L2: Cell growth & Differentiation Flashcards
What are the types of diseases related to cell growth and differentiation?
→Developmental conditions
Can be related to cell growth or differentiation (or both)
E.g. Neural tube defects like spina bifida
→Neoplasia (and metaplasia)
E.g. cancer, tumours
→Others, e.g. cardiac hypertrophy
What is the most common type of cell growth? Give an example
→hyperplasia
What drives hypertrophy? Give an example
→More proteins, more membrane etc etc.
→Elevated protein synthesis is a big driver of increased cell size
What are post-mitotic cells?
→Exit from the cell cycle
→differentiated cells
What are the three types pf extracellular signals?
→paracrine
→autocrine
→endocrine
What are mitogens?
→Stimulate proliferation and promote survival
Give examples of mitogens
→Growth factors and interleukins (EGF, FGF, NGF, PDGF, IGF1, IL2, IL4
What can extracellular signals do?
→Stimulate proliferation and promote survival
→Induce differentiation and inhibit proliferation, e.g. TGF
→Can do either, e.g. Wnt ligands
→Induce apoptosis, e.g. TNFα and other members of the TNF family
What are the phases of the cell cycle?
mitosis
→G1
→synthesis
→G2
What allows FACS analysis to work?
DNA content ie ploidy
2N or 4N
Compare FACs analysis in normal and highly proliferative population
→in a highly proliferative population, G1 phase has a lower peak
→increased S-phase
→similar G2 phase because it is time limited
What is fluorescence microscopy used for?
→ visualising stages of the cell cycle
What do the colours of fluorescence microscopy represent?
Blue= DNA Red = γ-tubulin Green = CHEK2
Yellow = centrioles
(γ-tubulin and CHEK2 colocalised)
What are the four main phases of mitosis?
→prophase
→metaphase
→anaphase
→telophase
What happens in prophase?
→Nucleus becomes less definite
→Microtubular spindle apparatus assembles
→Centrioles migrate to poles
What happens in prometaphase?
→Nuclear membrane breaks down
→Kinetochores attach to spindle in nuclear region
What happens in metaphase?
Chromosomes align in equatorial plane
What happens in anaphase?
Chromatids separate and migrate to opposite poles
What happens in telophase?
Daughter nuclei form
What happens in cytokinesis?
→Division of cytoplasm
→Chromosomes decondense
What are the cell cycle checkpoints and what do they check for?
→Restriction point: DNA not damaged, Cell size, metabolite/nutrient stores Happens just before S-phase →DNA completely replicated, DNA not damaged Happens at M →Chromosomes aligned on spindle Happens at mid-M phase
How many genes code for CDKs?
→10 genes
What do active cyclin-CDK complex do?
→Phosphorylates specific substrates
How many genes encode cyclins?
→20 genes
What induces cyclins(regulatory subunits)?
→expression of growth factors
What is retinoblastoma protein?
→a key substrate of G1 and G1/S cyclin-dependent kinases
Describe how RB works
→Unphosphorylated RB binds E2F transcription factor preventing its stimulation of S-phase protein expression
→CD-CDK4 and CE-CDK2 phosphorylate RB
→ E2F is released
→Released E2F stimulates expression of more Cyclin E and S-phase proteins e.g. DNA polymerase, thymidine kinase, PCNA etc.
DNA replication starts.
What are hyperphosphorylated RB dephosphorylated by?
→protein phosphatase 1
Describe the sequence of events triggered by growth factors
→Growth factor signalling activates early gene expression (transcription factors – FOS, JUN, MYC)
Early gene products stimulate delayed gene expression (includes Cyclin D, CDK2/4 and E2F transcription factors)
E2F sequestered by binding to unphosphorylated retinoblastoma protein (RB)
G1 cyclin-CDK complexes hypophosphorylate RB and then G1/S cyclin-CDK complexes hyperphosphorylate RB releasing E2F
E2F stimulates expression of more Cyclin E and S-phase proteins (e.g. DNA polymerase, thymidine kinase, Proliferating Cell Nuclear Antigen etc.)
S-phase cyclin-CDK and G2/M cyclin-CDK complexes build up in inactive forms. These switches are activated by post-translational modification or removal of inhibitors, driving the cell through S-phase and mitosis.
What can happen if there is DNA damage?
→Stop the cycle
(cyclin dependent kinase inhibitors, CHEK2 etc.)
→Attempt DNA repair
(nucleotide or base excision enzymes, mismatch repair etc.)
→if repair impossible
Programmed Cell Death (BCL2 family, caspases)
What can TP53 loss of function lead to?
→Prevent cell cycle arrest
→Prevent apoptosis
→Prevent DNA repair
What can more mutations lead to?
= more heterogeneity
= more adaptation
= cancer progression
What are the objectives of traditional chemotherapeutic drugs?
stop proliferation, induce apoptosis
Give examples of S-phase drugs and how they work
→5-fluorouracil (prevents synthesis of thymidine)
→Cisplatin (binds to DNA causing damage and blocking repair)
How do M-phase drugs work?
Vinca alkaloids
→stabilize free tubulin
→prevent microtubule polymerization- no
→mitotic spindle arrest cells in mitosis
how does Paclitaxel work?
→stabilizes microtubules
→preventing de-polymerization
→arrests cell in mitosis
What is colchicine?
→similar mode of action to vinca alkaloids
→ is used for immune-suppression
