Regulation of the mTOR Complex 1 Pathway by Nutrients, Growth Factors, and Stress

The large serine/threonine protein kinase mTOR regulates cellular and organismal homeostasis by coordinating anabolic and catabolic processes with nutrient, energy, and oxygen availability and growth factor signaling. Cells and organisms experience a wide variety of insults that perturb the homeostatic systems governed by mTOR and therefore require appropriate stress responses to allow cells to continue to function. Stress can manifest from an excess or lack of upstream signals or as a result of genetic perturbations in upstream effectors of the pathway. mTOR nucleates two large protein complexes that are important nodes in the pathways that help buffer cells from stresses, and are implicated in the progression of stress-associated phenotypes and diseases, such as aging, tumorigenesis, and diabetes. This review focuses on the key components of the mTOR complex 1 pathway and on how various stresses impinge upon them

The role of mammalian target of rapamycin complex 1 in hepatic physiology and disease

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2010.Cataloged from PDF version of thesis.Includes bibliographical references.The multi-component kinase mTOR complex 1 (mTORC 1) coordinates nutrient and growth factor inputs with numerous downstream processes including protein translation, autophagy, metabolism and cell growth. We have found that inhibition of mTORC 1 with rapamycin treatment suppressed whole-body postnatal growth similar to reduced caloric intake. We found that while feeding activated mTORC 1 in almost every tissue, there was variability in the upstream activating stimuli. The role of mTORCl in organ growth was further elucidated by studies we performed using liver-specific mTORC1 gain and loss of function mutants. Confirming our studies with rapamycin, genetic activation or suppression of mTORC 1 increased and decreased liver size respectively, and rendered the liver insensitive to nutrients. Rendering the liver insensitive to nutrients also had functional consequences. In response to starvation, the liver shifts to fatty acid catabolism and generates ketone bodies to supplement lowered glucose levels. We find that constitutive activation of mTORC1 prevents the liver from initiating fatty-acid oxidation and ketone production in response to fasting. Many aspects of the hepatic fasting response malfunction in old age including fatty acid catabolism and ketogenesis. We find this aging-dependent process is mediated by mTORC 1, and thus loss of mTORC 1 function throughout the adult life of the animal prevents the aging induced decrease in hepatic ketogenesis. As such, pharmaceutical inhibition of mTORC 1 may be beneficial in battling metabolic disorders due to aging.(cont.) Pharmaceutical inhibition of mTORC is a potential treatment for patients suffering from tuberous sclerosis complex (TSC). The disease TSC in humans is initiated by loss of TSC1 or TSC2, which results in hyperactive mTORC 1 activity. The disease can involve development of multiple lesions including brain harmatomas, angiomyolipomas (AMLs), and lymphangioleiomyomatosis (LAM). We have engineered transgenic mice that express Rheb2, an mTORC 1 activator, in a doxycycline-inducible manner. Overexpression of Rheb2 led to cystic growths with characteristics of both LAM and AML. We hope this mouse model will be helpful in furthering our understanding of the pathology behind these lesions, and provide a mouse model for therapeutic intervention for TSC.by Shomit Sengupta.Ph.D

mTORC1 in the Paneth cell niche couples intestinal stem cell function to calorie intake

How adult tissue stem and niche cells respond to the nutritional state of an organism is not well understood. Here we find that Paneth cells, a key constituent of the mammalian intestinal stem-cell (ISC) niche, augment stem-cell function in response to calorie restriction. Calorie restriction acts by reducing mechanistic target of rapamycin complex 1 (mTORC1) signalling in Paneth cells, and the ISC-enhancing effects of calorie restriction can be mimicked by rapamycin. Calorie intake regulates mTORC1 in Paneth cells, but not ISCs, and forced activation of mTORC1 in Paneth cells during calorie restriction abolishes the ISC-augmenting effects of the niche. Finally, increased expression of bone stromal antigen 1 (Bst1) in Paneth cells—an ectoenzyme that produces the paracrine factor cyclic ADP ribose—mediates the effects of calorie restriction and rapamycin on ISC function. Our findings establish that mTORC1 non-cell-autonomously regulates stem-cell self-renewal, and highlight a significant role of the mammalian intestinal niche in coupling stem-cell function to organismal physiology.National Institutes of Health (U.S.) (CA103866)National Institutes of Health (U.S.) (CA129105)David H. Koch Institute for Integrative Cancer Research at MIT (Initiator Award)Ellison Medical FoundationNational Cancer Institute (U.S.) (NCI (T32CA09216) fellowship support)Academy of FinlandFoundations’ Postdoc PoolNational Institutes of Health (U.S.) (NIH (1F32AG032833-01A1))Jane Coffin Childs Memorial Fund for Medical Researc

