A 55-year-old woman with a recently diagnosed right-sided breast carcinoma undergoes a lumpectomy followed by adjuvant external beam radiation therapy. The primary therapeutic effect of the ionizing radiation on residual neoplastic cells relies on the generation of reactive oxygen species and the direct induction of double-strand DNA breaks, which ultimately trigger programmed cell death.
Arrange the following subcellular events in the correct chronological order to accurately describe the intrinsic apoptotic cascade that leads to the death of these malignant cells.
- 1Activation of the p53 tumor suppressor protein in response to double-strand DNA breaks
- 2Upregulation and oligomerization of pro-apoptotic BAX and BAK proteins
- 3Formation of permeability pores in the outer mitochondrial membrane
- 4Efflux of cytochrome c from the intermembrane space into the cytosol
- 5Assembly of the apoptosome complex and activation of initiator caspases
Cevap
The correct chronological sequence begins with p53 activation, followed by BAX/BAK upregulation, mitochondrial membrane permeabilization, cytochrome c release, and finally apoptosome assembly.
The correct sequence reflects the intrinsic (mitochondrial) pathway of apoptosis initiated by severe DNA damage. Radiation induces double-strand DNA breaks, which directly activate p53. Activated p53 upregulates pro-apoptotic BCL-2 family members (BAX and BAK). These proteins oligomerize and permeabilize the outer mitochondrial membrane. This structural compromise allows cytochrome c to escape from the intermembrane space into the cytosol, where it binds Apaf-1 and procaspase-9 to form the apoptosome, culminating in caspase activation and programmed cell death.
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Anahtar Kavram
The intrinsic (mitochondrial) pathway of apoptosis is triggered by cellular stress such as radiation-induced DNA damage, progressing chronologically from p53 activation to mitochondrial permeabilization and culminating in apoptosome assembly.