Hepatocyte growth factor protects pulmonary endothelial barrier against oxidative stress and mitochondria-dependent apoptosis / 中华医学杂志(英文版)

BACKGROUND@#Pulmonary microvascular endothelial cells (PMVECs) were not complex, and the endothelial barrier was destroyed in the pathogenesis progress of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Previous studies have demonstrated that hepatocyte growth factor (HGF), which was secreted by bone marrow mesenchymal stem cells, could decrease endothelial apoptosis. We investigated whether mTOR/STAT3 signaling acted in HGF protective effects against oxidative stress and mitochondria-dependent apoptosis in lipopolysaccharide (LPS)-induced endothelial barrier dysfunction and ALI mice.@*METHODS@#In our current study, we introduced LPS-induced PMEVCs with HGF treatment. To investigate the effects of mammalian target of rapamycin (mTOR)/signal transducer and activator of transcription 3 (STAT3) pathway in endothelial oxidative stress and mitochondria-dependent apoptosis, mTOR inhibitor rapamycin and STAT3 inhibitor S3I-201 were, respectively, used to inhibit mTOR/STAT3 signaling. Moreover, lentivirus vector-mediated mTORC1 (Raptor) and mTORC2 (Rictor) gene knockdown modifications were introduced to evaluate mTORC1 and mTORC1 pathways. Calcium measurement, reactive oxygen species (ROS) production, mitochondrial membrane potential and protein, cell proliferation, apoptosis, and endothelial junction protein were detected to evaluate HGF effects. Moreover, we used the ALI mouse model to observe the mitochondria pathological changes with an electron microscope in vivo.@*RESULTS@#Our study demonstrated that HGF protected the endothelium via the suppression of ROS production and intracellular calcium uptake, which lead to increased mitochondrial membrane potential (JC-1 and mitochondria tracker green detection) and specific proteins (complex I), raised anti-apoptosis Messenger Ribonucleic Acid level (B-cell lymphoma 2 and Bcl-xL), and increased endothelial junction proteins (VE-cadherin and occludin). Reversely, mTOR inhibitor rapamycin and STAT3 inhibitor S3I-201 could raise oxidative stress and mitochondria-dependent apoptosis even with HGF treatment in LPS-induced endothelial cells. Similarly, mTORC1 as well as mTORC2 have the same protective effects in mitochondria damage and apoptosis. In in vivo experiments of ALI mouse, HGF also increased mitochondria structural integrity via the mTOR/STAT3 pathway.@*CONCLUSION@#In all, these reveal that mTOR/STAT3 signaling mediates the HGF suppression effects to oxidative level, mitochondria-dependent apoptosis, and endothelial junction protein in ARDS, contributing to the pulmonary endothelial survival and barrier integrity.

mTOR-targeted cancer therapy: great target but disappointing clinical outcomes, why? / 医学前沿

The mammalian target of rapamycin (mTOR) critically regulates several essential biological functions, such as cell growth, metabolism, survival, and immune response by forming two important complexes, namely, mTOR complex 1 (mTORC1) and complex 2 (mTORC2). mTOR signaling is often dysregulated in cancers and has been considered an attractive cancer therapeutic target. Great efforts have been made to develop efficacious mTOR inhibitors, particularly mTOR kinase inhibitors, which suppress mTORC1 and mTORC2; however, major success has not been achieved. With the strong scientific rationale, the intriguing question is why cancers are insensitive or not responsive to mTOR-targeted cancer therapy in clinics. Beyond early findings on induced activation of PI3K/Akt, MEK/ERK, and Mnk/eIF4E survival signaling pathways that compromise the efficacy of rapalog-based cancer therapy, recent findings on the essential role of GSK3 in mediating cancer cell response to mTOR inhibitors and mTORC1 inhibition-induced upregulation of PD-L1 in cancer cells may provide some explanations. These new findings may also offer us the opportunity to rationally utilize mTOR inhibitors in cancer therapy. Further elucidation of the biology of complicated mTOR networks may bring us the hope to develop effective therapeutic strategies with mTOR inhibitors against cancer.

