Hepatocyte growth factor is a potent stimulator of human melanocyte DNA synthesis and growth

Steroidogenic factor-1 lineage origin of skin lesions in Carney complex syndrome

Carney complex (CNC) is a rare familial multi-neoplastic syndrome predisposing to endocrine and non-endocrine tumors due to inactivating mutations of PRKAR1A leading to perturbations of the cAMP protein kinase A (PKA) signaling pathway. Skin lesions are the most common manifestation of CNC, including lentigines, blue nevi and cutaneous myxomas, in unusual locations such as oral and genital mucosa. Unlike endocrine disorders, the pathogenesis of skin lesions remains unexplained. Here, we show that embryonic invalidation of the Prkar1a gene in Steroidogenic Factor-1-expressing cells, leads to the development of familial skin pigmentation alterations reminiscent of those in patients. Immunohistological and molecular analyses coupled with genetic monitoring of recombinant cell lineages in mouse skin, suggest that familial lentiginosis and myxomas occurs in skin areas specifically enriched in dermal melanocytes. In lentigines and blue nevi-prone areas from mutant mice and patients, Prkar1a/PRKAR1A invalidation occurs in a subset of dermal fibroblasts capable of inducing, under the influence of PKA signaling, the production of pro-melanogenic EDN3 and HGF signals. Our model strongly suggests that the origin of the typical CNC cutaneous lesions is the result of non-cell-autonomous pro-melanogenic activity of a dermal fibroblast population sharing a community of origin with SF-1 lineage.

Participation of keratinocyte- and fibroblast-derived factors in melanocyte homeostasis, the response to UV, and pigmentary disorders

Human epidermal melanocytes play a central role in sensing the environment and protecting the skin from the drastic effects of solar ultraviolet radiation and other environmental toxins or inflammatory agents. Melanocytes survive in the epidermis for decades, which subjects them to chronic environmental insults. Melanocytes have a poor self-renewal capacity; therefore, it is critical to ensure their survival with genomic stability. The function and survival of melanocytes is regulated by an elaborate network of paracrine factors synthesized mainly by epidermal keratinocytes and dermal fibroblasts. A symbiotic relationship exists between epidermal melanocytes and keratinocytes on the one hand, and between melanocytes and dermal fibroblasts on the other hand. Melanocytes protect epidermal keratinocytes and dermal fibroblasts from the damaging effects of solar radiation, and the latter cells synthesize biochemical mediators that maintain the homeostasis, and regulate the stress response of melanocytes. Disruption of the paracrine network results in pigmentary disorders, due to abnormal regulation of melanin synthesis, and compromise of melanocyte survival or genomic stability. This review provides an update of the current knowledge of keratinocyte- and fibroblast-derived paracrine factors and their contribution to melanocyte physiology, and how their abnormal production is involved in the pathogenesis of common pigmentary disorders.

The dark side of daylight: photoaging and the tumor microenvironment in melanoma progression

Continued thinning of the atmospheric ozone, which protects the earth from damaging ultraviolet radiation (UVR), will result in elevated levels of UVR reaching the earth's surface, leading to a drastic increase in the incidence of skin cancer. In addition to promoting carcinogenesis in skin cells, UVR is a potent extrinsic driver of age-related changes in the skin known as "photoaging." We are in the preliminary stages of understanding of the role of intrinsic aging in melanoma, and the tumor-permissive effects of photoaging on the skin microenvironment remain largely unexplored. In this Review, we provide an overview of the impact of UVR on the skin microenvironment, addressing changes that converge or diverge with those observed in intrinsic aging. Intrinsic and extrinsic aging promote phenotypic changes to skin cell populations that alter fundamental processes such as melanogenesis, extracellular matrix deposition, inflammation, and immune response. Given the relevance of these processes in cancer, we discuss how photoaging might render the skin microenvironment permissive to melanoma progression.

Solar ultraviolet-induced DNA damage response: Melanocytes story in transformation to environmental melanomagenesis

Exposure to sunlight is both beneficial, as it heats the planet to a comfortable temperature, and potentially harmful, since sunlight contains ultraviolet radiation (UVR), which is deemed detrimental for living organisms. Earth's ozone layer plays a vital role in blocking most of the extremely dangerous UVC; however, low frequency/energy UVR (i.e., UVB and UVA) seeps through in minute amount and reaches the Earth's surface. Both UVB and UVA are physiologically responsible for a plethora of skin ailments, including skin cancers. The UVR is readily absorbed by the genomic DNA of skin cells, causing DNA bond distortion and UV-induced DNA damage. As a defense mechanism, the DNA damage response (DDR) signaling in skin cells activates nucleotide excision repair (NER), which is responsible for the removal of UVR-induced DNA photolesions and helps maintain the genomic integrity of the cells. Failure of proper NER function leads to mutagenesis and development of skin cancers. One of the deadliest form of skin cancers is melanoma which originates upon the genetic transformation of melanocytes, melanin producing skin cells. NER is a well-studied DNA repair system in the whole skin, as a tissue, but not much is known about it in melanocytes. Therefore, this review encapsulates NER in melanocytes, with a specific focus on its functional regulators and their cross talks due to skin heterogeneity and divulging the potential knowledge gap in the field.

Establishment of Two Dimensional (2D) and Three-Dimensional (3D) Melanoma Primary Cultures as a Tool for In Vitro Drug Resistance Studies

Characteristics of melanoma cells have been deciphered by studies carried out in two dimensional cell cultures growing as adherent monolayers on the bottom of plastic flasks. Melanoma cells can be cultured with a considerable degree of success, and, depending on the further use of the cells obtained in the culture, methodologies have to be adjusted to obtain reliable results. Although there are many melanoma continuous cell lines, in vitro 2D and 3D melanoma primary cell culture may be a more useful model to investigate interactions between cancer cells and immune system, as well as the effect of cytotoxic treatments and personalized medicine in environments more similar to the physiological conditions.Here, we described a protocol which employs many strategies to obtain primary 2D and 3D melanoma cultures as a model to study cell-cell and cell-microenvironment interactions that must be considered to properly design personalized cancer treatments, as well as for testing novel anticancer drugs and drug delivery vehicles.

HGF/c-MET Signaling in Melanocytes and Melanoma

Hepatocyte growth factor (HGF)/ mesenchymal-epithelial transition factor (c-MET) signaling is involved in complex cellular programs that are important for embryonic development and tissue regeneration, but its activity is also utilized by cancer cells during tumor progression. HGF and c-MET usually mediate heterotypic cell–cell interactions, such as epithelial–mesenchymal, including tumor–stroma interactions. In the skin, dermal fibroblasts are the main source of HGF. The presence of c-MET on keratinocytes is crucial for wound healing in the skin. HGF is not released by normal melanocytes, but as melanocytes express c-MET, they are receptive to HGF, which protects them from apoptosis and stimulates their proliferation and motility. Dissimilar to melanocytes, melanoma cells not only express c-MET, but also release HGF, thus activating c-MET in an autocrine manner. Stimulation of the HGF/c-MET pathways contributes to several processes that are crucial for melanoma development, such as proliferation, survival, motility, and invasiveness, including distant metastatic niche formation. HGF might be a factor in the innate and acquired resistance of melanoma to oncoprotein-targeted drugs. It is not entirely clear whether elevated serum HGF level is associated with low progression-free survival and overall survival after treatment with targeted therapies. This review focuses on the role of HGF/c-MET signaling in melanoma with some introductory information on its function in skin and melanocytes.

