During cancer metastasis, tumor cells penetrate tissues through tight interstitial spaces, requiring extensive deformation of the cell and its nucleus. Here, we investigated tumor cell migration in confining microenvironments in vitro and in vivo. Nuclear deformation caused localized loss of nuclear envelope (NE) integrity, which led to the uncontrolled exchange of nucleo-cytoplasmic content, herniation of chromatin across the NE, and DNA damage. The incidence of NE rupture increased with cell confinement and with depletion of nuclear lamins, NE proteins that structurally support the nucleus. Cells restored NE integrity using components of the endosomal sorting complexes required for transport-III (ESCRT-III) machinery. Our findings indicate that cell migration incurs substantial physical stress on the NE and its content, requiring efficient NE and DNA damage repair for survival.

The physical limits of cell migration in dense porous environments are dependent upon the available space and the deformability of the nucleus and are modulated by matrix metalloproteinases, integrins and actomyosin function.

Directional cell migration in dense three-dimensional (3D) environments critically depends upon shape adaptation and is impeded depending on the size and rigidity of the nucleus. Accordingly, the nucleus is primarily understood as a physical obstacle; however, its pro-migratory functions by stepwise deformation and reshaping remain unclear. Using atomic force spectroscopy, time-lapse fluorescence microscopy and shape change analysis tools, we determined the nuclear size, deformability, morphology and shape change of HT1080 fibrosarcoma cells expressing the Fucci cell cycle indicator or being pre-treated with chromatin-decondensating agent TSA. We show oscillating peak accelerations during migration through 3D collagen matrices and microdevices that occur during shape reversion of deformed nuclei (recoil), and increase with confinement. During G1 cell-cycle phase, nucleus stiffness was increased and yielded further increased speed fluctuations together with sustained cell migration rates in confinement when compared to interphase populations or to periods of intrinsic nuclear softening in the S/G2 cell-cycle phase. Likewise, nuclear softening by pharmacological chromatin decondensation or after lamin A/C depletion reduced peak oscillations in confinement. In conclusion, deformation and recoil of the stiff nucleus contributes to saltatory locomotion in dense tissues. This article is part of a discussion meeting issue ‘Forces in cancer: interdisciplinary approaches in tumour mechanobiology’.

2Abbreviations: 2D, two-dimensional; 3D, three-dimensional; AFS, atomic force spectroscopy; ECM, extracellular matrix; H2B, histone-2B; MMP matrix metalloproteinase; NII, nuclear irregularity index; NT, non-targeting control; PDMS, polydimethylsiloxane SummaryNuclear deformability during cancer cell invasion and metastasis is critically regulated by lamin A. Here, researchers showed that lamin B2 also contributes to nuclear mechanics, implicating cooperating lamin networks regulating nuclear integrity, migration efficacy, and metastatic tumor progression. AbstractInterstitial tumor cell invasion depends upon complex mechanochemical adaptation of both cell body and the rigid nucleus in response to extracellular tissue topologies. Nuclear mechanics during cell migration through confined environments is controlled by A-type lamins, however, the contribution of B-type lamins to the deformability of the nucleus remains unclear. Using systematic expression regulation of different lamin isoforms, we applied multi-parameter wet-lab and in silico analysis to test their impact on nuclear mechanics, shape regulation, and cancer cell migration. Modulation of lamin A/C and B2 but not B1 isoforms controlled nuclear deformation and viscoelasticity, whereby lamin B2 generally followed lamin A/C-mediated effects. Cell migration rates were altered by 5 to 9fold in dense collagen environments and synthetic devices, with accelerated rates after lamin downregulation and reverse effects after lamin upregulation, with migration rates strongly depending on nuclear shape change. These findings implicate cooperation of lamin B2 with lamin A/C in regulating nuclear mechanics for shape adaptation and migration efficacy.