Influence of Co-inhibiting mTORC2 and HSP90 on Proliferation Apoptosis of Multiple Myeloma Cells / 中国实验血液学杂志

<p><b>UNLABELLED</b>Objective：To explore the influence of co-inhibiting mTORC2 and HSP90 on the proliferation and apoptosis of multiple myeloma(MM) cell line U266.</p><p><b>METHODS</b>During culture, the human MM cell line U266 were treated with 20 nmol/L of rapamycin, 600 nmol/L 17-AAG, 20 nmol/L of rapamycin + 600 nmol/L 17-AGG and phosphate-buffered saline (PBS), then the growth inhibition rate, morphologic changes, apoptosis rate and the expression of caspase 3 and ATK protein in U266 cells were compared and analyzed.</p><p><b>RESULTS</b>The rapamycin and 17-AAG both could inhibit the growth of U266 cells, while the inhibitory effect of rapamycin in combination with 17-AAG on growth of U266 cells was significantly higher them that of rapamycin and 17-AAG alone and control (PBS); the apoptosis rate of U266 cells treated with rapamycin, 17-AAG and their combination was higher than that of control PBS groups, and the efficacy of 2 drug conbination was higher than that of control PBS group, and the efficacy of 2 drug combination was superior to single drug. The expression levels of caspase 3 and ATK in U266 cells treated with rapamycin, 17-AAG and their combination were higher and lower than those in control group respectively, and the efficacy of 2 drug combination was superior to signle drug. There were significant difference between them (P<0.05).</p><p><b>CONCLUSION</b>The co-inhibition of mTORC2 and HSP90 can suppress the proliferation and induce the apoptosis of MM cells.</p>

Research on multiple myeloma cell apoptosis by inhibition of mTORC2 and chaperon pathways / 中华血液学杂志

<p><b>OBJECTIVE</b>To explore apoptosis of multiple myeloma (MM) cells and its mechanism by the combined inhibition of mTORC2 signaling pathway and heat shock protein 90.</p><p><b>METHODS</b>The effects of Rapamycin, 17-AAG and the combination on proliferation of MM cell lines U266 and KM3 were assessed using MTT at different time points (0, 8, 24, 48 hour). Cell apoptosis and cell cycle distribution were measured by flow cytometry. The specific proteins p-AKT (ser473), p-AKT (thr450), p-S6 (S235/236) and AKT were detected by Western blotting.</p><p><b>RESULTS</b>Rapamycin, 17- AAG and the combination suppressed the proliferation of MM cell lines U266 and KM3, especially the combination of Rapamycin and 17-AAG synergistically inhibited the proliferation (P<0.05); Rapamycin induced G1 arrest both at 24 and 48 hours, 17-AAG also induced G1 arrest, especially at 48 hours (P<0.01); Rapamycin, 17-AAG alone decreased the expression of AKT and induced MM cell apoptosis to some extent (P<0.01); Chronic rapamycin treatment inhibited mTORC2; Inhibition of both mTORC2 and chaper on pathways degraded AKT and induced MM cell apoptosis, which was significantly higher than that of any single agent (P<0.01).</p><p><b>CONCLUSION</b>Inhibition of both mTORC2 and chaper on pathways decreased the expression of AKT to induce apoptosis of MM cells in vitro.</p>

Dual phosphorylation of Sin1 at T86 and T398 negatively regulates mTORC2 complex integrity and activity

Mammalian target of rapamycin (mTOR) plays essential roles in cell proliferation, survival and metabolism by forming at least two functional distinct multi-protein complexes, mTORC1 and mTORC2. External growth signals can be received and interpreted by mTORC2 and further transduced to mTORC1. On the other hand, mTORC1 can sense inner-cellular physiological cues such as amino acids and energy states and can indirectly suppress mTORC2 activity in part through phosphorylation of its upstream adaptors, IRS-1 or Grb10, under insulin or IGF-1 stimulation conditions. To date, upstream signaling pathways governing mTORC1 activation have been studied extensively, while the mechanisms modulating mTORC2 activity remain largely elusive. We recently reported that Sin1, an essential mTORC2 subunit, was phosphorylated by either Akt or S6K in a cellular context-dependent manner. More importantly, phosphorylation of Sin1 at T86 and T398 led to a dissociation of Sin1 from the functional mTORC2 holo-enzyme, resulting in reduced Akt activity and sensitizing cells to various apoptotic challenges. Notably, an ovarian cancer patient-derived Sin1-R81T mutation abolished Sin1-T86 phosphorylation by disrupting the canonical S6K-phoshorylation motif, thereby bypassing Sin1-phosphorylation-mediated suppression of mTORC2 and leading to sustained Akt signaling to promote tumorigenesis. Our work therefore provided physiological and pathological evidence to reveal the biological significance of Sin1 phosphorylation-mediated suppression of the mTOR/Akt oncogenic signaling, and further suggested that misregulation of this process might contribute to Akt hyper-activation that is frequently observed in human cancers.

