Activated Thyroid Hormone Promotes Differentiation and Chemotherapeutic Sensitization of Colorectal Cancer Stem Cells by Regulating Wnt and BMP4 Signaling.

Thyroid hormone is a pleiotropic factor that controls many cellular processes in multiple cell types such as cancer stem cells (CSC). Thyroid hormone concentrations in the blood are stable, but the action of the deiodinases (D2-D3) provides cell-specific regulation of thyroid hormone activity. Deregulation of deiodinase function and thyroid hormone status has been implicated in tumorigenesis. Therefore, we investigated the role of thyroid hormone metabolism and signaling in colorectal CSCs (CR-CSC), where deiodinases control cell division and chemosensitivity. We found that increased intracellular thyroid hormone concentration through D3 depletion induced cell differentiation and sharply mitigated tumor formation. Upregulated BMP4 expression and concomitantly attenuated Wnt signaling accompanied these effects. Furthermore, we demonstrate that BMP4 is a direct thyroid hormone target and is involved in a positive autoregulatory feedback loop that modulates thyroid hormone signaling. Collectively, our findings highlight a cell-autonomous metabolic mechanism by which CR-CSCs exploit thyroid hormone signaling to facilitate their self-renewal potential and suggest that drug-induced cell differentiation may represent a promising therapy for preventing CSC expansion and tumor progression.

Estrogens and stem cells in thyroid cancer.

Recent discoveries highlight the emerging role of estrogens in the initiation and progression of different malignancies through their interaction with stem cell (SC) compartment. Estrogens play a relevant role especially for those tumors bearing a gender disparity in incidence and aggressiveness, as occurs for most thyroid diseases. Although several experimental lines suggest that estrogens promote thyroid cell proliferation and invasion, their precise contribution in SC compartment still remains unclear. This review underlines the interplay between hormones and thyroid function, which could help to complete the puzzle of gender discrepancy in thyroid malignancies. Defining the association between estrogen receptors' status and signaling pathways by which estrogens exert their effects on thyroid cells is a potential tool that provides important insights in pathogenetic mechanisms of thyroid tumors.

CD44v6 is a marker of constitutive and reprogrammed cancer stem cells driving colon cancer metastasis.

Cancer stem cells drive tumor formation and metastasis, but how they acquire metastatic traits is not well understood. Here, we show that all colorectal cancer stem cells (CR-CSCs) express CD44v6, which is required for their migration and generation of metastatic tumors. CD44v6 expression is low in primary tumors but demarcated clonogenic CR-CSC populations. Cytokines hepatocyte growth factor (HGF), osteopontin (OPN), and stromal-derived factor 1α (SDF-1), secreted from tumor associated cells, increase CD44v6 expression in CR-CSCs by activating the Wnt/ß-catenin pathway, which promotes migration and metastasis. CD44v6(-) progenitor cells do not give rise to metastatic lesions but, when treated with cytokines, acquire CD44v6 expression and metastatic capacity. Importantly, phosphatidylinositol 3-kinase (PI3K) inhibition selectively killed CD44v6 CR-CSCs and reduced metastatic growth. In patient cohorts, low levels of CD44v6 predict increased probability of survival. Thus, the metastatic process in colorectal cancer is initiated by CSCs through the expression of CD44v6, which is both a functional biomarker and therapeutic target.

Tumor and its microenvironment: a synergistic interplay.

The mutual and interdependent interaction between tumor and its microenvironment is a crucial topic in cancer research. Recently, it was reported that targeting stromal events could improve efficacies of current therapeutics and prevent metastatic spreading. Tumor microenvironment is a "complex network" of different cell types, soluble factors, signaling molecules and extracellular matrix components, which orchestrate the fate of tumor progression. As by definition, cancer stem cells (CSCs) are proposed to be the unique cell type able to maintain tumor mass and survive outside the primary tumor at metastatic sites. Being exposed to environmental stressors, including reactive oxygen species (ROS), CSCs have developed a GSH-dependent antioxidant system to improve ROS defense capability and acquire a malignant phenotype. Nevertheless, tumor progression is dependent on extracellular matrix remodeling, fibroblasts and macrophages activation in response to oxidative stress, as well as epithelial mesenchymal transition (EMT)-inducing signals and endothelial and perivascular cells recruitment. Besides providing a survival advantage by inducing de novo angiogenesis, tumor-associated vessels contribute to successful dissemination by facilitating tumor cells entry into the circulatory system and driving the formation of pre-metastatic niche. In this review, we focus on the synergistic effect of hypoxia inducible factors (HIFs) and vascular endothelial growth factors (VEGFs) in the successful outgrowth of metastasis, integrating therefore many of the emerging models and theories in the field.

DUSP6/MKP3 is overexpressed in papillary and poorly differentiated thyroid carcinoma and contributes to neoplastic properties of thyroid cancer cells.

