Hedgehog signalling in skin development and cancer

Developmental signaling pathways in cancer stem cells of solid tumors

BACKGROUND

The intricate regulation of several signaling pathways is essential for embryonic development and adult tissue homeostasis. Cancers commonly display aberrant activity within these pathways. A population of cells identified in several cancers, termed cancer stem cells (CSCs) show similar properties to normal stem cells and evidence suggests that altered developmental signaling pathways play an important role in maintaining CSCs and thereby the tumor itself.

SCOPE OF REVIEW

This review will focus on the roles of the Notch, Wnt and Hedgehog pathways in the brain, breast and colon cancers. We describe the roles these pathways play in normal tissue homeostasis through the regulation of stem cell fate in these three tissues, and the experimental evidence indicating that the role of these pathways in cancers of these is directly linked to CSCs.

MAJOR CONCLUSIONS

A large body of evidence is accumulating to indicate that the deregulation of Notch, Wnt and Hedgehog pathways play important roles in both normal and cancer stem cells. We are only beginning to understand how these pathways interact, how they are coordinated during normal development and adult tissue homeostasis, and how they are deregulated during cancer. However, it is becoming increasingly clear that if we are to target CSCs therapeutically, it will likely be necessary to develop combination therapies.

GENERAL SIGNIFICANCE

If CSCs are the driving force behind tumor maintenance and growth then understanding the molecular mechanisms regulating CSCs is essential. Such knowledge will contribute to better targeted therapies that could significantly enhance cancer treatments and patient survival. This article is part of a Special Issue entitled Biochemistry of Stem Cells.

Developing a sense of taste

Taste buds are found in a distributed array on the tongue surface, and are innervated by cranial nerves that convey taste information to the brain. For nearly a century, taste buds were thought to be induced by nerves late in embryonic development. However, this view has shifted dramatically. A host of studies now indicate that taste bud development is initiated and proceeds via processes that are nerve-independent, occur long before birth, and governed by cellular and molecular mechanisms intrinsic to the developing tongue. Here we review the state of our understanding of the molecular and cellular regulation of taste bud development, incorporating important new data obtained through the use of two powerful genetic systems, mouse and zebrafish.

Early-occurring proliferation defects in peripheral tissues of the Ts65Dn mouse model of Down syndrome are associated with patched1 over expression

Down syndrome (DS) is a genetic pathology due to the triplication of human chromosome 21. In addition to mental retardation, individuals with DS exhibit a large range of variable traits, including co-occurring congenital malformations. It is now clear that neurogenesis impairment underlies the typically reduced brain size and, hence, mental retardation in individuals with DS. The small body size and the constellation of congenital malformations in children with DS suggest that proliferation defects may involve peripheral tissues, in addition to the brain. The goal of the current study was to establish whether a generalized impairment of cell proliferation is a key feature of the trisomic condition. We used the Ts65Dn mouse, a widely used DS model, and examined proliferation in tissues with different embryological origin by 5-bromo-2-deoxyuridine immunohistochemistry. We found that 2-day-old (P2) Ts65Dn mice had notably fewer proliferating cells in the heart and liver, and in all proliferating niches of the skin and intestine. A reduced proliferation rate was still present in the intestine at P15. In all tissues, Ts65Dn mice had a similar number of apoptotic cells as euploid mice, indicating no unbalance in cell death. In the skin, liver and intestine of trisomic mice, we found a higher expression of patched1 (Ptch1), a receptor that represses the mitogenic sonic hedgehog (Shh) pathway. This suggests that Ptch1-dependent inhibition of Shh signaling may underlie proliferation impairment in trisomic peripheral tissues. In agreement with the widespread reduction in proliferation, neonate trisomic mice had a reduced body weight and this defect was still present at 30 days of age. Our findings show that, in all examined peripheral tissues, Ts65Dn mice exhibit a notable reduction in proliferation rate, suggesting that proliferation impairment may be a generalized defect of trisomic precursor cells.

Cutaneous wound healing: recruiting developmental pathways for regeneration

Following a skin injury, the damaged tissue is repaired through the coordinated biological actions that constitute the cutaneous healing response. In mammals, repaired skin is not identical to intact uninjured skin, however, and this disparity may be caused by differences in the mechanisms that regulate postnatal cutaneous wound repair compared to embryonic skin development. Improving our understanding of the molecular pathways that are involved in these processes is essential to generate new therapies for wound healing complications. Here we focus on the roles of several key developmental signaling pathways (Wnt/β-catenin, TGF-β, Hedgehog, Notch) in mammalian cutaneous wound repair, and compare this to their function in skin development. We discuss the varying responses to cutaneous injury across the taxa, ranging from complete regeneration to scar tissue formation. Finally, we outline how research into the role of developmental pathways during skin repair has contributed to current wound therapies, and holds potential for the development of more effective treatments.

Hairy tale of signaling in hair follicle development and cycling

Hair follicles (HFs) is an appendage from the vertebrate skin epithelium, and is critical for environmental sensing, animal appearance, and body heat maintenance. HFs arise from the embryonic ectoderm and regenerate cyclically during adult life. Distinct morphological and functional stages from development through homeostasis have been extensively studied for the past decades to dissect the critical molecular mechanisms. Accumulating work suggests that different signaling cascades, such as Wnt, Bmp, Shh, and Notch, together with specific combinations of transcription factors are at work at different stages. Here we provide a comprehensive review of mouse genetics studies, which include lineage tracing along with knockout and over-expression of core genes from key signaling pathways, to paint an updated view of the molecular regulatory network that govern each stage of hair follicle development and adult cycling.

