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. 2009 Feb;129(2):422-31.
doi: 10.1038/jid.2008.255. Epub 2008 Oct 30.

MiTF regulates cellular response to reactive oxygen species through transcriptional regulation of APE-1/Ref-1 (V体育官网)

Feng Liu  1 , Yan Fu, Frank L Meyskens Jr
Affiliations

MiTF regulates cellular response to reactive oxygen species through transcriptional regulation of APE-1/Ref-1

Feng Liu et al. J Invest Dermatol. 2009 Feb.

Abstract

Microphthalmia-associated transcription factor (MiTF) is a key transcription factor for melanocyte lineage survival. Most previous work on this gene has been focused on its role in development VSports手机版. A role in carcinogenesis has emerged recently, but the mechanism is unclear. We classified melanoma cells into MiTF-positive and -negative groups and explored the function of MiTF in regulating cellular responses to reactive oxygen species (ROS). The MiTF-positive melanoma cell lines accumulated high levels of apurinic/apyrimidinic endonuclease (APE-1/Ref-1, redox effector-1), a key redox sensor and DNA endonuclease critical for oxidative DNA damage repair. We demonstrate that APE-1 is a transcriptional target for MiTF. Knocking down MiTF led to reduced APE-1 protein accumulation, as well as abolished induction of APE-1 by ROS. MiTF-negative melanoma cells survived more poorly under ROS stress than the MiTF-positive cells based on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and Trypan blue staining. Overexpression of APE-1 partially rescued ROS-induced cell death when MiTF was depleted. We conclude that MiTF regulates cellular response to ROS by regulation of APE-1, and this may provide a mechanism of how MiTF is involved in melanoma carcinogenesis. .

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Conflict of interest statement

CONFLICT OF INTEREST

The authors state no conflict of interest.

