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Spring 2017

Cancer as a Metabolic Disease

Javaria Haseeb Merrimack College, [email protected]

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Cancer as a Metabolic Disease Javaria Haseeb

Department of Biochemistry, Merrimack College, North Andover MA 01845, USA

Abstract Despite decades of intensive scientific and medical efforts to develop efficient and effective treatments for cancer, it remains one of the prime causes of death today. For example, in 2016, there will be an estimated 1,685,210 new cases of cancer and 595,690 deaths due to cancer in the United States alone (National Cancer Institute). Worldwide in 2012, there were an estimated 14 million new cases of cancer and 8.2 million deaths due to cancer. In order to come up with better methods of detection and more successful modes of treatment, it is crucial that scientists understand the depth of not only what causes cancer but also what sustains it. This literature review examines cancer as a metabolic disease. More specifically, it summarizes carbohydrate and compares and contrasts the roles of the transporter, the metabolic , pyruvate , , , , ATP synthase, and the tumor suppressor protein in normal versus cancer cells. The review focuses on the altered cellular function of these molecules and the significance of their dysfunctionality in the transformation of normal to cancer cells. Introduction (cell death); 4) enabling replicative immortality; 5) inducing Research has established that cancer angiogenesis and 6) activating invasion and is not a single disease but multiple diseases metastasis. Conceptual progress in the last and epigenetic change contributes to its decade has added two emerging hallmarks to formation (Hirschey et.al, 2015). Cancer is this list: evading immune destruction and characterized by unrestrained cellular reprogramming of energy metabolism proliferation, which may arise from nuclear (Weinberg & Hanahan, 2011) genetic mutations or from mitochondrial DNA damage which alters the metabolic This review focuses on several pathways – a network of chemical reactions differences in carbohydrate energy either building () or breaking metabolism between normal and cancer cells (catabolism) molecules in an organism – of and their significance in the cause and/or a cell. maintenance of the malignant phenotype. comprises the The hallmarks of cancer comprise different biochemical processes responsible six biological functions acquired during the for anabolism and catabolism of development of human tumors, which carbohydrates in an organism. include: 1) cell proliferative signals; 2) and the are two of the many evading growth suppressors (also known as biochemical processes used by cells for the tumor suppressors); 3) inhibition of 2 catabolism of glucose molecules, which are together to build various types of tissues ultimately converted into useable energy in needed for organismic survival, cancer cells the form of ATP. Normal cells produce up have a different agenda. All they want to do to 32 ATP molecules per glucose molecule is make more copies of themselves and the oxidized through glycolysis, citric acid Warburg effect helps them with that cycle, and oxidative . 2 ATP (Weinberg, 2014). molecules are produced from glycolysis in 1. Glucose transport the cytosol and the other 30 in the oxidative phosphorylation using NADH and FADH2 Normal and cancer cells alike need generated from glycolysis and the citric acid glucose for survival. Our cells acquire cycle. glucose from the blood stream via transporters located on the cell’s membrane. In the 1920s, Dr. Otto Warburg first The glucose transporters (GLUT) are a observed the glucose metabolism in normal group of 14 different uniporter membrane vs. cancer cells. He observed that the proteins that transport glucose through the amount of glucose uptake in cancer cells plasma membrane into the cell. GLUT-1, was significantly greater than that in normal which is encoded by the SLC2A1 in cells. He also observed that while normal humans, is of primary importance to this mammalian cells usually convert all of their review (Serra et.al, 2014). In normal cells, glucose into pyruvate via glycolysis, cancer the level of GLUT-1 on the membrane cells converted more than half of their fluctuates depending on how much glucose glucose into lactate (M.D. Hirschey et.al, is available in the blood stream, such that 2015) in the presence or absence of oxygen the GLUT-1 level is inversely proportional (Bensinger & Christofk, 2012). This effect is to glucose level. However, it has been known as the Warburg effect (Bensinger & observed that GLUT-1 is expressed in high Christofk, 2012). However, the mechanism levels in many tumors, regardless of the of how do this is yet to be level of glucose present in the blood stream determined. (Serra et.al, 2014). This allows for an One metabolic aberration in cancer increase in glucose uptake to serve the high cells includes a broken link between energy demands of cancer cells (i.e, rapid, glycolysis and the oxidative phosphorylation uncontrolled cell division). High levels of (OP). OP is oxygen dependent whereas GLUT-1 are also found in fetal tissues, adult glycolysis is oxygen independent. Cancer erythrocytes, and endothelial cells. cells take advantage of glycolysis being Interestingly, cancer cells are known to independent of oxygen and thus excel it, mimic fetal and undifferentiated cells in breaking the homeostatic link between many ways. glycolysis and OP. The rate of ATP production in cancer cells is 100 times faster than that of normal cells. Thus, even by taking an insufficient pathway for ATP production, cancer cells are able to proliferate at high rates. Where normal cells are strategically programmed to work 3

