DNA Damage Follows Repair Factor Depletion and Portends Genome Variation in Cancer Cells after Pore Migration

Abstract

Migration through micron-size constrictions has been seen to rupture the nucleus, release nuclear-localized GFP, and cause localized accumulations of ectopic 53BP1-a DNA repair protein. Here, constricted migration of two human cancer cell types and primary mesenchymal stem cells (MSCs) increases DNA breaks throughout the nucleoplasm as assessed by endogenous damage markers and by electrophoretic "comet" measurements. Migration also causes multiple DNA repair proteins to segregate away from DNA, with cytoplasmic mis-localization sustained for many hours as is relevant to delayed repair. Partial knockdownof repair factors that also regulate chromosome copy numbers is seen to increase DNA breaks in U2OS osteosarcoma cells without affecting migration and with nucleoplasmic patterns of damage similar to constricted migration. Such depletion also causes aberrant levels of DNA. Migration-induced nuclear damage is nonetheless reversible for wild-type and sub-cloned U2OS cells, except for lasting genomic differences between stable clones as revealed by DNA arrays and sequencing. Gains and losses of hundreds of megabases in many chromosomes are typical of the changes and heterogeneity in bone cancer. Phenotypic differences that arise from constrictedmigration of U2OS clones are further illustrated by a clone with a highly elongated and stableMSC-like shape that depends on microtubuleassembly downstream of the transcription factor GATA4. Such changes are consistent with reversion to a more stem-like state upstream ofcancerous osteoblastic cells. Migration-induced genomic instability can thus associate with heritable changes.