Potential for cripto-1 in defining stem cell-like characteristics in human malignant melanoma

Targeting Nodal and Cripto-1: Perspectives Inside Dual Potential Theranostic Cancer Biomarkers

BACKGROUND

Elucidating the mechanisms of recurrence of embryonic signaling pathways in tumorigenesis has led to the discovery of onco-fetal players which have physiological roles during normal development but result aberrantly re-activated in tumors. In this context, Nodal and Cripto-1 are recognized as onco-developmental factors, which are absent in normal tissues but are overexpressed in several solid tumors where they can serve as theranostic agents.

OBJECTIVE

To collect, review and discuss the most relevant papers related to the involvement of Nodal and Cripto-1 in the development, progression, recurrence and metastasis of several tumors where they are over-expressed, with a particular attention to their occurrence on the surface of the corresponding sub-populations of cancer stem cells (CSC).

RESULTS

We have gathered, rationalized and discussed the most interesting findings extracted from some 370 papers related to the involvement of Cripto-1 and Nodal in all tumor types where they have been detected. Data demonstrate the clear connection between Nodal and Cripto-1 presence and their multiple oncogenic activities across different tumors. We have also reviewed and highlighted the potential of targeting Nodal, Cripto-1 and the complexes that they form on the surface of tumor cells, especially of CSC, as an innovative approach to detect and suppress tumors with molecules that block one or more mechanisms that they regulate.

CONCLUSION

Overall, Nodal and Cripto-1 represent two innovative and effective biomarkers for developing potential theranostic anti-tumor agents that target normal as well as CSC subpopulations and overcome both pharmacological resistance and tumor relapse.

Investigating the role of CRIPTO-1 (TDGF-1) in glioblastoma multiforme U87 cell line

Cripto-1 has been implicated in a number of human cancers. Although there is high potential for a role of Cripto-1 in glioblastoma multiforme (GBM) pathogenesis and progression, few studies have tried to define its role in GBM. These studies were limited in that Cripto-1 expression was not studied in detail in relation to markers of cancer initiation and progression. Therefore, these correlative studies allowed limited interpretation of Criptos-1's effect on the various aspects of GBM development using the U87 GBM cell line. In this study, we sought to delineate the role of Cripto-1 in facilitating pathogenesis, stemness, proliferation, invasion, migration and angiogenesis in GBM. Our findings show that upon overexpressing Cripto-1 in U87 GBM cells, the stemness markers Nanog, Oct4, Sox2, and CD44 increased expression. Similarly, an increase in Ki67 was observed demonstrating Cripto-1's potential to induce cellular proliferation. Likewise, we report a novel finding that increased expression of the markers of migration and invasion, Vimentin and Twist, correlated with upregulation of Cripto-1. Moreover, Cripto-1 exposure led to VEGFR-2 overexpression along with higher tube formation under conditions promoting endothelial growth. Taken together our results support a role for Cripto-1 in the initiation, development, progression, and maintenance of GBM pathogenesis. The data presented here are also consistent with a role for Cripto-1 in the re-growth and invasive growth in GBM. This highlights its potential use as a predictive and diagnostic marker in GBM as well as a therapeutic target.

Development of conformational antibodies targeting Cripto-1 with neutralizing effects in vitro

Human Cripto-1 (Cripto-1), the founding member of the EGF-CFC superfamily, is a key regulator of many processes during embryonic development and oncogenesis. Cripto-1 is barely present or even absent in normal adult tissues while it is aberrantly re-expressed in various tumors. Blockade of the CFC domain-mediated Cripto-1 functions is acknowledged as a promising therapeutic intervention point to inhibit the tumorigenic activity of the protein. In this work, we report the generation and characterization of murine monoclonal antibodies raised against the synthetic folded CFC [112-150] domain of the human protein. Through subtractive ELISA assays clones were screened for the ability to specifically recognize "hot spot" residues on the CFC domain, which are crucial for the interaction with Activin Type I receptor (ALK4) and GRP78. On selected antibodies, SPR and epitope mapping studies have confirmed their specificity and have revealed that recognition occurs only on a conformational epitope. Furthermore, FACS analyses have confirmed the ability of 1B4 antibody to recognize the membrane-anchored and soluble native Cripto-1 protein in a panel of human cancer cells. Finally, we have evaluated its functional effects through in vitro cellular signaling assays and cell cycle analysis. These findings suggest that the selected anti-CFC mAbs have the potential to neutralize the protein oncogenic activity and may be used as theranostic molecules suitable as tumor homing agents for Cripto-1-overexpressing cancer cells and tissues and to overcome drug-resistance in routine cancer therapies.

Cripto-1 Plasmid DNA Vaccination Targets Metastasis and Cancer Stem Cells in Murine Mammary Carcinoma

Metastatic breast cancer is a fatal disease that responds poorly to treatment. Cancer vaccines targeting antigens expressed by metastatic breast cancer cells and cancer stem cells could function as anticancer therapies. Cripto-1 is an oncofetal protein overexpressed in invasive breast cancer and cancer-initiating cells. In this study, we explored the potential of a Cripto-1-encoding DNA vaccine to target breast cancer in preclinical mouse models. BALB/c mice and BALB-neuT mice were treated with a DNA vaccine encoding mouse Cripto-1 (mCr-1). BALB/c mice were challenged with murine breast cancer 4T1 cells or TUBO spheres; BALB-neuT mice spontaneously developed breast cancer. Tumor growth was followed in all mouse models and lung metastases were evaluated. In vitro assays were performed to identify the immune response elicited by vaccination. Vaccination against mCr-1 reduced primary tumor growth in the 4T1 metastatic breast cancer model and reduced lung metastatic burden. In BALB-neuT mice, because the primary tumors are Cripto-1 negative, vaccination against mCr-1 did not affect primary tumors but did reduce lung metastatic burden. Spheroid-cultured TUBO cells, derived from a BALB/neuT primary tumor, develop a cancer stem cell-like phenotype and express mCr-1. We observed reduced tumor growth in vaccinated mice after challenge with TUBO spheres. Our data indicate that vaccination against Cripto-1 results in a protective immune response against mCr-1 expressing and metastasizing cells. Targeting Cripto-1 by vaccination holds promise as an immunotherapy for treatment of metastatic breast cancer. Cancer Immunol Res; 6(11); 1417-25. ©2018 AACR.

