification, localization, and targeting of CSCs in many tumors. Despite the huge progress in other solid tumors such as brain, breast, and colon cancers no substantial advancements have been made in lung cancer. This is most likely due to the current rudimentary understanding of lung stem cell hierarchy and heterogeneous nature of lung disease. In this review, we will discuss the most recent findings related to identification of normal lung stem cells and CSCs, pathways involved in regulating the development of CSCs, and the importance of the stem cell niche in development and maintenance of CSCs. Additionally, we will examine the development and feasibility of novel CSC-targeted therapeutic strategies aimed at eradicating lung CSCs.

Increased Resistance of Breast, Prostate, and Embryonic Carcinoma Cells against Herpes Simplex Virus in Three-Dimensional Cultures

In previous studies we found that uveal melanoma cells grown in extracellular matrix (ECM)-containing three-dimensional (3D) cultures have increased resistance against herpes simplex virus type 1 (HSV-1)-mediated destruction relative to cells cultured without ECM. Using additional tumor cell types including MB-231 human breast cancer cells, PC-3 human prostate cancer cells, and P19 mouse embryonal carcinoma cells, we show here that tumor cell lines other than melanoma are also more resistant to HSV-1-mediated destruction in 3D cultures than cells grown in 2D. We also demonstrate here that one mechanism responsible for the increased resistance of tumor cells to HSV-1 infection in 3D cultures is an ECM-mediated inhibition of virus replication following virus entry into cells. These findings confirm and extend previous observations related to the role of the ECM in tumor resistance against HSV-1 and may lead to improved strategies of oncolytic virotherapy.

Mammary epithelial cell interactions with fibronectin stimulate epithelial-mesenchymal transition

In the mammary gland, the stromal extracellular matrix (ECM) undergoes dramatic changes during development and in tumorigenesis. For example, normal adult breast tissue is largely devoid of the ECM protein fibronectin (FN) whereas high FN levels have been detected in the stroma of breast tumors. FN is an established marker for epithelial-mesenchymal transition (EMT), which occurs during development and has been linked to cancer. During EMT, epithelial cell adhesion switches from cell-cell contacts to mainly cell-ECM interactions raising the possibility that FN may have a role in promoting this transition. Using MCF-10A mammary epithelial cells, we show that exposure to exogenous FN induces an EMT response including up-regulation of the EMT markers FN, Snail, N-cadherin, vimentin, the matrix metalloprotease MMP2, α-smooth muscle actin, and phospho-Smad2 as well as acquisition of cell migratory behavior. FN-induced EMT depends on Src kinase and ERK/MAP kinase signaling but not on the immediate early gene EGR-1. FN initiates EMT under serum-free conditions; this response is partially reversed by a TGFβ neutralizing antibody suggesting that FN enhances the effect of endogenous TGFβ. EMT marker expression is up-regulated in cells on a fragment of FN containing the integrin-binding domain but not other domains. Differences in gene expression between FN and MG are maintained with addition of a sub-threshold level of TGFβ1. Together, these results show that cells interacting with FN are primed to respond to TGFβ. The ability of FN to induce EMT shows an active role for the stromal ECM in this process and supports the notion that the increased levels of FN observed in breast tumors facilitate tumorigenesis.

Tumor microenvironment and breast cancer progression: a complex scenario

It is now widely accepted that the development and progression of a tumor toward the malignant phenotype is highly dependent on interactions between tumor cells and the tumor microenvironment. Different components of the tumor microenvironment may have stimulatory or inhibitory effects on tumor progression by regulating the gene expression repertoire in tumor cells and stromal cells. This review analyzes novel research findings on breast cancer progression, discussing acquisition of the metastatic phenotype in breast disease in relation to different aspects of cross-talk among components of the tumor microenvironment. Knowledge of the interaction of all of these factors would contribute to elucidating the mechanisms that disrupt regulatory/signaling cascades and downstream effects in breast cancer.

The tumor microenvironment is a dominant force in multidrug resistance

The emergence of clinical drug resistance is still one of the most challenging factors in cancer treatment effectiveness. Until more recently, the assumption has been that random genetic lesions are sufficient to explain the progression of malignancy and escape from chemotherapy. Here we propose an additional perspective, one in which the tumor cells despite the malignant genome could find a microenvironment either within the tumor or as a dormant cell to remain polar and blend into an organized context. Targeting this dynamic interplay could be considered a new avenue to prevent therapeutic resistance, and may even provide a promising effective cancer treatment.

The difficulty of targeting cancer stem cell niches

Normal stem cell niches typically are identified by their distinctive anatomical features and by association with tissue-specific stem cells. Identifying cancer stem cell (CSC) niches presents a special problem because there are few if any common anatomical features among tumors, and the physical phenotypes that reportedly describe the CSCs as entities may be subject to the host's microenvironment, sex, and tumor stage. Irrespective of a niche's location, the occupant's phenotype, or the precise molecular composition, all niches must do basically the same thing: maintain the activities in a stem cell that define it as such. Therefore, a potentially successful strategy, both for elaborating a molecular and cellular portrait of a CSC niche, and for therapeutically targeting them, is to identify components in the tumor microenvironment that are required for maintaining the functions of self-renewal, differentiation, and quiescence in the face of cytotoxic therapeutic regimens.

