Cancer

Ras

-EGF binds to its receptor which could be many things. When EGF binds to receptor it causes the receptor to dimerize. This dimrization causes it to phosphorylate itself. The phosphates on the receptor (Receptor Tyrosine Kinase) provide a docking site for other proteins.The adapter protein GRB2 binds to a specific phosphotyrosine on the activated RTK and to Sos which in turn interacts with inactive Ras-GDP. The guanine nucleotide exchange factor activity of Sos promotes the formation of the active Ras-GTP

To kill cancer cells we need to do one of the following

-Induce necrosis by depleting the cell's ATP - inhibit HK2. -*Induce apoptosis - cause the Apoptosis Inducing Factor (AIF) to be released from the mitochondria by covalently altering HK2 so it cannot bind to VDAC and thereby prevent the release of AIF. -Decrease the pH within the cell - inhibit the release of the H ions generated by the cancer cell by inhibiting the production and release of lactate. -*Increase the reactive oxygen species within the cancer cell -turn on oxidative phosphorylation (OX-PHOS) by allowing more pyruvate to enter the mitochondria

HK-2/VDAC/ATP synthasome complex

-The up-regulated hexokinase 2 (HK-2) is bound to the VDAC on the outter membrane of the mitochondria which is connected to the ATP synthasome complex. VDAC=voltage gated anion channel. -The ATP from the ATP synthasome complex is used to phosphorylate glucose to make glucose 6-phosphate. -*The binding of HK-2 to VDAC prevents Apoptosis Inducing Factor (AIF) from being released from the mitochondria thereby preventing apoptosis. - *Once AIF is released, it goes to the nucleus and induces chromatin condensation and induces caspase expression.

Loss of Function Mutations in Tumor Suppressor Genes are Oncogenic

-Tumor suppressor genes usually inhibit cell proliferation. Loss of these genes contributes to the development of many cancers. Considered the brakes. -p16 and 21 etc etc are cyclin kinase inhibitoors that regulate or inhibit progression through a specific stage of the cell cycle, and they primarily work at G1 check point. -growth factor genes -checkpoint control proteins -proteins that promoted apoptosis -enzymes that participate in DNA repair.

Pentose Phosphate Pathway

-When DNA damage occurs we need the products off the pentose phosphate pathway such as nucleotides, NADPH and DNA and RNA. So p53 inhibits glycolysis at 2 points and we get a increase in F6P and G6P and this pushes the formation of the products of the PPP. -p53 get's stablilized by a kinase that recognizes DNA damage. This turns on TIGAR which is TP53 induced glycolysis and apoptosis regulator and will also inhibit PGM. TIGAR inhibits so therfroe reduces the production of fructose 2,6 BPG which can't make PFK1 which is needed to make F 1,6 BPG for glycolysis. This is how it's inhibiting glycolysis.

Growth factor receptors

-When you have a growth factor receptor you need to have something that will dimirize it to get the effect.But there are a couple of things that can cause dimierization without binding to the receptor. -A mutation that alters a single amino acid valine to glutamine in the transmembrane region of Her2 receptors causes dimerization of 2 receptor proteins in the absence of the normal EGF-related ligand, making the protein active as a kinase. - Also a deletion that causes loss of the extracellular ligand binding domain in the EGF receptor leads to activation of the protein kinase.

Ras proto-oncogene

Can become oncogene by a substitution of any amino acid fro glycine at position 12 of the amino acid sequence. This mutation reduces the Ras GTPase activity. This constantly active Ras oncoprotein are expressed by many types of human tumors including bladder, colon, mammary, skin, and lung carcinomas, neuroblastomas, and leukemias.

7 types of proteins that participate in controlling cell growth

Cancer can result from expression of mutant forms of these proteins : 1.growth factors 2.growth factor receptors 3.signal transduction proteins 4.transcription factors 5.pro or anti apoptotic proteins 6.cell cycle control proteins 7.DNA repair proteins.

Oxidative and non-oxidative pathways in tumors

In cancer many times p53 is broken so we can't inhibit F16 bIP from being made becasue you don't inhibit Fructose 2-6 bIP and as a result of this the Fructose 16bIP builds up and inhibits G6PD and we lose ability to make the reducing power. But we have the slow pyruvate kinase pk-m2 that is very slow and the TKTL1 is turned on. And the non-oxidative pathway is opened up so although we don't get the products of the oxidative pathway we still get the products of the non-oxidative pathway. For the cancer cell to work it will need the R5P and the reducing power.

