a-quantitative-measurement-reactive-oxygen-species-senescence

A Quantitative Measurement of Reactive Oxygen Species and Senescence-associated Secretory Phenotype in Normal Human Fibroblasts During Oncogene-induced Senescence

Cellular senescence has been considered a state of irreversible growth arrest upon exhaustion of proliferative capacity or exposure to various stresses. ...

sensitive-measurement-mitophagy-flow-cytometry-using-ph-dependent

Sensitive Measurement of Mitophagy by Flow Cytometry Using the pH-dependent Fluorescent Reporter mt-Keima

Mitophagy is a process of selective removal of damaged or unnecessary mitochondria using autophagy machinery. Close links have been found between ...

Dong-A University

Akt/PKB plays a pivotal role in cell proliferation and survival. However, the isotype-specific roles of Akt in mitochondrial function have not been fully addressed. In this study, we explored the role of Akt in mitochondrial function after stable knockdown of the Akt isoforms in EJ human bladder cancer cells. We found that the mitochondrial mass was significantly increased in the Akt1- and Akt3-knockdown cells, and this increase was accompanied by an increase in TFAM and NRF1. Akt2 knockdown did not cause a similar effect. Interestingly, Akt3 knockdown also led to severe structural defects in the mitochondria, an increase in doxorubicin-induced senescence, and impairment of cell proliferation in galactose medium. Consistent with these observations, the mitochondrial oxygen consumption rate was significantly reduced in the Akt3-knockdown cells. An Akt3 deficiency-induced decrease in mitochondrial respiration was also observed in A549 lung cancer cells. Collectively, these results suggest that the Akt isoforms play distinct roles in mitochondrial function and that Akt3 is critical for proper mitochondrial respiration in human cancer cells. 

Akt3 knockdown induces mitochondrial dysfunction in human cancer cells.

Cellular senescence has been implicated in normal aging, tissue homeostasis, and tumor suppression. Although p53 has been shown to be a central mediator of cellular senescence, the signaling pathway by which it induces senescence remains incompletely understood. In this study, we have shown that both Akt and p21 are required to induce cellular senescence in response to p53 expression. In a p53-induced senescence model, we found that Akt activation was essential for inducing a cellular senescence phenotype. Surprisingly, Akt inhibition did not abolish p53-induced cell cycle arrest, but it suppressed the increase in intracellular reactive oxygen species (ROS) levels. The results of the cell cycle and morphological analysis suggest that p53 induced quiescence, not senescence, following Akt inhibition. Conversely, the inhibition of p21 induction abolished cell cycle arrest but did not affect the p53-induced increase in ROS levels. Additionally, p21 and Akt separately controlled cell cycle arrest and ROS levels, respectively, during H-Ras-induced senescence in human normal fibroblasts. The mechanistic analysis revealed that Akt increased ROS levels through NOX4 induction, and increased Akt-dependent NF-κB binding to the NOX4 promoter is responsible for NOX4 induction upon p53 expression. We further showed that Akt activation upon p53 expression is mediated by mammalian target of rapamycin complex 2. In addition, p53-mediated IL6 and IL8 induction was abrogated by Akt inhibition, suggesting that Akt activation is also required for the senescence-associated secretory phenotype. Collectively, these results suggest that p53 simultaneously controls multiple pathways to induce cellular senescence through p21 and Akt.

Cooperation between p21 and Akt is required for p53-dependent cellular senescence.

Dynamin-related protein 1 (Drp1), a dynamin-related GTPase, is a key regulator of mitochondrial fission. Although recent studies have shown that Drp1 plays important roles in various important cellular processes, such as maintaining proper mitochondrial function, apoptosis and necrosis, the potential involvement of Drp1 in cancer development has not been fully addressed. To explore the role of Drp1 in cancer, we examined Drp1 levels in various human cancer tissues. Tissue array analysis showed that the level of Drp1 was decreased significantly in malignant colon and lung cancer tissues, whereas no change in Drp1 was observed in breast and prostate tumors. Pairwise comparisons of cancer tissue and adjacent normal tissue from colon and lung cancer patients further confirmed decreases in Drp1 expression of 75% in colon cancer patients and 78% in lung cancer patients. Moreover, Drp1 levels were decreased further with advanced grade in both colon and lung cancers, suggesting that loss of Drp1 is associated with the progression of human lung and colon cancer. Consistent with this observation, knockdown of Drp1 increased cellular migration activity in human lung cancer cells and tumor formation in a xenograft tumor model. Taken together, these results suggest that the loss of Drp1 expression could contribute to the development of human lung and colon cancers.

Young Yeon Kim

Department of Biochemistry,
College of Medicine,
Peripheral Neuropathy Research Center

Dong-A University

A Quantitative Measurement of Reactive Oxygen Species and Senescence-associated Secretory Phenotype in Normal Human Fibroblasts During Oncogene-induced Senescence

Sensitive Measurement of Mitophagy by Flow Cytometry Using the pH-dependent Fluorescent Reporter mt-Keima

Young Yeon Kim

Department of Biochemistry,College of Medicine,Peripheral Neuropathy Research Center

Dong-A University

A Quantitative Measurement of Reactive Oxygen Species and Senescence-associated Secretory Phenotype in Normal Human Fibroblasts During Oncogene-induced Senescence

Sensitive Measurement of Mitophagy by Flow Cytometry Using the pH-dependent Fluorescent Reporter mt-Keima

Department of Biochemistry,
College of Medicine,
Peripheral Neuropathy Research Center