Phospho-enriched protein in astrocytes (PEA-15) is a 15-kDa phosphoprotein that slows cell proliferation by binding to and sequestering extracellular signal-regulated kinase (ERK) in the cytoplasm, thereby inhibiting ERK-dependent transcription and proliferation. In previous studies of E1A human gene therapy for ovarian cancer, we discovered that PEA-15 induced the antitumor effect of E1A by sequestering activated ERK in the cytoplasm of cancer cells. Here, we investigated the role of PEA-15 in ovarian cancer tumorigenesis, the expression levels of PEA-15 in human ovarian cancer, and whether PEA-15 expression correlated with overall survival in women with ovarian cancer. We overexpressed PEA-15 in low-PEA-15-expressing cells and knocked down PEA-15 in high-PEA-15-expressing cells and analyzed the effects on proliferation, anchorage-independent growth, and cell cycle progression. We then assessed PEA-15 expression in an annotated tissue microarray of tumor samples from 395 women with primary epithelial ovarian cancer and tested whether PEA-15 expression was linked with overall survival. PEA-15 expression inhibited proliferation, and cell cycle analysis did not reveal apoptosis but did reveal autophagy, which was confirmed by an increase in LC3 cleavage. Inhibition of the ERK1/2 pathway decreased PEA-15-induced autophagy. These findings suggest that the antitumor activity of PEA-15 is mediated, in part, by the induction of autophagy involving activation of the ERK1/2 pathway. Multivariable analyses indicated that the women with high-PEA-15-expressing tumors survived longer than those with low-PEA-15-expressing tumors (hazard ratio, 1.973; P = 0.0167). Our findings indicate that PEA-15 expression is an important prognostic marker in ovarian cancer. [Cancer Res 2008;68(22):9302-10]

Purpose: To determine the role of PEA-15 in breast cancer. Experimental Design: A reverse-phase protein array was used to measure PEA-15 expression levels in 320 human breast cancers; these levels were correlated with clinical and tumor characteristics. PEA-15 was overexpressed by an adenovirus vector or by stably expressing PEA-15 in different breast cancer cell lines. The effects on breast cancer cell survival and on the downstream apoptotic signaling pathway were measured in terms of cell proliferation (trypan blue for cell viability, bromodeoxyuridine incorporation for DNA synthesis), anchorage-independent growth (soft agar colony formation), and apoptosis (fluorescence-activated cell sorter analysis). The preclinical efficacy of Ad.PEA-15 given intratumorally was evaluated in nude mice bearing tumors from s.c. implanted human MDA-MB-468 triple-negative breast cancer cells.Results: In human breast cancers, low levels of PEA-15 expression correlated with high nuclear grade (P < 0.0001) and with negative hormone receptor status (P = 0.0004). Overexpression of PEA-15 in breast cancer cells resulted in growth inhibition, reduction in DNA synthesis, and onset of caspase-8-dependent apoptosis. In athymic nude mice bearing MDA-MB-468 xenografts, tumor volumes were significantly smaller in mice treated intratumorally with Ad.PEA-15 than in control mice (P < 0.0001). Tumors from mice treated with Ad.PEA-15 had increased levels of activated (phosphorylated) extracellular signal-regulated kinase and reduced levels of Ki-67 compared with tumors from nontreated or control-adenovirustreated mice.Conclusion: PEA-15 has therapeutic potential in breast cancer. Further preclinical and clinical exploration of PEA-15 as a druggable target is warranted. Clin Cancer Res; 16(6); 1802-11. ©2010 AACR.Breast cancer is the most common cancer in women in the United States and most of the Western world (1). In 2008, 182,460 cases are expected to be diagnosed (26% of all cancers in women), and 40,480 women are expected to die of the disease (accounting for 15% of all cancer deaths in women, making this disease the second most common cause of cancer death among women). Breast cancer that is negative for estrogen receptor, progesterone receptor, and HER-2 is known as triple receptor-negative breast cancer. It is the only major type of breast cancer for which no specific targeted therapy is available to improve patient outcomes (2). A deeper understanding of the molecular mechanisms responsible for breast cancer is imperative if more effective treatments are to be discovered.PEA-15 (also called PED) is an acidic, serine-phosphorylated, 15-kDa phosphoprotein that contains a death effector domain and is associated with microtubules (3). In primary astrocytes (the first cells in which this protein was identified), PEA-15 was shown to regulate the nuclear localization of extracellular signal-regulated kinase (ERK) and consequently affect the transcription of ERK-dependent targets such as transcription factor Elk. This function was shown...

Clear cell carcinoma (CCC) of the ovary tends to show resistance to standard chemotherapy, which results in poor survival for patients with CCC. Developing a novel therapeutic strategy is imperative to improve patient prognosis. Epidermal growth factor receptor (EGFR) is frequently expressed in epithelial ovarian cancer. One of the major downstream targets of the EGFR signaling cascade is ERK. PEA-15, a 15-kDa phosphoprotein, can sequester ERK in the cytoplasm. MEK1/2 plays a central role in integrating mitogenic signals into the ERK pathway. We tested the hypothesis that inhibition of the EGFR-ERK pathway suppresses tumorigenicity in CCC, and we investigated the role of PEA-15 in ERK-targeted therapy in CCC. We screened a panel of four CCC cell lines (RMG-I, SMOV-2, OVTOKO, and KOC-7c) and observed that the EGFR tyrosine kinase inhibitor erlotinib inhibited cell proliferation of EGFR-overexpressing CCC cell lines through partial dependence on the MEK/ERK pathway. Further, erlotinib-sensitive cell lines were also sensitive to the MEK inhibitor selumetinib (AZD6244), which is under clinical development. Knockdown of PEA-15 expression resulted in reversal of selumetinib-sensitive cells to resistant cells, implying that PEA-15 contributes to selumetinib sensitivity. Both selumetinib and erlotinib significantly suppressed tumor growth (P < 0.0001) in a CCC xenograft model. However, selumetinib was better tolerated; erlotinib-treated mice exhibited significant toxic effects (marked weight loss, severe skin peeling) at high doses. Our findings indicate that the MEK/ERK pathway is a potential target for EGFR-overexpressing CCC and indicate that selumetinib and erlotinib are worth exploring as therapeutic agents for CCC.