Thyroid carcinomas derived from follicular cells comprise papillary thyroid carcinoma (PTC), follicular thyroid carcinoma, poorly differentiated thyroid carcinoma (PDTC) and undifferentiated anaplastic thyroid carcinoma (ATC). PTC, the most frequent thyroid carcinoma histotype, is associated with gene rearrangements that generate RET/PTC and TRK oncogenes and with BRAF-V600E and RAS gene mutations. These last two genetic lesions are also present in a fraction of PDTCs. The ERK1/2 pathway, downstream of the known oncogenes activated in PTC, has a central role in thyroid carcinogenesis. In this study, we demonstrate that the BRAF-V600E, RET/PTC, and TRK oncogenes upregulate the ERK1/2 pathway's attenuator cytoplasmic dual-phase phosphatase DUSP6/MKP3 in thyroid cells. We also show DUSP6 overexpression at the mRNA and protein levels in all the analysed PTC cell lines. Furthermore, DUSP6 mRNA was significantly higher in PTC and PDTC in comparison with normal thyroid tissues both in expression profile datasets and in patients' surgical samples analysed by real-time RT-PCR. Immunohistochemical and western blot analyses showed that DUSP6 was also overexpressed at the protein level in most PTC and PDTC surgical samples tested, but not in ATC, and revealed a positive correlation trend with ERK1/2 pathway activation. Finally, DUSP6 silencing reduced the neoplastic properties of four PTC cell lines, thus suggesting that DUSP6 may have a pro-tumorigenic role in thyroid carcinogenesis.

CD133 as a target for colon cancer.

INTRODUCTION: Recent evidence based on cancer stem cell (CSC) models, is boosting the progress of translational research and providing relevant clinical implications in many tumour types, including colorectal cancer. The current failure of standard therapies is attributed to a small fraction of the primary cell population with stem-like characteristics, such as self-renewal and differentiation. Identification of CSCs is based on two different criteria of selection: stemness-selective conditions and direct isolation based on putative stem cell markers expression. CD133, a transmembrane glycoprotein, was associated with tumor-initiating cells derived from several histological variants of tumors, including colon. AREAS COVERED: In this review the current understandings about CD133 as putative marker of tumour-initiating cells in colorectal cancer (CRC) is described. The focus of the discussion is on the need for additional markers to better identify the cell population able to recapitulate the parental tumor in immunocompromised mice. EXPERT OPINION: Identification and characterization of CSCs represents a relevant issue to define innovative therapeutic approaches, overcoming the emergence of cancer cell clones capable of evading standard therapy.

Functional characterization of the MTC-associated germline RET-K666E mutation: evidence of oncogenic potential enhanced by the G691S polymorphism.

Activating mutations of RET, a gene encoding two isoforms of a tyrosine kinase receptor physiologically expressed in several neural crest-derived cell lineages, are associated with the inherited forms of medullary thyroid carcinoma (MTC). The identification and characterization of novel RET mutations involved in MTC is valuable, as RET gene testing plays a crucial role in the management of these patients. In an MTC patient, we have identified a germline c.1996A>G transition in heterozygosis leading to K666E substitution. In addition, the conservative S904S (c.2712C>G) and the non-conservative functional G691S (c.2071G>A) polymorphisms have been identified. Through functional studies, we demonstrate for the first time that K666E is a gain-of-function mutation with oncogenic potential, based on its ability to transform NIH3T3 cells. It was not possible to define whether K666E is a de novo or inherited RET variant in the patient, as the family history was negative for MTC, and the carrier status of family members could not be tested. Our results, together with a recent report of co-segregation of the mutation in three MTC families, suggest that K666E is a causative MTC mutation. As we have shown that the same patient allele carries both K666E and G691S variants, the latter known to increase downstream RET signaling, a possible role for the G691S polymorphism has also been investigated. We have demonstrated that, although RET-G691S is not oncogenic per se, it enhances the transforming activity of the RET-K666E mutant, thus suggesting a modifier role for this functional polymorphism.

Colorectal cancer stem cells and cell death.

Nowadays it is reported that, similarly to other solid tumors, colorectal cancer is sustained by a rare subset of cancer stem-like cells (CSCs), which survive conventional anticancer treatments, thanks to efficient mechanisms allowing escape from apoptosis, triggering tumor recurrence. To improve patient outcomes, conventional anticancer therapies have to be replaced with specific approaches targeting CSCs. In this review we provide strong support that BMP4 is an innovative therapeutic approach to prevent colon cancer growth increasing differentiation markers expression and apoptosis. Recent data suggest that in colorectal CSCs, protection from apoptosis is achieved by interleukin-4 (IL-4) autocrine production through upregulation of antiapoptotic mediators, including survivin. Consequently, IL-4 neutralization could deregulate survivin expression and localization inducing chemosensitivity of the colon CSCs pool.

Therapeutic implications of Cancer Initiating Cells.

BACKGROUND: Until few years ago, all neoplastic cells within a tumour were suggested to have tumorigenic capacity, but recent evidences hint to the possibility that such feature is confined to a subset of Cancer Initiating Cells (CICs), also called Cancer Stem Cells (CSCs). These cells are the reservoir of the heterogeneous populations of differentiated cancer cells constituting the tumour bulk. Mechanisms shared with somatic stem cells, such as quiescence, self-renewal ability, asymmetric division and multidrug resistance, allow to these cells to drive tumour growth and to evade conventional therapy. OBJECTIVE: Here, we give a brief overview on the origin of CICs, the mechanisms involved in chemoresistance and therapeutic implications. CONCLUSION: Current cancer treatments, based on the assumption that tumour cell population responds homogeneously, have been developed to eradicate proliferating cells. The new model of tumorigenesis entails significant therapeutic implications, in fact if a small fraction of CICs survives conventional therapy it may lead to recurrence after month or years of apparent remission. Selective targeting of CICs could eliminate the tumour from the root, overcoming the emergence of clones capable of evading traditional therapy and increasing overall disease free survival.