2. Glycolysis Once glucose enters the cytosol, it can undergo oxidation by glycolysis, a series of 10 catalyzed chemical reactions in which glucose is broken down to two pyruvate molecules (as shown in Fig.2). Energy is required in the first half of the process and then generated in the second half. For each glucose molecule, 2 molecules of pyruvate, 2 NADH, and 2 ATP molecules are generated (Pratt & Cornely, 2014).

Fig. 1: Difference in Metabolism between Normal vs. Cancer cells. The figure shows the glucose metabolic pathway in a) a normal cell and b) in cancer cell. In a) a normal cell, glucose is transported into the cell via GLUT-1 where catabolism takes place through glycolysis, where glucose is committed to catabolism by HK (not shown) and broken down in to pyruvate by PKM-1. 2 ATP molecules are generated in this process. Pyruvate is then transported in to the mitochondria where it is converted to acetyl- coA which goes through the citric acid cycle. The

NADH and FADH2 generated from glycolysis and citric acid cycle goes through oxidative phosphorylation (OP) through which the proton gradient (not shown) is established, O2 is reduced to form water, and 32 ATP molecules are synthesized. Increase levels of P53 (refer to 5. P53) inhibits glycolysis when necessary blocking glucose metabolism with no net ATP production. In b) cancer cell, glucose is transported in the cell via GLUT-1 where catabolism takes place through glycolysis, Fig.2: Glycolysis. A series of 10 enzyme catalyzed where glucose is committed to catabolism by HK2 chemical reactions in which glucose is broken down (not shown) and broken down in to pyruvate by to two pyruvate molecules. There is a preparatory PKM-2. Pyruvate is then converted to lactate by LDH phase where two ATP molecules are consumed and a and leaves the cell creating an acidic environment payoff phase where 4 ATP and 2 NADH molecules (not shown). The chain between glycolysis and OP is are generated, producing a total of 2 ATP, 2 NADH, broken (marked as red) and P53 is either silenced or and 2 Pyruvate molecules in the end (Giri, 2016). completely lost from the cell.

