Browsing by Subject "Liver"
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Item Acetaminophen and the liver: poison or panacea?(2016-05-20) Lee, William M.Item Acute liver failure 2006(2006-10-13) Lee, William M.Item Bile acid therapy - status in 1993(1993-02-25) Combes, BurtonItem Biochemical Characterization of Niemann-Pick C: A Disease of Cholesterol Transport(2012-08-15) Infante, Rodney Elwood; Brown, Michael S.; Goldstein, Joseph L.Despite intense scientific interest, the mechanism by which cholesterol is transported between membrane compartments in animal cells remains obscure. One transport pathway begins in lysosomes where cholesterol is liberated from plasma lipoproteins that have entered the cell through receptor-mediated endocytosis. This cholesterol is transported from the lysosome to other cellular membranes to perform structural and regulatory roles. A clue to the mechanism of this cholesterol movement comes from observations in cells from patients with Niemann-Pick Type C (NPC) disease. These individuals accumulate large amounts of cholesterol throughout the body caused by mutations in either one of two genes encoding the lysosomal proteins NPC1 and NPC2. Unlike the membrane protein NPC1, evidence suggests that the soluble protein NPC2 is a cholesterol binding protein. In the course of isolating a cholesterol-homeostasis membrane protein that binds sterols, we encountered NPC1. Using rabbit membranes, an integral membrane protein that bound sterols was isolated with a 14,000-fold purification while maintaining 8% final yield. Mass spectrometry identified the protein to be NPC1. Recombinant human NPC1 was expressed, purified, and confirmed to be a high affinity sterol receptor. NPC1's sterol binding domain was localized to it's N-terminal luminal soluble domain, which can be prepared as a soluble protein of 240 amino acids, NPC1(NTD), that is secreted by cells. The binding properties of NPC1(NTD) binds cholesterol similar to NPC2 with a Kd of ~130nM. Cross-competition studies between purified NPC1(NTD) and the soluble NPC2 protein revealed differences in sterol specificity depicting the different parts of the cholesterol moiety the NPC proteins bind. Finally, an in vitro assay was established to measure transfer of [³H]cholesterol between the two NPC proteins and phosphatidylcholine liposomes. NPC1(NTD) donates or accepts cholesterol from liposomes very slowly, whereas NPC2 acts quickly. NPC2 stimulates the bidirectional transfer of cholesterol between NPC1(NTD) and liposomes. A naturally-occurring human mutant of NPC2 (Pro120Ser) failed to facilitate the movement of cholesterol from NPC1(NTD) to lipid bilayers. These studies directly link both proteins to the cholesterol egress process from lysosomes, explaining how mutations in either protein produce similar clinical phenotypes.Item Characterization of Liver-Specific ChREBP Knockout Mice(2017-02-13) Linden, Albert George; Ye, Jin; Brown, Michael S.; Goldstein, Joseph L.; Horton, Jay D.; Repa, Joyce J.ChREBP (Carbohydrate Response Element-Binding Protein) and SREBP-1c (Sterol Regulatory Element-Binding Protein-1c) both stimulate the transcription of genes required for lipid synthesis in the liver. My project was designed to investigate the roles of these two factors in regulating the lipogenic pathway. ChREBP and SREBP-1c are induced by carbohydrates, but by different mechanisms. SREBP-1c is stimulated by insulin, while ChREBP is insulin-independent, but dependent on intracellular glucose levels. This issue was studied previously using mice with a germline deletion in ChREBP, but these experiments were limited because these whole-body ChREBP knockout mice did not tolerate a high sucrose diet. To circumvent this problem, we produced mice with a liver-specific knockout of ChREBP (L-ChREBP-/-). When L-ChREBP-/- mice were fasted and refed a high-sucrose diet, they consumed a normal amount of food, but lipogenic gene mRNAs were not induced by refeeding. However, this effect could not be solely attributed to the loss of ChREBP because the L-ChREBP-/- mice unexpectedly also had reduced levels of nuclear SREBP-1. Previous experiments have shown that SREBP-1c is required for the postprandial induction of lipogenic gene mRNAs in the livers of mice subjected to fasting and refeeding. To determine whether the decreased lipogenesis in L-ChREBP-/- mice was caused by reductions in SREBP-1c, ChREBP, or both transcription factors, we injected the L-ChREBP-/- mice with an adeno-associated virus encoding the active nuclear form of SREBP-1c. The expression of some lipogenic genes was restored by normalizing the content of nuclear SREBP-1c, but others were not. Therefore, both SREBP-1c and ChREBP are required for full stimulation of lipogenesis in