Induction of c-fos but not c-myc in S-91 cells by melanization signals

SF3B1, NRAS, KIT, and BRAF Mutation; CD117 and cMYC Expression; and Tumoral Pigmentation in Sinonasal Melanomas: An Analysis With Newly Found Molecular Alterations and Some Population-Based Molecular Differences

Sinonasal melanomas encompass melanoma arising in the nasal cavity and paranasal sinuses. Despite recent advances in tumor genomics, correlation between mutational status and protein expression with prognosis and tumor pigmentation has not been carried out in sinonasal melanomas. Ninety-five sinonasal melanomas from 95 patients were included. As per univariate analyses, age was the only variable that significantly correlated with progression-free survival. SF3B1, NRAS, KIT, and BRAF mutations were documented in 7% (5/72), 22% (16/72), 22% (16/72), and 8% (6/72) of cases, respectively. Comutation was detected in 6 cases: NRAS and KIT in 2 cases; NRAS and BRAF in 2 cases; SF3B1, KIT, and BRAF in one case; and SF3B1, NRAS, and KIT in one case. Correlations approaching statistical significance were observed between BRAF mutation status and poorer overall survival and progression-free survival (log-rank P-values=0.054 and 0.061). Increased CD117 expression (33%, 29/88) and decreased nuclear cMYC expression (40%, 39/84) significantly correlated with cytoplasmic pigmentation. Several SF3B1, NRAS, and KIT mutations not previously documented in sinonasal melanomas were detected in our series, suggesting a potential role for targeted therapies. A similar frequency of SF3B1, NRAS, and KIT mutations was noted in Asian cases, whereas NRAS, KIT, and BRAF mutations were predominant in the United States and European cases; however, the number of included cases was small. The significant association between CD117 and cMYC expression with increased cytoplasmic pigmentation in our series suggests that the pigmented morphologic appearance of sinonasal melanomas could be attributed to the underlying oncogenic mutations and metabolic interaction.

Genetic background of coat colour in sheep

Abstract. The coat colour of animals is an extremely important trait that affects their behaviour and is decisive for survival in the natural environment. In farm animal breeding, as a result of the selection of a certain coat colour type, animals are characterized by a much greater variety of coat types. This makes them an appropriate model in research in this field. A very important aspect of the coat colour types of farm animals is distinguishing between breeds and varieties based on this trait. Furthermore, for the sheep breeds which are kept for skins and wool, coat/skin colour is an important economic trait. Until now the study of coat colour inheritance in sheep proved the dominance of white colour over pigmented/black coat or skin and of black over brown. Due to the current knowledge of the molecular basis of ovine coat colour inheritance, there is no molecular test to distinguish coat colour types in sheep although some are available for other species, such as cattle, dogs, and horses. Understanding the genetic background of variation in one of the most important phenotypic traits in livestock would help to identify new genes which have a great effect on the coat colour type. Considering that coat colour variation is a crucial trait for discriminating between breeds (including sheep), it is important to broaden our knowledge of the genetic background of pigmentation. The results may be used in the future to determine the genetic pattern of a breed. Until now, identified candidate genes that have a significant impact on colour type in mammals mainly code for factors located in melanocytes. The proposed candidate genes code for the melanocortin 1 receptor (MC1R), agouti signaling protein (ASIP), tyrosinase-related protein 1 (TYRP1), microphthalmia-associated transcription factor MITF, and v-kit Hardy–Zuckerman 4 feline sarcoma viral oncogene homologue (KIT). However, there is still no conclusive evidence of established polymorphisms for specific coat colour types in sheep.

Reduction of Melanogenic Activity and Responsiveness to α-Melanocyte-Stimulating Hormone during Serial Passage of Melanoma Cells

Background:

Murine melanoma cells such as Cloudman S91 or B16 mouse melanoma cells have been used extensively to study mechanisms involved in pigmentation because these cells have tyrosinase, the key enzyme in pigmentation, and produce pigment. We have observed that serial passaged S91 cells tend to decrease their basal pigment content and to lose their responsiveness to α-melanocyte-stimulating hormone (α-MSH).

Objective:

Because this reduction of melanogenic capacity is a widely acknowledged but virtually unstudied characteristic of both human and murine melanoma cell lines in culture, we wished to document and quantify the phenomenon.

Methods:

Commercially attained S91 melanoma cells were serially passaged. Basal pigmentation as well as α-MSH responsiveness and expression of protein kinase C-beta (PKC-β) were assessed.

Results:

S91 cells progressively lost their basal pigmentation under standardized conventional conditions of culture, from an initial melanin content of 20 ± 4 pg/cell content to 12 ± 5 pg/cell within 70 population doublings (16 passages) and to 4.5 ± 6 pg/cell, a level at or below the detectable level of our melanin assay, by 110 population doublings (28 passages). When responsiveness to α-MSH was assessed, a 6-day treatment with 10−6M α-MSH initially induced the pigment content four-fold from 20 ± 4 to 82 ± 2 pg/cell. In contrast, after 110 population doublings, identical treatment with α-MSH induced pigment content less than two-fold from 4.5 ± 6 to 7.5 ± 2 pg/cell. PKC-β expression was readily detected by immunofluorescence in early passage pigmented cells, but not in late passage nonpigmented cells.

