Final answer:
p53 and MDM2 are indeed inversely expressed; p53 functions as a tumor suppressor gene and halts cell division amidst DNA damage, while MDM2 ubiquitinates p53 leading to its degradation.
Step-by-step explanation:
The statement that p53 and MDM2 are inversely expressed is true. p53, known as a tumor suppressor gene, plays a crucial role in preventing cancer formation by halting cell division and promoting DNA repair or apoptosis when DNA damage is detected. MDM2, on the other hand, is responsible for the ubiquitination and subsequent degradation of p53, thus negating its effects. In a healthy cell, when DNA damage is detected, p53 is activated and MDM2 is inhibited, allowing p53 to exert its protective effects. However, if p53 is mutated, which is a common occurrence in cancer cells, it fails to arrest the cell cycle or initiate apoptosis, leading to tumor progression. CHK2 is another kinase that is involved in cell cycle regulation, activated by ATM kinase along with p53, and it negatively regulates the cell cycle like p53.