Abstract 4938: Aberrant methylation and expression of p21 on lung cancer and malignant pleural mesothelioma

Abstract

Abstract Background: The cell cycle progression of which alteration is well known in human cances involves sequential activation and inactivation of cyclin-dependent kinases. The p21 (CDKN1A) plays a key role in regulating the cell cycle. Loss of expression or function of p21 (CDKN1A) has been implicated in the genesis or progression of many human malignancies. DNA methylation in tumor suppressor gene has been established as an important mechanism for gene silencing in human malignancies. In this study, we examined the methylation and expression status of P21 gene in lung cancer and malignant pleural mesothelioma (MPM). Methods: We used 14 non-small-cell lung cancer (NSCLC) cell lines and 20 primary tumors, 12 small-cell lung cancer (SCLC) cell lines, 7 MPM cell lines and 10 primary MPMs. Methylation of P21 gene was examined with methylation-specific PCR assay. p21 expression was examined by RT-PCR and western blotting. Cell lines with methylation were treated with 5-aza-CdR to confirm restoration of p21 expression. Results: Aberrant methylation of P21 was found in 20.6% of NSCLCs (28.6% and 15% in cell lines and primary NSCLCs, respectively), 8.3% of SCLC cell lines, 5.9% of MPMs (0% and 10% in MPM cell lines and primary MPMs, respectively). In NSCLC tumors, P21 methylation was detected only in smokers and squamous cell carcinoma cases but not in never smokers and adenocarinomas with bronchioloalveolar carcinoma feature. Loss of P21 mRNA expression were observed in 4 NSCLC cell lines (50.0%), 4 SCLC cell lines (33.3%) and none of MM cell lines (0%) while loss of protein expression was present in 10 NSCLC cell lines (83.3%), 6 SCLC cell lines (58.3%) and 2 MM cell lines (33.3%). mRNA expression of P21 was restored with 5-Aza-CdR treatment, indicating that methylation was responsible for silencing. These results suggested that 1) P21 methylation was one of the mechanisms of loss of P21 mRNA expression, and 2) post-transcriptional modification is responsible for loss of p21 protein expression. Conclusion: Aberrant methylation of p21 is present in lung cancer, especially for NSCLC, and rare in MPM. p21 protein expression was frequently loss in NSCLC and SCLC, partially due to DNA methylation. 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 4938.