Conclusion:

These results confirm that while murine melanoma cells are a useful model system for pigmentation studies, it is important to monitor changes in the cells' basal abilities to pigment and to respond to exogenous pigment-inducing factors. They further suggest that factors in the culture environment or the internal milieu of melanoma cells exposed to continuous mitogenic stimulation inhibit melanogenesis. One candidate mechanism is down regulation of PKC-β.

Gene expression analysis identifies new candidate genes associated with the development of black skin spots in Corriedale sheep

The white coat colour of sheep is an important economic trait. For unknown reasons, some animals are born with, and others develop with time, black skin spots that can also produce pigmented fibres. The presence of pigmented fibres in the white wool significantly decreases the fibre quality. The aim of this work was to study gene expression in black spots (with and without pigmented fibres) and white skin by microarray techniques, in order to identify the possible genes involved in the development of this trait. Five unrelated Corriedale sheep were used and, for each animal, the three possible comparisons (three different hybridisations) between the three samples of interest were performed. Differential gene expression patterns were analysed using different t-test approaches. Most of the major genes with well-known roles in skin pigmentation, e.g. ASIP, MC1R and C-KIT, showed no significant difference in the gene expression between white skin and black spots. On the other hand, many of the differentially expressed genes (raw P-value < 0.005) detected in this study, e.g. C-FOS, KLF4 and UFC1, fulfil biological functions that are plausible to be involved in the formation of black spots. The gene expression of C-FOS and KLF4, transcription factors involved in the cellular response to external factors such as ultraviolet light, was validated by quantitative polymerase chain reaction (PCR). This exploratory study provides a list of candidate genes that could be associated with the development of black skin spots that should be studied in more detail. Characterisation of these genes will enable us to discern the molecular mechanisms involved in the development of this feature and, hence, increase our understanding of melanocyte biology and skin pigmentation. In sheep, understanding this phenomenon is a first step towards developing molecular tools to assist in the selection against the presence of pigmented fibres in white wool.

C-fos protein expression in Spitz nevi, common melanocytic nevi, and malignant melanomas

The expression of c-fos protein was studied in formalin-fixed, paraffin-embedded sections of 11 compound Spitz nevi (SNs), 16 ordinary compound melanocytic nevi (MNs), and 17 malignant melanomas (MMs) using monoclonal antibody MAB1283 and an immunoperoxidase technique. Eleven (100%) SNs, 15 (94%) MNs, and 16 (94%) MMs showed positive reactions in some of the tumor cells (p = nonsignificant). In the majority of the tumors the staining was located in nuclei and graded as moderate to strong in intensity. The percentages of positively stained cells did not differentiate the three types of tumor, although they were higher in the melanocytic nevi. Most of the lesions with a significant dermal component did not show stratification of staining with progressive descent into the dermis. Positive staining for c-fos was also frequently found in the normal skin constituents within and adjacent to the melanocytic tumors. In conclusion, the pattern of expression of c-fos in routinely processed specimens does not differentiate between SNs, MNs, and MMs.

DNA damage enhances melanogenesis

Although the ability of UV irradiation to induce pigmentation in vivo and in vitro is well documented, the intracellular signals that trigger this response are poorly understood. We have recently shown that increasing DNA repair after irradiation enhances UV-induced melanization. Moreover, addition of small DNA fragments, particularly thymine dinucleotides (pTpT), selected to mimic sequences excised during the repair of UV-induced DNA photoproducts, to unirradiated pigment cells in vitro or to guinea pig skin in vivo induces a pigment response indistinguishable from UV-induced tanning. Here we present further evidence that DNA damage and/or the repair of this damage increases melanization. (i) Treatment with the restriction enzyme Pvu II or the DNA-damaging chemical agents methyl methanesulfonate (MMS) or 4-nitroquinoline 1-oxide (4-NQO) produces a 4- to 10-fold increase in melanin content in Cloudman S91 murine melanoma cells and an up to 70% increase in normal human melanocytes, (ii) UV irradiation, MMS, and pTpT all upregulate the mRNA level for tyrosinase, the rate-limiting enzyme in melanin biosynthesis. (iii) Treatment with pTpT or MMS increases the response of S91 cells to melanocyte-stimulating hormone (MSH) and increases the binding of MSH to its cell surface receptor, as has been reported for UV irradiation. Together, these data suggest that UV-induced DNA damage and/or the repair of this damage is an important signal in the pigmentation response to UV irradiation. Because Pvu II acts exclusively on DNA and because MMS and 4-NQO, at the concentrations used, primarily interact with DNA, such a stimulus alone appears sufficient to induce melanogenesis. Of possible practical importance, the dinucleotide pTpT mimics most, if not all, of the effects of UV irradiation on pigmentation, tyrosinase mRNA regulation, and response to MSH without the requirement for antecedent DNA damage.

