C32 human melanoma cell endogenous lectins: characterization and implication in vesicle-mediated melanin transfer to keratinocytes

The biochemistry of melanogenesis: an insight into the function and mechanism of melanogenesis-related proteins

Melanin is an amino acid derivative produced by melanocyte through a series of enzymatic reactions using tyrosinase as substrate. Human skin and hair color is also closely related to melanin, so understanding the mechanisms and proteins that produce melanin is very important. There are many proteins involved in the process of melanin expression, For example, proteins involved in melanin formation such as p53, HNF-1α (Hepatocyte nuclear factor 1α), SOX10 (Sry-related HMg-Box gene 10) and pax3 (paired box gene 3), MC1R(Melanocortin 1 Receptor), MITF (Microphthalmia-associated transcription factor), TYR (tyrosinase), TYRP1 (tyrosinase-related protein-1), TYRP2 (tyrosinase-related protein-2), and can be regulated by changing their content to control the production rate of melanin. Others, such as OA1 (ocular albinism type 1), Par-2 (protease-activated receptor 2) and Mlph (Melanophilin), have been found to control the transfer rate of melanosomes from melanocytes to keratinocytes, and regulate the amount of human epidermal melanin to control the depth of human skin color. In addition to the above proteins, there are other protein families also involved in the process of melanin expression, such as BLOC, Rab and Rho. This article reviews the origin of melanocytes, the related proteins affecting melanin and the basic causes of related gene mutations. In addition, we also summarized the active ingredients of 5 popular whitening cosmetics and their mechanisms of action.

Melanin's Journey from Melanocytes to Keratinocytes: Uncovering the Molecular Mechanisms of Melanin Transfer and Processing

Skin pigmentation ensures efficient photoprotection and relies on the pigment melanin, which is produced by epidermal melanocytes and transferred to surrounding keratinocytes. While the molecular mechanisms of melanin synthesis and transport in melanocytes are now well characterized, much less is known about melanin transfer and processing within keratinocytes. Over the past few decades, distinct models have been proposed to explain how melanin transfer occurs at the cellular and molecular levels. However, this remains a debated topic, as up to four different models have been proposed, with evidence presented supporting each. Here, we review the current knowledge on the regulation of melanin exocytosis, internalization, processing, and polarization. Regarding the different transfer models, we discuss how these might co-exist to regulate skin pigmentation under different conditions, i.e., constitutive and facultative skin pigmentation or physiological and pathological conditions. Moreover, we discuss recent evidence that sheds light on the regulation of melanin exocytosis by melanocytes and internalization by keratinocytes, as well as how melanin is stored within these cells in a compartment that we propose be named the melanokerasome. Finally, we review the state of the art on the molecular mechanisms that lead to melanokerasome positioning above the nuclei of keratinocytes, forming supranuclear caps that shield the nuclear DNA from UV radiation. Thus, we provide a comprehensive overview of the current knowledge on the molecular mechanisms regulating skin pigmentation, from melanin exocytosis by melanocytes and internalization by keratinocytes to processing and polarization within keratinocytes. A better knowledge of these molecular mechanisms will clarify long-lasting questions in the field that are crucial for the understanding of skin pigmentation and can shed light on fundamental aspects of organelle biology. Ultimately, this knowledge can lead to novel therapeutic strategies to treat hypo- or hyper-pigmentation disorders, which have a high socio-economic burden on patients and healthcare systems worldwide, as well as cosmetic applications.

Melanin Transfer in the Epidermis: The Pursuit of Skin Pigmentation Control Mechanisms

The mechanisms by which the pigment melanin is transferred from melanocytes and processed within keratinocytes to achieve skin pigmentation remain ill-characterized. Nevertheless, several models have emerged in the past decades to explain the transfer process. Here, we review the proposed models for melanin transfer in the skin epidermis, the available evidence supporting each one, and the recent observations in favor of the exo/phagocytosis and shed vesicles models. In order to reconcile the transfer models, we propose that different mechanisms could co-exist to sustain skin pigmentation under different conditions. We also discuss the limited knowledge about melanin processing within keratinocytes. Finally, we pinpoint new questions that ought to be addressed to solve the long-lasting quest for the understanding of how basal skin pigmentation is controlled. This knowledge will allow the emergence of new strategies to treat pigmentary disorders that cause a significant socio-economic burden to patients and healthcare systems worldwide and could also have relevant cosmetic applications.

