Abira Khan

  In young animal, cell multiplication exceeds cell death, so animal increase in size  In adults, the process of cell birth and death are balanced  Sometimes, control system for cell multiplication break down, and a cell begins to grow and divide in an unregulated fashion  Descendant cells inherit this property proliferate without responding to regulation, forming a mass called a tumor  Cancer: Uncontrolled clonal proliferation of cells that can arise from virtually any cell type in the body  A cancer is mainly caused by mutation in somatic cells, number of mutation may vary from 3-20 Oncology

  Oncogenes: Encode proteins that associated with oncgenesis  Transformation: Stable and heritable change in the genes for growth control  Contact inhibition: Stop growing upon contact with neighboring cell  Immortalization: Cell divides for indefinite period  Benign tumor: Composed of cells with abnormal growth but non-invasive  Malignant tumor: Composed of cells with abnormal growth that invade to other organs  Metastasis: Invasion of cancer to other part of the body  Neoplasm: Formation of new cells  Hyper plastic: Abnormal cell growth Terminologies

  Cancers must occur in dividing cells so that mutations are passed on many progeny cells  Mutations in non-dividing cells do not induce cancer  Stem cell present in different organs and tissues divide continuously and generate more stem cells  Oncogenic mutations in theses stem cells DNA can accumulate and eventually transforming them into cancer cells  Cells that have acquired mutations have abnormal proliferation capacity but can not undergo normal process of differentiation Origin of Cancer

  Benign  Named according to the tissue from which they arise, and includes the suffix - “oma”  Lipoma  Glioma  Leiomyoma  Chondroma Classification

  Malignant tumors  Named according to the tissue type from which they arise  Epithelial tissue – carcinoma  Ductal or glandular epithelium – adenocarcinoma Example: mammary adenocarcinoma  Connective tissue – sarcoma Example: rhabdomyosarcoma  Lymphatic – lymphomas  Blood forming cells – leukemia Classification

 Carcinoma in situ (CIS)  Preinvasive epithelial malignant tumors of glandular or  Squamous cell origin that have not broken through the basement membrane or invaded the surround stroma  Cervix, skin, oral cavity, esophagus and bronchus (epithelium)  Stomach, endometrium, breast, large bowel (glandular) Classification

 Benign vs Malignant

  Most cancer cells have increased number of mutations then the normal cells  As the cancer progresses, the number of mutation increases  Inactivation of mutator genes decreases the repair damage of DNA, and increase the rate of mutation  The occurrence of different mutations creates an opportunity to select population of cells with particular properties Cancer- Mutations

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  The occurrence of different mutations creates an opportunity to select the cells with particular properties  In the case of cancer, a mutation that increases the growth potential of a cell will give it a selective advantage  A cell that divides more often, will generate more descendants  At each stage during the progression of a cancer, the cell population is selected for those cells that can grow more aggressively Cancers Arise from Clones

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  Three types of changes that occur when a cell becomes tumorigenic 1.Immortalization 2.Transformation 3.Metastasis  When cells are placed in culture 1.Grow for division 2.Enter a senescent stage 3.Go through the crisis 4.Survival of crisis are capable of dividing indefinitely Tumor Cells

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 Most prominent changes are  Alteration in growth pattern- increased growth rate, anchorage independence  Alteration in cell surface  Alteration in intracellular component and biochemical processes- increase protease and protease activators  Tumorigenecity- forms tumor upon injection in animals Properties of Transformed Cells

  Cells cultured from tumors show changes in some or all of these properties. They are said to be transformed  A transformed cell grows in a much less restricted manner  It has reduced serum-dependence,  It does not need to attach to a solid surface  The cells pile up into a focus instead of growing as a surface monolayer.  The cells may form tumors when injected into appropriate test animals Altered Morphology

  Telomerases systematically replaces telomeric segment that are usually trimmed away during cell cycle  Over activation of gene that codes for the enzyme telomerases during the development of most cancer cell  Maintaining integrity of telomeres enables the cell to replicate endlessly that allows- 1.Tumor cell to grow large 2.Give time to accumulate for mutation in cells 3.Increase the ability of cells proliferation and ultimately metastasize Telomerase in Cancer