Immunohistochemical expression of C-myc oncogene, heat shock protein 70 and HLA-DR molecules in malignant cutaneous melanoma

The clinical course of malignant melanomas is frequently unpredictable, although a number of prognostically useful variables can be identified. There is a need for additional markers of prognostic value. In a series of 60 malignant cutaneous melanomas, we analysed the immunohistochemical expression of c-myc proto-oncogene, heat shock protein 70 (HSP70) and HLA-DR molecules in order to investigate their prognostic significance. C-myc, HSP70 and HLA-DR were expressed in 43.3%, 56.6% and 38.3% of all melanoma cases, respectively. Advanced Clark levels (Clark III-V) were significantly associated with c-myc expression rate (P < 0.05), HSP70 detection (P < 0.01) and HLA-DR positivity (P < 0.01). Increased Breslow thickness (> 1.5 mm) was related to HLA-DR expression (P < 0.05). High mitotic rate was closely associated with c-myc positivity (P < 0.05), while HSP70 and HLA-DR expression separately correlated to clinical stage of the disease (P < 0.05). The evaluation of these variables may be of immunological and prognostic significance. They were found to be associated with melanocyte subpopulations of the vertical growth phase which are arguably characterized by an increased invasive potential.

ACTH-related peptides: receptors and signal transduction systems involved in their neurotrophic and neuroprotective actions

ACTH-related peptides are promising neurotrophic and neuroprotective agents, as demonstrated in many in vivo and in vitro studies. They accelerate nerve repair after injury, improving both sensor and motor function. Furthermore, ACTH-related peptides have neuroprotective properties against cisplatin- and taxol-induced neurotoxicity, they improve neuronal function in animals with neuropathy due to experimental diabetes, and they prevent degeneration of myelinated axons in rats suffering from experimental allergic neuritis, a model of peripheral demyelinating neuropathy. Studies in neuronal cultures have corroborated these clinical observations and serve to investigate the mechanism of action of the ACTH-related peptide effects. This paper reviews both in vitro and in vivo effects and emphasizes the mechanism of action. Recent data on melanotrophic receptors and signal transduction systems will be discussed in this context.

Protein kinase C: biochemical characteristics and role in melanocyte biology

The protein kinase C (PKC) family of proteins, consisting of at least ten isoforms, has been shown to regulate major cellular functions, including the growth and differentiation in many cell types. Use of PKC activators and inhibitors in combination with molecular biology techniques, has permitted detailed exploration of their specific intracellular actions. Recently, studies have implicated PKC specifically in the regulation of growth and differentiated function in melanocytes. In particular, the beta-isoform of PKC was shown to regulate human melanogenesis through activation of tyrosinase, the rate limiting enzyme in melanogenesis. This article reviews the role of PKC in melanocyte biology.

Ageing and photoageing of the skin: observations at the cellular and molecular level

It is now well established that ageing occurs at the level of individual cells in the skin and other organ systems. Changes in cell behaviour, protein production and gene expression in response to standardized stimuli are readily observed in cultured cells derived from young vs old donors and from photoaged vs sun-protected body sites. Whether these changes are best viewed as a cause or a consequence of ageing cannot be determined at present. Nevertheless, available data now provide cellular and molecular correlates for the well-known differences in clinical responsiveness between newborn, adult and photoaged skin. From this basis, it will hopefully be possible to develop a more comprehensive understanding of cutaneous ageing processes.

Modulation of mRNA levels during human keratinocyte differentiation

Cultures of human keratinocytes provide an excellent model system in which to study differentiation. Using the phorbol ester 12-O-tetradecanoyl-phorbol 13-acetate (TPA) and calcium, two agents known to induce keratinocyte differentiation in vitro, we examined the expression of the genes encoding c-fos, c-myc, and c-jun; involucrin, a protein precursor of the keratinocyte cornified envelope; and L-7, a ribosomal protein. Overall, at the doses studied, TPA induced a more rapid and profound differentiation than did calcium, as evaluated by culture morphology and northern blot analysis. Our studies showed a constant low level of c-fos and c-jun expression in unstimulated cells with no significant change after addition of either TPA or calcium except when transcript breakdown was inhibited by cycloheximide. The c-myc proto-oncogene, known to have a high constitutive expression in actively proliferating cells, was strongly downregulated by TPA, but calcium had no effect over a 32 hour period, consistent with the greater growth inhibition of TPA in this system. Involucrin was induced about ninefold by both TPA and calcium as early as 8 hours after stimulation, suggesting transcriptional regulation of this gene during differentiation. L-7, recently demonstrated to be downregulated in late passage human fibroblasts in an in vitro model of senescence, was also strongly downregulated by either TPA or calcium, consistent with an interrelationship between the basic cellular processes of aging and differentiation. These finding expand our knowledge of the differentiation process in human keratinocytes.