Mammalian target of rapamycin regulates androgen receptor and Akt phosphorylation in prostate cancer 22RV1 cells / 中华男科学杂志

<p><b>OBJECTIVE</b>To investigate the roles of the mammalian target of rapamycin-1 and -2 (mTORC1 and TORC2) in the proliferation and apoptosis of prostate cancer 22RV1 cells.</p><p><b>METHODS</b>After silencing mTORC1 and TORC2, we examined the proliferation and apoptosis of prostate cancer 22RV1 cells by methylthiazol tetrazolium (MTT) assay and flow cytometry, respectively, and detected the expressions of the androgen receptor (AR) and Akt phosphorylation in the prostate cancer 22RV1 cells by Western blot after transfecting Raptor-siRNA and Rictor-siRNA to the 22RV1 cells.</p><p><b>RESULTS</b>MTT showed that the prostate cancer 22RV1 cells had no significant change in the growth rate after mTORC1 silence (P > 0.05), but their proliferation was markedly inhibited after mTORC2 silence (P < 0.01). Flow cytometry revealed a dramatic increase in the apoptosis of the 22RV1 cells after mTORC1 silence (P < 0.01), but no obvious change after mTORC2 silence (P > 0.05). Western blot exhibited that mTORC1 silence significantly increased the expression of AR and Akt phosphorylation (P < 0.05), while mTORC2 silence markedly decreased them (P < 0.05).</p><p><b>CONCLUSION</b>mTORC2 is not only required for the survival of prostate cancer 22RV1 cells, but also a promising therapeutic target of prostate cancer.</p>

Function of mTORC2 and its roles in hematological malignancies / 中国实验血液学杂志

Mammalian target of rapamycin complex (mTORC) is an important center for regulating cellular growth, survival and metabolism. mTORC plays a vital role in maintenance of normal physiological activities and homeostasis in organism. According to protein components, mTORC can be divided into two distinct protein complexes: mTORC1 and mTORC2. The main protein components of mTORC2 include mTOR, Rictor, mLST8, Deptor, mSin1, Protor and Hsp70. By means of activating AKT, PKCα, SGK1 and so on, the mTORC regulates many vital activities:embryonic development, cytoskeletal reconstitution,cell migration and protein post-translational modification. The abnormality of mTORC2 signaling pathway has been confirmed to be associated with tumorigenesis, therefore, further understanding the components, functions and signalling pathway of mTORC2 will provide a new insights in developing targeted cancer therapy. In this review, the structure and signalling pathway of mTORC2 and its roles in hematological malignancies are discussed and summarised.

Current development of the second generation of mTOR inhibitors as anticancer agents / 癌症

The mammalian target of rapamycin (mTOR), a serine/threonine protein kinase, acts as a "master switch" for cellular anabolic and catabolic processes, regulating the rate of cell growth and proliferation. Dysregulation of the mTOR signaling pathway occurs frequently in a variety of human tumors, and thus, mTOR has emerged as an important target for the design of anticancer agents. mTOR is found in two distinct multiprotein complexes within cells, mTORC1 and mTORC2. These two complexes consist of unique mTOR-interacting proteins and are regulated by different mechanisms. Enormous advances have been made in the development of drugs known as mTOR inhibitors. Rapamycin, the first defined inhibitor of mTOR, showed effectiveness as an anticancer agent in various preclinical models. Rapamycin analogues (rapalogs) with better pharmacologic properties have been developed. However, the clinical success of rapalogs has been limited to a few types of cancer. The discovery that mTORC2 directly phosphorylates Akt, an important survival kinase, adds new insight into the role of mTORC2 in cancer. This novel finding prompted efforts to develop the second generation of mTOR inhibitors that are able to target both mTORC1 and mTORC2. Here, we review the recent advances in the mTOR field and focus specifically on the current development of the second generation of mTOR inhibitors as anticancer agents.