Project description:Inhibition of the nutrient-responsive mTOR (mammalian target of rapamycin) signalling pathway including the key downstream S6 kinase 1 (S6K1) extends lifespan and improves healthspan in mice. However, the underlying mechanisms contributing to the profound age-related benefits observed with loss of S6K1 signalling are unclear. Cellular senescence is a stable growth arrest accompanied by an inflammatory phenotype (termed the senescence-associated secretory phenotype, or SASP). Whileboth cellular senescence and SASP-mediated chronic inflammation contribute to age-related pathology the specific role of S6K1 signalling in these process have not been determined . Here, focussing on mouse liver a key target tissue for the beneficial health effects of loss of S6K1 signalling, we show that S6K1 deletion does not reduce senescence but ameliorates inflammation and immune cell infiltration in aged livers. Using human and mouse models of senescence, we demonstrated that reduced inflammation is a liver intrinsic effect associated with S6K deletion. Furthermore, gene expression analysis suggested that downregulated cGAS/STING and IRF3 activation might mediate the impaired SASP observed upon S6K deletion. Using a hepatic oncogene induced senescence model, we showed in vivo that S6K1 deletion results in reduced IRF3 activation, impaired production of cytokines such as IL1 and reduced immune infiltration. Overall, deletion of S6K reduces inflammation in the liver suggesting that suppression of the inflammatory SASP by S6K could contribute to explain the beneficial effects of inhibiting these pathways on healthspan and lifespan.
Project description:Inhibition of the nutrient-responsive mTOR (mammalian target of rapamycin) signalling pathway including the key downstream S6 kinase 1 (S6K1) extends lifespan and improves healthspan in mice. However, the underlying mechanisms contributing to the profound age-related benefits observed with loss of S6K1 signalling are unclear. Cellular senescence is a stable growth arrest accompanied by an inflammatory phenotype (termed the senescence-associated secretory phenotype, or SASP). Whileboth cellular senescence and SASP-mediated chronic inflammation contribute to age-related pathology the specific role of S6K1 signalling in these process have not been determined . Here, focussing on mouse liver a key target tissue for the beneficial health effects of loss of S6K1 signalling, we show that S6K1 deletion does not reduce senescence but ameliorates inflammation and immune cell infiltration in aged livers. Using human and mouse models of senescence, we demonstrated that reduced inflammation is a liver intrinsic effect associated with S6K deletion. Furthermore, gene expression analysis suggested that downregulated cGAS/STING and IRF3 activation might mediate the impaired SASP observed upon S6K deletion. Using a hepatic oncogene induced senescence model, we showed in vivo that S6K1 deletion results in reduced IRF3 activation, impaired production of cytokines such as IL1 and reduced immune infiltration. Overall, deletion of S6K reduces inflammation in the liver suggesting that suppression of the inflammatory SASP by S6K could contribute to explain the beneficial effects of inhibiting these pathways on healthspan and lifespan.
Project description:Inhibition of the nutrient-responsive mTOR (mammalian target of rapamycin) signalling pathway including the key downstream S6 kinase 1 (S6K1) extends lifespan and improves healthspan in mice. However, the underlying mechanisms contributing to the profound age-related benefits observed with loss of S6K1 signalling are unclear. Cellular senescence is a stable growth arrest accompanied by an inflammatory phenotype (termed the senescence-associated secretory phenotype, or SASP). Whileboth cellular senescence and SASP-mediated chronic inflammation contribute to age-related pathology the specific role of S6K1 signalling in these process have not been determined . Here, focussing on mouse liver a key target tissue for the beneficial health effects of loss of S6K1 signalling, we show that S6K1 deletion does not reduce senescence but ameliorates inflammation and immune cell infiltration in aged livers. Using human and mouse models of senescence, we demonstrated that reduced inflammation is a liver intrinsic effect associated with S6K deletion. Furthermore, gene expression analysis suggested that downregulated cGAS/STING and IRF3 activation might mediate the impaired SASP observed upon S6K deletion. Using a hepatic oncogene induced senescence model, we showed in vivo that S6K1 deletion results in reduced IRF3 activation, impaired production of cytokines such as IL1 and reduced immune infiltration. Overall, deletion of S6K reduces inflammation in the liver suggesting that suppression of the inflammatory SASP by S6K could contribute to explain the beneficial effects of inhibiting these pathways on healthspan and lifespan.
Project description:Phosphorylation of Ribosomal Protein S6 (RPS6) was the first post-translational modification of the ribosome to be identified and is a commonly-used readout for mTORC1 activity. Although the cellular and organismal functions of RPS6 phosphorylation are known, its molecular consequences on translation are less well understood. Here we use selective ribosome footprinting to analyze the location of ribosomes containing phosphorylated RPS6 on endogenous mRNAs in cells. We find that RPS6 becomes progressively dephosphorylated on ribosomes as they translate an mRNA. As a consequence, average RPS6 phosphorylation is higher on mRNAs with short coding sequences (CDSs) compared to mRNAs with long CDSs. Loss of RPS6 phosphorylation causes a correspondingly larger drop in translation efficiency of mRNAs with short CDSs than long CDSs. Interestingly, mRNAs with 5’ TOP motifs are translated well also in the absence of RPS6 phosphorylation despite short CDS lengths, suggesting they are translated via a different mode. In sum this provides a dynamic view of RPS6 phosphorylation on ribosomes as they translate mRNAs and the functional consequence on translation.
Project description:The Serine/Threonine protein kinase family, p90 ribosomal S6 kinases (RSK) are downstream effectors of extracellular signal regulated kinase 1/2 (ERK1/2) and are activated in response to tyrosine kinase receptor or G-protein coupled receptor signaling. RSK contains two distinct kinase domains, an N-terminal kinase (NTKD) and a C-terminal kinase (CTKD). The sole function of the CTKD is to aid in the activation of the NTKD, which is responsible for substrate phosphorylation. RSK regulates various homeostatic processes including those involved in transcription, translation and ribosome biogenesis, proliferation and survival, cytoskeleton, nutrient sensing, excitation and inflammation. RSK also acts as a major negative regulator of ERK1/2 signaling. RSK is associated with numerous cancers and has been primarily studied in the context of transformation and metastasis. The development of specific RSK inhibitors as cancer therapeutics has lagged behind that of other members of the mitogen-activated protein kinase signaling pathway. Importantly, a pan-RSK inhibitor, PMD-026, is currently in phase I/1b clinical trials for metastatic breast cancer. However, there are four members of the RSK family, which have overlapping and distinct functions that can vary in a tissue specific manner. Thus, a problem for transitioning a RSK inhibitor to the clinic may be the necessity to develop isoform specific inhibitors, which will be challenging as the NTKDs are very similar to each other. CTKD inhibitors have limited use as therapeutics as they are not able to inhibit the activity of the NTKD but could be used in the development of proteolysis-targeting chimeras.