Ligand-independent activation of the Hedgehog pathway displays non-cell autonomous proliferation during eye development in Drosophila

Deregulation of the Hedgehog (Hh) signaling pathway is associated with the development of human cancer including medullobastoma and basal cell carcinoma. Loss of Patched or activation of Smoothened in mouse models increases the occurrence of tumors. Likewise, in a Drosophila eye model, deregulated Hedgehog signaling causes overgrowth of eye and head tissues. Surprisingly, we show that cells with deregulated Hh signaling do not or only little contribute to the tissue overgrowth. Instead, they become more sensitive to apoptosis and may eventually be eliminated. Nevertheless, these mutant cells increase proliferation in the adjacent wild-type tissue, i.e., in a non-cell autonomous manner. This non-cell autonomous effect is position-dependent and restricted to mutant cells in the anterior portion of the eye. We also observe precocious non-cell autonomous differentiation in genetic mosaics with deregulated Hh signaling. Together, these non-cell autonomous growth and differentiation phenotypes in the Drosophila eye model reveal another strategy by which oncogenes may generate a supportive micro-environment for tumor growth.

Cells of origin and tumor-initiating cells for nonmelanoma skin cancers

The epidermis of the skin is a multilayered stratified epithelium whose primary function is to provide a barrier against our external environment. As a result, cells in the epidermis are subject to constant assault from environmental pathogens, many of which can cause deleterious mutations. However, most of these mutations do not lead to skin cancer. One explanation is that most genetic hits are sustained by mature or transit cells with limited proliferative capacity and only stem cells that acquire genetic alterations have the potential to propagate a frank tumor. In this mini-review we will discuss recent studies that provide some of the first genetic evidence to support a stem cell origin for a number of skin cancer types.

Keratinocyte stem cells and the targets for nonmelanoma skin cancer

The mammalian skin is a complex dynamic organ composed of thin multilayered epidermis and a thick underlying connective tissue layer dermis. The epidermis undergoes continuous renewal throughout life. The stems cells uniquely express particular surface markers utilized for their identification, isolation and localization in specific niches in epidermis as well as hair follicles (HFs). The two stage skin carcinogenesis model involves stepwise accumulation of genetic alterations and ultimately leading to malignancy. Whereas early research on skin carcinogenesis focused on the molecular nature of carcinogens and tumor promoters, more recent studies have focused on the identification of the target cells and tumor promoting cells for both chemical and physical carcinogens and promoters. Recent studies support the hypothesis that keratinocyte stem cells are the targets in skin carcinogenesis. In this review, we discuss briefly the localization of stem cells in the epidermis and HFs, and review the possibility that skin papillomas and carcinomas are derived from stem cells, as well as from other cells in the cutaneous epithelium whose stem cell properties are not well known.

Tumor Suppressor Function of CYLD in Nonmelanoma Skin Cancer

Ubiquitin and ubiquitin-related proteins posttranslationally modify substrates, and thereby alter the functions of their targets. The ubiquitination process is involved in various physiological responses, and dysregulation of components of the ubiquitin system has been linked to many diseases including skin cancer. The ubiquitin pathways activated among skin cancers are highly diverse and may reflect the various characteristics of the cancer type. Basal cell carcinoma and squamous cell carcinoma, the most common types of human skin cancer, are instances where the involvement of the deubiquitination enzyme CYLD has been recently highlighted. In basal cell carcinoma, the tumor suppressor protein CYLD is repressed at the transcriptional levels through hedgehog signaling pathway. Downregulation of CYLD in basal cell carcinoma was also shown to interfere with TrkC expression and signaling, thereby promoting cancer progression. By contrast, the level of CYLD is unchanged in squamous cell carcinoma, instead, catalytic inactivation of CYLD in the skin has been linked to the development of squamous cell carcinoma. This paper will focus on the current knowledge that links CYLD to nonmelanoma skin cancers and will explore recent insights regarding CYLD regulation of NF-κB and hedgehog signaling during the development and progression of these types of human tumors.

Hedgehog signaling in skin cancers

An increasing progress on the role of Hedgehog (Hh) signaling for carcinogenesis has been achieved since the link of Hh pathway to human cancer was firstly established. In particular, the critical role of Hh signaling in the development of Basal cell carcinoma (BCC) has been convincingly demonstrated by genetic mutation analyses, mouse models of BCCs, and successful clinical trials of BCCs using Hh signaling inhibitors. In addition, the Hh pathway activity is also reported to be involved in the pathogenesis of Squamous Cell Carcinoma (SCC), melanoma and Merkel Cell Carcinoma. These findings have significant new paradigm on Hh signaling transduction, its mechanisms in skin cancer and even therapeutic approaches for BCC. In this review, we will summarize the major advances in the understanding of Hh signaling transduction, the roles of Hh signaling in skin cancer development, and the current implications of "mechanism-based" therapeutic strategies.

Cutaneous malignancies: melanoma and nonmelanoma types

This article reviews melanoma and nonmelanoma cutaneous malignancies.

