Abstract 4686: MAL is down-regulated in oral squamous cell carcinoma and suppresses proliferation, invasion, tumorigenicity of oral cancer cells, in vitro and in vivo

Abstract

Abstract Purpose: The molecular mechanisms involved in oral squamous cell carcinoma (OSCC) still remain unclear to date. Our previous study revealed that MAL was down-regulated in the tissues of oral squamous cell carcinomas tested by cDNA microarray analysis. In order to identify the function of MAL, the effects on the proliferation, invasion and apoptotic potential in oral cancer cell lines were investigated, in vitro and in vivo. Methods: Expression levels of MAL mRNA in oral squamous cell carcinoma (OSCC) tissues and oral cancer cell lines were examined by semi-quantitive reverse transcription (RT)-PCR and quantitive Real-time PCR. OSCC cell line, Tca cells, were transiently and stably transfected with the full-length MAL cDNA sequence or the empty expression vector pcDNA3.1. Transient and stable gene transfers were verified by Western blot analysis and RT-PCR. Subsequently, WST-8 assay, colony-formation assay, and flow cytometry were used to assess the effects of MAL on the proliferation of Tca cells. Furthermore, PI staining, 7-AAD and annexin V staining and detecting the level of cleavage PARP protein were used to examine apoptosis of Tca cells by MAL gene transfer. Finally, Invasion and tumorigenicity potential of MAL-expressing or MAL-nonexpressing Tca cells was investigated by invasion assay in vitro and tumorigenicity assay in vivo. All statistical tests were two-sided. Results: Expression of MAL was decreased in 86.7% (26/30) OSCC tissues compared with the matched normal tissues by semi-quantitive RT-PCR (P=0.0004). In concordance with the results from OSCC tissues, the relative transcript levels of MAL gene were significantly five-fold lower in 9 OSCC cell lines than in normal oral epithelium cells by real-time PCR. A significant reduction in cell proliferation and a change in cell cycle phase were observed in MAL transfectants. Matrigel assays demonstrated that the OSCC cell invasiveness was significantly decreased. A strong increase in population of apoptotic cells by MAL gene transfer was also observed. Xenografts growth was inhibited in cells expressing MAL compared with cells not expressing MAL (P=0.018). Conclusion: The results showed that MAL is able to suppress malignant phenotypes of OSCC, such as proliferation, apoptosis and invasion, and inhibit tumorigenicity in vivo by transient and stable transfection and suggested MAL might be a candidate of tumor suppression gene. This gene may become a promising target molecule for OSCC diagnosis and gene therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4686.