the postprandial state. Insulin stimulates fatty acid synthesis by activating SREBP-1c. However, glucose is also necessary for lipogenesis, and the additional requirement of ChREBP to induce lipogenic enzymes ensures that the liver will not produce fatty acids unless both insulin and glucose are present.Item Clinical Parameters Are More Predictive of Mortality in Alcoholic Hepatitis than Histopathologic Severity(2017-03-24) Yeluru, Apurva; Cuthbert, Jennifer; Thiele, Dwain L.; Lee, William M.BACKGROUND: Alcoholic hepatitis (AH) is primarily diagnosed by clinical parameters, but is often misdiagnosed due to nonspecific symptoms, leading to high mortality rates. While histology aids definitive diagnosis, the role of the liver biopsy in its workup is still controversial. Currently, there is no widely accepted grading histologic grading system for AH. The relationship between biopsy findings and clinical course is also yet unknown. The Alcoholic Hepatitis Histologic Score (AHHS) was recently developed to define patient prognosis by histologic criteria. OBJECTIVE: The purpose of this study was to compare histologic severity defined by the AHHS with clinical severity of AH, as seen with symptoms, laboratory markers, and patient survival. METHODS: We conducted a retrospective case series of 56 patients with biopsy-proven AH from two hospitals in Dallas, TX, USA. Clinical and demographic data were collected from electronic medical records. Two trained pathologists blinded to patients' outcomes graded liver biopsies using the AHHS criteria. Relationships between clinical symptoms and complications, laboratory investigations, patient outcomes, individual histologic features, and the AHHS were analyzed. RESULTS: No hematologic or biochemical laboratory markers significantly correlated with the AHHS. Higher AST correlated with a greater degree of steatosis on biopsy (p<0.0019). Severe neutrophil infiltration on biopsy correlated with higher serum bilirubin, INR, MELD, and DF (p=0.034). Survival analysis by Kaplan-Meier curves and log-rank tests showed no significant correlation between AHHS and 90-day survival (p=0.09), while multiple clinical scoring systems accurately stratified prognosis (p<0.018 for all). Severe neutrophil infiltration on biopsy also correlated significantly with death (p=0.0001). CONCLUSION: Retrospective analysis in a diverse U.S. urban cohort did not confirm the validity of AHHS to predict survival in AH. In contrast, clinical parameters were better predictors of survival. Our results suggest that clinical deterioration, rather than histopathologic severity, is more informative in determining prognosis in AH. The relationship between neutrophil infiltration and mortality deserves further study.Item Drug-induced liver injury 2009(2009-05-01) Lee, William M.Item Drug-induced liver injury: the threat continues(2000-06-08) Lee, William M.Item The Effects of Chromatin Remodeling and Pseudokinase Activity on Liver Pathophysiology(August 2021) Moore, Austin Bradley; Agathocleous, Michalis; Hobbs, Helen H.; Hoshida, Yujin; Zhu, HaoThe liver exhibits a remarkable capability to regenerate itself in the face of injury; however, in the setting of sustained damage, this capability can be overwhelmed and eventually lead to chronic liver diseases such as non-alcoholic steatohepatitis, cirrhosis, and hepatocellular carcinoma. Although these processes are complex and not completely understood, specific genetic and epigenetic factors that drive aspects of this pathophysiology can shed further light on both how these diseases develop and on how normal, healthy regeneration differs from liver disease. In this body of work, we show that loss of Arid1a, a DNA-binding component of the SWI/SNF chromatin remodeling complex, shifts hepatocyte metabolism to promote lipid accumulation in a manner similar to that seen in non-alcoholic fatty liver disease. We further explore the dynamics of the SWI/SNF complex by examining a mutually exclusive homolog of Arid1a, Arid1b, and provide evidence to suggest that its role is to stabilize the hepatocyte SWI/SNF complex in the absence of Arid1a seen in regeneration and hepatocellular carcinoma. Finally, we harness the power of in vivo CRISPR screening within the liver to identify the pseudokinase STK31 as a positive regulator of hepatocyte proliferation and liver oncogenesis. Our findings underscore the important role that chromatin remodeling has in enforcing hepatocyte identity and functionality as well as allowing for plasticity. Additionally, our work with STK31 highlights the power of in vivo screening within the liver to identify new potential therapeutic targets not only for hepatocellular carcinoma, but other tumor types as well.Item The effects of oral contraceptive