Endoplasmic Reticulum (ER) Stress Enhances Tip60 (A Histone Acetyltransferase) Binding to the Concanavalin A

MHY1485 enhances X-irradiation-induced apoptosis and senescence in tumor cells

The mammalian target of rapamycin (mTOR) is a sensor of nutrient status and plays an important role in cell growth and metabolism. Although inhibition of mTOR signaling promotes tumor cell death and several mTOR inhibitors have been used clinically, recent reports have shown that co-treatment with MHY1485, an mTOR activator, enhances the anti-cancer effects of anti-PD-1 antibody and 5-fluorouracil. However, it remains unclear whether MHY1485 treatment alters the effects of radiation on tumor cells. In this study, the radiosensitizing effects of MHY1485 were investigated using murine CT26 and LLC cell lines. We examined mTOR signaling, tumor cell growth, colony formation, apoptosis, senescence, oxidative stress, p21 accumulation and endoplasmic reticulum (ER) stress levels in cells treated with MHY1485 and radiation, either alone or together. We found that MHY1485 treatment inhibited growth and colony formation in both cell lines under irradiation and no-irradiation conditions, results that were not fully consistent with MHY1485's known role in activating mTOR signaling. Furthermore, we found that combined treatment with MHY1485 and radiation significantly increased apoptosis and senescence in tumor cells in association with oxidative stress, ER stress and p21 stabilization, compared to radiation treatment alone. Our results suggested that MHY1485 enhances the radiosensitivity of tumor cells by a mechanism that may differ from MHY1485's role in mTOR activation.

Effects of the Combination of the Main Active Components of Astragalus and Panax notoginseng on Inflammation and Apoptosis of Nerve Cell after Cerebral Ischemia-Reperfusion

Astragalus and Panax notoginseng are commonly used to treat cardio-cerebrovascular diseases in China and are often combined together to promote curative effect. We speculate that the enhancement of the combination on anticerebral ischemia injury may come from the main active components. The purpose of this work was to probe the effects and mechanisms of Astragaloside IV (the active component of Astragalus) combined with Ginsenoside Rg1, Ginsenoside Rb1, and Notoginsenoside R1 (the active components of P. notoginseng) to antagonize ischemia/reperfusion (I/R) injury via inflammation and apoptosis. C57BL/6 mice were randomly divided into sham, model, Astragaloside IV, Ginsenoside Rg1, Ginsenoside Rb1, Notoginsenoside R1, four active components combination, and Edaravone groups. After administration for 3 days, bilateral common carotid arteries (CCA) were occluded with artery clip for 20[Formula: see text]min followed by reperfusion for 24[Formula: see text]h. Our results showed that the survival rate of nerve cell in hippocampal CA1 decreased while the apoptotic rate increased, and the level of caspase-3 protein in brain tissues was elevated, the expressions of TNF-a, IL-1, and ICAM-1 mRNA as well as phosphorylated nuclear factor kappa B (NF-[Formula: see text]B) inhibitor protein [Formula: see text] (p-I[Formula: see text]Ba) in brain tissues were up-regulated, and the nuclear translocation rate of NF-[Formula: see text]B was raised. Additionally, the protein expressions of phosphorylated tyrosine kinase 1 (p-JAK1), phosphorylated signal transducer and activator of transcription-1 (p-STAT1), glucose regulated protein 78 (GRP78), caspase-12, and phosphorylated c-Jun N-terminal kinases 1/2 (p-JNK1/2) in brain tissues were also significantly strengthened after I/R for 24[Formula: see text]h. All drugs could increase neurocyte survival rate in hippocampal CA1, decrease the apoptotic rate, and inhibit caspase-3 protein expression, in contrast, the effects of four active components combination were better than those of active components alone. In addition, Astragaloside IV and Ginsenoside Rg1 could down-regulate the level of TNF-[Formula: see text], and ICAM-1 mRNA, respectively, Notoginsenoside R1 reduced both TNF-[Formula: see text] and ICAM-1 mRNA, and the combination of the 4 effective components had inhibitory effects on the expressions of TNF-[Formula: see text], IL-1[Formula: see text], and ICAM-1 mRNA. Astragaloside IV, Ginsenoside Rg1, Notoginsenoside R1, and 4 effective components combination were able to restrain the phosphorylation of I[Formula: see text]B[Formula: see text], and relieve the nuclear translocation rate of NF-[Formula: see text]B. Moreover, the effects of the combination are greater than those of active components alone. All drugs could suppress the phosphorylation of JAK1 induced by I/R; meanwhile the expression of p-STAT1 exhibited a decrease in Ginsenoside Rg1 and four active components combination groups. The decreases of p-JAK1 and p-STAT1 in the four active components combination group were more obvious than those in active components alone groups. Astragaloside IV, Ginsenoside Rg1, and Notoginsenoside R1 further augmented GRP78 expression caused by I/R, Notoginsenoside R1 attenuated caspase-12 protein expression, Astragaloside IV and Ginsenoside Rg1 lessened the phosphorylation of JNK1/2, and the four active components combination was capable of up-regulating GRP78 protein while down-regulating the expressions of caspase-12 and p-JNK1/2. Similarly, the effects of the four active components combination were greater than those of effective components alone. These suggested that the combination of the main active components of Astragalus and Panax notoginseng could strengthen protective effects on cerebral ischemia injury via anti-apoptosis and anti-inflammation, and the mechanisms might be associated with restraining the activation of NF-[Formula: see text]B and JAK1/STAT1 signal pathways and regulating endoplasmic reticulum stress (ERS) after cerebral ischemia.