Developmental signaling pathways regulating mammary stem cells and contributing to the etiology of triple-negative breast cancer

Cancer has been considered as temporal and spatial aberrations of normal development in tissues. Similarities between mammary embryonic development and cell transformation suggest that the underlying processes required for mammary gland development are also those perturbed during various stages of mammary tumorigenesis and breast cancer (BC) development. The master regulators of embryonic development Cripto-1, Notch/CSL, and Wnt/β-catenin play key roles in modulating mammary gland morphogenesis and cell fate specification in the embryo through fetal mammary stem cells (fMaSC) and in the adult organism particularly within the adult mammary stem cells (aMaSC), which determine mammary progenitor cell lineages that generate the basal/myoepithelial and luminal compartments of the adult mammary gland. Together with recognized transcription factors and embryonic stem cell markers, these embryonic regulatory molecules can be inappropriately augmented during tumorigenesis to support the tumor-initiating cell (TIC)/cancer stem cell (CSC) compartment, and the effects of their deregulation may contribute for the etiology of BC, in particular the most aggressive subtype of BC, triple-negative breast cancer (TNBC). This in depth review will present evidence of the involvement of Cripto-1, Notch/CSL, and Wnt/β-catenin in the normal mammary gland morphogenesis and tumorigenesis, from fMaSC/aMaSC regulation to TIC generation and maintenance in TNBC. Specific therapies for treating TNBC by targeting these embryonic pathways in TICs will be further discussed, providing new opportunities to destroy not only the bulk tumor, but also TICs that initiate and promote the metastatic spread and recurrence of this aggressive subtype of BC.

Cripto-1: an extracellular protein - connecting the sequestered biological dots

Cripto-1 (CR-1) is a multifunctional embryonic protein that is re-expressed during inflammation, wound repair, and malignant transformation. CR-1 can function either as a tethered co-receptor or shed as a free ligand underpinning its flexible role in cell physiology. CR-1 has been shown to mediate cell growth, migration, invasion, and induce epithelial to mesenchymal transition (EMT). The main signaling pathways mediating CR-1 effects include Nodal-dependent (Smad2/3) and Nodal-independent (Src/p44/42/Akt) signaling transduction pathways. In addition, there are several naturally occurring binding partner proteins (BPPs) for CR-1 that can either agonize or antagonize its bioactivity. We will review the collective role of CR-1 as an extracellular protein, discuss caveats to consider in developing a quantitation assay, define possible mechanistic avenues applicable for drug discovery, and report on our experimental approaches to overcome these problematic issues.

CD271 is an imperfect marker for melanoma initiating cells

Understanding the molecular and cellular processes underlying melanoma plasticity and heterogeneity is of paramount importance to improve the efficiency of current treatment and to overcome resistance to chemotherapy drugs. The notion of plasticity and heterogeneity implies the existence of melanoma cell populations with different phenotypic and tumorigenic properties.

Using melanoma cell lines and melanoma cells freshly isolated from patient biopsies, we investigated the relationship between ABCB5+, CD271+ and low-MITF, expressing populations that were reported to display melanoma initiating cell properties. Here, we showed that ABCB5+ and CD271+ populations poorly overlap. However, we found that the CD271+ population is enriched in low-MITF cells and expresses a higher level of stemness genes, such as OCT4, NANOG and NES. These features could explain the increased tumorigenicity of the CD271+ cells. The rapid conversion of CD271+ to CD271− cells in vitro demonstrates the plasticity ability of melanoma cells. Finally, we observed that the transient slow-growing population contains only CD271+ cells that are highly tumorigenic. However, the fast growing/CD271+ population exhibits a poor tumorigenic ability. Taking together, our data show that CD271 is an imperfect marker for melanoma initiating cells, but may be useful to identify melanoma cells with an increased stemness and tumorigenic potential.

Cancer stem cells: a systems biology view of their role in prognosis and therapy

Evidence has accumulated that characterizes highly tumorigenic cancer cells residing in heterogeneous populations. The accepted term for such a subpopulation is cancer stem cells (CSCs). While many questions still remain about their precise role in the origin, progression, and drug resistance of tumors, it is clear they exist. In this review, a current understanding of the nature of CSC, their potential usefulness in prognosis, and the need to target them will be discussed. In particular, separate studies now suggest that the CSC is plastic in its phenotype, toggling between tumorigenic and nontumorigenic states depending on both intrinsic and extrinsic conditions. Because of this, a static view of gene and protein levels defined by correlations may not be sufficient to either predict disease progression or aid in the discovery and development of drugs to molecular targets leading to cures. Quantitative dynamic modeling, a bottom up systems biology approach whereby signal transduction pathways are described by differential equations, may offer a novel means to overcome the challenges of oncology today. In conclusion, the complexity of CSCs can be captured in mathematical models that may be useful for selecting molecular targets, defining drug action, and predicting sensitivity or resistance pathways for improved patient outcomes.

The multifaceted role of the embryonic gene Cripto-1 in cancer, stem cells and epithelial-mesenchymal transition

Cripto-1 (CR-1)/Teratocarcinoma-derived growth factor1 (TDGF-1) is a cell surface glycosylphosphatidylinositol (GPI)-linked glycoprotein that can function either in cis (autocrine) or in trans (paracrine). The cell membrane cis form is found in lipid rafts and endosomes while the trans acting form lacking the GPI anchor is soluble. As a member of the epidermal growth factor (EGF)/Cripto-1-FRL-1-Cryptic (CFC) family, CR-1 functions as an obligatory co-receptor for the transforming growth factor-β (TGF-β) family members, Nodal and growth and differentiation factors 1 and 3 (GDF1/3) by activating Alk4/Alk7 signaling pathways that involve Smads 2, 3 and 4. In addition, CR-1 can activate non-Smad-dependent signaling elements such as PI3K, Akt and MAPK. Both of these pathways depend upon the 78kDa glucose regulated protein (GRP78). Finally, CR-1 can facilitate signaling through the canonical Wnt/β-catenin and Notch/Cbf-1 pathways by functioning as a chaperone protein for LRP5/6 and Notch, respectively. CR-1 is essential for early embryonic development and maintains embryonic stem cell pluripotentiality. CR-1 performs an essential role in the etiology and progression of several types of human tumors where it is expressed in a population of cancer stem cells (CSCs) and facilitates epithelial-mesenchymal transition (EMT). In this context, CR-1 can significantly enhance tumor cell migration, invasion and angiogenesis. Collectively, these facts suggest that CR-1 may be an attractive target in the diagnosis, prognosis and therapy of several types of human cancer.

Nodal as a biomarker for melanoma progression and a new therapeutic target for clinical intervention

Nodal, an embryonic morphogen belonging to the TGF-β superfamily, is an important regulator of embryonic stem cell fate. We have recently demonstrated that Nodal is expressed significantly in aggressive melanoma. Surprisingly, expression of the Nodal coreceptor, Cripto-1, was detected in only a small fraction of the melanoma tumor cell population, indicating a primary role for Cripto-1-independent signaling of Nodal in melanoma. In this review, we discuss how regulatory factors present in an embryonic environment, such as Lefty, can downregulate Nodal expression and inhibit tumorigenicity and plasticity of melanoma cells. Our translational studies show that antibodies against Nodal are capable of repressing melanoma vasculogenic mimicry and of inducing apoptosis in melanoma tumors in an in vivo lung-colonization assay. Our previous work and ongoing studies suggest that Nodal may represent a novel diagnostic marker and therapeutic target in melanoma.