agents and steroids on liver function(1967-11-09) Combes, BurtonItem The Efficacy of Immunotherapy in Preventing Liver Cancer and the Role of Metabolic Zonation in Its Development(August 2021) Chung, Andrew Seungjae; McFadden, David G.; DeBerardinis, Ralph J.; Mani, Ram; Zhu, HaoIn order to study the development and progression of liver cancer, as well as the efficacy of novel therapeutic strategies, accurate models of human disease are needed. In particular, in vivo mouse models capture critical characteristics that are relevant to human hepatocellular carcinoma (HCC). There is a diverse array of mouse HCC models available, falling into three major categories: transplantation-based models, chemically-induced models, and genetically-induced models. Within these categories, models differ in factors such as the source of the tumor cells and the chemicals or genetic drivers used to induce tumorigenesis. All of these models offer specific advantages over the others but also have some disadvantages as well. Thus, the utility of any model is dependent on the specific investigatory aims of the study. In our case, we used two types of models to try to address two questions about HCC. First, we asked if immune checkpoint inhibition could prevent tumorigenesis in a chemically-induced mouse model of HCC. We found that initiation of anti-PD-1 immunotherapy prior to tumorigenesis could prevent up to 46% of liver tumors. This reduction in tumor burden was accompanied by infiltration of CD4+ T helper and CD8+ cytotoxic T cells into the liver parenchyma. Importantly, anti-PD-1 therapy did not exacerbate liver dysfunction or worsen overall health in this model. Given the safety and preservation of quality of life observed with long-term immunotherapy use, an immunotherapy chemoprevention strategy is likely associated with a low risk-to-benefit ratio and high value care in select patients. Along the portal-to-central axis within the hepatic lobule, there are profound differences in gene expression, metabolic processes, oxygen tension, and ploidy. Whether or not these differences reflect any differences in neoplastic potential is unclear. To address this, we turned to genetically-induced HCC models. We used various hepatic zone-specific CreERT2 mouse lines to induce activating mutations in Ctnnb1 and to delete Arid2. We found that mutant clones arising from zone 1 gradually expanded and persisted, while mutant clones arising from Zone 3 rapidly disappeared over time. However, more tumors ultimately developed in the zone 3 livers than in the zone 1 livers, suggesting that expression of some zonated metabolic genes may influence the fate of mutant hepatocytes. This could have major implications for prevention and treatment of HCC, as these metabolic genes could represent actionable preventive or therapeutic targets.Item From Feast to Famine: A Tale of Satiety and Hunger Hormones(2016-04-18) Zhang, Yuanyuan; Repa, Joyce J.; Horton, Jay D.; Chen, Zhijian J.; Goldstein, Joseph L.; Brown, Michael S.Ghrelin is a peptide hormone secreted mainly from the stomach. It has a unique octanoylation on Ser-3 by Ghrelin-O-Acyltransferase (GOAT). We have previously shown that Goat−/− mice developed severe hypoglycemia under 60% calorie restriction. Liver autophagy has been reported to play a crucial role in maintaining blood glucose during fasting. The present work was carried out to explore whether autophagy plays a role in the onset of hypoglycemia in Goat−/− mice. We observed a deficiency in autophagy in livers of calorie-restricted Goat−/− mice by showing lower expression level of LC3-II, an autophagy marker. This was further demonstrated by showing 10-fold fewer autolysosomes in livers of calorie-restricted Goat−/− mice as compared to the control mice (20 electron microscopic images analyzed for each group). We then went on to show that the deficiency in autophagy in Goat−/− mice can be restored by infusion of growth hormone. It can also be restored by injections of lactate, a gluconeogenic precursor, or octanoate, a fatty acid that spares the usage of glucose. Protein expression of p- STAT 5, a downstream target of growth hormone action, was significantly lower in livers of calorie-restricted Goat−/− mice, and was restored by infusion of growth hormone and by injections of lactate or octanoate. Protein expression levels of LC3-II and p-STAT 5 showed a strong correlation (r2=0.87, p<10-6) through the time course of calorie-restriction. Considered together, these data suggest that the onset of autophagy during calorie restriction is strongly correlated with the ghrelin-growth hormone axis, and that autophagy plays an important role in maintaining blood glucose homeostasis during chronic starvation.Item Hepatic drug reactions(1982-05-13) Ware, Athol J.Item Hepatic transplantation(1985-10-31) Cuthbert, Jennifer A.Item Insig-Mediated Regulation of Hepatic Lipid Synthesis(2007-05-22) Engelking, Luke James; Brown, Michael S.Cholesterol synthesis in mammals is tightly regulated by end-product feedback inhibition. 