Downregulation of tyrosinase activity in human melanocyte cell cultures by yohimbine
Downregulation of tyrosinase activity in human melanocyte cell cultures by yohimbine
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DOI：
10.1046/j.1523-1747.2000.00860.x
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发表时间：
2000-02-01
影响因子：
6.5
通讯作者：
Chaudhry, F
中科院分区：
文献类型：
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作者：
Fuller, BB;Drake, MA;Chaudhry, F
用α-2肾上腺素能受体拮抗剂育亨宾处理人黑素细胞培养物导致酪氨酸酶活性显著下调。在细胞暴露于育亨宾（100 μ M）的12小时内，酪氨酸酶活性降低30%，到48小时，处理的黑素细胞中的酪氨酸酶活性小于对照培养物的五分之一。抑制是剂量依赖性的，并且发生在来自黑色或白色皮肤类型的人黑素细胞中，也发生在小鼠黑素瘤细胞中。育亨宾诱导的酪氨酸酶活性降低是可逆的，去除药物后48小时酶水平恢复到对照值的90%。虽然酪氨酸酶活性被育亨宾显著抑制，但该化合物对细胞增殖、细胞翻译或DNA合成没有影响。用育亨宾处理黑素细胞培养物阻断了3-异丁基-1-甲基黄嘌呤、二丁酰cAMP或毛喉素引起的酪氨酸酶活性的增加。cAMP免疫测定的结果表明，在用育亨宾处理的细胞中，环核苷酸的细胞内水平不受影响，育亨宾对酪氨酸酶的抑制并不涉及底物利用率的降低，因为酪氨酸摄取研究表明育亨宾对酪氨酸酶的量没有影响。酪氨酸进入细胞。育亨宾与黑素体富集组分的孵育不会降低酪氨酸酶活性，表明育亨宾作用需要完整的细胞。此外，酪氨酸酶提取物直接与育亨宾一起孵育时活性没有降低，表明该药物不作为酶的直接抑制剂。最后，Western免疫印迹结果显示，育亨宾不显著降低人黑素细胞中酪氨酸酶蛋白的量。这些发现表明育亨宾通过一种尚未确定的信号通路来降低黑素细胞中预先存在的酪氨酸酶分子的催化活性。
Treatment of human melanocyte cell cultures with the alpha-2 adrenergic receptor antagonist yohimbine results in a marked down-regulation of tyrosinase activity. A 30% decrease occurs within 12 h of exposure of cells to yohimbine (100 mu M), and by 48 h tyrosinase activity in treated melanocytes is less than a fifth that of control cultures, The inhibition is dose dependent and occurs in human melanocytes derived from either black or white skin types, and also in mouse melanoma cells. The yohimbine-induced decrease in tyrosinase activity is reversible, with enzyme levels returning to 90% of control values 48 h after removal of drug. Although tyrosinase activity is markedly suppressed by yohimbine, the compound has no effect on cell proliferation, cellular translation, or DNA synthesis. Treatment of melanocyte cultures with yohimbine blocks the increase in tyrosinase activity by either 3-isobutyl-1-methylxanthine, dibutyryl cAMP, or forskolin, Results of cAMP immunoassays, show that intracellular levels of the cyclic nucleotide are unaffected in cells treated with yohimbine, Tyrosinase inhibition by yohimbine does not involve a decrease in substrate availability since tyrosine uptake studies show that yohimbine has no effect on the amount of tyrosine entering the cell. Incubation of a melanosome-enriched fraction with yohimbine does not clause a lowering of tyrosinase activity, suggesting that an intact cell is required for yohimbine action. In addition, tyrosinase extracts show no reduction in activity when incubated directly with yohimbine, indicating that the drug does not act as a direct inhibitor of the enzyme, Finally, results of western immunoblotting show that yohimbine does not significantly lower the amount of tyrosinase protein in human melanocytes. These findings suggest that yohimbine acts through an as yet unidentified signaling pathway to lower the catalytic activity of pre-existing tyrosinase molecules present in melanocytes.