cancer bio exam 3

cancer development

is usually a timely process that can take decades, strong evidence that cancer takes a long time to develop after the initial mutational events came from the association between lunger cancer and smoking

must overcome lots of barrier

tumor formation is a complex process that involved similar biological mechanisms, which can increase when exposed to carcinogens, mutagens, and or tumor promoting stimuli

squamous carcinoma

follows the generalized long-term timline

retinoblastoma and testicular

do not fit the generalized long-term timeline

malignant tumors arise from

pre-malignant growths, tissues with both benign malignant growth co-existing, removal of polys decrease risk of CRC by 60%, repeated surveillance (2.5/1000 growth)

multiple alterations required for progression

analyzed genomes of various stages in colorectal cancer progression, they found a common pattern in the samples analyzed, the majority of sample harbor inactivating mutation in APC (tumor suppressor), genetic and epigenetic changes vary after the initial loss of APC

tumor formation

complex process that involved similar biological and genetic (epigenetic) mechanisms

development and evolution

both used to describe the carcinogenic process

promotion and development

early shows development, cell competition at tissue level within boundaries set by tissue homeostatic control mechanisms (no growth autonomy

progression and evolution

cell competition at single-cell level, growth autonomy and evolutionary drift

does carcinogenesis fit into Darwinian evolution

partially by Johns Hopkins study; limitations are that there is no direct link between genetic change and advantage conferred, epigenetic changes critical to carcinogenesis, rate-limiting steps are hard to identify

dynamic clonal diversification

simple linear clonal expansion vastly oversimplifies the progressive growth of cancer cells during carcinogenesis

mutation rates changing

Darwinian selection might eliminate phenotypically less fit clones through selective pressure

genetic diversity

likely from genetic instability that outpaces selection; clones of cells during expansion aren’t actually a ‘stable’ homogeneous population containing similar genetic alterations, cells that are presumably part of a single clonal population vary greatly in copies of chromosomes

cancer stem cells

complicate the clonal expansion model; they are organized in a hierarchy, stem cells produce progenitor cells which then undergo rapid cell divisions, progenitor cells then differentiate to produce specialized cells in tissues

clonal evolution theory

based on the clonal expansion model of tumorigenesis, individual cells acquire mutations that confers advantages giving rise to clonal populations in the tumor (ALL cells in the clonal population are tumorigenic)

cancer stem cell theory

rooted in the idea that a cancer stem cell population produces all cancer cells, the resultant cancer cell population is highly heterogenous however is unable to self-renew (ONLY the cancer stem cells are truly tumorigenic)

cancer stem cell hypothesis

only cancer stem cells have self-renewal and tumorigenic capabilitiest

tumorspheres

cancer stem cells usually form these in culture and express stem cell specific antigens

are all cells in a growing mass tumorigenically equivalent

select cells that express antigens present in cancer stem cells from rest of tumor cell population, test for tumor formation in immunocompromised mouse model, cancer stem cells form tumors while general tumor cell population doesn’t

why are cancer stem cells clinically important

more resistant to chemotherapy and radiation, more resistant to checkpoint immunotherapies, can generate phenotypically distinct populations independent of genetic diversification, most recent experimental evidence suggests that cell populations in tumor collaborate rather than compete

unlocking phenotypic plasticity

altered differentiation potential potential in cancer cells including de-differentiation and trans-differentiation

nonmutational epigenetic reprogramming

certain stimuli induce epigenetic plasticity that allows cells to sample alternate chromatin or transcriptional states, a subset of which confer fitness and are maintained through cell division

senescent cells

senescent altered secretory phenotypes, tumor promotion by senescent cells in microenvironments

increase glucose

cancer cells do this from their environment and utilize fermentation more than oxidative phosphorylation

warburg effect

the use of aerobic glycolysis by cancer cells

three modes of carbohydrate metabolism

glycolytic phenotype, OXPHOS phenotype, combined phenotype

glycolytic phenotype

aerobic glycolysis, high glucose/low O2 consumption, high lactate production, high proliferation, low mitochondrial function

OXPHOS phenotype

oxidative phosphorylation, high O2 consumption, low lactate production, low proliferation, high mitochondrial function

combined phenotype

transitional, high glycolysis/OXPHOS, high metastatic ability, high plasticity

increase glucose transport

GLUT1 glucose transported, increase GLUT1 in membrane, Ras src and myc increased expression of GLUT1, PI3K pathway increased GLUT1 and translocation of GLUT1

increased glucose uptake

provides mechanisms for visualizing tumors, glucose-2 deoyglucose replace OH with radioactive fluorine (which can be detected by PET scanner)

cancer cells highly express M2

isoform of pyruvate kinase, ATP not only focus, nucleotides (protein synthesis, other macromolecules), pyruvate kinase (forms pyruvate in last stem)

