Heat induced ‘masking’ of redox sensitive component(s) of the DNA-nuclear matrix anchoring complex

Abstract

The 'masking effect' is the observation that heat shock reduces or masks the apparent expression of ionizing radiation (IR) damage to DNA. The mechanism of this effect is thought to involve the aggregation of proteins to the nuclear matrix or chromatin, thereby stabilizing these structures and masking actual DNA damage from assays and presumably from DNA repair complexes. Previously, using the 'halo assay', it has been shown that nucleoids treated with 1 mM dithiothreitol (DTT) and/or inhibited the rewinding of DNA supercoils and that this effect was masked in nucloids isolated from heated cells. Here it is reported that treatment of living cells with reducing agents diminishes the interaction between DNA and Protein Disulphide Isomerase (PDI) and that hyperthermia restored the PDI-DNA interaction, indicating that the masking effect occurred in vivo. PDI is a nuclear matrix protein which binds MAR DNA sequences and may be involved in regulating the degree of DNA supercoiling. It is hypothesized that heat-induced stabilization of PDI-DNA interaction will mask changes in supercoiling observed with reducing reagents and also IR. This stabilization may be affected through either the heat-induced association or enhancement of the binding of proteins to MAR DNA at the NM. Several proteins, including B23 and Hsp60, have been identified whose interaction with DNA increased following heat shock. Further work will be needed to determine if these proteins do, in fact, play a role in the masking effect.

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

“…1A). These results are consistent with previous reports showing that hyperthermia increases NPM association with DNA in vivo (5) binds DNA in vitro (32). …”

“…Further, the enhanced association between NPM and MAR DNA was reversed in a time dependent manner during post heat incubation (Fig. 5D), typical for post heat recovery from the masking effect (5). Since the ability to rewind DNA supercoils depends upon DNA-nuclear matrix anchoring, the association of NPM with MAR DNA is consistent with the observation that the masking effect detected by the halo assay depends on NPM.…”

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.…”

Investigations concerning the impact of consumption of hot beverages on acute cytotoxic and genotoxic effects in oral mucosa cells

“…The indicator cells were grown in these experiments continuously at temperatures ≤ 40 °C; therefore, the exposure conditions were quite different compared to those in consumers of hot beverages where the maximal temperatures reach 70 °C and cells are exposed for a relatively short time. It was postulated that high temperatures lead to impairment of DNA-repair processes and DNA-damage 33 – 35 ; in this context it is notable that Kampinga and Laszlo 33 criticized a Japanese study 36 which postulated that heat induced cell killing is caused by double strand breaks (DSBs). Our results underline the validity of this criticism and show that pronounced cytotoxicity is observed in mucosa cells already in absence of chromosomal damage (which results from DSBs).…”