ABSTRACT
The nucleus is the defining organelle of eukaryotic cells. It is usually considered a target organelle for cellular inputs. Here, we find that the nucleus is not simply a “passive” responder, but an active organelle directing the mechanical properties of the actin cytoskeleton it engages. Biochemically, interaction of FHOD formins with nesprin-2 of the nuclear LINC complex activates their actin bundling activity making them more potent than known bundlers like fascin or α-actinin. In cells, FHOD-associated LINC complexes enhance the mechanical resistance of nuclear-engaged actin cables in polarizing fibroblasts and sarcomeres in developing cardiomyocytes. Hypertrophic cardiomyopathy-associated variants of FHOD3 are defective in these processes. In mice, the FHOD3 R637P disease-causing allele results in embryonic lethality when homozygous and in stress-induced cardiac hypertrophy when heterozygous. These results show that the nucleus actively directs its mechanical environment and that disruption of this capability in heart leads to cardiac hypertrophy.
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