LY294002 and Rapamycin promote coxsackievirus-induced cytopathic effect and apoptosis via inhibition of PI3K/AKT/mTOR signaling pathway
37
Citation
40
Reference
10
Related Paper
Citation Trend
Keywords:
RPTOR
LY294002
mTORC2
Resveratrol (RSV) is a natural polyphenol produced by plants and is proposed to have multiple beneficial effects on health. In recent years, the interest in this molecule has increased nearly exponentially following the major findings that RSV (I) is chemo-preventive in some cancer models, (II) is cardio-protective and (III) has positive effects on metabolism in mammals and increases lifespan in lower organisms. Mechanistic target of rapamycin (mTOR) is a central controller of cell growth, proliferation, metabolism and angiogenesis. As a part of the mTORC1 and mTORC2 complexes, the mTOR kinase plays a key role in several pathways involved in cancer and metabolic diseases. Recent studies suggest that modulation of the mTOR signalling pathway could play an important role in mediating the beneficial effects of RSV. Therefore, this review summarises the current findings regarding RSV and its inhibition/activation of the proteins in the mTOR pathway, and thereby propose the proteins of the mTOR cascade to be primary targets for RSV. RSV affects many different targets related to mTOR, and it is not clear which is most relevant. However, most frequently, RSV is found to inhibit the activity of the mTOR pathway proteins, and to activate AMPK and LKB1, which can suppress mTOR signalling. Thus, it appears that RSV plays a role in modulation of proteins of the mTOR pathway although more research is still needed to fully understand the interaction.
mTORC2
RPTOR
Cite
Citations (47)
AbstractThe mammalian target of rapamycin (mTOR) is centrally involved in growth, survival and metabolism. In cancer, mTOR is frequently hyperactivated and is a clinically validated target for drug development. Until recently, we have relied largely on the use of rapamycin to study mTOR function and its anticancer potential. Recent insights now indicate that rapamycin is a partial inhibitor of mTOR through allosteric inhibition of mTOR complex-1 (mTORC1) but not mTOR complex-2 (mTORC2). Both the mechanism of action and the cellular response to mTORC1 inhibition by rapamycin and related drugs may limit the effectiveness of these compounds as antitumor agents. We and others have recently reported the discovery of second-generation ATP-competitive mTOR kinase inhibitors (TKIs) that bind to the active sites of mTORC1 and mTORC2, thereby targeting mTOR signaling function globally (see refs. 1-4). The discovery of specific, active-site mTOR inhibitors has opened a new chapter in the 40-plus year old odyssey that began with the discovery of rapamycin from a soil sample collected on Easter Island (see Vézina C, et al. J Antibiot 1975). Here, we discuss recent studies that highlight the emergence of rapamycin-resistant mTOR function in protein synthesis, cell growth, survival and metabolism. It is shown that these rapamycin-resistant mTOR functions are profoundly inhibited by TKIs. A more complete suppression of mTOR global signaling network by the new inhibitors is expected to yield a deeper and broader antitumor response in the clinic.
mTORC2
RPTOR
Sirolimus
Cite
Citations (157)
Mammalian Target of Rapamycin (mTOR) is a serine/threonine kinase and that forms two multiprotein complexes known as the mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). mTOR regulates cell growth, proliferation and survival. mTORC1 is composed of the mTOR catalytic subunit and three associated proteins: raptor, mLST8/$G{\beta}L$ and PRAS40. mTORC2 contains mTOR, rictor, mLST8/$G{\beta}L$ , mSin1, and protor. Here, we discuss mTOR as a promising anti-ischemic agent. It is believed that mTORC2 lies down-stream of Akt and acts as a direct activator of Akt. The different functions of mTOR can be explained by the existence of two distinct mTOR complexes containing unique interacting proteins. The loss of TSC2, which is upstream of mTOR, activates S6K1, promotes cell growth and survival, activates mTOR kinase activities, inhibits mTORC1 and mTORC2 via mTOR inhibitors, and suppresses S6K1 and Akt. Although mTOR signaling pathways are often activated in human diseases, such as cancer, mTOR signaling pathways are deactivated in ischemic diseases. From Drosophila to humans, mTOR is necessary for Ser473 phosphorylation of Akt, and the regulation of Akt-mTOR signaling pathways may have a potential role in ischemic disease. This review evaluates the potential functions of mTOR in ischemic diseases. A novel mTOR-interacting protein deregulates over-expression in ischemic disease, representing a new mechanism for controlling mTOR signaling pathways and potential therapeutic strategies for ischemic diseases.