Intrinsic and extrinsic regulation of human skin melanogenesis and pigmentation

In human skin, melanogenesis is a tightly regulated process. Indeed, several extracellular signals are transduced via dedicated signalling pathways and mostly converge to MITF, a transcription factor integrating upstream signalling and regulating downstream genes involved in the various inherent mechanisms modulating melanogenesis. The synthesis of melanin pigments occurs in melanocytes inside melanosomes where melanogenic enzymes (tyrosinase and related proteins) are addressed with the help of specific protein complexes. The melanosomes loaded with melanin are then transferred to keratinocytes. A more elaborate level of melanogenesis regulation comes into play via the action of non-coding RNAs (microRNAs, lncRNAs). Besides this canonical regulation, melanogenesis can also be modulated by other non-specific intrinsic pathways (hormonal environment, inflammation) and by extrinsic factors (solar irradiation such as ultraviolet irradiation, environmental pollution). We developed a bioinformatic interaction network gathering the multiple aspects of melanogenesis and skin pigmentation as a resource to better understand and study skin pigmentation biology.

Precise role of dermal fibroblasts on melanocyte pigmentation

Dermal fibroblasts are traditionally recognized as synthesizing, remodeling and depositing collagen and extracellular matrix, the structural framework for tissues, helping to bring thickness and firmness to the skin. However, the role of fibroblasts on skin pigmentation arouses concern recently. More is known about the interactions between epidermal melanocytes and keratinocytes. This review highlights the importance of fibroblast-derived melanogenic paracrine mediators in the regulation of melanocyte activities. Fibroblasts act on melanocytes directly and indirectly through neighboring cells by secreting a large number of cytokines (SCF), proteins (DKK1, sFRP, Sema7a, CCN, FAP-α) and growth factors (KGF, HGF, bFGF, NT-3, NRG-1, TGF-β) which bind to receptors and modulate intracellular signaling cascades (MAPK/ERK, cAMP/PKA, Wnt/β-catenin, PI3K/Akt) related to melanocyte functions. These factors influence the growth, the pigmentation of melanocytes via the expression of melanin-producing enzymes and melanosome transfer, as well as their dendricity, mobility and adhesive properties. Thus, fibroblasts are implicated in both skin physiological and pathological pigmentation. In order to investigate their contribution, various in vitro models have been developed, based on cellular senescence. UV exposure, a major factor implicated in pigmentary disorders, may affect the secretory crosstalk between dermal and epithelial cells. Therefore, identification of the interactions between fibroblasts and melanocytes could provide novel insights not only for the development of melanogenic agents in the clinical and cosmetic fields, but also for a better understanding of the melanocyte biology and melanogenesis regulation.

Varying effects of EGF, HGF and TGFβ on formation of invadopodia and invasiveness of melanoma cell lines of different origin

The understanding of melanoma malignancy mechanisms is essential for patient survival, because melanoma is responsible for ca. 75% of deaths related to skin cancers. Enhanced formation of invadopodia and extracellular matrix (ECM) degradation are two important drivers of cell invasion, and actin dynamics facilitate protrusive activity by providing a driving force to push through the ECM. We focused on the influence of epidermal growth factor (EGF), hepatocyte growth factor (HGF) and transforming growth factor β (TGFβ) on melanoma cell invasiveness, since they are observed in the melanoma microenvironment. All three factors stimulated invasion of A375 and WM1341D cells derived from primary tumor sites. In contrast, only EGF and HGF stimulated invasion of WM9 and Hs294T cells isolated from lymph node metastasis. Enhanced formation of invadopodia and ECM degradation underlie the increased amount of invasive cells after stimulation with the tested agents. Generally, a rise in invasive potential was accompanied by a decrease in actin polymerization state (F:G ratio). The F:G ratio remained unchanged or was even increased in cell lines from a metastasis treated with TGFβ. Our findings indicate that the effects of stimulation with EGF, HGF and TGFβ on melanoma cell invasiveness could depend on melanoma cell progression stage.

Significance of the Melanocortin 1 and Endothelin B Receptors in Melanocyte Homeostasis and Prevention of Sun-Induced Genotoxicity

The membrane bound melanocortin 1 receptor (MC1R), and the endothelin B receptor (ENDBR) are two G-protein coupled receptors that play important roles in constitutive regulation of melanocytes and their response to ultraviolet radiation (UVR), the main etiological factor for melanoma. The human MC1R is a G_s protein-coupled receptor, which is activated by its agonists α-melanocyte stimulating hormone (α-melanocortin; α-MSH) and adrenocorticotropic hormone (ACTH). The ENDBR is a G_q coupled-receptor, which is activated by Endothelin (ET)-3 during embryonic development, and ET-1 postnatally. Pigmentation and the DNA repair capacity are two major factors that determine the risk for melanoma. Activation of the MC1R by its agonists stimulates the synthesis of eumelanin, the dark brown photoprotective pigment. In vitro studies showed that α-MSH and ET-1 interact synergistically in the presence of basic fibroblast growth factor to stimulate human melanocyte proliferation and melanogenesis, and to inhibit UVR-induced apoptosis. An important function of the MC1R is reduction of oxidative stress and activation of DNA repair pathways. The human MC1R is highly polymorphic, and MC1R variants, particularly those that cause loss of function of the expressed receptor, are associated with increased melanoma risk independently of pigmentation. These variants compromise the DNA repair and antioxidant capacities of human melanocytes. Recently, activation of ENDBR by ET-1 was reported to reduce the induction and enhance the repair of UVR-induced DNA photoproducts. We conclude that α-MSH and ET-1 and their cognate receptors MC1R and ENDBR reduce the risk for melanoma by maintaining genomic stability of melanocytes via modulating the DNA damage response to solar UVR. Elucidating the response of melanocytes to UVR should improve our understanding of the process of melanomagenesis, and lead to effective melanoma chemoprevention, as well as therapeutic strategies.

Platelet-derived growth factor regulates the proliferation and differentiation of human melanocytes in a differentiation-stage-specific manner

BACKGROUND

Although many kinds of keratinocyte-derived factors are known to regulate the proliferation and differentiation of human melanocytes, it is not well defined whether dermis-derived factors work in a similar way.

OBJECTIVE

The aim of this study is to clarify whether dermal factors are involved in regulating the proliferation and differentiation of human melanocytes.

METHODS

Human epidermal melanoblasts were cultured serially in a serum-free growth medium. Platelet-derived growth factor-BB (PDGF-BB) was supplemented to the medium, and the effects on the proliferation of melanoblasts/melanocytes and the differentiation of melanocytes were studied.

RESULTS

PDGF-BB stimulated the proliferation of melanoblasts cultured in melanoblast-proliferation medium, but inhibited the proliferation of melanocytes cultured in melanocyte-proliferation medium. By contrast, PDGF-BB stimulated the differentiation, dendritogenesis, and melanogenesis of melanocytes through the stimulation of tyrosinase activity and the expressions of tyrosinase and tyrosinase-related protein-1.

