Mitogen-Activated Protein Kinase Phosphatase-1 in Human Breast Cancer Independently Predicts Prognosis and Is Repressed by Doxorubicin

Abstract

Purpose: Mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1) dephosphorylates mitogen-activated protein kinase [extracellular signal-regulated kinase (ERK), c-Jun NH 2 -terminal kinase (JNK), and p38], mediates breast cancer chemoresistance, and is repressible by doxorubicin in breast cancer cells. We aimed to characterize doxorubicin effects on MKP-1 and phospho-MAPKs in human breast cancers and to further study the clinical relevance of MKP-1 expression in this disease. Experimental Design: Doxorubicin effects on MKP-1, phospho-ERK1/2 (p-ERK1/2), phospho-JNK (p-JNK), and phospho-p38 were assayed in a panel of human breast cancer cells by Western blot and in human breast cancer were assayed ex vivo by immunohistochemistry (n = 50). MKP-1 expression was also assayed in a range of normal to malignant breast lesions (n = 30) and in a series of patients (n = 96) with breast cancer and clinical follow-up. Results: MKP-1 was expressed at low levels in normal breast and in usual ductal hyperplasia and at high levels in in situ carcinoma. MKP-1 was overexpressed in ∼50% of infiltrating breast carcinomas. Similar to what was observed in breast cancer cell lines, ex vivo exposure of breast tumors to doxorubicin down-regulated MKP-1, and upregulated p-ERK1/2 and p-JNK, in the majority of cases. However, in a proportion of tumors overexpressing MKP-1, doxorubicin did not significantly affect MKP-1 or phospho-MAPKs. With regard to patient outcome, MKP-1 overexpression was an adverse prognostic factor for relapse both by univariate (P < 0.001) and multivariate analysis (P = 0.002). Conclusions: MKP-1 is overexpressed during the malignant transformation of the breast and independently predicts poor prognosis. Furthermore, MKP-1 is repressed by doxorubicin in many human breast cancers.

Mitogen-activated protein kinase phosphatase-1 (MKP-1) impairs the response to anti-epidermal growth factor receptor (EGFR) antibody cetuximab in metastatic colorectal cancer patients

“…Immunohistochemistry was performed according to the methodology previously described by our group (Rojo et al, 2009). In brief, formalin-fixed paraffin-embedded 3 mm tissue sections were used for immunostaining using the Dako-Link platform.…”

“…To score a cell as positive, nuclear staining was required for MKP-1 expression. The expression was evaluated by calculating a semiquantitative histoscore (H-score) that included the determination of both the percentage of stained target cells and staining intensity (low, medium or high), as described in Rojo et al, (2009). The final score was determined after applying a weighting factor to each estimate and the following formula was used: H-score ¼ (low%) Â 1 þ (medium%) Â 2 þ (high%) Â 3; the results ranged from 0 to 300.…”

“…MKP-1 was expressed in histologically normal colon epithelial cells and the pattern and intensity of staining were similar in all assayed specimens. MKP-1 overexpression was considered when the intensity of staining in the nuclei of tumour cells was higher than that observed in corresponding normal epithelial cells (Rojo et al, 2009). …”

“…MKP-1 is located in the nucleus and regulates the three MAPKs with different substrate preferences based on cell type and context (Chu et al, 1996;Keyse (2008)). MKP-1 is overexpressed in human tumours such as lung, breast and colon cancer, and has been involved in tumourigenesis (Loda et al, 1996;Vicent et al, 2004;Rojo et al, 2009). Oncogenic activation of MKP-1 is mediated by EGFR signalling by poorly understood mechanisms that include transcriptional regulation mediated by p38 and ERK (Xing et al, 1996;Li et al, 2001) and post-translational control by ERK (Brondello et al, 1999;Lin et al, 2003;Lin and Yang, 2006).…”

“…The molecular mechanism underlying MKP-1-mediated resistance to anti-cancer drugs is in part due to the activation of JNK-driven apoptosis by several anti-tumour agents such as anthracyclines, taxanes, cisplatin, proteasome inhibitors and more recently anti-EGFR drugs. High levels of MKP-1 inhibit JNK and counterbalance the cytotoxic effects of such drugs (Sanchez-Perez et al, 1998Small et al, 2004Small et al, , 2007Wang et al, 2006Wang et al, , 2007Workman and de Bono, 2008;Rojo et al, 2009). With respect to anti-EGFR therapy, in vitro results with the anti-EGFR drug AG1478 showed that MKP-1-modulated JNK activation was critical for drug-induced apoptosis.…”