Uropathogenic Escherichia coli Induces Extrinsic and Intrinsic Cascades To Initiate Urothelial Apoptosis

A murine model of urinary tract infection identified urothelial apoptosis as a key event in the pathogenesis mediated by uropathogenic Escherichia coli (UPEC), yet the mechanism of this important host response is not well characterized. We employed a culture model of UPEC-urothelium interactions to examine the biochemical events associated with urothelial apoptosis induced by the UPEC strain NU14. NU14 induced DNA cleavage within 5 h that was inhibited by the broad caspase inhibitor ZVAD, and urothelial caspase 3 activity was induced within 3 h of exposure to type 1 piliated NU14 and was dependent upon interactions mediated by the type 1 pilus adhesin FimH. Flow cytometry experiments using chloromethyl-X-rosamine and Indo-1 revealed FimH-dependent mitochondrial membrane depolarization and elevated [Ca(2+)](in), respectively, indicating activation of the intrinsic apoptotic pathway. Consistent with this possibility, overexpression of Bcl(XL) inhibited NU14 activation of caspase 3. Immunoblotting, caspase inhibitors, and caspase activity assays implicated both caspase 2 and caspase 8 in apoptosis, suggesting the involvement of the intrinsic and extrinsic apoptotic cascades. To reconcile the apparent activation of both extrinsic and intrinsic pathways, we examined Bid-green fluorescent protein localization and observed translocation from the cytosol to mitochondria in response to either NU14 or purified FimH. These data suggest that FimH acts as a tethered toxin of UPEC that activates caspase-dependent urothelial apoptosis via direct induction of the extrinsic pathway and that the intrinsic pathway is activated indirectly as a result of coupling by caspase 8-mediated Bid cleavage

Discovery of NV-5138, the first selective Brain mTORC1 activator

AbstractThe mechanistic target of rapamycin complex 1 (mTORC1) has been linked to several important chronic medical conditions many of which are associated with advancing age. A variety of inputs including the amino acid leucine are required for full mTORC1 activation. The cytoplasmic proteins Sestrin1 and Sestrin2 specifically bind to the multiprotein complex GATOR2 and communicate leucine sufficiency to the mTORC1 pathway activation complex. Herein, we report NV-5138, a novel orally bioavailable compound that binds to Sestrin2 and activates mTORC1 both in vitro and in vivo. NV-5138 like leucine transiently activates mTORC1 in several peripheral tissues, but in contrast to leucine uniquely activates this complex in the brain due lack of metabolism and utilization in protein synthesis. As such, NV-5138 will permit the exploration in areas of unmet medical need including neuropsychiatric conditions and cognition which have been linked to the activation status of mTORC1.</jats:p

mTOR Complex 1 Regulates Lipin 1 Localization to Control the SREBP Pathway

SummaryThe nutrient- and growth factor-responsive kinase mTOR complex 1 (mTORC1) regulates many processes that control growth, including protein synthesis, autophagy, and lipogenesis. Through unknown mechanisms, mTORC1 promotes the function of SREBP, a master regulator of lipo- and sterolgenic gene transcription. Here, we demonstrate that mTORC1 regulates SREBP by controlling the nuclear entry of lipin 1, a phosphatidic acid phosphatase. Dephosphorylated, nuclear, catalytically active lipin 1 promotes nuclear remodeling and mediates the effects of mTORC1 on SREBP target gene, SREBP promoter activity, and nuclear SREBP protein abundance. Inhibition of mTORC1 in the liver significantly impairs SREBP function and makes mice resistant, in a lipin 1-dependent fashion, to the hepatic steatosis and hypercholesterolemia induced by a high-fat and -cholesterol diet. These findings establish lipin 1 as a key component of the mTORC1-SREBP pathway.PaperCli

Tumor predisposition in mice mutant for p63 and p73: Evidence for broader tumor suppressor functions for the p53 family

Summaryp63 and p73 are functionally and structurally related to the tumor suppressor p53. However, their own role in tumor suppression is unclear. Given the p53-like properties of p63 and p73, we tested whether they are involved in tumor suppression by aging mice heterozygous for mutations in all p53 family genes and scored for spontaneous tumors. We show here that p63+/−;p73+/− mice develop spontaneous tumors. Loss of p63 and p73 can also cooperate with loss of p53 in tumor development. Mice heterozygous for mutations in both p53 and p63 or p53 and p73 displayed higher tumor burden and metastasis compared to p53+/− mice. These findings provide evidence for a broader role for the p53 family than has been previously reported

Closing Concert

The High School Piano Institute concert performed at the UNT College of Music Recital Hall