Role of Ca2+ in radiation-induced damage in murine splenocytes

Mutations of charged amino acids at the cytoplasmic end of transmembrane helix 2 affect transport activity of the budding yeast multidrug resistance protein Pdr5p

Pdr5p is a major ATP-binding cassette (ABC) transporter in Saccharomyces cerevisiae. It displays a sequence and functional homology to the pathogenic Candida albicans multidrug resistance protein Cdr1p. The transmembrane helices of Pdr5p act in substrate recognition, binding, translocation and eventual removal of toxic substances out of the plasma membrane via the formation of a binding pocket. In this study, we identify two novel Pdr5 mutants (E574K and E580K), which exhibit impaired substrate efflux functions. Both mutants remained hypersensitive to all tested Pdr5p substrates without affecting their protein expression levels, localization or ATPase activities. As E574 and E580 are both located adjacent to the predicted cytoplasmic end of transmembrane helix 2, this implies that such charged residues are functionally essential for Pdr5p. Molecular docking studies suggest the possibility that oppositely charged substitution at residue E574 may disturb the interaction between the substrates and Pdr5p, resulting in impaired transport activity. Our results present new evidence, suggesting that transmembrane helix 2 plays an important role for the efflux function of Pdr5p.

Comparison of proton and electron radiation effects on biological responses in liver, spleen and blood

PURPOSE

To determine whether differences exist between proton and electron radiations on biological responses after total-body exposure.

MATERIALS AND METHODS

ICR mice (n=45) were irradiated to 2 Gray (Gy) using fully modulated 70 MeV protons (0.5 Gy/min) and 21 MeV electrons (3 Gy/min). At 36 h post-irradiation liver gene expression, white blood cell (WBC), natural killer (NK) cell and other analyses were performed.

RESULTS

Oxidative stress-related gene expression patterns were strikingly different for irradiated groups compared to 0 Gy (P<0.05). Proton radiation up-regulated 15 genes (Ctsb, Dnm2, Gpx5, Il19, Il22, Kif9, Lpo, Nox4, Park7, Prdx4, Prdx6, Rag2, Sod3, Srxn1, Xpa) and down-regulated 2 genes (Apoe, Prdx1). After electron irradiation, 20 genes were up-regulated (Aass, Ctsb, Dnm2, Gpx1, Gpx4, Gpx5, Gpx6, Gstk1, Il22, Kif9, Lpo, Nox4, Park7, Prdx3, Prdx4, Prdx5, Rag2, Sod1, Txnrd3, Xpa) and 1 was down-regulated (Mpp4). Of the modified genes, only 11 were common to both forms of radiation. Comparison between the two irradiated groups showed that electrons significantly up-regulated three genes (Gstk1, Prdx3, Scd1). Numbers of WBC and major leukocyte types were low in the irradiated groups (P<0.001 vs. 0 Gy). Hemoglobin and platelet counts were low in the electron-irradiated group (P<0.05 vs. 0 Gy). However, spleens from electron-irradiated mice had higher WBC and lymphocyte counts, as well as enhanced NK cell cytotoxicity, compared to animals exposed to protons (P<0.05). There were no differences between the two irradiated groups in body mass, organ masses, and other assessed parameters, although some differences were noted compared to 0 Gy.

CONCLUSION

Collectively, the data demonstrate that at least some biological effects induced by electrons may not be directly extrapolated to protons.

Effects of corticosterone, cAMP, cGMP, Ca2+, and protein kinase C on apoptosis of mouse thymocytes induced by X-ray irradiation

OBJECTIVE

To observe the effects of signal factors of corticosterone (CS), cAMP, cGMP, Ca2+ andprotein kinase C (PKC) on lymphocyte apoptosis in mouse thymus induced by X-rays of 4 Gy in vitro.

METHODS

The DNA lytic rate for thymocytes was measured by fluorospectrophotometry.

RESULTS

The DNA lyric rate for thymocytes 4-8 hours after irradiation with 2-8 Gy was significantly higher than that in the control (P<0.01). As compared with the control, the DNA lytic rate for thymocytes treated with 0.01 micromol/L CS (P<0.01), 50 ng/mL cAMP (P<0.01), 0.05-0.4 microg/mL ionomycin (Iono, P<0.05 or P<0.01) or 0.05-0.4 ng/mL phorbol myristate acetate (PMA, P<0.05 or P<0.01), respectively, was significantly increased, while the rate for thymocytes treated with 50 ng/mL cGMP was not significantly increased. The DNA lytic rate for thymocytes treated with 0.01 micromol/L CS (P<0.01), 50 ng/mL cAMP (P<0.01), 0.2 and 0.4 microg/mL Iono (P<0.05), and 0.2 and 0.4 ng/mL PMA (P<0.05) plus 4-Gy irradiation, respectively, was significantly higher than that treated with single 4-Gy irradiation, while the rate for thymocytes treated with 50 ng/mL cGMP plus 4-Gy irradiation was not increased. When both 0.4 microg/mL Iono and 0.4 ng/mL PMA acted on the thymocytes, the DNA lytic rate for thymocytes was significantly higher than that in the control (P<0.01), the DNA lytic rate for thymocytes treated with both 0.4 microg/mL Iono and 0.4 ng/mL PMA plus 4-Gy irradiation was significantly higher than that treated with single 4-Gy irradiation (P<0.05), but was not significantly higher than that treated with 0.4 microg/mL Iono plus 4-Gy irradiation or 0.4 ng/mL PMA plus 4-Gy irradiation.