mTORC2
RPTOR
Cite
Citations (55)
Abstract Through alterations in the PTEN and PI3K genes, the PI3K / Akt pathway is constitutively activated in human cancers. mTOR kinase plays an unique role in this pathway as the key component of two independent signaling complexes (mTORC1 (raptor - rapamycin sensitive) and mTORC2 (rictor - rapamycin insensitive)) that are involved at multiple branch points in this signaling cascade. As such, inhibition of mTOR kinase inactivates both mTOR complexes and therefore serves as an attractive means to target this integral pathway for the treatment of human malignancy. We report the biological and pharmaceutical evaluation of our selective mTOR 1/2 kinase inhibitor AR-mTOR-1. AR-mTOR-1 inhibits mTOR kinase with an IC50 of < 10 nM while maintaining selectivity against PI3K as well as a panel of additional lipid kinases, serine/threonine kinases and cytoplasmic and receptor tyrosine kinases. In mechanistic cellular assays, AR-mTOR-1 inhibits pAkt (Ser473), 4E-BP1 (Thr36/46) and pS6 (Ser235/6) with nanomolar potency, thus demonstrating inhibition of signaling from both mTORC1 and mTORC2 complexes. In line with its enzymatic selectivity over PI3K , AR-mTOR-1 does not significantly inhibit pAkt (Thr308) in cells. AR-mTOR-1 is broadly anti-proliferative in both epithelial and hematologic cancer cell lines, irrespective of mutational status, with IC50's ranging from 30 to 550 nM across 20 cell lines, suggesting the potential for broad clinical activity. Once daily dosing of AR-mTOR-1 in several mouse xenograft models, including PC3 prostate, U87 glioblastma, and H460 lung, results in robust anti-tumor activity. Finally, AR-mTOR-1 possesses desired in vitro and in vivo preclinical ADME properties including low clearance, high permeability and good absorption in three preclinical species. In total these data demonstrate that selectively targeting mTORC1 and mTORC2 with AR-mTOR-1 holds promise for broad spectrum clinical utility as a single agent across a wide array of cancer types. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B267.
mTORC2
RPTOR
Cite
Citations (0)
Abstract Nematode EAK-7 (enhancer-of-akt-1-7) regulates dauer formation and controls life span; however, the function of the human ortholog mammalian EAK-7 (mEAK-7) is unknown. We report that mEAK-7 activates an alternative mechanistic/mammalian target of rapamycin (mTOR) signaling pathway in human cells, in which mEAK-7 interacts with mTOR at the lysosome to facilitate S6K2 activation and 4E-BP1 repression. Despite interacting with mTOR and mammalian lethal with SEC13 protein 8 (mLST8), mEAK-7 does not interact with other mTOR complex 1 (mTORC1) or mTOR complex 2 (mTORC2) components; however, it is essential for mTOR signaling at the lysosome. This phenomenon is distinguished by S6 and 4E-BP1 activity in response to nutrient stimulation. Conventional S6K1 phosphorylation is uncoupled from S6 phosphorylation in response to mEAK-7 knockdown. mEAK-7 recruits mTOR to the lysosome, a crucial compartment for mTOR activation. Loss of mEAK-7 results in a marked decrease in lysosomal localization of mTOR, whereas overexpression of mEAK-7 results in enhanced lysosomal localization of mTOR. Deletion of the carboxyl terminus of mEAK-7 significantly decreases mTOR interaction. mEAK-7 knockdown decreases cell proliferation and migration, whereas overexpression of mEAK-7 enhances these cellular effects. Constitutively activated S6K rescues mTOR signaling in mEAK-7–knocked down cells. Thus, mEAK-7 activates an alternative mTOR signaling pathway through S6K2 and 4E-BP1 to regulate cell proliferation and migration. Citation Format: Joe T. Nguyen, Connor Ray, Alexandra L Fox, Daniela B Mendonca, Jin Koo Kim, Paul H. Krebsbach. Mammalian EAK-7 activates alternative mTOR signaling to regulate cell proliferation and migration [abstract]. In: Proceedings of the AACR Special Conference on Targeting PI3K/mTOR Signaling; 2018 Nov 30-Dec 8; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(10_Suppl):Abstract nr A13.
mTORC2
RPTOR
TOR signaling
Cite
Citations (0)
It has been shown that mammalian target of rapamycin (mTOR) inhibitors activate Akt while inhibiting mTOR signaling. However, the underlying mechanisms and the effect of the Akt activation on mTOR-targeted cancer therapy are unclear. The present work focused on addressing the role of mTOR/rictor in mTOR inhibitor-induced Akt activation and the effect of sustained Akt activation on mTOR-targeted cancer therapy. Thus, we have shown that mTOR inhibitors increase Akt phosphorylation through a mechanism independent of mTOR/rictor because the assembly of mTOR/rictor was inhibited by mTOR inhibitors and the silencing of rictor did not abrogate mTOR inhibitor-induced Akt activation. Moreover, Akt activation during mTOR inhibition is tightly associated with development of cell resistance to mTOR inhibitors. Accordingly, cotargeting mTOR and phosphatidylinositol 3-kinase/Akt signaling prevents mTOR inhibition-initiated Akt activation and enhances antitumor effects both in cell cultures and in animal xenograft models, suggesting an effective cancer therapeutic strategy. Collectively, we conclude that inhibition of the mTOR/raptor complex initiates Akt activation independent of mTOR/rictor. Consequently, the sustained Akt activation during mTOR inhibition will counteract the anticancer efficacy of the mTOR inhibitors.
