We show p 63 regulates growth of esophageal squamous carcinoma cells via the Akt signaling pathway

p63 is a member of the p53 protein family and plays a crucial role in epithelial development. p63 is expressed in many types of tumors including esophageal cancer; however, its function in cancer is controversial and its role in esophageal cancer has not been clearly established. In the present study, we aimed to identify the mechanisms by which p63 promotes proliferation of esophageal squamous carcinoma cells. Four human esophageal cancer cell lines (TE-8, TE-12, BE3 and OE33) were used in this study. We found that ΔNp63 was the predominantly expressed p63 isoform in esophageal squamous cancer cells. Silencing of p63 mRNA in the esophageal cancer cell lines TE-8 and TE-12 resulted in significant inhibition of cell proliferation in a dose-dependent manner. A colony formation assay also showed that colony formation by TE-8 and TE-12 cells was significantly inhibited by p63 siRNA. Furthermore, p63 siRNA significantly suppressed p-Akt and induced Akt expression in esophageal squamous carcinoma cell lines. On the other hand, overexpression of p63 in the esophageal cell lines BE3 and OE33 increased p-Akt expression. Silencing of p63 in TE-8 and TE-12 cell lines induced p53 and p27 expression and suppressed cyclin D1 and cyclin E1 expression, whereas overexpression of p63 in BE3 and OE33 cell lines resulted in decreased levels of p53 and p27 and increased levels of cyclin D1 and cyclin E1. Taken together, our results suggest that p63 may play a pivotal role in the progression of esophageal squamous carcinoma cells through regulation of the cell cycle via the Akt signaling pathway. Introduction Esophageal squamous carcinoma (ESC) is the sixth most common cancer among males and the ninth most common cancer among females worldwide (1,2). Many environmental influences and genetic factors have been implicated in ESC development. Because of the high rate of metastasis and invasion of surrounding tissues in the early stages of ESC, the overall 5-year survival rate of this cancer is less than 14% (1,3). Although ESC arises from the alteration of gene function, the molecular events required for tumorigenesis have not been clearly elucidated. p63, a member of the p53 family, plays a role in the processes of cell proliferation, survival and differentiation (4). p63 is a transcription factor that is known to be a key regulator of epidermis development and epithelial cell differentiation (4,5). In the esophagus, p63 plays an important role in differentiation and morphogenesis (4). The roles of p63 in the formation of epithelial structures during development have been reported in several studies (6-8); for example, p63 knockout mice exhibit striking developmental defects including abnormal formation of stratified epithelium of the esophagus and skin (6-8). In particular, the esophageal lining of these mice shows a pseudostratified columnar appearance that indicates a critical role for p63 in the regulation of esophagus formation (7). Since the human p63 gene was cloned, two isoforms of p63 that either contain an N-terminal transactivation domain (TAp63) or lack this domain (ΔNp63) have been identified (4,9). ΔNp63 is overexpressed in a variety of human cancers, including head and neck, lung, breast, esophagus and bladder tumors (10,11). The TAp63 and ΔNp63 isoforms perform different functions. It is clear that the ΔNp63 isoform promotes survival of cells and the TAp63 isoform induces cell death; however, the function of p63 in esophageal cancer is still controversial. The PI3K/Akt pathway is a key regulator of differentiation in a number of cell types including esophageal cells (12). Activation of Akt has been found in a variety of types of cancer including esophageal squamous carcinoma (13-15). However, there is limited information on the relationship between p63 and Akt in cancer progression, and especially on its role in ESC. In this study, we examined whether p63 regulates the Akt pathway during ESC progression. We show p63 regulates growth of esophageal squamous carcinoma cells via the Akt signaling pathway SHUAI YE1*, KWANG BOK LEE1*, MAN HEE PARK2, JU-SEOG LEE3 and SOO MI KIM4 1Department of Orthopedic Surgery, Chonbuk National University Medical School and Hospital, Jeonju; 2Catholic University of Pusan, Busan, Republic of Korea; 3Department of Systems Biology, University of Texas M.D. Anderson Cancer Center, Houston, TX, USA; 4Department of Physiology, Institute for Medical Sciences, Chonbuk National University Medical School, Jeonju, Republic of Korea Received January 22, 2014; Accepted March 27, 2014 DOI: 10.3892/ijo.2014. 2374 Correspondence to: Dr Soo Mi Kim, Department of Physiology, Chonbuk National University Medical School, 2-20 Keum-AmDong-San, Jeonju 561-180, Republic of Korea E-mail: soomikim@jbnu.ac. kr *Contributed equally