M1 isoform

highly catalytically active tetramers

M2 isoform

mostly dimers, not very active, builds up intermediates used to make other stuff

lactate alters

the tumor microenviroment, not just a product of glycologsis, decreases pH or acidifies enviroment, decreases function of immune cells that target cancer cells, increases macrophages that pro-tumorigenic properties, ste

altered amino acid metabolism

glutamine is a critical amino acid for cancer cells, cancer cells mimic wound healing which both increases glutamine in cell, increase glutamine transport by myc, glutamine intermdiate in the citric acid cycle, glutathione is an antioxidant

cancer cells have mechanisms

to transport nutrients from extracellular space

altered lipid metabolism

high rates of lipid synthesis and lipid uptake in cancer cells, lipid signaling molecules (promote inflammation, invasion, formation of blood vessels, MUFA/PUFA (unsaturated fatty acids) in cell membranes, increase membrane saturation (plasma membrane) increase cholesterol (increases rigidity, decreases permeability, decreases oxidative stress)

carcinogensis also influenced by

organismal metabolic regulation, obesity/type 2 diabetes (critical risk factors for cancer)

no IGF-1

almost never get cancer, pro-survival/bio-synthesis, regulated by food intake

DNA repair pathways

often mutated in cancer cells, mutations in DNA repair proteins increases genomic instability, genome instability increases mutation rate, increases mutation rate increases the probability of a cell acquiring mutations required to overcome barriers to malignancy

structure of DNA

permits replication and transciption

DNA provides instructions

for making RNA and proteins that ulimtately drive phenotype and function

all DNA bonds are

covalent, except between the bases (hydrogen bonds)

bases are

inward facing, provides some protection from mutation, still susceptible to modification from exogenous and endogenous sources

DNA replication

mis-incorporation of bases, incorporation of chemically-altered bases, double-stand break repair (doesn’t just happen during replication)

spontaneous chemical changes

deamination of DNA bases, hydrolysis of glycosidic bonds connecting nucleobases to backboned, depurination depyrimidination leading to abasic sites

chemical changes induces by mutagenic agents

ROS produced by normal cells metabolism, exogenous agents (X-rays, UV rays, alkylating agents), ROS and NOS produces by carcinogens, reactive species produced by inflammations

DNA polymerases

proof-reading ability is critical line of defense against cancer, around 10^5 nucleotide there is one mistake then exonuclease domain chews up DNA with mistake (10^7 error rate)

mutations in exonuclease domain

can promote cancer because of mutations in DNA polymerases

mouse model

germline mutation in DNA polymerase delta (lagging strand) increase mortality by various cancers

double strand breaks

can occur during DNA replication, single-stranded DNA during replication is susceptible to breaks, single-strand DNA breaks that arise during replication are essentially double stranded DNA breaks, cells have several pathways to repair dsDNA breaks

homology-directed repair

double-strand breaks are repaired by this during S and G2 phases of cell cycle, HDR utilizes the sister chromatid to repair double-strand break (genetically identical), key proteins involved in dsDNA breaks repair includes BRAC1 and BRCA2

mutations in BRAC1 and BRAC2

are associated with increased risk of cancer, germline mutations in BRAC1 or BRAC2 increase risk of developing breast or ovarian cancer before the age of 70 by 50-70%

germline BRAC mutations

associated with increased risk of prostate cancer in males before the age of 65

BRCA1 or BRCA2 germline mutations

70-80% of all familial ovarian cancers

BRCA1 or BRCA2 promoter methylation

20-30% of sporadic breast cancers exhibit loss of function due to this

BRCA1

participates in large multi-protein complexes, disruption leads to abnormalities in S-phase checkpoint, G2/M checkpoint, spindle checkpoint, deficiency can also lead to apoptosis and inhibition of proliferation, facilities end resection, phosphorylates which leads to DNA damage response, indirectly recruit rad51

BRCA1 localizes to sites

of double-strand breaks, hydroxyurea causes replication fork to stall

BRCA2

critical in the recruitment of RAD51 to dsDNA breaks, participates in large multi-protein complexes to regulate cell cycle progression, telomere homeostasis, DNA replication, centrosome duplication and of course genome stability

disruption of BRCA2 in mouse models

leads to extensive chromosomal abnormalities, expression of truncated protein in mice results in a huge increase in chromosomal abnormalities, these chromosomal abnormalities are due to dysfunctional repair of dsDNA breaks

