Endothelin-1 as a New Melanogen: Coordinated Expression of Its Gene and the Tyrosinase Gene in UVB-Exposed Human Epidermis

Abstract

We previously demonstrated that human keratinocytes produce and secrete endothelins (ET), which can be strong mitogens for human melanocytes. Ultraviolet B (UVB) exposure highly stimulated the paracrine linkage of endothelins between keratinocytes and melanocytes, indicating that they are keratinocyte-derived intrinsic mitogens in UVB-induced pigmentation. In this study, the role of ET-1 as a melanogen in UVB melanogenesis was investigated in vitro and in vivo. In the conditioned medium of keratinocytes exposed to UVB, melanin synthesis by human melanocytes, as measured by 14C-thiouracil incorporation, was significantly accentuated. This stimulatory effect was reduced by anti-ET-1 to the level of that in the non-UVB-exposed control, suggesting an essential role of ET-1 as an intrinsic melanogen in UVB-induced melanogenesis. In a parallel study, the addition of 10 nM ET-1 induced an increase in tyrosinase activity in cultured human melanocytes and was accompanied by elevated levels of tyrosinase and tyrosinase-related protein-1 mRNA expression as shown by Northern blotting. Reverse transcription-polymerase chain reaction of RNA isolated from the epidermis of human skin exposed to UVB revealed that, whereas in non-exposed sites ET-1, IL-1 alpha, and tyrosinase mRNA signals were scarcely detected, UVB-irradiation, with a dose of twice the minimal erythema dose, caused a significant increase in the expressions of the three genes 5 d after irradiation. These findings suggest that ET-1 is an important mediator for UVB-induced pigmentation in the epidermis in vivo.

Inhibitory Mechanism of an Extract of Althaea officinalis L. on Endothelin-1-Induced Melanocyte Activation.

“…DAG has been reported to activate MAPK via protein kinase C. The action of ET-1 is transmitted to stimulate cell proliferation mainly via MAPK. 9,20) The present study showed that the extract of A. officinalis did not affect the intracellular signal transduction pathway located upstream of calcium mobilization, i.e., the binding of ET-1 to the ET B R on NHMC or the production of IP 3 . In contrast, the ET-1-induced activation of MAPK was inhibited by the extract.…”

“…However, it may be very difficult for such agents to reach the melanosomes 22) in which tyrosinase acts at a sufficient dose to be effective. On the other hand, since ET-1 has been reported to promote transcription of tyrosinase, 3) this extract might inhibit tyrosinase function by inhibiting its activation The extract at concentrations of 0.01-0.5% was added to NHKC and the cells were cultured for 2 d. The amount of ET-1 secreted into the culture medium was analyzed by ELISA, as described in Materials and Methods. The values reported are meansϮS.E.M.…”

“…The supernatants were subjected to IP 3 assay using an IP 3 assay kit (Amersham Pharmacia Biotech, Buckinghamshire, United Kingdom). The content of IP 3 in each sample was quantitatively determined from a calibration curve established using the binding protein specific for IP 3 3 . Extraction of Cellular Proteins Cells were incubated with ET-1 in 6-well culture trays, then solubilized in 500 ml of ice-cold RIPA (radioimmunoprecipitation) buffer containing 50 mM Tris-HCl (pH 7.5), 150 mM NaCl, 1% Nonidet P-40, 0.25% Na deoxycholate, 1 mM EDTA, 50 mM NaF, 1 mM sodium orthovanadate, 50 mM phenylmethylsulfonyl fluoride, and 1 mg/ml aprotinin.…”

A Phase II study of bosentan, a dual endothelin receptor antagonist, as monotherapy in patients with stage IV metastatic melanoma

“…Activation of ET B receptors by ET-1 promotes proliferation of melanogenic precursor cells and inhibits their differentiation, two characteristic features of melanoma genesis [11]. Furthermore, ET-1 mediates ultraviolet light-induced melanin synthesis in human melanocytes [12]. In melanocytes and melanoma cells, ET-1 increases the expression of the melanoma invasion promoter MCAM (melanoma cell adhesion molecule) while decreasing expression of the melanoma invasion suppressor E-cadherin [13,14].…”

UV-B Radiation Induces Macrophage Migration Inhibitory Factor–Mediated Melanogenesis through Activation of Protease-Activated Receptor-2 and Stem Cell Factor in Keratinocytes

“…A few of these cytokines are known mitogens for human melanocytes, including basic fibroblast growth factor, SCF, granulocyte-macrophage colony-stimulating factor, hepatocyte growth factor, and ET-1. [42][43][44][45][46] Several cytokines, such as IL-1␣ and TNF-␣, significantly increase the expression of SCF protein by cultured human keratinocytes. 5 Accordingly, MIF may induce PAR-2 to mediate cutaneous pigmentation by increasing both the uptake of melanosomes by keratinocytes and the release of SCF, which stimulates melanogenesis.…”