Developmental genes and cancer: role of patched in basal cell carcinoma of the skin

Differential modulation of Ku70/80 DNA-binding activity in a patient with multiple basal cell carcinomas

Ku70/80 nonhomologous end-joining activity is essential for resolving random DNA double-strand breaks, and the Ku70/80 protein complex has been proposed as "caretaker" of genomic stability. We studied the Ku70/80 heterodimer activity in a patient affected by multiple basal cell carcinomas with a personal history of moderate exposure to ionizing radiation. The Ku70/80 DNA-binding activity was analyzed, by electrophoretic mobility shift assay, in five tumor biopsies from different sites and at distinct clinical stages, and in three matched normal skin samples from the same patient. As control normal tissues from healthy individuals were also tested. The five basal cell carcinomas were classified as "non aggressive" and "aggressive" on the basis of morphologic parameters and expression of the molecular markers bcl-2, Ki67/MIB1, and p53. A 62% increase in the Ku70/80 DNA-binding activity was found in normal skin from the patient, compared to unexposed individuals (p<0.0001). The nuclear activity of the heterodimer was further increased in nonaggressive basal cell carcinomas compared to both matched normal skin from the patient (31%, p=0.0001) and tissues from healthy controls (73%, p=0.0001). Strikingly, the two aggressive basal cell carcinomas tested showed very low Ku70/80 DNA-binding activity with a reduction of 87% compared to normal skin from the patient (p<0.0001) and 64% compared to controls (p=0.001). Although these results are limited to only one patient, together with other recent studies they support the hypothesis that downregulation of the nonhomologous end-joining pathway may be associated with tumor progression.

Kinetics of v-src-induced epithelial-mesenchymal transition in developing glandular stomach

The oncogene function in primary epithelial cells is largely unclear. Recombination organ cultures in combination with the stable and transient gene transfer techniques by retrovirus and electroporation, respectively, enable us to transfer oncogenes specifically into primary epithelial cells of the developing avian glandular stomach (proventriculus). In this system, the epithelium and mesenchyme are mutually dependent on each other for their growth and differentiation. We report here that either stable or transient expression of v-src in the epithelium causes budding and migration of epithelial cells into mesenchyme. In response to the transient expression of v-Src or a constitutive active mutant of MEK, we observed immediate downregulation of the Sonic hedgehog gene and subsequent elimination of E-cadherine expression in migrating cells, suggesting the involvement of MAP kinase signaling pathway in these processes. v-src-expressing cells that were retained in the epithelium underwent apoptosis (anoikis) and detached from the culture. Continuous expression of v-src by, for example, Rous sarcoma virus (RSV) was required for the epithelial cells to acquire the ability to express type I collagen and fibronectin genes (mesenchymal markers), and finally to establish the epithelial-mesenchymal transition. These observations would partly explain why RSV does not apparently cause carcinoma formation, but induces sarcomas exclusively.

Sonic hedgehog in normal and neoplastic proliferation: insight gained from human tumors and animal models

Cancer arises when a cell accumulates multiple genetic changes that allow it to elude the highly regulated balance between proliferation and apoptosis that an organism employs to suppress inappropriate growth. It has become evident that malignant transformation of a cell or group of cells often involves pathways that are active during normal development but are inappropriately regulated in neoplastic proliferation. Signaling via the Sonic hedgehog pathway is critical to vertebrate development and also appears to play an integral role in the initiation and propagation of some tumors of the muscle, skin and nervous system. Analyses of human tumors have revealed mutations in various components of the Sonic hedgehog signaling pathway that appear to result in the activation of this pathway, as inferred by the increased expression of the transcription factor, Gli1. Interestingly, a proportion of the human tumors and most of those arising in mouse models continue to express the normal Patched allele, suggesting the involvement of additional molecular events in the transformation of the haploinsufficient cells.

Expression of homeobox genes in cervical cancer

OBJECTIVE

Members of the homeobox (HB) gene superfamily encode transcription factors crucial for development and may be associated with tumorigenesis. In this study, we aimed to develop a procedure to survey the expression of the dispersed-type HB genes in cervical cancer cells.