CONCLUSION

These results suggest that PDGF-BB regulates the proliferation and differentiation of human melanocytes in a differentiation-stage-specific manner. PDGF-BB seems to be one of the dermal factors that regulate the proliferation and differentiation of human melanocytes.

Hepatocyte growth factor and alternative splice variants - expression, regulation and implications in osteogenesis and bone health and repair

INTRODUCTION

Bone marrow-derived mesenchymal stem cells (MSCs) can differentiate into multiple cell types, including osteoblasts, chondrocytes, and adipocytes. These pluripotent cells secrete hepatocyte growth factor (HGF), which regulates cell growth, survival, motility, migration, mitogenesis and is important for tissue development/regeneration. HGF has four splice variants, NK1, NK2, NK3, and NK4 which have varying functions and affinities for the HGF receptor, cMET. HGF promotes osteoblastic differentiation of MSCs into bone forming cells, playing a role in bone development, health and repair.

AREAS COVERED

This review will focus on the effects of HGF in osteogenesis, bone repair and bone health, including structural and functional insights into the role of HGF in the body.

EXPERT OPINION

Approximately 6.2 million Americans experience a fracture annually, with 5-10% being mal- or non-union fractures. HGF is important in priming MSCs for osteogenic differentiation in vitro and is currently being studied to assess its role during bone repair in vivo. Due to the high turnover rate of systemic HGF, non-classic modes of HGF-treatment, including naked-plasmid HGF delivery and the use of HGF splice variants (NK1 & NK2) are being studied to find safe and efficacious treatments for bone disorders, such as mal- or non-union fractures.

Environment-induced lentigines: formation of solar lentigines beyond ultraviolet radiation

There is no doubt that ultraviolet radiation (UVR) contributes to the generation of acquired lentigines in human skin, as indicated by the term solar lentigo. A growing number of recent epidemiological and mechanistic studies, however, strongly suggest that in addition to UVR, other environmental factors contribute to lentigines' formation as well. We therefore here introduce the term 'environment-induced lentigo' (EIL) to refer to acquired pigment spots of human skin. In this view point, we (i) summarize the existing evidence to support a role of environmental toxicants other than UVR in the pathogenesis of EILs, (ii) we argue that activation of aryl hydrocarbon receptor (AHR) signalling by UVR and environmental toxicants is critically involved in triggering and sustaining a crosstalk between melanocytes, keratinocytes and fibroblasts, which then causes the development and persistence of EILs in human skin, and (iii) we discuss clinical implications for the prevention and treatment of EILs resulting from this concept.

Key regulatory role of dermal fibroblasts in pigmentation as demonstrated using a reconstructed skin model: impact of photo-aging

To study cutaneous pigmentation in a physiological context, we have previously developed a functional pigmented reconstructed skin model composed of a melanocyte-containing epidermis grown on a dermal equivalent comprising living fibroblasts. The present studies, using the same model, aimed to demonstrate that dermal fibroblasts influence skin pigmentation up to the macroscopic level. The proof of principle was performed with pigmented skins differing only in the fibroblast component. First, the in vitro system was reconstructed with or without fibroblasts in order to test the global influence of the presence of this cell type. We then assessed the impact of the origin of the fibroblast strain on the degree of pigmentation using fetal versus adult fibroblasts. In both experiments, impressive variation in skin pigmentation at the macroscopic level was observed and confirmed by quantitative parameters related to skin color, melanin content and melanocyte numbers. These data confirmed the responsiveness of the model and demonstrated that dermal fibroblasts do indeed impact the degree of skin pigmentation. We then hypothesized that a physiological state associated with pigmentary alterations such as photo-aging could be linked to dermal fibroblasts modifications that accumulate over time. Pigmentation of skin reconstructed using young unexposed fibroblasts (n = 3) was compared to that of tissues containing natural photo-aged fibroblasts (n = 3) which express a senescent phenotype. A stimulation of pigmentation in the presence of the natural photo-aged fibroblasts was revealed by a significant increase in the skin color (decrease in Luminance) and an increase in both epidermal melanin content and melanogenic gene expression, thus confirming our hypothesis. Altogether, these data demonstrate that the level of pigmentation of the skin model is influenced by dermal fibroblasts and that natural photo-aged fibroblasts can contribute to the hyperpigmentation that is associated with photo-aging.

Hepatocyte Growth Factor Isoforms in Tissue Repair, Cancer, and Fibrotic Remodeling

Hepatocyte growth factor (HGF), also known as scatter factor (SF), is a pleotropic factor required for normal organ development during embryogenesis. In the adult, basal expression of HGF maintains tissue homeostasis and is up-regulated in response to tissue injury. HGF expression is necessary for the proliferation, migration, and survival of epithelial and endothelial cells involved in tissue repair in a variety of organs, including heart, lung, kidney, liver, brain, and skin. The administration of full length HGF, either as a protein or using exogenous expression methodologies, increases tissue repair in animal models of tissue injury and increases angiogenesis. Full length HGF is comprised of an N-terminal hairpin turn, four kringle domains, and a serine protease-like domain. Several naturally occurring alternatively spliced isoforms of HGF were also identified. The NK1 variant contains the N-terminal hairpin and the first kringle domain, and the NK2 variant extends through the second kringle domain. These alternatively spliced forms of HGF activate the same receptor, MET, but they differ from the full length protein in their cellular activities and their biological functions. Here, we review the species-specific expression of the HGF isoforms, their regulation, the signal transduction pathways they activate, and their biological activities.

Ethanolic extract of sharah, Plectranthus aegyptiacus, enhances healing of skin wound in rats

Sharah, Plectranthus aegyptiacus (Forssk.) C. Chr. is a common native plant in the Taif region of Saudi Arabia. An ethanolic extract of freeze dried sharah leaves was added as 10% (w/w) to an ointment base of beeswax and sesame oil. The resultant ointment was examined as a potential enhancer of wound healing. Excision wounds in the nape region of the skin were induced in sixty albino Wistar rats. Animals were allocated in 4 groups (n=15) and kept individually in clean cages. The first group served as negative untreated controls without medication; the second group was treated with ointment base (vehicle); the third group represented the positive control and was treated with a reference ointment and the fourth one served as the experimental group and received the test plant extract (as ointment). Animal groups received the respective medications for 14 successive days. Wounds were measured and photographed every 3 days till the end of the experiment (day 21) in order to determine the wound closure rate (WCR). Specimens from wounds and surrounding skin were collected from sacrificed animals for histological and molecular studies. Both morphometric (based on WCR) and histological findings showed that the healing in animals treated with the sharah plant extract was better than those in control group or vehicle-treated group and was similar to that in the group that received the reference ointment. Moreover, the molecular findings concerning the expression levels of hepatocyte growth factor (HGF) and its receptor (c-Met) displayed a reasonable healing enhancing effect of the plant extract with the expression levels of both being higher in the extract-treated group than in the control group.