Intercellular transfer of organelles during body pigmentation

The intercellular transfer of the melanin-producing organelle, called melanosome, from melanocytes to adjacent keratinocytes, is largely responsible for the coat colors and skin pigmentation of amniotes (birds, reptiles, and mammals). Although several hypotheses of melanin-transfer were proposed mainly by in vitro studies and electron microscopies, how the melanosome transfer takes place in the actual skin remained unclear. With advances in technologies of gene manipulations and high-resolution microscopy that allow direct visualization of plasma membrane, we are beginning to understand the amazing behaviors and dynamics of melanocytes. Studies in melanosome transfer further provide a clue to understand a general principle of intercellular organelle transport, including the intercellular translocations of mitochondria.

Melanosome transfer to keratinocyte in the chicken embryonic skin is mediated by vesicle release associated with Rho-regulated membrane blebbing

During skin pigmentation in amniotes, melanin synthesized in the melanocyte is transferred to keratinocytes by a particle called the melanosome. Previous studies, mostly using dissociated cultured cells, have proposed several different models that explain how the melanosome transfer is achieved. Here, using a technique that labels the plasma membrane of melanocytes within a three-dimensional system that mimics natural tissues, we have visualized the plasma membrane of melanocytes with EGFP in chicken embryonic skin. Confocal time-lapse microscopy reveals that the melanosome transfer is mediated, at least in part, by vesicles produced by plasma membrane. Unexpectedly, the vesicle release is accompanied by the membrane blebbing of melanocytes. Blebs that have encapsulated a melanosome are pinched off to become vesicles, and these melanosome-containing vesicles are finally engulfed by neighboring keratinocytes. For both the membrane blebbing and vesicle release, Rho small GTPase is essential. We further show that the membrane vesicle-mediated melanosome transfer plays a significant role in the skin pigmentation. Given that the skin pigmentation in inter-feather spaces in chickens is similar to that in inter-hair spaces of humans, our findings should have important consequences in cosmetic medicine.

Involvement of pigment globules containing multiple melanosomes in the transfer of melanosomes from melanocytes to keratinocytes

The mechanism of melanosome transfer from melanocytes to keratinocytes has not been fully clarified. We now show a route of melanosome transfer using co-cultures of normal human melanocytes and keratinocytes. Substantial levels of melanosome transfer were elicited in co-cultures of melanocytes and keratinocytes separated by a microporous membrane filter. The melanocyte dendrites penetrated into the keratinocyte layer through the filter and many pigment globules were observed in keratinocytes. Electron microscopic observations revealed that melanosomes incorporated in keratinocytes were packed in clusters enclosed by a double membrane. Numerous pigment globules budded off from melanocyte dendrites and were released into the culture medium. Those pigment globules were filled with multiple melanosomes and a few mitochondria but no nuclei. When those globules were added to the culture medium of keratinocytes, they were incorporated and showed double membrane-enclosed melano-phagolysosomes consistent with the structures obtained from the co-culture system. In contrast, when individual naked melanosomes isolated from melanocytes were added to keratinocytes, they were also phagocytosed by keratinocytes but were enclosed by a single membrane in a manner distinct from the co-culture system. These results suggest a novel mechanism of melanosome transfer, wherein melanosomes are packed in membrane globules that bud off from melanocyte dendrites, where they are released into the extracellular space and then phagocytosed by keratinocytes.

Improvement of polyphenol properties upon glucosylation in a UV-induced skin cell ageing model

OBJECTIVE

Polyphenols are strong antioxidant molecules allowing prevention of skin photo-ageing damages, but their use is limited due to low solubility and toxicity towards skin cells. We postulated that enzymatic glucosylation could improve their solubility, stability and, consequently, their efficacy. The aim of this work was to study changes induced by addition of a glucose moiety on two polyphenols displaying very different chemical structures [caffeic acid (CA), epigallocatechin-3-gallate (EGCG) and there glucosylated form, Glc-CA and Glc-EGCG] by assessing their cytotoxic properties and their antioxidant and anti-inflammatory activities.

