Shikonin Promotes Skin Cell Proliferation and Inhibits Nuclear Factor-κB Translocation via Proteasome Inhibition In Vitro

Yan Yan, Minao Furumura, Takako Gouya, Atsufumi Iwanaga, Kwesi Teye, Sanae Numata, Tadashi Karashima, Xiao-Guang Li, Takashi Hashimoto

Shikonin is a major active chemical component extracted from Lithospermi Radix, an effective traditional herb in various types of wound healing. Shikonin can accelerate granulomatous tissue formation by the rat cotton pellet method and induce neovascularization in granulomatous tissue. The purpose of the study was to investigate its mechanism of action in human skin cells. MTS assay was used to measure cell growth. The collagen type I (COL1 ) mRNA expression and procollagen type I C-peptide (PIP) production were detected by real-time quantitative reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Immunofluorescence and western blot analyses were carried out to investigate nuclear factor-κB (NF-κB) signaling pathway. Cell-based proteasome activity assay was used to determine proteasome activity. In this study, we found that 10 μmol/L shikonin stimulated the growth of normal human keratinocytes and 1 μmol/L shikonin promoted growth of human dermal fibroblasts. However, shikonin did not directly induce COL1 mRNA expression and PIP production in dermal fibroblasts in vitro. In addition, 1 μmol/L shikonin inhibited translocation of NF-κB p65 from cytoplasm to nucleus induced by tumor necrosis factor-α stimulation in dermal fibroblasts. Furthermore, shikonin inhibited chymotrypsin-like activity of proteasome and was associated with accumulation of phosphorylated inhibitor κB-α in dermal fibroblasts. These results suggested that shikonin may promote wound healing via its cell growth promoting activity and suppress skin inflammation via inhibitory activity on proteasome. Thus, shikonin may be a potential therapeutic reagent both in wound healing and inflammatory skin diseases.