David M. Sabatini - US grants

Studies into the mechanism of action of rapamycin, a potent anti- proliferative drug, have led to the discovery of a novel translational control pathway with critical roles in eukaryotic cell division. The central component of the pathway is the in vivo target of rapamycin, a protein that we call RAFT1 but is also known as FRAP or mTOR. RAFT1 is a large protein kinase related to the cell-cycle regulators ataxia telangiectasia mutated (ATM) and DNA-dependent protein kinase (DNA-PKcs). The RAFT1 mechanism of action is poorly understood, but the anti- proliferative properties of rapamycin reveal an essential, drug- sensitive role in cell division for the RAFT1-mediated translation of specific mRNAs. To elucidate how RAFT1 regulates mRNA translation and cell cycle progression we propose to: (1) identify downstream components of the RAFT1 signaling pathway, (2) understand their in vivo function in RAFT1 signaling, and (3) identify the rapamycin- sensitive mRNAs whose translational inhibition leads to cell cycle arrest. We are taking two approaches to discover components of the pathway: a biochemical one to identify functionally important RAFT1 interacting proteins (RIPs) and a genetic one for suppressors of the anti-proliferative effects of rapamycin. We have already identified two components whose role in RAFT1 signaling we will analyze in detail: p60, a novel RIP that may regulate downstream stages of the pathway, and FRAT1, an oncogene whose overexpression, we have shown, confers resistance to the anti-proliferative effects of rapamycin. We have used a microarray-based strategy to identify mRNAs whose translation is inhibited by rapamycin in T-cells. With biochemical and genetic experiments we will determine how RAFT1 controls the translation of these mRNAs and address why their inhibition leads to cell cycle arrest. The anti-proliferative effects of rapamycin are of medical value and the drug is now in clinical trials for immunosuppressive and anti-cancer uses. Thus, our study of the RAFT1 signaling pathway will not only elucidate the workings of a critical regulator of cell division, but also explain how a clinically useful drug exerts its effects.

DESCRIPTION (provided by applicant): Growth (mass accumulation) is a critical determinant of cell, organ, and body size and is often deregulated in diseases such as cancer and diabetes. Our long-term research goal is to identify and characterize the molecular mechanisms that control growth and to elucidate their roles in the normal and diseased physiology of mammals. We are studying the mammalian TOR (mTOR) pathway, a conserved signaling system that is emerging as a critical regular of growth in eukaryotes and is the target of the FDA-approved immunosuppressant rapamycin. Recent clinical trials indicate that rapamycin may also be useful for treating certain cancers and autoimmune diseases and for preventing the restenosis of vessels opened with balloon angioplasty. From human cells we recently purified an mTOR-containing protein complex and identified several novel proteins essential for the function of the mTOR pathway within cells. One of these proteins, which we termed raptor, controls the mTOR kinase activity by binding to mTOR in a nutrient-regulated fashion. Our preliminary evidence indicates that the mTOR-raptor complex does not sense nutrients directly but responds, through an unknown mechanism(s), to a signal(s) generated by mitochondria through the metabolism of nutrients. In addition, in certain human cancer cells the regulation of the mTOR pathway is deranged so that neither the mTOR-raptor association nor the activity of downstream effects of mTOR, such as S6K1, responds to nutrients or mitochondrial function. To understand how nutrients regulate the mTOR growth pathway we propose to: (1) identify and characterize the nutrient-regulated post-translational mechanisms that control the mTOR-raptor association and pathway; (2) determine why GbetaL, a novel 36 kDa mTOR-binding protein we discovered in our preliminary studies, is essential for nutrients to regulate the raptor-mTOR association; and (3) determine the mechanisms that cause the mTOR-raptor association and pathway to become nutrient-insensitive in certain human cancer cells and to understand the role of this type of deregulation in the formation and growth of tumors in vivo. Our work will not only lead to a fundamental advance in our understanding of the mechanisms that regulate growth in mammals, but also to the discovery of novel signaling mechanisms that are likely of value as targets for drug development.

