Effects of interleukin-22 on the expression of tazarotene-induced gene 3 in HaCaT cells

Objective To evaluate the effects of interleukin-22 (IL-22) on the expression of tazarotene-induced gene 3 (TIG3) in HaCaT cells. Methods Cultured HaCaT cells were randomly divided into several groups to be treated with different concentrations (12.5, 25, 50, 100 μg/L) of IL-22 alone, or the combination of 50 μg/L IL-22 with the MAPK-ERK1/2 inhibitor PD98059 or the JAK/STAT inhibitor AG490 for 24 hours. Those HaCaT cells treated with phosphate buffered saline served as the control group. Subsequently, total proteins and mRNAs were extracted from the HaCaT cells. An immunofluorescence assay, Western blot and enzyme-linked immunosorbent assay (ELISA) were performed to determine the protein expression level of TIG3, and real-time fluorescence-based quantitative PCR to quantify the mRNA expression of TIG3 in HaCaT cells. Results The immunofluorescence assay showed that TIG3 protein was mainly expressed in the cytoplasm of HaCaT cells. As Western blot revealed, the protein expression level of TIG3 was 0.743 ± 0.035, 0.678 ± 0.040, 0.582 ± 0.041 and 0.328 ± 0.032 in HaCaT cells treated with IL-22 of 12.5, 25, 50 and 100 μg/L, respectively, significantly lower than that in the control group (0.839 ± 0.045, all P < 0.05). ELISA also showed a decrease in the protein expression of TIG3 in IL-22-treated HaCaT cells, which was consistent with Western blot results. Further more, the mRNA expression level (2-△△Ct) of TIG3 was significantly weaker in HaCaT cells treated with IL-22 of 12.5, 25, 50 and 100 μg/L than in the control group (0.838 ± 0.036, 0.686 ± 0.061, 0.565 ± 0.047 and 0.457 ± 0.033vs. 1.000, all P < 0.05). The decrease in TIG3 mRNA and protein expressions was significantly attenuated in HaCaT cells treated with the combination of 50 μg/L IL-22 with PD98059 or AG490 compared with those treated with 50 μg/L IL-22 alone. Conclusion IL-22 can dose-dependently inhibit the expression of TIG3 in HaCaT cells, likely through the MAPK-ERK1/2 and JAK2/STAT3 signaling pathways. Key words: Interleukin-22; Janus kinase 2; MAP kinase kinase 1/2; Tazarotene-induced gene 3; HaCaT cells; STAT3 transcription factor