Neurocutaneous melanocytosis

Neurocutaneous melanosis or neurocutaneous melanocytosis is a rare sporadic congenital disorder characterized by the presence of giant and/or multiple satellite congenital melanocytic nevi in the skin and benign melanocytic pigmentation of the leptomeninges. These two defining features were recognized more than a century ago. A third characteristic feature is proliferative nodules arising from giant nevi. The etiology is unknown, but neurocutaneous melanosis is considered a developmental disorder of melanocyte precursors from neural crest. The distinctive unique distribution of the congenital giant nevi that gives a "garment" appearance is also an expression of the neural crest. The neurological manifestations often appear in infancy.The special association of neurocutaneous melanosis with Dandy-Walker malformation complex may be explained by a common pathogenesis. Mortality in infancy and childhood is high.

Effects of fibroblast-derived factors on the proliferation and differentiation of human melanocytes in culture

BACKGROUND

Although keratinocyte-derived factors are known to promote the proliferation and differentiation of human epidermal melanocytes, it is not fully understood whether fibroblast-derived factors work in a similar way.

OBJECTIVE

The aim of this study is to clarify whether fibroblast-derived factors are involved in regulating the proliferation and differentiation of human melanocytes with or without keratinocytes using serum-free culture system.

METHODS

Human epidermal melanoblasts and melanocytes were cultured in a serum-free growth medium supplemented with fibroblast-derived factors such as keratinocyte growth factor (KGF) with or without keratinocytes, and the effects of KGF on the proliferation and differentiation of melanocytes were studied.

RESULTS

KGF stimulated the proliferation of melanoblasts in the presence of dibutyryl cAMP (DBcAMP), basic fibroblast growth factor (bFGF), transferrin (Tf), and endothelin-1 (ET-1). Although KGF stimulated the differentiation, melanogenesis, and dendritogenesis in the presence of DBcAMP, Tf, and ET-1 without keratinocytes, KGF required the presence of keratinocytes for the stimulation of melanocyte proliferation.

CONCLUSION

These results suggest that fibroblast-derived KGF stimulates the proliferation of human melanoblasts in synergy with cAMP, bFGF, Tf, and ET-1, the differentiation of melanocytes in synergy with cAMP, Tf, and ET-1, and the proliferation of melanocytes in synergy with cAMP, Tf, ET-1, and undefined keratinocyte-derived factors.

Vitiligo road map

Vitiligo is a depigmenting disorder stemming from melanocyte loss or dysfunction. It has a complex, multifaceted etiology. We constructed a "vitiligo road map," consisting of basic science, clinical, and treatment components, in order to better portray our current understanding of vitiligo pathogenesis and reflect upon novel biomarkers and therapeutic targets for future research. The melanocyte map elaborates on the molecular processes and intracellular signaling pathways initiated by various external autocrine/paracrine factors in representing normal melanocyte homeostatic functions modulating its viability, proliferation, differentiation, dendricity, migration, and melanogenic processes. This vitiligo map identifies known inducers/triggers of vitiligo onset and progression that cultivate a microenvironment for melanocyte disappearance, real or functional. This map describes the molecular mechanisms of currently utilized clinical and experimental treatments of vitiligo that facilitate repigmentation.

Integrin-linked kinase (ILK) modulates wound healing through regulation of hepatocyte growth factor (HGF)

Integrin-linked kinase (ILK) is an intracellular effector of cell-matrix interactions and regulates many cellular processes, including growth, proliferation, survival, differentiation, migration, invasion and angiogenesis. The present work analyzes the role of ILK in wound healing in adult animals using a conditional knock-out of the ILK gene generated with the tamoxifen-inducible Cre-lox system (CRE-LOX mice). Results show that ILK deficiency leads to retarded wound closure in skin. Intracellular mechanisms involved in this process were analyzed in cultured mouse embryonic fibroblast (MEF) isolated from CRE-LOX mice and revealed that wounding promotes rapid activation of phosphatidylinositol 3-kinase (PI3K) and ILK. Knockdown of ILK resulted in a retarded wound closure due to a decrease in cellular proliferation and loss of HGF protein expression during the healing process, in vitro and in vivo. Alterations in cell proliferation and wound closure in ILK-deficient MEF or mice could be rescued by exogenous administration of human HGF. These data demonstrate, for the first time, that the activation of PI3K and ILK after skin wounding are critical for HGF-dependent tissue repair and wound healing.

Comprehensive analysis of receptor tyrosine kinase activation in human melanomas reveals autocrine signaling through IGF-1R

Melanomas depend on autocrine signals for proliferation and survival; however, no systematic screen of known receptor tyrosine kinases (RTKs) has been performed to identify which autocrine signaling pathways are activated in melanoma. Here, we performed a comprehensive analysis of 42 RTKs in six individual human melanoma tumor specimens as well as 17 melanoma cell lines, some of which were derived from the tumor specimens. We identified five RTKs that were active in almost every one of the melanoma tissue specimens and cell lines, including two previously unreported receptors, insulin-like growth factor receptor 1 (IGF-1R) and macrophage-stimulating protein receptor (MSPR), in addition to three receptors (vascular endothelial growth factor receptor, fibroblast growth factor receptor, and hepatocyte growth factor receptor) known to be autocrine activated in melanoma. We show, by quantitative real time PCR, that all melanoma cell lines expressed genes for the RTK ligands such as HGF, IGF-1, and MSP. Addition of antibodies to either IGF-1 or HGF, but not to MSP, to the culture medium blocked melanoma cell proliferation, and even caused net loss of melanoma cells. Antibody addition deactivated IGF-1R and hepatocyte growth factor receptors, as well as mitogen-activated protein kinase signaling. Thus, IGF-1 is a new growth factor for autocrine driven proliferation of human melanoma in vitro. Our results suggest that IGF-1-IGF-1R autocrine pathway in melanoma is a possible target for therapy in human melanomas.

UV-B radiation induces macrophage migration inhibitory factor-mediated melanogenesis through activation of protease-activated receptor-2 and stem cell factor in keratinocytes

UV radiation indirectly regulates melanogenesis in melanocytes through a paracrine regulatory mechanism involving keratinocytes. Protease-activated receptor (PAR)-2 activation induces melanosome transfer by increasing phagocytosis of melanosomes by keratinocytes. This study demonstrated that macrophage migration inhibitory factor (MIF) stimulated PAR-2 expression in human keratinocytes. In addition, we showed that MIF stimulated stem cell factor (SCF) release in keratinocytes; however, MIF had no effect on the release of endothelin-1 or prostaglandin E2 in keratinocytes. In addition, MIF had no direct effect on melanin and tyrosinase synthesis in cultured human melanocytes. The effect of MIF on melanogenesis was also examined using a three-dimensional reconstituted human epidermal culture model, which is a novel, commercially available, cultured human epidermis containing functional melanocytes. Migration inhibitory factor induced an increase in melanin content in the epidermis after a 9-day culture period. Moreover, melanin synthesis induced by UV-B stimulation was significantly down-regulated by anti-MIF antibody treatment. An in vivo study showed that the back skin of MIF transgenic mice had a higher melanin content than that of wild-type mice after 12 weeks of UV-B exposure. Therefore, MIF-mediated melanogenesis occurs mainly through the activation of PAR-2 and SCF expression in keratinocytes after exposure to UV-B radiation.

