Feeling the force : role of AmotL2 in normal development and cancer

Cells that fabricate the body, dwell in a very heterogeneous environment. Self-organization of individual cells into complex tissues and organs at the time of growth and revival is brought about by the combinatory action of biomechanical and biochemical signaling processes. Tissue generation and functional organogenesis, requires distinct cell types to unite together and associate with their corresponding microenvironment in a spatio-temporal manner. Furthermore, the cell-cell and cell-extracellular matrix (ECM) contact points are tethered together by the cytoskeletal protein network within the cell, which in turn connects to the nucleoskeleton. These uninterrupted networks from cell junctions to nucleus enable the cells to sense it’s surrounding. Recently it was found that relay of mechanical cues from cell exterior to interior (Mechanotransduction) is key to cellular fate determination and also behavior of an individual cell. However, deregulation of this signal processing has been reported to cause adverse consequences, for example increased stiffness in the ECM can result in loss of tissue architecture and promotes tumor progression. Mechanotransduction of the cell and its ECM have been extensively studied and elucidated to be important in driving various pathophysiological processes. However, the mechanisms underlying force transmission via cell-cell junctions and their role in morphogenesis and maintaining homeostasis still remain elusive. In this thesis, we have reported Angiomotin-Like-2 (p100AmotL2) as a novel linker protein, connecting VE/E-cadherin at the adherens junction (AJ) and the nucleus. Furthermore, we show that p100AmotL2 enables radial actin filament organization, which is essential for force generation/transmission required for various developmental processes such as aortic lumen expansion and blastocyst hatching. In paper 3 of this thesis, we identified the stress responsive shorter isoform of AmotL2 (p60AmotL2), which acts in a dominant negative fashion, by disrupting the VE/E-cadherin/p100AmotL2/nucleus mechanotransduction. Additionally, we also show that p60AmotL2 weakens cell-cell cohesion and alters nuclear integrity contributing to loss of tissue architecture and promote cellular invasion. The normal physiological function of p60AmotL2 has not yet been revealed, in Paper 4 of this thesis; we have elucidated novel molecular mechanism of p60AmotL2 in maintaining tissue homeostasis by promoting apical extrusion of cells. As cancer is known to hijack several physiological pathways, it is tempting to speculate that cancer cells might hijack p60AmotL2 mediated extrusion process to invade the surrounding tissues. LIST OF SCIENTIFIC PAPERS I. AmotL2 integrates polarity and junctional cues to modulate cell shape. Sara Hultin, Aravindh Subramani, Sebastian Hildebrand, Yujuan Zheng, Arindam Majumdar and Lars Holmgren. Sci Rep. 2017; 7: 7548. II. The E-cadherin/AmotL2 complex organizes actin filaments required for epithelial hexagonal packing and blastocyst hatching. Sebastian Hildebrand, Sara Hultin, Aravindh Subramani, Sophie Petropoulos, Yuanyuan Zhang, Xiaofang Cao, John Mpindi, Olli Kalloniemi, Staffan Johansson, Arindam Majumdar, Fredrik Lanner & Lars Holmgren. Sci Rep. 2017; 7: 9540 III. Uncoupling of the Nuclear LINC-complex from E-cadherin/radial actin filaments trigger single cell migration and invasion. Aravindh Subramani, Tomas Friman, Yuanyuan Zhang, Weyingqi Cui, Malgorzatta Lekka, VaniNarayanan, Daniel Conway and Lars Holmgren. IV. p60AmotL2 induces epithelial apical extrusion. Aravindh Subramani, Weiyingqi Cui and Lars Holmgren. *These authors contributed equally LIST OF ABBREVIATIONS