DESCRIPTION (provided by applicant): The process of mass accumulation (cell growth) is an important regulator of cell, organ, and body size and can be deregulated in diverse diseases such as cancer and diabetes. Our lab is studying the mammalian TOR (mTOR) pathway, a signaling network that regulates growth in response to growth factors, stress, nutrients, and metabolism. The mTOR pathway is medically important, as it is the target of the FDA-approved immunosuppressant rapamycin that also prevents vessel restenosis after angioplasty and has potential as an anti-cancer agent. Moreover, recent work suggests that in the cancer-prone genetic syndrome tuberous sclerosis complex the mTOR pathway becomes hyperactive and deregulated. Over the last few years we have been studying the biochemistry of the mTOR pathway in human tissue culture cells and have discovered two distinct mTOR-containing protein complexes. The first contains mTOR and two novel proteins, raptor and GbL, and mediates the rapamycin-sensitive roles of mTOR (like S6K1 phosphorylation). The second complex also contains mTOR and GbetaL but, instead of raptor, another novel protein that we named rictor. Our proposed work focuses on understanding the biochemical, cellular and organismal functions of the rictor protein, the central component of the rapamycin-insensitive mTOR pathway. Although we know little about this pathway compared to the rapamycin-sensitive branch, our preliminary results suggest that rictor plays critical roles in the control of cell survival and proliferation by regulating the activity of known effectors of these processes. Our unexpected discovery that mTOR has rapamycin-insensitive functions suggests that direct inhibitors of the mTOR kinase activity will likely have different pharmacological effects and clinical applications than rapamycin. Therefore, our proposed work will lead to an important advance in our understanding of the molecular mechanisms that regulate cell growth and survival and that may be exploited to tackle diseases in which these processes are deregulated.

DESCRIPTION (provided by applicant): The process of growth (mass accumulation) is a critical determinant of cell, organ, and body size and is often deregulated in diseases such as cancer and diabetes. We are studying the TOR (mTOR in mammals; dTOR in drosophila) pathway, a conserved signaling system that is emerging as the critical regulator of growth in eukaryotes and is regulated by metabolism, growth factors and stress. The TOR pathway is the target of the FDA-approved immuno suppressant rapamycin that is also used to prevent vessel restenosis after angioplasty and is in trials for the treatment of cancer and autoimmune diseases. Over the last few years we have been studying the biochemistry of the mTOR pathway in human tissue culture cells. Although this work has been fruitful and has lead to the discovery of several proteins that interact with mTOR (e.g. raptor and GbetaL), we have come to realize that many of the important questions about TOR signaling are more easily answered in a model system that uses drosophila rather than human tissue culture cells. The human and drosophila TOR (dTOR) pathways are highly conserved and our preliminary data suggests that both pathways respond alike to nutrient metabolism, contain an unidentified TOR-regulated phosphatase, and have similar effects on cell size. In contrast, the yeast TOR pathway is missing several important components, including S6 kinase (S6K), TSC1, and TSC2, senses different nutrients and does not have growth factor inputs. There are several advantages to studying TOR signaling in drosophila rather than human tissue culture cells. The fly pathway has less redundancy than the human version, loss of function mutations are remarkably easy and efficient to make, and we have developed an ultra high-throughput technology (RNAi-cell microarrays) for undertaking genome-scale RNAi screens in drosophila cells. To exploit the potential of the drosophila system to study TOR signaling we propose to: (1) identify and characterize the metabolism-regulated mechanisms that control the TOR pathway; (2) identify and understand the regulation of a TOR controlled phosphatase that inhibits TOR effectors; and (3) use RNAi-cell microarrays to undertake large scale loss of function screens to discover new components of the TOR pathway. In general, we will begin our experiments in the drosophila system and, as our knowledge of a particular problem increases, extend our work to human cells and proteins. Our research will not only lead to a fundamental advance in our understanding of the mechanisms that regulate growth in eukaryotes, but also to the discovery of novel signaling mechanisms that will likely be of value as drug development targets.

