HepG2 cells recovered from apoptosis show altered drug responses and invasiveness.

BACKGROUND: Cancer relapse, associated with increased drug resistance and rate of metastasis, often follows completion of chemotherapy but the cancer escape mechanisms are still incompletely understood. Percutaneous ethanol injection (PEI) has been used for treating hepatocellular carcinoma (HCC) for decades, while the recurrence after PEI treatment remains a major limitation. Recent evidence mounted that cancer cells could survive from chemical induced apoptosis, suggesting a potential route through which cancer relapse may occur. This study focuses on the consequence of HepG2 recovery from ethanol-induced apoptotic event. METHODS: The model of HepG2 recovery from ethanol-induced apoptotic event was established by live cell imaging, BrdU assay and Western blotting. MTT assay, wound healing assay and invasion assay were used to investigate the behavior of HepG2 after recovery. RESULTS: HepG2 cells could recover from ethanol-induced apoptosis. These cells changed their behaviors such as drug resistance, mobility and invasiveness. On average, the recovered HepG2 cell clones were found to be 46% more resistant to ethanol and 84% higher in mobility. The recovered clones became 58.2% more sensitive to 5-fluorouracil. CONCLUSIONS: HepG2 cells can recover from ethanol-induced apoptotic event. These cells became more resistant to ethanol and more invasive. Although the recovered cell clones were more resistant to ethanol, they became more sensitive to 5-fluorouracil treatment.

Cell survival, DNA damage, and oncogenic transformation after a transient and reversible apoptotic response.

Apoptosis serves as a protective mechanism by eliminating damaged cells through programmed cell death. After apoptotic cells pass critical checkpoints, including mitochondrial fragmentation, executioner caspase activation, and DNA damage, it is assumed that cell death inevitably follows. However, this assumption has not been tested directly. Here we report an unexpected reversal of late-stage apoptosis in primary liver and heart cells, macrophages, NIH 3T3 fibroblasts, cervical cancer HeLa cells, and brain cells. After exposure to an inducer of apoptosis, cells exhibited multiple morphological and biochemical hallmarks of late-stage apoptosis, including mitochondrial fragmentation, caspase-3 activation, and DNA damage. Surprisingly, the vast majority of dying cells arrested the apoptotic process and recovered when the inducer was washed away. Of importance, some cells acquired permanent genetic changes and underwent oncogenic transformation at a higher frequency than controls. Global gene expression analysis identified a molecular signature of the reversal process. We propose that reversal of apoptosis is an unanticipated mechanism to rescue cells from crisis and propose to name this mechanism "anastasis" (Greek for "rising to life"). Whereas carcinogenesis represents a harmful side effect, potential benefits of anastasis could include preservation of cells that are difficult to replace and stress-induced genetic diversity.