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Hexokinase many different studies. In one of the studies, tissues of 48 patients were Hexokinase (HK) catalyzes the first studied for mRNA expression of proteins step of glycolysis in the cytosol (in most including but not limited to HK2, GLUT-1, glycolytic pathways) converting glucose to PKM2, and VDAC-1 (Graziano et.al, 2016). glucose-6- (G6P). This is a rate- Significantly high levels of these proteins limiting step for glycolytic pathway, which were observed in primary tumor and commits glucose molecules to undergo metastasis with respect to the levels in complete oxidation (Bioinformatics, 2016). normal mucosa. Other experiments have The role of HK in committing glucose shown enhanced glycolytic rate when molecules to energy metabolism may play a solubilized HK2 was added in a liver tumor crucial role in supporting cancer, since these cytosol (Hirschey et.al, 2015). In mouse cells require an abundance of glucose energy models of kRas-driven cancer and Erb- for survival. HK is an enzyme located on the driven , HK2 was shown to be outer membrane of mitochondria, which is necessary to initiate and maintain tumor expressed in four isoforms, HK1, HK2, cells (Patra et.al, 2013). HK3, and HK4 all of which are found in humans (Patra, et.al 2013). HK1 is common Studies have shown a correlation in various types of cells in adults, HK4 is between low levels of HK2 and down- common in liver and pancreatic cells, little is regulation of the Warburg effect (a decrease known about HK3, and high levels of HK2 in the rate of glycolysis). In one study of have been observed in many types of cancer epithelial ovarian cancer (EOC), low levels including epithelial ovarian, breast, and of Glucose transporter 1 (GLUT1), HK2, colon cancer. and down-regulation of the Warburg effect and cell proliferation were observed when a HK2 has two catalytic domains, the known as FOXM1 gene N- and C-terminals (Ahn et.al, 2009). Both expression was suppressed (Wang et.al, domains have enzyme activity with N- 2016). FOXM1 bind directly to the promoter terminal having a higher activity than the C- region of GLUT1 and HK2 gene and terminal. Even though there are two binding promotes synthesis at the transcriptional sites for glucose on HK2, only one molecule level, so when FOXM1 was knocked down, binds at a time. Studies suggest that when the levels of GLUT1 and HK2 were one glucose molecule binds on one of the observed to decrease (Wang et.al, 2016). In two sites, it causes the enzyme to go through another study, the inhibition of HK2 was a conformational change, which then shown to improve the effects of anticancer prevents another glucose molecule from drugs (Peng, et.al, 2009). Thus high levels binding to the enzyme during catalysis of HK2 may very well be involved in the (Cardenas et.al, 1998). It is not completely alteration of cancer cell’s metabolism and known why HK2 has two glucose binding the transformation of normal cells into sites when it only catalyzes one molecule at cancer cells. The mechanism of how HK2 a time. may be involved in tumorigenesis, however, High levels of HK2 are of great is still unknown. significance to cancer cells as observed in

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Pyruvate Kinase tetrameric form favors the conversion of glucose to pyruvate. catalyzes the last step in glycolysis where it converts The alteration of normal enzymes phospenolpyruvate (PEP) and ADP to within the glycolytic complex hinders how pyruvate and ATP. This is another rate the intermediates are processed. The shift limiting step in the glycolytic path after from oxidative phosphorylation to glycolysis HK2 (Bensinger & Christofk, 2012). The for ATP production with feedback inhibition PKM gene encodes for isoenzymes PKM1 accelerates glycolysis, which leads to and PKM2. They are located in the cytosol enhanced lactate production. Glycolysis within the glycolytic enzyme “complex”. becomes the fastest way for energy The two isoforms only differ in 23 amino production as well as the best pathway to acids within a 56 band on the C- synthesize nutrients (that are the terminus. PKM1 is commonly found in intermediates) to help with cell proliferation. normal cells and assures the import of (Icard, 2011). pyruvate in to the mitochondria, whereas In one study that investigated the PKM2 is active in embryos and more effects of PKM2 expression in osteosarcoma common in tumor cells where it diverts (Liu, et.al, 2016); PKM2 expression was pyruvate to -A (LDH- observed to be elevated in cancerous tissues A), which reduces pyruvate to lactate. Our with respect to the adjacent normal tissues. focus is on PKM2 which is expressed in The same study also showed an overall organs with high energy demands such as decrease in patient survival rate in the muscle, brain, and all cells that have high presence of high PKM2 levels than low rate of nucleic acid synthesis, such as PKM2 levels. In another study, silencing of normal proliferating cells, embryonic cells, PKM2 was shown to increase docetaxel (a and tumor cells (Gupta & Bamezai, 2010). chemotherapy drug) sensitivity in cells PKM2 is present in two forms, leading to strong suppression of cell tetrameric and dimeric. The tetrameric form viability (Yuan, et.al, 2016). High levels of has high affinity to PEP and is highly active PKM2 can be detrimental for patients and at physiological PEP concentration, whereas inhibition may increase the survival rate. the dimeric form has low affinity to PEP and This suggests the great importance of PKM2 is almost inactive at physiological PEP levels present in cancer cells. concentration. The dimeric form of PKM2, Other experiments have also shown that termed as Tumor M2-PK, is observed in the growth of tumors depend on PKM2 many tumor cells (Mazurek, et.al, 2005). An expression, high levels of GLUT-1, and increase in glycolysis helps to meet energy LDH-A. Inhibition of either of these demands of high synthesis in cancer cells proteins have been observed to noticeably and PKM-2 plays an important role in slow down tumor growth. These generating synthetic intermediates. The low observations show that the altered glucose tetramer to high dimer ratio of PKM2 effects metabolism of cancer cells creates a the conversion of glucose. High levels of physiological system favorable for cancer dimeric form of PKM2 favors the growth and proliferation (Weinberg, 2014). conversion of glucose to lactate, whereas the 6