Activation of sonic hedgehog signaling in oral squamous cell carcinomas: a preliminary study

Sonic hedgehog signaling is important for human development, and aberrant regulation of this pathway can result in the development of tumors. The aim of this study was to examine the expression of sonic hedgehog signaling molecules in oral squamous cell carcinoma. By quantitative real-time polymerase chain reaction, the expression of SHH, SMO, PTCH-1, and GLI-1 was analyzed in 30 oral squamous cell carcinoma cases and 8 samples of nonneoplastic oral mucosa and associated to clinical pathologic features. The expression of β-catenin, cyclin D1, Wnt-1, and Egfr was evaluated by immunohistochemistry in 26 available cases of oral squamous cell carcinoma. Normal oral mucosa from healthy individuals was negative for all genes that were evaluated. SHH, PTCH-1, SMO, and GLI-1 were not expressed in nonneoplastic oral mucosa, and low levels of GLI-1 were observed in nonneoplastic oral mucosa that was adjacent to the tumor. All oral squamous cell carcinoma cases expressed high levels of PTCH-1, SMO, and GLI-1 and were devoid of SHH. The expression of SMO was associated with clinical stage (P = .022) and a borderline association in cervical lymph node metastasis (P = .053). PTCH-1 expression showed a strong correlation with SMO (rs = 0.64; P < .001) and GL-1 (rs = 0.70; P < .001); SMO and GLI-1 also correlated with each other (rs, 0.55; P < .001). All proteins evaluated were expressed as cyclin D1 (92% of samples), β-catenin (73%), Egfr (46%), or Wnt-1 (32%). Our data demonstrate that sonic hedgehog signaling is activated in oral squamous cell carcinoma and suggest that this pathway mediates its tumorigenesis.

Prospects for skin cancer treatment and prevention: the potential contribution of an engineered virus

Nonmelanoma skin cancers are among the most common human malignancies. Although typically not lethal, they are responsible for tissue deformity and substantial morbidity, particularly in high-risk populations. Solar UVB radiation-a major etiologic factor for this kind of malignancy-produces DNA lesions such as cyclobutane pyrimidine dimers and 6-4 photoproducts in skin. These lesions are removed through nucleotide excision repair because humans lack a DNA glycosylase required to initiate base excision repair of pyrimidine-pyrimidine photoproducts but produce all the other proteins required for this process. In this issue, Johnson et al. show that a DNA glycosylase derived from Chlorella virus and engineered to enhance tissue penetration and nuclear localization can remove UVB-induced DNA lesions in a human skin equivalent model and that the protein can be incorporated into a topical formulation for the prevention and treatment of UVB-induced DNA damage. These results suggest that such an enzyme may be incorporated into regimens for the chemoprevention of skin cancers.

Basal cell carcinoma: cell of origin, cancer stem cell hypothesis and stem cell markers

Cancer stem cells have recently been described in several high-grade neoplasms. It is still unclear if they also occur in cutaneous malignancies. Cancer stem cells are not identical with somatic stem cells. The presence of tumour stem cells in a neoplasm does not in itself equal that the tumour derives from a somatic stem cell. A cell originally lacking stem cell characteristics could also acquire those features during the course of carcinogenesis and then becomes the clonal founder cell of a tumour. Basal cell carcinoma (BCC) is the most common cutaneous malignancy. A plethora of various stem cell markers has been applied to study its cellular origin. Intriguingly, the anatomical origin of BCC is still uncertain. This review will discuss the various stem cell markers used in BCC and the cellular origin of this tumour, and touches briefly on the possibility of cancer stem cells in BCC. If BCC or other skin cancers harbour tumour stem cells, these cells could be specifically targeted, making use of specific cell surface molecules such as receptor proteins. Novel drugs directed against those receptor proteins could replace currently available shotgun approaches including imiquimod.

Role of sonic hedgehog signaling in migration of cell lines established from CD133-positive malignant glioma cells

The sonic hedgehog (SHH) signaling pathway is essential for normal development and embryogenic morphogenesis. In malignant neoplasms its inappropriate activation correlates with tumorigenesis, proliferation, and migration. However, the role of SHH in infiltrative growth of glioblastoma remains to be elucidated. CD133 is a marker of tumor stem cells in glioblastoma, which are thought to play important roles in tumorigenesis, drug resistance, and tumor recurrence. We investigated the role of the SHH signaling pathway in migration of glioblastoma cell lines derived from CD133-positive cells. Two cell lines, GBM1 and GBM2, were established from CD133-positive cells sorted on an automagnetic cell separator from dispersed human glioblastoma cells. Both cell lines exhibited sphere-like growth in serum-free medium containing growth factor. Expression of patched (PTCH)-, a receptor of SHH, of smoothened (SMO)-, a 7 transmembrane receptor, and of GLI1- and GLI2, PTCH cascade signal proteins, was evaluated by reverse-transcription polymerase chain reaction (RT-PCR). The effects of recombinant SHH in the medium, and of knockdown of SMO-, GLI1- or GLI2 messenger RNA (mRNA) on the migratory ability of neoplastic cells were evaluated by scratch assays. RT-PCR revealed the presence of PTCH-, SMO-, GLI1-, and GLI2 mRNA in these cells. Their migratory ability was significantly enhanced (P < 0.05) by addition of recombinant SHH to the medium. Knockdown of SMO-, GLI1- or GLI2 mRNA resulted in significant decrease in the mobility of the neoplastic cells. Our study suggests that the SHH pathway plays an important role in the migratory ability of cells derived from CD133-positive human glioblastoma cells.

Hedgehog antagonist GDC-0449 is effective in the treatment of advanced basal cell carcinoma

OBJECTIVES/HYPOTHESIS

To demonstrate the efficacy of the hedgehog pathway inhibitor GDC-0449 in the treatment of advanced basal cell carcinoma.

DESIGN STUDY

Case series.

METHODS

Three patients treated in a referral center for locally advanced basal cell carcinoma, one with metastases, were referred for treatment in a GDC-0449 phase I clinical trial. The treatment was once per day continuous therapy with oral GDC-0449.

RESULTS

Two patients showed complete clinical and radiologic resolution of disease, whereas one patient had significant reduction in tumor burden with radiologic evidence of slowly progressive local disease. Side effects were taste changes, mild to moderate hair loss, and muscle cramps in one patient.

CONCLUSIONS

GDC-0449 showed significant inhibitory activity in the treatment of advanced basal cell carcinoma.