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) catalyzes a rate determining reaction that is highly regulated by transcriptional and post-transcriptional mechanisms. As cellular cholesterol accumulates, the transcription of HMGR mRNA is suppressed and the proteosomal degradation of HMGR protein is accelerated. The sterol-regulated transcription of HMGR and other lipogenic genes is controlled by sterol regulatory element binding proteins (SREBPs). These membrane-bound transcription factors are escorted by SREBP cleavage activating protein (SCAP) from the endoplasmic reticulum (ER) to the Golgi apparatus where SREBPs are proteolytically processed to their active forms. In cultured cells, feedback inhibition of SREBP processing is mediated by Insigs. When sterols accumulate, Insigs block SREBP activation by retaining SCAP in the ER. Insigs also mediate rapid, sterol-dependent turnover of HMGR protein. When sterols accumulate, Insigs bind to HMGR and stimulate its ubiquitination and degradation. Although Insigs are key regulators of cholesterol homeostasis in cultured cells, their role in the intact mammal was undefined. To explore this question, gain-of-function and loss-of-function analyses were performed by studying the livers of genetically engineered mice. First, transgenic mice that overexpress Insig-1 in liver (TgInsig-1) were generated. In the livers of TgInsig-1 mice, nuclear SREBPs (nSREBPs) were reduced and SREBP processing was supersensitive to inhibition by feeding high-cholesterol diets. The block in SREBP processing reduced the mRNA levels of SREBP target genes. Levels of HMGR protein were reduced and declined further with cholesterol feeding. Next, knockout mice that lack Insig-1, Insig-2, or both Insigs were generated. In the livers of Insig double knockout mice, cholesterol and triglycerides accumulated to high levels, and despite their accumulation, nSREBPs and mRNAs of SREBP target genes were not suppressed. SREBP processing was insensitive to inhibition by feeding high-cholesterol diets. HMGR protein levels were increased and failed to decline with cholesterol feeding. As a consequence of Insig overexpression or deficiency and the respective effect on SREBPs and HMGR, hepatic cholesterol and fatty acid synthesis in living animals was decreased in TgInsig-1 mice and increased in Insig double knockout mice. These studies indicate that Insigs are essential regulators of hepatic lipid synthesis.Item Insulin Stimulation of Sterol Regulatory Element-Binding Protein-1c Processing in Liver: Lessons from Transgenic Rats(2015-01-16) Owen, Joshua Lee; Scherer, Philipp; Cobb, Melanie H.; Russell, David W.; Zinn, Andrew R.Transcriptional control of hepatic fatty acid (FA) and triglyceride (TG) synthesis is mediated by SREBP-1c, one of three sterol regulatory element-binding protein (SREBP) isoforms. SREBPs are endoplasmic reticulum (ER) membrane-bound transcription factors that require escort to the Golgi apparatus followed by proteolytic cleavage from the membrane. This process liberates the active transcription factor portion of SREBP to translocate to the nucleus to activate transcription of its target genes. SREBP-1c is unique among the SREBP isoforms since it is highly enriched in liver and is activated by insulin. Therefore the best cell culture model system to study SREBP-1c function is freshly isolated primary rat hepatocytes due to their tissue origin and insulin sensitivity (cultured mouse hepatocytes lose insulin responsiveness). Using this model, insulin has been shown to activate the transcription of SREBP-1c, requiring mechanistic target of rapamycin complex 1 (mTORC1), but not its downstream target, p70 ribosomal protein S6 kinase (S6K). Insulin has also been implicated in the activation of proteolytic processing of SREBP-1c, but previous attempts to study this process have been confounded by the concomitant increase in SREBP-1c mRNA and precursor protein when primary hepatocytes are treated with insulin. To circumvent this problem, transgenic rats were created that express epitope-tagged human SREBP-1c under control of the apolipoprotein E (apoE) promoter/enhancer, which imparts constitutive, liver-specific expression to the transgene. Since the expression of the transgene is not regulated by insulin, the effect of insulin on the processing of SREBP-1c per se can now be studied. When hepatocytes isolated from transgenic rats were treated with insulin, the amount of cleaved nuclear SREBP-1c rapidly