Deactivating the initiating oncogenic lesion

Inactivation of an oncogene leads to rapid and complete regression of most cancers, but some tumors return and usually have additional oncogenic lesions.

c-Src

Is another oncogene that encodes a constitutively active cytosolic protein tyrosine kinase src. Due to Tyrosine 527 which is often missing or altered in Src oncoproteins that have constitutive kinase activity. -Another oncogene that encodes a constitutively active cytosolic proteintyrosine kinase is src. • v-src from Rous sarcoma retrovirus was the first oncogene to be discovered. • The kinase activity of c-src is normally inactivated by phosphorylation of the tyrosine residue at position 527, which is six residues from the C-terminus. • Hydrolysis of phosphotyrosine 527 by a phosphatase activates c-Src. • Tyrosine 527 is often missing or altered in Src oncoproteins that have constitutive kinase activity. - They do not require activation by a phosphatase. • In Rous sarcoma virus, the src gene has a deletion that eliminates the C- terminal 18 amino acids of c-Src making the v-Src kinase constitutively active.

Burkitt's lymphoma

Is due to translocation of the c-myc gene near the heavy chain anti-body genes.The myc gene is now regulated by the antibody enhancer and is continually expressed, causing the B cells to become cancerous.

HER2 gene amplification

Mutations leading to over-expression of a normal receptor protein can be oncogenic. Many human breast cancers over express a normal Her2 receptor. As a result the cells are stimulated to proliferate in the presence of very low concentrations of EGF, concentrations too low to stimulate proliferation of normal cells.

TGF Beta

TGF Beta induces the expression of p15 leading to arrest in G1, and synthesis of extracellular matrix proteins such as collagens and plasminogen activator inhibitor 1. Loss of TGF beta or Smad 4 a characteristics of human tumors, abolishes TGF Beta signaling. This promotes cell proliferation and development of malignancy.

Follicular lymphoma

The translocation fuses the transcriptional enhancer element of a gene, on chromosome 14, that makes one protein subunit of an antibody to the transcription unit of a gene, on chromosome 18, that encodes Bc12 a negative regulator of apoptosis. In this way the Bc12 protein is produced in antibody producing cells, blocking any self-destruction signals from inducing apoptosis in those cells. So the immune cells never die.

Summary

Tumor-suppressor genes encode proteins that slow or inhibit progression through a specific stage of the cell cycle, checkpoint-control proteins that arrest the cell cycle if DNA is damaged or chromosomes are abnormal, receptors for secreted hormones that function to inhibit cell proliferation, proteins that promote apoptosis, and DNA repair enzymes. • Inherited mutations causing retinoblastoma led to the identification of RB, the first tumor-suppressor gene to be recognized. • Inheritance of a single mutant allele of many tumorsuppressor genes (e.g., RB, APC, and BRCA1) increases to almost 100 percent the probability that a specific kind of tumor will develop. • Loss of heterozygosity of tumor-suppressor genes occurs by mitotic recombination or chromosome missegregation.

Cancer

a disease where the cell cycle can no longer be controlled. Usually there is some genetic alteration that starts the hyerproliferation of cells.The cell responds by changing its biochemistry so that the cellular conditions favor the uncontrolled growth that is the hall mark of cancer.

Cooperativity between glucose and glutamine metabolism in growing tumors

• Glutamine and glucose are the major nutrients consumed by tumors - Precursors for nucleic acids, proteins and lipids • The metabolism of glutamine (blue arrows) and glucose (red arrows) are complementary, converging onthe production of citrate (purple arrows). • Glutamine metabolism produces oxaloacetate (OAA) and NADPH coming off of malate enzyme. • Glutamine metabolism also supplements the pyruvate pool. • As a result, lactate, alanine and NH4+ are secreted by the tumor.

Potent anticancer effect of 3 bromopyruvate

-3-BP covalently modifies HK- 2 so that it cannot bind to VDAC. +AIF is then released from the outer mitochondrial membrane and enters the nucleus to induce apoptosis. -3-BP's mode of action extends beyond apoptotic effects appears to also involve necrotic events. +The inability of HK-2 to bind to VDAC sets up a condition where ATP gets depleted and necrosis also occurs.

Gain-of-Function Mutations convert Proto-Oncogenes into Oncogenes

-Conversion of a proto-oncogene into an oncogene generally involves a gain-of-function. -3 mechanisms: +point mutation that results in a proto-oncogene doing what it normally does, maybe with slight variation, but it is doing it all the time. +localized gene reduplication (gene amplification) that includes proto-oncogene leading to over expression of the encoded protein. Usually a protooncogene is only needed so much for so long. +Chromosomal trans-location is when you get one chromosome interacting with another chromosome. The chromosome translocated brings a growth-regulatory gene that is under the control of a different promoter and this causes inappropriate expression of the gene.

How we should attack cancer

-DNA alterations are essential for cancer to form. -But, cancer also develops an alteration in the metabolism of oxygen. -Although both changes must interact for the development of cancer, the altered oxygen metabolism of tumor cells is not subject to the high genetic complexity and variability (over 11,000 genetic alterations have been identified) of tumors and may therefore be a more reliable target for cancer therapy.