Figures

Figure 1
Figure 1. APE-1 is a transcriptional target for MiTF
(a) The APE-1 promoter and gene structure. nCaRE, binding site for negative calcium response elements; Sox site, SOX transcription factor binding site; cAMP response element-binding protein, cAMP response element binding site; E2F site, E2F binding site; E-box, consensus MiTF binding site; ATG, translation initiation site; 3′ UTR, 3′ untranslated region. (b) MiTF binds to APE-1 promoter. Chromatin immunoprecipitation was performed using SK-Mel-28 cells and anti-Mek1 or anti-MiTF antibodies. The precipitated chromatin was PCR amplified with either APE-1 promoter-specific primers (top) or α-tubulin primers (bottom). (c) MiTF activates APE-1 promoter activity. pAPE1-Luc reporter construct was co-transfected with MiTF expression plasmid into Lu1205 cells, luciferase activities were assayed 48 hours after transfection and normalized by β-galatosidase activity (pCH110) that is also co-transfected. (d) knockdown of MiTF in Sk-Mel-28 cells decreased APE-1 promoter activity. pAPE-Luc reporter construct was co-transfected with MiTF shRNA plasmids pTER-mi3 or pTER-mi5 or control plasmid pTER-GFPi that carries shRNA targeting GFP. Luciferase activity was assayed 48 hours after transfection. Western blot in the top right corner indicates the MiTF level (top) and α-tubulin level from cells in lanes 2, 3, and 4. (e) A dominant-negative MiTF protein inhibited APE-1 promoter activity in SK-Mel-28 cells. At 12 hours after transfection with the APE-1 wild-type promoter, cells were infected with adenovirus expressing a control nonsense polypeptide (PolyP), wild-type MiTF (MiTF-WT) or dominant-negative MiTF (MiTF-DN) (Miller et al., 2004). Luciferase activities were measured 48 hours after transfection. Cells transfected but not infected with any virus were used as a control (uninfected). (f) MiTF regulates APE-1 promoter activity through E-boxes. Mutant APE-1 promoters lacking the first E box (pΔ1E-Luc) or all three E boxes (pΔ3E-Luc) were analyzed as above along with the wild-type APE-1 promoter in A375 cells. (g) The first E box is critical for MiTF regulation. Site mutagenesis was performed to make point-mutated promoters, which were used for activity analysis in the presence or absence of MiTF construct. The data were normalized to co-transfected β-galactosidase activity and the induction fold of each promoter was calculated by comparing activity in the presence of MiTF to that in the absence of MiTF.
Figure 2
Figure 2. APE-1 protein level is correlated with that of MiTF
(a) Knockdown of MiTF led to a decrease in APE-1 protein accumulation. MNT1 cells were infected with Ad-shMiTF or Ad-shLuc and collected for western blot analysis at the indicated days. (b) Western blot analysis of MiTF and APE-1 accumulation in normal human melanocytes and melanoma cell lines: (1) Normal human melanocytes, (2) c8161, (3) c81-46A, (4) WM3211, (5) Lu1205, (6) A375, (7) SK-Mel-28, (8) MNT1, and (9) c83-2C. α-Tubulin serves as a loading control. Numbers below the western blot indicate the quantitated relative APE-1 levels (see c). (c) Quantitative analysis of APE-1 accumulation levels based on (b). The western results were quantitated by a densitometer and APE-1 level is normalized to α-tubulin. Normalized APE-1 accumulation in normal human melanocytes was defined as 1.0 and its levels in other cell lines were relative to normal human melanocytes. (d) APE-1 protein level is correlated to MiTF upregulation by α-MSH. Normal human melanocytes were cultured in media without 12-O-tetradecanoylphorbol-13-acetate and reduced bovine pituitary extract levels for 24 hours (lane 1), α-MSH was then added and cells were collected at 6 and 12 hours (lanes 2 and 3) for western blot analysis.
Figure 3
Figure 3. MiTF is phosphorylated and required for APE-1 induction after ROS treatment
(a) Western blot analysis of MiTF in SK-Mel-28 cells after H2O2 treatment. The Sk-Mel-28 cells were treated with 0.1mM H2O2 and collected for western blot analysis at the indicated time points. p84 serves as a loading control. (b) MiTF and APE-1 accumulation in c83-2C cells after GOX (150mUml−1) treatment. Cells were incubated with GOX for 1 hour, washed with 1 × phosphate-buffered saline, and then returned to incubator with fresh media (time 0). The bottom graph is quantiated MiTF (total) and APE-1 protein levels based on the western blot on top. (c) Western blot analysis of MiTF and APE-1 accumulation in normal human melanocytes after treatment with 0.1mM H2O2. (d) Western blot analysis of APE-1 accumulation in two MiTF-negative melanoma cells A375 (top) and c81-46A (bottom) after 0.15mM H2O2 treatment. (e) Induction of APE-1 promoter activity requires MiTF. SK-Mel-28 cells were transfected with pAPE-Luc and one of the following plasmids: pcDNA3.1, pcDNA-MiTF, pTER-mi3, or pTER-GFPi, together with pCH110. Cells were treated with 0.1mM H2O2 36 hours after transfection and luciferase activity was assayed 48 hours after transfection.
Figure 4
Figure 4. Knockdown of MiTF led to poor survival under ROS stress in melanoma cells
(a) MiTF is knocked down by pTER-mi3 in SK-Mel-28 cells. SK-Mel-28 cells were transiently transfected by vector pTER-GFPi or pTER-mi3, cells were collected at the indicated time point for western blot analysis. p84 serves as loading control. Ctrl, cells without transfection. (b) Western blot analysis of APE-1 protein level in cells with depleted MiTF after 0.1mM H2O2 treatment. The pTER-mi3-transfected cells were treated with 0.1mM H2O2 24 hours after transfection, and collected for western blot analysis. Again p84 serves as loading control and JunB serves as a positive control. (c) Western blot analysis of APE-1 protein induction in SK-Mel-28 cells treated with 0.1mM H2O2. (d) Cell viability and cell-death analysis after MiTF knockdown. SK-Mel-28 cells were transfected with pTER-GFPi or pTER-mi3, 12 hours later cells were trypsinized and plated in 24-well plates. At 24 hours after transfection, 0 (lane 1), 0.1mM (lane 2), or 0.15mM (lane 3) of H2O2 was added into the media and continued to incubate for another 16 hours, when 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay (left) or Trypan blue staining (right) was performed. (e, f) Cell death after H2O2 (e) or GOX (f) treatment in MNT1 infected with either adenovirus Ad-shLuc or Ad-shMiTF. Time 0 is 48 hours after infection, when treatment started. Cell death was analyzed 24 hours after treatment.
Figure 5
Figure 5. Over-expression of APE-1 rescued ROS-induced cell viability in MiTF-depleted cells
(a) Concomitant knock-down of MiTF and over-expression of APE-1 in SK-MEL-28 cells. Cells were transiently transfected with pFlag-APE-1, and then infected with Ad-shLuc or Ad-shMiTF 24 hours later. (1) Control SKMel- 28 cells; (2) Cells transfected with pFlag-APE-1 and infected with Ad-shLuc; (3) Cells transfected with pFlag-APE-1 and infected with Ad-shMiTF. α-Tubulin serves as a loading control. (b) Cells with or without MiTF knock-down or APE-1 overexpression were treated with various concentration of glucose oxidase (Gox, left) or H2O2 (right) 48 hours post-infection, and MTT assay was performed to measure cell viability. All data is normalized to cells with Luc-ShRNA transfection.
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