The Roles of p21(Waf1/CIP1) and Hus1 in Generation and Transmission of Damage Signals Stimulated by Low-Dose Alpha-Particle Irradiation

Abscopal Effects, Clastogenic Effects and Bystander Effects: 70 Years of Non-Targeted Effects of Radiation

In vitro and in vivo observations accumulated over several decades have firmly shown that the biological effects of ionizing radiation can spread from irradiated cells/tissues to non-targeted cells/tissues. Redox-modulated intercellular communication mechanisms that include a role for secreted factors and gap junctions, can mediate these non-targeted effects. Clearly, the expression of such effects and their transmission to progeny cells has implications for issues related to radiation protection. Their elucidation is also relevant towards enhancing the efficacy of cancer radiotherapy and reducing its impact on the development of normal tissue toxicities. In addition, the study of non-targeted effects is pertinent to our basic understanding of intercellular communications under conditions of oxidative stress. This review will trace the history of non-targeted effects of radiation starting with early reports of abscopal effects which described radiation induced effects in tissues distant from the site of radiation exposure. A related effect involved the production of clastogenic factors in plasma following irradiation which can induce chromosome damage in unirradiated cells. Despite these early reports suggesting non-targeted effects of radiation, the classical paradigm that a direct deposition of energy in the nucleus was required still dominated. This paradigm was challenged by papers describing radiation induced bystander effects. This review will cover mechanisms of radiation-induced bystander effects and the potential impacts on radiation protection and radiation therapy.

Multiple functions of p21 in cancer radiotherapy

BACKGROUND

Greater than half of cancer patients experience radiation therapy, for both radical and palliative objectives. It is well known that researches on radiation response mechanisms are conducive to improve the efficacy of cancer radiotherapy. p21 was initially identified as a widespread inhibitor of cyclin-dependent kinases, transcriptionally modulated by p53 and a marker of cellular senescence. It was once considered that p21 acts as a tumour suppressor mainly to restrain cell cycle progression, thereby resulting in growth suppression. With the deepening researches on p21, p21 has been found to regulate radiation responses via participating in multiple cellular processes, including cell cycle arrest, apoptosis, DNA repair, senescence and autophagy. Hence, a comprehensive summary of the p21's functions in radiation response will provide a new perspective for radiotherapy against cancer.

METHODS

We summarize the recent pertinent literature from various electronic databases, including PubMed and analyzed several datasets from Gene Expression Omnibus database. This review discusses how p21 influences the effect of cancer radiotherapy via involving in multiple signaling pathways and expounds the feasibility, barrier and risks of using p21 as a biomarker as well as a therapeutic target of radiotherapy.

CONCLUSION

p21's complicated and important functions in cancer radiotherapy make it a promising therapeutic target. Besides, more thorough insights of p21 are needed to make it a safe therapeutic target.

Radiation-Induced Bystander Effect can be Transmitted Through Exosomes Using miRNAs as Effector Molecules

The radiation-induced bystander effect (RIBE) is a destructive reaction in nonirradiated cells and is one primary factor in determining the efficacy and success of radiation therapy in the field of cancer treatment. Previously reported studies have shown that the RIBE can be mediated by exosomes that carry miRNA components within. Exosomes, which are one type of cell-derived vesicle, exist in different biological conditions and serve as an important additional pathway for signal exchange between cells. In addition, exosome-derived miRNAs are confirmed to play an important role in RIBE, activating the bystander effect and genomic instability after radiotherapy. After investigating the field of RIBE, it is important to understand the mechanisms and consequences of biological effects as well as the role of exosomes and exosomal miRNAs therein, from different sources and under different circumstances, respectively. More discoveries could help to establish early interventions against RIBE while improving the efficacy of radiotherapy. Meanwhile, measures that would alleviate or even inhibit RIBE to some extent may exist in the near future.

Bystander autophagy mediated by radiation-induced exosomal miR-7-5p in non-targeted human bronchial epithelial cells

Radiation-induced bystander effect (RIBE) describes a set of biological effects in non-targeted cells that receive bystander signals from the irradiated cells. RIBE brings potential hazards to adjacent normal tissues in radiotherapy, and imparts a higher risk than previously thought. Excessive release of some substances from irradiated cells into extracellular microenvironment has a deleterious effect. For example, cytokines and reactive oxygen species have been confirmed to be involved in RIBE process via extracellular medium or gap junctions. However, RIBE-mediating signals and intercellular communication pathways are incompletely characterized. Here, we first identified a set of differentially expressed miRNAs in the exosomes collected from 2 Gy irradiated human bronchial epithelial BEP2D cells, from which miR-7-5p was found to induce autophagy in recipient cells. This exosome-mediated autophagy was significantly attenuated by miR-7-5p inhibitor. Moreover, our data demonstrated that autophagy induced by exosomal miR-7-5p was associated with EGFR/Akt/mTOR signaling pathway. Together, our results support the involvement of secretive exosomes in propagation of RIBE signals to bystander cells. The exosomes-containing miR-7-5p is a crucial mediator of bystander autophagy.