Genetics of basal cell carcinoma

Basal cell carcinoma is the most common human malignancy in populations of European origin, and Australia has the highest incidence of basal cell carcinoma in the world. Great advances in the understanding of the genetics of this cancer have occurred in recent years. Mutations of the patched 1 gene (PTCH1) lead to basal cell carcinoma predisposition in Gorlin syndrome. PTCH1 is part of the hedgehog signalling pathway, and derangements within this pathway are now known to be important in the carcinogenesis of many different cancers including sporadic basal cell carcinoma. The molecular biology of the hedgehog pathway is discussed, and mouse models of basal cell carcinoma based on this pathway are explored. New developments in non-surgical treatment of basal cell carcinoma are based on this knowledge. Other genes of importance to basal cell carcinoma development include the tumour suppressor gene P53 and the melanocortin-1 receptor gene. In addition, we discuss molecules of possible importance such as the glutathione-S-transferases, DNA repair genes, cyclin-dependent kinase inhibitor 2A, Brahma and connexins. Evidence of familial aggregation of this cancer is explored and supports the possibility of genetic predisposition to this common malignancy.

Deciphering squamous cell carcinoma using multidimensional genomic approaches

Squamous cell carcinomas (SqCCs) arise in a wide range of tissues including skin, lung, and oral mucosa. Although all SqCCs are epithelial in origin and share common nomenclature, these cancers differ greatly with respect to incidence, prognosis, and treatment. Current knowledge of genetic similarities and differences between SqCCs is insufficient to describe the biology of these cancers, which arise from diverse tissue origins. In this paper we provide a general overview of whole genome approaches for gene and pathway discovery and highlight the advancement of integrative genomics as a state-of-the-art technology in the study of SqCC genetics.

Rab GTPases implicated in inherited and acquired disorders

The endocytotic machinery imports, transports and exports receptors and associated molecules between the plasma membrane and various cytoplasmic chambers resulting in selective recycling, degradation, or secretion of molecules and signaling complexes. Trafficking of receptors, growth factors, nutrients, cytokines, integrins as well as pathogens dictates the kinetics and magnitude of signal transduction cascades. Understandably, alterations in the 'fate' of such cargo complexes have profound physiologic and pathophysiologic implications. Rab GTPases regulate endocytosis by decorating intracellular vesicles and targeting these vesicles along with their cargoes to appropriate subcellular compartments. In the last decade, the number of genetic diseases driven by germline mutations in Rab GTPases or their interacting proteins, has increased and there is growing evidence of aberrant Rab GTPase function in acquired pathophysiologies such as immune deficiency, infection, obesity, diabetes and cancer.

Hair and skin sterols in normal mice and those with deficient dehydrosterol reductase (DHCR7), the enzyme associated with Smith-Lemli-Opitz syndrome

Our recent studies have focused on cholesterol synthesis in mouse models for 7-dehydrosterolreductase (DHCR7) deficiency, also known as Smith-Lemli-Opitz syndrome. Investigations of such mutants have relied on tissue and blood levels of the cholesterol precursor 7-dehydrocholesterol (7DHC) and its 8-dehydro isomer. In this investigation by gas chromatography/mass spectrometry (GC/MS) we have identified and quantified cholesterol and its precursors (7DHC, desmosterol, lathosterol, lanosterol and cholest-7,24-dien-3β-ol) in mouse hair. The components were characterized and their concentrations were compared to those found in mouse skin and serum. Hair appeared unique in that desmosterol was a major sterol component, almost matching in concentration cholesterol itself. In DHCR7 deficient mice, dehydrodesmosterol (DHD) was the dominant hair Δ(7) sterol. Mutant mouse hair had much higher concentrations of 7-dehydrosterols relative to cholesterol than did serum or tissue at all ages studied. The 7DHC/C ratio in hair was typically about sevenfold the value in serum or skin and the DHD/D ratio was 100× that of the serum 7DHC/C ratio. Mutant mice compensate for their DHCR7 deficiency with maturity, and the tissue and blood 7DHC/C become close to normal. That hair retains high relative concentrations of the dehydro precursors suggests that the apparent up-regulation of Dhcr7 seen in liver is slower to develop at the site of hair cholesterol synthesis.

The use of animal models for cancer chemoprevention drug development

Animal models currently are used to assess the efficacy of potential chemopreventive agents, including synthetic chemicals, chemical agents obtained from natural products, and natural product mixtures. The observations made in these models as well as other data are then used to prioritize agents to determine which are qualified to progress to clinical chemoprevention trials. Organ-specific animal models are employed to determine which agents or classes of agents are likely to be the most effective at nontoxic doses to prevent organ-specific forms of cancer. These results are then used to target specific organs in high-risk populations in clinical trials. The animal models used are either carcinogen-induced with carcinogens specific for particular organ sites or they are transgenic/mutant animals with insertions, deletions, or mutations at targeted gene sites known to enhance cancers in a specific organ. Animal tumor models with characteristics favorable to chemoprevention studies are available for cancers of the lung, colon, skin, bladder, mammary, prostate, head and neck, esophagus, ovary, and pancreas. In addition to single-agent dose-response testing, such models are frequently used for testing combinations of agents, testing different routes of administration, evaluating surrogate endpoint biomarkers, and generating initial pharmacokinetics and toxicology data. For some of the more standard animal models there is significant correlation with human chemopreventive trial results. There are a growing number of positive human chemoprevention trials that have used agents or combinations that were positive in animal testing. There have been fewer negative human clinical trials, but their results again correlate with negative animal results. Clearly the validation of animal models to predict the efficacy of agents in human clinical trials will await further human data on positive and negative outcomes with chemopreventive agents. Whether validated or not, animal efficacy data remain central to the clinical trial decision-making process.