Breast cancer cells in three-dimensional culture display an enhanced radioresponse after coordinate targeting of integrin alpha5beta1 and fibronectin

Tactics to selectively enhance cancer radioresponse are of great interest. Cancer cells actively elaborate and remodel their extracellular matrix (ECM) to aid in survival and progression. Previous work has shown that beta1-integrin inhibitory antibodies can enhance the growth-inhibitory and apoptotic responses of human breast cancer cell lines to ionizing radiation, either when cells are cultured in three-dimensional laminin-rich ECM (3D lrECM) or grown as xenografts in mice. Here, we show that a specific alpha heterodimer of beta1-integrin preferentially mediates a prosurvival signal in human breast cancer cells that can be specifically targeted for therapy. 3D lrECM culture conditions were used to compare alpha-integrin heterodimer expression in malignant and nonmalignant cell lines. Under these conditions, we found that expression of alpha5beta1-integrin was upregulated in malignant cells compared with nonmalignant breast cells. Similarly, we found that normal and oncofetal splice variants of fibronectin, the primary ECM ligand of alpha5beta1-integrin, were also strikingly upregulated in malignant cell lines compared with nonmalignant acini. Cell treatment with a peptide that disrupts the interactions of alpha5beta1-integrin with fibronectin promoted apoptosis in malignant cells and further heightened the apoptotic effects of radiation. In support of these results, an analysis of gene expression array data from breast cancer patients revealed an association of high levels of alpha5-integrin expression with decreased survival. Our findings offer preclinical validation of fibronectin and alpha5beta1-integrin as targets for breast cancer therapy.

Tissue architecture and function: dynamic reciprocity via extra- and intra-cellular matrices

Mammary gland development, functional differentiation, and homeostasis are orchestrated and sustained by a balance of biochemical and biophysical cues from the organ's microenvironment. The three-dimensional microenvironment of the mammary gland, predominantly 'encoded' by a collaboration between the extracellular matrix (ECM), hormones, and growth factors, sends signals from ECM receptors through the cytoskeletal intracellular matrix to nuclear and chromatin structures resulting in gene expression; the ECM in turn is regulated and remodeled by signals from the nucleus. In this chapter, we discuss how coordinated ECM deposition and remodeling is necessary for mammary gland development, how the ECM provides structural and biochemical cues necessary for tissue-specific function, and the role of the cytoskeleton in mediating the extra--to intracellular dialogue occurring between the nucleus and the microenvironment. When operating normally, the cytoskeletal-mediated dynamic and reciprocal integration of tissue architecture and function directs mammary gland development, tissue polarity, and ultimately, tissue-specific gene expression. Cancer occurs when these dynamic interactions go awry for an extended time.

Laminin-1 induces E-cadherin expression in 3-dimensional cultured breast cancer cells by inhibiting DNA methyltransferase 1 and reversing promoter methylation status

This study determines the role of laminin-1 in promoting metastatic colonization during breast cancer. For this purpose, human mammary epithelial cell lines representing normal (MCF-10A), adenocarcinoma (MCF-7), and malignant carcinoma (MDA-MB-231) were propagated in 3-dimensional cultures composed of laminin-1, collagen I, or mixtures of the two, and analyzed by Western blot, immunocytochemistry, semiquantitative reverse transcription polymerase chain reaction, and methylation-specific PCR. Here we demonstrate that laminin-1 decreases methylation of the E-cadherin promoter, resulting in increased mRNA and protein expression for malignant mammary epithelial cells. This decreased methylation is associated with dramatic changes in the cellular and structural morphology as well as a 70-fold decrease in DNA methyltransferase 1 (DNMT1) and a 6-fold decrease in cadherin 11 protein expression. To control for specificity of laminin-1 interactions, cells were also cultured on 2-dimensional plastic substrata and collagen I hydrogels for analysis, and the MCF-10A and MCF-7 were used as nonmalignant controls. Using a 3-dimensional model, we present evidence that laminin-1 is capable of inducing epigenetic change by inhibiting expression of DNMT1 and preventing methylation of the E-cadherin promoter, resulting in E-cadherin expression and the formation of cell-cell bonds in malignant carcinoma.

Seed in soil, with an epigenetic view

It is becoming increasingly evident that discrete genetic alterations in neoplastic cells alone cannot explain multistep carcinogenesis whereby tumor cells are able to express diverse phenotypes during the complex phases of tumor development and progression. The epigenetic model posits that the host microenvironment exerts an initial, inhibitory constraint on tumor growth that is followed by acceleration of tumor progression through complex cell-matrix interactions. This review emphasizes the epigenetic aspects of breast cancer development in light of such interactions between epithelial cells ("seed") and the tumor microenvironment ("soil"). Our recent research findings suggest that epigenetic perturbations induced by the tumor microenvironment may play a causal role in promoting breast cancer development. It is believed that abrogation of these initiators could offer a promising therapeutic strategy.