Role of fibroblast-derived growth factors in regulating hyperpigmentation of solar lentigo

BACKGROUND

Cutaneous pigmentation is regulated by a complex melanogenic network in which both keratinocytes and fibroblasts synthesize growth factors and cytokines. Solar lentigo (SL) is characterized by hyperpigmented lesions occurring on photodamaged skin areas. Despite the association of SL to ultraviolet (UV) exposure, the mechanisms underlying the development of these spots are not completely defined.

OBJECTIVES

To analyse the involvement of the fibroblast-derived growth factors, hepatocyte growth factor (HGF), keratinocyte growth factor (KGF) and stem cell factor (SCF) in SL hyperpigmentation; to evaluate whether the photoageing process occurring in fibroblasts could be responsible for the altered expression of these cytokines; and to investigate a new possible role of KGF in regulating pigmentation through the specific induction of melanogenic cytokines by keratinocytes.

METHODS

We performed immunohistochemical analysis of HGF, KGF and SCF on SL biopsies. We analysed the mRNA expression of these cytokines using an in vitro model of photoageing induced on fibroblasts. Finally, we evaluated the effects of KGF on the expression of melanogenic cytokines at the mRNA and protein levels on keratinocytes.

RESULTS

We found positive staining for HGF, KGF and SCF in the upper dermis of SL lesions and a significant induction of the three cytokines in photoaged fibroblasts. We also demonstrated the contribution of KGF to pigmentation, showing its ability specifically to modulate the expression of SCF in keratinocytes.

CONCLUSIONS

Fibroblasts may be persistently activated by UV exposure to release melanogenic growth factors; this inducible cytokine network acts both directly and indirectly through keratinocytes and may contribute to the hyperpigmentation of SL.

Acquired bilateral naevus of Ota-like macules: an immunohistological analysis of dermal melanogenic paracrine cytokine networks

BACKGROUND

Acquired bilateral naevus of Ota-like macules (ABNOM) is similar to melasma with regard to their clinical features, including female predominance, acquired onset, and predominant involvement of the malar area. The similar clinical features suggest the possibility of a shared pathogenesis. Dermal factors including vascularity and melanogenic paracrine networks such as the stem cell factor (SCF)/c-kit pathway have recently been suggested to play an important role in the pathogenesis of melasma. However, the role of dermal factors in ABNOM remains unknown.

OBJECTIVES

To provide a novel view on the pathogenesis of ABNOM, we studied the expression of melanogenic paracrine cytokines such as SCF/c-kit, and assessed dermal vascularity.

METHODS

Thirty-seven patients with ABNOM and 20 patients with melasma were enrolled in this study. Skin samples were obtained from lesional and perilesional normal skin. Immunohistochemistry was performed.

RESULTS

Solar elastosis was slightly more intense in the lesional skin of ABNOM. In contrast to dermal pigmentation and melanocytes, the amounts of epidermal pigmentation and melanocytes were not increased in the lesional skin of patients with ABNOM. The expression of dermal SCF and c-kit was increased; however, the expression of epidermal SCF and c-kit and dermal factor VIII-related antigen was not increased in the lesional skin of ABNOM.

CONCLUSIONS

These results suggest that the increased expression of the SCF/c-kit pathway between dermal fibroblasts and dermal melanocytes may play an important role in the pathogenesis of ABNOM.

Growth factor signaling pathways as targets for prevention of epithelial carcinogenesis

Growth factor receptor (GFR) signaling controls epithelial cell growth by responding to various endogenous or exogenous stimuli and subsequently activating downstream signaling pathways including Stat3, PI3K/Akt/mTOR, MAPK, and c-Src. Environmental chemical toxicants and UVB irradiation cause enhanced and prolonged activation of GFR signaling and downstream pathways that contributes to epithelial cancer development including skin cancer. Recent studies, especially those with tissue-specific transgenic mouse models, have demonstrated that GFRs and their downstream signaling pathways contribute to all three stages of epithelial carcinogenesis by regulating a wide variety of biological functions including proliferation, apoptosis, angiogenesis, cell adhesion, and migration. Inhibiting these signaling pathways early in the carcinogenic process results in reduced cell proliferation and survival, leading to decreased tumor formation. Collectively, these studies suggest that GFR signaling and subsequent downstream signaling pathways are potential targets for the prevention of epithelial cancers including skin cancer.

Life cycle of human melanocytes is regulated by endothelin-1 and stem cell factor in synergy with cyclic AMP and basic fibroblast growth factor

BACKGROUND

Although the function of human melanocytes is well characterized at cellular and molecular levels, the mechanism of the regulation of the life cycle (proliferation, differentiation, and cell death) of human melanocytes is not fully understood.

OBJECTIVE

This study aims to clarify what factors are involved in regulating the life cycle of human melanocytes using serum-free culture system.

METHODS

Human epidermal melanocytes were cultured in a serum-free growth medium supplemented with several kinds of growth factors, cytokines, and hormones and the effects of these factors on the life cycle of melanocytes were investigated in detail.

RESULTS

Of the factors tested, endothelin-1 (ET-1) stimulated the proliferation of melanoblasts and melanocytes in the presence of cyclic AMP (cAMP)-elevating factor such as dibutyryl cAMP (DBcAMP) and of basic fibroblast growth factor (bFGF). ET-1 also stimulated the proliferation and differentiation of human melanocytes in the presence of DBcAMP. Moreover, stem cell factor (SCF) stimulated the proliferation of melanoblasts and melanocytes synergistically with ET-1. The removal of ET-1 and SCF from the culture medium greatly inhibited the proliferation of melanocytes followed by apoptotic cell death.

CONCLUSION

These results suggest that the life cycle of human melanocytes is regulated by ET-1 and SCF in synergy with cAMP and bFGF.

Epistatic connections between microphthalmia-associated transcription factor and endothelin signaling in Waardenburg syndrome and other pigmentary disorders

Waardenburg syndrome (WS) is an inherited sensorineural deafness condition in humans caused by melanocyte deficiencies in the inner ear and forelock. Mutation of microphthalmia-associated transcription factor (MITF) is known to produce WS type IIA whereas mutations of either endothelin (EDN) or its receptor endothelin receptor B (EDNRB) produce WS type IV. However, a link between MITF haploinsufficiency and EDN signaling has not yet been established. Here we demonstrate mechanistic connections between EDN and MITF and their functional importance in melanocytes. Addition of EDN to cultured human melanocytes stimulated the phosphorylation of MITF in an EDNRB-dependent manner, which was completely abolished by mitogen-activated protein kinase kinase inhibition. The expression of melanocyte-specific MITF mRNA transcripts was markedly augmented after incubation with EDN1 and was followed by increased expression of MITF protein. Up-regulated expression of MITF was found to be mediated via both the mitogen-activated protein kinase-p90 ribosomal S6 kinase-cAMP response element-binding protein (CREB) and cAMP-protein kinase A-CREB pathways. In addition, EDNRB expression itself was seen to be dependent on MITF. The functional importance of these connections is illustrated by the ability of EDN to stimulate expression of melanocytic pigmentation and proliferation markers in an MITF-dependent fashion. Collectively these data provide mechanistic and epistatic links between MITF and EDN/EDNRB, critical melanocytic survival factors and WS genes.