The molecular genetics underlying basal cell carcinoma pathogenesis and links to targeted therapeutics

Mutations in the sonic hedgehog signaling pathway play a key role in the development of basal cell carcinomas. Specifically, mutations in the PTCH1 (also known as PTCH or PTC1) and SMO genes cause tumor formation through constitutive activation of the pathway. Misregulation of the pathway has also been implicated in the nevoid basal cell carcinoma syndrome and other tumors. Understanding the function of the sonic hedgehog pathway has led to novel strategies for treatment. In this review we highlight the role of the pathway in the pathogenesis of basal cell carcinoma and review potential targeted therapies.

Expression of hedgehog signaling molecules in lung cancer

Abnormal hyperactivation of the hedgehog (Hh) pathway has been reported in many types of human cancers, including lung cancer. However, most reports are based on studies of fewer than three Hh target genes and the data vary between different studies. In the present report, we have determined the expression levels of several important components of the Hh pathway in lung cancers by using RT-PCR, in situ hybridization and immunohistochemistry. These molecules include Smoothened (SMO), Rab23, the downstream target platelet-derived growth factor receptor alpha (PDGFRα), hedgehog interacting protein (HIP) and hepatocyte nuclear factor 3-beta (HNF3β). Our data show that some components of the hedgehog pathway, such as SMO, Rab23 and PDGFRα are expressed in many lung cancer specimens, although other hedgehog target genes are infrequently detected in lung cancer. Loss of HIP expression was found in several cases of lung cancers. Our study indicates that there might be some additional mechanisms involved in the hyperactivation of the Hh pathway. Thus, we suggest that lung cancer with heterogeneous tumor type harboring Hh signaling activation may have some novel and different regulatory mechanisms.

Expression of hedgehog signaling molecules in Merkel cell carcinoma

BACKGROUND

The Hedgehog signaling pathway is important for human development and carcinogenesis in various malignancies.

METHODS

One tissue microarray with triplets of 28 samples from 25 patients with Merkel cell carcinoma (MCC) was constructed. Six samples of normal skin and 5 samples of normal oral mucosa served as controls. All samples were analyzed immunohistochemically with antibodies directed against Sonic hedgehog, Indian hedgehog, Patched, Smoothened, Gli-1, Gli-2, and Gli-3.

RESULTS

All investigated proteins were frequently and intensely overexpressed in MCCs (Sonic hedgehog, 93%; Indian hedgehog, 84%; Patched, 86%; Smoothened, 79%; Gli-1, 79%; Gli-2, 79%; Gli-3, 86%) compared with control samples. High levels of Patched and Indian hedgehog were significantly associated with an increase in patients overall (p = .015) and recurrence-free survival (p = .011), respectively.

CONCLUSIONS

Our results indicate that the Hedgehog signaling pathway is strongly activated in MCC and thus may play a role in carcinogenesis.

Role of oxidative stress in stem, cancer, and cancer stem cells

The term ‘‘oxidative stress” refers to a cell’s state characterized by excessive production of reactive oxygen species (ROS) and oxidative stress is one of the most important regulatory mechanisms for stem, cancer, and cancer stem cells. The concept of cancer stem cells arose from observations of similarities between the self-renewal mechanism of stem cells and that of cancer stem cells, but compared to normal stem cells, they are believed to have no control over the cell number. ROS have been implicated in diverse processes in various cancers, and generally the increase of ROS in cancer cells is known to play an important role in the initiation and progression of cancer. Additionally, ROS have been considered as the most significant mutagens in stem cells; when elevated, blocking self-renewal and at the same time, serving as a signal stimulating stem cell differentiation. Several signaling pathways enhanced by oxidative stress are suggested to have important roles in tumorigenesis of cancer or cancer stem cells and the self-renewal ability of stem or cancer stem cells. It is now well established that mitochondria play a prominent role in apoptosis and increasing evidence supports that apoptosis and autophagy are physiological phenomena closely linked with oxidative stress. This review elucidates the effect and the mechanism of the oxidative stress on the regulation of stem, cancer, and cancer stem cells and focuses on the cell signaling cascades stimulated by oxidative stress and their mechanism in cancer stem cell formation, as very little is known about the redox status in cancer stem cells. Moreover, we explain the link between ROS and both of apoptosis and autophagy and the impact on cancer development and treatment. Better understanding of this intricate link may shed light on mechanisms that lead to better modes of cancer treatment.

Emerging anticancer therapeutic targets and the cardiovascular system: is there cause for concern?

The race for a cure to cancer continues, fueled by unprecedented discoveries of fundamental biology underlying carcinogenesis and tumorigenesis. The expansion of the target list and tools to approach them is moving the oncology community extraordinarily rapidly to clinical trials, bringing new hope for cancer patients. This effort is also propelling biological discoveries in cardiovascular research, because many of the targets being explored in cancer play fundamental roles in the heart and vasculature. The combined efforts of cardiovascular and cancer biologists, along with clinical investigators in these fields, will be needed to understand how to safely exploit these efforts. Here, we discuss a few of the many research foci in oncology where we believe such collaboration will be particularly important.

