ULK1 regulates melanin levels in MNT-1 cells independently of mTORC1.
Melanosomes are lysosome-related organelles that serve as specialized sites of melanin synthesis and storage in melanocytes. The progression of melanosomes through the different stages of their formation requires trafficking of specific proteins and membrane constituents in a sequential manner, which is likely to deploy ubiquitous cellular machinery along with melanocyte-specific proteins. Recent evidence revealed a connection between melanogenesis and the autophagy machinery, suggesting a novel role for members of the latter in melanocytes. Here we focused on ULK1, a key autophagy protein which is negatively regulated by mTORC1, to assess its potential role in melanogenesis in MNT-1 cells. We found that ULK1 depletion causes an increase in melanin levels, suggesting an inhibitory function for this protein in melanogenesis. Furthermore, this increase was accompanied by increased transcription of MITF (microphthalmia-associated transcription factor) and tyrosinase and by elevated protein levels of tyrosinase, the rate-limiting factor in melanin biogenesis. We also provide evidence to show that ULK1 function in this context is independent of the canonical ULK1 autophagy partners, ATG13 and FIP200. Furthermore we show that regulation of melanogenesis by ULK1 is independent of mTORC1 inhibition. Our data thus provide intriguing insights regarding the involvement of the key regulatory autophagy machinery in melanogenesis.
Secretory Pathways Laboratory, London Research Institute, Cancer Research UK, London, United Kingdom.
Eyal
E
Kalie
Minoo
M
Razi
Sharon A
SA
Tooze
D000071189:Autophagy-Related Protein-1 Homolog; D015153:Blotting, Western; D002460:Cell Line; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D000076222:Mechanistic Target of Rapamycin Complex 1; D008543:Melanins / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism
D047908:Intracellular Signaling Peptides and Proteins; D008543:Melanins; D046912:Multiprotein Complexes; D000071189:Autophagy-Related Protein-1 Homolog; D000076222:Mechanistic Target of Rapamycin Complex 1; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; C484754:ULK1 protein, human