[4-t-butylphenyl]-N-(4-imidazol-1-yl phenyl)sulfonamide (ISCK03) inhibits SCF/c-kit signaling in 501mel human melanoma cells and abolishes melanin production in mice and brownish guinea pigs

It is well known that c-kit is related to pigmentation as well as to the oncology target protein. The objective of this study was to discover a skin-whitening agent that regulates c-kit activity. We have developed a high-throughput screening system using recombinant human c-kit protein. Approximately 10,000 synthetic compounds were screened for their effect on c-kit activity. Phenyl-imidazole sulfonamide derivatives showed inhibitory activity on c-kit phosphorylation in vitro. The effects of one derivative, [4-t-butylphenyl]-N-(4-imidazol-1-yl phenyl)sulfonamide (ISCK03), on stem-cell factor (SCF)/c-kit cellular signaling in 501mel human melanoma cells were examined further. Pretreatment of 501mel cells with ISCK03 inhibited SCF-induced c-kit phosphorylation dose dependently. ISCK03 also inhibited p44/42 ERK mitogen-activated protein kinase (MAPK) phosphorylation, which is known to be involved in SCF/c-kit downstream signaling. However ISCK03 did not inhibit hepatocyte growth factor (HGF)-induced phosphorylation of p44/42 ERK proteins. To determine the in vivo potency of ISCK03, it was orally administered to depilated C57BL/6 mice. Interestingly, oral administration of ISCK03 induced the dose-dependent depigmentation of newly regrown hair, and this was reversed with cessation of ISCK03 treatment. Finally, to investigate whether the inhibitory effect of ISCK03 on SCF/c-kit signaling abolished UV-induced pigmentation, ISCK03 was applied to UV-induced pigmented spots on brownish guinea pig skin. The topical application of ISCK03 promoted the depigmentation of UV-induced hyperpigmented spots. Fontana-Masson staining analysis showed epidermal melanin was diminished in spots treated with ISCK03. These results indicate that phenyl-imidazole sulfonamide derivatives are potent c-kit inhibitors and might be used as skin-whitening agents.

Up-regulation of MET Expression by α-Melanocyte-stimulating Hormone and MITF Allows Hepatocyte Growth Factor to Protect Melanocytes and Melanoma Cells from Apoptosis

The MET proto-oncogene encodes for the hepatocyte growth factor (HGF) receptor, a plasma membrane tyrosine kinase that is involved in melanocyte growth and melanoma development. In mouse melanoma cells, Met expression is increased by alphaMSH via the activation of the cAMP pathway. However, the mechanism by which cAMP regulates MET and the biological consequences of this increase were not known. In the present report, we show that alphaMSH regulates MET expression in both human melanocytes and mouse melanoma cells through a transcriptional mechanism that requires MITF. Furthermore, the adenovirus driven expression of MITF is sufficient to increase MET in melanoma cells. Functional analysis of the MET promoter allows us to identify an E-box motif conserved in both human and mouse promoter that mediates the effect of MITF. Interestingly, up-regulation of MET expression by cAMP leads to an exacerbated HGF signaling and allows HGF to protect melanocytes and melanoma cells from apoptosis. Thus, physiological stimuli or pathological events that would induce MITF expression may lead to increased MET expression thereby favoring melanoma survival. These observations strengthen the roles of MITF and MET in melanoma development.

Effect of hepatocyte growth factor on long term hematopoiesis of human progenitor cells in transgenic-sever combined immunodeficiency mice

Hepatocyte growth factor (HGF), which was originally isolated as a liver generating factor, enhances hematopoiesis. To study the effect of HGF on hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs), we generated severe combined immunodeficiency (SCID) mice producing human (h) HGF and/or stem cell factor (SCF) by transferring the relevant genes to fertilized eggs, and then transplanted hematopoietic progenitors from human cord blood into the transgenic (Tg) SCID mice. Six months after transplantation, a significantly larger number of human cells were found in the Tg SCID mice than in non-Tg controls. Characteristically, the recipient SCID mice producing h HGF (HGF-SCID) had a significantly increased number of h CD41+ cells, whereas the SCF-SCID recipients had more CD11b+ cells. Significantly large numbers of CD34+ progenitors were found in the SCID mice transferred with both h HGF and h SCF genes (HGF/SCF-SCID) when compared with HGF-SCID or SCF-SCID mice. These results imply that HGF supports the differentiation of progenitors in megakaryocyte lineage, whereas SCF supports that in myeloid lineage. The results also imply that HGF acts on HSCs/HPCs as a synergistic proliferative factor combined with SCF. We have demonstrated the advantage of the human cytokine-producing animal in the maintenance of human HSCs.

Human skin pigmentation: melanocytes modulate skin color in response to stress

All organisms, from simple invertebrates to complex human beings, exist in different colors and patterns, which arise from the unique distribution of pigments throughout the body. Pigmentation is highly heritable, being regulated by genetic, environmental, and endocrine factors that modulate the amount, type, and distribution of melanins in the skin, hair, and eyes. In addition to its roles in camouflage, heat regulation, and cosmetic variation, melanin protects against UV radiation and thus is an important defense system in human skin against harmful factors. Being the largest organ of the body that is always under the influence of internal and external factors, the skin often reacts to those agents by modifying the constitutive pigmentation pattern. The focus of this review is to provide an updated overview of important physiological and biological factors that increase pigmentation and the mechanisms by which they do so. We consider endocrine factors that induce temporary (e.g., during pregnancy) or permanent (e.g., during aging) changes in skin color, environmental factors (e.g., UV), certain drugs, and chemical compounds, etc. Understanding the mechanisms by which different factors and compounds induce melanogenesis is of great interest pharmaceutically (as therapy for pigmentary diseases) and cosmeceutically (e.g., to design tanning products with potential to reduce skin cancer risk).

Hepatocyte growth factor and inducible nitric oxide synthase are involved in multidrug resistance-induced angiogenesis in hepatocellular carcinoma cell lines

Based on literature, it is possible to hypothesize that multidrug resistance (MDR) and angiogenic phenotypes are linked to each other in human liver cancer cells. Our goal is to assess whether MDR cells trigger angiogenesis and to study the possible molecular mechanisms involved. Conditioned medium from parental drug-sensitive P5 cells (P5-CM) and MDR-positive P1(0.5) cells [P1(0.5)-CM] stimulated human umbilical vein endothelial cells (HUVEC) survival, proliferation, migration, and microtubular structure formation, but P1(0.5)-CM had a significantly greater effect than P5-CM. Cell implants were done in the rabbit avascular cornea to measure angiogenesis in vivo: P1(0.5) cells induced an important neovascular response in rabbit cornea after 1 week, whereas P5 cells had no effect. P1(0.5) and P5 cells produced vascular endothelial growth factor, but only P1(0.5) secreted hepatocyte growth factor (HGF) into the medium, and small interfering RNA specific for MDR1 clearly reduced HGF production in P1(0.5) cells. The transcription factor Ets-1 and the HGF receptor c-Met were up-regulated in P1(0.5) cells and in HUVEC cultured in P1(0.5)-CM. Inducible nitric oxide synthase (iNOS) seemed to play a major role in the proangiogenic effect of P1(0.5), and its inhibition by 1400W blunted the capacity of P1(0.5) cells to stimulate HUVEC proliferation, migration, and Ets-1 expression. In conclusion, these data show that development of MDR and angiogenic phenotypes are linked to each other in MDR cells. HGF production, Ets-1 and c-Met up-regulation, and iNOS expression can be part of the molecular mechanisms that enhance the angiogenic activity of the MDR-positive hepatocellular carcinoma cell line.