Regulation of human Cripto-1 expression by nuclear receptors and DNA promoter methylation in human embryonal and breast cancer cells

Human Cripto-1 (CR-1) plays an important role in regulating embryonic development while also regulating various stages of tumor progression. However, mechanisms that regulate CR-1 expression during embryogenesis and tumorigenesis are still not well defined. In the present study, we investigated the effects of two nuclear receptors, liver receptor homolog (LRH)-1 and germ cell nuclear factor receptor (GCNF) and epigenetic modifications on CR-1 gene expression in NTERA-2 human embryonal carcinoma cells and in breast cancer cells. CR-1 expression in NTERA-2 cells was positively regulated by LRH-1 through direct binding to a DR0 element within the CR-1 promoter, while GCNF strongly suppressed CR-1 expression in these cells. In addition, the CR-1 promoter was unmethylated in NTERA-2 cells, while T47D, ZR75-1, and MCF7 breast cancer cells showed high levels of CR-1 promoter methylation and low CR-1 mRNA and protein expression. Treatment of breast cancer cells with a demethylating agent and histone deacetylase inhibitors reduced methylation of the CR-1 promoter and reactivated CR-1 mRNA and protein expression in these cells, promoting migration and invasion of breast cancer cells. Analysis of a breast cancer tissue array revealed that CR-1 was highly expressed in the majority of human breast tumors, suggesting that CR-1 expression in breast cancer cell lines might not be representative of in vivo expression. Collectively, these findings offer some insight into the transcriptional regulation of CR-1 gene expression and its critical role in the pathogenesis of human cancer.

Association between tumorigenic potential and the fate of cancer cells in a syngeneic melanoma model

The self-renewal potential of a cancer cell can be estimated by using particular assays, which include xenotransplantation in immunocompromised animals or culturing in non-adherent serum-free stem-cells media (SCM). However, whether cells with self-renewal potential actually contribute to disease is unknown. Here we investigated the tumorigenic potential and fate of cancer cells in an in-vivo melanoma model. We examined cell lines which were derived from the same parental line: a non-metastatic cell line (K1735/16), a metastatic cell line (K1735/M4) and a cell line which was selected in non-adherent conditions (K1735/16S). All cell lines exhibited similar proliferation kinetics when grown on culture plates. K1735/16 cells grown in soft agar or in suspension non-adherent conditions failed to form colonies or spheroids, whereas the other cell lines showed prominent colonogenicity and spheroid formation capacity. By using sphere limiting dilution analysis (SLDA) in serum-free media, K1735/16S and K1735/M4 cells grown in suspension were capable of forming spheroids even in low frequencies of concentrations, as opposed to K1735/16 cells. The tumorigenic potential of the cell lines was determined in SCID mice using intra footpad injections. Palpable tumors were evident in all mice. In agreement with the in-vitro studies, the K1735/M4 cell line exhibited the highest growth kinetics, followed by the K1735/16S cell line, whereas the K1735/16 cell line had the lowest tumor growth potential (P<0.001). In contrast, when we repeated the experiments in syngeneic C3H/HeN mice, the K1735/16 cell line produced macroscopic tumors 30–100 days after injection, whereas K1735/M4 and K1735/16S derived tumors regressed spontaneously in 90–100% of mice. TUNEL analysis revealed significantly higher number of apoptotic cells in K1735/16S and K1735/M4 cell line-derived tumors compared to K1735/16 tumors (P<0.001). The models we have examined here raised the possibility, that cells with high-tumorigenic activity may be more immunogenic and hence are more susceptible to immune-regulation.

The significance of a Cripto-1 positive subpopulation of human melanoma cells exhibiting stem cell-like characteristics

Cripto-1 (CR-1) protein function differs according to cellular or extracellular expression. In this study, we explore the significance of cell surface CR-1 expression in human melanoma cells. Cell surface CR-1-expressing human melanoma cells (CR1-CS+) were selected by fluorescence-activated cell sorting (FACS) and grown in vitro and in vivo in nude mice to study their growth characteristics. The CR1-CS+ melanoma cells were found to express increased levels of Oct4, MDR-1 and activated c-Src compared with cells lacking this subpopulation (CR1-CS-) or unsorted cells, used as control. CR1-CS+ show reduced proliferation rates and diminished spherical colony formation compared with control cells when cultured in vitro. Orthotopic injections of CR1-CS+ in nude mice formed slow growing tumors with histologic variability across different areas of the CR1-CS+ xenografts. CR-1-expressing cells from first generation CR1-CS+ tumors showed significantly increased tumor-forming rate and aggressiveness following subsequent transplants in nude mice. These data demonstrate that within a heterogeneous melanoma cell population there resides a slow proliferating, cell surface CR-1-expressing subpopulation capable of giving rise to a fast growing, aggressive progeny that may contribute to disease recurrence and progression.

Hypoxia-inducing factors as master regulators of stemness properties and altered metabolism of cancer- and metastasis-initiating cells

Accumulating lines of experimental evidence have revealed that hypoxia-inducible factors, HIF-1α and HIF-2α, are key regulators of the adaptation of cancer- and metastasis-initiating cells and their differentiated progenies to oxygen and nutrient deprivation during cancer progression under normoxic and hypoxic conditions. Particularly, the sustained stimulation of epidermal growth factor receptor (EGFR), insulin-like growth factor-1 receptor (IGF-1R), stem cell factor (SCF) receptor KIT, transforming growth factor-β receptors (TGF-βRs) and Notch and their downstream signalling elements such as phosphatidylinositol 3′-kinase (PI3K)/Akt/molecular target of rapamycin (mTOR) may lead to an enhanced activity of HIFs. Moreover, the up-regulation of HIFs in cancer cells may also occur in the hypoxic intratumoral regions formed within primary and secondary neoplasms as well as in leukaemic cells and metastatic prostate and breast cancer cells homing in the hypoxic endosteal niche of bone marrow. The activated HIFs may induce the expression of numerous gene products such as induced pluripotency-associated transcription factors (Oct-3/4, Nanog and Sox-2), glycolysis- and epithelial-mesenchymal transition (EMT) programme-associated molecules, including CXC chemokine receptor 4 (CXCR4), snail and twist, microRNAs and angiogenic factors such as vascular endothelial growth factor (VEGF). These gene products in turn can play critical roles for high self-renewal ability, survival, altered energy metabolism, invasion and metastases of cancer cells, angiogenic switch and treatment resistance. Consequently, the targeting of HIF signalling network and altered metabolic pathways represents new promising strategies to eradicate the total mass of cancer cells and improve the efficacy of current therapies against aggressive and metastatic cancers and prevent disease relapse.

