Robbins Ch7 Neoplasia.txt

• 1. Transformation
• 2. Growth
• 3. Local invasion
• 4. Distant metastasis

• 1. Doubling time of the tumor cells.
• 2. Fraction of cells in cell cycle = growth fraction
• 3. Rate of loss of cells
• NOTE: Cell cycle is not shorter in neoplastic cells, just more cells in it.

• Cells able to self-renew, seen in breast cancer and AML.
• Leukemic forms express the gene BMI1 --- represses cell cycle inhibitors: p161NK4a and p14ARF

• 1. Direct seeding of body cavity or surface - carcinomas
• 2. Lymphatics - carcinomas
• 3. Hematogenous - sarcomas, liver and lungs most frequently involved

• 1. growth promoting protooncogenes - dominant since only one needs to be damaged for transformation to occur
• 2. tumor suppressor genes - recessive since both alleles need to be hit
• 3. genes regulating apoptosis - can be dominant or recessive
• 4. DNA repair genes - usually recessive - both alleles need to be damaged

• 1. Self-sufficiency in growth signals (ie. don't need external signals for growth)
• 2. Insensitive to inhib signals
• 3. Evasion of apoptosis (often d/t inactivation of p53)
• 4. Defective DNA repair
• 5. limitless replicative potential (maintenance of telomere length and telomerase fxn)
• 6. Sustained angiogenesis - VEGF
• 7. Ability to invade and met

G0 -- G1 -- S -- G2 --M

• Cyclins and cyclin dependent kinases
• CDKs phosporylate proteins, exrpressed constitutively in an inactive form
• Cyclins synthesized during the cycle and rapidly decline after completion.

• 1. Signal (ex. GFs, integrins)
• 2. MYC, RAS, other genes
• 3. Production of cyclin D -- activation of CDK4
• 4. RB phosphorylation within RB/E2F/DP1 complex (when RB is hypophos it forms a tight inactive complex with trans factor E2F and DP1)
• - RB/E2F/DP1 binds to promoter regions of E2F responsive genes needed for progression of cell cycle - RB recruits histone deacetylase - compacts chromatin
• - when RB is phos, it dissasociates and allows transscription of genes needed for progression ex. cyclin E, DNA polymerases, thymidine kinase etc.
• 5. Cyclin E then activates CDK2 and cell moves from G1 to S (G1-S transition is restriction point) and DNA synthesis occurs
• 6. E2F then mediates transcription of cyclin A which activates CDK2 - complex regulates prophase
• 7. Cyclin B-CDK1 then causes breakdown of nuclear envelope and intiates mitosis
• 8. Exit from mitosis - need inactivation of cyclin B/CDK1
• 9. Return to G1 or to G0
• So - D/4 then E/2 then A/2 then B/1

• Cip.Kip: p21 (induced by p53), p27 (responds to TGFb)
• INK4/ARF: p16INK4a (binds D/4) promotes inh effects of RB, p14ARF (incr. p53 levels by inh MDM2)

• 1. G1/S - p53 - needed for p21 which inhibits cell cycle - slows or stops cycle if DNA damage
• 2. G2/M - mediated through p53 dependent and independent mechanisms
• NOTE: ATM senses DNA damage

• 1. GF binding
• 2. Activation of GF receptor - signal transduction
• 3. Signal transport via mesenger proteins to nucleus
• 4. Activation of nuclear regulatory factors -- DNA transcription
• 5. Entry to cell cycle --- cell division

Genes that support autonomous cell growth in cancer cells. Protooncogenes are their normal counterparts.

• 1. GFs
• 2. GF receptors
• 3. Signal transduction proteins
• 4. Nuclear regulatory proteins
• 5. Cell cycle regulators

• SIS - encodes b chain of PDGF, often same tumors express more of receptor as well - autocrine. But not enough for mal transformation but incr prol contributes to it.
• Id'ed in OSA and astrocytomas
• Also TGFa, HGF and Fibroblast GFs

• GFR are transmembrane proteins with GF binding site extracellular domain and intracellular domain with tyrosine kinase activity, when GF binds the receptor dimerizes and tyrosine phosporylation of signaling proteins.
• Oncogenic versions often have constituent dimerization and become activated without binding of GF
• Gives constant mitogenic signals to cell
• ex. ERB B1 (EGF receptor gene) overexpressed in SCC, ERB B2 in breast cancer, GIST overexpress c-KIT

• RAS - most common oncogene - mutations reduce GTPase activity of RAS proteins
• carcinomas - KRAS, bladder HRAS, hematopoeitic NRAS
• NORMAL RAS: Inactive RAS binds GDP, when activated exchanges for GTP, active RAS recruits RAF-1 and activates MAP kinase pathway which activates nuclear transcription and mitogenesis.
• Usually activation is transient d/t GTPases which return RAS to inactive state with GDP
• Cycling of RAS depends on: 1. nucleotide exchange - GDP to GTP by nucleotide releasing prot recruited by GFR and 2. GTP hydrolysis with GTPases
• GAPs - increase GTPase activity 1000 fold thereby preventing uncontrolled RAS activity
• Mutations in RAS prevent proper GAP activity and stops the GAP break
• RAS can also activate MAP kinase path and AP-1 transcription factor regulating cell cycle

c-ABL translocated from chromosome 9 to 22 where it fuses with BCR gene - fusion protein has potent tyrosine kinase activity - see in CML and some ALL

