Lamin B1 loss promotes lung cancer development and metastasis by epigenetic derepression of RET

Although abnormal nuclear structure is an important criterion for cancer diagnostics, remarkably little is known about its relationship to tumor development. Here we report that loss of lamin B1, a determinant of nuclear architecture, plays a key role in lung cancer. We found that lamin B1 levels were reduced in lung cancer patients. Lamin B1 silencing in lung epithelial cells promoted epithelial-mesenchymal transition, cell migration, tumor growth, and metastasis. Mechanistically, we show that lamin B1 recruits the polycomb repressive complex 2 (PRC2) to alter the H3K27me3 landscape and repress genes involved in cell migration and signaling. In particular, epigenetic derepression of the RET proto-oncogene by loss of PRC2 recruitment, and activation of the RET/p38 signaling axis, play a crucial role in mediating the malignant phenotype upon lamin B1 disruption. Importantly, loss of a single lamin B1 allele induced spontaneous lung tumor formation and RET activation. Thus, lamin B1 acts as a tumor suppressor in lung cancer, linking aberrant nuclear structure and epigenetic patterning with malignancy.

Cell type-selective pathways and clinical associations of lysophosphatidic acid biosynthesis and signaling in the ovarian cancer microenvironment

The peritoneal fluid of ovarian carcinoma patients promotes cancer cell invasion and metastatic spread with lysophosphatidic acid (LPA) as a potentially crucial mediator. However, the origin of LPA in ascites and the clinical relevance of individual LPA species have not been addressed. Here, we show that the levels of multiple acyl‐LPA species are strongly elevated in ascites versus plasma and are associated with short relapse‐free survival. Data derived from transcriptome and secretome analyses of primary ascite‐derived cells indicate that (a) the major route of LPA synthesis is the consecutive action of a secretory phospholipase A₂ (PLA₂) and autotaxin, (b) that the components of this pathway are coordinately upregulated in ascites, and (c) that CD163+CD206+ tumor‐associated macrophages play an essential role as main producers of PLA₂G7 and autotaxin. The latter conclusion is consistent with mass spectrometry‐based metabolomic analyses of conditioned medium from ascites cells, which showed that tumor‐associated macrophages, but not tumor cells, are able to produce 20:4 acyl‐LPA in lipid‐free medium. Furthermore, our transcriptomic data revealed that LPA receptor (LPAR) genes are expressed in a clearly cell type‐selective manner: While tumor cells express predominantly LPAR1‐3, macrophages and T cells also express LPAR5 and LPAR6 at high levels, pointing to cell type‐selective LPA signaling pathways. RNA profiling identified cytokines linked to cell motility and migration as the most conspicuous class of LPA‐induced genes in macrophages, suggesting that LPA exerts protumorigenic properties at least in part via the tumor secretome.

Abstract 2604: Involvement of circulating fibrocytes in the progression of adenocarcinomas by modulating EMT and tumor microenvironment

Background: Circulating fibrocytes (CFs) are bone marrow derived, mesenchymal progenitor cells that have emerging role in many diseases. CFs was shown to participate in tissue remodeling in pulmonary hypertension and fibrosis, via secretion of different cytokines and growth factors. Nevertheless, their role in the lung cancer still has to be delineated. Thus, our aim is to identify the role of CFs in lung cancer progression and metastatic potential.

Results/methods: We generated CFs by isolating human peripheral blood mononuclear cells (PBMCs) and culturing them for 10 days until they differentiated into CFs. Purity (≥95%) of the CFs population was analyzed by flow cytometry and immunofluorescence. Co-culturing of A549 (human alveolar adenocarcinoma cells) and CFs for 12 and 24 hrs, followed by collection of conditioned medium (CM) and RNA from both cells yielded interesting results. Co-cultured CM promoted proliferation (1.31±0.07 versus 1.5±0.13) and migrating capacity (64.6±26.5 versus 472.8±103.4) of A549 tumor cells. In addition, co-cultured CM caused epithelial-to-mesenchymal transition (EMT) of A549 cells; epithelial markers (E-cadherin, cytokeratin) were downregulated, and mesenchymal markers (α-smooth muscle actin, fibronectin) were upregulated.

In vivo to study the CFs involvement in lung cancer, we co-injected CFs with A549 cells or A549 cells alone and measured the tumor growth after 28 days. The tumor size was significantly increased (1354.8±333.6 versus 3042.4±373.4) in co-injected group (CF+A549) compared to A549 alone. Screening for genes regulated in co-injected group tumors showed regulation of tumor microenvironment, an increase in macrophage markers (CSF1R, CD68, CD200, MMD), angiogenesis markers (EDNRB, THBS1) and ECM remodeling markers (MMP14, CTSB, CTSH) compared to A549 tumor alone.

Conclusions: We believe that circulating fibrocytes may play positive role in the tumor growth and progression. The increase in EMT and migration, may suggest their involvement in invasion and metastasis. Targeting CFs and their secretory molecules can be of therapeutic importance in lung cancer.

Citation Format: Alina Asafova, Vandana Nikam, Anja Schmall, Werner Seeger, Robert Voswinckel, Rajkumar Savai. Involvement of circulating fibrocytes in the progression of adenocarcinomas by modulating EMT and tumor microenvironment. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2604. doi:10.1158/1538-7445.AM2013-2604