Radiation-induced intercellular signaling mediated by cytochrome-c via a p53-dependent pathway in hepatoma cells

Abstract

The tumor suppressor p53 has a crucial role in cellular response to DNA damage caused by ionizing radiation, but it is still unclear whether p53 can modulate radiation-induced bystander effects (RIBE). In the present work, three different hepatoma cell lines, namely HepG2 (wild p53), PLC/PRF/5 (mutation p53) and Hep3B (p53 null), were irradiated with γ-rays and then co-cultured with normal Chang liver cell (wild p53) in order to elucidate the mechanisms of RIBE. Results showed that the radiosensitivity of HepG2 cells was higher than that of PLC/PRF/5 and Hep3B cells. Only irradiated HepG2 cells, rather than irradiated PLC/PRF/5 or Hep3B cells, could induce bystander effect of micronuclei (MN) formation in the neighboring Chang liver cells. When HepG2 cells were treated with 20 μm pifithrin-α, an inhibitor of p53 function, or 5 μm cyclosporin A (CsA), an inhibitor of cytochrome-c release from mitochondria, the MN induction in bystander Chang liver cells was diminished. In fact, it was found that after irradiation, cytochrome-c was released from mitochondria into the cytoplasm only in HepG2 cells in a p53-dependent manner, but not in PLC/PRF/5 and Hep3B cells. Interestingly, when 50 μg/ml exogenous cytochrome-c was added into cell co-culture medium, RIBE was significantly triggered by irradiated PLC/PRF/5 and Hep3B cells, which previously failed to provoke a bystander effect. In addition, this exogenous cytochrome-c also partly recovered the RIBE induced by irradiated HepG2 cells even with CsA treatment. Our results provide new evidence that the RIBE can be modulated by the p53 status of irradiated hepatoma cells and that a p53-dependent release of cytochrome-c may be involved in the RIBE.

Intercellular Communication in Response to Radiation Induced Stress: Bystander Effects in Vitro and in Vivo and Their Possible Clinical Implications

“…In the same experiments we noticed that the level of micronuclei induced in cells co-cultured with non-irradiated ones did not differ between both lines. Recently, He et al (2010) found that the bystander effect after irradiation can be modulated by the p53 status of irradiated hepatoma cells and that a p53-dependent release of cytochrome c may be involved in the RIBE. Following irradiation cytochrome c was released from mitochondria into the cytoplasm only in HepG2 (wild-type p53) cells, but not in PLC/PRF/5 (p53 mutated) or Hep3B (p53-null) cells.…”

Multitargeting and Antimetastatic Potentials of Silibinin in Human HepG-2 and PLC/PRF/5 Hepatoma Cells

“…Inherent features of the cells may explain their differences in responding to silibinin (i.e., PLC is a HBV-positive and P53 mutated), but HepG2 is a HBV-negative and P53 intact cell [ATCC and (43,44)]. A significant correlation between HBVinfection with both development and recurrence of HCC has been documented (10,45).…”

Time and Cell Type Dependency of Survival Responses in Co-cultured Tumor and Fibroblast Cells after Exposure to Modulated Radiation Fields

“…Using different combinations of media transfer from p53 wild-type and p53 null HTC116 cells, Mothersill et al (28) showed that both p53 wild-type and p53 null cells are capable of producing signals that induce RIBEs, but that only p53 wild-type cells can respond to signals produced from either cell type. Furthermore, He et al (33) showed that RIBEs can be modulated by the p53 status of irradiated hepatoma cells and that a p53-dependent release of cytochrome-c may be involved in mediating response.…”