Phosphorylation of Tip60 Tyrosine 327 by Abl Kinase Inhibits HAT Activity through Association with FE65

The transfer of acetyl groups from acetyl coenzyme A to the ε amino group of internal lysine residues is catalyzed by Tip60, which is in the MYST family of nuclear histone acetyltransferases (HATs). The tyrosine phosphorylation of Tip60 seems to be a unique modification. We present evidence that Tip60 is modified on tyrosine 327 by Abl kinase. We show that this causes functional changes in HAT activity and the subcellular localization of TIP60, which forms a complex with Abl kinase. The Tip60 mutation Y327F abolished tyrosine phosphorylation, reduced the inhibition of Tip60 HAT activity, and caused G0-G1 arrest and association with FE65. Thus, our findings for the first time suggested a novel regulation mechanism of Tip60. Regulation was through phosphorylation of tyrosine 327 by Abl tyrosine kinase and depended on environmental conditions, suggesting that the tyrosine residue of Tip60 is important for the activation process.

Phosphorylation of Tip60 Tyrosine 327 by Abl Kinase Inhibits HAT Activity through Association with FE65

The transfer of acetyl groups from acetyl coenzyme A to the ε amino group of internal lysine residues is catalyzed by Tip60, which is in the MYST family of nuclear histone acetyltransferases (HATs). The tyrosine phosphorylation of Tip60 seems to be a unique modification. We present evidence that Tip60 is modified on tyrosine 327 by Abl kinase. We show that this causes functional changes in HAT activity and the subcellular localization of TIP60, which forms a complex with Abl kinase. The Tip60 mutation Y327F abolished tyrosine phosphorylation, reduced the inhibition of Tip60 HAT activity, and caused G0-G1 arrest and association with FE65. Thus, our findings for the first time suggested a novel regulation mechanism of Tip60. Regulation was through phosphorylation of tyrosine 327 by Abl tyrosine kinase and depended on environmental conditions, suggesting that the tyrosine residue of Tip60 is important for the activation process.

Stabilization of p21 (Cip1/WAF1) following Tip60-dependent acetylation is required for p21-mediated DNA damage response

The molecular mechanisms controlling post-translational modifications of p21 have been pursued assiduously in recent years. Here, utilizing mass-spectrometry analysis and site-specific acetyl-p21 antibody, two lysine residues of p21, located at amino-acid sites 161 and 163, were identified as Tip60-mediated acetylation targets for the first time. Detection of adriamycin-induced p21 acetylation, which disappeared after Tip60 depletion with concomitant destabilization of p21 and disruption of G1 arrest, suggested that Tip60-mediated p21 acetylation is necessary for DNA damage-induced cell-cycle regulation. The ability of 2KQ, a mimetic of acetylated p21, to induce cell-cycle arrest and senescence was significantly enhanced in p21 null MEFs compared with those of cells expressing wild-type p21. Together, these observations demonstrate that Tip60-mediated p21 acetylation is a novel and essential regulatory process required for p21-dependent DNA damage-induced cell-cycle arrest.