mTORC2
RPTOR
Cite
Citations (160)
mTORC2
RPTOR
Cite
Citations (2)
The serine/threonine kinase mammalian target of rapamycin (mTOR) is the catalytic subunit of two complexes, mTORC1 and mTORC2, which have common and distinct subunits that mediate separate and overlapping functions. mTORC1 is activated by plenty of nutrients, and the two complexes can be activated by PI3K signaling. mTORC2 acts as an upstream regulator of AKT, and mTORC1 acts as a downstream effector. mTOR signaling integrates both intracellular and extracellular signals, acting as a key regulator of cellular metabolism, growth, and survival. A dysregulated activation of mTOR, as result of PI3K pathway or mTOR regulatory protein mutations or even due to the presence of cellular or viral oncogenes, is a common finding in cancer and represents a central mechanism in cancerogenesis. In the final part of this review, we will focus on the PI3K/AKT/mTOR activation by the human gammaherpesviruses EBV and KSHV that hijack this pathway to promote their-mediated oncogenic transformation and pathologies.
mTORC2
RPTOR
RHEB
Cite
Citations (24)
mTOR is a serine/threonine protein kinase that has been shown to be a key player in
the regulation of cell growth and proliferation. Furthermore, mTOR forms the
catalytic core of two known mTOR complexes, mTORC1 and mTORC2. These
complexes sense various intra and extracellular signals, and regulate cellular
processes that are critical for cell growth and proliferation. However, when
conventional mTOR signalling is deregulated, cellular homeostasis is disrupted,
resulting in a wide range of human diseases such as diabetes, neurodegeneration and
cancer. Due to its involvement in tumorigenesis, mTOR has attracted enormous
interest as a therapeutic target. Initially, the classical mTOR inhibitor rapamycin was
tested as a potential treatment. However, when the compound was assessed in clinical
trials, it proved to be of limited efficacy. This led to the design of novel types of
inhibitors, which are currently being evaluated. The results obtained with rapamycin
clearly indicated that our understanding of the mTOR signalling pathway is far from
complete.
In addition, mTOR is currently known to exist in two isoforms, which are
generated by alternative splicing of the transcript. These are known as mTORα and
mTORβ respectively. The mTORα protein was the first isoform discovered and is
2,549 residues long. mTORβ is approximately one third of the length at 706 amino
acids. Both proteins share identical C-terminal domains, but mTORβ lacks the Nterminal
HEAT and FAT repeats that mTORα possesses. Work done in our lab has
shown that mTORβ is capable of forming complexes with Raptor and Rictor, which
are the key components of mTORC1 and mTORC2. Furthermore, overexpression of
mTORβ transforms immortal cells and causes tumour formation in nude mice. It is thought that modulation of cell proliferation via the mTOR signalling pathway could
be achieved through mTORβ, which behaves as a protooncogene. Thus, mTORβ has
the potential to be used as a target for anti-cancer therapies.
The first chapter of my thesis consisted of comparative modelling of
mTORβ’s C-terminal region from the FRB domain to the kinase domain. The model
that was generated could then be used to give us insight into potential mechanisms for
the inhibition of mTOR by either rapamycin or ATP-competitive inhibitors.
The second chapter examined the effects of two different mutations in
mTOR’s kinase domain on its activity. A point mutation (S2215Y) and a deletion of
12 amino acids (12del) were introduced into the kinase domain of mTORβ. Mutant
proteins were expressed in HEK293 mammalian cells and the phosphorylation status
of various mTOR substrates was assessed under different experimental conditions.
The final chapter of my thesis described how a TAP-tag fusion protein was
created. This would have been used to search for novel mTORβ binding partners in
mammalian cells had I chosen to complete my PhD studies.
mTORC2
RPTOR
Cite
Citations (0)
The Akt/mTOR signaling cascade is a critical pathway involved in various physiological and pathological conditions, including regulation of cell proliferation, survival, invasion, and angiogenesis. In the present study, we investigated the anti-neoplastic effects of casticin (CTC), identified from the plant Vitex rotundifolia L., alone and/or in combination with BEZ-235, a dual Akt/mTOR inhibitor in human tumor cells. We found that CTC exerted a significant dose-dependent cytotoxicity and reduced cell proliferation in a variety of human tumor cells. Also, CTC effectively blocked the phosphorylation levels of Akt (Ser473) and mTOR (Ser2448) proteins as well as induced substantial apoptosis. Additionally treatment with CTC and BEZ-235 in conjunction resulted in a greater apoptotic effect than caused by either agent alone thus implicating the anti-neoplastic effects of this novel combination. Overall, the findings suggest that CTC can interfere with Akt/mTOR signaling cascade involved in tumorigenesis and can be used together with pharmacological agents targeting Akt/mTOR pathway.
RPTOR
mTORC2
Cite
Citations (52)