Objective To investigate the expression of Dickkopf-3 (DKK3) in human malignant melanoma cell lines and tissues,and to evaluate effects of DKK3 on the proliferation and apoptosis of malignant melanoma cell line A375.Methods Reverse transcription PCR (RT-PCR) and real-time fluorescence-based quantitative PCR (qRT-PCR) were performed to measure the mRNA expression of DKK3 in human malignant melanoma cell lines HM,A375,WM451,WM35,SK-MEL-1,Hs-695T and MDA-MB-435s,as well as in 38 primary melanoma tissues,4 metastatic melanoma tissues and 20 pigmented nevus tissues.Cultured malignant melanoma A375 cells were divided into 2 groups to be transfected with pcDNA3.1 (+)-Flag-DKK3 (experiment group) and pcDNA3.1 (+)-Flag-Vector (control group) respectively.The overexpression of DKK3 was verified by RT-PCR.Cell counting kit-8 (CCK8) assay and plate colony formation assay were performed to evaluate the proliferative activity of A375 cells,flow cytometry was conducted to detect apoptosis of A375 cells,and Western blot analysis was performed to determine the expression of cell cycle-and cell apoptosis-related proteins.Results The mRNA expression of DKK3 was downregulated in WM35 cells,absent in HM cells,A375 cells,WM451 cells,SK-MEL-1 cells and Hs-695T cells,but upregulated in MDA-MB-435s cells.Compared with pigmented nevus tissues,the mRNA expression of DKK3 was significantly decreased in malignant melanoma tissues (P ＜ 0.001).Compared with the control group (100％),cell colony formation was markedly suppressed in the experiment group (23.22％ ± 3.55％),and the proliferative activity of A375 cells was also significantly inhibited in the experiment group 24,48,72 hours after the transfection (all P ＜ 0.05).Flow cytometry showed that compared with the control group,A375 cells were significantly arrested in G1 phase (48.68％ ± 3.92％ vs.25.38％ + 2.92％,P ＜ 0.001),and the apoptosis rate of A375 cells was significantly increased in the experiment group (P ＜ 0.001).Compared with the control group,the experiment group showed significantly higher expression of p21,Bax,cleaved-parp and cleaved-casp3,but significantly lower expression of cyclin D1 and Bcl2 (all P ＜ 0.001).Conclusion DKK3 expression is downregulated in human malignant melanoma tissues,so it may serve as a potential tumor suppressor gene involved in the development of cutaneous malignant melanoma.

Objective To investigate the expression of DKK3 in human cutaneous malignant melanoma cells and tissues,and to evaluate the effect of transfection with DKK3 gene on migration and invasion of a malignant melanoma cell line A375.Methods Western blot analysis was performed to measure the relative expression of DKK3 in human cutaneous melanoma cell lines HM,A375,WM451,SK-MEL-1,Hs-695T,MDA-MB-435s and WM35,as well as pigmented nevus tissues.Real-time fluorescence-based quantitative PCR (RT-PCR) was conducted to determine the mRNA expression of DKK3 in 58 melanoma tissues (including primary melanoma and metastatic melanoma) and 30 pigmented nevus tissues from Chongqing Traditional Chinese Medicine Hospital between August 2014 and June 2017.The pcDNA3.1 (+)-Flag-Vector (control group) and pcDNA3.1 (+)-Flag-DKK3 (transfection group) were transfected into A375 melanoma cells separately.RT-PCR and Western blot analysis were performed to verify the overexpression of DKK3,and to evaluate the effect of DKK3 overexpression on the expression of molecules related to the migration and invasion of melanoma cells.Cell scratch assay,Transwell migration and invasion assay were conducted to assess the effect of DKK3 on the migration and invasion of A375 cells.Statistical analysis was done by a two-sample t-test for comparisons between two groups,one-way analysis of variance (ANOVA) for intergroup comparison,and least significant difference (LSD)-t test for multiple comparisons with the SPSS 13.0 software.Results DKK3 protein was absent or lowly expressed in the human melanoma cell lines,but highly expressed in the pigmented nevus tissues.There were significant differences in the mRNA expression of DKK3 among the primary melanoma tissues (2-ΔΔCt:[0.325 ± 0.150] × 10-3),metastatic melanoma tissues ([0.142 ± 0.210] × 103) and pigmented nevus tissues ([0.634 ±:0.120] × 10-3,F =46.57,P ＜ 0.05).In addition,the mRNA expression of DKK3 was significantly lower in the metastatic melanoma tissues than in the primary melanoma tissues and pigmented nevus tissues (LSD-t =2.48,3.12,both P ＜ 0.05).After transfection with DKK3,cell scratch assay showed that the migration rate was significantly lower in the transfection group (22.11％ ± 5.11％) than in the control group (54.36％ ± 23.22％,t =2.36,P ＜ 0.001).Transwell migration and invasion assay revealed that the number of A375 cells crossing the Transwell chamber was significantly lower in the transfection group (265 ± 33,76 ± 18 respectively) than in the control group (429 ± 41,135 ± 21 respectively;t =1.24,1.35 respectively,both P ＜ 0.001).After overexpression of DKK3 in the A375 cells in the transfection group,the mRNA and protein expression of E-cadherin were up-regulated,while the mRNA and protein expression of N-cadherin,vimentin,matrix metalloproteinase 2 (MMP2),MMP7 and MMP11 were down-regulated compared with the control group.Conclusions The expression of DKK3 is down-regulated in the melanoma cell lines and tissues,and the migration and invasion of A375 cells are markedly inhibited by overexpression of DKK3.DKK3 may be a target for inhibiting the metastasis of cutaneous malignant melanoma.

