The mitogen-activated protein kinase phosphatase-1 (MKP-1) gene is a potential methylation biomarker for malignancy of breast cancer

Abstract

The mitogen-activated protein kinase (MAPK) phosphatase- 1 (MKP-1) belongs to the MAPK cascades which are central to cell proliferation and apoptosis. The carcinogenic role of MKP-1 has been reported in many types of cancer but it has rarely been investigated in breast cancer. The present study was designed to evaluate the MKP-1 mRNA expression and its possible regulation by methylation of MKP-1 promoter in the model of several breast cancer cell lines and tissues as well as controls. Our data demonstrate MKP-1 mRNA expression significantly decreased in five breast cancer cell lines compared to breast controls (P<0.01). Using the methylation-specific PCR (MSP) analysis, the unmethylated reaction (U) is dominant in both normal cell lines and benign breast tumors (100% vs. 86.2%), whereas the methylated reaction (M) is dominant in both breast cancer cell lines and invasive breast tumors (100% vs. 57.2%). In terms of methylation ratio (M/M+U), methylation level in MKP-1 promoter is significantly higher in the invasive breast tumor tissues (n = 152) than in benign breast tumor tissues (n = 29) (P<0.0001). Assessing the methylation ratio of the promoter of MKP-1 gene to diagnose the breast malignancy (invasive vs. benign), the area under the receiver- operating characteristic (ROC) curve was 0.809 (95% CI: 0.711-0.906, P<0.001). The best performance for this prediction has a sensitivity of 76.32% and a specificity of 82.76% at the cutoff value of 0.38. Taken together, we firstly demonstrated that the promoter methylation of MKP-1 gene is a potential breast cancer biomarker for breast malignancy.

Figure 1

The mRNA expression of MKP-1 gene in several breast cancer cell lines. Normal breast cell lines (M10) and breast cancer cell lines (MCF7, T47D, MDA-MB-231, SKBR3, and BT474) were included. The quantity of cDNA in each preparation was estimated by real time RT-PCR in the reference of the internal control actin gene. Experiments were repeated in triplicate. ^*P < 0.01.

Figure 2

MSP of the promoter of MKP-1 gene in several breast cell lines (normal vs. cancer) and breast tissues (benign vs. invasive tumor). (A) Demonstration of MSP in a normal breast cell lines and several benign breast tissues. (B) Demonstration of MSP in several breast cancer cell lines and invasive breast tumor tissues. (C) Methylation status in all breast cell lines (normal and cancer) and tissues (benign and invasive) tested. M, methylated (155-bp); U, unmethylated (158-bp).

Figure 3

Receiver-operating characteristic (ROC) analysis for malignancy prediction of breast cancer based on the mathylation ratio for MKP-1 gene. AUC, area under curve.