Correlation between age and the secretions of melanocyte-stimulating cytokines in cultured keratinocytes and fibroblasts

BACKGROUND

The majority of skin changes associated with ageing are caused by photoageing and reflect cumulative sun exposure. Although the actinic damage plays a major role in skin pigmentation, it is also important to examine the effects of chronological cellular ageing on the pigmentation. The chief cellular components of the skin other than melanocytes are keratinocytes and fibroblasts, and the influences of age-related changes in those cells on skin pigmentation have not been elucidated.

OBJECTIVE

To clarify the effects of cellular ageing of keratinocytes and fibroblasts on age-related skin pigmentation.

METHODS

Using ELISA analysis, we measured the level of melanogenic cytokines secreted by cultured keratinocytes and fibroblasts derived from skin of various chronological ages. We also compared the cytokine secretion by cultured keratinocytes between the second and fifth cultures.

RESULTS

There was no correlation between age and hepatocyte growth factor (HGF), stem cell factor (SCF), and basic fibroblast growth factor (bFGF) secretion by fibroblasts. On the other hand, a significant positive correlation existed between age and interleukin ((IL)-1alpha secretion (R2=0.50, P=0.002), and a relatively weak correlation existed between age and endothelin-1 (ET-1) secretion (R2=0.17, P=0.051, not significant). The IL-1alpha secretion by keratinocytes was significantly increased in the fifth cultures compared with the second cultures (P<0.005).

CONCLUSIONS

These findings suggest that IL-1alpha secretion increases as cells grow older, and the increased secretion of IL-1alpha by aged keratinocytes may stimulate HGF production in dermal fibroblasts paracrinely and ET-1 production in keratinocytes autocrinely, which stimulates melanocyte proliferation and induces an increase of tyrosinase activity in melanocytes. Because IL-1alpha is a primary mediator that responds to inflammation and injury, the transcription of genes involved in skin inflammation may be persistently induced in the aged skin. Thus the increased secretion of IL-1alpha by aged keratinocytes in the aged skin may play a role in the accentuated cutaneous pigmentation and other skin ageing.

Epidermal hyperpigmentation in non-syndromic solitary cafe-au-lait macules may be associated with increased secretion of endothelin-1 by lesional keratinocytes

To clarify the mechanism of accentuated melanisation in non-syndromic solitary cafe-au-lait macules we used an enzyme-linked immunosorbent assay (ELISA) to measure the concentration of melanogenic cytokines secreted by cultured keratinocytes and fibroblasts derived from the skins of the macules and compared them with those derived from normal people. Endothelin-1 (ET-1) was significantly increased in cultured keratinocytes in the macules compared with the normals. In contrast, the secretion of other cytokines secreted by keratinocytes or fibroblasts did not differ between the groups. It may be that the increased secretion of ET-1 by epidermal keratinocytes has a role in the accentuated epidermal melanisation seen in non-syndromic macules.

Hepatocyte growth factor delivered by ultrasound-mediated destruction of microbubbles induces proliferation of cardiomyocytes and amelioration of left ventricular contractile function in Doxorubicin-induced cardiomyopathy

At present, there is no curative strategy for advanced cardiomyopathy except for cardiac transplantation, which is not easily performed, mainly due to a shortage of donors. It has been reported that myocardial progenitor cells exist even in the postnatal heart, suggesting that myocardial progenitor cells could proliferate under some situations and might improve cardiac function in cardiomyopathy-induced hearts. In this study, recombinant human hepatocyte growth factor (rhHGF) was delivered using ultrasound-mediated destruction of microbubbles (UMDM) into the cardiomyopathy-induced heart by doxorubicin (20 mg/kg). Intravenous injection of rhHGF (IV-rhHGF) alone or UMDM alone failed to improve the morphology or the function of the cardiomyopathy-induced heart, but (IV-rhHGF + UMDM) treatment significantly improved the heart morphologically and functionally, and repetitive treatments of (IV-rhHGF + UMDM) enhanced the effects. The number of bromodeoxy-uridine-positive cardiomyocytes significantly increased in the (IV-rhHGF + UMDM)-treated hearts compared with the untreated hearts. Moreover, Sca-1+ myocardial progenitor cells express c-Met, a receptor for HGF. These results suggest that (IV-rhHGF + UMDM) treatment could morphologically and functionally improve the heart in the case of doxorubicin-induced cardiomyopathy through the proliferation of the myocardial progenitor cells.

Suppression of Progressive Loss of Coat Color in Microphthalmia-Vitiligo Mutant Mice

The coat color of C57BL/6-Mitfvit/vit mice whitens with age, because of a one-nucleotide mutation in the DNA-binding region of the microphthalmia-associated transcription factor (MITF), which plays an important role in melanocyte growth and differentiation. To investigate the signals regulating MITF function, we prepared transgenic mice expressing three of the external signals that are important for melanocyte development, i.e., hepatocyte growth factor (HGF), stem cell factor (SCF), and endothelin-3 (ET3), and crossed these mice with Mitfvit/vit mice. We found that the age-dependent coat color whitening of the Mitfvit/vit mice was completely suppressed by the overexpression of HGF or SCF in the skin, but not by that of ET3. Moreover, HGF, but not ET3, promoted the proliferation of Mitfvit/vit mice-derived melanocytes in culture. These results suggest that the signals from exogenous HGF and SCF rescued the mi-vitiligo mutation and also that ET3 does not stimulate the common signal transduction pathway for MITF activation shared by HGF and SCF.

Serum levels of hepatocyte growth factor in patients with breast cancer

OBJECTIVE

Hepatocyte growth factor (HGF) has been reported the cause of many biological events, including cell proliferation, movement, invasiveness, morphogenesis, and angiogenesis. Elevated hepatocyte growth factor content in tumor tissue was reported to predict a more aggressive biology in non-small cell lung cancer patients. However, there is still limited knowledge about the role of HGF in breast cancer. This study was designed with the aim to elucidate the possible relationship between the preoperative circulating soluble HGF and breast cancer.

MATERIALS AND METHODS

One hundred twenty-four consecutive patients with invasive breast cancer undergoing surgery were prospectively included and evaluated. Venous blood samples were collected before the surgery. Sera were obtained by centrifugation and stored at -70 degrees C until assayed. The control group consisted of 35 patients with benign breast tumor (20 with fibrocystic disease and 15 with fibroadenoma). Serum concentrations of soluble HGF were measured by the quantitative sandwich enzyme immunoassay technique. The data on primary tumor staging, age, estrogen receptor status, lymph node status, distant metastases status, histologic grading, and tumor-node-metastasis (TNM) staging were reviewed and recorded.

