Graduate School of Medical and Pharmaceutical Sciences, Kumamoto University, Kumamoto 862-0973, Japan.
J Biol Chem. 2010 Apr 23;285(17):13254-63. doi: 10.1074/jbc.M110.103051. Epub 2010 Feb 22.
Skin hyperpigmentation disorders due to abnormal melanin production induced by ultraviolet (UV) irradiation are both a clinical and cosmetic problem. UV irradiation stimulates melanin production in melanocytes by increasing intracellular cAMP. Expression of heat shock proteins (HSPs), especially HSP70, is induced by various stressors, including UV irradiation, to provide cellular resistance to such stressors. In this study we examined the effect of expression of HSP70 on melanin production both in vitro and in vivo. 3-Isobutyl-1-methylxanthine (IBMX), a cAMP-elevating agent, stimulated melanin production in cultured mouse melanoma cells, and this stimulation was suppressed in cells overexpressing HSP70. IBMX-dependent transcriptional activation of the tyrosinase gene was also suppressed in HSP70-overexpressing cells. Expression of microphthalmia-associated transcription factor (MITF), which positively regulates transcription of the tyrosinase gene, was up-regulated by IBMX; however, this up-regulation was not suppressed in HSP70-overexpressing cells. On the other hand, immunoprecipitation and immunostaining analyses revealed a physical interaction between and co-localization of MITF and HSP70, respectively. Furthermore, the transcription of tyrosinase gene in nuclear extract was inhibited by HSP70. In vivo, UV irradiation of wild-type mice increased the amount of melanin in the basal layer of the epidermis, and this increase was suppressed in transgenic mice expressing HSP70. This study provides the first evidence of an inhibitory effect of HSP70 on melanin production both in vitro and in vivo. This effect seems to be mediated by modulation of MITF activity through a direct interaction between HSP70 and MITF.
由于紫外线 (UV) 照射引起的异常黑色素生成导致的皮肤色素沉着障碍既是临床问题也是美容问题。UV 照射通过增加细胞内 cAMP 刺激黑色素细胞中的黑色素生成。热休克蛋白 (HSPs)，特别是 HSP70 的表达，是由各种应激源诱导的，包括 UV 照射，以提供细胞对这些应激源的抵抗力。在这项研究中，我们检查了 HSP70 的表达对体外和体内黑色素生成的影响。3-异丁基-1-甲基黄嘌呤 (IBMX)，一种 cAMP 升高剂，刺激培养的小鼠黑素瘤细胞中的黑色素生成，而这种刺激在过表达 HSP70 的细胞中受到抑制。IBMX 依赖性的酪氨酸酶基因转录激活也在 HSP70 过表达细胞中受到抑制。小眼畸形相关转录因子 (MITF) 的表达上调，MITF 正向调节酪氨酸酶基因的转录；然而，在 HSP70 过表达的细胞中，这种上调并没有受到抑制。另一方面，免疫沉淀和免疫染色分析分别显示了 MITF 和 HSP70 之间的物理相互作用和共定位。此外，HSP70 抑制核提取物中转录酶基因的转录。在体内，野生型小鼠的 UV 照射增加了表皮基底层中黑色素的含量，而过表达 HSP70 的转基因小鼠中这种增加受到抑制。这项研究提供了 HSP70 对体外和体内黑色素生成的抑制作用的第一个证据。这种作用似乎是通过 HSP70 和 MITF 之间的直接相互作用来调节 MITF 活性来介导的。