METHODS

Their antioxidant effect was assessed first by the classical DPPH radical-scavenging method. Then, a panel of human skin cells (keratinocytes, melanocytes, fibroblasts and endothelial cells) was used to evaluate their effect on cell toxicity and their antioxidant activities. With this aim, a photo-ageing model based on UV irradiation of skin cells was established. Molecule activity was assessed on reactive oxygen species (ROS) production, on superoxide dismutase (SOD) and catalase activities and, finally, on inflammatory factor production IL-6, IL-8 and IL-1β.

RESULTS

In an acellular model, antioxidant activity assessed by DPPH method was strongly reduced for Glc-CA compared to CA, whereas it remained the same for Glc-EGCG compared to EGCG. Glucosylated derivatives did not display more toxic effect on various skin cells. Moreover, toxicity was even strongly reduced for caffeic acid upon glucosylation. The efficacy of glucosyl-compounds against UV-induced ROS production was preserved, both with pre- and post-UV treatments. Particularly, a better antioxidant efficacy was shown by Glc-EGCG, vs. EGCG, on keratinocytes. In addition, an induction of SOD and catalase activity was clearly observed for Glc-CA. Both glucosyl-polyphenols display the same activity as their parent molecule in decreasing inflammatory factor production.

CONCLUSION

Our results demonstrated that enzymatic glucosylation of CA and EGCG led to an improved or preserved antioxidant activity in a cellular model of UV-induced skin ageing, despite the decrease in instantaneous antioxidant properties observed for Glc-CA. Glc-EGCG is specifically more active on keratinocytes, suggesting a specific targeting. Such glucosylated polyphenols displaying improved physicochemical and biological properties should be better candidates than natural ones for use in food additives and cosmetics.

Pheomelanin in the skin of Hymenochirus boettgeri (Amphibia: Anura: Pipidae)

Pheomelanin is supposed to be the first type of melanin found in vertebrates, in contrast to the main type - eumelanin. Our study aimed at detecting pheomelanin in the skin of Hymenochirus boettgerii. We employed electron paramagnetic resonance (EPR) spectroscopy, and transmission electron microscopy (TEM), supplemented with standard histology and immunochemistry. We identified pheomelanin in the dorsal skin of adult frogs (not only in the dermis, but also in the epidermis) and in the dorsal tadpole. Our work identifies Hymenochirus boettgerii as a model in the basic study on the mechanism, evolution and role of melanogenesis in animals, including human.

News on microenvironmental physioxia to revisit skin cell targeting approaches

The skin is a multifunctional organ and a first line of defense actively protecting from environmental stress caused by injury, microbial treat, UV irradiation and environmental toxins. Diverse cutaneous cell types together with extracellular matrix elements and factors create a dynamic scene for cellular communication crucial in vital processes such as wound healing, inflammation, angiogenesis, immune response. Direct functional success of skin equilibrium depends on its microenvironment settings and particularly the local oxygen tension. Indeed, skin entire milieu is characterized by and highly dependent on its low oxygen tension called physioxia as emphasized in this review. In the context of skin physioxia, we review and propose here new approaches to minimize age-related changes in skin state and function. We particularly emphasize carbohydrate-mediated interactions and new 3D models of engineered skin substitutes. We highlight newly emerged tools and targets including stem cells, miRNAs, matrix metalloproteinases, mitochondria and natural antioxidants that are promising in prevention of skin ageing and disease restraint. In the era of advanced dermatology, new attempts are bringing us closer to 'well being' perception.

Clinicopathologic and immunohistochemical features of pigmented Basal cell carcinomas of the eyelids

PURPOSE

To describe the clinical and microscopic features of pigmented basal cell carcinomas (pBCC) of the eyelid.

DESIGN

Retrospective observational case series collected at one institution.

METHODS

An analysis of clinical records, photographs, and histopathologic characteristics of 257 BCCs with a review of the literature. The frequencies of clinically pigmented, and of microscopically pigmented but clinically nonpigmented, BCCs were determined. Cytochemical stains (Fontana-Masson, Prussian blue) and immunohistochemical probes (S-100, microphthalmia-associated transcription factor [MiTF], HMB-45, MART-1, CK20, synaptophysin, chromogranin, CD1a, Ki-67) were then employed and the findings correlated with the degree of clinical pigmentation.

