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-145- Melanocyte(2) 9/5 Room-C
PHOSPHOLIPASE A2 STIMULATES MELANOGENESIS IN HUMAN MELANOCYTE CULTURES.
Kazuhisa Maeda, Masako Naganuma.
Shiseido Research Center, Yokohama, Japan.
Phospholipase(PL) catalyzes the release of free fatty acids from membrane phospholipids, and the products derived from these fatty acids, such as prostaglandins and leukotrienes, significantly up-regulate the key melanogenic enzyme, tyrosinase, in melanocytes. We recently demonstrated that the number of dopa-positive melanocytes increased and the morphology of melanocytes became dendritic when PLs were added to organ-cultured skin (1). The present study has provided evidence of the direct up-regulation of melanogenic protein synthesis by PLA2. The amount of melanin, and the expression levels of tyrosinase and tyrosinase-related protein-1 were significantly increased by treatment with PLA2. These melanogenic effects of PLA2 were completely inhibited by treatment with a phospholipase inhibitor, p-bromophenacyl bromide, or partly inhibited by treatment with a cyclooxygenase inhibitor, indomethacin. These findings suggest that catalytic activity of PLA2 is required to promote melanogenesis in the human melanocytes, presumably via liberation of arachidonic acid from membrane phospholipids, leading to the production of melanogenic factors such as prostaglandins, leukotrienes, and lysophospholipids. (1) Maeda, K. et al., Photochem. Photobiol. 64, 220-223, 1996.
-146- Melanocyte(2) 9/5 Room-C
HISTAMINE H2 RECEPTOR-MEDIATED MELANOGENESIS IN CULTURED HUMAN MELANOCYTES.
Masaki Yoshida, Yoshito Takahashi, Shintaro Inoue.
Basic Research Laboratory, Kanebo LTD., Kanagawa, Japan.
It has been reported that histamine-induced melanogenesis of human normal melanocytes is mediated by an imidazoline/guanidium receptor but not by histamine receptor. Involvement of histamine in physiological melanogenesis remains obscure. In this report, we examined whether histamine stimulates melanocytes using a specific receptor. Morphological changes and tyrosinase activity of cultured human melanocytes were estimated at 24h after histamine treatment with or without active agents for histamine receptors, and following results were obtained. 1. Enlargement and the increased number of dendrite of human melanocytes induced by histamine were specifically suppressed by H2 antagonists (famotidine, ranitidine) but not by H1 nor H3 antagonists. 2. Histamine-induced tyrosinase activation was suppressed by H2 antagonists. 3. Dimaprit, an H2 histamine agonist, induced the same effects of histamine as above in a dose dependent manner. These findings suggest histamine stimulation of normal melanocytes is mediated through H2 receptor.
-147- Melanocyte(2) 9/5 Room-C
ROLE OF ENDOTHELIN-1 IN HYPERPIGMENTATION IN SENILE FRECKLE.
Satsuki Tajima1, Izumi Manaka1, Masako Ichikawa1, Makoto Kawashima1, Tsuyosi Kobayashi2, Genji Imokawa2.
1Department of Dermatology, Tokyo Women's Medical College, Tokyo, 2Biological Science Laboratories, Kao Corporation, Tochigi, Japan.
Little is known about mechanisms involved in hyperpigmentation in senile freckle(SF). We have previously reported that endothelins are important paracrin melanogen, being secreted by keratinocytes and stimulating melanocyte proliferation and melanization. In this study, we have clarified the roles of endothelin-1 in hyperpigmentary mechanisms involved in senile freckle by immunohistochemistry and RT-PCR analysis. The number of anti-tyrosinase immunopositive melanocytes in senile freckle increased by 200% relative to non-lesional epidermis. Immunohistochemistry using anti ET-1 demonstrated relatively stronger staining through the lesional epidermis, especially intercellular space of granular layers, than that of non-lesional epidermis did. In pararell,RT-PCR of ET-1 mRNA demonstrated accentuated expression of ET-1 transcript in SF in comparison with that in the perilesional normal control, accompanied by a similarly accentutated expression of tyrosinase mRNA. These findings suggest that ET-1 plays a part in the hyperpigmentation seen in SF.
-148- Melanocyte(2) 9/5 Room-C
EXPRESSION OF MELANOCORTIN 1 RECEPTOR(MC1-R) AND ENDOTHELIN B RECEPTOR (ETB-R) IN CULTURED NORMAL HUMAN MELANOCYTES, NEVUS CELLS AND MELANOMA CELLS.
Akiko Ohashi1, Yoko Funasaka1, Genji Imokawa2, Tsuyoshi Kobayashi2, Masamitsu Ichihashi1.
1Department of Dermatology, Kobe University Medical School,Kobe, 2Institute for Fundamental Research,Kao Corporation,Haga,Tochigi,Japan.
During malignant transformation, melanocytes gain the ability of autonomous growth and invasiveness, resulting in metastatic potential. -MSH endows metastatic ability in murine melanoma cells, meanwhile, ET-1 enhances the perivascular proliferation and invasiveness, and further, -MSH and ET-1 possess synergestic effects on melanocyte growth. To clarify the involvement of these ligands in melanoma transformation, expression of MC1-R and ETB-R was examined by Northern and Western blotting using cultured epidermal melanocytes, junctional and dermal nevus cells and metastatic melanoma cells. All cell lines examined expressed both MC1-R and ETB-R. Further, these benign and malignant pigment cells were stimulated or inhibited in their growth and tyrosinase activity by 100nM MSH, 0.1and 10nM ET-1. Taken together, our data indicates that benign and malignant pigment cells express functional MC1-R and ETB-R.
-149- Melanocyte(2) 9/5 Room-C
REGULATION OF TYROSINASE ACTIVITIES IN HUMAN GENITAL MELANOCYTES BY ANDROGEN.
Taketsugu Tadokoro, Satoshi Itami, Kunihiko Yoshikawa.
Department of Dermatology, Osaka University Medical School, Osaka, Japan.
We have already reported that human genital melanocytes are androgen target cells and tyrosinase activities are up-regulated by androgen. In order to clarify the precise mechanism by androgen, we investigated the effects of PKC on the regulation of tyrosinase activities. Tyrosinase activity, which was measured by the oxidation of L-dopa, was increased by androgen in the presence of TPA, a potent activator of PKC. In contrast, androgen inhibited tyrosinase activities in the absence of TPA. Northern blot analysis showed that the mRNA expressions of tyrosinase were not affected by androgen and anti-androgen. These results suggest that androgen and PKC have an synergistic effect on the tyrosinase activity at post-transcriptional in human genital melanocytes.