Tumor stroma-derived Wnt5a induces differentiation of basal cell carcinoma of Ptch-mutant mice via CaMKII

Basal cell carcinoma (BCC) is the most common skin tumor in humans. Although BCCs rarely metastasize, they can cause significant morbidity due to local aggressiveness. Approximately 20% of BCCs show signs of spontaneous regression. The understanding of molecular events mediating spontaneous regression has the potential to reduce morbidity of BCC and, potentially, other tumors, if translated into tumor therapies. We show that BCCs induced in conditional Ptch(flox/flox)ERT2(+/-) knockout mice regress with time and show a more differentiated phenotype. Differentiation is accompanied by Wnt5a expression in the tumor stroma, which is first detectable at the fully developed tumor stage. Coculture experiments revealed that Wnt5a is upregulated in tumor-adjacent macrophages by soluble signals derived from BCC cells. In turn, Wnt5a induces the expression of the differentiation marker K10 in tumor cells, which is mediated by Wnt/Ca(2+) signaling in a CaMKII-dependent manner. These data support a role of stromal Wnt5a in BCC differentiation and regression, which may have important implications for development of new treatment strategies for this tumor. Taken together, our results establish BCC as an easily accessible model of tumor regression. The regression of BCC despite sustained Hedgehog signaling activity seems to be mediated by tumor-stromal interactions via Wnt5a signaling.

CXCR3/ligands are significantly involved in the tumorigenesis of basal cell carcinomas

Basal cell carcinoma (BCC) is the most common skin malignancy encountered worldwide. We hypothesized that CXC chemokines, small cytokines involved in inducing directed leukocyte chemotaxis, could play a key role in the modulation of BCC growth. In this study, quantitative RT-PCR revealed that the chemokines CXCL9, 10, 11, and their receptor CXCR3 were significantly upregulated by an average 22.6-fold, 9.2-fold, 26.6-fold, and 4.9-fold, respectively in BCC tissue samples as compared with nonlesional skin epithelium. Immunohistochemistry analysis revealed that CXCR3, CXCL10, and CXCL11, but not CXCL9, colocalized with cytokeratin 17 (K17) in BCC keratinocytes. In addition, CXCR3 and its ligands were expressed in cells of the surrounding BCC stroma. The chemokines and K17 were also expressed in cultured human immortalized HaCaT keratinocytes. Exposure of HaCaT cells or primary BCC-derived cells to CXCL11 peptides in vitro significantly increased cell proliferation. In primary BCC-derived cell cultures, addition of CXCL11 progressively selected for K17+/CXCR3+ co-expressing cells over time. The expression of CXCR3 and its ligands in human BCC keratinocytes, the enhancement of keratinocyte cell proliferation by CXCL11, and the homogeneity of K17+ BCC cells in human BCC-isolated cell population supported by CXCR3/CXCL11 signaling all suggest that CXCR3 and its ligands may be important autocrine and/or paracrine signaling mediators in the tumorigenesis of BCC.

Targeting ornithine decarboxylase for the prevention of nonmelanoma skin cancer in humans

Bailey et al. report in this issue of the journal (beginning on page 35) one of the first successful trials of basal cell carcinoma (BCC) prevention. Oral alpha-difluoromethyl-dl-ornithine (DFMO) reduced new BCCs in patients with a prior history of nonmelanoma skin cancer. DFMO is an inhibitor of ornithine decarboxylase, a key enzyme in the polyamine biosynthetic pathway. This perspective on Bailey et al. discusses our knowledge of the contribution of polyamines to BCC pathogenesis, how this knowledge advanced the development of a new method to prevent BCCs, and prospects for future studies of DFMO in BCC prevention.

Hedgehog signaling maintains hair follicle stem cell phenotype in young and aged human skin

Skin hair follicles (HF) contain bulge stem cells (SC) that regenerate HFs during hair cycles, and repair skin epithelia following injury. As natural aging is associated with decreased skin repair capacity in humans, we have investigated the impact of age on human scalp HF bulge cell number and function. Here, we isolated human bulge cells, characterized as CD200+/KRT15+/KRT19+ cells of the HF, by dissection-combined CD200 selection in young and aged human skin. Targeted transcriptional profiling indicates that KRT15, KRT19, Dkk3, Dkk4, Tcf3, S100A4, Gas1, EGFR and CTGF/CCN2 are also preferentially expressed by human bulge cells, compared to differentiated HF keratinocytes (KC). Our results demonstrate that aging does not alter expression or localization of these HF SC markers. In addition, we could not detect significant differences in HF density or bulge cell number between young and aged human scalp skin. Interestingly, hedgehog (Hh) signaling is activated in human bulge cells in vivo, and down-regulated in differentiated HF KCs, both in young and aged skin. In addition, activation of Hh signaling by lentivirus-mediated overexpression of transcription factor Gli1 induces transcription of HF SC markers KRT15, KRT19, and Gas1, in cultured KCs. Together with previously reported knock-out mouse results, these data suggest a role for Hh signaling in maintaining bulge cell phenotype in young and aged human skin.

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.

Bone morphogenetic protein antagonist noggin promotes skin tumorigenesis via stimulation of the Wnt and Shh signaling pathways

Bone morphogenetic proteins (BMPs) play pivotal roles in the regulation of skin development. To study the role of BMPs in skin tumorigenesis, BMP antagonist noggin was used to generate keratin 14-targeted transgenic mice. In contrast to wild-type mice, transgenic mice developed spontaneous hair follicle-derived tumors, which resemble human trichofolliculoma. Global gene expression profiles revealed that in contrast to anagen hair follicles of wild-type mice, tumors of transgenic mice showed stage-dependent increases in the expression of genes encoding the selected components of Wnt and Shh pathways. Specifically, expression of the Wnt ligands increased at the initiation stage of tumor formation, whereas expression of the Wnt antagonist and tumor suppressor Wnt inhibitory factor-1 decreased, as compared with fully developed tumors. In contrast, expression of the components of Shh pathway increased in fully developed tumors, as compared with the tumor placodes. Consistent with the expression data, pharmacological treatment of transgenic mice with Wnt and Shh antagonists resulted in the stage-dependent inhibition of tumor initiation, and progression, respectively. Furthermore, BMP signaling stimulated Wnt inhibitory factor-1 expression and promoter activity in cultured tumor cells and HaCaT keratinocytes, as well as inhibited Shh expression, as compared with the corresponding controls. Thus, tumor suppressor activity of the BMPs in skin epithelium depends on the local concentrations of noggin and is mediated at least in part via stage-dependent antagonizing of Wnt and Shh signaling pathways.

