Apoptosis

Question 1

list the steps in intrinsic pathway of apoptosis

Answer 1

• Cellular and DNA damage activate protein kinases that phosphorylate and activate p53
• p53 binds to DNA and causes transcription of BAX and cell cycle inhibitor p21
• BAX protein inserts into the mitochondrial membrane and causes the release of cyotochrome c
• cytochrome c binds to Apaf-1 causing aggregates and binds to procaspases (apoptosome complex)
• procaspases are cleaved to form caspases

Question 2

describe the extrinsic death pathway

Answer 2

• killer lymphocytes express Fas ligand (FasL) on their cell surface
• killer lymphocyte binds to target cell via the Fas Death Receptor
• FasL and Fas Death Receptor binding recruits adaptor molecules via binding between the receptor “death domain” and adaptor death domain
• Procaspases aggregate by binding to the “death effector domain” of the adaptor forming the death-inducing signaling complex (DISC)
• procaspases are cleaved and lead to apoptosis

Question 3

how are extrinsic and intrinsic pathways linked?

Answer 3

• Extrinsic pathway activates caspase-8
• caspase-8 leads to BID cleavage
• BID causes BAX to incorporate itself into the mitochondria and cause cytochrome c release

Question 4

describe the perforin/granzyme pathway

Answer 4

• this occurs in response to viral infected cells

1. cytotoxic T-cell secretes perforin and granzymes
2. Perforin forms pore in target cell
3. Granzyme B enters cell and activates caspase 10 by cleavage resulting in the inactivation of apoptotic inhibitors
4. also activates caspase 3 = execution of apoptosis

Question 5

describe the extracellular survival factors that can inhibit apoptosis

Answer 5

• binding of an extracellular signaling molecule (survival factor) to a cell surface can activate signaling pathways that can result in the activation and production of apoptotic inhibitors such as Bcl-2 and the inactivation of proapoptotic proteins such as Bad

Question 6

name the 3 ways p53 can influence apoptosis

Answer 6

• p53 can induce apoptosis by increasing expression of:

1. pro-apoptotic Bcl-2 family members
2. Fas receptor
3. IGFBP-3 (sequesters cell survival proteins like IGF1/2 away from receptors)

Question 7

describe TUNEL

Answer 7

• labeled nucleotides are enzymatically

Question 8

describe the role of annexin 5 as a marker

Answer 8

• annexin 5 binds to phosphatidylserine
  
  • in apoptotic cells, it is present on the outer surface
• labeled antibodies for annexin 5 can label apoptotic cells

Question 9

describe the link between apoptosis and Alzheimers

Answer 9

• in Alzheimer diseased brains
  
  • proapoptotic Bak and Bad protein levels increased (antiapoptotic proteins Bcl-2 and Bcl-xL also increased which is thought be a compensatory action in surviving neurons)

Question 10

describe the link between HIV and apoptosis

Answer 10

1. HIV infection can lead to inactivation of anti-apoptotic protein Bcl-2 and activate procaspases priming the cell for entry into the apoptotic pathway/
2. appears to promote the extrinsic Fas-mediated apoptosis pathway in CD4+ cells
3. HIV proteins such as tat, nef and vpr may induce apoptosis by interacting with p53
4. HIV tat protein secreted by infected cell may taken up by other cells inducing apoptosis