RESULTS

Histopathologically, 13 of 257 cases (5.06%) were found to have pigment; of these 13, 6 (all white patients) had clinically apparent pigmentation (2.33%), either focal or diffuse. Eight of 13 lesions developed on the lower eyelids. All stained positively for melanin but negatively for iron. MiTF highlighted numerous melanocytic nuclei in the tumor lobules, while MART-1 and HMB-45 revealed the dendritic shapes of the entrapped melanocytes. There was a subtotal blockage of melanin transfer to the surrounding basaloid cells. Intralobular S-100-positive cells included CD1a-positive Langerhans cells, while CK20 did not identify any Merkel cells.

CONCLUSIONS

Only 1 of 6 lesions was uniformly clinically pigmented, whereas the other 5 were only focally brown-black. The clinical pigmentation was imparted by varying densities and distributions of melanocytes with arborizing dendrites, which were present in all BCCs. Melanophages within the stroma and basaloid cell melanization also contributed to pigmentation. No behavioral or biologic differences in pBCC were documented compared with clinically nonpigmented lesions.

Melanosomes are transferred from melanocytes to keratinocytes through the processes of packaging, release, uptake, and dispersion

Recent studies have described the role of shedding vesicles as physiological conveyers of intracellular components between neighboring cells. Here we report that melanosomes are one example of shedding vesicle cargo, but are processed by a previously unreported mechanism. Pigment globules were observed to be connected to the filopodia of melanocyte dendrites, which have previously been shown to be conduits for melanosomes. Pigment globules containing multiple melanosomes were released from various areas of the dendrites of normal human melanocytes derived from darkly pigmented skin. The globules were then captured by the microvilli of normal human keratinocytes, also derived from darkly pigmented skin, which incorporated them in a protease-activated receptor-2 (PAR-2)-dependent manner. After the pigment globules were ingested by the keratinocytes, the membrane that surrounded each melanosome cluster was gradually degraded, and the individual melanosomes then spread into the cytosol and were distributed primarily in the perinuclear area of each keratinocyte. These results suggest a melanosome transfer pathway wherein melanosomes are transferred from melanocytes to keratinocytes via the shedding vesicle system. This packaging system generates pigment globules containing multiple melanosomes in a unique manner.

The Quest for the Mechanism of Melanin Transfer

Skin pigmentation is accomplished by production of melanin in specialized membrane-bound organelles termed melanosomes and by transfer of these organelles from melanocytes to surrounding keratinocytes. The mechanism by which these cells transfer melanin is yet unknown. A central role has been established for the protease-activated receptor-2 of the keratinocyte which effectuates melanin transfer via phagocytosis. What exactly is being phagocytosed - naked melanin, melanosomes or melanocytic cell parts - remains to be defined. Analogy of melanocytes to neuronal cells and cells of the haemopoietic lineage suggests exocytosis of melanosomes and subsequent phagocytosis of naked melanin. Otherwise, microscopy studies demonstrate cytophagocytosis of melanocytic dendrites. Other plausible mechanisms are transfer via melanosome-containing vesicles shed by the melanocyte or transfer via fusion of keratinocyte and melanocyte plasma membranes with formation of tunnelling nanotubes. Molecules involved in transfer are being identified. Transfer is influenced by the interactions of lectins and glycoproteins and, probably, by the action of E-cadherin, SNAREs, Rab and Rho GTPases. Further clues as to what mechanism and molecular machinery will arise with the identification of the function of specific genes which are mutated in diseases that affect transfer.