BRCA2 deficiency can also

lead to deregulation of centrosome duplication, multipolar spindles (too many sprindles)

are major threats to DNA

reactive oxygen and nitrogen species

oxidative stress

imbalance between the production of oxidants and their removal by antioxidants, can be induces by aging, inflammatory disease, smoking, drinking, exposure to certain carcinogens

reactive nitrogen species

are released from macrophages, neutrophils and dendritic cells in response to an inflammatory stimulus

8-oxoguanine

the most common DNA lesion induced by ROS, mispairs with adenine if left unrepaired, can lead to G:C base pair to become a T:A base pair, cells have repair enzymes that recognize and repair with this and it’s mispairing

deamination of 5-methycytosine

can lead to point mutations, is necessary in regulation of gene expression (methylated DNA, repressed transcription), susceptible to spontaneous deamination which converts it into thymine, switches C:G to T:A mutations, estimated that 63% of point mutations in tumors arise in CpG sequences

oxidation of 5-methylcytosine

creases an unstable intermediate that quickly undergoes deamination forming thymine glycol (strongly blocks replication), leads to formation of a highly unstable intermediate product that rapidly undergoes deamination

products of UV radiation

are predominantly pyrimidine dimers

pyrimidine dimers

adjacent pyrimidines become covalently link to each other (CC, CT and TT dimers), block replication and transcription

base excision repair

repairs non-bulky DNA lesion, thymine glycol, 8-oxoguanine G-T mismatches

MUTY

DNA glycosylase that selectively recognizes and repiars 8-oxoG mispairs with adenine

germline mutations in MUTY

associated with increased risk of colorectal cancer

nucleotide excision repair

repairs bulky, helix distorting lesions, bulky base adducts, pyrimidine dimers (transcription-coupled repairs and global genomic repair)

chromosomal instability

contributes to genomic instability in cancer cells, high rate of loss or gain of whole or parts of chromosomes, results from errors in chromosome segregation during mitosis, cause of aneuploidy in cancer cells

multipolar spindles

can also contribute to CIN and aneuploidy, incorrect spindle organization can also lead to mistakes during mitosis and aneuploidy, supernumerary centrosome can lead to mis-segregation of chromosomes, centrosome duplication is closely related with cell cycle progression

merotely

kinetochore attached to 2 spindle fibers, gets stuck in the middle, this process malfunctions in cancer cells which significantly drives aneuploidy, don’t trigger spindle assembly checkpoint

mutator phenotype

normal mutation rates are insufficient to account for the multiple mutations observed in human tumors

heterotypic interactions

communication between different cells maintain normal tissue organization

stromal cells

a wide variety of these populate tumors (fibroblasts, myofibroblasts, endothelial cells, macrophages

reactive stroma

the composition of this surround tumors is vastly different from normal stromal tissue

PDGF

recruits and stimulates proliferation of fibroblasts and convers them to myofibroblasts, cancer cells continuously release this which leads to MMP secretion by myofibroblasts

myofibroblasts release matrix

proteinases that participates in ECM degradation

tumor associated endothelial cells

vasculature of human glioblastoma expresses both CD31 (endothelia cell specific marker) and NCAM (neuroectodermal marker), contain the same genomic alterations as the bulk of cells in the glioblastoma

cancer-associated fibroblasts

facilitate cancer progression, cancer-associated fibroblasts in stroma significantly drive aggressive tumor, promoting proliferation, promoting survival, activating angiogensis

promoting proliferation

ECM remodeling and growth factors

promoting survival

modulating immune cells that infiltrate and escape of immune surveillance

activating angiogenesis

formation new blood vessels

drive angiogenesis

cancer associated fibroblasts

breast cancer cells

mixed with normal mammary fibroblasts or CAFs and injected into immunodeficient mice to xenograft tumors

tumor associated marcophages

appear to promote tumor development, tumor cells secreting numerous substances that recruit immune cells as well, the recruited cells include monocytes which then undergo differentiation into macrophages

density of TAMs plotted versus the density of capillaries

correlation further supports the proposed role that TAMs play in angiogenesis

expression of MMP

by tumor-associated macrophages degrade the extracellular matrix frees up angiogenic factors

angiogensis

process by which new blood vessels are formed from existing vessels

heterotypic interactions required

communication between tumor cells/stroma to active tumorigenesis

blood vessels

cancer cells tend to preferentially grow around blood vessels, p53 stimulates hypoxia-induced apoptosis

pVHL

angiogensis in response to hypoxia regulated by this

hypoxia

proline hydroxylase can’t function, pH regulate glucose transport anaerobic glycoloysis

under hypoxic conditions

HIF-1 and HIF-2 drive expression of genes involved in angiogenesis and other cellular pathways