Growth factor genes

-Is a growth factor oncogene which encodes for a type of platelet derived growth factor (PDGF) that can autostimulate proliferation of cells that normally express the PDGF receptor. -Binding of Epo dimerizes the receptor and induces formation of erythrocytes from erthroid progenitor cells. Porgenitor cells infected by the spleen focus-forming virus (SFFV) co-express viral gp55 and Epo receptor. Binding of gp55 activates the Epo receptor in the absence of Epo, leading to inappropriate proliferation of progenitors and eventually erythroluekemia. Specific binding of dimeric gp55 to the Epo receptor is mediated by the membrane-spanning domains. -Polycythemia vera is a similar condition -In HPV a DNA virus that causes genital warts. A papilloma protein designated E5, which contains only 44 amino acids, spans the plasma membrane and forms a dimer or trimer. Each E5 polypeptide can form a stable complex with one endogenous receptor to PDGF this aggregates 2 or more PDGF receptors within the plane of the plasma membrane. This mimics homone-mediated receptor dimerization and activation, causing sustained receptor activation and leading to cell transformation.

Glutamine metabolism effect on cancer cells

-Its important to get rid of NADH and get back to its oxidized state NAD+. Citrate leaves the TCA cycle and breaks from a 6 carbon molecule to a 4 carbon molecule (oxaloacetate) and a 2 carbon molecule Ac-Coa. Ac-Coa goes on to make fatty acid palmitate and it takes 14 NADPH to make it . Oxaloacetate with the enzyme MDH and NADH forms malate. This helps get rid of NADH. Malate with the ME enzyme produces NADPH and pyruvate. Then pyruvatewith the enzyme LDH-A usees NADH to produce Lactate. -Whenevermalate or citrate leave the TCA they both get rid of NADH and malate is what's used to generate the NADPH that's lacking in the oxidative pentose phosphate pathway. -In cancer cells we are losing citrate and malate in the TCA cycle, but Glutamine is coming in to keep the cycle going. Cancer cells are glutamin addictied.

Mutations

-Mutations in proteins classes 1-4 give rise to oncogenes. -Proteins in class 6 mainly act as tumor suppressors. -Class 7 mutations greatly increase the probability of mutations in the other classes. -Viruses can also induce cancer

Ras

1. GEF facilitates dissociation of GDP from Ras. 2.GTP then binds spontaneously and GEF dissociates yielding the active Ras-GTP form. 3 and 4. Hydrolysis of the bound GTP to regenerate the inactive Ras. GDP form is accelerated a hundred fold by GTPase-activation protein(GAP). -*Cycling of Ras thus requires two proteins, GEF and GAP. -Understand that the active form Ras has GTPase activity within itself. Ras breaks down GTP to GDP and inactivates itself, but it has a protein helping it called GAP which activates the RAS to destroy GTP to GDP and inactivting itself.

Step in signal Transduction beyond Ras

Activated Ras binds to Raf a serine/threonine kinase. Raf binds to and phosphorylates MEK a dual specificity protein kinase that phosphorylates both tyrosine and serine residues. MEK phosphorylates and activates MAP kinase such as ERK another serine/threonine kinase. ERK phosphorylates many different proteins, including nuclear transcription factors, that mediate a cellular responce.

Summary

Dominant gain-of-function mutations in proto-oncogenes and recessive loss-of-function mutations in tumor-suppressor genes are oncogenic. • Among the proteins encoded by proto-oncogenes are positive-acting growth factors and their receptors, signal-transduction proteins, transcription factors, and cell-cycle control proteins. • An activating mutation of one of the two alleles of a proto-oncogene converts it to an oncogene, which can induce transformation in cultured cells or cancer in animals. • Activation of a proto-oncogene into an oncogene can occur by point mutation, gene amplification, and gene translocation. • The first recognized oncogene, v-src, was identified in Rous sarcoma virus, a cancer-causing retrovirus. - Retroviral oncogenes arose by transduction of cellular proto-oncogenes into the viral genome and subsequent mutation. • The first human oncogene to be identified encodes a constitutively active form of Ras, a signal-transduction protein. - This oncogene was isolated from a human bladder carcinoma. • Slow-acting retroviruses can cause cancer by integrating near a protooncogene in such a way that gene transcription is activated continuously and inappropriately.

HER 2 testing

If a cell is HER2 positive there is a antibody called Herceptin which can be used to treat the cancer cells.

Transcription factors as oncognes

One of the earliest effects of growth factors is to induce transcription of c-fos and c-myc. C-Fos and C-Myc stimulate transcription of genes encoding proteins that promote progression through the G1 phase of the cell cycle and the G1 to S transition. In tumors, the oncogenic forms of these or other transcription factors are frequently expressed at high unregulated levels.

Over expression of cyclins or the loss of tumor suppressor genes

Over expression of the proto-oncogene encoding cyclin D1 or loss of the tumor-suppressor genes encoding p16 and Rb can cause inappropriate unregulated passage through the restriction point in late G1 a key element in cell cycle control. P 16 should block Cyclin D's expression but if missing this will lead to over expression and passage through the restriction point in late G1.