Siegrist W, Stutz S, Eberle A N
Department of Research, University Hospital, Basel, Switzerland.
Cancer Res. 1994 May 15;54(10):2604-10.
Specific high-affinity receptors for alpha-melanocyte-stimulating hormone (alpha-MSH) are found in variable abundance on many melanoma cell lines. We have examined melanocortin peptides and other factors for their ability to regulate the number of MSH receptors in eleven human and two mouse melanoma cell lines. MSH induced up-regulation of its own receptors in three human cell lines and down-regulation in six human and two mouse melanoma cell lines. No regulation was observed in two human lines. Scatchard analysis revealed modulation of the number of receptors per cell without any change in affinity. The concentrations inducing half-maximal response for up- and down-regulation were 1.6 nM and 0.23 nM, respectively. ACTH1-17 and [Nle4,D-Phe7]-alpha-MSH were more potent, whereas ACTH1-24, desacetyl-alpha-MSH, and [Nle4]-alpha-MSH were less potent in receptor up-regulation as compared to alpha-MSH. Down-regulation but not up-regulation could be fully mimicked by Gs-protein activation and partially by elevation of cellular cAMP. Combination of different agents which increase cAMP was found to be counterregulatory. TPA and retinoic acid generally down-regulated MSH receptors but had no effect on HBL cells. Several protein kinase inhibitors increased MSH binding in B16 cells. MSH-induced receptor down-regulation and melanin synthesis were most effectively antagonized by selective inhibitors of cAMP-dependent protein kinase in these cells. Taken together, MSH receptors on melanoma cells are both positively and negatively regulated. Whereas cAMP-dependent protein kinase activation seems to be involved in down-regulation, the mechanism responsible for up-regulation remains to be elucidated.
在许多黑色素瘤细胞系中可发现α-黑素细胞刺激素（α-MSH）的特异性高亲和力受体，其丰度各不相同。我们研究了黑素皮质素肽和其他因子调节11种人源和2种鼠源黑色素瘤细胞系中MSH受体数量的能力。MSH在3种人源细胞系中诱导其自身受体上调，而在6种人源和2种鼠源黑色素瘤细胞系中诱导下调。在2种人源细胞系中未观察到调节作用。Scatchard分析显示每个细胞的受体数量发生调节，而亲和力没有任何变化。诱导上调和下调的半数最大反应浓度分别为1.6 nM和0.23 nM。与α-MSH相比，促肾上腺皮质激素1-17和[Nle4，D-Phe7]-α-MSH在受体上调方面更有效，而促肾上腺皮质激素1-24、去乙酰-α-MSH和[Nle4]-α-MSH则效果较差。Gs蛋白激活可完全模拟下调作用，而细胞内cAMP升高可部分模拟下调作用。发现增加cAMP的不同药物组合具有反向调节作用。佛波酯和视黄酸通常下调MSH受体，但对HBL细胞无影响。几种蛋白激酶抑制剂增加了B16细胞中MSH的结合。在这些细胞中，cAMP依赖性蛋白激酶的选择性抑制剂最有效地拮抗了MSH诱导的受体下调和黑色素合成。综上所述，黑色素瘤细胞上的MSH受体受到正向和负向调节。虽然cAMP依赖性蛋白激酶激活似乎参与下调过程，但上调的机制仍有待阐明。