RESULTS

The mean value of serum soluble HGF in patients with invasive breast cancer was 529.05 +/- 123.33 pg/mL and that of control group was 343.00+/- 31.03 pg/mL and the difference was significant (P < 0.001). Furthermore, there were significantly higher serum levels of soluble HGF in patients with negative estrogen receptor (P = 0.035), in patients with poorer differentiated tumor (P < 0.001), in patients with more advanced primary tumor staging (P < 0.001), in patients with more advanced lymph node status (P < 0.001), in patients with distant metastases (P < 0.001), and in patients with more advanced TNM staging (P < 0.001). In multivariate analysis by the multiple linear regression method, TNM staging (P < 0.001) seemed an independent factor regarding the significant higher serum levels of soluble HGF.

CONCLUSION

Patients with more advanced TNM staging were shown to have higher serum soluble HGF. Thus, preoperative serum soluble HGF levels might reflect the severity of invasive breast cancer and deserve further evaluation.

Role of keratinocyte-derived factors involved in regulating the proliferation and differentiation of mammalian epidermal melanocytes

Melanocytes characterized by the activities of tyrosinase, tyrosinase-related protein (TRP)-1 and TRP-2 as well as by melanosomes and dendrites are located mainly in the epidermis, dermis and hair bulb of the mammalian skin. Melanocytes differentiate from melanoblasts, undifferentiated precursors, derived from embryonic neural crest cells. Because hair bulb melanocytes are derived from epidermal melanoblasts and melanocytes, the mechanism of the regulation of the proliferation and differentiation of epidermal melanocytes should be clarified. The regulation by the tissue environment, especially by keratinocytes is indispensable in addition to the regulation by genetic factors in melanocytes. Recent advances in the techniques of tissue culture and biochemistry have enabled us to clarify factors derived from keratinocytes. Alpha-melanocyte-stimulating hormone, adrenocorticotrophic hormone, basic fibroblast growth factor, nerve growth factor, endothelins, granulocyte-macrophage colony-stimulating factor, steel factor, leukemia inhibitory factor and hepatocyte growth factor have been suggested to be the keratinocyte-derived factors and to regulate the proliferation and/or differentiation of mammalian epidermal melanocytes. Numerous factors may be produced in and released from keratinocytes and be involved in regulating the proliferation and differentiation of mammalian epidermal melanocytes through receptor-mediated signaling pathways.

Autocrine and paracrine regulation of melanocytes in human skin and in pigmentary disorders

Recently melanogenic paracrine or autocrine cytokine networks have been discovered in vitro between melanocytes and other types of skin cells. These include endothelin (ET)-1, granulocyte macrophage colony stimulating factor, membrane-type stem cell factor (SCF) and growth-related oncogene-alpha for interactions between keratinocytes and melanocytes, and hepatocyte growth factor and soluble type SCF for interactions between fibroblasts and melanocytes. These networks are also associated with corresponding receptors expressed on melanocytes, including ET B receptor and the SCF receptor, c-KIT. Consistent with in vitro findings on the melanogenic paracrine or autocrine cytokine networks, we have found that the up- or down-regulation of such networks is intrinsically involved in vivo in the stimulation of melanocyte functions in several epidermal hyper- or hypo-pigmentary disorders. These are ET-1/ET B receptor as well as membrane type SCF/c-KIT for ultraviolet B-melanosis, granulocyte macrophage colony stimulating factor for ultraviolet A-melanosis, ET-1/ET B receptor as well as membrane type SCF for lentigo senilis, growth related oncogene-alpha for Riehl's melanosis, sphingosylphosphorylcholine for hyperpigmentation in atopic dermatitis, ET-1 for seborrhoeic keratosis, soluble type SCF as well as hepatocyte growth factor for dermatofibroma and café-au-lait macules, and c-KIT for vitiligo vulgaris. These unveiled regulatory mechanisms involved in the abnormal up- or down-regulated levels of lesional melanocyte function provide new insights into therapeutic tools utilizing blockage of responsible cytokine networks.

Sphingosine kinase activation regulates hepatocyte growth factor induced migration of endothelial cells

Hepatocyte growth factor (HGF)-induced migration of endothelial cells is critical for angiogenesis. Sphingosine kinase (SPK) is a key enzyme catalyzing the formation of sphingosine-1-phosphate (S1P), a lipid messenger that is implicated in the regulation of a wide variety of important cellular events through both intracellular and extracellular mechanisms. The aim of this study was to investigate whether activation of SPK is involved in the migration of endothelial cells induced by HGF. The biological functions of HGF are mediated through the activation of its high-affinity tyrosine kinase receptor, c-met protooncogene. In the present study, Treatment of ECV304 endothelial cells with HGF resulted in tyrosine phosphorylation of c-Met and activation of SPK in a concentration-dependent manner. Either Ly294002 or PD98059, specific inhibitor of the PI3K and ERK/MAPK pathways, respectively, blocked the HGF-induced activation of SPK. HGF stimulation significantly increased intracellular S1P level, but no detectable secretion of S1P into the cell culture medium was observed. Treatment of ECV304 cells with pertussis toxin (PTX) has no effect on the HGF-induced migration, indicating extracellular S1P is dispensable for this process. Overexpression of wild-type SPK gene in ECV 304 cells increased the intracellular S1P and enhanced the HGF-induced migration, whereas inhibition of cellular SPK activity by N,N-dimethylsphingosine (DMS), a potent inhibitor of SPK, or by expression of a dominant-negative SPK (DN-SK) blocked the HGF-induced migration of ECV 304 cells. It is suggested that PI3K and ERK/MAPK mediated the activation of SPK and would be involved in the HGF-induced migration of endothelial cells. These results elucidate a novel mechanism by which intracellularly generated S1P mediates signaling from HGF/c-Met to the endothelial cell migration.

Hepatocyte growth factor controls the proliferation of cultured epidermal melanoblasts and melanocytes from newborn mice

Mouse epidermal melanoblasts and melanocytes preferentially proliferated from disaggregated epidermal cell suspensions derived from newborn mouse skin in a serum-free melanocyte-proliferation medium (MDMD) and melanoblast-proliferation medium (MDMDF) supplemented with dibutyryl adenosine 3':5'-cyclic monophosphate (DBcAMP) and/or basic fibroblast growth factor (bFGF). Pure cultured primary melanoblasts and melanocytes were further cultured with MDMD/MDMDF supplemented with hepatocyte growth factor (HGF) from 14 days (keratinocyte depletion). The HGF increased the number of melanoblasts and melanocytes, but not the percentage of differentiated melanocytes in the melanoblast-melanocyte population in the absence of keratinocytes. Flow cytometry analysis showed that melanoblasts and melanocytes in the S and/or G2/M phases of the cell cycle were increased by the treatment with HGF. Moreover, an anti-HGF antibody supplemented to MDMD/MDMDF from the initiation of the primary culture (in the presence of keratinocytes) inhibited the proliferation of melanoblasts and melanocytes, but not the differentiation of melanocytes. These results suggest that HGF is a keratinocyte-derived factor involved in regulating the proliferation of epidermal melanoblasts and melanocytes from newborn mice in cooperation with cAMP elevators and/or bFGF.