Abstract
Melanogenesis and melanosome secretion are regulated by several mechanisms. In this study, we found that the oxindole derivative GIF-2209 accelerated melanogenesis associated with the discrimination in the expression and intracellular distributions of two melanogenic enzymes, tyrosinase (TYR) and tyrosinase-related protein-1 (TYRP-1). GIF-2209 upregulated the expression of TYR via a microphthalmia transcription factor (MITF)-independent mechanism, leading to high expression of protein. In contrast, GIF-2209 did not alter the mRNA levels of TYRP-1 and suppressed its protein levels. GIF-2209 induced the dissociation of TYR from TYRP-1 but did not alter the association between TYR and CD63, a melanosome and lysosome marker. The protein levels of CD63 were also upregulated by GIF-2209. GIF-2209 induced lysosome expansion and redistribution in all areas of the cytosol, accompanied by autophagy acceleration (upregulation of LC3BII protein levels and downregulation of p62 protein levels). In addition, GIF-2209 stimulated the secretion of melanosomes containing high levels of TYR, TYRP-1, and CD63 proteins. The GIF-2209 mediated melanosome secretion was sensitive to the lysosome inhibitor chloroquine. These results suggest that GIF-2209 may activate lysosomal functions with TYR gene expression, while it accelerates melanosome secretion, which finally leads to the depletion of intracellular melanogenic enzyme, especially TYRP-1 protein.
Highlights
Melanosomes are classified as lysosome-related organelles in which melanin is synthesized to protect the skin from ultraviolet (UV) irradiation [1,2]
We found that 5 μM of trifluoro derivatives, GIF-2208 and GIF-2209, accelerated melanogenesis induced by the cAMP elevator Fsk (Figure 1C)
As the 4 -hydroxy type, GIF-2216, showed no or rather inhibitory effect on Fsk-induced melanogenesis, we used GIF-2216 as a control compound
Summary
Melanosomes are classified as lysosome-related organelles in which melanin is synthesized to protect the skin from ultraviolet (UV) irradiation [1,2]. In response to cellular signaling pathways, for example, including cAMP and p38, melanogenic enzymes such as tyrosinase (TYR) and tyrosinase-related protein 1/2 (TYRP-1/2)] are synthesized and transferred to melanosomes in melanocytes [3]. Post-translational modulators of melanogenic factors are often associated with intracellular trafficking and affect the maturation and fate of melanosomes and related organelles [10]. The CD63 protein participates in vesicle transport systems, interacting with melanogenic and lysosomal enzymes and exosome factors, and is redistributed to melanosomes, lysosomes, and exosomes [13,14]. In mouse melanoma B16F10 cells, this compound had multiple effects, including the upregulation of TYR and CD63 mRNA(s) and protein(s), without affecting the levels of the melanogenic master transcriptional regulator microphthalmia transcription factor (MITF) or TYRP-1 mRNA(s). GIF-2209 increased melanosome secretion, suggesting lysosomal activation may promote this process
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