METHODS

Nineteen sets of degenerate primers were designed based on conserved homeodomains of known dispersed-type HB genes. A cDNA library derived from HeLa, a cervical cancer cell line, was used. Two successive rounds of PCR were performed using a combination of the HB degenerate primers and a primer recognizing the flanking sequence of the vector used in the cDNA library construction.

RESULTS

On cloning and sequence analysis of the PCR fragments generated, 10 known and 3 putative novel HB genes were detected in HeLa. RT-PCR expression analysis further showed that HOXD9 and ATBF1 were differentially expressed in cancer cells and not in normal cervix.

CONCLUSIONS

Our data demonstrate the feasibility of using degenerate primers in PCR experiments in a collective analysis of complex gene families. Our data indicate that HOXD9 and ATBF1 are expressed in cervical cancer, but not in normal cervix.

PATCHED and p53 gene alterations in sporadic and hereditary basal cell cancer

It is widely accepted that disruption of the hedgehog-patched pathway is a key event in development of basal cell cancer. In addition to patched gene alterations, p53 gene mutations are also frequent in basal cell cancer. We determined loss of heterozygosity in the patched and p53 loci as well as sequencing the p53 gene in tumors both from sporadic and hereditary cases. A total of 70 microdissected samples from tumor and adjacent skin were subjected to PCR followed by fragment analysis and DNA sequencing. We found allelic loss in the patched locus in 6/8 sporadic basal cell cancer and 17/19 hereditary tumors. All sporadic and 7/20 hereditary tumors showed p53 gene mutations. Loss of heterozygosity in the p53 locus was rare in both groups. The p53 mutations detected in hereditary tumors included rare single nucleotide deletions and unusual double-base substitutions compared to the typical ultraviolet light induced missense mutations found in sporadic tumors. Careful microdissection of individual tumors revealed genetically linked subclones with different p53 and/or patched genotype providing an insight on time sequence of genetic events. The high frequency and co-existence of genetic alterations in the patched and p53 genes suggest that both these genes are important in the development of basal cell cancer.

Cell biology of precancer

This article explores the possibilities of understanding the natural history of human cancers. In particular it attempts to understand precancer in cell biological or molecular rather than clinical or pathological terms. The questions discussed on the relevance of precancer in the neoplastic development are: are all cancers preceded by precancer? Is a precancer in the cell lineage characterised by hypermutability? Is there a direct DNA lineage from precancer to cancer? How many mutations have been added as a function of a number of DNA generations in the process to neoplastic transformation? Is precancer reversible? Can analysis of precancer provide a short cut to assessment of carcinogenic risk? The present data addressing these questions are discussed and the still unexplained phenomena are highlighted.

Mutations in the human homologue of the Drosophila segment polarity gene patched in oral squamous cell carcinoma cell lines

In the present study, we have analyzed tumor deoxyribonucleic acid from oral squamous cell carcinoma (OSCC) cells for patched mutations using an exon-by-exon single strand conformation polymorphism assay and direct sequencing. We found two missense mutations which affected the conserved residue in the transmembrane domains of the gene product and in the intracellular loop at the C-terminal residue implicated in regulating the smoothened molecule. In addition, we demonstrated that the N-terminal fragment of sonic hedgehog (Shh-N) stimulates the growth of normal epithelial cells, the OSCC cell line, NA, and the salivary gland adenocarcinoma cell lines, HSG and HSY, which have no detectable mutation in patched. On the other hand, Shh has no effect on human SCC cells (UE, KA, KO, NI, A431 cells) that have mutations in patched. These results strongly suggest that an Shh-patched signaling is involved in the cell growth of oral epithelial cells and in the tumorigenesis of OSCCs.