[unreadable] DESCRIPTION (provided by applicant): Growth is the process through which cells accumulate mass and increase in size. mTORC1 is a protein kinase composed of the mTOR catalytic subunit and the associated proteins raptor and mLST8 and the central component of a signaling network that regulates growth in response to growth factors, nutrients, and stress. It is increasingly apparent that many cancer-promoting lesions activate the mTORC1 pathway. Most notably, the TSC1-TSC2 tumor suppressor complex--whose inactivation causes the tumor- prone syndrome Tuberous Sclerosis Complex (TSC) and the related disease Lymphangioleiomyomatosis (LAM)--is a major negative regulator of mTORC1. The TSC1-TSC2 heterodimer is a GTPase activating protein (GAP) that inhibits rheb, a GTP-binding protein that activates mTORC1 through a poorly understood mechanism. TSC1-TSC2 and rheb are also important for the activation of mTORC1 that occurs in cells that have lost the PTEN, NF1, LKB1, or p53 tumor suppressors. We propose to address key gaps in our understanding of mTORC1 biology. First, we will determine the molecular mechanisms that activate mTORC1 in response to growth factors or inactivation of TSC1- TSC2 or PTEN. Second, using mouse models we are developing, we will rigorously test the role of mTORC1 in tumorigenesis caused by inactivation of PTEN. Third, we will obtain structural information about intact mTORC1 and the mTOR kinase domain. We will accomplish our goals with a collaborative multi-disciplinary approach that exploits the tools of biochemistry, molecular biology, mouse models of cancer, and structural biology. We believe that our results are likely to have significant medical implications for the treatment of Tuberous Sclerosis Complex. An understanding of how the inactivation of TSC1-TSC2 activates mTORC1 is necessary for the rational development of therapies for TSC. With our animal models we will obtain a definitive genetic answer to the potential value of inhibiting mTORC1 in patients with tumors missing PTEN. Lastly, modified versions of our novel mTORC1 kinase assay may be useful for the high- throughput screening of small molecules that inhibit mTORC1 and our structural work will inform the development of inhibitors of the mTOR kinase. PUBLIC HEALTH RELEVANCE: Growth is the process through which cells and organisms accumulate mass and increase in size. It is increasingly apparent that this basic biological process is deregulated in common human diseases, most notably in cancer. In this application we propose to study one of the major growth regulators in mammals, a complex of several proteins called mTORC1. We propose to elucidate the molecular mechanisms that activate mTORC1 in cancer and normal cells, to determine if inhibiting mTORC1 is likely to be a good treatment for tumors that have a common cancer-causing genetic alteration, and, lastly, to determine the molecular structure of mTORC1. The overall goal of our proposed work is to increase the capacity of the oncology community to rationally exploit mTORC1 in the treatment of cancer. We anticipate that our work will help understand which tumor classes should be treated with mTORC1 inhibitors, aid in the development of more specific mTORC1 inhibitors, and lead to the discovery of mechanisms that may be targets for future drug development. [unreadable] [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Growth is the process through which cells accumulate mass and increase in size. mTORC1 is a protein kinase composed of the mTOR catalytic subunit and the associated proteins raptor, mLST8/G2L, and PRAS40, and the central component of a signaling network that regulates growth in response to growth factors, energy levels, amino acids, and stress. Many cancer-promoting lesions activate the mTORC1 pathway. Most notably, the TSC1-TSC2 tumor suppressor complex--whose inactivation causes Tuberous Sclerosis Complex (TSC) and the related disease Lymphangioleiomyomatosis (LAM)--is a major negative regulator of mTORC1. The TSC1-TSC2 heterodimer is a GTPase activating protein (GAP) that inhibits Rheb, a GTP-binding protein that directly binds and activates mTORC1. mTORC1 deregulation also occurs in cancer cells that have lost the PTEN, NF1, LKB1, or p53 tumor suppressors. The TSC1/TSC2/Rheb axis signals insulin and energy levels but not amino acids to mTORC1, suggesting that an amino acid-induced pathway upstream of mTORC1 remains unknown. We propose to understand how the mTORC1 pathway senses amino acids. First, we will determine the molecular mechanisms through which novel regulators of mTORC1 that we have identified in our preliminary studies signal amino acids to mTORC1. Second, by exploiting the results of RNAi and proteomics screens as well as candidate-molecule approaches, we will identify and understand the regulatory steps upstream of these novel regulators. Third, using