Nucleophosmin Redistribution following Heat Shock: A Role in Heat-Induced Radiosensitization

Abstract

Cellular survival from radiation-induced DNA damage requires access to sites of damage for the assembly of repair complexes and the subsequent repair, particularly the repair of DNA double strand breaks (DSB). Hyperthermia causes changes in protein-protein/DNA interactions in the nucleus that block access to sites of DNA damage. Studies presented here indicate that the nucleolar protein, nucleophosmin (NPM), redistributes from the nucleolus following hyperthermia, increases its association with DNA, and blocks access to DNA DSBs. Reduction of NPM significantly reduces heat-induced radiosensitization, but reduced NPM level does not alter radiation sensitivity per se. NPM knockdown reduces heat-induced inhibition of DNA DSB repair. Also, these results suggest that NPM associates with nuclear matrix attachment region DNA in heat-shocked cells. [Cancer Res 2009;69(16):6454-62]

Recruitment of Phosphorylated NPM1 to Sites of DNA Damage through RNF8-Dependent Ubiquitin Conjugates

“…Our results suggest that the pT199-NPM1-dependent HR repair is involved in the first mechanism. A previous report (44) and our results showed that depletion of total NPM1 had no effect on survival after IR, probably reflecting the multiple functions of NPM1 in addition to DSB repair. Although overexpression of NPM1 inhibits ARF, depletion of NPM1 also inhibits ARF because NPM1 binds to and protects ARF from degradation (43,45,46).…”

Effects of hyperthermia on Hsp27 (HSPB1), Hsp72 (HSPA1A) and DNA repair proteins hMLH1 and hMSH2 in human colorectal cancer hMLH1-deficient and hMLH1-proficient cell lines

“…Although hyperthermia may mask the DNA damage from repair pathways due (in part) to the heat-induced association of the nucleolar protein, nucleophosmin (NPM) with matrix attachment region (MAR) DNA [51], the DNA damage induced by the heat treatment decreased near to the basal levels in MMR-proficient and deficient cells. The higher nuclear expression of Hsp27 and Hsp72 after hyperthermia, especially in HCT116 þ ch3 cells, may be indicative of their participation in the repair of the heat-induced DNA damage.…”

Nucleolin and nucleophosmin: nucleolar proteins with multiple functions in DNA repair

“…While this hypothesis is compelling, it should be noted that Goldstein et al (2013) did find a partial abrogation of H3-H4 eviction in their assay following depletion of ASF1, a separate H3-H4 histone chaperone with roles in nucleosome reassembly after UV irradiation in humans (Battu et al 2011) and DSBs in S. cerevisiae (Chen et al 2008;Kim and Haber 2009), suggesting that if NPM1 does act at DSBs, it may share this activity with other histone chaperones. In addition, others have reported contrary activities for NPM1, identifying the protein as a "shielding" factor that blocks DSB repair in heat-shocked cells, possibly through tethering of DSB-containing DNA to the nuclear matrix (Vanderwaal et al 2009;Vanderwaal and Roti Roti 2004). How these apparently contradictory D r a f t 20 observations can be resolved with the above model of NPM1 function within DSB repair remains to be seen.…”

“…NPM1 undergoes rapid and reversible translocation from the nucleolus to the nucleoplasm (nucleoplasmic translocation) upon exposure to UV irradiation, oxidative stress, heat shock or numerous DNA-damaging agents including mitomycin C, methyl methanesulfonate (MMS) and cisplatin; however, NPM1 does not alter its localization in response to ionizing radiation (IR) or exposure to double strand break (DSB)-inducing topoisomerase inhibitors such as etoposide or camptothecin (Kurki et al 2004;Vanderwaal et al 2009;Yogev et al 2008). Importantly, these localization changes do not coincide with relocalization of NCL or a generalized dissociation of the nucleolus as seen in response to RNA Pol I inhibition, and evidence is emerging for their control by particular, DNA-damage-responsive signaling pathways and/or post-translational modifications (Kurki et al 2004;Liu et al 2007;Sato et al 2004;Vanderwaal et al 2009;Yogev et al 2008). Given such evidence, it is likely that the nucleoplasmic translocation of NPM1 is an active and controlled response to particular genotoxic stress conditions and not the result of generalized nucleolar disruption.…”