increased. Insulin-induced processing of SREBP-1c required both mTORC1 and S6K. This indicated a bifurcation in the insulin signal downstream of mTORC1, with SREBP-1c processing requiring S6K and SREBP-1c transcription bypassing this requirement. These findings have implications for the role of insulin in the control of hepatic FA and TG synthesis through SREBP-1c. This is relevant in states of insulin resistance and Type 2 diabetes where abnormally high levels of insulin cause pathologic accumulation of FAs and TGs.Item The liver in congestive heart failure(1969-12-11) Schenker, StevenNote: Some information has been redacted in the publicly-available version due to privacy issues. For questions, contact archives@utsouthwestern.edu.Item The Liver-Derived Endocrine Hormone FGF21 Alters Metabolism and Diurnal Behavior via the Nervous System(2012-07-09) Bookout, Angie Lynn; Mangelsdorf, David J.Fuel acquisition is essential to survival. During privation, the body protects glucose concentrations acutely by glycogenolysis, and later by gluconeogenesis and ketogenesis. Additionally, animals alter daily behavioral patterns to seek food, but eventually reduce energetically costly activities (growth, reproduction, locomotion). Little is known about the mechanisms that orchestrate and coordinate these physiological and behavioral responses to starvation. The liver-derived endocrine hormone fibroblast growth factor 21 (FGF21) is induced in chronic fasting and acts as a global starvation signal. Previous studies focusing on FGF21 as an anti-diabetic drug indicate that FGF21 coordinates whole-body fat utilization and energy expenditure. However, its basic physiological role is underexplored. Acute injection of recombinant FGF21 quickly elicits a coordinated program between tissues resulting in reduced plasma insulin and gluconeogenic and thermogenic gene expression programs in liver and brown adipose, effects that require an intact animal. Mice with chronic FGF21 overexpression (FGF21tg) are smaller in size, females are infertile, and if fasted, they undergo torpor, an energy-conserving process. Taken together, these data suggest that FGF21 may exert some effects through the nervous system. To explore this idea, I utilized anatomically-guided laser capture microdissection followed by quantitative, real-time PCR to profile expression of the FGF receptor/co-receptor family in specific hypothalamic nuclei of mice. Surprisingly, the FGFR1-IIIc/βKlotho complex is found in the suprachiasmatic nucleus (SCN), area postrema (AP), nucleus tractus solitarii (NTS), and nodose ganglion (cell body of vagus nerve), implicating roles in circadian and metabolic regulation. Results of surgical, pharmacological, and genetic strategies indicate the vagus senses circulating FGF21, resulting in adrenergic efferent responses that reduce insulin secretion, while a different adrenergic site modulates liver and brown adipose gene expression. Analyses of the effects of FGF21 on the SCN, the body’s master clock, using running wheels show FGF21tg mice have dramatically altered circadian activity, likely as a consequence of inhibiting SCN output functions. Deletion of βKlotho specifically from the SCN rescues this behavior in addition to growth defects of FGF21tg mice. To date, this is the first description of a liver-derived endocrine hormone that affects such diverse aspects of the starvation response by acting on the nervous system.Item Metabolic Regulation by Fibroblast Growth Factor 21(2011-12-12) Dutchak, Paul Anthony; Kliewer, Steven A.Fibroblast growth factor 21 (FGF21) is a secreted hormone that can beneficially regulate glucose and lipid homeostasis. Through a reverse endocrinology approach, we uncovered that FGF21 expression is transcriptionally regulated by the peroxisome proliferator activated-receptor alpha (PPARa) in liver. PPARa is a member of the nuclear hormone receptor superfamily that is physiologically activated by increased fatty acid mobilization to liver during fasting, and regulates the genetic program whereby lipids are converted to ketone bodies through a process known as ketogenesis. Here, I show the effects of FGF21 as a fasting hormone that is expressed in liver and contributes to the regulation of adipose tissue and hepatic ketogenesis during the fasted state. Using in vitro and in vivo methods to investigate the effects of FGF21, a model whereby FGF21 stimulates lipolysis in adipose tissue was generated. Intriguingly, using our FGF21 transgenic mice, I observed the expression of many genes involved in lipogenesis was highly induced in adipose tissue in an FGF21-dependent manner. Moreover, many of these lipogenic genes were found to be down-regulated in adipose of the FGF21 knockout mouse. The inhibition of lipogenic