conditional null alleles of the genes encoding the novel regulators we will understand their roles in vivo in controlling mTORC1 activity and organ growth. We will accomplish our goals with a multi-disciplinary approach that exploits the tools of biochemistry, molecular biology, proteomics, high-throughput RNAi screening, and mouse models. Our results are likely to have important consequences for our understanding of the clinically important mTORC1 pathway. Knowledge of how amino acids signal to mTORC1 is necessary to test if these mechanisms are deranged in human cancers, as are known upstream components of the mTORC1 pathway. Furthermore, some of the signaling mechanisms we uncover may serve in the future as targets for drug development. PUBLIC HEALTH RELEVANCE: Growth is the process through which cells and organisms accumulate mass and increase in size. Over the last few years it has become apparent that this basic biological process is deregulated in common human diseases, most notably in cancer and diabetes. In this proposal we will study one of the key growth regulators in human beings, a multi-protein complex called mTORC1. We propose to elucidate the molecular mechanisms that activate mTORC1 in response to environmental amino acid levels, as well as use mouse models to understand how these mechanisms control organ growth in vivo. The overarching goal of our proposed work is to increase the molecular understanding of the mTORC1 pathway so as to enable the oncology community to rationally exploit mTORC1 in the treatment of cancer. We anticipate that our work will elucidate molecular mechanisms that may be deranged in human cancers and thus may serve as targets for future drug development.

DESCRIPTION (provided by applicant): The mTOR kinase is the central component of a pathway controls growth in eukaryotes and is deregulated in common human diseases like cancer and diabetes. Within cells mTOR exists within two distinct protein complexes, mTOR Complex 1 (mTORC1) and 2 (mTORC2). mTORC1 contains mTOR, mLST8/G2L, raptor, and PRAS40, is partially sensitive to rapamycin, and controls cell size through translational regulators like S6K1 and 4E-BP1. mTORC2 also contains mTOR and mLST8, but, instead of raptor and PRAS40, it contains rictor, mSin1, and protor. We know less about mTORC2 than mTORC1 but it is now accepted that mTORC2 is an activating kinase for Akt/PKB and SGK and therefore part of the PI3K pathway that controls cell survival, proliferation, and metabolism. Recently, we discovered that DEPTOR, a protein of previously unknown function, interacts directly with mTOR and inhibits mTORC1 and mTORC2 signaling in cells through unclear mechanisms. DEPTOR protein levels are highly regulated by the same growth stimuli and stresses that regulate mTORC1 and mTORC2. Overexpression of DEPTOR inhibits mTORC1 signaling, which, in turn, activates the PI3K pathway by suppressing a known inhibitory feedback from mTORC1 to PI3K. In cancers like Multiple Myeloma, DEPTOR is highly overexpressed and the resulting activation of PI3K is a new mechanism for promoting cell survival. We propose to: (1) determine how DEPTOR inhibits mTORC1 and mTORC2 signaling;(2) identify and characterize the molecular mechanisms that regulate the expression level of DEPTOR;and (3) determine the in vivo role of DEPTOR in the mTORC1 and mTORC1 pathways and in controlling liver growth and function. We will accomplish our goals with a multi-disciplinary approach that uses the tools of biochemistry, molecular biology, proteomics, high-throughput RNAi screening, and engineered mouse models. Our results are likely to have important consequences for our understanding of the clinically important mTOR pathway and the signaling mechanisms we uncover may serve in the future as targets for drug development. PUBLIC HEALTH RELEVANCE: Growth is the process through which cells and organisms accumulate mass and increase in size. Over the last few years it has become clear that this basic biological process is deregulated in common human diseases like cancer and diabetes. We have recently discovered a protein called DEPTOR that our preliminary evidence indicates is an important new regulator of growth. DEPTOR is part of a network within cells called the 'mTOR pathway'that is known to be a major growth regulator. We propose to elucidate the molecular mechanisms through which DEPTOR regulates the mTOR pathway in response to growth factors like insulin, and to use engineered mouse models to understand how DEPTOR regulates organ growth in vivo. The overarching goal of our proposed work is to increase the molecular understanding of the mTOR pathway so as to enable the medical community to rationally exploit the mTOR pathway in the treatment of disease. Our work will also elucidate molecular mechanisms that are deranged in human cancers and thus may serve as targets for future drug development.

