Gidrol1* Abstract The Intracellular Localization of ID2 Expression Has a Predictive Value in Non Small Cell Lung Cancer Je´ roˆ me Rollin1, Claire Ble´ chet2,3, Sandra Re´ gina2,4, Arthur Tenenhaus1, Serge Guye´ tant2,3, Xavier 1 CEA, DSV, IRCM, Laboratoire d’Exploration Fonctionnelle des Ge´nomes, Evry, France, 2 INSERM, U618, and IFR 135, Tours, France, 3 Laboratoire d’anatomie pathologique, Bretonneau Hospital, Tours, France, 4 Service d’He´matologie-He´mostase, Trousseau Hospital, Tours, France Background: ID2 is a member of a subclass of transcription regulators belonging to the general bHLH (basic-helix-loop- helix) family of transcription factors. In normal cells, ID2 is responsible for regulating the balance between proliferation and differentiation. More recent studies have demonstrated that ID2 is involved in tumor progression in several cancer types such as prostate or breast. Methodology/Principal Findings: In this work, we investigated, for the first time, the relationship between the expression of ID2 in non-small cell lung cancer (NSCLC) patients and the clinicopathological features and prognosis of these patients. Immunohistochemistry was performed on tissue microarrays, which included 62 NSCLC tumors. In malignant tissues, ID2 expression has been detected in both the nuclear and cytoplasmic compartments, but we have demonstrated that only nuclear expression of ID2 is inversely correlated with the differentiation grade of the tumor (p = 0.007). Interestingly, among patients with poorly differentiated tumors, high nuclear expression of ID2 was an independent and unfavorable prognostic factor for survival (p = 0.036). Conclusions: These results suggest that ID2 could be involved in tumor dedifferentiation processes of NSCLC, and could be used as prognostic marker for patients with poorly differentiated tumors. Citation: Rollin J, Ble´chet C, Re´gina S, Tenenhaus A, Guye´tant S, et al. (2009) The Intracellular Localization of ID2 Expression Has a Predictive Value in Non Small Cell Lung Cancer. PLoS ONE 4(1): e4158. doi:10.1371/journal.pone.0004158 Editor: Axel Imhof, University of Munich and Center of Integrated Protein Science, Germany Received July 8, 2008; Accepted December 4, 2008; Published January 8, 2009 Copyright: 2009 Rollin et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: The authors have no support or funding to report. Competing Interests: The authors have declared that no competing interests exist. * E-mail: xavier.gidrol@cea.fr Introduction ID2 (Inhibitor of DNA binding 2) belongs to a subclass of proteins, the ID family, found within the large bHLH (basic-helix- loop-helix) group of transcription factors. Interestingly, as they do not possess the basic domain, ID proteins do not directly bind to DNA and, instead, act as dominant negative antagonists of class A bHLH transcription factors. Among the known targets of ID proteins are the E protein and members of the Ets family [1]. ID proteins are involved in tissue development [2,3], and have been described as inhibitors of differentiation in numerous cell types including myeloid cells [4], B lymphocytes [5], and muscle cells [6]. ID2 expression is generally low in normal tissues, and is up- regulated in tumors. High levels of expression have been observed in malignancies such as neuroblastoma [7,8], colorectal adeno- carcinoma [9], Ewing sarcoma [10], prostate cancer [11], and pancreatic cancer [12]. Altogether, these results suggest that ID2 may play an important role in tumor initiation and progression. To date, there is only a single study evaluating the role of ID2 in lung cancer, specifically in small cell lung cancer (SCLC) [13]. Lung cancer is a leading cause of deaths from cancer worldwide. The most abundant histological type that affects about 80% of patients is non-small cell lung cancer (NSCLC), as opposed to small cell lung cancer. The overall 5-year survival rate of NSCLC patients is about 15% [14]. Once a diagnosis has been established, treatment options are typically based on stage and histology [15], although this stratification scheme does not consistently reflect the biology of tumor. As a result, over 50% of patients with early-stage lung cancer will eventually die, while others at a more advanced stage will survive [14,16], underlying the need for additional prognostic markers to better predict the outcome of the disease [17]. In this paper, we have evaluated the expression of ID2 by immunohistochemistry on NSCLC tissue microarrays containing 62 tumors. We then further investigated the relationships between ID2 expression and clinicopathologic parameters, in order to assess its possible role as a prognostic marker for NSCLC. Results ID2 Expression in Normal Lung and in NSCLC Tissues Immunostaining for ID2 was performed on a tumor microarray (TMA) containing 62 NSCLC samples from human patients. The clinical and histological features of patients are described in Table 1. In non-cancerous lung tissue, weak to moderate ID2 expression was detected in bronchial epithelial cells in both the cytoplasm and nuclei. In addition, weak ID2 staining was observed in the cytoplasm of endothelial cells (Figure 1A–D). PLoS ONE | www.plosone.org 1 January 2009 | Volume 4 | Issue 1 | e4158