Low PHLDA 3 Expression in Oesophageal Squamous Cell Carcinomas Is Associated with Poor Prognosis

Background/Aim: Patients with oesophageal squamous cell carcinoma (ESCC) have a poor prognosis. Akt has been associated with malignant potential in several cancers, including ESCC. Pleckstrin homology-like domain, family A, member 3 (PHLDA3) has been identified as a direct target gene of p53 and as a potent inhibitor of Akt activation. The present study investigated the role of PHLDA3 expression and its ability to predict prognosis in patients with ESCC who did not receive induction therapy. Materials and Methods: The intensity of PHLDA3 expression was immunohistochemically analyzed in tumor and adjacent normal tissue samples from 84 patients with ESCC, 22 who underwent endoscopic submucosal dissection and 62 who underwent thoracic oesophagectomy. Results: High expression of PHLDA3 was observed in 60 (71.4%) patients and low expression in 24 (28.6%). Cancerspecific (p=0.029) and disease-free (p<0.001) survival rates were significantly lower in the PHLDA3 low-than in the PHLDA3 high-expression group, and low PHLDA3 expression was an independent predictor of postoperative recurrence (relative risk (RR)=0.38; 95% confidence interval (CI)=0.1660.78; p=0.0074). Conclusion: Low PHLDA3 expression in ESCC may be predictive of tumor recurrence suggesting that Akt activation may be a therapeutic target in ESCCs. Oesophageal squamous cell carcinoma (ESCC), the major histological type of oesophageal cancer in East Asian countries, is the eighth most common form of cancer in the world and one of the most lethal (1). Despite improvements in surgical techniques for reduced perioperative mortality and the introduction of multi-modal therapies, oesophageal cancer remains difficult to cure (2, 3). Patients with oesophageal cancer have a poor prognosis with a 5-year survival rate less than 20% (4). Tumor markers that could predict tumor progression, recurrence or overall prognosis would, therefore, be useful. Since conventional therapeutic methods have been limited in their effects on treatment outcomes, innovative strategies for treating ESCCs are being explored, especially those that are molecularly targeted. Akt and its downstream agents have been recently reported to be important in ESCC tumorigenesis. The phosphatidylinositol-3 kinase (PI3K)-Akt signaling pathway plays a critical role in human cancer cell growth, survival and proliferation (5-9). Akt translocates to the cell membrane, where its pleckstrin homology (PH) domain interacts with PI (3,4,5)P3, converted from PI (4,5)P2 by PI3K, resulting in Akt phosphorylation on Thr308 and Ser473. This activated Akt transduces downstream survival signals, promoting carcinogenesis (6, 10). Activation of the PI3K/Akt pathway has also been reported in oesophageal cancers, promoting cancer cell survival, tumorigenicity and metastasis (11-13). Inhibition of Akt activation may, therefore, be a target of treatment of ESCCs. Although the mammalian target of rapamycin complex (mTORC) PP2A and PHLPP have been reported to inhibit Akt, pleckstrin homology-like domain, family A, member 3 (PHLDA3), which is directly targeted by p53, was shown to potently inhibit Akt activation (10, 14-18). p53 negatively regulates Akt through several p53 target genes, including PTEN and PHLDA3 (19). PHLDA3 induced by p53 directly inhibits Akt binding to PIP3 at the cell membrane resulting in cell apoptosis. PHLDA3 expression was found to inhibit Akt translocation to the plasma membrane and subsequent Akt phosphorylation and activation. Repression of PHLDA3 was found to enhance Akt activation and inhibit p53mediated apoptosis. PHLDA3 was also found to inhibit anchorage-independent cell growth, with PHLDA3 expression being frequently lost in human endocrine tumors. Despite its identification as a tumor suppressor gene, the clinicopathological significance of PHLDA3 expression in 949 Correspondence to: Hiroto Muroi, MD, Department of Surgery 1, Dokkyo Medical University, 880 Kitakobayashi, Mibu-mati, Shimotsuga-gun, Tochigi 321-0293, Japan. Tel: +81 282872157, Fax: +81 282866213, e-mail: muroi-h@dokkyomed.ac.jp