CONCLUSION

CS, cAMP, Ca2+, and PKC signal factors can promote thymocyte apoptosis induced by larger dose X-rays.

Reversal of tumor resistance to apoptotic stimuli by alteration of membrane fluidity: therapeutic implications

In recent years, significant development and improvement have been observed in the treatment of cancer; however, relapses and recurrences occur frequently and there have not been any current therapies to treat such cancers. Cancers resistant to conventional therapies develop several mechanisms to escape death-inducing stimuli. A poorly understood mechanism is the involvement of the cancer cell plasma membrane composition and architecture and their involvement in regulating drug-inducing stimuli leading to cell death. Although the basic structure of the biological membrane was established 80 years ago, study of the physical properties of lipid bilayers still provides significant information regarding membrane organization and dynamics. Membrane fluidity is probably the most important physicochemical property of cell membranes. Alterations of membrane fluidity can seriously affect functional properties of the cell and induction of apoptotic pathways resulting in cell death. The role of membrane fluidity in the apoptotic process is clearly exemplified as it is seriously disrupted as a result of cell injury. The molecular signaling pathways leading to apoptosis are currently promising areas of research investigation and lead to unravel the underlying molecular mechanisms of tumor cells resistance to apoptotic stimuli and hence the development of new effective therapeutic agents. Recent findings indicate that most anticancer agents induce apoptosis, directly or indirectly, through alterations of tumor cell membrane fluidity. The present chapter summarizes the relationship between alterations of tumor cell membrane fluidity and tumor cell response to apoptotic-inducing stimuli. Several potential therapeutic applications directed at tumor cell membrane fluidity are proposed.

Lipid peroxidation, oxidative stress genes and dietary factors in breast cancer protection: a hypothesis

We have recently proposed that lipid peroxidation may be a common mechanistic pathway by which obesity and hypertension lead to increased renal cell cancer risk. During this exercise, we noted a risk factor swap between breast and kidney cancer (oophorectomy and increased parity, detrimental for kidney, beneficial for breast; high blood pressure, detrimental for kidney, beneficial for breast when it occurs during pregnancy; alcohol, beneficial for kidney, detrimental for breast, and so on). We have subsequently proposed the hypothesis that lipid peroxidation represents a protective mechanism in breast cancer, and reviewed the evidence of the role of lipid peroxidation on established hormonal and non-hormonal factors for breast cancer. Here, we review the evidence in support of lipid peroxidation playing a role in the relationships between dietary factors and breast cancer. Available evidence implicates increased lipid peroxidation products in the anti-carcinogenic effect of suspected protective factors for breast cancer, including soy, marine n-3 fatty acids, green tea, isothiocyanates, and vitamin D and calcium. We also review the epidemiological evidence supporting a modifying effect of oxidative stress genes in dietary factor-breast cancer relationships.

Apoptotic index as predictive marker for radiosensitivity of cervical carcinoma: Evaluation of membrane fluidity, biochemical parameters and apoptosis after the first dose of fractionated radiotherapy to patients

BACKGROUND

This study was aimed to develop possible predictive response of cervical carcinoma in stage IIIA and B patients by evaluating the changes in physical parameter, such as, membrane fluidity, biochemical parameters, such as, intracellular calcium, antioxidant enzymes [superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx)] and apoptotic cell death in cervical cancer cells from patients after treating with the first fractionated dose of 2 Gy in radiation therapy protocol.

METHODS

Biopsies of cervical carcinoma patients were collected before and 24h after first fractionated radiation dose of 2 Gy. Cell suspensions and tissue of cervix cancer biopsies were used to measure various physical and biochemical parameters.

RESULTS AND CONCLUSIONS

A negative correlation was found to exist between observed fluidity of membrane/SOD level with the degree of apoptosis in cervical cells. On the other hand, a positive correlation was observed between intracellular calcium level and percent cellular apoptosis. These results suggest that changes in membrane fluidity, SOD and calcium level were involved in the mechanism of radiation induced cervical apoptosis as measured by TUNEL assay. Moreover, apoptotic sensitivity of these cells after the first dose of radiation treatment showed a direct correlation with the radiation treatment outcome in patients after completion of radiotherapy protocol (70 Gy) in the clinic suggesting that apoptotic index may form a basis for prognosis in radiotherapy in stage III cervix cancer patients.