Radiation and microgravity – Associated stress factors and carcinogensis

Defects in signaling networks that regulate cellular activities, such as growth and survival can lead to cancer development. Space environment affects signal molecules and genes involve in DNA damage response, cell proliferation, cell metabolism, and cytoskeleton signaling among others. Reduced gravity and exposure to harmful radiation are the main stress factors encountered in space. While a potential risk of tumor initiation has been extensively investigated for space-radiation, research efforts on the effects of microgravity on cancer cells have focused mainly on tumor progression and migration. However, the space environment comprises both cosmic radiation and reduced gravity, and, therefore, potential additive or synergistic effects need to be considered. For instance, impaired DNA repair processes due to lack of gravity can compromise the cellular response to radiation, which in turn leads to accumulation of DNA damage and increase of the risk of tumor initiation and progression. In this review, recent research aiming at identifying the association between space radiation, microgravity or the combination of both with tumor development and the possible underlying cellular mechanisms is summarized. Furthermore, space-associated stress factors, such as psychological stress, sleep disturbances or the potential role of the immune system in tumor initiation and development in space are discussed.