Effective inhibition of melanosome transfer to keratinocytes by lectins and niacinamide is reversible

Skin pigmentation results in part from the transfer of melanized melanosomes synthesized by melanocytes to neighboring keratinocytes. Plasma membrane lectins and their glycoconjugates expressed by these epidermal cells are critical molecules involved in this transfer process. In addition, the derivative of vitamin B(3), niacinamide, can inhibit melanosome transfer and induce skin lightening. We investigated the effects of these molecules on the viability of melanocytes and keratinocytes and on the reversibility of melanosome-transfer inhibition induced by these agents using an in vitro melanocyte-keratinocyte coculture model system. While lectins and neoglycoproteins could induce apoptosis in a dose-dependent manner to melanocytes or keratinocytes in monoculture, similar dosages of the lectins, as opposed to neoglycoproteins, did not induce apoptosis to either cell type when treated in coculture. The dosages of lectins and niacinamide not affecting cell viability produced an inhibitory effect on melanosome transfer, when used either alone or together in cocultures of melanocytes-keratinocytes. Cocultures treated with lectins or niacinamide resumed normal melanosome transfer in 3 days after removal of the inhibitor, while cocultures treated with a combination of lectins and niacinamide demonstrated a lag in this recovery. Subsequently, we assessed the effect of niacinamide on facial hyperpigmented spots using a vehicle-controlled, split-faced design human clinical trial. Topical application of niacinamide resulted in a dose-dependent and reversible reduction in hyperpigmented lesions. These results suggest that lectins and niacinamide at concentrations that do not affect cell viability are reversible inhibitors of melanosome transfer.

Formation of melanocyte spheroids on the chitosan-coated surface

The search for biocompatible materials that can maintain function of melanocytes as the cellular patch is a feasible alternative for use in the autologous melanocyte transplantation for vitiligo. In this study, we demonstrated that the surface of chitosan-coated polystyrene wells supported the growth and phenotype expression of melanocytes. Depending on the seeding density and culture time, melanocytes were monolayered or spheroidal in morphology. At seeding densities above 10 x 10(3) cells/cm2, human melanocytes started to aggregate on the surface of chitosan after 2 days in culture. These aggregates grew into compact melanocyte spheroids on day 3 and more melanocyte spheroids were observed when a higher seeding density was used. Cells remained viable in the spheroids and grew into dendritic melanocytes when they were reinoculated on polystyrene wells. Conversely, the time for the formation of melanocyte spheroids needed a longer period at lower seeding density. For example, melanocytes at as low as 1.25 x 10(3) cells/cm2 did not aggregate until the 20th day of culture. In order to interpret the phenomenon further, we proposed the formation of melanocyte spheroids on the chitosan is mediated by a balance between two competing forces: the interactions of cell-chitosan and cell-cell.

Melanosome transfer to and translocation in the keratinocyte

Complexion coloration in humans is primarily regulated by the amount and type of melanin synthesized by the epidermal melanocyte. However, additional and equally contributing factors consist of (1) efficient transfer of melanin from the melanocytes to the neighboring keratinocytes and (2) distribution and degradation of the transferred melanosomes by the recipient keratinocytes. Once synthesized in the cell body of the epidermal melanocyte, pigmented melanosomes are translocated down the dendrites and captured at the dendritic tips via various cytoskeletal elements. Molecules recently identified that participate in this process consist of Rab27a, myosin-Va and melanophilin. Eventually, these peripherally localized melanosomes are transferred to keratinocytes by a presently undefined mechanism. The protease-activated receptor-2 (PAR-2) and unidentified surface lectins and glycoproteins facilitate this transfer process. Once incorporated into the keratinocytes, melanosomes are distributed individually or as clusters, aggregated towards the apical pole of the nucleus, and degraded as the keratinocytes undergo terminal differentiation and desquamation. Ultraviolet irradiation (UVR) can modulate the process of melanosome transfer from the melanocytes to the keratinocytes. UVR can upregulate expression of PAR-2 and lectin-binding receptors and increase phagocytic activity of cultured keratinocytes. Therefore, many cellular and molecular events that occur after melanogenesis contribute to skin color.