Hematopoietic stem cells are regulated by Cripto, as an intermediary of HIF-1α in the hypoxic bone marrow niche

Cripto has been known as an embryonic stem (ES)- or tumor-related soluble/cell membrane protein. In this study, we demonstrated that Cripto has a role as an important regulatory factor for hematopoietic stem cells (HSCs). Recombinant Cripto sustained the reconstitution ability of HSCs in vitro. Flow cytometry analysis uncovered that GRP78, one of the candidate receptors for Cripto, was expressed on a subset of HSCs and could distinguish dormant/myeloid-biased HSCs and active/lymphoid-biased HSCs. Cripto is expressed in hypoxic endosteal niche cells where GRP78(+) HSCs mainly reside. Proteomics analysis revealed that Cripto-GRP78 binding stimulates glycolytic metabolism-related proteins and results in lower mitochondrial potential in HSCs. Furthermore, conditional knockout mice for HIF-1α, a master regulator of hypoxic responses, showed reduced Cripto expression and decreased GRP78(+) HSCs in the endosteal niche area. Thus, Cripto-GRP78 is a novel HSC regulatory signal mainly working in the hypoxic niche.

Nodal expression and detection in cancer: experience and challenges

Nodal is a TGF-β-related embryonic morphogen that is expressed in multiple human cancers. Detection of Nodal expression in these tissues can be challenging if issues related to Nodal transcription and protein processing are not considered. Here, we discuss certain characteristics related to Nodal expression and function and how these can facilitate acquisition and interpretation of expression data, contributing to our understanding of the potential role of Nodal in human cancer. We also discuss how Nodal could be exploited clinically as a novel biomarker for cancer progression and therapeutic target.

Potential for the embryonic morphogen Nodal as a prognostic and predictive biomarker in breast cancer

Introduction

The re-emergence of the tumour growth factor-beta (TGF-beta)-related embryonic morphogen Nodal has recently been reported in several different human cancers. In this study, we examined the expression of Nodal in a series of benign and malignant human breast tissues to determine the clinical significance of this expression and whether Nodal could represent a potential therapeutic target in breast cancer.

Methods

Tissue sections from 431 therapeutically naive patients diagnosed with benign or malignant breast disease were stained for Nodal by immunohistochemistry and analysed in a blinded manner. The degree of Nodal staining was subsequently correlated with available clinical data, such as diagnoses and disease stage. These tissue findings were further explored in breast cancer cell lines MDA-MB-231 and MDA-MB-468 treated with a Nodal blocking antibody to determine biological effects for target validation.

Results

A variable degree of Nodal staining was detected in all samples. The intensity of Nodal staining was significantly greater in undifferentiated, advanced stage, invasive breast cancer compared with benign breast disease or early stage breast cancer. Treatment of human breast cancer cells in vitro with Nodal blocking antibody significantly reduced proliferation and colony-forming ability in soft agar, concomitant with increased apoptosis.

Conclusions

These data suggest a potential role for Nodal as a biomarker for disease progression and a promising target for anti-Nodal therapy in breast cancer.

An evolving web of signaling networks regulated by Cripto-1

Over the past few decades, our understanding of the embryonic gene Cripto-1 has considerably advanced through biochemical, cell biology, and animal studies. Cripto-1 performs key functions during embryonic development, while it dramatically disappears in adult tissues, except possibly in adult tissue stem cells. Cripto-1 is re-expressed in human tumors promoting cell proliferation, migration, invasion, epithelial to mesenchymal transition, and tumor angiogenesis. This diversity of biological effects is dependent upon interaction of Cripto-1 with an extensive array of signaling molecules. In fact, Cripto-1 modulates signaling of transforming growth factor-β family members, including Nodal, GDF-1/-3, Activin, and TGF-β1, activates c-src/MAPK/Protein Kinase B (AKT) pathway in a Glypican-1 and GRP78-dependent manner, and cross-talks with erbB4, Wnt/β-catenin, Notch, Caveolin-1, and Apelin/putative receptor protein related to Angiotensin-type I receptor (APJ) pathways. This article provides an updated survey of the various signaling pathways modulated by Cripto-1 with a focus on mechanistic insights in our understanding of the biological function of Cripto-1 in eukaryotic cells.

Acquired cancer stem cell phenotypes through Oct4-mediated dedifferentiation

There is enormous interest to target cancer stem cells (CSCs) for clinical treatment because these cells are highly tumorigenic and resistant to chemotherapy. Oct4 is expressed by CSC-like cells in different types of cancer. However, function of Oct4 in tumor cells is unclear. In this study, we showed that expression of Oct4 gene or transmembrane delivery of Oct4 protein promoted dedifferentiation of melanoma cells to CSC-like cells. The dedifferentiated melanoma cells showed significantly decreased expression of melanocytic markers and acquired the ability to form tumor spheroids. They showed markedly increased resistance to chemotherapeutic agents and hypoxic injury. In the subcutaneous xenograft and tail vein injection assays, these cells had significantly increased tumorigenic capacity. The dedifferentiated melanoma cells acquired features associated with CSCs such as multipotent differentiation capacity and expression of melanoma CSC markers such as ABCB5 and CD271. Mechanistically, Oct4 induced dedifferentiation was associated with increased expression of endogenous Oct4, Nanog and Klf4, and global gene expression changes that enriched for transcription factors. RNAi mediated knockdown of Oct4 in dedifferentiated cells led to diminished CSC phenotypes. Oct4 expression in melanoma was regulated by hypoxia and its expression was detected in a subpopulation of melanoma cells in clinical samples. Our data indicate that Oct4 is a positive regulator of tumor dedifferentiation. The results suggest that CSC phenotype is dynamic and may be acquired through dedifferentiation. Oct4 mediated tumor cell dedifferentiation may play an important role during tumor progression.

The homeobox gene MSX2 determines chemosensitivity of pancreatic cancer cells via the regulation of transporter gene ABCG2

Pancreatic cancer is one of the life-threatening cancers due to the difficulty in the curative surgery and resistance against conventional therapeutic strategies. Recent studies indicated that cancer stem cells, which exist as a small number of cells within the entire cancer tissue, contribute to the disease progression. Cancer stem cells reveal resistance against conventional chemotherapy, which is derived from the high-expression of multiple transporter genes. Our previous study demonstrated the aggravating role of the homeobox gene MSX2 as an inducer of epithelial-mesenchymal transition, and MSX2 turned out to correlate with the chemoresistance in the current study. Comprehensive analysis of the MSX2-target gene has identified ABCG2 as the responsible gene. Since previous studies reported the pivotal role of ABCG2 as a determining factor of cancer stem cells, the detailed regulatory mechanism of ABCG2 expression by MSX2 was investigated. As a result, the MSX2 expression level in each cell line well correlated with the ABCG2 expression level, and alteration of the MSX2 expression level by over-expression or siRNA-based knockdown affected the ABCG2 expression accordingly. Finally, we identified the functional cooperation of MSX2 and SP1 in the transcriptional regulation of ABCG2 via the SP1 binding elements within the ABCG2 promoter. These findings clarified the intriguing regulatory mechanism of the cancer stem cell-related gene, and will delineate a novel therapeutic target in pancreatic cancer.