Basal cell carcinoma originating from a nevus sebaceus on the scalp of a 7-year-old boy

Basal cell carcinoma (BCC) occurs rarely in children and is most often associated with an underlying condition that predisposes patients to the development of malignancy. There have been numerous reports of BCC developing after puberty in nevus sebaceus; however, such occurrences have rarely been described in children. We report a 7-year-old boy with BCC forming in a nevus sebaceus.

Patched1 interacts with cyclin B1 to regulate cell cycle progression

The initiation of mitosis requires the activation of M-phase promoting factor (MPF). MPF activation and its subcellular localization are dependent on the phosphorylation state of its components, cdc2 and cyclin B1. In a two-hybrid screen using a bait protein to mimic phosphorylated cyclin B1, we identified a novel interaction between cyclin B1 and patched1 (ptc1), a tumor suppressor associated with basal cell carcinoma (BCC). Ptc1 interacted specifically with constitutively phosphorylated cyclin B1 derivatives and was able to alter their normal subcellular localization. Furthermore, addition of the ptc1 ligand, sonic hedgehog (shh), disrupts this interaction and allows cyclin B1 to localize to the nucleus. Expression of ptc1 in 293T cells was inhibitory to cell proliferation; this inhibition could be relieved by coexpression of a cyclin B1 derivative that constitutively localizes to the nucleus and that could not interact with ptc1 due to phosphorylation-site mutations to ALA: In addition, we demonstrate that endogenous ptc1 and endogenous cyclin B1 interact in vivo. The findings reported here demonstrate that ptc1 participates in determining the subcellular localization of cyclin B1 and suggest a link between the tumor suppressor activity of ptc1 and the regulation of cell division. Thus, we propose that ptc1 participates in a G(2)/M checkpoint by regulating the localization of MPF.

The Hedgehog signalling pathway and cancer

The Hedgehog signalling pathway is important in embryological development and is highly conserved through evolution. Recently Patched, a member of the pathway, was found to be important in Gorlin's syndrome. Inherited Patched gene mutations underlie the syndrome, in which a key feature is multiple basal cell carcinomas (BCCs). The gene is also mutated in sporadic BCCs as well as in sporadic occurrences of other tumours seen in Gorlin's syndrome. The precise mechanism whereby Patched gene mutation leads to tumour development is not known, but BCC is characterized by relentless local invasion and only rarely metastasizes. This suggests that abnormalities of the Hedgehog pathway account for these features. This proposal is discussed in the context of what is already known about the normal function of the Hedgehog pathway and its deregulation in cancer.

From developmental biology to developmental toxicology

Progress derived from the human genome project will have tremendous impact on toxicology. Questions concerning genetic susceptibility or resistance to toxic compound exposure and the dissection of the molecular mechanisms involved will be at the forefront of future toxicological research. In recent years, it was recognized that many of the molecular control mechanisms of embryogenesis have been conserved during evolution. The relevance of these observations for toxicology and the application of genetic approaches using mouse mutants as a tool for functional genome analysis are discussed.

Punctate keratoderma-like lesions on the palms and soles in a patient with chloracne: a new clinical manifestation of dioxin intoxication?

We report what we believe to be a novel skin manifestation of dioxin intoxication. A 30-year-old woman with 2,3,7, 8-tetrachlorodibenzo-p-dioxin levels of 144,000 pg g-1 blood fat presented with severe chloracne that affected the entire integument. She also exhibited acral granuloma annulare-like lesions and distal onycholysis and, at a later time point, showed signs of hypertrichosis, as well as brownish-grey hyperpigmentation of the face. In addition, she developed punctate keratoderma-like lesions on the palms and soles. These lesions were negative for human papillomavirus and histologically characterized by cone-shaped hyperkeratoses invaginating, but not penetrating, into the dermis. Squamous syringometaplasia of the eccrine glands was observed in the immediate vicinity of these lesions. Both clinically and histologically these alterations are essentially indistinguishable from what is described as keratosis punctata palmaris et plantaris (KPPP). Although a fortuitous coincidence of chloracne and KPPP cannot be formally excluded, the possibility exists that in our patient toxic levels of dioxin were causally involved in this disorder of keratinization.

