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: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:Treatment induced senescence (TIS) is a terminal cell cycle arrest program, increasingly recognized as a tumor suppressor mechanism complementing apoptosis in response to standard chemotherapy regimens. In particular cells with blocked apoptotic pathways rely on senescence as the only remaining failsafe mechanism to keep the neoplastic growth in check. However, little is known about biological properties, long-term fate of senescent tumor cells and their impact on the microenvironment. We used global gene expression profiling by microarrays to gain insight in the molecular programme underlying the treatment-induced senescence in Emu-myc transgenic B-cell lymphomas (apoptosis protected by Bcl2 overexpression), which robustly enter senescence in response to DNA-damaging anticancer agents such as Adriamycin (ADR). Primary lymphoma cells isolated from lymph nodes of Emu-Myc transgenic mice were used. In this model the the c-Myc oncogene is constitutively expressed in the cells of B-cell lineage, leading to spontaneous development of aggressive B-cell lymphomas, resembling Burkitt lymphoma in humans. In order to bring up the senescence as the main failsafe mechanism, primary lymphoma cells are protected from apoptosis by retroviral over-expression of a strong antiapoptotic protein Bcl2. These cells (Myc;Bcl2) massively undergo senescence upon DNA-damaging treatment. Adriamycin (ADR) is a cytostatic drug, used as a standard part of several lymphoma treatment regimens. In this study, transcriptional profiles of matched pairs of untreated vs. 5 days ADR treated Myc;Bcl2 lymphomas were analysed.
Project description:TGFβ signaling induces several cell phenotypes including cellular senescence, a stable form of cell cycle arrest accompanied by a secretory program, and epithelial-mesenchymal transition (EMT) in normal epithelial cells. During carcinogenesis cells lose the ability to undergo senescence in response to TGFβ but they maintain an EMT, which can contribute to tumor progression and resistance. A screen with active kinases in HMECs upon TGFβ treatment identified that the serine threonine kinase RSK3, or RPS6KA2, reverted TGFβ-induced senescence. Interestingly, RSK3 expression decreased in response to TGFβ in a SMAD3-dependent manner, and its constitutive expression rescued SMAD3-induced premature senescence, indicating that decrease of RSK3 itself contributes to TGFβ-induced senescence. Mechanistically, using transcriptomic analyses and affinity purification coupled to mass spectrometry-based proteomics, we unveiled that RSK3 regulates senescence by inhibiting NF-κΒ pathway through the decrease in proteasome-mediated IκBα degradation. Strikingly, senescent TGFβ-treated HMEC display features of epithelial to mesenchymal transition (EMT) and during RSK3-induced senescence escape HMEC conserve EMT features. Importantly, RSK3 expression correlates with EMT and invasion, and anti-correlates with senescence and NF-κΒ in human claudin-low breast tumors and its expression accelerates formation of breast invasive tumors in the mouse mammary gland. We conclude that RSK3 switches cell fate from senescence to malignancy in response to TGFβ signals.
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.
Project description:Therapy-induced senescence (TIS) is a DNA damage-triggered irreversible cell-cycle block that terminates further expansion of (pre-)malignant lesions. Utilizing the Eµ-myc transgenic mouse lymphoma model (apoptosis protected by retroviral Bcl2-overexpression), we sought to elucidate the biological properties, long-term fate of senescent tumor cells and their impact on the microenvironment. We used global gene expression profiling by microarrays to gain insight into the molecular program underlying the treatment-induced senescence in Emu-myc transgenic B-cell lymphomas (apoptosis protected by Bcl2 overexpression), which robustly enter senescence in response to DNA-damaging anticancer agents such as Adriamycin (ADR).
Project description:Cellular senescence is an irreversible growth arrest with a highly dynamic secretome, termed the senescence-associated secretory phenotype (SASP). Senescence has been implicated in somatic reprogramming to pluripotency. The cell-intrinsic proliferation arrest is a barrier for reprogramming, whereas the SASP facilitates the cell fate conversion in nonsenescent cells. However, the mechanisms by which reprogramming-induced senescence regulates cell plasticity are not well understood. Here, we have further investigated how the heterogeneity of paracrine senescence impacts reprogramming. We show that senescence promotes in vitro reprogramming in a stress-dependent manner. We identified a catalog of SASP factors and pathways potentially involved in the cell fate conversion using an unbiased proteomic analysis. Amphiregulin (AREG), a growth factor frequently secreted by the senescent cells, promotes in vitro reprogramming by accelerating proliferation and MET via the EGFR signaling pathway. Of note, AREG treatment diminished the negative effect of donor age on reprogramming. Finally, AREG enhances in vivo reprogramming in the skeletal muscle. Hence, senescence could facilitate cellular plasticity via various SASP factors to promote reprogramming and tissue repair.
Project description:Treatment induced senescence (TIS) is a terminal cell cycle arrest program, increasingly recognized as a tumor suppressor mechanism complementing apoptosis in response to standard chemotherapy regimens. In particular cells with blocked apoptotic pathways rely on senescence as the only remaining failsafe mechanism to keep the neoplastic growth in check. However, little is known about biological properties, long-term fate of senescent tumor cells and their impact on the microenvironment. We used global gene expression profiling by microarrays to gain insight in the molecular programme underlying the treatment-induced senescence in Emu-myc transgenic B-cell lymphomas (apoptosis protected by Bcl2 overexpression), which robustly enter senescence in response to DNA-damaging anticancer agents such as Adriamycin (ADR).