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Negative Regulator Molecules

Negative Regulator Molecules

Positive regulators allow a cell to advance through cell cycle checkpoints. Negative regulators have an equally important role as they terminate a cell’s progression through the cell cycle—or pause it—until the cell meets specific criteria.

DNA Damage can Stall the Cell Cycle

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In response to DNA damage, cells can pause the cell cycle to assess and repair the breaks. However, the cell must check the DNA at certain critical stages during the cell cycle. If the cell cycle pauses before DNA replication, the cells will contain twice the amount of DNA. On the other hand, if cells arrest after DNA replication but before mitosis, they will contain four times the normal amount of DNA. With a host of specialized proteins at their disposal,cells must use the right protein at...

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Inhibition of Cdk Activity

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The orderly progression of the cell cycle depends on the activation of Cdk protein by binding to its cyclin partner. However, the cell cycle must be restricted when undergoing abnormal changes. Most cancers correlate to the deregulated cell cycle, and since Cdks are a central component of the cell cycle, Cdk inhibitors are extensively studied to develop anticancer agents. For instance, cyclin D associates with several Cdks, such as Cdk 4/6, to form an active complex. The cyclin D-Cdk4/6 complex...

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The cell cycle is a series of events leading to DNA duplication followed by the division of cell content to form two daughter cells. The cell cycle progresses in four stages—the cell increases in size (gap 1 or G1-phase), duplicates its DNA (synthesis or S-phase), prepares to divide (gap 2 or G2-phase), and divides (mitosis or M-phase).
Two states at the origin of replication
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Under normal conditions, most adult cells remain in a non-proliferative state unless stimulated by internal or external factors to replace lost cells. Abnormal cell proliferation is a condition in which the cell's growth exceeds and is uncoordinated with normal cells. In such situations, cell division persists in the same excessive manner even after cessation of the stimuli, leading to persistent tumors. The tumor arises from the damaged cells that replicate to pass the damage to the...

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Quantifying Replication Stress in Ovarian Cancer Cells Using Single-Stranded DNA Immunofluorescence

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p21CIP1 controls the squamous differentiation response to replication stress.

Isabel de Pedro¹, Jesús Galán-Vidal¹, Ana Freije¹

¹Cell Cycle, Stem Cell Fate and Cancer Laboratory, Institute for Research Marqués de Valdecilla (IDIVAL), 39011, Santander, Spain.

|October 24, 2020

Summary

The cell cycle inhibitor p21 (also known as p21CIP1) is crucial for controlling cell fate, driving differentiation in response to DNA damage. Its absence allows damaged cells to proliferate or undergo apoptosis, impacting cancer development.

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Area of Science:

Cell Biology
Cancer Research
Molecular Biology

Background:

Cell fate control is vital for tissue homeostasis and cancer development.
The cell cycle inhibitor p21CIP1 plays a paradoxical role in cell fate decisions like senescence, apoptosis, and differentiation.
p21CIP1 is a key target of the tumor suppressor p53 but also has independent regulatory pathways.

Purpose of the Study:

To investigate the role of p21CIP1 in the squamous differentiation response to cell cycle deregulation and replication stress.
To elucidate the mechanisms by which p21CIP1 controls cell fate in squamous epithelia.
To understand the dual role of p21CIP1 in keratinocyte response to genomic stress.

Main Methods:

Investigated the role of endogenous p21CIP1 in human primary keratinocytes.
Examined the effects of p53 loss and Cyclin E overexpression on differentiation.
Analyzed the impact of p21CIP1 inactivation on cell cycle progression and DNA damage response.
Studied keratinocyte apoptosis following UV irradiation in the absence of p21CIP1.

Main Results:

p21CIP1 is essential for the mitosis block required for squamous differentiation following cell cycle deregulation and replication stress.
Inactivation of p21CIP1 in keratinocytes reduced differentiation in response to p53 loss or Cyclin E overexpression.
Bypassing the p21CIP1-induced mitotic block, via Cyclin B upregulation, allowed DNA-damaged cells to proliferate.
Loss of p21CIP1 promoted apoptosis over differentiation in UV-irradiated keratinocytes.

Conclusions:

p21CIP1 is required to promote keratinocyte differentiation in response to genomic stress.
The study highlights the dual and paradoxical role of p21CIP1 in carcinogenesis.
Understanding p21CIP1's function is critical for developing cancer therapies targeting cell fate.