DESCRIPTION (provided by applicant): The goal of this project is the discovery and development of selective small molecule inhibitors of 3- phosphoglycerate dehydrogenase (PHGDH), the first enzyme of the serine biosynthetic pathway. We have found that this pathway is upregulated in estrogen-receptor negative (ER-) breast cancers, which account for 20-25% of breast cancers but are responsible for 50% of breast cancer-related deaths. Breast cancer cells that overexpress PHGDH have higher flux through the serine biosynthesis pathway and are sensitive to knockdown of this enzyme, indicating that inhibitors of this pathway may be useful candidates for the treatment of ER- breast cancer. At present there are no small molecule inhibitors of PHGDH. We have developed a nicotinamide adenine dinucleotide (NADH)-linked high-throughput assay for PHGDH and carried out a pilot screen of 1400 known bioactive compounds, including FDA-approved pharmaceuticals, at the Laboratory for Drug Discovery in Neurodegeneration (LDDN) at the Brigham and Women's Hospital. This screen had a Z' factor of 0.61 and a coefficient of variation of 2%. The screen identified two compounds that dose-dependently inhibit PHGDH. Our first aim is to transfer this assay to an MLPCN center for a high- throughput screen of the MLPCN collection of over 350,000 small molecules. Our second aim is validation of these hits using a coupled assay of serine biosynthesis, amino acid and metabolic flux analysis to measure inhibition of serine and ¿-ketoglutarate production by the serine biosynthesis pathway in vitro and in cells, and counterscreening of these hits against GAPDH to eliminate non-specific dehydrogenase inhibitors. Our third aim is assessment of the biological activity of these hits by determining their selective cytotoxicity towards a tumor cell line that overexpresses PHGDH and has high flux through the serine biosynthesis pathway, while sparing a tumor cell line that has low expression of PHGDH and has low serine biosynthesis pathway flux. Inhibitors of PHGDH will be tested in vivo in xenograft models of mouse tumors that overexpress PHGDH. Identification of specific inhibitors of PHGDH will permit the evaluation of serine biosynthesis inhibition as a novel therapeutic target for ER- breast cancer.