  Neoplasia is an abnormality of cell growth and multiplication characterized by  At cellular level 1.Excessive cellular proliferation 2.Uncoordinated growth 3.Tissue infiltration  At molecular level 1.Disorder of growth regulatory genes 2.Develops in a multistep fashion Carcinogenesis

  Initiation of a tumor requires several steps  Multiple genetic changes must occur to convert a normal cell into malignant one.  Number of mutations may be 3-8 or more.  There are intermediate stages  Long time is usually needed  Cancer cells accumulate mutations at a high rate  At each stage cell population with aggressive growth rate is selected Multi-Step Carcinogenesis

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 Development of colon cancer Normal colon cell Increased cell growth Early stage adenoma Intermediate stage adenoma Late stage adenoma CarcinomaMetastasis APC gene loss DNA methyl group loss ras gene mutation DCC gene loss P 53 gene loss PRL3 over expression 

 Hallmarks of Cancer

  Genetic factors: mutations, translocation, amplifications  Environmental factors: UV, chemicals, viral infections  Conversion of proto-oncogenes (potential for cell transformation) to oncogenes (cell transformation)  Alteration in tumor suppressor genes Etiology of Cancer

  Normal cells contains highly related but not identical copies of retroviral transforming genes  Oncogenes are genes whose products have the ability to transform eukaryotic cells so that they grow in a manner analogous to tumor cells. Oncogenes carried by retroviruses have names of the form v-onc.  Proto-oncogenes are the normal counterparts in the eukaryotic genome to the (v-onc) oncogenes carried by some retroviruses. They are given names of the form c-onc  Components of regulatory pathways to control cell proliferation, division and differentiation.  Incorrect expression of any component might result in uncontrolled growth of cells Oncogenes & Proto-oncogenes

  Mechanisms of activation of proto-oncogene and converting to a cancer gene vary 1.Over expression 2.Constituently active 3.Express in wrong time 4.Express in wrong place  Interaction of proto-oncogene product with other proteins altered Oncogenic Activation

  Transduction by retroviruses  Insertional mutagenesis  Translocation  Gene amplification  Mutation Oncogenic Activation

  Cellular proto oncogenes may be transduced into retroviral genome  Transduced gene replicated and transmitted like viral genes  Upon infection the transduced gene expressed abundantly under viral signal Transduction

  Insertion of a retroviral promoter adjacent to cellular oncogene  First occurred in avian leucosis virus Insertion Host gene 5’LTR 3’LTR C - myc

  Translocation of a proto-oncogene near a strong regulatory sequence  Translocation may affect the expression of proto- oncogene or gene product  Translocation in Burkitt’s lymphoma Translocation H pro. H-gene C-myc pro. C-myc gene H pro. C-myc gene C-myc pro. H-gene Chromosome 14 8

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  Increase in copy number of a potential gene resulting in excess production of the encoded protein  Amplification of oncogene HER-2/neu occur in breast cancer  Gene amplification mostly occur at the late stage of tumor progression Gene Amplification

  Point mutation or deletion might change the function of a protein 1.Substrate specificity 2.cell binding property 3.Binding specificity of a transcription factors etc.  Altered protein may lead to oncogenic activation, eg. C-ras gene Mutation

  Cancers can result from expression of mutant form of proteins like: 1.Growth factors (I) 2.Growth factor receptors (II) 3.Signal transduction Proteins (III) 4.Transcription factors (IV) 5.Pro- or anti- apoptotic proteins (V) 6.Cell cycle control proteins (VI) 7.DNA repair proteins (VII) Mutation of Cellular Growth Control Proteins

. Growth factor (I) Growth factor receptor (II) Intracellular transducer (III) Intracellular effector region (PTK) Second messenger (phosphorylated proteins) Transcription factors (IV) DNA Transcription DNA repair Proteins (VII) RNA Cell cycle control proteins (VI) mRNA Proteins Anti-apoptosis proteins (V) Intracellular receptors (II) Virus encoded activators of growth –factor receptors (Ia)