Expression and functional role of CRIPTO-1 in cutaneous melanoma

Background:

CRIPTO-1 (CR-1) is involved in the pathogenesis and progression of human carcinoma of different histological origin. In this study we addressed the expression and the functional role of CR-1 in cutaneous melanoma.

Methods:

Expression of CR-1 protein in melanomas and melanoma cell lines was assessed by immunohistochemistry, western blotting and/or flow cytometry. Levels of mRNA were evaluated by real-time PCR. Invasion assays were performed in Matrigel-coated modified Boyden chambers.

Results:

Expression of CR-1 protein and/or mRNA was found in 16 out of 37 primary human cutaneous melanomas and in 12 out of 21 melanoma cell lines. Recombinant CR-1 protein activated in melanoma cells c-Src and, at lesser extent, Smad signalling. In addition, CR-1 significantly increased the invasive ability of melanoma cells that was prevented by treatment with either the ALK4 inhibitor SB-431542 or the c-Src inhibitor saracatinib (AZD0530). Anti-CR-1 siRNAs produced a significant inhibition of the growth and the invasive ability of melanoma cells. Finally, a close correlation was found in melanoma cells between the levels of expression of CR-1 and the effects of saracatinib on cell growth.

Conclusion:

These data indicate that a significant fraction of cutaneous melanoma expresses CR-1 and that this growth factor is involved in the invasion and proliferation of melanoma cells.

Reactivation of embryonic nodal signaling is associated with tumor progression and promotes the growth of prostate cancer cells

BACKGROUND

Nodal is a member of the transforming growth factor β (TGFβ) superfamily that directs embryonic patterning and promotes the plasticity and tumorigenicity of tumor cells, but its role in the prostate is unknown. The goal of this study was to characterize the expression and function of Nodal in prostate cancer and determine whether, like other TGFβ ligands, it modulates androgen receptor (AR) activity.

METHODS

Nodal expression was investigated using immunohistochemistry of tissue microarrays and Western blots of prostate cell lines. The functional role of Nodal was examined using Matrigel and soft agar growth assays. Cross-talk between Nodal and AR signaling was assessed with luciferase reporter assays and expression of endogenous androgen regulated genes.

RESULTS

Significantly increased Nodal expression was observed in cancer compared with benign prostate specimens. Nodal was only expressed by DU145 and PC3 cells. All cell lines expressed Nodal's co-receptor, Cripto-1, but lacked Lefty, a critical negative regulator of Nodal signaling. Recombinant human Nodal triggered downstream Smad2 phosphorylation in DU145 and LNCaP cells, and stable transfection of pre-pro-Nodal enhanced the growth of LNCaP cells in Matrigel and soft agar. Finally, Nodal attenuated AR signaling, reducing the activity of a PSA promoter construct in luciferase assays and down-regulating the endogenous expression of androgen regulated genes.

CONCLUSIONS

An aberrant Nodal signaling pathway is re-expressed and functionally active in prostate cancer cells.

Expression of nodal and nodal receptors in prostate stem cells and prostate cancer cells: autocrine effects on cell proliferation and migration

BACKGROUND

Nodal, a TGFβ like growth factor, functions as an embryonic morphogen that maintains the pluripotency of embryonic stem cells. Nodal has been implicated in cancer progression; however, there is no information on expression and functions of Nodal in prostate cancer. In this study, we have investigated the expression of Nodal, its receptors, and its effects on proliferation and migration of human prostate cells.

METHODS

RT-PCR, qPCR, and Western blot analyses were performed to analyze expression of Nodal and Nodal receptors and its effects on phosphorylation of Smad2/3 in prostate cells. The effects on proliferation and migration were determined by (3) H-Thymidine incorporation and cell migration assays in the presence or absence of Nodal receptor inhibitor (SB431542).

RESULTS

Nodal was highly expressed in WPE, DU145, LNCaP, and LNCaP-C81 cells with low expression in RWPE1 and RWPE2 cells, but not in PREC, PC3 and PC3M cells. Nodal receptors are expressed at varying levels in all prostate cells. Treatment with exogenous Nodal induced phosphorylation of Smad2/3 in WPE, DU145, and PC3 cells, which was blocked by SB431542. Nodal dose-dependently inhibited proliferation of WPE, RWPE1 and DU145 cells, but not LNCaP and PC3 cells. Nodal induced cell migration in PC3 cells, which was inhibited by SB431542; Nodal had no effect on cell migration in WPE and DU145 cells. The effects of Nodal on cell proliferation and migration are mediated via ALK4 and ActRII/ActRIIB receptors and Smad 2/3 phosphorylation.

CONCLUSIONS

Nodal may function as an autocrine regulator of proliferation and migration of prostate cancer cells.

Finding the root of the problem: the quest to identify melanoma stem cells

Melanoma is an exceptionally aggressive cancer with limited treatment options. As such, the idea that a minority of tumor cells, termed melanoma stem cells, are actually responsible for the progression of the disease offers up new possibilities for targeted therapies. However, reliable identification of these melanoma stem cells is complicated by the lack of clearly defined markers to distinguish them from the general tumor cell population. Additionally, there is evidence that under permissive conditions, a high proportion of melanoma cells are capable of forming tumors in mice. This review summarizes a number of the possible markers being considered for identifying melanoma stem cells, the potential role of transcription factors that regulate pluripotency and stem cell maintenance in melanoma, and evidence that may undermine the applicability of the cancer stem cell hypothesis to melanoma.

Melanoma spheroids grown under neural crest cell conditions are highly plastic migratory/invasive tumor cells endowed with immunomodulator function

Background

The aggressiveness of melanoma tumors is likely to rely on their well-recognized heterogeneity and plasticity. Melanoma comprises multi-subpopulations of cancer cells some of which may possess stem cell-like properties. Although useful, the sphere-formation assay to identify stem cell-like or tumor initiating cell subpopulations in melanoma has been challenged, and it is unclear if this model can predict a functional phenotype associated with aggressive tumor cells.

Methodology/Principal Findings

We analyzed the molecular and functional phenotypes of melanoma spheroids formed in neural crest cell medium. Whether from metastatic or advanced primary tumors, spheroid cells expressed melanoma-associated markers. They displayed higher capacity to differentiate along mesenchymal lineages and enhanced expression of SOX2, NANOG, KLF4, and/or OCT4 transcription factors, but not enhanced self-renewal or tumorigenicity when compared to their adherent counterparts. Gene expression profiling attributed a neural crest cell signature to these spheroids and indicated that a migratory/invasive and immune-function modulating program could be associated with these cells. In vitro assays confirmed that spheroids display enhanced migratory/invasive capacities. In immune activation assays, spheroid cells elicited a poorer allogenic response from immune cells and inhibited mitogen-dependent T cells activation and proliferation more efficiently than their adherent counterparts. Our findings reveal a novel immune-modulator function of melanoma spheroids and suggest specific roles for spheroids in invasion and in evasion of antitumor immunity.