Interactions of heparin with human skin cells: Binding, location, and transdermal penetration

The development of new materials for tissue engineering of skin substitutes requires an increasing knowledge of their interactions with human skin cells. Since carbohydrate recognition is involved in numerous biologic processes, including skin regeneration, the aim of this study was to identify sugar receptors expressed at the surface of human dermic and epidermic cells. Binding of fluorescent sugar-polyhydroxyethylacrylamide derivatives was analyzed by flow cytofluorimetry on cultured human skin fibroblasts, keratinocytes, and melanocytes. We observed that these three cell types express a membrane receptor specific for GlcNAc6S. Since the polysaccharide heparin contains this sugar moiety, we further investigated the interactions of heparin with skin cells. We analyzed the in vitro cell binding and ex vivo diffusion with the Franz cell of heparin and of two other polysaccharides of similar molecular weight, dextran and chondroitin sulfate. We found evidence of the preferential binding of heparin on keratinocytes and its high transcutaneous penetration of skin. Altogether, our results describe the affinity of heparin for human skin cells and suggest it may be an excellent candidate for use in the skin delivery of drugs or cosmetics and also as an active component in engineered skin.

Stimulation of C32 and G361 melanoma cells using oleoyl acetyl glycerol and its effect on sulphur mustard cytotoxicity

Epidermal melanocytes have a higher sensitivity to sulphur mustard (HD) compared with other skin cell types. This may be due to the enzymatic production of melanin precursors exerting an additional cytotoxic effect following HD depletion of the cellular protectant, GSH. Stimulation of the protein kinase C pathway in melanocytes is known to increase melanin production in melanocytes and melanoma cell lines. In order to investigate the role of pigment synthesis in HD toxicology, cultures of an unpigmented melanoma cell line (C32) and of a pigmented melanoma line (G361) were treated with the potent diacyl glycerol analogue, oleoyl acetyl glycerol (OAG), in order to determine if protein kinase C-mediated increases in pigment production could increase sensitivity to subsequent HD exposure. Stimulation of C32 cells with OAG exerted a significant protective effect against the cytotoxic effects of HD. However, this was not due to increased melanin synthesis because this cell line cannot synthesize melanin pigments. The protective action observed is postulated to be due to modulation of protein kinase C activity. In contrast, stimulation of G361 melanoma cells with OAG resulted in an increased level of cytotoxicity upon subsequent exposure to HD. Protein kinase C controls several cellular pathways including checkpoints in the cell cycle, stalling the cell in G and promoting transition through the G2/M boundary. Given the genotoxic properties of HD, these two points in the cell cycle are important in determining the overall cytotoxic effect of HD. Control of the cell cycle by protein kinase C modulation and manipulation of melanin synthetic pathways may have therapeutic benefits.

Pigmented squamous cell carcinoma of the skin: report of two cases and review of the literature

Melanoma is the most common malignant tumor in which melanin synthesis occurs, although other nonmelanocytic tumors synthesize melanin or contain nonneoplastic melanocytes. We present two cases of infiltrating pigmented squamous cell carcinoma of the skin and review the clinical, morphologic, and ultrastructural features. Melanin was found in epithelial tumor cells as well as in macrophages and dendritic melanocytes. Interestingly, one of the neoplasms was associated with an adjacent melanocytic nevus and pigmented solar keratosis. Immunohistochemical analysis showed that neoplastic cells stained for keratin and melanin-filled dendritic cells were found to be S-100 protein and HMB45 positive. A careless examination of the immunohistochemical stains for S-100 protein and HMB45 could cause the misdiagnosis of melanoma, a neoplasm that has a more ominous outlook.

Ultraviolet rays induced expression of lectins on the surface of a squamous carcinoma keratinocyte cell line

Human keratinocytic cells from squamous carcinoma (SCL-1) present, under resting conditions, relatively low amounts of endogenous lectins (sugar-binding proteins). Upon uv irradiation, they express on their cell surface large amounts of endogenous lectin molecules able to bind neoglycoproteins bearing either alpha-L-rhamnosyl or alpha-D-glucosyl residues. A similar binding specificity was found with normal human keratinocytes under the same culture conditions. At sunlike doses, uv.A (365 nm) was more efficient than uv.B (312 nm) in the expression of such receptors on the surface of SCL-1 cells. The increased presentation of lectins by SCL-1 cells was transient and reached a maximum 4 h after irradiation. Such a specific modulation of receptor expression upon uv irradiation might be biologically significant, considering the numerous intercellular recognition phenomena in skin biology. alpha-L-Rhamnose-specific receptor on SCL-1 could not be distinguished from alpha-D-glucose-specific receptor on the basis of neoglycoproteins binding, uptake, and related inhibitions. Lectin expression was mainly detected on the cell surface, and its overexpression due to uv rays required a de novo protein synthesis process.

