Evaluate each of the following defects. Which could lead to uncontrolled growth in cancer? Select True or False for each statement. T/F The overexpression of MPF activity. T/F A nonfunctional Rb protein. T/F The overexpression of G1 cyclin. T/F A nonfunctional E2F protein.

Verified step by step guidance

1. Identify the role of each component in cell cycle regulation: MPF (M-phase promoting factor) triggers the cell's entry into mitosis, Rb (retinoblastoma protein) prevents excessive cell growth by inhibiting cell cycle progression until the cell is ready, G1 cyclin binds to and activates CDKs to promote cell cycle progression, and E2F is a transcription factor that is essential for the progression from G1 to S phase in the cell cycle.
2. Analyze the impact of overexpression of MPF activity: Overexpression of MPF activity could lead to premature or uncontrolled entry into mitosis, bypassing the normal regulatory mechanisms, which could contribute to uncontrolled cell division seen in cancer. Thus, True.
3. Evaluate the effect of a nonfunctional Rb protein: Rb normally inhibits the cell cycle; a nonfunctional Rb would fail to regulate the cell cycle properly, potentially allowing for uncontrolled cell division. Thus, True.
4. Consider the consequences of overexpression of G1 cyclin: Overexpression of G1 cyclin could lead to excessive activation of CDKs, pushing the cell through the G1/S checkpoint inappropriately and contributing to uncontrolled cell growth. Thus, True.
5. Assess the impact of a nonfunctional E2F protein: A nonfunctional E2F would impair the transition from G1 to S phase, likely reducing cell proliferation rather than causing uncontrolled growth. Thus, False.

Key Concepts

MPF Activity

MPF, or M-phase promoting factor, is a complex of cyclin and cyclin-dependent kinase (CDK) that regulates the cell cycle's transition from G2 to M phase. Overexpression of MPF activity can lead to premature entry into mitosis, disrupting normal cell cycle control and potentially contributing to uncontrolled cell proliferation, a hallmark of cancer.

Rb Protein

The retinoblastoma (Rb) protein is a crucial tumor suppressor that regulates the cell cycle by inhibiting progression from the G1 phase to the S phase. A nonfunctional Rb protein fails to restrain cell cycle progression, allowing cells to divide uncontrollably, which is a significant factor in the development of various cancers.

G1 Cyclin and E2F Protein

G1 cyclins are proteins that promote the transition from the G1 phase to the S phase of the cell cycle by activating CDKs. E2F proteins are transcription factors that, when released from Rb inhibition, drive the expression of genes necessary for DNA synthesis. Overexpression of G1 cyclins or a nonfunctional E2F protein can disrupt normal cell cycle regulation, leading to uncontrolled cell growth and cancer.