Basic Pathological Mechanisms April 20-24 Flashcards
Describe G1 phase.
Organelles are duplicated; cell growth (duplication of the cytoplasm)
Describe G2 phase.
pause to check the integrity of the reproduced genome
What is the key grow and divide pathway?
growth factors (TGFalpha); MEK/MAPK
What is the key don’t die pathway?
survival factors (IGF1); AKT/NFkappaB
What is the key don’t grow and don’t divide pathway?
anti-growth factors (TGFbeta); Smad/cyclin-dependent kinase inhibitor
What is the key die pathway?
3: cytochrome C, FasL, and p53
REVIEW: What are adult labile cells?
intestinal epithelial, skin epithelial, breast ducts, uterine epithelial cells, fibroblasts, leukocytes, and myelocytes
What are the two best known gatekeepers (tumor suppressors)?
p53 and pRb; control cellular responses to damage (eliminates or arrests cells with mutations)
What is the role of cyclin/CDK complexes?
phosphorylate and inactivate Rb, allowing the cell cycle to proceed
Rb dissociates from E2F
Name CDK inhibitors.
p16INK4A, p21, p27, and p57
How is the cell cycle of cancer cells different from normal cells?
can divide without appropriate external signals; do not exhibit contact inhibition; can divide by ignoring checkpoints
Describe steps of cancer development?
Transformation (gain of oncogenes and loss of tumor suppressors; rate limiting step); tumor expansion and evolution
Describe the Knudson hypothesis.
Alfred Knudson proposed a “two hit” hypothesis suggesting the development of retinoblastoma required two mutations in the same gene in the same cell to occur.
He predicted that one of these mutations was inherited in the germline of patients that develop Retinoblastoma at an early age
What are clinical features of Retinoblastoma?
thickening of optic nerve and displacement of retina
What are common alterations in Rb pathway during cancer development?
methylation or mutation of Rb; sequestration of pRb by viral proteins; overexpression of cyclins; mutation in CKIs; (loss of f(x)); mutation in cyclin-dependent kinases (gain of f(x))
T/F: high total cyclin E levels suggest poor prognosis?
T; high in the aggressive basal-like breast cancer subtype
Describe discovery of p53.
co-precipitated with SV40 virus large T antigen (originally classified as oncogenic; mutated)
Describe p53?
stop transmission of damage or mutated DNA to daughter cells
DNA damage induces accumulation of the p53 protein
induces cell cycle arrest as a transcription factor for p21
upregulates its own expression following DNA damage
Describe the p53-Mdm2 autoregulatory
feedback loop.
The mdm-2 gene is shown here to contain a p53 DNA-binding site and a genetically responsive element such that expression of the mdm-2 gene can be regulated by the level of wild-type p53 protein. The mdm-2 protein, in turn, can complex with p53 and decrease its ability to act as a positive transcription factor at the mdm-2 gene-responsive element. In this way, the mdm-2 gene is autoregulated. The p53 protein regulates the mdm-2 gene at the level of transcription, and the mdm-2 protein regulates the p53 protein at the level of its activity. This creates a feedback loop that regulates both the activity of the p53 protein and the expression of the mdm-2 gene.
How can E2F activate p53?
p14ARF inhibits mdm2, thus promoting p53, which promotes p21 activation, which then binds and inactivates certain cyclin-CDK complexes, which would otherwise promote transcription of genes that would carry the cell through the G1/S checkpoint of the cell cycle
How can extracellular signals impact p53-p21-Rb axis?
PI3K/AKT pathway upregulates mdm2 (inhibiting p53 and p21 and upregulates CDK-cyclin complexes and releases E2F for modulation of S-phase)
What are the two most frequently mutated genes in human tumors?
p53 (point) and INK4a (frameshift)
Where are most mutations in p53 found on the locus?
DNA binding domain
Describe Li Fraumeni syndrome.
linked to germline mutation in p53; Characterized by multiple primary neoplasms in children and young adults
T/F: positive IHC staining for p53 in a tumor suggests that the p53 gene has been mutated?
T
T/F: MDM2 is downregulated in cancer?
F
What proteins are upregulated in tumors?
PI3K/AKT, MDM2, E2F, cyclins
How can the p53 pathway be altered with therapeutics?
block p53-MDM2 binding; inhibition of SIRT deacteylase (stabilizes p53); transformation of mutant p53 to wild-type
What signaling molecules are required for normal cell division?
integrins (cell-cell contact)
Describe the schematic of transformation discussed in lecture
gain of function of Ras mutation (activated tumor suppressor cascades resulting in cell cycle arrest or cell death); deterioration of tumor suppressor mechanisms
What is the only virus with a known association with tumorigenesis?
HPV (blocks tumor suppressors)
T/F: mutated p53 can activate p21 and MDM2?
F
Describe Tyzzer’s experiment.
Tyzzer (1915) studied the susceptibility of Japanese
waltzing mice and of other mice to inoculation with a
transplantable tumor which had originated spontaneously in Japanese waltzing mice. He
found that Japanese waltzing mice were without exception susceptible. All common varieties of
fancy mice were found to be completely immune.
