Abstract 1883: Fibrillar 1D tumor microenvironment is the key driver associating high-speed tumor cell motility with nuclear shape in breast cancer
Authors: Sharma Ved P. , Williams James , Leung Edison , Sanders Joseph , Eddy Robert , Castracane James , Condeelis John 
Published: July 2017

Abstract
Unlike normal breast stroma, which contains curly collagen fibrils, aligned collagen fibers oriented perpendicular to blood vessels are seen in both human breast tumors and mouse models of breast cancer. These linear collagen fibers provide “highways” for tumor cells to migrate toward blood vessels in a directional migration mode known as tumor cell streaming. Streaming is characterized by tumor cell migration at high speed and directional persistence on 1D collagen fibers. Previous studies utilizing linear ECM substrates have shown that tumor cells adopt elongated morphology and display increased speeds on linear 1D substrates compared to their 2D motility. However, the relationship between 1D geometry of ECM fibers in breast tumor microenvironment and the underlying mechanotransduction mechanism regulating high-speed migration of tumor cells is not well understood. Here, we analyzed in vivo ECM architecture by SHG intravital imaging and found a narrow peak of fiber diameters falling in the range 2-3 µm. These fibers were composed of collagen I and fibronectin. Based on these findings, we developed a high fidelity in vitro nanofiber system to study the molecular mechanisms underlying tumor cell streaming migration. Breast carcinoma cells plated on 2 µm ECM-coated fibers showed enhanced motility matching in vivo velocities averaging 1.2 µm/min. We varied 1D fiber diameter (0.7-20 µm) and found that tumor cells move the fastest with highest persistence on smaller fibers within a narrow range of diameters from 0.7-3 µm. High tumor cell speeds correlated with enhanced alignments of F-actin and focal adhesions along the fiber axial dimension. Unexpectedly, we also observed nuclear deformation during carcinoma cell migration on narrow fibers in vitro, similar to nuclear deformation observed in vivo. This was a surprising finding because nuclear deformation in vivo was assumed to be caused by squeezing through ECM pores. Thus, we hypothesized that actomyosin forces not only regulate cell motility parameters, but also nuclear deformation independently of ECM pore size. To test this hypothesis, we disrupted the transmission of cytoskeletal forces to the nucleus by knocking down LINC complex proteins - SUN1 and SUN2, and found increased nuclear elongation and cell motility parameters, through the upregulation of actin polymerization. These results indicate that in carcinoma cells, F-actin associated forces are shared between the leading edge (to maintain cell speed) and the nucleus (to dynamically regulate nuclear shape). LINC complex disruption releases F-actin forces acting on the nucleus to the cell front, leading to higher tumor cell motility speeds. In summary, our results provide new insights into the interplay between actomyosin contractility and the LINC complex in the regulation of nuclear shape and high-speed tumor cell motility during carcinoma cell metastasis.
Citation Format: Ved P. Sharma, James Williams, Edison Leung, Joseph Sanders, Robert Eddy, James Castracane, John Condeelis. Fibrillar 1D tumor microenvironment is the key driver associating high-speed tumor cell motility with nuclear shape in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1883. doi:10.1158/1538-7445.AM2017-1883