Late reactivation of sonic hedgehog by Helicobacter pylori results in population of gastric epithelial cells that are resistant to apoptosis: implication for gastric carcinogenesis

As much as that a disturbance of tissue homeostasis through dysregulated apoptosis is generally associated with carcinogenesis, gastric carcinogenesis after Helicobacter pylori infection could be the accumulated consequence of imbalances between apoptosis and proliferation. Since sonic hedgehog (Shh) has been reported to play versatile roles in various tumorigenesis, we hypothesized that late reactivation of sonic hedgehog by H. pylori infection results in population of gastric epithelial cells that are resistant to apoptosis. The Resistant Clones against H. pylori-induced Apoptosis (RCHA) were established and maintained up to 19th cell passages, during which the serial changes of Shh expression were measured. Apoptosis was measured in N-Shh over-expressed stable cell lines and compared with parent cell line after either infected with H. pylori or treated with cyclopamine. For clinical relevance, the expressions of Shh were compared in tissues from gastric adenoma or adenocarcinoma according to H. pylori infection. Longer passages of RCHA after H. pylori infection, the higher expressions of Shh, suggesting RCHA was associated with the reactivation of Shh. Significant decrement in subG1 phase of cell cycle and attenuated executions of apoptosis after H. pylori infection in cells of Shh overexpression, whereas either Shh siRNA or cyclopamine increased the H. pylori-induced cytotoxicity and significantly abrogated anti-apoptotic actions imposed by Shh. Significantly higher expressions of Shh were seen in H. pylori-associated gastric cancers than H. pylori-not associated gastric cancer. Late reactivation of sonic hedgehog by H. pylori infection results in population of gastric epithelial cells that are resistant to apoptosis and imposes proliferative changes under the background of atrophic gastritis, providing the carcinogenic basis.

Review of the hair follicle origin hypothesis for basal cell carcinoma

BACKGROUND

Basal cell carcinoma (BCC) is the most common type of skin cancer treated by the dermatologic surgeon. The discovery that patients with the nevoid BCC syndrome had mutations in the human homologue of the Drosophila patched gene led to a rapid increase in our understanding of the pathogenesis of BCC. It is theorized that altered regulation at multiple steps in the patched signal transduction pathway may contribute to the development of BCC. This pathway also plays an essential role in embryonic hair follicle development and during the hair cycle. Taken together, a considerable body of evidence suggests that at least some BCC may be derived from deregulated patched signaling in hair follicle stem cells.

OBJECTIVE

To review evidence of a follicular derivation of BCC and to highlight emerging therapeutic strategies to block deregulated patched signaling in BCC.

CONCLUSION

Deregulation of the patched signal transduction pathway is present in the vast majority of human BCCs. Pharmacologic inhibitors of this pathway may offer a therapeutic strategy to block tumor growth. The author has indicated no significant interest with commercial supporters.

Emerging roles for Rab family GTPases in human cancer

Member of the Ras-associated binding (Rab) family of small GTPases function as molecular switches regulating vesicular transport in eukaryotes cells. Their pathophysiological roles in human malignancies are less well-known compared to members of Ras and Rho families. Several members of the Rab family have, however, been shown to be aberrantly expressed in various cancer tissues. Recent findings have also revealed , in particular, Rab25 as a determinant of tumor progression and aggressiveness of epithelial cancers. Rab25 associates with alpha5beta1 integrin, and enhances tumor cell invasion by directing the localization of integrin-containing vesicles to the leading edge of matrix invading pseudopodia. We summarized here recent integrin on Rab25 and other Rabs implicated to be involved in a variety of human cancers, and discussed plausible mechanisms of how dysregulation of Rab expression could be tumorigenic or tumor suppressive.

Transgenic zebrafish line with over-expression of Hedgehog on the skin: a useful tool to screen Hedgehog-inhibiting compounds

We generated a transgenic line Tg(k18:shh:RFP) with overexpression of Sonic hedgehog in the skin epidermis. By 5 day-post-fertilization (dpf), many epidermal lesions were clearly observed, including a swollen yolk sac, epidermis growth malformation around the eyes and at the basement of the pectoral fins. Skin histology revealed embryos derived from Tg(k18:shh:RFP) displayed an elevated Nuclear/Cytoplasmic ratio and pleomorphic nuclei compared to their wild type littermates, suggesting the abnormal growth pattern on the epidermis of Tg(k18:shh:RFP) embryos were dysplasia. Later (by 7 dpf), Tg(k18:shh:RFP) embryos displayed broader pectoral fins which are similar to the polydactyly phenotypes of Nevoid basal cell carcinoma syndrome (NBCCS)/Gorlin patients and polydactylous mice. In addition, treatment with cyclopamine is able to enhance and prolong the survival rates and survival durations of Tg(k18:shh:RFP) embryos. In conclusion, this unique Tg(k18:shh:RFP) fish line, should be an excellent experimental animal for screening for a lower toxicity level of the new Hh-inhibitor and can even be used as a new anti-cancer drug-screening platform.

The role of hedgehog signaling during gastric regeneration

BACKGROUND

Hedgehog signaling plays critical roles during embryonic development. It is also involved in tissue regeneration and carcinogenesis in various adult tissues. Moreover, it regulates the maintenance of cancer stem cells and adult stem cells. Although hedgehog signaling is important in gastric carcinogenesis, its role in gastric regeneration has not been previously examined. In the present study, we evaluated the expression and roles of hedgehog signaling during gastric regeneration.

