Caspase Activity in Apoptotic Cells Cell Bio 220 Tenzin Dolkar Stephanie Kim Victoire Ndong Patricia Wong

Caspases Are families of proteases which are involved in initiating apoptotic events Synthesized in the cell as precursors- procaspase Cleave proteins at aspartic acid residue sites There are initiator caspase (procaspase-8) And executioner/effector caspase (procaspase-3)

Caspase Structure NH 2 -terminal domain Large subunit (~20kD) – (lavender) Small subunit (~10kD) – (gray) Red represents an inhibitor Thornberry and Lazebnik. Caspases: Enemies Within p 1313

Caspase Role in Apoptosis Cut off contact with surrounding cells Reorganize cytoskeleton Shut down DNA replication and repair Interrupt splicing Destroy DNA Disrupt nuclear structure Induce cell to display signals marking it for phagocytosis Disintegrate cells into apoptotic bodies

Initiator Caspase Activation Initiator Caspases are activated by either internal (DNA damage) or external signals (ligand binding) External: caspase-8, an initiator caspase is activated by binding to it’s specific cofactor, FADD (Fas-associated protein with death domain)

Executioner/Effector Caspase Activation Effector caspase are activated generally by other caspases. Caspase activation results in proteolytic cascade which is self-amplifying and irreversible. Caspase-3 is an effector caspase

Our Experiment MDCK cells treated with camptothecin (interferes with DNA replication and transcription) Added “D 2 -R110,” a bis-L-aspartic acid amide of Rhodamine 110 When the compound is cleaved by caspase, such as caspase-3, it fluoresces green

Hypothesis/Goal Cells treated with camptothecin will have a greater number of fluorescing cells, indicating a higher rate of caspase activity and the occurrence of apoptosis To compare caspase activity in MDCK cells treated with camptothecin with control cells in order to determine the rate of caspase activity

Sample A – Camptothecin Treated Average Percentage of Apoptotic Cells: 73.40%

Sample B - Control Average Percentage of Apoptotic Cells: 2.95%

Cellular Pathway

Sources of Error and Uncertainty Human errors Direct causal relationship between caspase activity and fluorescence not proven

Further Experimentation Disable caspase-3 activation to see the extent of its importance in apoptosis Disable caspase-9 to determine if apoptosis is a result of internal signaling Compare caspase activity in cells undergoing apoptosis to those undergoing necrosis Examine caspase activity at different time intervals