DESCRIPTION (provided by applicant): The mechanisms underlying the pro-aging consequences of mTOR activity are obscure. Deregulated mTOR activity leads to accelerated aging and upregulated mTORC1 activity occurs in aging organisms. We recently described the Rag family of proteins as key for mTORC1 activation by amino acids, through a mechanism that requires mTORC1 shuttling to the lysosomal surface. We have generated a series of immortalized cell lines derived from genetically-engineered mice that lack the RagA gene. Although mTORC1 activity is barely detectable in RagA-deficient embryos, cell lines derived from them have reactivated mTORC1 signaling, which is now insensitive to amino acids withdrawal, but sensitive to growth factors withdrawal. Intriguingly, in these lines mTORC1, although active, does not localize to lysosomes, indicating that an additional unknown mechanism of mTORC1 activation is at work. Based on a combination of transcriptional profiling and proteomic-based approaches, we plan to find the genes responsible for the lysosomal-independent activation of mTORC1 and to understand how this occurs. We will then take advantage of RagA-null livers to study in vivo the consequences of altering the expression of the candidates found. Further elucidation of the molecular mechanism leading to mTORC1 desensitization to amino acid withdrawal, together with the identification of druggable targets within this pathway, may pave the way for novel therapeutic approaches to aging and age-related diseases. PUBLIC HEALTH RELEVANCE: Deregulated cell growth signals arising from the mechanistic target of rapamycin (mTOR) protein kinase occur in diabetes, cancer and aging. Thus, understanding mTOR signaling pathway will enable the pursuit of improved therapies against these diseases. Taking advantage of novel mouse models of deregulated mTOR activity we have generated cell lines with a unique and intriguing regulation of mTOR activation, resistant to nutrient deprivation, which normally inactivates this signaling pathway. The identification of the responsible genes and the molecular mechanisms governing this particular signaling alteration that we plan to investigate in the present proposal will help understand deregulated cell growth states. The series of novel mouse models will also allow us to explore the consequences of this deregulated growth state in mammalian physiology, helping us to develop novel therapeutic avenues to manipulate the mTORC1 pathway in human disease.

Aging has a profound impact on tissue regeneration and cancer incidence. However, the mechanisms of how aging reduces the function of stem cells, alters the transformability of stem cells to beget tumors, or influences tumor progression are poorly understood. Although aging is the single biggest risk factor for cancer in humans and laboratory animals, cancer has been modeled and interrogated solely in young rodent models. Our system for addressing these questions is the mammalian intestine where a majority of intestinal stem cells (ISCs) in the small intestine and colon express Lgr5. Our preliminary studies suggest that ISC numbers are diminished and less proliferative in old mice and humans and that elderly ISCs are less functional in an in vitro organoid (3-D mini-intestinal) assay of stem cell function, indicating that cell autonomous mechanisms contribute to intestinal stem cell aging. Finally, we find that aged mice, like aged humans, develop spontaneous intestinal adenomas and carcinoma; however, the mechanisms of how aging reduces the function of stem cells, alters the transformability of stem cells to give rise to tumors, or influences tumor progression/metastasis are poorly understood. In this proposal, we will study how aging influences the genesis, progression, and treatment response of intestinal adenomas and carcinomas in inducible, genetically defined mouse models of intestinal tumors. Specifically, we will establish aging mouse colonies to interrogate how age- related changes in the tumorigenic potential of intestinal stem and progenitor cells contribute to enhanced tumor incidence in old age (Aim 1); that aging has autonomous and non-autonomous effects on tumor progression (Aim 2), and that aging alters the treatment response of intestinal tumors to chemotherapy or radiation (Aim 3).

Project Summary Title: Exploiting mitochondrial heteroplasmy for cancer chemotherapy Roughly a third of patient cancers are heteroplasmic -- that is, individual cells harbor a mixture of genetically distinct mitochondrial genomes -- and a substantial fraction of these bear severe loss-of-function mutations affecting genes necessary for respiration. These mutations appear to be passengers rather than drivers of tumorgenesis, but our lab recently discovered that they can render cancer cell lines and xenografts more vulnerable to biguanides, mitochondrial inhibitors used to treat type 2 diabetes. Since heteroplasmy is relatively rare in normal tissues, these findings suggest that mitochondrial inhibitors may have a therapeutic window for treating heteroplasmic cancers, but specifically when and how this heteroplasmy may be exploited for treatment remains poorly understood. Additionally, our work showed that heteroplasmy is a reversible genetic defect, since heteroplasmic cells generally still contain wild-type copies of the mitochondrial genome, and that partial reversion is a route to drug resistance. This reduction of heteroplasmy is not a simple mutational processes, and its mechanisms are unknown. The proposed work aims to fill both of these gaps in current knowledge with a systematic study of how heteroplasmy affects susceptibility to a variety of relevant inhibitors and how these inhibitors may drive changes in heteroplasmy leading to drug resistance.

