#Question id: 1514

Following statements are regarding to multiple signaling pathways in vertebrate cells that regulate outer mitochondrial membrane permeability and apoptosis.

A. In healthy cells, the anti-apoptotic protein Bcl-2, or its homolog Bcl-xL, binds to Bak or Bax pro-apoptotic proteins, blocking the ability of Bak or Bax to oligomerize and form pores in the outer mitochondrial membrane.

B. The presence of specific trophic factors (e.g., NGF) leads to activation of their cognate receptor tyrosine kinases (e.g., TrkA) and inactivation of the PI-3 kinase–PKB (protein kinase B) pathway.

C. PKB phosphorylates Bad, and phosphorylated Bad forms a complex with a cytosolic 14-3-3 protein. This sequestered Bad is unable to bind to Bcl-2.

D. In the absence of trophic factors, nonphosphorylated Bad binds to Bcl-2, releasing Bax and Bak and allowing them to form oligomeric membrane pores and holes.

E. DNA damage or ultraviolet irradiation leads to induction of synthesis of the BH3-only Puma protein. Puma binds to Bak and Bax as well as to Bcl-2, allowing Bak and Bax to form oligomeric pores.

F. Removal of a cell from its substratum disrupts integrin signaling, leading to release of the BH3-only Bim protein from the cytoskeleton. Bim also binds to Bak and Bax to promote pore formation.

Which of the following is incorrect?