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Mechanism of genotoxicity induced by targeted cytoplasmic irradiation.

Hong M, Xu A, Zhou H, Wu L, Randers-Pehrson G, Santella RM, Yu Z, Hei TK - Br. J. Cancer (2010)

Bottom Line: A microbeam that can target the cytoplasm of cells with high precision was used to study mechanisms involved in mediating the genotoxic effects in irradiated human-hamster hybrid (A(L)) cells.Moreover, cytoplasmic irradiation of A(L) cells increased expression of cyclooxygenase-2 (COX-2) and activation of extracellular signal-related kinase (ERK) pathway.We herein proposed a possible signalling pathway involving reactive oxygen/nitrogen species and COX-2 in the cytoplasmic irradiation-induced genotoxicity effect.

View Article: PubMed Central - PubMed

Affiliation: Center for Radiological Research, Department of Radiation Oncology, College of Physicians and Surgeons, Columbia University Medical Center, 630 West 168th Street, New York, NY 10032, USA.

ABSTRACT

Background: Direct damage to DNA is generally accepted as the main initiator of mutation and cancer induced by environmental carcinogens or ionising radiation. However, there is accumulating evidence suggesting that extracellular/extranuclear targets may also have a key role in mediating the genotoxic effects of ionising radiation. As the possibility of a particle traversal through the cytoplasm is much higher than through the nuclei in environmental radiation exposure, the contribution to genotoxic damage from cytoplasmic irradiation should not be ignored in radiation risk estimation. Although targeted cytoplasmic irradiation has been shown to induce mutations in mammalian cells, the precise mechanism(s) underlying the mutagenic process is largely unknown.

Methods: A microbeam that can target the cytoplasm of cells with high precision was used to study mechanisms involved in mediating the genotoxic effects in irradiated human-hamster hybrid (A(L)) cells.

Results: Targeted cytoplasmic irradiation induces oxidative DNA damages and reactive nitrogen species (RNS) in A(L) cells. Lipid peroxidation, as determined by the induction of 4-hydroxynonenal was enhanced in irradiated cells, which could be suppressed by butylated hydroxyl toluene treatment. Moreover, cytoplasmic irradiation of A(L) cells increased expression of cyclooxygenase-2 (COX-2) and activation of extracellular signal-related kinase (ERK) pathway.

Conclusion: We herein proposed a possible signalling pathway involving reactive oxygen/nitrogen species and COX-2 in the cytoplasmic irradiation-induced genotoxicity effect.

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Related in: MedlinePlus

Extracellular signal-related kinase (ERK) activity in cytoplasmic-irradiated AL cells. (A) Relative fluorescence intensity of p-ERK in AL cells with 0 (control) or after irradiation with eight α-particles (8 α) through cytoplasm with or without 100 μ BHT treatment. (B) Relative fluorescence intensity of COX-2 in AL cells after irradiated with 0 (control) or eight α-particles through the cytoplasm with or without treatment with 50 μ PD98059, a specific inhibitor of the MAPK ERK (MEK). Data were averaged from three independent experiments. Bars indicate ±s.e. of sample means (asterisk indicated P<0.05).
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fig4: Extracellular signal-related kinase (ERK) activity in cytoplasmic-irradiated AL cells. (A) Relative fluorescence intensity of p-ERK in AL cells with 0 (control) or after irradiation with eight α-particles (8 α) through cytoplasm with or without 100 μ BHT treatment. (B) Relative fluorescence intensity of COX-2 in AL cells after irradiated with 0 (control) or eight α-particles through the cytoplasm with or without treatment with 50 μ PD98059, a specific inhibitor of the MAPK ERK (MEK). Data were averaged from three independent experiments. Bars indicate ±s.e. of sample means (asterisk indicated P<0.05).

Mentions: The MAPK pathways are responsible for the various growth factor-mediated cellular events such as proliferation, senescence, differentiation, and apoptosis. Numerous studies have shown that exposure of cells to ionising radiation as well as other toxic stresses can induce simultaneous compensatory activation of different MAPK pathways (Dent et al, 2003). There is evidence that 4-HNE can act as an inducer for COX-2, possibly through MAPK pathways (Kumagai et al, 2004). As shown in Figure 4A, cells irradiated with eight α-particles had a higher level of phospho-ERK when compared with that of the control, non-irradiated cells, suggesting that ERK is activated after cytoplasmic irradiation. Treatment of cells with BHT before irradiation reduced phospho-ERK to control levels, indicating that lipid peroxidation may act as an upstream activator of the ERK signalling pathway. If activation of ERK is critical in mediating the irradiation-induced up-regulation of COX-2, it should be possible to mitigate the later response by using a specific inhibitor of the MEK–ERK signalling pathway. Indeed, AL cells treated with a non-cytotoxic dose of PD 98059 showed suppression of COX-2 expression after ionising irradiation (Figure 4B). This result indicated that the MEK–ERK pathway may have a role in the COX-2 induction after cytoplasmic irradiation.