Treatment with any of several VEGF receptor-targeted tyrosine kinase inhibitors (TKIs) results in prolonged disease stability or even regression in the majority of patients with metastatic renal cell carcinoma (RCC). This antitumor effect is generally transient and incomplete, however, due to the rapid development of drug resistance. This project emerged from our earlier work in RCC xenografts on the mechanisms of acquired TKI resistance. We observed that p53 activation was essential for a robust response to sunitinib. We also noted that the expression of p53-dependent genes was transient and down modulated with the onset of TKI resistance. Finally, we demonstrated that the concurrent administration of a drug that blocks HDM2- dependent p53 ubiquitylation and degradation prevented the development of TKI resistance. At least two potential mechanisms for this effect were documented, one of which involved in the induction of the E3 ligase Fbw7 and the degradation of the oncoprotein HIF-2alpha. Another potential mechanism by which HDM2 antagonists prevent TKI resistance is their ability to block the expression of hypoxia-driven chemokines such as SDF-1 (CXCL-12) and to prevent the influx of CD11b+/Gr-1+ myeloid-derived tumor suppressor cells (MDSC). In this project, we propose to carry out a Phase I/Ib clinical trial examining a combination of sunitinib with the HDM2 antagonist CGM097 (Novartis). This trial will have a 20 patient expansion cohort in which the administration of the HDM2 antagonist will be delayed in half of the patients. Tumor biopsies will be performed on these patients (half of which will be receiving sunitinib alone and half the drug combination at the time of biopsy) to assess the effects of treatment on p53 activation and MDSC and Treg trafficking. We will examine the effects of MDSC depletion on treatment outcome in murine RCC models and will determine if targeting the SDF-1 receptor (CXCR4) with the CXCR4 inhibitor AMD11070 prevents MDSC recruitment and the onset of TKI resistance as effectively as HDM2 blockade. Finally, we will assess the effects of HDM2 blockade on the expression of IL-8, FGF, and other factors previously implicated in the development of TKI resistance

Lysosomes are membrane-bound degradative compartments that break down macromolecules from endocytic, phagocytic and autophagic pathways, and serve the role of key metabolic and signaling hubs. Accumulating evidence suggests that in Alzheimer's disease and other neurodegenerative disorders lysosomes fail to correctly perform their functions. However, due to the paucity of tools to study organelles in vivo, so far there has been no systematic assessment of lysosomal alterations during progression of Alzheimer's disease, and the exact molecular nature of the proposed impairments is not known. Our understanding of the involvement of the lysosome in the disease is further limited because lysosomes are rare, constituting <3% of the cell. Here, we seek to combine powerful, state-of-the-art approaches including recently developed rapid lysosomal isolations (LysoIPs) and unbiased proteomic and metabolomic analyses to determine if and how lysosomes change in vivo in murine models of Alzheimer's disease. We propose to focus on lysosomes isolated from neurons and microglia which we expect to be critical to the pathology of the disease. Complex reciprocal interactions between neurons and microglia are essential for regulation of the most important aspects of brain function, and we hypothesize that alterations of the endolysosomal systems in these two cell types compromise the integrity of the central nervous system. Here, in Aim I we propose to define lysosomal alterations in neurons and microglia over a time course of Alzheimer's disease progression generating a dynamic atlas of lysosomal proteins and metabolites in these cells. This aim will generate novel mouse models and robust protocols enabling rapid lysosomal isolations from neurons and microglia. In Aim 2 we will validate bioinformatically filtered candidates from Aim 1, paving the way for future mechanistic dissections. The proposed research utilizes innovative technologies and concepts to address fundamental molecular aspects of pathobiology of Alzheimer's disease, building a comprehensive atlas of in vivo lysosomal changes in neurons and microglia. We believe that this work will shed light on novel aspects of lysosomal biology in the brain and has the potential to transform our understanding of the mechanistic basis of Alzheimer's disease, informing future developments in the treatment of this devastating disorder.