F1 hybrids between the Japanese waltzing mouse and
the house mouse were as susceptible as pure Japanese
waltzing mice. Among the F2 individuals, however, susceptibility was very rare.
Susceptibility depends on a number of independent (dominant)
genetic factors. Unless all of these are present
simultaneously, the individual is not susceptible.
T/F: Grafts from F1 hybrids are accepted by animals of either parental strain?
F
T/F: Grafts from isogenic parental strain animals to their F1 hybrids are always accepted?
T
What are features of tumor rejection?
antigen specific and show memory
if a mouse is immunized with irradiated tumor cells and injected with viable cells of the same tumor, the tumor will be eliminated
Describe immune surveillance theory.
major function of cell-mediated immunity was thought to be rejection of neoplastic cells (altered-self)
REVIEW: What cells express MHC class 1? class 2?
express on the surface of almost all nucleated cell types (not including CNS)
expressed mainly on the surface of some hematopoietic cells (professional APCs)
T/F: Rejection of tumor requires the presence of T cells?
T
How can tumor immunity be induced?
Exogenous: use non-immunological agents, such as bacteria or immunological reagents, such as antibodies; cytokines; chemokines or immune cells in attempts to control or eliminate tumor (like a vaccine; Coley’s toxin)
Endogenous: use agents to activate, enhance or suppress host immune system in attempts to control or eliminate tumor
How does the cell-mediated immunity kill a tumor cell?
T cell mediated cytotoxicity; mainly CD8+ cytotoxic T cell, which release enzymes to kill the tumor cells by inducing apoptosis
T cell mediated release of anti-tumor growth factors, such as TNF
Natural Killer cell mediated killing
Phagocytic cell mediated destruction
What are mechanisms by which tumors avoid immune recognition?
no peptide: MHC ligand, no adhesion molecules, or no co-stimulatory molecules; anergy (tumor treated as self-antigen); loss of antigens; inhibition of T cells (TGF-beta); may secrete factors that create a physical barrier to the immune system.
What can interfere with antigen processing machineries?
oncogenic viruses
T/F: Tumor cells that lack MHC are more susceptible to NK cells?
T
How do tumors evade NK cell response?
Loss of expression of activating ligands for NK receptors, such as NKG2D, NKp46, or DNAM-1
persistent stimulation of NK cells in the absence of inflammatory cytokines, which may induce a state of NK cell anergy
Loss of tumor suppressors that induce secretion of chemokines that recruit NK cells
T/F: Viral transformation protein may act as a tumor associated antigen?
T
What are examples of tumor associated antigens?
a point mutation in a self protein allows binding of a new peptide to MHC molecules
a point mutation in a self peptide creates a new epitope for recognition by T cells
What are potential tumor rejection antigens?
reactivation of germ-cell genes in a tumor not normally expressed in the differentiated cell results in presentation of antigens novel to the adult immune system.
Describe naming of chimeric and humanized monoclonal antibodies.
mouse (o), chimeric (xi), humanized (zu), human (u)
What effects stability of monoclonal antibodies?
aggregates, deamidation products, glycosylation variants, oxidized amino acid side chains, and amino acids additions to either amino- or carboxy-terminal
What antigen is found on B-cell lymphomas?
CD20
What was the target of the immunotoxin mentioned in lecture?
Anti-CD22
What T cell growth factor has been used in an attempt to control tumor growth? What are adverse effects?
IL-2; vascular leakage (acute inflammation)
What is downstream of CD28? What is the receptor called? What else can the receptor bind?
PI3K/AKT; Ras/MEK/MAPK; Lck/Itk
B7; CTLA-4
What is the antibody against CTLA-4 called? PDL-1?
nivolumab; ipilimumab
T/F: Pre-conditioning enhances the efficacy of tumor infiltrating lymphocytes?
T; IL-2 driven and lacks specificity
T/F: enumeration of cytotoxic and memory T cells in the tumor bed are markers to predict patient outcomes?
T
Describe dendritic cell vaccination.
A patient’s own white blood cells, primarily dendritic cells, are isolated
The DCs are then incubated with a fusion protein (PA2024) consisting of two parts: the antigen prostatic acid phosphatase (PAP) and an immune signaling factor granulocyte-macrophage colony stimulating factor (GM-CSF) that helps the APCs to mature
T/F: vaccination of mRNA-electroporated dendritic cells induces robust tumor specific antigen response?
T
Describe chimeric antigen receptor T cell therapy.
Artificially create a T cell by expressing a genetically engineered monoclonal antibody fragment in the T cell to provide the antigen specificity
hybrid of humoral- and cell-mediated- adaptive immunity
T cell collection followed by transduction with construct, and transfer of CARTs to patient
What is the target of the majority of CART molecules?
CD19
Are monoclonal antibodies cross-reactive?
Yes (not mono-specific)
Tumors located in what part of the body exhibit the highest rates of mutagenesis?
lung and melanoma
