Project description:Cells responding to DNA damage implement complex adaptive programs that often culminate in two distinct outcomes: apoptosis or senescence. Here, to systematically identify factors driving each response, we analyzed human IMR-90 fibroblasts exposed to increasing doses of the genotoxin etoposide. We identified SRC as a key kinase contributing to this decision fork. SRC was activated by low (50 μM) etoposide but not by high (200 μM) etoposide levels. At low DNA damage, SRC-mediated activation of p38 critically promoted cell survival and senescence, and increased pro-survival BCL2L2 levels, while SRC-mediated repression of p53 prevented a rise in pro-apoptotic PUMA levels. At high DNA damage, SRC was not active, leading to elevation of p53, inhibition of p38, and apoptosis. In mice exposed to DNA damage, pharmacologic inhibition of SRC prevented the tissue accumulation of senescent cells. Inhibiting SRC could be exploited for inducing senescent-cell apoptosis in tissues to improve health outcomes.
Project description:Cells responding to DNA damage implement complex adaptive programs that often culminate in one of two distinct outcomes: apoptosis or senescence. To systematically identify factors driving each response, we analyzed human IMR-90 fibroblasts exposed to increasing doses of the genotoxin etoposide and identified SRC as a key kinase contributing early to this dichotomous decision. SRC was activated by low but not high levels of etoposide. With low DNA damage, SRC-mediated activation of p38 critically promoted expression of cell survival and senescence proteins, while SRC-mediated repression of p53 prevented a rise in proapoptotic proteins. With high DNA damage, failure to activate SRC led to elevation of p53, inhibition of p38, and apoptosis. In mice exposed to DNA damage, pharmacologic inhibition of SRC prevented the accumulation of senescent cells in tissues. We propose that inhibiting SRC could be exploited to favor apoptosis over senescence in tissues to improve health outcomes.
Project description:The emergence of anti-estrogen resistance in breast cancer is an important clinical phenomenon affecting long-term survival in this disease. Identifying factors that convey cell survival in this setting may guide improvements in treatment. Estrogen (E2) can induce apoptosis in breast cancer cells that have been selected for survival after E2 deprivation for long periods (MCF-7:5C cells), but the mechanisms underlying E2-induced stress in this setting have not been elucidated. Here, we report that the c-Src kinase functions as a key adapter protein for the estrogen receptor (ER, ESR1) in its activation of stress responses induced by E2 in MCF-7:5C cells. E2 elevated phosphorylation of c-Src, which was blocked by 4-hydroxytamoxifen (4-OHT), suggesting that E2 activated c-Src through the ER. We found that E2 activated the sensors of the unfolded protein response (UPR), IRE1? (ERN1) and PERK kinase (EIF2AK3), the latter of which phosphorylates eukaryotic translation initiation factor-2? (eIF2?). E2 also dramatically increased reactive oxygen species production and upregulated expression of heme oxygenase HO-1 (HMOX1), an indicator of oxidative stress, along with the central energy sensor kinase AMPK (PRKAA2). Pharmacologic or RNA interference-mediated inhibition of c-Src abolished the phosphorylation of eIF2? and AMPK, blocked E2-induced ROS production, and inhibited E2-induced apoptosis. Together, our results establish that c-Src kinase mediates stresses generated by E2 in long-term E2-deprived cells that trigger apoptosis. This work offers a mechanistic rationale for a new approach in the treatment of endocrine-resistant breast cancer. MCF-7:5C cells were treated with vehicle (0.1% EtOH) as control, E2 (10-9mol/L), 4-OHT (10-6mol/L), E2 (10-9mol/L) plus 4-OHT (10-6mol/L), PP2 (5x10-6mol/L), and E2 (10-9mol/L) plus PP2 (5x10-6mol/L) respectively for 72 hours.
Project description:The emergence of anti-estrogen resistance in breast cancer is an important clinical phenomenon affecting long-term survival in this disease. Identifying factors that convey cell survival in this setting may guide improvements in treatment. Estrogen (E2) can induce apoptosis in breast cancer cells that have been selected for survival after E2 deprivation for long periods (MCF-7:5C cells), but the mechanisms underlying E2-induced stress in this setting have not been elucidated. Here, we report that the c-Src kinase functions as a key adapter protein for the estrogen receptor (ER, ESR1) in its activation of stress responses induced by E2 in MCF-7:5C cells. E2 elevated phosphorylation of c-Src, which was blocked by 4-hydroxytamoxifen (4-OHT), suggesting that E2 activated c-Src through the ER. We found that E2 activated the sensors of the unfolded protein response (UPR), IRE1α (ERN1) and PERK kinase (EIF2AK3), the latter of which phosphorylates eukaryotic translation initiation factor-2α (eIF2α). E2 also dramatically increased reactive oxygen species production and upregulated expression of heme oxygenase HO-1 (HMOX1), an indicator of oxidative stress, along with the central energy sensor kinase AMPK (PRKAA2). Pharmacologic or RNA interference-mediated inhibition of c-Src abolished the phosphorylation of eIF2α and AMPK, blocked E2-induced ROS production, and inhibited E2-induced apoptosis. Together, our results establish that c-Src kinase mediates stresses generated by E2 in long-term E2-deprived cells that trigger apoptosis. This work offers a mechanistic rationale for a new approach in the treatment of endocrine-resistant breast cancer.
Project description:Induction of hepatocyte senescence is known to inhibit hepatocellular carcinoma (HCC). Until now, it has not been clear how the degree of liver injury dictates hepatocyte senescence and carcinogenesis. In this study, we investigated whether the severity of injury determines cell fate decisions between hepatocyte senescence and carcinogenesis. After testing of different degrees of liver injury, we found that hepatocyte senescence is strongly induced in the setting of severe acute liver injury. Longer-term, moderate liver injury did not result into hepatocyte senescence, but instead led to a significant incidence of HCC. In addition, carcinogenesis was significantly reduced by the induction of severe acute injury after chronic moderate liver injury. We conclude that severe acute liver injury leads to hepatocyte senescence along with a low incidence of HCC, whereas chronic moderate injury allows hepatocytes to proliferate rather than to enter into senescence, and correlates with a high incidence of HCC. This study improves our understanding in hepatocyte cell fate decisions and suggests a potential clinical strategy to induce senescence to treat HCC.