Targeting Tumor Cells by Actin-Regulated Nuclear Envelope Rupture

Abstract

The survival and plasticity of cancer cells depend of numerous factors which distinguish them from normal cells. Epithelial cancers characteristically deregulate cell mechanics. Tumor cells often show reduced stiffness and generate more contractile forces, as a result of both cellular intrinsic oncogenic alterations and microenvironment changes. Notably, changes in nuclear envelope protein expression, that modify nuclear shape and rigidity, influence cell invasiveness. However, a decrease in nuclear stiffness can lead to nuclear envelope rupture due to focal forces generated by the perinuclear actin structures in metastazing cells that migrate through tight interstitial spaces. Therefore, it has been suggested that an increase propensity to nuclear rupturing represents a new cancer cell vulnerability, which could promote genomic instability. Viral proteins with a tumor cell-selective killing activity offer powerful tools to uncover fundamental differences in cancer cells. In this study, we sought to interrogate the relevance of actomyosin contractility for the tumor cell-selective action of the adenovirus (Ad) type 2 early region 4 (E4) ORF4 (E4orf4) along with the mechanisms involved. We found that E4orf4 tumoricidal activity correlates with actomyosin-driven changes in nuclear shape. Live cell imaging revealed that E4orf4 promoted repeated cycles of nuclear envelope rupture and repair in various tumor cell lines, which caused the nuclear efflux of E4orf4 and exacerbated actomyosin contractility. Such process ultimately led to a prolonged loss of nuclear compartment integrity, overcoming the cellular capacity to repair the nuclear envelope. Furthermore, E4orf4-induced nuclear rupture, as other death-associated endpoint phenotypes, were impaired by depletion of LINC complex proteins. These results suggest that E4orf4 toxicity is regulated nucleo-cytoskeletal connections. We propose that E4orf4 harnesses nuclear envelope mechanical regulation to kill tumor cells, hence offering a unique tool to decipher novel pathways controlling cell invasiveness.