Animal lectins

Protein and lipid glycosylation is no longer considered as a topic whose appeal is restricted to a limited number of analytical experts perseveringly pursuing the comprehensive cataloguing of structural variants. It is in fact arousing curiosity in various areas of basic and applied bioscience. Well founded by the conspicuous coding potential of the sugar part of cellular glycoconjugates which surpasses the storage capacity of oligonucleotide- or oligopeptide-based code systems, recognition of distinct oligosaccharide ligands by endogenous receptors, i.e. lectins and sugar-binding enzymes or antibodies, is increasingly being discovered to play salient roles in animal physiology. Having inevitably started with a descriptive stage, research on animal lectins has now undubitably reached maturity. Besides listing the current categories for lectin classification and providing presentations of the individual families and their presently delineated physiological significance, this review places special emphasis on tracing common structural and functional themes which appear to reverberate in nominally separated lectin and animal categories as well as lines of research which may come to fruition for medical sciences.

Different growth rates of pigmented and white hair in the beard: differentiation vs. proliferation?

A considerable difference in growth rates of pigmented and white anagen beard hair (0.47 mm/day vs. 1.12 mm/day, on average) was measured in three individuals over a 3-year period. Nuclear differentiation in the suprabulbar region of hair shafts revealed an earlier, and more intensive, condensation of chromatin in pigmented hair than in white hair. As other differences (diameter, presence or absence of medulla) between the two hair types could be excluded, the results suggest earlier terminal differentiation of pigmented hair compared with white hair.

Role of gene expression and protein synthesis of tyrosinase, TRP-1, lamp-1, and CD63 in UVB-induced melanogenesis in human melanomas

Using melanotic cells (SK-MEL-23 and G361) and amelanotic cells (C32 and SK-MEL-24) of human melanoma, this study examined whether UV-B irradiation has a direct stimulatory effect on the expression of genes involved in melanogenesis. Our initial screening of methylthiazol tetrazolium (MTT)-formazan formation assay indicated a low dose of ultraviolet (UV)-B irradiation, 2.5 and 5.0 mJ/cm2, can metabolically stimulate these cells. Repeated exposure of UV-B at 5.0 mJ/cm2 for seven consecutive days resulted in increased tyrosinase activity and melanin synthesis in SK-MEL-23 and G361 cells, but not in C32 and SK-MEL-24 cells. On reverse-transcription-polymerase chain reaction and immunoprecipitation studies, the two melanotic cell lines exhibited upregulated expression of mRNA and antigenic epitopes of tyrosinase, tyrosinase-related protein (TRP-1; gp75/HMSA-5), and lysosomal membrane associated protein (Lamp-1). The amelanotic cell line, C32, expressed the tyrosinase gene and protein constitutively but revealed no active tyrosinase or melanin synthesis even after UV-B exposure. Another amelanotic cell line, SK-MEL-24, exhibited no expression of tyrosinase gene and protein before and after UV-B exposure and, therefore, no melanin synthesis. Both C32 and SK-MEL-24 showed no gene or protein expression of TRP-1 before or after UV exposure, but upregulation of the Lamp-1 gene and protein expressions after exposure. We conclude that tyrosinase is the key enzyme responsible for UVB-induced melanogenesis. Both TRP-1 and Lamp-1 act together in melanogenesis, TRP-1 being essential and necessary. There is no change in the expression of CD63 lysosomal membrane protein at either the mRNA or protein level.

Pigmented squamous cell carcinoma of the alveolar ridge in the oral mucosa

The clinical and morphologic features of a pigmented squamous cell carcinoma of the alveolar ridge in an 81-year-old Japanese woman are reported. The tumor was typical, well-differentiated squamous cell carcinoma but had many melanin-containing cells within it. Electron microscopy showed melanosomes in macrophages, melanocytes, and neoplastic squamous cells. Those in the neoplastic squamous cells seemed to have been excreted from the cytoplasmic processes of melanocytes.