Conclusion/Significance

The association of a more plastic, invasive and evasive, thus a more aggressive tumor phenotype with melanoma spheroids reveals a previously unrecognized aspect of tumor cells expanded as spheroid cultures. While of limited efficiency for melanoma initiating cell identification, our melanoma spheroid model predicted aggressive phenotype and suggested that aggressiveness and heterogeneity of melanoma tumors can be supported by subpopulations other than cancer stem cells. Therefore, it could be constructive to investigate melanoma aggressiveness, relevant to patients and clinical transferability.

An antibody-cytotoxic conjugate, BIIB015, is a new targeted therapy for Cripto positive tumours

BIIB015 is an immunoconjugate created for the treatment of solid tumours and is currently in Phase I of clinical evaluation. BIIB015 consists of a humanised monoclonal antibody against the Cripto protein carrying a payload, via a hindered disulphide linker, of the maytansinoid derivative, DM4. Cripto is a GPI-linked protein required for signal transduction of the TGF-beta ligand, Nodal. Cripto has been previously described as an oncogene and fits the classic pattern of an embryonic gene that is re-expressed in a transformed tumour cell. Cripto expression is highly prevalent on a number of solid tumours, including greater than 75% of breast, lung, and colorectal tumours. Our report documents for the first time that targeting the cell surface Cripto protein with an anti-Cripto antibody-cytotoxic conjugate is an effective means of inhibiting or regressing growth of Cripto positive tumours. BIIB015 which utilises a 'cleavable' linker containing a disulphide bond exhibits superior activity when compared to huB3F6 mAb conjugates with different linker systems, including one with a 'non-cleavable' linker. BIIB015 displays specificity for Cripto in both in vitro and in vivo experiments. In human xenograft models originating from lung (Calu-6), colon (CT-3), testicular (NCCIT) and breast (MDA-MB-231) tumour samples, BIIB015 shows robust activity with results ranging from >50% tumour inhibition to complete tumour regression. The efficacy seen in the MDA-MB-231 model, a triple negative (-HER2, -ER, and -PR) tumour, is particularly exciting since there is currently no approved therapy for this indication. In addition, BIIB015 can be combined with standard of care chemotherapeutics for enhanced efficacy.

Alantolactone Inhibits Cell Proliferation by Interrupting the Interaction between Cripto-1 and Activin Receptor Type II A in Activin Signaling Pathway

It has been suggested that deregulation of activin signaling contributes to tumor formation. Activin signaling is blocked in cancer cells due to the complex formed by Cripto-1, activin, and activin receptor type II (ActRII). In this study, the authors used a mammalian two-hybrid system to construct a drug screening model to obtain a small molecular inhibitor capable of interrupting the interaction between Cripto-1 and ActRII. They screened 300 natural components and identified alantolactone. Data suggested that alantolactone induced activin/SMAD3 signaling in human colon adenocarcinoma HCT-8 cells. The authors also found that alantolactone exhibited antiproliferative function specific to tumor cells, with almost no toxicity to normal cells at a concentration of 5 µg/mL. Furthermore, they proved that the antiproliferative function of alantolactone was activin/SMAD3 dependent. These results suggest that alantolactone performs its antitumor effect by interrupting the interaction between Cripto-1 and the activin receptor type IIA in the activin signaling pathway. Moreover, screening for inhibitors of Cripto-1/ActRII is a potentially beneficial approach to aid in discovering novel cancer treatment.

Mitf is the key molecular switch between mouse or human melanoma initiating cells and their differentiated progeny

In melanoma, as well as in other solid tumors, the cells within a given tumor exhibit strong morphological, functional and molecular heterogeneity that might reflect the existence of different cancer cell populations, among which are melanoma-initiating cells (MICs) with 'stemness' properties and their differentiated, fast-growing progeny. The existence of a slow-growing population might explain the resistance of melanoma to classical chemotherapies that target fast growing cells. Therefore, elucidating the biologic properties of MICs and, more importantly, the molecular mechanisms that drive the transition between MICs and their proliferating progeny needs to be addressed to develop an efficient melanoma therapy. Using B16 mouse melanoma cells and syngeneic mice, we show that the inhibition of microphthalmia-associated transcription factor (Mitf), the master regulator of melanocyte differentiation, increases the tumorigenic potential of melanoma cells and upregulates the stem cell markers Oct4 and Nanog. Notably, p27, the CDK inhibitor, is increased in Mitf-depleted cells and is required for exacerbation of the tumorigenic properties of melanoma cells. Further, a slow-growing population with low-Mitf level and high tumorigenic potential exists spontaneously in melanoma. Ablation of this population dramatically decreases tumor formation. Importantly, these data were confirmed using human melanoma cell lines and freshly isolated human melanoma cell from lymph node and skin melanoma metastasis. Taken together our data, identified Mitf and p27 as the key molecular switches that control the transition between MICs and their differentiated progeny. Eradication of low-Mitf cells might be an appealing strategy to cure melanoma.

Cripto-1 is a cell surface marker for a tumorigenic, undifferentiated subpopulation in human embryonal carcinoma cells

Deregulation of stem cells is associated with the generation and progression of malignant tumors. In addition, genes that are associated with early embryogenesis are frequently expressed in cancer. Cripto-1 (CR-1), a glycosylphosphatidylinositol-linked glycoprotein, is expressed during early embryogenesis and in various human carcinomas. We demonstrated that human embryonal carcinoma (EC) cells are heterogeneous for CR-1 expression and consist of two distinct subpopulations: a CR-1(High) and a CR-1(Low) population. By segregating CR-1(High) and CR-1(Low) populations of NTERA2/D1 EC cells by fluorescence-activated cell sorting, we demonstrated that CR-1(High) cells were more tumorigenic than CR-1(Low) cells by an in vitro tumor sphere assay and by in vivo xenograft formation. The CR-1(High) population was enriched in mRNA expression for the pluripotent embryonic stem (ES) cell genes Oct4, Sox2, and Nanog. CR-1 expression in NTERA2/D1 cells was regulated by a Smad2/3-dependent autocrine loop, by the ES cell-related transcription factors Oct4/Nanog, and partially by the DNA methylation status of the promoter region. These results demonstrate that CR-1 expression is enriched in an undifferentiated, tumorigenic subpopulation and is regulated by key regulators of pluripotent stem cells.

Targeting the embryonic gene Cripto-1 in cancer and beyond

IMPORTANCE OF THE FIELD

Emerging evidence has clearly implicated an inappropriate activation of embryonic regulatory genes during cell transformation in adult tissues. An example of such a case is the embryonic gene Cripto-1. Cripto-1 is critical for embryonic development and is considered a marker of undifferentiated embryonic stem cells. Critpo-1 is expressed at low levels in adult tissues, but is re-expressed at a high frequency in a number of different types of human carcinomas, therefore, representing an attractive therapeutic target in cancer.