High frequency of loss of heterozygosity on chromosome region 9p21-p22 but lack of p16INK4a/p19ARF mutations in greek patients with basal cell carcinoma of the skin

Basal cell carcinoma of the skin is the most common neoplasia in humans. Previous studies have shown the existence of allelic imbalance (loss of heterozygosity and microsatellite instability) in BCC on several human chromosomes. Chromosome region 9p21-p22 harbors the CDKN2a/p16INK4a, p19ARF, and p15INK4b tumor suppressor genes. To determine the contribution of these genes to the development of basal cell carcinomas we looked for evidence of allelic imbalance in 67 sporadic basal cell carcinoma specimens from Greek patients and screened 28 of them presenting loss of heterozygosity at 9p21-p22 for germline mutations in p16INK4a and p19ARF genes. Chromosome regions 17q21 and 17p13 were also screened for allelic imbalance in all the 67 basal cell carcinoma specimens. Overall, 69% (46 of 67) of the specimens displayed loss of heterozygosity in at least one microsatellite marker, whereas only six of the 67 (9%) exhibited microsatellite instability. For the 9p21-p22 locus the overall frequency of loss of heterozygosity reached 55% (37 of 67) and is the highest reported. The overall frequency of loss of heterozygosity for the 17q21 locus is 34% (22 of 64) and for the 17p13 locus is 11% (seven of 65). Two of the 28 loss of heterozygosity positive cases were heterozygous for a previously described polymorphism, Ala148Thr, in exon 2 of the CDKN2a gene. This is the first demonstration of polymorphism in the CDKN2a gene in human basal cell carcinomas. No sequence variation in exon 1beta of the p19ARF gene was found. Our results provide evidence of a significantly high occurrence of loss of heterozygosity for the 9p21-p22 locus; however, lack of p16INK4a/p19ARF mutation suggests that these genes seem not to be implicated by mutational inactivation in the development of basal cell carcinoma. Other(s), yet unidentified, tumor suppressor gene(s) located in this locus may be related to this specific type of skin cancer.

Applications of developmental biology to medicine and animal agriculture

With the complete sequence of the human genome expected by winter 2001, genomic-based drug discovery efforts of the pharmaceutical industry are focusing on finding the relatively few therapeutically useful genes from among the total gene set. Methods to rapidly elucidate gene function will have increasing value in these investigations. The use of model organisms in functional genomics has begun to be recognized and exploited and is one example of the emerging use of the tools of developmental biology in recent drug discovery efforts. The use of protein products expressed during embryo-genesis and the use of certain pluripotent cell populations (stem cells) as candidate therapeutics are other applications of developmental biology to the treatment of human diseases. These agents may be used to repair damaged or diseased tissues by inducing or directing developmental programs that recapitulate embryonic processes to replace specialized cells. The activation or silencing of embryonic genes in the disease state, particularly those encoding transcription factors, is another avenue of exploitation. Finally, the direct drug-induced manipulation of embryonic development is a unique application of developmental biology in animal agriculture.

UV-specific mutations of the human patched gene in basal cell carcinomas from normal individuals and xeroderma pigmentosum patients

Germline mutations of the human patched gene, PTCH, are responsible for the nevoid basal cell carcinoma (NBCC) syndrome or Gorlin's syndrome, characterized by multiple skin cancers, internal cancers and severe developmental abnormalities. The patched gene codes for a developmental regulator protein implicated in the sonic hedgehog (SHH) signalling pathway which plays an important role in oncogenic transformation. Patched exhibits tumor suppression function and has been shown to be mutated in skin cancers isolated from DNA repair-proficient patients or from xeroderma pigmentosum (XP), a DNA repair-deficient syndrome. We have reviewed and analyzed in detail the different mutation spectra found on the PTCH gene in these various models. The type and distribution of mutations are quite different between germline, sporadic and XP cancers. Among the germline alterations, there is a preponderance (70%) of rearrangements compared to other tumour types analysed where less than 30% of rearrangements is observed. Typical UV-induced mutations of the patched gene are found prominently in XP basal cell carcinomas (BCCs) and in particular, a significantly higher level (63%) of the UV signature tandem mutations is found compared to sporadic BCC (11%). The location of mutations along the PTCH protein delineates several important functional domains implicated in the biology of this transmembrane receptor.

