Effect of IGF-1 on the Proliferation of Cultured Normal Human Melanocytes / 대한피부과학회지

ABSTRACT

BACKGROUND: Human growth hormone(hGH) plays a central role in linear bone growth and body metabolism. Its mitogenic effect in human tissues is mediated via direct and indirect actions. As proposed by the "somatomedin hypothesis", many circulating GH-mediated effects are exerted indirectly and systemically via stimulation of hepatic synthesis of insulin-like growth factor 1(IGF-1). Given additional evidences for the expression of growth hormone receptor(GH-R) and IGF-1 receptor(IGF-1R) on many target tissues including keratinocytes, melanocytes, and fibroblasts, it is now evident that the GH can act via systemic IGF-1 secreted by the liver and locally produced IGF-1, as well as directly through the GH receptor. OBJECTIVE: The purpose of this study was to investigate not only the effect of IGF-1 on the morphologic changes, proliferation, and melanization of cultured human melanocytes but also on its signal transduction pathway through the IGF-1R. METHODS: Melanocytes were exposed to IGF-1 at 10, 25, 50, 75, 100ng/ml and we examined the changes of cell morphology, number of cells, [3H]-thymidine incorporation, MTS assay, and melanization according to the concentrations and exposure times of IGF-1. Also, the activity of p44/42 MAPK/ERK according to the various exposure times of IGF-1(25ng/ml) was examined using the Western blotting method to find out about the signal transdution pathway of IGF-1. RESULTS: The results were as follows 1. There were no significant morphological changes of cells between the control and experimental groups according to the concentrations and exposure times of IGF-1. 2. The effects on melanocytes according to the concentrations of IGF-1 5 days after adding IGF-1 1) The number of cells, [3H]-thymidine incorporation, and MTS assay were significantly higher than those of control group in all experimental groups(p<0.05). 2) The melanin content showed an insignificant decrease in all experimental groups. 3) The melanocytes responded independent of the IGF-1 concentration in the assay of cell number, [3H]-thymidine incorporation and MTS. 3. The effects on melanocytes according to the exposure times(3 days, 5 days, 7 days) of IGF-1(25 ng/ml) 1) The number of cells, [3H]-thymidine incorporation, and MTS assay increased as time went by, and was significantly higher than those of control group at all exposure times(p<0.05). 2) The melanin content decreased after exposure of IGF-1, especially that of 3 days exposure group showed a significant decrease(p<0.05). 4. The activities of p44/42 MAPK/ERK increased suddenly at 5 minutes with a peak at 60 minutes and then abruptly decreased at 120 minutes after adding IGF-1 CONCLUSION: In summary, this study demonstrates that IGF-1 has no effect on the morphology, but it does increase the proliferation and slightly decrease the melanization of cultured human melanocytes. In addition, it is suggested that IGF-1 plays a role in regulation of proliferation of melanocytes via the receptor PTK pathway with activation of p44/42 MAPK/ERK.