Radiation-induced senescent melanoma cells secrete soluble factors that trigger bystander senescence

Senescence is a key cellular response to ionizing radiation. Senescent cells experience irreversible growth arrest while remaining metabolically active and secrete a distinct set of proteins, collectively referred to as the senescence-associated secretory phenotype (SASP). These secreted factors influence neighboring non-irradiated cells through a mechanism known as the bystander effect. This study aimed to investigate and characterize the bystander effect in a melanoma cell model. Murine melanoma B16F0 cells were exposed to X-irradiation (10 Gy), and senescence was induced 3 days later. Conditioned media from the senescent cells was collected and used to culture non-irradiated B16F0 cells. Proliferation, viability, clonogenic capacity, DNA damage foci formation, apoptosis, and senescence were assessed. The composition of the senescence-associated secretory phenotype was analyzed using mass spectrometry and bioinformatics tools. Conditioned media from senescent cells induced by radiation reduced growth and promoted senescence in tumor cell cultures not exposed to ionizing radiation. Mass spectrometry analysis revealed greater protein diversity and abundance in conditioned media from senescent cells compared to that from non-irradiated cells. Additionally, conditioned media from senescent cells contained higher concentrations of proteins related to immune response, cellular aging, and responses to oxidative stress. Cells undergoing radiation-induced senescence promote bystander senescence by secreting soluble factors involved in the induction and maintenance of senescence.