Question

Describe the steps by which the TP53 gene responds to DNA damage and/or cellular stress to promote cell-cycle arrest and apoptosis. Given that TP53 is a recessive gene and is not located on the X chromosome, why would people who inherit just one mutant copy of a recessive tumor-suppressor gene be at higher risk of developing cancer than those without the recessive gene?

Accepted Answer

Step 1: Understand the role of the TP53 gene. TP53 encodes the p53 protein, which is a tumor suppressor. It plays a critical role in maintaining genomic stability by responding to DNA damage and cellular stress. When activated, p53 can induce cell-cycle arrest, allowing time for DNA repair, or trigger apoptosis (programmed cell death) if the damage is irreparable. Step 2: Describe the mechanism of TP53 activation. Upon DNA damage or cellular stress, sensors such as ATM (Ataxia Telangiectasia Mutated) and ATR (ATM and Rad3-related) kinases phosphorylate p53, stabilizing it and preventing its degradation. This allows p53 to accumulate in the nucleus, where it acts as a transcription factor to regulate the expression of target genes involved in cell-cycle arrest (e.g., CDKN1A/p21) and apoptosis (e.g., BAX, PUMA). Step 3: Explain cell-cycle arrest and apoptosis. p53 promotes cell-cycle arrest by upregulating CDKN1A/p21, which inhibits cyclin-CDK complexes, halting the progression of the cell cycle at the G1/S checkpoint. If the damage is severe, p53 activates pro-apoptotic genes like BAX and PUMA, leading to mitochondrial dysfunction and activation of caspases, which execute apoptosis. Step 4: Discuss the recessive nature of TP53 and cancer risk. TP53 is recessive, meaning both alleles must typically be mutated for complete loss of function. However, individuals with one mutant copy (heterozygous) are at higher risk because the remaining functional allele may be lost or mutated over time (a phenomenon called 'loss of heterozygosity'). This leaves cells without functional p53, impairing their ability to respond to DNA damage and increasing the likelihood of cancer development. Step 5: Highlight the importance of TP53 in cancer prevention. TP53 is often referred to as the 'guardian of the genome' because of its critical role in preventing the accumulation of mutations. A single mutant copy increases susceptibility to cancer because it compromises the cell's ability to maintain genomic integrity, especially under conditions of stress or DNA damage.

비슷한 문제에 대한 검증된 영상 답변:

주요 개념

TP53 Gene Function

Recessive Inheritance

Cancer Risk and Tumor Suppressor Genes