Effect of low dose irradiation on estrogen receptor level in MCF-7 breast cancer cells

Different Roles of CHOP and JNK in Mediating Radiation-Induced Autophagy and Apoptosis in Breast Cancer Cells

Unfolded protein response (UPR) is comprised of complex and conserved stress pathways that function as a short-term adaptive mechanism to reduce levels of unfolded or misfolded proteins and maintain homeostasis in the endoplasmic reticulum (ER). UPR can be triggered by prolonged or persistent ER stress under many physiological or pathological conditions, including radiation exposure. Radiation-induced ER stress elicits autophagy and apoptosis in cancer cells, where C/EBP homologous protein (CHOP) and c-Jun NH2-terminal kinase (JNK) may play crucial roles. However, the specific mechanisms that regulate autophagy and apoptosis through CHOP and JNK after radiation exposure and how the balance of these activities determines the cellular radiosensitivity remain largely unclear. In this study, we found that exposure to X-ray radiation induced ER stress, UPR and high expression of CHOP and JNK. Furthermore, autophagy and apoptosis occurred in sequential order when breast cancer MDA-MB-231 and MCF-7 cells were exposed to X-ray radiation. CHOP gene knockdown with RNA interference inhibited autophagy and enhanced radiosensitivity in MDA-MB-231 cells, while impacting apoptosis and subsequently increasing radioresistance in MCF-7 cells. However, treatment with JNK inhibitor decreased autophagy while promoting apoptosis, thereby leading to radiosensitivity in both cell lines. Our results indicate that CHOP mediates radiation-induced autophagy and apoptosis in a cellular environment. Importantly, the functional consistency of regulating apoptosis and autophagy in these two irradiated breast cancer cell lines suggests that JNK may be more useful as a potential target for maximizing the efficacy of radiation therapy for breast cancers.

Concurrent hormone and radiation therapy in patients with breast cancer: what is the rationale?

Endocrine therapy is often given together with postoperative radiotherapy in patients with breast cancer and positive hormone-receptor status. However, few experimental or clinical studies address the combined effects of hormone and radiation therapy. Preclinical models have shown changes in tumour cell kinetics with the addition of tamoxifen, and some show reduced tumour cell death with concurrent anti-oestrogen treatment and radiotherapy. Although data from in-vitro studies support the notion of antagonistic effects of concurrent tamoxifen and radiotherapy on tumour cells, in-vivo research suggests a synergistic effect that could be attributable to micro-environmental changes in tumour responsiveness to ionising radiation and hormone therapy. Retrospective studies suggest that in practical application, concurrent administration of tamoxifen with radiotherapy does not compromise local control but might increase toxicity. Preliminary results from simultaneous treatment with aromatase inhibitors and radiation indicate that this combination of endocrine and radiation therapy could enhance cytotoxicity and improve tumour response. Further studies are needed to clarify the physiological mechanisms activated by oestrogens, which will allow a more thorough understanding of the complex interactions between 17beta-oestradiol and P53/P21(WAF1/CIP1)/Rb pathways and of the interaction between endocrine therapy and radiotherapy.

Interaction Between Estrogen Receptor Alpha, Ionizing Radiation and (anti-) Estrogens in Breast Cancer Cells

PURPOSE

Estrogen receptor alpha (ERalpha) plays a major role in breast cancer development. It acts as ligand-inducible transcription factor which determines growth, survival and differentiation of breast cancer cells. The aim of this study is to evaluate the potential interference between radiotherapy and estrogen receptor responsiveness. Materials and methods. The effect of ionizing radiation was assessed on the estrogen receptor alpha status, growth (proliferation and apoptosis) and sensitivity of MCF-7 breast cancer cells to estrogenic (17beta-estradiol (E2)), selective estrogen receptor modulator (SERM) and anti-estrogenic compounds. Results. We have observed a ligand-independent decrease in ERalpha expression after radiation, resulting from a specific reduction in mRNA level and protein synthesis. This ERalpha disappearance occurred 72 h post-irradiation at 8 Gy and decreased the transcriptional activity in ERalpha of these cells. On the other hand, E2 impedes the growth inhibitory effects (essentially on proliferation) of ionizing radiation in MCF-7 cells, which potentially decreases radiosensitivity of these cells. This effect was totally blocked by SERM and anti-estrogenic treatments. Moreover, this growth effect of concurrent anti-estrogenic drugs and ionizing radiation appeared to be strongly synergistic.

CONCLUSIONS

This study may increase general comprehension of ERalpha modulation by radiotherapy and improve adjuvant therapeutic approaches based on co-administration of radiation and endocrine therapy.

The effect of green laser light irradiation on whole blood platelets

BACKGROUND

Laser light irradiation is assumed to have biostimulating effect in various cell types. However, there is still a lack of information concerning response of blood platelets to laser light irradiation.

METHODS

In our study we used flow cytometry to monitor the effect of a green Nd-YAG laser (532 nm, 30 mW) irradiation on platelet activation and the expression of activated GPIIbIIIa glycoprotein complex (fibrinogen receptor) of whole blood platelets stained with fluorolabelled monoclonal antibody PAC-1. Also the formation of platelet microparticles and aggregates in a population of whole blood platelets following such irradiation was evaluated.

RESULTS

Effects of laser light on platelet activation and reactivity were significant over a wide range of applied energies (p<0.01). While low and medium laser light energies (18 and 54 J) increased platelet activation, the irradiation with a high-energy laser light (108 J) resulted in depressed platelet reactivity and attenuated platelet response to activators. In addition, laser light irradiation had significant influence on the formation of platelet microparticles in either resting (p<0.05) or ADP-activated (p<0.05) platelets, while no significant effect was observed in collagen-activated platelets. On the other hand, laser light irradiation significantly increased the formation of platelet aggregates both in resting (p<0.01) and agonists-activated (p<0.05) platelets.

CONCLUSIONS

Our results clearly point that the laser light irradiation of blood platelets can trigger signal transduction, leading to platelet activation, as well as the gradual loss of natural platelet reactivity and platelets' ability to respond to activating agents.