3. Citric Acid Cycle Citrate Synthase Citric acid cycle, also known as the Citrate synthase (CS) is an enzyme Tricarboxcylic acid (TCA) or krebs cycle, is in the first step in the citric acid cycle a pathway located in the inner matrix of (commonly assumed to be the rate limiting mitochondria. When pyruvate enters the step) in which it catalyzes the condensation mitochondria it is converted into acetyl-co- reaction of acetyl-coA and oxaloacetate to A, which then proceeds in the TCA cycle, citrate. It is located in the mitochondrial producing 2 CO2, 3 NADH, 2 FADH2, and 1 matrix, transcribed by the nuclear DNA, and ATP molecule. Note that amino acids, fatty serves as a central enzyme in the process of acids, and carbohydrates can enter the cycle glucose oxidation. It is comprised of 437 and go through the same process as well. amino acids, which are organized into two The cycle is a series of enzyme catalyzed subunits with 20 alpha helices each. Three chemical reactions (as shown in Fig. 3), quarters of the helices have tertiary structure where the intermediates can serve as while the remaining have irregular structure precursors of many reactions and products and a beta sheet composed of 13 amino acid of different biological molecules (Pratt and residues. The active site is roughly located Cornely, 2014). between the two subunits where each subunit has a binding site, one for acetyl- coA and the other for oxaloacetate (http://pdb101.rcsb.org/motm/93). High levels of ATP:ADP, acetyl-coA:CoA, and NADH:NAD ratio inhibit CS; these signal that the cell has enough energy and does not need to generate more energy until the ATP, acetyl-coA, and NADH levels decline. The catalysis of the condensation reaction of acetyl-coA and oxaloacetate to citrate by CS means that CS activity is proportional to citrate concentration. Increase in CS activity will yield high levels of citrate, which has shown anti-cancer properties that sensitize cancer cells to chemotherapy (Icard, et.al, 2012). In normal Fig.3: Citric Acid Cycle. The cycle is a series of cells, the Pasteur Effect – the process of enzyme catalyzed chemical reactions that take place fermentation inhibited in the presence of in the mitochondria to catabolize pyruvate. The oxygen (opposite of the Warburg effect) – is intermediates can serve as precursors of many reactions and products of different biological regulated by ATP and citrate. Under molecules (not shown). 2 CO2, 1 ATP, 3 NADH, and hypoxic conditions, the cell undergoes 2 FADH2 molecules are generated oxidative stress that results in low level of (http://www.chemistrylearning.com/krebs-cycle/). ATP and citrate in the mitochondria. This in turn increases the activity of phosphofructokinase-1 (PFK1) – the enzyme 7 catalyst in the third step of glycolysis – It is interesting to note how CS activity which in turn increases the rate of glycolysis regulated in normal cells under hypoxic to generate sufficient energy to keep the cell conditions resembles the activity in cancer alive (Icard, et.al, 2012). cells. The majority of tumor cells are found to be hypoxic and exhibit the same kind of Alterations in CS activity have been behavior, which is catabolizing glucose in to observed in many types of cancers (Chen higher yields of lactate than pyruvate. et.al, 2014). In a study of ovarian carcinoma, the cell line of benign tumor was compared Succinate Dehydrogenase with normal human ovarian surface Succinate Dehydrogenase (SD) is epithelium, and ovarian tumor cell line was one of the many tumor suppressor protein compared with ovarian cancer cell line (encoded by a tumor suppressor gene, which (Chen et.al, 2014). High levels of CS were regulates cell cycle by slowing down cell observed in benign versus normal and division, repairing DNA, and inducing tumors versus cancer cell line. These apoptosis when necessary) located on the observations show the proportionality inner membrane of the mitochondria (King between cell transformation and CS levels et al, 2006). It is involved in both, the citric and suggest that CS expression is correlated acid cycle and the oxidative phosphorylation with tumor progression. It has also been (OP) also known as the electron transport observed that the knock down of CS in chain (ETC), which will be discussed later ovarian cancer cell lines slowed down the in this review. SD catalyzes step 7 of the process of cell proliferation and inhibited citric acid cycle and is also known as invasion and migration of cancer cells in complex II in OP where it couples the vitro. The knock down also helped sensitize oxidation of succinate to fumarate in the cancer cells to chemotherapeutic drugs like citric acid cycle with the reduction of cisplatin, which subsequently showed ubiquinone to ubiquinol in OP. Mutations in enhanced apoptotic results (Chen et.al, SD are found to promote cancer 2014). In another study, however, the effects transformation through the production of of knocked down CS were analyzed in carcinogens (Ciriolo & Cardaci, 2012). The human cervical cancer cell lines in which mechanism and detailed effects of SD in the silencing of CS showed an increase in cancer metabolism is still under cell proliferation, invasion, and migration in investigation. vitro (Lin, et.al, 2012). The metabolic shift of normal cells to cervical tumor cells was 4. Oxidative Phosphorylation observed and results showed that low levels of CS corresponded to the switch from Oxidative Phosphorylation is the main normal aerobic respiration to glycolysis source of ATP production in normal cells. It (Lin, et.al, 2012). The contradiction is the final stage of catabolism of metabolic regarding the effects of CS activity in fuels, a process whereby free energy from different types of cancer is one of the many the transfer of electrons is conserved in a examples demonstrating that cancer is not a transmembrane gradient of protons that is single disease but multiple diseases with then used to power ATP synthesis (Pratt & distinct alteration in metabolism that thus Cornely, 2014). The OP pathway is require different treatments. comprised of 5 complexes as shown in 8

