Abstract 2726: Nuclear checkpoints for melanoma and breast cancer lung metastasis

Abstract

Abstract Introduction Metastasis involves cancer cell intravasation and extravasation from blood vessels at target organs. The mechanisms by which the nuclei of metastatic tumor cells squeeze through different vascular and epithelial barriers are poorly understood. The nuclear lamina attaches chromatin domains to the nuclear periphery and controls the mechanical properties of the nucleus and its crosstalk with the cell cytoskeleton. A-type lamins, lamin A and its splice variant lamin C, are key nuclear lamina proteins that control nucleus stiffness and regulate chromatin conformation. Reduced lamin A was reported in some aggressive cancers. Results and Discussion Using a new in vitro transendothelial migration (TEM) assay we found that melanoma and breast cancer cells slowly squeeze their nuclei and complete TEM through endothelial junctions irrespective of their relative lamin A/C levels, suggesting that lamin A/C dependent nuclear stiffening is not a rate-limiting step for cancer cell squeezing through endothelial cells in vitro. In contrast, reduced lamin A/C enhanced cancer cell squeezing through rigid pores. Tumor emigration analysis across blood vessels in vivo was performed by new 3D imaging of fluorescently labeled cancer cells with high and low lamin A/C levels. This imaging was based on light sheet microscopy of lipid-cleared lungs of recipient mice in situ labeled with anti-vascular CD31 mAb. Using this technology, we found that reduced lamin A/C expression did not enhance the emigration of circulating murine melanoma and breast cancer cells across lung capillaries in vivo. Lower lamin A/C levels reduced the constitutive, transcriptionally repressed, heterochromatin in both melanoma and breast cancer cells. Decreased lamin A/C expression did not enhance however, nuclear rupture in the tumor cells that entered the lung parenchyma. The outcomes of the epigenetic and mechanical changes resulting of lamin A/C suppression on tumor growth and metastasis are under current investigation. Conclusions Our results suggest that subsets of tumor cells may benefit from reducing their nuclear content of lamin A/C mainly at the level of rigid barrier crossing (e.g. dense interstitial spaces), but not at the level of extravasation or post extravasation survival at target organs. How alterations in lamin A/C content contribute to tumor heterogeneity and metastatic potential of singular cancer cells remains an open question. Citation Format: Francesco Roncato, Ofer Regev, Nehora Levi, Sara W. Feigelson, Gabi Gerlitz, Ronen Alon. Nuclear checkpoints for melanoma and breast cancer lung metastasis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2726.