PUB086 Concurrent Loss of Tumour Suppressors LKB1 and BRG1 Contribute to Epigenetic Dysregulation in NSCLC

Abstract

Lung cancer is the leading cause of cancer-related death in men and women worldwide. Symptoms of lung cancer do not usually present themselves until the disease is at an advanced stage, where traditional methods are generally ineffective. Therefore, there exists a need to identify proteins and biomarkers for earlier detection. LKB1 is a multitasking tumour suppressor kinase that regulates many biological processes including cell metabolism, the immune system and is found mutated in 40% of NSCLC. BRG1 is another tumour suppressor found mutated in 35% of NSCLC and is involved in chromatin remodelling and epigenetic regulation; epigenetic dysregulation has been well regarded in altering gene expression and contributes to genomic instability and cancer progression. Interestingly, LKB1 binds to and interacts with BRG1, both are located in close chromosomal proximity and are found mutated together in NSCLC. Given that BRG1 is involved in epigenetic regulation and LKB1 interacts with BRG1, distinct global histone modification changes may serve as predictive biomarkers when both tumour suppressors are lost in NSCLC. Human NSCLC cell lines which differ in expression of LKB1 and BRG1 were used: H1299 (LKB1+/BRG1-), H460 (LKB1-/BRG1+), A549 (LKB1-/BRG1-), and calu-3 (LKB1+/BRG1+). The LKB1/BRG1 expression profile was confirmed for each cell line by western blot analysis. Cell lines were screened for differences in expression of various global H3 and H4 acetylation, methylation and phosphorylation modification patterns by western blot analysis. The majority of screened global H3 and H4 acetylation, phosphorylation and methylation modifications displayed a reduced expression when tumour suppressors LKB1 and BRG1 were concurrently lost. A dramatic decrease in global H4K20me3 expression, typically associated with transcriptional repression was observed in the double negative A549 cell line. These findings suggest that distinct histone modification changes occur when LKB1 and BRG1 are concurrently lost in NSCLC. Taken together, screening for epigenetic histone changes may help to serve as a predictive biomarker in this subset of NSCLC.