Fig.4, two of which are of particular reduction. Four cytochrome c molecules significance in cancer cell metabolism. transfer 4 electrons, one at a time, to CuA, which passes the electrons to cytochrome, and then on to the binuclear center where oxygen is reduced and 2 water molecules are formed. During this process, COX attracts 8 protons, 4 of which are used in the formation of water molecules and the other 4 are pumped out in the intermembrane space enhancing the protein gradient (Pratt & Cornely, 2014). COX is present in three

configurations: fully oxidized (also known Fig.4: Oxidative Phosphorylation. There are five as pulsed), partially reduced, and fully complexes involved in oxidative phosphorylation located in the inner mitochondrial membrane space. reduced. Different types of inhibitors have Complexes I-IV are in sequence on the right and affinity towards different conformational complex V is shown on the left. Complexes I and II states. Cyanide, for example, is a take the electrons from NADH and FADH2 generated competitive inhibitor and has a high affinity from the citric acid cycle and pass it on to complex to the partially reduced state of COX. It III and IV through ubiquinone and cytochrome c. During this process, protons are pumped from the binds slowly but efficiently to binuclear site matrix into the intermembrane space creating a when the complex is in that state. On the proton gradient. Complex V then utilizes the proton other hand, high levels of ATP can gradient to synthesize ATP from ADP and Pi allosterically inhibit cytochrome c oxidase (https://www.khanacademy.org/science/biology/cellu (Arnold & Kadenbach, 1997). lar-respiration-and-fermentation/oxidative- phosphorylation/a/oxidative-phosphorylation-etc). Since COX is a central part of the Cytochrome c oxidase (Complex IV) oxidative metabolism, an alteration in this enzyme may have proportional effects on Cytochrome c oxidase (COX), also alterations in metabolism seen in cancer known as complex IV, is a large cells (Krieg et.al, 2004). In cancer cells, the transmembrane protein located on the inner homeostasis between the glycolytic pathway membrane of mitochondria. It is the central and oxidative phosphorylation is disrupted. part of the oxidative phosphorylation The high level of glycolysis is used to metabolic pathway where oxygen is acquire immense level of ATP production reduced. In mammals, it is composed of 13 and the cell is not dependent on oxidative subunits, 10 of which have a nuclear origin phosphorylation (OP) to fulfill its energy and the other three have a needs, unlike normal cells. Studies have origin (Krieg, et.al, 2004). Each complex shown an increase in the level of nuclear has multiple metal prosthetic groups that are encoded versus mitochondrial encoded COX integral to the electron transfer process. subunits in tumor derived cell lines of There are two hemes present on the prostate and urothelial epithelium (Krieg complex, one of which forms a binuclear et.al, 2004). High activity of COX was also center (a3-CuB) that carries out oxygen observed in these cell lines and was 9 correlated with an increase in glycolysis. ATP Synthase (Complex V) High activity of COX is thought to assist ATP Synthase (ATPs), also known tumor by depleting the citric acid cycle as complex V, is a part of the OP metabolic intermediates, which will lower the citrate pathway. It is involved in the catalysis of concentration so it cannot inhibit PFK, ATP synthesis by forming therefore creating an environment that phosphoanhydride bond between ADP and favors high rate of glycolysis (Krieg et.al, P , as well as in the decomposition of ATP 2004). Further research needs to be done to i to ADP and P and thus serves as the rate understand the correlation between the COX i, limiting step in OS (Whitford, 2005). ATPs proteomics and its link to metabolic is located on the inner membrane of alteration. mitochondria and has two domains, Fo and Another study has shown the F1, both of which are known to have correlation between altered COX function