UV mutation signature in tumor suppressor genes involved in skin carcinogenesis in xeroderma pigmentosum patients

Molecular analysis of p53 and patched (PTCH), two candidate tumor suppressor genes for non-melanocytic skin cancer, was performed in skin tumors from six patients affected by the cancer-prone disease xeroderma pigmentosum (XP). UV-specific p53 mutations were detected at a frequency of 38-50% in all the tumor types analysed, including melanomas. Additional analysis of PTCH mutations in the subset of eight basal call carcinomas (BCC) revealed a very high mutation frequency of this gene (90%) which exceeded that detected in the p53 gene in the same tumors (38%). PTCH mutations were predominantly UV-specific C>T transitions. This mutation pattern is different from that reported in BCC from normal donors where PTCH mutation frequency is 27% and mutations are frequently deletions and insertions. These findings suggest that PTCH mutations represent an earlier event in BCC development than p53 alterations and that the inability of XP patients to repair UV-induced PTCH mutations might significantly contribute to the early and frequent appearance of BCC observed in these patients.

Papillomaviruses in non-melanoma skin cancer: epidemiological aspects

Worldwide, non-melanoma skin cancers (NMSCs), which include squamous cell carcinoma (SCC) and basal cell carcinoma (BCC), are the most commonly diagnosed cancers among Caucasians. It is well established that ultraviolet radiation (UVR) plays a central role in the development of these cancers, and more recently, a role for specific genetic mutations in the pathogenesis of BCC has been identified. The possibility that certain types of HPV, either alone or in conjunction with UVR, may play a role in the pathogenesis of these cancers is suggested by several lines of evidence reviewed below.*9 @2depidemiology / non-melanoma skin cancer / papillomavirus

Human papillomaviruses in non-melanoma skin cancer

Recent data suggest that additional factors, other than UV radiation, are involved in the etiology of non-melanoma skin cancer. These include alterations in the tumor suppressor genes, p53, p16$L*I*U$LINK4a$L*I$L/CDKN2A, p21$L*I*U$LWAF1/CIP1$L*I$L and the PTCH gene, as well as cytokines. Papillomavirus infections have been implicated in the etiology of non-melanoma skin cancer. The interaction of tumor suppressor genes and cytokines with the oncoproteins of high-risk mucosal HPV types have been studied in detail, but very little is known about the cutaneous HPV types. We have studied the effect of UV radiation on the URRs of HPV 1, 2, 3, 5, 7, 20, 23, 27, 38, 41, and 77. Neither the CAT-expression and promoter activity of these HPV types, nor presence or absence of wild-type or mutated p53 in the cell lines used, could be related to the DNA sequence homology between the different HPV types or their biological behavior.

Tumor suppression in human skin carcinoma cells by chromosome 15 transfer or thrombospondin-1 overexpression through halted tumor vascularization

The development of skin carcinomas presently is believed to be correlated with mutations in the p53 tumor suppressor and ras gene as well as with the loss of chromosome 9. We now demonstrate that, in addition, loss of chromosome 15 may be a relevant genetic defect. Reintroduction of an extra copy of chromosome 15, but not chromosome 4, into the human skin carcinoma SCL-I cells, lacking one copy of each chromosome, resulted in tumor suppression after s.c. injection in mice. Transfection with thrombospondin-1 (TSP-1), mapped to 15q15, induced the same tumor suppression without affecting cell proliferation in vitro or in vivo. Halted tumors remained as small cysts encapsulated by surrounding stroma and blood vessels. These cysts were characterized by increased TSP-1 matrix deposition at the tumor/stroma border and a complete lack of tumor vascularization. Coinjection of TSP-1 antisense oligonucleotides drastically reduced TSP-1 expression and almost completely abolished matrix deposition at the tumor/stroma border. As a consequence, the tumor phenotype reverted to a well vascularized, progressively expanding, solid carcinoma indistinguishable from that induced by the untransfected SCL-I cells. Thus, these data strongly suggest TSP-1 as a potential tumor suppressor on chromosome 15. The data further propose an unexpected mechanism of TSP-1-mediated tumor suppression. Instead of interfering with angiogenesis in general, in this system TSP-1 acts as a matrix barrier at the tumor/stroma border, which, by halting tumor vascularization, prevents tumor cell invasion and, thus, tumor expansion.

