尽管先前的研究已经检查了参与黑色素生成的信号通路,紫外线(UV)或α-黑素细胞刺激激素(α-MSH)刺激作为在表皮基底层产生黑色素的关键诱导物,调节黑素生成的信号通路仍然存在争议。本研究报道α-MSH,不是UVA和UVB,在B16F10黑色素瘤细胞中作为黑色素生成的主要刺激。使用基因敲低技术和化学抑制剂进行信号通路分析,丝裂原活化蛋白激酶激酶(MEK)/细胞外信号调节激酶(ERK)/p90核糖体S6激酶2(RSK2)在黑素生成中起重要作用。出乎意料的是,LY294002,一种PI3K抑制剂,在没有紫外线或α-MSH刺激的情况下增加黑素生成,提示PI3K/AKT信号通路可能不是黑素生成的主要信号通路。使用U0126或BI-D1870对MEKs/ERKs/RSK2信号通路的化学抑制通过刺激UVA或α-MSH刺激来抑制黑素生成,或者两者兼而有之。特别是,RSK2的基因缺失或组成型活性(CA)-RSK2过表达表明,RSK2在黑素生成中起关键作用。有趣的是,叉头框蛋白O4(FOXO4)被RSK2磷酸化,导致FOXO4的反式激活活性增加。值得注意的是,FOXO4突变体在磷酸化位点进行丝氨酸到丙氨酸的置换,完全消除了反式激活活性并减少了黑色素的产生,表明RSK2介导的FOXO4活性在黑素生成中起关键作用。此外,山奈酚,抑制RSK2活性的类黄酮,抑制黑色素生成。此外,FOXO4-wt过表达表明FOXO4增强黑色素合成。总的来说,RSK2-FOXO4信号通路在调节黑素生成中起关键作用。
Although previous studies have examined the signaling pathway involved in
melanogenesis through which ultraviolet (UV) or α-melanocyte-stimulating hormones (α-MSH) stimuli act as key inducers to produce melanin at the stratum basal layer of the epidermis, the signaling pathway regulating melanogenesis is still controversial. This study reports that α-MSH, not UVA and UVB, acted as a major stimulus of
melanogenesis in B16F10 melanoma cells. Signaling pathway analysis using gene knockdown technology and chemical inhibitors, the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK)/p90 ribosomal S6 kinase 2 (RSK2) played an important role in melanogenesis. Unexpectedly, LY294002, a PI3K inhibitor, increased melanogenesis without UV or α-MSH stimulation, suggesting that the PI3K/AKT signaling pathway may not be a major signaling pathway for
melanogenesis. Chemical inhibition of the MEKs/ERKs/RSK2 signaling pathway using U0126 or BI-D1870 suppressed melanogenesis by stimulation of UVA or α-MSH stimulation, or both. In particular, the genetic depletion of RSK2 or constitutive active (CA)-RSK2 overexpression showed that RSK2 plays a key role in melanogenesis. Interestingly, forkhead box protein O4 (FOXO4) was phosphorylated by RSK2, resulting in the increase of FOXO4\'s transactivation activity. Notably, the FOXO4 mutant harboring serine-to-alanine replacement at the phosphorylation sites totally abrogated the transactivation activity and reduced melanin production, indicating that RSK2-mediated FOXO4 activity plays a key role in melanogenesis. Furthermore, kaempferol, a flavonoid inhibiting the RSK2 activity, suppressed
melanogenesis. In addition, FOXO4-wt overexpression showed that FOXO4 enhance melanin synthesis. Overall, the RSK2-FOXO4 signaling pathway plays a key role in modulating
melanogenesis.