different biological and chemical properties. and the Warburg effect, a hallmark of Fo is the hydrophobic domain embedded in metabolic reprogramming. In this study, two the inner mitochondrial membrane where it of the 10 nuclear encoded COX subunits, functions as a proton translocator using the IVi1 and Vb were knocked down to disrupt proton gradient created by the electron the COX normal function (Srinivasan et.al, transport chain. F1 is the hydrophilic domain 2016). These cytochrome c oxidase knock located in the and down (COXKD) cells showed a loss of consists of 5 different subunits. Fo and F1 COX activity, which was linked to the domains of ATPs work together by using the metabolic switch to glycolysis. The knock energy generated from the proton gradient to down of either subunit showed an increase form or break the phosphoanhydride bonds in HK and phosphofructokinase (PFK) in for the synthesis or decomposition of ATP cells. This led to an increase in glucose (Whitford, 2005). consumption and GLUT4 mRNA levels by ATPs plays an important role in greater than 2 folds compared to normal human carcinoma, and its malfunction is cells. However, the level of GLUT-1 was known to be involved in mediation and not affected, which is quite interesting as progression of different types of human GLUT-1 is found in high levels in many pathologies (Cenizo et.al, 2010). Studies cancer types. All these observations show a have shown the importance of ATPs and link between the disrupted COX and how the malfunctioning could contribute in metabolic reprogramming in cancer cells. carcinogenesis. In normal cells, a protein The COXKD cells were observed to have known as inhibitory factor 1 (IF1) is known invasive phenotype, a decrease in to prevent ATPs from shifting to ATP transmembrane potential, and upregulation hydrolysis under hypoxic conditions. The of that regulate cell growth, motility, expression of IF1 varies among different invasiveness, and other hall marks of cancer tissues, as it is highly expressed in , cells. The induction of tumorigenesis may moderately in liver, and almost negligible in potentially be caused by defected COX, breast, colon, and lung. In human which may very well be used as a biomarker carcinoma, studies have shown that IF1 is (Srinivasan et.al, 2016). found in abundance even in the cells that 10 once had negligible levels. This resulted in cancer cells is its ability to evade tumor the malfunctioning of ATPs and promoted suppression (Weinberg & Hanahan, 2011). the switch to high rates of aerobic P53 gene is located on glycolysis. As expected, the silencing of IF1 number 7 and it is a phosphoprotein with was shown to have reverse effects as it 393 amino acids that build its 4 domains decreased the rate of glycolysis (Arago et.al, (Bioinformatics). Each domain has a distinct 2012). What causes the upregulation of IF1 function to activate transcription factors, is still unknown. One may wonder what recognize specific DNA sequences, causes IF1 to not interfere with ATPs tetramerize the protein, or recognize DNA activity when it is highly expressed in damage. normal tissues such as the heart. It is hypothesized that perhaps the IF1 protein P53 also regulates mouse double minute goes through post-translational 2 (Mdm2), also known as E3 ubiquitin- modifications which do not allow it to protein ligase, encoded by the Mdm2 gene, interfere with normal ATPs activity and and uses it to regulate its own levels. P53 perhaps that modification is subdued in proteins that are not phosphorylated binds to carcinoma (Arago et.al, 2012). Mdm2, which then degrades it through ubiquitination (Bioinformatics). P53 helps In another study, elevated expression of maintain the cell’s genome stability by IF1 was shown to be involved in mediating preventing mutations through regulating the switch to Warburg phenotypes by DNA damage repair proteins (Jones regulating tumor metabolism through ATPs &Thompson, 2009). Low levels of P53 are activity. Monoclonal antibodies were used present in normal cells which are activated against