Hinokitiol-induced decreases of tyrosinase and microphthalmia-associated transcription factor are mediated by the endoplasmic reticulum-associated degradation pathway in human melanoma cells.

Abstract

Tyrosinase (TYR) is a key enzyme for melanin production. We previously showed that hinokitiol, a naturally occurring seven-membered ring terpenoid, potently inhibits human TYR activity. Interestingly, hinokitiol was recently reported to decrease expression of TYR and microphthalmia-associated transcription factor (MITF), which is a main transcription factor of the TYR gene, in murine melanoma cells. However, the mechanisms by which hinokitiol decreases the intracellular levels of TYR and MITF have not been fully elucidated. Here, we investigated the underlying mechanisms of the decreases using cultured human melanoma cells. As a result, hinokitiol treatment decreased TYR protein level in a time- and dose-dependent manner in G361 human melanoma cells, while MITF protein level was decreased only at higher concentrations after 3 days treatment. Notably, the mRNA levels of TYR and MITF were slightly increased by hinokitiol treatment. Therefore, we focused on the degradation of TYR and MITF in endoplasmic reticulum (ER)-associated protein degradation (ERAD) pathway. Importantly, co-treatment of ERAD inhibitor with hinokitiol restored the protein levels of TYR and MITF to approximately 30% and 20% of total those in untreated control cells, respectively. Hinokitiol affected the ER homeostasis as well as degradation of TYR and MITF in two human melanoma cell lines, G361 and HT-144, but the changes of ER-stress markers under the hinokitiol treatment were different in the two human melanoma cell lines. Taken together, these observations indicate that hinokitiol may induce ER stress and trigger the degradation of unfolded newly synthesizing TYR and MITF via the ERAD pathway.

• Authors: Takahiro Oyama, Haruka Ogawa, Yoko Shirai, Hideaki Abe, Takanori Kamiya, Takehiko Abe, Sei-Ichi Tanuma
• Journal: Biochimie (Biochimie) Vol. 192 Pg. 13-21 (Jan 2022) ISSN: 1638-6183 [Electronic] France
• PMID: 34536557 (Publication Type: Journal Article)
• Copyright: Copyright © 2021 Elsevier B.V. and Société Française de Biochimie et Biologie Moléculaire (SFBBM). All rights reserved.

Chemical References

• MITF protein, human
• Microphthalmia-Associated Transcription Factor
• Monoterpenes
• Neoplasm Proteins
• Tropolone
• Monophenol Monooxygenase
• beta-thujaplicin

Topics

• Cell Line, Tumor
• Endoplasmic Reticulum-Associated Degradation (drug effects)
• Humans
• Melanoma (drug therapy, metabolism, pathology)
• Microphthalmia-Associated Transcription Factor (metabolism)
• Monophenol Monooxygenase (metabolism)
• Monoterpenes (pharmacology)
• Neoplasm Proteins (metabolism)
• Tropolone (analogs & derivatives, pharmacology)