genes in adipose tissue was associated with increased SUMOylation of PPARg protein in this tissue. Using a feeding-fasting paradigm, I found that FGF21 expression in the liver and adipose tissue was rhythmic, peaking in liver prior to feeding and peaking in the adipose after feeding. Furthermore, the induction of FGF21 by PPARg ligands suggested a unique function for this protein in adipose, independent from its role in the fasted state. To assess the contribution of FGF21 to the anti-diabetic properties of PPARg agonists (ie. thiazolidinediones), diet-induced obese wild type and Fgf21-/- mice were treated with the TZD rosiglitazone. Rosiglitazone produced a significant increase in adipose FGF21 expression, but decreased hepatic FGF21 mRNA and circulating FGF21 protein. These data suggest that FGF21 functions as an autocrine factor within adipose tissue. Moreover, the therapeutic effects of rosiglitazone as an insulin sensitizer were lost in the Fgf21-/- mouse, as assessed by glucose and insulin tolerance tests. Several other effects of rosiglitazone were lost in the Fgf21-/- mice, including increased adipose mass, edema, and PPARg target gene expression in the adipose. These data indicated that PPARg can control the expression of FGF21, which functions as a feed-forward mechanism to stimulate PPARg target genes and PPARg dependent physiology. Since PPARg can be modified by SUMO on two different sites on the protein, in vitro experiments were performed to show that PPARg is SUMOylated at Lysine-107, a previously identified negative regulator of its transcriptional activity. Importantly, I found that treatment of Fgf21-/- adipocytes with FGF21 reduced the amount of SUMOylated PPARg, thereby allowing it to be it an active state. Collectively, these data reveal that FGF21 has two independent roles in regulating metabolism in vivo: as a hepatic endocrine hormone that is induced during the fasting response through PPARa, and as an adipose autocrine/paracrine factor that is induced in a feed-forward loop to stimulate PPARg activity.Item Metabolic Regulation of Protein Phosphorylation and Acetylation(2018-07-12) Zhang, Menglu; Kohler, Jennifer J.; Tu, Benjamin; Nijhawan, Deepak; Yu, HongtaoCelluar metabolism can influence phosphorylation and acetylation modifications on proteins as part of an intricate network of cellular and organismal regulation. We have investigated one molecular mechanism through which protein phosphorylation and acetylation can be regulated based on metabolic status and how metabolic enzymes are regulated by nutrient availability. In the first part of this study, we report that a simple enzyme involved in acetate utilization, Acetyl-CoA synthetase 2 (ACSS2), promotes systemic fat storage and utilization through selective regulation of genes involved in lipid metabolism. We reveal that mice lacking ACSS2 exhibit a significant reduction in body weight and hepatic steatosis in a diet-induced obesity model. ACSS2 deficiency reduces dietary lipid absorption by the intestine, and perturbs repartitioning and utilization of triglycerides from adipose tissue to the liver due to lowered expression of lipid transporters and fatty acid oxidation genes. In this manner, ACSS2 promotes the systemic storage or metabolism of fat according to the fed or fasted state. Targeting ACSS2 may therefore offer therapeutic benefit for the treatment of fatty liver disease. We also report that ACSS2 may play a critical role in the development of pancreatic cancer. We have demonstrated that ACSS2 expression in a KRas-driven mouse model of pancreatic ductal adenocarcinoma (PDAC) showed that ACSS2 was absent in normal pancreatic tissue but expressed at very high levels in precancerous lesions of PDAC. The absence of ACSS2 in mouse pancreatic cancer models reduced the tumor burdens, and ACSS2 expression is correlated with tumor size. These data indicate that ACSS2 has a potential function in the development of PDAC. The experiments reported in the first two chapters of this thesis were performed in close collaboration with a former postdoc in the lab, Dr. Zhiguang Huang. In the second part of the study, we report that methylation of Protein Phosphatase 2A (PP2A) may play a critical role in regulating cell growth and autophagy. We have reconstituted the methylation activity of leucine carboxyl methyltransferase 1 (LCMT-1) in vitro and determined the kinetic parameters of LCMT-1-catalyzed methylation of PP2A. We reveal that LCMT-1 might be a "SAM sensor" as it is very sensitive to the SAM/SAH ratio. Methionine deprivation study in cell lines revealed that methionine depletion boosts PP2A demethylation. We further conducted a high-throughput screen to identify potent and specific small molecule inhibitors of LCMT-1.