• Proteins that enter nucleus, bind DNA and activate or inhibit transcription of adjacent genes
• Ex of oncogenes: MYC, MYB, JUN, FOS

• MYC goes to nucleus, binds to DNA and activates transcription of: ornithine decarboxylase, cyclin D2,
• Also have range of other activities: histone acetylation, decr. cell adhesion, incr. cell mobility, incr. prot sythesis, decr proteinase activity
• Needs survival signals to not apoptose after prol though
• MYC mutations seen in burkitt lymphoma, and carcinomas - breast, colon, lung

• Cyclin D/ CDK4 common
• Cyclin D1 in mantle cell lymphoma
• CDK4 in glioblastoma and sarcomas
• Cyclin E in breast

• 1. RB
• 2. p53
• 3. APC/b-catenin
• 4. Others: INK4a/ARF locus, TGFb, NF1, FN2, VHL, PTEN, WT-1, Cadheins, KLF6, PTCH

1. RB, 2. p16INK4a 3. cyclin D, 4. CDK4

• p53 is DNA binding protein in nucleus, need mutation in both alleles to have effect
• p53 results in transcription of p21 which arrests G1 before S
• fxn is cell cycle arrest and initiation of apoptosis after DNA damage
• DNA dep kinases and ATM phosphorylate p53 which unfolds then becomes transcription factor and incr. p21
• Has short T1/2 and degraded with ubiquitin mediated proteolysis
• Also induces transcription of GADD45 - encodes protein for DNA repair
• If repair successful then p53 activates MDM2 which degrades p53
• If no repair then p53 activates BAX --- apoptosis (BAX binds to bcl-2 anti-apoptotic -- so initiates apoptosis)
• Summary: p53 phosphorylated by genes that sense DNA damage -- incr p21 (cell cycle arrest), GADD45 (DNA repair) --
• if no repair then BAX, if repair then MDM2 and p53 degraded

P63 and p73

• b-catenin forms complex with TCF in nucleus (transcription factor) and results in upreg of cMyc, cyclin D1 - leading to prol
• APC binds b-catenin in cytoplasm and degrades it
• mutated b-catenin can occur which cannot be inh by APC
• ALSO b-catenin binds to E-cadherin - NB for adhesiveness, so mutations in b-catenin may result in less cell adhessiveness

• Melanomas, carcinomas
• lose capacity to block cyclin D/CDK4 so do not prev RB phosphorylation

• Colon and gastric cancers
• SMAD4 encodes component of TGFb -- mutated in pancreatic cancer, 2 mutated in colon cancer

NF1 regulates signal transduction via RAS - with mutations RAS trapped in active state

• Also called merlin, protein product is protein 4.1 in RBC cytoskeleton - bindins to actin and CD44
• mutations result in no cell-to-cell junctions and insensitivity to growth arrest signals

Ubiquitin ligase, mutations prevent ubiquitination and degradation of HIF1 --- increased angiogenic GF (VEGF and PDGF)

Causes cell cycle arrest and apoptosis - by incr p27, loss of PTEN - prol

Wilms tumor

• cell to cell adherence, reduced in many cancers - local invasion and mets
• Can be 2ry decr d/t mutation in b-catenin (b-catenins bind to them and stabalize expression)

• Transcription protein - target genes: TGFb and TGFR
• Incr transcription of p21 independent of p53 so inh cell cycle
• mutation stop cell cycle block by p21

Receptor for hedghod proteins - regulates genes such as TGFb and PDGF-R

• 1. BCL-2 overexpression (anti-ap)
• 2. p53 mutations --- decr BAX and/or BIM transcription (both pro-ap)
• 3. MYC - prol. over expression along with incr. BCL-2 cooperate to give cancer
• 4. Incr survival signals - ex. PI3/AKT pathway - often incr. AKT in cancer d/t mutation

• 1. Mismatch repair - spell checker - without it errors slowly accumulate - microsatellite instability is hallmark
• 2. Nucleotide excision repair - uv light causes xlinking of pyrimidine residues - prevents DNA replication, NERs repair these
• 3. Recombination repair - ex. ATM mutation (ATM senses DNA double strand breaks and stops cell cycle via p53), BRCA-1 and 2
• in breast cancer - both involved in DNA repair and in G1/S checkpoint

• 1. DNA break sensed by ATM and CHEK 2 and phosphorylate BRCA1
• 2. BRCA1 migrates to the break site and complexes with Fanconi anemia protein D2
• 3. BRCA2 then migrates to the break site with RAD51 and together they repair the break

• 1. Supplies nutrients and oxygen
• 2. New endothelium produces GF (IGF, PDGF) which are also needed for tumor met

