Reduced symmetric dimethylation stabilizes vimentin and promotes metastasis in MTAP-deficient lung cancer.

The aggressive nature and poor prognosis of lung cancer led us to explore the mechanisms driving disease progression. Utilizing our invasive cell-based model, we identified methylthioadenosine phosphorylase (MTAP) and confirmed its suppressive effects on tumorigenesis and metastasis. Patients with low MTAP expression display worse overall and progression-free survival. Mechanistically, accumulation of methylthioadenosine substrate in MTAP-deficient cells reduce the level of protein arginine methyltransferase 5 (PRMT5)-mediated symmetric dimethylarginine (sDMA) modification on proteins. We identify vimentin as a dimethyl-protein whose dimethylation levels drop in response to MTAP deficiency. The sDMA modification on vimentin reduces its protein abundance but trivially affects its filamentous structure. In MTAP-deficient cells, lower sDMA modification prevents ubiquitination-mediated vimentin degradation, thereby stabilizing vimentin and contributing to cell invasion. MTAP and PRMT5 negatively correlate with vimentin in lung cancer samples. Taken together, we propose a mechanism for metastasis involving vimentin post-translational regulation.

EGFR-Mutant SCLC Exhibits Heterogeneous Phenotypes and Resistance to Common Antineoplastic Drugs.

INTRODUCTION: Approximately 5% of patients with EGFR-activating mutations acquire EGFR tyrosine kinase inhibitor (TKI) resistance through SCLC transformation. However, the reason for the poor outcome and the molecular basis of EGFR-mutant SCLC that has transformed from adenocarcinoma remain unclear. METHODS: In this study, we established two EGFR-mutant SCLC cell lines from lung adenocarcinoma patients after failed EGFR-TKI treatment to investigate their molecular basis and potential therapeutic strategies in the hope of improving patient outcome. RESULTS: These two EGFR-mutant SCLC cell lines displayed two different phenotypes: suspensive and adherent. Both phenotypes shared the same genomic alterations analyzed by array-based comparative genomic hybridization assay. Increased expression of EGFR and mesenchymal markers and decreased expression of neuroendocrine markers were observed in adherent cells. Principal component analysis and hierarchical clustering analysis of RNA microarray revealed that these two cell lines displayed a unique gene expression pattern that was distinctly different from that in NSCLC and classical SCLC cells. Combined treatment using an EGFR-TKI and an AKT inhibitor attenuated cell viabilities in our two cell lines. Moreover, the use of a histone deacetylase inhibitor significantly inhibited the cell viabilities of both cell lines in vitro and in vivo. CONCLUSION: Our findings suggest that EGFR-mutant SCLC may be a distinct subclass of SCLC that exhibits epithelial-mesenchymal transition phenotypes, and adding an AKT or histone deacetylase inhibitor to pre-existing therapies may be one of the therapeutic choices for transformed EGFR-mutant SCLC.