  The c-ras proto-oncogene can transformed to oncogene by single base mutation.  The mutations at position 12 or 61, found in several human tumors.  The ras genes appear to be finely balanced at the edge of oncogenesis. Almost any mutation at either position 12 or 61 can convert a c-ras proto-oncogene into an active oncogene.  All three c-ras genes have glycine at position 12. If it is replaced in vitro by any other of the 19 amino acids except proline, the mutated c-ras gene can transform cultured cells.  Position 61 is occupied by glutamine in wild-type c-ras genes. Its change to another amino acid usually creates a gene with transforming potential  When the expression of a normal c-ras gene is increased, either by placing it under control of a more active promoter or by introducing multiple copies into transfected cells, recipient cells are transformed.  Some mutant c-ras genes that have changes in the protein sequence also have mutation that increases the level of expression by 10x.  Also, some tumor lines have amplified ras genes. A 20-fold increase in the level of a nontransforming Ras protein is sufficient to allow the transformation of some cells.  Oncogenesis depends on over-activity of Ras protein, and is caused either by increasing the amount of protein or (more efficiently) by mutations that increase the activity of the protein. Ras Proto-oncogenes

  Ras is active when bound to GTP and inactive when bound to GDP. It has an intrinsic GTPase activity. The activation of Ras is controlled by GTP.  GAP stimulate the ability of Ras to hydrolyze GTP, thus converting active Ras into inactive Ras.  GEF stimulate the replacement of GDP by GTP, thus reactivating the protein Ras Activities-Control

  Constitutive activation of Ras caused by mutations allow the GDP-bound form of Ras to be active or prevent hydrolysis of GTP.  Many mutations that confer transforming activity inhibit the GTPase activity.  GAP cannot increase the GTPase activity of Ras proteins that have been activated by oncogenic mutations.  Inability to hydrolyze GTP causes Ras to remain in a permanently activated form  Its continued action upon its target protein is responsible for its oncogenic activity. Ras Oncogene

  Cytoplasmic tyrosine kinase  The protein product of v-src was the first retroviral transforming protein to be identified  Posses protein tyrosine kinases activity  Myristoylation of the N-terminus enables Src to associate with the plasma membrane. Src Proto-oncogene 416 SH3 SH Mutation alter morphology of transformed cells; some also confers transforming activity Sequence homology to other kinase catalytic domains; tyr-416 is autophosphorylated Phosphorylated at Tyr- 527 in c-src inhibits kinase Myris tylati on Membranebinding domain ModulatoryCatalyticSuppressor SH2= Phosphotyrosine SH3= proline rich sequence SH4 =Myristoylation

  Src autophosphorylates and its activity is controlled by the state of phosphorylation at two Tyr residues.  Oncogenic variants are derived from c-Src by mutations that cause decreased phosphorylation at Tyr-527 and increased phosphorylation at Tyr-416.  v-Src lacks Tyr-527 and is constitutively active.  Src was the protein in which the SH2 and SH3 motifs were originally identified  Two sites in Src control its kinase activity.  It is inactivated by phosphorylation at tyrosine residue 527, which is part of the C-terminal sequence of 19 amino acids that is missing from v-Src.  The c-Src protein is phosphorylated in vivo at this position by the kinase Csk, which maintains it in an inactive state.  Src is activated by phosphorylation at Tyr-416, which is located in the activation loop of the kinase domain. Src Activity- Control

  The c-Src and v-Src proteins are similar, share N-terminal modification, cellular location, protein tyrosine kinase activity  c-Src is expressed at high level in seveal types of cells, a large number of signaling proteins are target for src kinase.  c-Src is activated by growth actor receptors, e.g PDGF receptor.  SH2 and SH3 are modulatory domains;  Mutation in SH2 reduce transforming activity, ie. Activate c-Src  Mutation in SH3 domain increase transforming activity, ie. has a negative regulatory role  In the inactive state, Tyr-527 is phosphorylated and enables c- terminal regions of Src to bind to SH2 domain  Auto phosphorylation creates binding site for SH2 that displaces Tyr-527  This leads to its dephosphorylation and conformational change and allow Tyr-416 to be phosphorylated Src Oncogene

  A tumor suppressor is identified by a loss-of- function mutation that contributes to cancer formation. They usually function to prevent cell division or to cause death of abnormal cells. The two most important are p53 and RB  Negative regulator of cell growth, also known as anti- oncogene  Transformation of normal cells also accompanied by loss of function of one or more tumor suppressor genes Tumor Suppressor Genes