IF1 to show high expression of IF1 and increased if the cell has been insulted in human carcinomas compared to normal with DNA damage, , and oxidative cells and high levels were shown to increase stress, shunting the cell to go under the rate of aerobic glycolysis with a decrease apoptosis (Jones & Thompson, 2009). in OP. The silencing of IF1 had the opposite effects as a decrease in the rate of aerobic With the tumor suppressor functions, glycolysis and an increase in the rate of OP P53 also has an important role in terms of was observed. These observations were metabolism. It has the ability to reduce the correlated to the Warburg effect in this study glycolytic flux, thus oppose the Warburg (Cenizo et. al, 2010). effect (Hirschey, et.al, 2015). Approximately 50% of all tumors have 5. P53 mutations in p53 (Bioinformatics). P53, also known as TP53, is a well- Energy homeostasis pathways are known tumor suppressor encoded by a regulated by stress-induced transcriptional tumor suppressor gene. A tumor suppressor programs, which in turn are regulated by gene is an anti-oncogene that regulates cell p53 (Jones & Thompson, 2009). When a cell cycle by slowing down cell division, goes under hypoxia induced oxidative stress, repairing DNA, and inducing apoptosis the level of (cyclic adenosine when necessary. One of the hallmarks of monophosphate) cAMP:ATP increases which activates 5’ adenosine 11 monophosphate-activated protein kinase behave abnormally (Jones & Thompson, (AMPK), which then not only activates p53 2009). The silencing or complete loss of P53 but also inhibits lipid and protein synthesis, allows the switch in the metabolism from crucial for cell growth. The increase in p53 OP to glycolysis without blocking the cell then triggers a protein called TIGAR (TP53- cycle and inducing apoptosis. inducible glycolysis and apoptosis regulator), which inhibits the glycolytic pathway. Studies have also shown that the activity of P53 favors the formation of ATP from OP, which is common in normal cells (Jones & Thompson, 2009). It does this by regulating fructose-2-6-biphosphate (in the glycolytic pathway), TIGAR, and the assembly of COX by cytochrome c oxidase assembly protein (SCO2). It is interesting to note that a lack of SCO2 assists the cell to shift from OS to glycolysis to generate ATP (Jones & Thompson, 2009). Another study has shown an interesting relationship between PKM2 and p53. An increase in PKM2 resulted in a decrease in p53 protein level with a short half-life (Wu, Table. 1: Compares the significance of GLUT-1, et.al, 2016). However, when PKM2 was HK, PKM, SD, CS, COX, ATPs, and P53 in cancer verses normal cells. knocked down in the cell, the p53 level increased with a greater half-life. It was also Conclusion observed that PKM2 is capable of directly All that is known about cancer and binding to p53 and MDM2 complex and the advances in treatment seen today have promote p53 ubiquitination (dimeric form of been a direct result of a terrifying historical PKM2 has a greater significance) (Wu, et.al, background. It was an era of trial and error 2016). in the scientific community where thousands Defects or a loss in P53 results in of cancer patients had no choice but to go abnormal cell proliferation, which is one of through treatments that were nothing more the hall marks of cancer. This provides a than an educated guess from doctors and great growth opportunity for normal cells to scientists. The patients ended up having transform in to cancer cells. When normal severe side effects, making the approach to cells are insulted with multiple DNA death as horrific as it could be. The trials damage, hypoxic oxidative stress, and other ranged from directly injecting toxins in cell insults, the absence of p53 would mean patients with no knowledge of dosage and the absence of repair mechanism and side effects, to performing radical apoptosis induction, allowing the cell to mastectomy with no knowledge of what 12 cancer actually is and how it metastasizes. 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