Mechanism of genotoxicity induced by targeted cytoplasmic irradiation.

Hong M, Xu A, Zhou H, Wu L, Randers-Pehrson G, Santella RM, Yu Z, Hei TK - Br. J. Cancer (2010)

Extracellular signal-related kinase (ERK) activity in cytoplasmic-irradiated AL cells. (A) Relative fluorescence intensity of p-ERK in AL cells with 0 (control) or after irradiation with eight α-particles (8 α) through cytoplasm with or without 100 μ BHT treatment. (B) Relative fluorescence intensity of COX-2 in AL cells after irradiated with 0 (control) or eight α-particles through the cytoplasm with or without treatment with 50 μ PD98059, a specific inhibitor of the MAPK ERK (MEK). Data were averaged from three independent experiments. Bars indicate ±s.e. of sample means (asterisk indicated P<0.05).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2967061&req=5

fig4: Extracellular signal-related kinase (ERK) activity in cytoplasmic-irradiated AL cells. (A) Relative fluorescence intensity of p-ERK in AL cells with 0 (control) or after irradiation with eight α-particles (8 α) through cytoplasm with or without 100 μ BHT treatment. (B) Relative fluorescence intensity of COX-2 in AL cells after irradiated with 0 (control) or eight α-particles through the cytoplasm with or without treatment with 50 μ PD98059, a specific inhibitor of the MAPK ERK (MEK). Data were averaged from three independent experiments. Bars indicate ±s.e. of sample means (asterisk indicated P<0.05).
Mentions: The MAPK pathways are responsible for the various growth factor-mediated cellular events such as proliferation, senescence, differentiation, and apoptosis. Numerous studies have shown that exposure of cells to ionising radiation as well as other toxic stresses can induce simultaneous compensatory activation of different MAPK pathways (Dent et al, 2003). There is evidence that 4-HNE can act as an inducer for COX-2, possibly through MAPK pathways (Kumagai et al, 2004). As shown in Figure 4A, cells irradiated with eight α-particles had a higher level of phospho-ERK when compared with that of the control, non-irradiated cells, suggesting that ERK is activated after cytoplasmic irradiation. Treatment of cells with BHT before irradiation reduced phospho-ERK to control levels, indicating that lipid peroxidation may act as an upstream activator of the ERK signalling pathway. If activation of ERK is critical in mediating the irradiation-induced up-regulation of COX-2, it should be possible to mitigate the later response by using a specific inhibitor of the MEK–ERK signalling pathway. Indeed, AL cells treated with a non-cytotoxic dose of PD 98059 showed suppression of COX-2 expression after ionising irradiation (Figure 4B). This result indicated that the MEK–ERK pathway may have a role in the COX-2 induction after cytoplasmic irradiation.

Bottom Line: A microbeam that can target the cytoplasm of cells with high precision was used to study mechanisms involved in mediating the genotoxic effects in irradiated human-hamster hybrid (A(L)) cells.Moreover, cytoplasmic irradiation of A(L) cells increased expression of cyclooxygenase-2 (COX-2) and activation of extracellular signal-related kinase (ERK) pathway.We herein proposed a possible signalling pathway involving reactive oxygen/nitrogen species and COX-2 in the cytoplasmic irradiation-induced genotoxicity effect.

View Article: PubMed Central - PubMed

Affiliation: Center for Radiological Research, Department of Radiation Oncology, College of Physicians and Surgeons, Columbia University Medical Center, 630 West 168th Street, New York, NY 10032, USA.

ABSTRACT

Background: Direct damage to DNA is generally accepted as the main initiator of mutation and cancer induced by environmental carcinogens or ionising radiation. However, there is accumulating evidence suggesting that extracellular/extranuclear targets may also have a key role in mediating the genotoxic effects of ionising radiation. As the possibility of a particle traversal through the cytoplasm is much higher than through the nuclei in environmental radiation exposure, the contribution to genotoxic damage from cytoplasmic irradiation should not be ignored in radiation risk estimation. Although targeted cytoplasmic irradiation has been shown to induce mutations in mammalian cells, the precise mechanism(s) underlying the mutagenic process is largely unknown.

Methods: A microbeam that can target the cytoplasm of cells with high precision was used to study mechanisms involved in mediating the genotoxic effects in irradiated human-hamster hybrid (A(L)) cells.

Results: Targeted cytoplasmic irradiation induces oxidative DNA damages and reactive nitrogen species (RNS) in A(L) cells. Lipid peroxidation, as determined by the induction of 4-hydroxynonenal was enhanced in irradiated cells, which could be suppressed by butylated hydroxyl toluene treatment. Moreover, cytoplasmic irradiation of A(L) cells increased expression of cyclooxygenase-2 (COX-2) and activation of extracellular signal-related kinase (ERK) pathway.

Conclusion: We herein proposed a possible signalling pathway involving reactive oxygen/nitrogen species and COX-2 in the cytoplasmic irradiation-induced genotoxicity effect.

Show MeSH
Related in: MedlinePlus