AREA COVERED IN THIS REVIEW

This review surveys different approaches that have been used to target Cripto-1 in cancer as reflected by the relevant patent literature as well as peer-reviewed publications. Potential involvement and targeting of Cripto-1 in neurodegenerative and degenerative muscle diseases are also discussed.

WHAT THE READER WILL GAIN

The reader will gain an overview of different mAbs, vaccines or oligonucleotides antisense targeting Cripto-1. A humanized anti-Cripto-1 antibody is currently being tested in a Phase I clinical trial in cancer patients.

TAKE HOME MESSAGE

Targeting Cripto-1 in human tumors has the potential to eliminate not only differentiated cancer cells but also destroy an undifferentiated subpopulation of cancer cells with stem-like characteristics that support tumor initiation and self-renewal.

Elimination of head and neck cancer initiating cells through targeting glucose regulated protein78 signaling

Background

Head and neck squamous cell carcinoma (HNSCC) is a highly lethal cancer that contains cellular and functional heterogeneity. Previously, we enriched a subpopulation of highly tumorigenic head and neck cancer initiating cells (HN-CICs) from HNSCC. However, the molecular mechanisms by which to govern the characteristics of HN-CICs remain unclear. GRP78, a stress-inducible endoplasmic reticulum chaperone, has been reported to play a crucial role in the maintenance of embryonic stem cells, but the role of GRP78 in CICs has not been elucidated.

Results

Initially, we recognized GRP78 as a putative candidate on mediating the stemness and tumorigenic properties of HN-CICs by differential systemic analyses. Subsequently, cells with GRP78 anchored at the plasma membrane (^memGRP78⁺) exerted cancer stemness properties of self-renewal, differentiation and radioresistance. Of note, xenotransplantation assay indicated merely 100 ^memGRP78⁺ HNSCCs resulted in tumor growth. Moreover, knockdown of GRP78 significantly reduced the self-renewal ability, side population cells and expression of stemness genes, but inversely promoted cell differentiation and apoptosis in HN-CICs. Targeting GRP78 also lessened tumorigenicity of HN-CICs both in vitro and in vivo. Clinically, co-expression of GRP78 and Nanog predicted the worse survival prognosis of HNSCC patients by immunohistochemical analyses. Finally, depletion of GRP78 in HN-CICs induced the expression of Bax, Caspase 3, and PTEN.

Conclusions

In summary, ^memGRP78 should be a novel surface marker for isolation of HN-CICs, and targeting GRP78 signaling might be a potential therapeutic strategy for HNSCC through eliminating HN-CICs.

Expression of the embryonic morphogen Nodal in cutaneous melanocytic lesions

Nodal, a potent embryonic morphogen in the transforming growth factor-beta family, is a proposed key regulator of melanoma tumorigenicity. However, there has been no systematic study of Nodal expression in melanocytic lesions. We investigated Nodal expression by immunohistochemistry in 269 melanocytic lesions, including compound nevi, dysplastic nevi, congenital nevi, Spitz nevi, melanoma in situ, malignant melanoma including the variant desmoplastic melanoma, and metastatic melanoma. We found that the Nodal expression was significantly increased in malignant lesions (including melanoma in situ, malignant melanoma, and metastatic melanoma) compared with compound nevi, Spitz nevi, and dysplastic nevi. Surprisingly, congenital nevi expressed a level of Nodal comparable with malignant lesions, whereas desmoplastic melanoma showed lower expression than nondesmoplastic malignant melanoma (P<0.05). Deep melanoma (Breslow depth >1 mm) displayed a higher percentage of Nodal-positive tumor cells than did superficial melanoma (Breslow depth < or =1 mm), although there was no statistical difference in the overall staining intensity (P=0.18). Melanomas in situ showed a lower level of Nodal expression than did deep melanomas and metastatic melanomas (P<0.05). The low expression of Nodal in normal and dysplastic nevi, and its increasing expression with the progression of malignant lesions, are suggestive of a role for Nodal in melanoma progression.

The embryonic morphogen, Nodal, is associated with channel-like structures in human malignant melanoma xenografts

Formation of channel-like structures, also termed vasculogenic mimicry (VM), describes the ability of aggressive melanoma cells to form PAS-positive anastomosing structures that correlate with tumor virulence. This phenomenon may indicate differentiation plasticity, a feature melanoma cells may share with stem cells in the developing embryo. Recent studies have indicated that VM and tumorigenicity of human malignant melanoma may depend on the signaling pathways of an embryonic morphogen, Nodal. However, given the secretory nature of Nodal protein and melanoma cell heterogeneity, it remains unclear whether the Nodal-expressing cells participate directly or indirectly in VM that is potentially related to tumorigenic growth. We have developed a humanized murine xenograft model in which developing human melanomas may be sequentially studied during early stages of tumorigenic growth within a physiological human dermal microenvironment. Nodal protein localized diffusely to melanoma cell membranes, with occasional foci of accentuated reactivity in patterns suggestive of channel formation. Similar findings were detected in a limited number of patient-derived tumors. In situ hybridization confirmed Nodal mRNA to be restricted to tumor cells within xenografts that formed arborizing networks in patterns consistent with VM. These data indicate that Nodal gene expression is associated with formation of VM-like structures in a physiologically relevant model of human melanoma tumorigenesis, and further support a key role for Nodal expression in the formation of channel-like structures. The humanized xenograft model should be useful in future studies to define the mechanistic pathways responsible for VM and melanoma progression.

Role of Cripto-1 in stem cell maintenance and malignant progression

Cripto-1 is critical for early embryonic development and, together with its ligand Nodal, has been found to be associated with the undifferentiated status of mouse and human embryonic stem cells. Like other embryonic genes, Cripto-1 performs important roles in the formation and progression of several types of human tumors, stimulating cell proliferation, migration, epithelial to mesenchymal transition, and tumor angiogenesis. Several studies have demonstrated that cell fate regulation during embryonic development and cell transformation during oncogenesis share common signaling pathways, suggesting that uncontrolled activation of embryonic signaling pathways might drive cell transformation and tumor progression in adult tissues. Here we review our current understanding of how Cripto-1 controls stem cell biology and how it integrates with other major embryonic signaling pathways. Because many cancers are thought to derive from a subpopulation of cancer stem-like cells, which may re-express embryonic genes, Cripto-1 signaling may drive tumor growth through the generation or expansion of tumor initiating cells bearing stem-like characteristics. Therefore, the Cripto-1/Nodal signaling may represent an attractive target for treatment in cancer, leading to the elimination of undifferentiated stem-like tumor initiating cells.

