Effects of rapamycin on cell proliferation and phosphorylation of mTOR and p70S6K in HepG2 and HepG2 cells overexpressing constitutively active Akt/PKB

Varma, Shailly; Khandelwal, Ramji L.

doi:10.1016/j.bbagen.2006.07.016

Cited by 32 publications

(25 citation statements)

References 30 publications

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“…1C). This lack of any significant effect of Rapa treatment on the proliferation rates of any of these cell types contrasts with reports that Rapa reduces the proliferation rates of HepG2 liver cells in vitro and muscle cells in vivo (Varma & Khandelwal, 2007; Drake et al ., 2013). Divergence from these previously published results may be explained by differences in the dose and method of Rapa administration, differences in the in vitro versus the in vivo effects of Rapa, or differences in cell types.…”

Section: Resultscontrasting

confidence: 91%

Reduced in vivo hepatic proteome replacement rates but not cell proliferation rates predict maximum lifespan extension in mice

et al. 2015

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SummaryCombating the social and economic consequences of a growing elderly population will require the identification of interventions that slow the development of age‐related diseases. Preserved cellular homeostasis and delayed aging have been previously linked to reduced cell proliferation and protein synthesis rates. To determine whether changes in these processes may contribute to or predict delayed aging in mammals, we measured cell proliferation rates and the synthesis and replacement rates (RRs) of over a hundred hepatic proteins in vivo in three different mouse models of extended maximum lifespan (maxLS): Snell Dwarf, calorie‐restricted (CR), and rapamycin (Rapa)‐treated mice. Cell proliferation rates were not consistently reduced across the models. In contrast, reduced hepatic protein RRs (longer half‐lives) were observed in all three models compared to controls. Intriguingly, the degree of mean hepatic protein RR reduction was significantly correlated with the degree of maxLS extension across the models and across different Rapa doses. Absolute rates of hepatic protein synthesis were reduced in Snell Dwarf and CR, but not Rapa‐treated mice. Hepatic chaperone levels were unchanged or reduced and glutathione S‐transferase synthesis was preserved or increased in all three models, suggesting a reduced demand for protein renewal, possibly due to reduced levels of unfolded or damaged proteins. These data demonstrate that maxLS extension in mammals is associated with improved hepatic proteome homeostasis, as reflected by a reduced demand for protein renewal, and that reduced hepatic protein RRs hold promise as an early biomarker and potential target for interventions that delay aging in mammals.

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Section: Resultscontrasting

confidence: 91%

Reduced in vivo hepatic proteome replacement rates but not cell proliferation rates predict maximum lifespan extension in mice

et al. 2015

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“…Its success in the treatment of these cancer types led to the evaluation of its effects on other cancers known to deregulate the PI3K/Akt/mTOR pathway. Preclinical studies demonstrated that inhibition of mTOR, which is well known to be up-regulated in a large proportion of HCC (hepatocellular carcinoma) cells, by rapamycin and everolimus yielded a positive outcome [109][110][111][112][113]. Subsequent Phase I/II studies also found that administration of everolimus to patients with advanced HCC was well tolerated and delayed disease progression [114].…”

Section: Mtor Inhibitor: Everolimusmentioning

confidence: 95%

Cellular and molecular effects of the mTOR inhibitor everolimus

2015

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mTOR (mechanistic target of rapamycin) functions as the central regulator for cell proliferation, growth and survival. Up-regulation of proteins regulating mTOR, as well as its downstream targets, has been reported in various cancers. This has promoted the development of anti-cancer therapies targeting mTOR, namely fungal macrolide rapamycin, a naturally occurring mTOR inhibitor, and its analogues (rapalogues). One such rapalogue, everolimus, has been approved in the clinical treatment of renal and breast cancers. Although results have demonstrated that these mTOR inhibitors are effective in attenuating cell growth of cancer cells under in vitro and in vivo conditions, subsequent sporadic response to rapalogues therapy in clinical trials has promoted researchers to look further into the complex understanding of the dynamics of mTOR regulation in the tumour environment. Limitations of these rapalogues include the sensitivity of tumour subsets to mTOR inhibition. Additionally, it is well known that rapamycin and its rapalogues mediate their effects by inhibiting mTORC (mTOR complex) 1, with limited or no effect on mTORC2 activity. The present review summarizes the pre-clinical, clinical and recent discoveries, with emphasis on the cellular and molecular effects of everolimus in cancer therapy.

