1 / 11

Ted Cybulski 11/19/09

Ted Cybulski 11/19/09. Non-genetic origins of cell-to-cell variability in TRAIL-induced apoptosis - Spencer et al., Nature 2009. TRAIL and Cell Death. Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) activates a broad signal cascade resulting in apoptosis

brone
Download Presentation

Ted Cybulski 11/19/09

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ted Cybulski 11/19/09 Non-genetic origins of cell-to-cell variability in TRAIL-induced apoptosis- Spencer et al., Nature 2009

  2. TRAIL and Cell Death • Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) activates a broad signal cascade resulting in apoptosis • Cells exhibit heterogeneous TRAIL response phenotype • Time response between TRAIL treatment varies greatly both in sensitive and resistant cells • “Fractional Killing” is a key problem for cancer theraputics Spencer et al., 2009

  3. Where does this variability come from? • Genetic/epigenetic differences, or stochastic “noise” • If caused by genetic differences, sister cells should behave identically • If caused by stochastic fluctuations, sister cells should not be correlated

  4. Correlation between sister cells decreases with time

  5. Is variance in protein levels to blame? • Did flow cytometry for expression of 5 proteins in TRAIL pathway • Ran ordinary differential simulation of TRAIL pathway • Measured differences in protein levels account for variability in Td

  6. What steps in the TRAIL pathway cause the time variance?

  7. How does pre-MOMP and apoptosis time vary? • Casp8 and Casp10 cleave BID to form a truncated BID (tBID) • tBID activates pore-forming proteins BAX and BAK • Timing of MOMP relies on the rate of tBID accumulation to a threshold set by BCL2 proteins • Can model this using the rate of IC-RP cleavage and fraction of IC-RP cleaved at MOMP

  8. Almost all variation comes from differences in tBIT accumulation rate • Td is more correlated with rate than threshold (R^2=.82 vs. R^2=.22) • Almost all variation in pre-MOMP time comes from the rate at which BID is converted to tBID

  9. Are levels of upstream proteins important to apoptosis time? • Several proteins play a role in the rate of tBID accumulation. • Modelling predicts that any single upstream protein will have minimal predictive value • Other variations in the system are too great

  10. Levels of BID have a predictive power on apoptotic death time • According to simulation, as BID levels increase, Td decreases • Similarly, Var(Td) decreases with BID levels • This is all confirmed in assays with GFP-tagged BID

  11. Conclusions • Cell-to-cell variation in TRAIL-response is transiently heritable • Variability in phenotype comes from cell-to-cell differences in protein level that exist pre-TRAIL exposure • The rate of apoptosis is correlated with the conversion of BID to tBID, but cannot be predicted by concentrations of other proteins in the pathway • Reducing cell-to-cell variability in protein concentrations could reduce problem of “fractional killing”

More Related