Increased VEGF

• 1. VEGF and 2. bFGF
• What effect does p53 have on tumor angiogenesis?
• Increase transcription of anti-angiogenic thrombospondin 1 and downreg of VEGF and HIF-1 (incr. VEGF prod)
• So no p53 --- no thrombospondin --- increased VEGF

Thrombospondin, p53, angiostatin, endostatin, tumstatin - latter three produced by cleavage of plasminogen and collagens

• 1. Detachment - loss of e-cad, sometimes d/t mutant b-catenin
• 2. Attachment to matrix proteins - receptor mediated attachement to laminin and fibronectin, normal epis have high affinity
• receptors on basal surface, carcinomal cells have more and all over -- more receptors, more invasive tumor
• tumor cells also express integrins which are receptors for ECM components
• 3. Degredation of ECM - proteolytic enzymes or induce host cells to make them, serine proteases, cystein proteases, MMP
• MMP2 and 9 cleave type IV collagen in BM and mobilizes VEGF in BM - have angiogenic effects d/t proteins uncovered but
• also antiangiogenic d/t collagen breakdown results in endostatin and tumstatin
• 4. Migration of tumor cells

CD44 expressed by T cells to home to high end venules, some tumor cells can express and home

• 1. Cleavage of collagen IV releases VEGF and degredation of laminin-5 results in a fragment that incr. motility
• 2. ECM stores growth factors in inactive forms: PDGF, TGFb, bFGF - paracrine effect

• 1. Translocations (common) - can results in overexp of protooncogenes d/t removal from reg elements
• ex. MYC gene translocated in burkitt lymphoma, removed from its regulatory sequences and get MYC overexpression
• similarly cyclin D overexpression in mantle cell lymphoma, activation of BCL2 (anti-ap) gene in fol lymphomas
• or can get recombination with new adjacent genes - growth promoting chimeric protein
• ex. phil chrom - fusion of BCR-ABL - hybrid protein which has tyrosine kinase - results in decr. apop, decr GF requirement,
• decr. cell adhesion, activates many pathways - PI3 kinase, RAS, STATs
• 2. Inversions

• Activation of protooncogenes - may see several hundred copies, microscopically can see dms or HSRs
• ex. amplification of N-MYC in neuroblastoma, ERB-B2 in breast cancer, cyclin D in others

• Can see hypermethylation of pormoter sequences without damage to DNA sequence, can inactivate tumor suppressor genes
• Methylation takes place on CpG islands in DNA
• Have seen this in P14ARF, p16INK4a, BRCA-1, VHL and MLH1 (mismatch repair gene)

• Gatekeepers - ongogenes and tumor sup genes that control tumor growth
• Caretakers - do not directly control tumor growth but affect genomic stability

• 1. RB - INK4, Cyclin D, assoc kinases, RB
• 2. p53 - p14ARF, MDM2, p53

• 1. iniation - permanent DNA damage - but carcinogen induced DNA damage does not always lead to initiation since can be repaired
• 2. Promoter - can induce tumor in initiated cells but not normal cells, do not affect DNA directly, reversible
• application of a promoter lead to prol and clonal exp of initiated (mutated) cells

• 1. Direct acting:
• Alkylating agents
• Acylating agents
• 2. Pro-carcinogens - need metabolic activation
• Polycyclic heterocyclic aromatic hydrocarbons
• Aromatic amines, amides, azo dyes
• Natural plant and microbial prodcuts - aflatoxin, griseofulvin, cycasin, etc.
• Others: nitrsamine, amides, vinyl chloride, chrominum, fungiides etc.

cigarette smoke, alcohol, viruses, hormones, bile salts

p53 and RAS - get formation of pyrimidine dimers in DNA - usually repaired by NER pathway:

• 1. recognition of DNA lesion
• 2. Incision of strand on both sides
• 3. Removal of damaged region
• 4. synthesis of patch
• 5. ligation

Adenovirues, fibroma in rabbits, BPV

FeLV, FIV, EIA, Papillomavirus

• viral DNA inserts, results in E6/E7 overexpression - overcome cell cycle inh.
• often see p53 mutations

Dz strains have CagA (pathogenicity island) - CagA injected into host cells, also VacA (other virulence gene)

• 1. Products of mutated oncogenes/tumor suppressor genes
• 2. Products of other mutated genes
• 3. Overexpressed proteins - may normally be in such small amts that there is no self-tolerance
• 4. virus products
• 5. oncofetal proteins - expressed on fetal tissues and by cancer cells but not adult cells
• ex. AFP, CEA
• 6. Altered cell surface glycolipids/proteins
• 7. CD antigens

CD8 Tcells, NK, Macs - NK and T cells produce IFNg which activate macs - ROS killing etc.

• 1. Selection of antigen-negative variants (survival of the fittest)
• 2. Loss or reduced MHC1 escape CTL
• 3. Lack of costim
• 4. Immunosuppression - ex. secrete TGFb
• 5. Antigen masking - ex. by glycocalyx molecules
• 6. Apoptosis of CTL - express FasL

• TNF, IL1, IFNg
• Also proteolyis-inducing factor - increases catabolism of fat and mm (not cytokine)