Mechanisms of melanogenesis inhibition by tumor necrosis factor-alpha in B16/F10 mouse melanoma cells.
The inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) is present in the dermal and epidermal layers of normal skin [Kilgus, O., Payer, E., Schreiber, S., Elbe, A., Strohal, R. & Stingl, G. (1993) J. Invest. Dermatol. 100, 674-680]. Its local concentrations are modified by several stimuli, including wound healing and ultraviolet irradiation. Moreover, TNF-alpha inhibits melanogenesis in normal melanocytes [Swope, V., Abdel-Malek, Z., Kassem, L. & Norlund, J. (1991) J. Invest. Dermatol. 96, 180-185], and is, therefore, a potential autocrine/paracrine regulator of pigmentation. We have analyzed the mechanisms of this effect using B16/F10 melanoma cells as a model. Nanomolar concentrations of TNF-alpha inhibit the tyrosine hydroxylase and dopa oxidase activities of B16/F10 melanocytes, to less than 30% control levels, without effects on tyrosinase-related protein 2/dopachrome tautomerase (TRP2/DCT). The 50% inhibition was obtained at 1 nM TNF-alpha and 48 h treatment. The effect of TNF-alpha was noticeable after 6 h treatment, and maximal after 24 h. This inhibition is explained by decreased intracellular levels of tyrosinase and tyrosinase-related protein 1 (TRP1), but not of TRP2/DCT as detected by Western blotting. Northern-blot experiments showed that the inhibitory effect is partially explained by a reduced accumulation of the corresponding mRNAs, that dropped to about 50% of control values (48 h treatment, 5 nM TNF-alpha). Moreover, the tyrosine hydroxylase and dopa oxidase activities decreased more rapidly in TNF-alpha-treated cells than in control cells, under conditions of inhibition of protein synthesis. This suggests a TNF-mediated reduction of tyrosinase half-life. However, the possibility of an inhibitory post-translational modification of the enzyme induced by TNF cannot be ruled out. Therefore, the inhibitory effect of TNF-alpha on tyrosinase and TRP-1 results from combined effect on mRNA levels and enzymatic activity or protein stability.
Martínez-Esparza
M
M
Department of Biochemistry and Molecular Biology, School of Medicine, University of Murcia, Spain.
Jiménez-Cervantes
C
C
Solano
F
F
Lozano
J A
JA
García-Borrón
J C
JC
D000818:Animals; D019746:Intramolecular Oxidoreductases / Q000187:drug effects / Q000235:genetics; D008543:Melanins / Q000096:biosynthesis*; D008544:Melanocytes / Q000187:drug effects* / Q000201:enzymology*; D008546:Melanoma, Experimental; D008562:Membrane Glycoproteins; D051379:Mice; D014442:Monophenol Monooxygenase / Q000187:drug effects / Q000235:genetics; D010088:Oxidoreductases; D011506:Proteins / Q000187:drug effects / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D012334:RNA, Neoplasm / Q000032:analysis; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D014446:Tyrosine 3-Monooxygenase / Q000187:drug effects / Q000235:genetics
D008543:Melanins; D008562:Membrane Glycoproteins; D011506:Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D014409:Tumor Necrosis Factor-alpha; D010088:Oxidoreductases; D014446:Tyrosine 3-Monooxygenase; C079621:Tyrp1 protein, mouse; C064056:tyrosinase-related protein-1; D014442:Monophenol Monooxygenase; D019746:Intramolecular Oxidoreductases; C042501:dopachrome isomerase