A Potent Inhibitor of SIK2, 3, 3′, 7-Trihydroxy-4′-Methoxyflavon (4′-O-Methylfisetin), Promotes Melanogenesis in B16F10 Melanoma Cells

Abstract

Flavonoids, which are plant polyphenols, are now widely used in supplements and cosmetics. Here, we report that 4′-methylflavonoids are potent inducers of melanogenesis in B16F10 melanoma cells and in mice. We recently identified salt inducible kinase 2 (SIK2) as an inhibitor of melanogenesis via the suppression of the cAMP-response element binding protein (CREB)-specific coactivator 1 (TORC1). Using an in vitro kinase assay targeting SIK2, we identified fisetin as a candidate inhibitor, possibly being capable of promoting melanogenesis. However, fisetin neither inhibited the CREB-inhibitory activity of SIK2 nor promoted melanogenesis in B16F10 melanoma cells. Conversely, mono-methyl-flavonoids, such as diosmetin (4′-O-metlylluteolin), efficiently inhibited SIK2 and promoted melanogenesis in this cell line. The cAMP-CREB system is impaired in Ay/a mice and these mice have yellow hair as a result of pheomelanogenesis, while Sik2+/−; Ay/a mice also have yellow hair, but activate eumelanogenesis when they are exposed to CREB stimulators. Feeding Sik2+/−; Ay/a mice with diets supplemented with fisetin resulted in their hair color changing to brown, and metabolite analysis suggested the presence of mono-methylfisetin in their feces. Thus, we decided to synthesize 4′-O-methylfisetin (4′MF) and found that 4′MF strongly induced melanogenesis in B16F10 melanoma cells, which was accompanied by the nuclear translocation of TORC1, and the 4′-O-methylfisetin-induced melanogenic programs were inhibited by the overexpression of dominant negative TORC1. In conclusion, compounds that modulate SIK2 cascades are helpful to regulate melanogenesis via TORC1 without affecting cAMP levels, and the combined analysis of Sik2+/− mice and metabolites from these mice is an effective strategy to identify beneficial compounds to regulate CREB activity in vivo.

Flavones as tyrosinase inhibitors: kinetic studies in vitro and in silico

“…Whereas methoxy flavones do competitively inhibit tyrosinase, their application in cosmetic or medicinal products that aim to decrease tyrosine or dopamine oxidation should be treated with caution. Experiments with murine B16/F10 melanoma cells have shown that treatment with polyhydroxy flavones results in reduced melanogenesis 45,46 but that polymethoxy flavones affect cell signalling, and induce tyrosinase expression and melanogenesis. [45][46][47][48][49][50][51][52] However, similar experiments with humans rather than murine melanocytes have shown that polymethoxy flavones inhibit the induction of melanogenesis.…”

SIK2 Is Critical in the Regulation of Lipid Homeostasis and Adipogenesis In Vivo

“…SIK2 has been implicated in various signaling cascades such as glucose and fat metabolism in the liver, neuroprotective effect in the brain, and the eumelanin synthetic pathway in melanocytes (34)(35)(36)(37)(38). To invariably delineate the functional consequences of the chronic depletion of SIK2 in vivo, we generated knockout mice for SIK2 by deleting two critical exons (exons 2 and 3) from the genomic sequences, resulting in .90% depletion of SIK2 in most tissues as confirmed by quantitative PCR and Western blot analysis (Fig.…”

Reversible Acetylation Regulates Salt-inducible Kinase (SIK2) and Its Function in Autophagy*

“…Furthermore, SIK2 is known to regulate the initiation of mitosis through phosphorylating the centrosome linker protein, C-Nap1 (5). An intimate link between SIK2 and the CREB coactivator TORC1/2 has also been established, particularly in the contexts of melanogenesis (6,7), cerebral ischemia-associated neuronal survival (8), and corticotropin-releasing hormone transcription (9). However, as an AMPK family kinase, its possible functional link to cellular stress response has not been reported and requires further clarification.…”