 Development of Cancer

  Retinoblastoma is a human childhood disease, involving a tumor of the retina  It occurs both as a heritable trait and sporadically (by somatic mutation)  Retinoblastoma arises when both copies of the RB gene are inactivated  In the inherited form of the disease, one parental chromosome carries a change in this position  A somatic event in retinal cells that causes loss of the other copy of the RB gene causes a tumor  In the sporadic form of the disease, the parental chromosomes are normal, and both RB alleles are lost by somatic events RB is a Recessive Trait

  RB is a nuclear phosphoprotein that influences the cell cycle  Non-phosphorylated RB prevents cell proliferation  In the normal cell cycle, phosphorylation of RB by cdk- cyclin kinases is necessary to proceed into S phase  In resting (G0/G1) cells, RB is not phosphorylated. RB is phosphorylated during the cell cycle by cyclin/cdk complexes, most particularly at the end of Gl; it is dephosphorylated during mitosis  The nonphosphorylated form of RB specifically binds several proteins, and these interactions therefore occur only during part of the cell cycle (prior to S phase). Phosphorylation releases these proteins  Certain tumor antigens suppress the inhibitory action by sequestering the nonphosphorylated form of RB.  Several tumor suppressors act by blocking the cdk-kinase complexes that phosphorylate RB. Rb

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  Guardian of the genome  p53 is a tumor suppressor that is lost or inactivated in >50% of all human cancers  p53 is a tetramer  p53 is a DNA-binding protein. The ability to bind to its specific target sequences is conferred by the central domain  p53 activates transcription at promoters  The N-terminal region provides the transactivator domain.  p53 may repress other genes; the mechanism is unknown.  p53 also has the ability to bind to damaged DNA  Induce apoptosis  Wild-type p53 is activated by damage to DNA.  The response may be to block cell cycle progression or to cause apoptosis depending on the circumstances. p53

  p53 activates various pathways through its role as a transcription factor  The major pathway is inhibition of the cell cycle at Gl is mediated via activation of p21, which is a CKI (cell cycle inhibitor)  CKI is involved with preventing cells from proceeding through Gl  Activation of GADD45 is involved with maintaining genome stability. p53

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  The major pathway controlling p53 is mediated through the protein Mdm2, which inactivates p53  Amplification of the Mdm2 gene causes an increase in expression of the protein, which reduces p53 function.  Mdm2 is itself inactivated by the protein pl9ARF, so deletions of the pl9ARF gene lead to increase in Mdm2 and thus to decrease in p53. p53 Control

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  The mutations in p53 itself lie in the DNA-binding region  In some cases, the mutations lie in the C-terminal region that is responsible for forming tetramers, so that active proteins are not produced.  The survival curves for wild type mice (p53+/+), heterozygotes who have lost one allele (p53+/~), and homozygotes who have lost both alleles (p53~/_).  The frequency of tumors is increased from 45% to 80% by loss of the first allele, causing the mice to die sooner; and loss of both alleles shortens the life span dramatically due to the occurrence of tumors in virtually 100% of the mice.  Same phenotype is produced either by the deletion of both alleles or by a missense point mutation in one allele.  Both situations are found in human cancers. p53 Mutation

  A chemical that increases the frequency with which cells are converted to a cancerous condition  Divided into those that "initiate" and those that "promote“ tumor formation  Carcinogens may cause epigenetic changes or (more often) may act, directly or indirectly, to change the genotype of the cell  They are electrophiles all of which will react with the amines or double-bonded O's.  These compounds have the ability to bind covalently to the component of most biological macromolecules Carcinogen

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  Direct: N-methyl-N-nitroso Urea are able to react directly with DNA, causing mutations  Indirect: A substance that is not itself a carcinogen can sometimes be turned into one by the chemistries carried out in the body of a metazoan  BP into a carcinogen in the liver Chemical Carcinogens

  Non-specific: NK cells, gd T cells macrophages  Antigen-specific: Antibody (ADCC, opsinization); T cells (cytokines, Fas-L, perforin/granzyme) Tumor Killing

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  Genes VIII- Lewin, Chapter 30 References