Genetic predisposition to skin cancer

Here we review recent insights in the genetics of skin cancer susceptibility as gleaned from studies of three hereditary syndromes: basal cell nevus syndrome, familial melanoma/dysplastic nevus syndrome, and xeroderma pigmentosum. We provide a brief synopsis of the recent findings related to these syndromes in an attempt to illustrate several emerging themes in the genetics of skin cancer. These themes include 1) the recent identification of multiple cancer susceptibility genes that occur in a myriad of cellular regulatory pathways; 2) the relative specificity of certain regulatory pathways to the development of specific types of cancer; and 3) the important role of DNA damage caused by ultraviolet radiation and defective DNA repair mechanisms in the development of skin cancer. We also review the implications of this knowledge to clinical practice relative to risk assessment, primary prevention, and therapy.

Multiple follicular hamartomas with sweat gland and sebaceous differentiation, vermiculate atrophoderma, milia, hypotrichosis, and late development of multiple basal cell carcinomas

We describe a 46-year-old woman with multiple symmetrical papulocystic lesions on the face, neck, chest, back, and upper arms since childhood. Vermiculate atrophoderma, entropion, and progressive loss of eyelashes was also noted. Since the age of 30, 12 basal cell carcinomas have developed on the face. Histopathologic examination revealed multiple anastomosing nests and strands that arose from the lower part of a hair follicle in early lesions. In more advanced lesions, multiple keratinizing microcysts within a moderately sclerotic stroma were noted in the upper and mid dermis. In some biopsy specimens, focal areas showing sweat gland (ductal) and sebaceous differentiation were also observed. Basal cell carcinomas developed from the basaloid component of the hamartomatous proliferation.

Stage-specific effects of sonic hedgehog expression in the epidermis

Sonic hedgehog (Shh) is expressed in the ectoderm of the forming hair follicle and feather bud during normal development. However, inappropriate activation of the Shh signal transduction cascade in human epidermis can cause basal cell carcinoma. Here we show that during normal development of avian skin, Shh is first expressed only after the responsiveness to this protein has been suppressed in most of the surrounding ectodermal cells. Forced expression of Shh in avian skin prior to this time causes a disorganized ectodermal proliferation. However, as skin begins to differentiate, the forced expression of Shh causes feather bud formation. Subsequently, expression of Shh in interfollicular epidermis has little or no morphological effect. Restricted responsiveness to Shh in developing skin has functional consequences for morphogenesis and may have important implications for cutaneous pathologies as well.

Human developmental disorders and the Sonic hedgehog pathway

Sonic hedgehog (Shh) is a morphogen that is crucial for normal development of a variety of organ systems, including the brain and spinal cord, the eye, craniofacial structures, and the limbs. Mutations in the human SHH gene and genes that encode its downstream intracellular signaling pathway cause several clinical disorders. These include holoprosencephaly (HPE, the most common anomaly of the developing forebrain), nevoid basal cell carcinoma syndrome, sporadic tumors, including basal cell carcinomas, and three distinct congenital disorders: Greig syndrome Pallister-Hall syndrome, and isolated postaxial polydactyly. These conditions caused by abnormalities in the SHH pathway demonstrate the crucial role of SHH in complex developmental processes, and molecular analyses of these disorders provide insight into the normal function of the SHH pathway in human development.