Objective:To determine the expression of the E2F6 transcription factor in human malignant melanoma tissues and cell lines, and to evaluate the effect of E2F6 on proliferation, migration and invasion of a malignant melanoma cell line A375.Methods:Frozen tissues and paraffin-embedded tissue sections were collected from 50 cases of cutaneous malignant melanoma and 30 cases of pigmented nevus in Department of Dermatology, Chongqing Traditional Chinese Medicine Hospital from January 2012 to December 2017. Quantitative reverse transcription-PCR (qRT-PCR) was performed to determine the mRNA expression of E2F6 in the malignant melanoma and pigmented nevus tissues, as well as in 7 malignant melanoma cell lines (HM, A375, WM451, WM35, SK-MEL-1, Hs-695T and MDA-MB-435s) and pigmented nevus cells, and immunohistochemical study and Western blot analysis were conducted to determine the protein expression of E2F6 and β-catenin in the malignant melanoma tissues. An E2F6-inhibiting plasmid and a control plasmid were separately transfected into A375 cells by using a liposome-mediated transfection method, and the E2F6 gene-knockdown efficiency was verified by qRT-PCR and Western blot analysis. Cell counting kit-8 (CCK8) assay, soft-agar plate cloning assay, Transwell migration and invasion assays and 3D cell culture assay were conducted to evaluate the effect of E2F6 gene knockdown on the proliferation, migration and invasion of A375 cells, flow cytometry was performed to detect the cell cycle and apoptosis rate, and Western blot analysis was conducted to determine the protein expression of total β-catenin, activated β-catenin, c-Myc and cyclin D1. The comparison between two groups was carried out by t test, the comparison among several groups by one-way analysis of variance, and multiple comparisons by least significant difference t test; Pearson correlation coefficient was used to analyze the correlation between E2F6 and β-catenin expression in cutaneous malignant melanoma. Results:The E2F6 mRNA expression was significantly higher in the 7 malignant melanoma cell lines than in the pigmented nevus cells (all P < 0.001). qRT-PCR showed that the relative mRNA expression of E2F6 was significantly higher in the cutaneous malignant melanoma tissues (0.000 55 ± 0.000 17) than in the pigmented nevus tissues (0.000 18 ± 0.000 09, t = 3.22, P < 0.001). Both the immunohistochemical study and Western blot analysis showed significantly increased E2F6 protein expression, but decreased β-catenin protein expression in the cutaneous malignant melanoma tissues compared with the pigmented nevus tissues (all P < 0.001). Correlation analysis showed that E2F6 protein expression was negatively correlated with β-catenin expression in the malignant melanoma tissues (immunohistochemical study: r = -0.56, Western blot analysis: r = -0.63, both P < 0.01). After knockdown of the E2F6 gene in A375 cells, the mRNA and protein expression of E2F6 was significantly lower in the E2F6 inhibition group than in the control group ( t = 3.38, 2.76 respectively, both P < 0.001). CCK8 assay showed that the cellular proliferative ability was significantly lower in the E2F6 inhibition group than in the control group ( t = 4.58, P < 0.01) 48 hours after transfection; soft-agar plate cloning assay showed that the colony-formation ratio was significantly lower in the E2F6 inhibition group than in the control group ( t = 2.26, P < 0.001) ; Transwell migration and invasion assays showed that the number of cells crossing the chamber was significantly lower in the E2F6 inhibition group (165 ± 23, 96 ± 11 respectively) than in the control group (376 ± 22, 315 ± 31, t = 3.14, 2.12, respectively, both P < 0.01) ; 3D cell culture assay showed that the cell morphology markedly changed, and the invasive pseudopodia disappeared in the E2F6 inhibition group. Flow cytometry revealed that the proportion of cells at G0-G1 phase and apoptosis rate were significantly higher in the E2F6 inhibition group than in the control group (both P < 0.001). Western blot analysis showed significantly decreased protein expression of β-catenin, activated β-catenin and its downstream target proteins c-Myc and cyclin D1, but significantly increased protein expression of P21 in the E2F6 inhibition group compared with the control group (all P < 0.001) ; additionally, the E2F6 inhibition group showed significantly decreased protein expression of epithelial-mesenchymal transition-related molecules vimentin and N-cadherin, but significantly increased expression of E-cadherin compared with the control group (all P < 0.001) . Conclusions:The E2F6 transcription factor is highly expressed in malignant melanoma. Knockdown of the E2F6 gene in A375 cells can inhibit cell proliferation, migration and invasion by antagonizing the β-catenin signaling pathway.