METHODS

Gastric ulcers were induced by serosal application of an acetic acid solution in mice. Sham-operated mice served as controls. The proliferation of gastric progenitor cells was studied using bromodeoxyuridine (BrdU). The expression of hedgehog signaling molecules and the differentiation of gastric progenitor cells were examined by immunohistochemical staining and Western blotting.

RESULTS

One day after the induction of gastric ulcer, the proliferation of gastric progenitor cells increased; however, the expression of hedgehog signaling molecules, including sonic hedgehog (Shh), Indian hedgehog (Ihh), desert hedgehog (Dhh), and patched (Ptch1) decreased at the ulcer margin. From 5 days after the induction of gastric ulcer, newly generated gastric glands and their differentiation were observed at the ulcer margin. The expression of hedgehog signaling molecules gradually increased in the newly generated gastric glands of the ulcer margin. Cyclopamine, a specific inhibitor of hedgehog signaling, significantly inhibited the differentiation of mucous cells and parietal cells during the gastric regeneration process.

CONCLUSION

The above results suggest that hedgehog signaling is involved in the differentiation of gastric progenitor cells during the gastric ulcer repair process.

Using naturally occurring tumours in dogs and cats to study telomerase and cancer stem cell biology

The recently described cancer stem cell theory opens up many new challenges and opportunities to identify targets for therapeutic intervention. However, the majority of cancer related therapeutic studies rely upon rodent models of human cancer that rarely translate into clinical success in human patients. Naturally occurring cancers in dogs, cats and humans share biological features, including molecular targets, telomerase biology and tumour genetics. Studying cancer stem cell biology and telomere/telomerase dynamics in the cancer bearing pet population may offer the opportunity to develop a greater understanding of cancer biology in the natural setting and evaluate the development of novel therapies targeted at these systems.

Role and regulation of human tumor suppressor SUFU in Hedgehog signaling

Originally identified as factors affecting Drosophila embryogenesis, the Hedgehog (Hh) pathway is one of the primary signaling systems that specify patterns of cell growth and differentiation during vertebrate development. Mutations in various components of this pathway frequently occur in tumors originated from the skin, cerebellum, and skeletal muscle, and abnormal pathway activity is associated with a subset of lung, digestive tract, pancreatic, and prostate cancers. Because of these potent biological activities, this pathway is negatively regulated at multiple levels to ensure appropriate signaling responses. Suppressor of fused (Sufu) is one such negative regulator of Hh signaling. Although not essential in Drosophila, Sufu is absolutely required for mouse embryonic development. Mutations of Sufu are associated with a childhood brain tumor in human and an increased susceptibility to the same type of cancer in the TP53 null background in mice, and RNAi-mediated silencing of Sufu is sufficient to activate the Hh signaling in cultured fibroblasts. All these data point to a central role of Sufu in controlling the vertebrate Hh signaling pathway; however, for years what exactly Sufu does in the Hh pathway and what controls its activity remains a deep mystery. This chapter will go over all studies curated in the PubMed database with Sufu as a main subject during the past 17 years, and attempt to provide a balanced view on Sufu gene and protein structure, activities in Drosophila as well as mammalian development, and its involvement in cancer.

Redox regulation of multidrug resistance in cancer chemotherapy: molecular mechanisms and therapeutic opportunities

The development of multidrug resistance to cancer chemotherapy is a major obstacle to the effective treatment of human malignancies. It has been established that membrane proteins, notably multidrug resistance (MDR), multidrug resistance protein (MRP), and breast cancer resistance protein (BCRP) of the ATP binding cassette (ABC) transporter family encoding efflux pumps, play important roles in the development of multidrug resistance. Overexpression of these transporters has been observed frequently in many types of human malignancies and correlated with poor responses to chemotherapeutic agents. Evidence has accumulated showing that redox signals are activated in response to drug treatments that affect the expression and activity of these transporters by multiple mechanisms, including (a) conformational changes in the transporters, (b) regulation of the biosynthesis cofactors required for the transporter's function, (c) regulation of the expression of transporters at transcriptional, posttranscriptional, and epigenetic levels, and (d) amplification of the copy number of genes encoding these transporters. This review describes various specific factors and their relevant signaling pathways that are involved in the regulation. Finally, the roles of redox signaling in the maintenance and evolution of cancer stem cells and their implications in the development of intrinsic and acquired multidrug resistance in cancer chemotherapy are discussed.

Cellular and molecular basis of deiodinase-regulated thyroid hormone signaling

The iodothyronine deiodinases initiate or terminate thyroid hormone action and therefore are critical for the biological effects mediated by thyroid hormone. Over the years, research has focused on their role in preserving serum levels of the biologically active molecule T(3) during iodine deficiency. More recently, a fascinating new role of these enzymes has been unveiled. The activating deiodinase (D2) and the inactivating deiodinase (D3) can locally increase or decrease thyroid hormone signaling in a tissue- and temporal-specific fashion, independent of changes in thyroid hormone serum concentrations. This mechanism is particularly relevant because deiodinase expression can be modulated by a wide variety of endogenous signaling molecules such as sonic hedgehog, nuclear factor-kappaB, growth factors, bile acids, hypoxia-inducible factor-1alpha, as well as a growing number of xenobiotic substances. In light of these findings, it seems clear that deiodinases play a much broader role than once thought, with great ramifications for the control of thyroid hormone signaling during vertebrate development and metamorphosis, as well as injury response, tissue repair, hypothalamic function, and energy homeostasis in adults.