Graeme Finlay 7

Question 1

What is the difference between oncosis and apoptosis?

Answer 1

Oncosis is passive cell death often following severe injury while apoptosis is cell death brought about by an active, physiological process

Question 2

How does apoptosis normally function?

Answer 2

In development where it can form vital structures such as the hollow blastocyst and remove unwanted structures such as webbing between digits
Throughout the life of the organism where it regulates cell turnover and removes unwanted cells

Question 3

What are the various physiological and pathological stimuli that can induce apoptosis>

Answer 3

Activation of death receptors involved in the elimination of abnormal cells
Removal of survival factors such as growth factors
Presence of apoptosis inducing growth factors or hormones
Loss of normal epithelial cell-cell adhesion
DNA damage, cell cycle deregulation, viral infection, oxidative stress and hypoxia

Question 4

How is apoptosis regulated?

Answer 4

By the cell death abnormal (ced) genes including ced3, ced 4, ced 9 and EGL-1

Question 5

What is ced 3?

Answer 5

It is a cysteine protease which cleaves specifically after aspartic acid residues

Question 6

What is the function of ced 4?

Answer 6

It is an activator of ced 3 protein

Question 7

What is the function of ced 9?

Answer 7

It is an inhibitor of ced 4 and therefore an inihibitor of apoptosis

Question 8

What is the function of EGL-1?

Answer 8

It is an inhibitor of ced 9 and therefore a promoter of apoptosis

Question 9

What are the mammalian homologs of the ced genes from C. Elegans?

Answer 9

13 homologes have been identified known as caspases and stored as zymogens until induced to oligemerize or autocatalytically cleave to P2010 oligomers which cleave key cellular proteins
Gelsolin which causes cytoplasmic blebbing by deregulating actin fibre breakdown,
Nuclear lamin which causes chromatin condensation and nuclear fragmentation poly(ADP-ribose) polymerase which leads to a suppression of DNA repair
An inhibitior of a DNAse which leads to intrnucleosomal DNA cleavage

Question 10

What is the oncogene involved in causing low-grade B cell lymphoma with a translocation at t(14:18)

Answer 10

BCL-2 which becomes translocated into the IgH locus and overexpressed. This oncogene does not stimulate proliferation but promotes cell survival in a quiescent state and is homologous to ced 9 of C. Elegans

Question 11

What are the different domains in the BCL-2 protein?

Answer 11

BH4 which has anti-apoptotic activity and BH3 which has proapoptotic activity and acts as an amphipathic ligand domain. The C-terminal hydrophobic transmembrane domain allows the protiens to localise to the outer mitochondrial membrane, ER and Nuclear membrane. They control the release of pro-apoptotic stored in the mitochondria

Question 12

What BCL-2 proteins are functional analogues of the EGL-1 of C. Elegans?

Answer 12

Those which only contain the BH3 domain

Question 13

How does altered expression of the Bcl-2 family cause resistance to apoptosis in cancer?

Answer 13

The ratio of pro and anti-apoptotic species controls cell fate. A truncated EGFR increases malignant character by up regulation of Bcl-XL. The tumour suppressor genes BAX and Bak are deleted and Bcl-2 is often increased in expression giving resistance to apoptotsis.

Question 14

How can the altered expression of the Bcl-2 family in cancer cells be combatted?

Answer 14

anti inflammatory drugs can induce apoptosis by decreasing Bcl-XL expression

Question 15

What is the link between apoptosis and metastasis?

Answer 15

Apoptosis may be the rate-limiting step for metastasis

Question 16

How can phosphorylation of Bcl-2 family cause resistance to apoptosis by cancer cells?

Answer 16

The Bcl-2 family is regulated by protein kinases.
Activated survival factor receptors such as recruit phosphatidylinositol-3-kinase to the cell membrane causing an increase in PtdIns-3,4,5-phosphate concentration. This then recruits inactive Akt allowing it to be phosphorylated by phospholipid-dependent kinase-1. Akt can then phosphorylate bad which will cause it to dissociate from Bcl-2 or Bcl-Xl maintaining the anti-apoptotic proteins in the active state. Akt will also phosphorylate procaspase 9 to suppress its activation

Question 17

How can cancer cells that have developed resistance to apoptosis via phosphorylation of the Bcl-2 proteins be combatted?

Answer 17

Anti-microtubule agents such as taxol can induce activation of apoptosis by a protein synthesis-dependent phosphorylation of Bcl-2 or Bcl-Xl which involves Raf activation

Question 18

How does proteolytic cleavage regulate apoptosis?

Answer 18

Activated caspases cleave Bcl-2 repelasing a fragement which exerts a pro-apoptotic function. Folowing death receptor activation Bid is cleaved by caspase 8 and translocated from the cytoplasm to the mitochondria where it mediates an apoptotic role