Brain metastatic outgrowth and osimertinib resistance are potentiated by RhoA in EGFR-mutant lung cancer.

The brain is a major sanctuary site for metastatic cancer cells that evade systemic therapies. Through pre-clinical pharmacological, biological, and molecular studies, we characterize the functional link between drug resistance and central nervous system (CNS) relapse in Epidermal Growth Factor Receptor- (EGFR-) mutant non-small cell lung cancer, which can progress in the brain when treated with the CNS-penetrant EGFR inhibitor osimertinib. Despite widespread osimertinib distribution in vivo, the brain microvascular tumor microenvironment (TME) is associated with the persistence of malignant cell sub-populations, which are poised to proliferate in the brain as osimertinib-resistant lesions over time. Cellular and molecular features of this poised state are regulated through a Ras homolog family member A (RhoA) and Serum Responsive Factor (SRF) gene expression program. RhoA potentiates the outgrowth of disseminated tumor cells on osimertinib treatment, preferentially in response to extracellular laminin and in the brain. Thus, we identify pre-existing and adaptive features of metastatic and drug-resistant cancer cells, which are enhanced by RhoA/SRF signaling and the brain TME during the evolution of osimertinib-resistant disease.

Tumor progression and chromatin landscape of lung cancer are regulated by the lineage factor GATA6.

Lineage selective transcription factors (TFs) are important regulators of tumorigenesis, but their biological functions are often context dependent with undefined epigenetic mechanisms of action. In this study, we uncover a conditional role for the endodermal and pulmonary specifying TF GATA6 in lung adenocarcinoma (LUAD) progression. Impairing Gata6 in genetically engineered mouse models reduces the proliferation and increases the differentiation of Kras mutant LUAD tumors. These effects are influenced by the epithelial cell type that is targeted for transformation and genetic context of Kras-mediated tumor initiation. In LUAD cells derived from surfactant protein C expressing progenitors, we identify multiple genomic loci that are bound by GATA6. Moreover, suppression of Gata6 in these cells significantly alters chromatin accessibility, particularly at distal enhancer elements. Analogous to its paradoxical activity in lung development, GATA6 expression fluctuates during different stages of LUAD progression and can epigenetically control diverse transcriptional programs associated with bone morphogenetic protein signaling, alveolar specification, and tumor suppression. These findings reveal how GATA6 can modulate the chromatin landscape of lung cancer cells to control their proliferation and divergent lineage dependencies during tumor progression.

Adaptive Protein Translation by the Integrated Stress Response Maintains the Proliferative and Migratory Capacity of Lung Adenocarcinoma Cells.

The integrated stress response (ISR) is a conserved pathway that is activated by cells that are exposed to stress. In lung adenocarcinoma, activation of the ATF4 branch of the ISR by certain oncogenic mutations has been linked to the regulation of amino acid metabolism. In the present study, we provide evidence for ATF4 activation across multiple stages and molecular subtypes of human lung adenocarcinoma. In response to extracellular amino acid limitation, lung adenocarcinoma cells with diverse genotypes commonly induce ATF4 in an eIF2α-dependent manner, which can be blocked pharmacologically using an ISR inhibitor. Although suppressing eIF2α or ATF4 can trigger different biological consequences, adaptive cell-cycle progression and cell migration are particularly sensitive to inhibition of the ISR. These phenotypes require the ATF4 target gene asparagine synthetase (ASNS), which maintains protein translation independently of the mTOR/PI3K pathway. Moreover, NRF2 protein levels and oxidative stress can be modulated by the ISR downstream of ASNS. Finally, we demonstrate that ASNS controls the biosynthesis of select proteins, including the cell-cycle regulator cyclin B1, which are associated with poor lung adenocarcinoma patient outcome. Our findings uncover new regulatory layers of the ISR pathway and its control of proteostasis in lung cancer cells. IMPLICATIONS: We reveal novel regulatory mechanisms by which the ISR controls selective protein translation and is required for cell-cycle progression and migration of lung cancer cells.

Human C6orf211 encodes Armt1, a protein carboxyl methyltransferase that targets PCNA and is linked to the DNA damage response.

Recent evidence supports the presence of an L-glutamyl methyltransferase(s) in eukaryotic cells, but this enzyme class has been defined only in certain prokaryotic species. Here, we characterize the human C6orf211 gene product as "acidic residue methyltransferase-1" (Armt1), an enzyme that specifically targets proliferating cell nuclear antigen (PCNA) in breast cancer cells, predominately methylating glutamate side chains. Armt1 homologs share structural similarities with the SAM-dependent methyltransferases, and negative regulation of activity by automethylation indicates a means for cellular control. Notably, shRNA-based knockdown of Armt1 expression in two breast cancer cell lines altered survival in response to genotoxic stress. Increased sensitivity to UV, adriamycin, and MMS was observed in SK-Br-3 cells, while in contrast, increased resistance to these agents was observed in MCF7 cells. Together, these results lay the foundation for defining the mechanism by which this post-translational modification operates in the DNA damage response (DDR).