Cripto-1: an embryonic gene that promotes tumorigenesis

Several studies have shown that cell fate regulation during embryonic development and oncogenic transformation share common regulatory mechanisms and signaling pathways. Indeed, an embryonic gene member of the EGF–Cripto-1/FRL1/Cryptic family, Cripto-1, has been implicated in embryogenesis and in carcinogenesis. Cripto-1 together with the TGF-β ligand Nodal is a key regulator of embryonic development and is a marker of undifferentiated human and mouse embryonic stem cells. While Cripto-1 expression is very low in normal adult tissues, Cripto-1 is re-expressed at high levels in several different human tumors, modulating cancer cell proliferation, migration, epithelial-to-mesenchymal transition and stimulating tumor angiogenesis. Therefore, inhibition of Cripto-1 expression using blocking antibodies or antisense expression vectors might be a useful modality not only to target fully differentiated cancer cells but also to target a subpopulation of tumor cells with stem-like characteristics.

Immuno-expression of human melanoma stem cell markers in tissues at different stages of the disease

BACKGROUND

Human cutaneous melanoma can be one of the most aggressive tumors and is extremely resistant to all current therapeutic modalities. Immunohistochemistry (IHC) studies were undertaken to assess independent relative frequency on preferential overexpression and simultaneous expression of four stem cell markers; CD133+, ABCB5+, CD166, and Nestin, at different stages of the disease.

MATERIAL AND METHODS

Five-micron sections from paraffin blocks from primary melanoma, lymph node (LN) metastases, distant metastases, benign nevi from non-melanoma patients (NMP), and patients with past history of melanoma (MP) were IHC stained with monoclonal antibodies (mAb) to the four stem cell markers.

RESULTS

Overexpression of CD133+ was noted in tissues from LN and distant metastases compared to benign nevi (P < 0.0022, P < 0.013, respectively). Overexpression of ABCB5+ was observed comparing primary melanoma, LN, and distant metastases to benign nevi from NMP (P < 0.0063, P < 0.001, P < 0.00058, respectively). Significant overexpression of ABCB5+ was noted in tissues from LN and distant metastases compared with benign nevi from MP (P < 0.0003, P < 0.0068). None of the benign nevi of NMP demonstrated ABCB5+.

CONCLUSIONS

This study clearly shows the existence of a distinct hyperpolarized population of stem cells and may implicate genetic factors in human cutaneous melanoma. Simultaneous overexpression of CD133+ and Nestin could reflect on their origin or lineage association with a neural stem cell. These findings may open new perspectives for therapeutic implication of a melanoma stem cell in specific cancer therapy.

Recent advances on skin-resident stem/progenitor cell functions in skin regeneration, aging and cancers and novel anti-aging and cancer therapies

Recent advances in skin-resident adult stem/progenitor cell research have revealed that these immature and regenerative cells with a high longevity provide critical functions in maintaining skin homeostasis and repair after severe injuries along the lifespan of individuals. The establishment of the functional properties of distinct adult stem/progenitor cells found in skin epidermis and hair follicles and extrinsic signals from their niches, which are deregulated during their aging and malignant transformation, has significantly improved our understanding on the etiopathogenesis of diverse human skin disorders and cancers. Particularly, enhanced ultraviolet radiation exposure, inflammation and oxidative stress and telomere attrition during chronological aging may induce severe DNA damages and genomic instability in the skin-resident stem/progenitor cells and their progenies. These molecular events may result in the alterations in key signalling components controlling their self-renewal and/or regenerative capacities as well as the activation of tumour suppressor gene products that trigger their growth arrest and senescence or apoptotic death. The progressive decline in the regenerative functions and/or number of skin-resident adult stem/progenitor cells may cause diverse skin diseases with advancing age. Moreover, the photoaging, telomerase re-activation and occurrence of different oncogenic events in skin-resident adult stem/progenitor cells may also culminate in their malignant transformation into cancer stem/progenitor cells and skin cancer initiation and progression. Therefore, the anti-inflammatory and anti-oxidant treatments and stem cell-replacement and gene therapies as well as the molecular targeting of their malignant counterpart, skin cancer-initiating cells offer great promise to treat diverse skin disorders and cancers.

The cyclin-dependent kinase inhibitor roscovitine and the nucleoside analog sangivamycin induce apoptosis in caspase-3 deficient breast cancer cells independent of caspase mediated P-glycoprotein cleavage: implications for therapy of drug resistant breast cancers

Resistance to multiple chemotherapeutic agents is a common clinical problem which can arise during cancer treatment. Drug resistance often involves overexpression of the multidrug resistance MDR1 gene, encoding P-glycoprotein (P-gp), a 170-kDa glycoprotein belonging to the ATP-binding cassette superfamily of membrane transporters. We have recently demonstrated apoptosis-induced, caspase-3-dependent P-gp cleavage in human T-lymphoblastoid CEM-R VBL100 cells. However, P-gp contain many aspartate residues which could be targeted by caspases other than caspase-3. To test whether other caspases could cleave P-gp in vivo, we investigated the fate of P-gp during roscovitine- and sangivamycin- induced apoptosis in MCF7 human breast cancer cells, as they lack functional caspase-3. MCF7 cells were stably transfected with human cDNA encoding P-gp. P-gp was cleaved in vitro by purified recombinant caspase-3, -6 and -7. However, P-gp cleavage was not detected in vivo in MCF7 cells induced to undergoing apoptosis by either roscovitine or sangivamycin, despite activation of both caspase-6 and -7. Interestingly, P-gp overexpressing MCF7 cells were more sensitive to either roscovitine or sangivamycin than wild-type cells, suggesting a novel potential therapeutic strategy against P-gp overexpressing cells. Taken together, our results support the concept that caspase-3 is the only caspase responsible for in vivo cleavage of P-gp and also highlight small molecules which could be effective in treating P-gp overexpressing cancers.

Molecular phenotyping of human ovarian cancer stem cells unravels the mechanisms for repair and chemoresistance

A major burden in the treatment of ovarian cancer is the high percentage of recurrence and chemoresistance. Cancer stem cells (CSCs) provide a reservoir of cells that can self-renew, can maintain the tumor by generating differentiated cells [non-stem cells (non-CSCs)] which make up the bulk of the tumor and may be the primary source of recurrence. We describe the characterization of human ovarian cancer stem cells (OCSCs). These cells have a distinctive genetic profile that confers them with the capacity to recapitulate the original tumor, proliferate with chemotherapy, and promote recurrence. CSC identified in EOC cells isolated form ascites and solid tumors are characterized by: CD44+, MyD88+, constitutive NFkappaB activity and cytokine and chemokine production, high capacity for repair, chemoresistance to conventional chemotherapies, resistance to TNFalpha-mediated apoptosis, capacity to form spheroids in suspension, and the ability to recapitulate in vivo the original tumor. Chemotherapy eliminates the bulk of the tumor but it leaves a core of cancer cells with high capacity for repair and renewal. The molecular properties identified in these cells may explain some of the unique characteristics of CSCs that control self-renewal and drive metastasis. The identification and cloning of human OCSCs can aid in the development of better therapeutic approaches for ovarian cancer patients.