Mechanisms of melanogenesis inhibition by tumor necrosis factor-alpha in B16/F10 mouse melanoma cells

Eur J Biochem. 1998 Jul 1;255(1):139-46. doi: 10.1046/j.1432-1327.1998.2550139.x.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Intramolecular Oxidoreductases / drug effects
  • Intramolecular Oxidoreductases / genetics
  • Melanins / biosynthesis*
  • Melanocytes / drug effects*
  • Melanocytes / enzymology*
  • Melanoma, Experimental
  • Membrane Glycoproteins*
  • Mice
  • Monophenol Monooxygenase / drug effects
  • Monophenol Monooxygenase / genetics
  • Oxidoreductases*
  • Proteins / drug effects
  • Proteins / genetics
  • RNA, Messenger / analysis
  • RNA, Neoplasm / analysis
  • Tumor Necrosis Factor-alpha / pharmacology*
  • Tyrosine 3-Monooxygenase / drug effects
  • Tyrosine 3-Monooxygenase / genetics

Substances

  • Melanins
  • Membrane Glycoproteins
  • Proteins
  • RNA, Messenger
  • RNA, Neoplasm
  • Tumor Necrosis Factor-alpha
  • Oxidoreductases
  • Tyrosine 3-Monooxygenase
  • Tyrp1 protein, mouse
  • tyrosinase-related protein-1
  • Monophenol Monooxygenase
  • Intramolecular Oxidoreductases
  • dopachrome isomerase