Role of nuclear protein denaturation and aggregation in thermal radiosensitization

Abstract

Hyperthermia at temperatures above 41 degrees C denatures a set of thermolabile cellular proteins located in all parts of the cell. Non-histone nuclear proteins, including those comprising the nuclear matrix, appear to be particularly thermolabile. Heating isolated nuclear matrices of Chinese hamster lung (CHL) V79 cells to 46 degrees C at 1 degree C/min results in approximately 15% denaturation. Protein unfolding during denaturation exposes buried hydrophobic residues, which increases protein-protein interactions and results in the co-aggregation of denatured thermolabile proteins and native, aggregative-sensitive nuclear proteins. This aggregated protein, the majority of which is native, is insoluble and resistant to extraction during isolation of nuclei and is responsible for the increased protein content, usually expressed as an increased protein:DNA ratio, of nuclei isolated from heated cells. A large fraction of the aggregated protein is found to be associated with the nuclear matrix, distributed throughout the fibre network and nucleolus. Three general consequences of nuclear protein denaturation and aggregation of relevance to cellular damage are: (1) protein (enzyme) inactivation, both direct inactivation of thermolabile proteins and indirect inactivation due to co-aggregation; (2) reduced accessibility and altered physical properties of DNA due to masking by aggregated protein; and (3) protein redistribution into and out of the nucleus. Functional impairment of the nucleus appears to be due to one or a combination of these basic mechanisms.

Hyperthermia, Radiation and Chemotherapy: The Role of Heat in Multidisciplinary Cancer Care

“…(29) The activation energeries for protein denaturization and heat induced cell death were noted to be within the same range. Further research suggested that nuclear proteins are most sensitive (30)(31)(32) and a high degree of correlation of nuclear protein aggregation and heat induced cell kill has been noted. Radiation sensitization is achieved in large part through nuclear protein aggregation which inhibits the DNA repair process thus converting potentially lethal radiation induced DNA breaks into lethal events.…”

Heat-Induced Perturbations of DNA Damage Signaling Pathways are Modulated by Molecular Chaperones

“…Understanding the mechanism of action of this potent radiosensitizer should yield information with translational implications, both in terms of improving the efficacy of the combined modality in the clinic, and the possible development of agents that mimic the radiosensitizing action of heat. Exposure to heat leads to alterations in chromatin structure, which reduce the accessibility to the DNA repair machinery, leading to the perturbations of DNA double-strand break (DSB) repair associated with heat sensitization (1,(3)(4)(5). Heat also induces cellular signaling pathways and perturbations in signaling pathways induced by other agents (6).…”

Improving efficacy of hyperthermia in oncology by exploiting biological mechanisms

“…This heat shock response consists of a rapid production of heat shock proteins (HSPs), a specific group of proteins that chaperone denatured proteins and thereby prevent formation of toxic protein aggregates ( Figure 1B) [45][46][47]. This defence mechanism is not limited to the response to heat, but is also activated by several other forms of stress, such as hypoxia and infection, and is therefore of vital importance for life [47].…”

“…Early biological and physical studies revealed that the various physiological and cellular changes induced by hyperthermia are dose dependent [3]. Therefore, heat treatment can be defined by the temperature that is applied: hyperthermia (39)(40)(41)(42)(43)(44)(45) C), with temperatures <42 C further defined as mild temperature hyperthermia, and thermal ablation (>45 C). A second distinction in hyperthermia treatment is based on which part of the body is heated.…”