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“…In the case of mTOR, formation of multiprotein complexes that are either sensitive or insensitive to rapamycin inhibition have been demonstrated (13,14), and only the rapamycin-sensitive complexes are responsible for phosphorylation and activation of S6K1 (15). Various studies in the heart and in other muscle types demonstrate that phosphorylation on the S2448 site of mTOR is indicative of its activation (4,(16)(17)(18)(19). S6K1 activation, in contrast, revolves around a complex series of multiple phosphorylations that regulate its kinase activity (20,21).…”

Section: Introductionmentioning

confidence: 99%

Regulation of mTOR and S6K1 activation by the nPKC isoforms, PKCε and PKCδ, in adult cardiac muscle cells

Moschella

Rao

McDermott

et al. 2007

Journal of Molecular and Cellular Cardiology

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SUMMARYActivation of both mTOR and its downstream target, S6K1 (p70 S6 kinase) have been implicated to affect cardiac hypertrophy. Our earlier work, in a feline model of 1-48 h pressure overload, demonstrated that mTOR/S6K1 activation occurred primarily through a PKC/c-Raf pathway. To further delineate the role of specific PKC isoforms on mTOR/S6K1 activation, we utilized primary cultures of adult feline cardiomyocytes in vitro and stimulated with endothelin-1 (ET-1), phenylephrine (PE), TPA, or insulin. All agonist treatments resulted in S2248 phosphorylation of mTOR and T389 and S421/T424 phosphorylation of S6K1, however only ET-1 and TPA-stimulated mTOR/S6K1 activation was abolished with infection of a dominant negative adenoviral c-Raf (DNRaf) construct. Expression of DN-PKC ε blocked ET-1-stimulated mTOR S2448 and S6K1 S421/ T424 and T389 phosphorylation but had no effect on insulin-stimulated S6K1 phosphorylation. Expression of DN-PKC δ or pretreatment of cardiomyocytes with rottlerin, a PKC δ specific inhibitor, blocked both ET-1 and insulin stimulated mTOR S2448 and S6K1 T389 phosphorylation. However, treatment with Gö6976, a specific classical PKC (cPKC) inhibitor did not affect mTOR/S6K1 activation. These data indicate that: (i) PKC ε is required for ET-1-stimulated T421/S424 phosphorylation of S6K1, (ii) both PKC ε and PKC δ are required for ET-1-stimulated mTOR S2448 and S6K1 T389 phosphorylation, (iii) PKC δ is also required for insulin-stimulated mTOR S2448 and S6K1 T389 phosphorylation. Together, these data delineate both distinct and combinatorial roles of specific PKC isoforms on mTOR and S6K1 activation in adult cardiac myocytes following hypertrophic stimulation.

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Effects of rapamycin on cell proliferation and phosphorylation of mTOR and p70S6K in HepG2 and HepG2 cells overexpressing constitutively active Akt/PKB

Cited by 32 publications

References 30 publications

Reduced in vivo hepatic proteome replacement rates but not cell proliferation rates predict maximum lifespan extension in mice

Reduced in vivo hepatic proteome replacement rates but not cell proliferation rates predict maximum lifespan extension in mice

Cellular and molecular effects of the mTOR inhibitor everolimus

Regulation of mTOR and S6K1 activation by the nPKC isoforms, PKCε and PKCδ, in adult cardiac muscle cells

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