Abstract
Structural features of the nucleus including shape, size and deformability impact its function affecting normal cellular processes such as cell differentiation and pathological conditions such as tumor cell migration. Despite the fact that abnormal nuclear morphology has long been a defining characteristic for diseases such as cancer relatively little is known about the mechanisms that control normal nuclear architecture. Mounting evidence suggests close coupling between F-actin cytoskeletal organization and nuclear morphology however, mechanisms regulating this coupling are lacking. Here we identify that Cofilin/ADF-family F-actin remodeling proteins are essential for normal nuclear structure in different cell types. siRNA mediated silencing of Cofilin/ADF provokes striking nuclear defects including aberrant shapes, nuclear lamina disruption and reductions to peripheral heterochromatin. We provide evidence that these anomalies are primarily due to Rho kinase (ROCK) controlled excessive contractile myosin-II activity and not to elevated F-actin polymerization. Furthermore, we demonstrate a requirement for nuclear envelope LINC (linker of nucleoskeleton and cytoskeleton) complex proteins together with lamin A/C for nuclear aberrations induced by Cofilin/ADF loss. Our study elucidates a pivotal regulatory mechanism responsible for normal nuclear structure and which is expected to fundamentally influence nuclear function.
Highlights
Cofilin-1 and ADF, products of separate genes, are best known for their ability to induce F-actin disassembly via filament severing or depolymerization[19,20]
Of control HeLa cells, 96% exhibited a stereotypic spherical nuclear morphology in contrast to Cof/ADF depleted cells where over 70% of cells displayed abnormalities classified in DAPI staining by the presence of multiple lobules and or invaginations, herniations or the presence of finger-like protrusions with bulbous ends (Fig. 1a–c)
Nuclear architectural defects following Cof/ADF depletion were not restricted to HeLa cells and were observed in multiple cell types including U2OS cells and non-transformed RPE-1 cells (Figs 1f,g, 2e and 2i for quantification of lamin structural deficits in RPE cells)
Summary
Cofilin-1 and ADF, products of separate genes, are best known for their ability to induce F-actin disassembly via filament severing or depolymerization[19,20]. We hypothesized that in addition to their well-known roles in regulating F-actin turnover, the cofilin/ADF proteins are important for the control of intracellular tensional homeostasis through modulation of actomyosin assembly. In further tests of this hypothesis we identify crucial roles for cofilin/ADF in control of cytoskeletal force modulation for maintenance of normal nuclear architecture. Our results support and extend to additional cell types the generality of the findings of Kanellos et al.[22], which were published during preparation of our manuscript. Both studies highlight an importance for deregulated myosin-II contractile activity, coupled to mechanotransduction by nuclear envelope LINC complex proteins, in the genesis of nuclear structural deficits following loss of cofilin/ADF. Our results provide insights as to how intracellular mechanical forces may act to influence nuclear morphology and chromatin organization
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