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The Ras Gene

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The Ras-gene-encoded proteins are regulators of signaling pathways controlling cell proliferation, differentiation, or cell survival. The Ras-gene family in humans constitutes three primary members—the HRas, NRas, and KRas. These genes code for four functionally distinct yet closely related proteins—the HRas, NRas, KRas4A, and KRas4B. The involvement of mutant Ras genes in human cancer was first discovered in 1982 and is among the most common causes of human tumorigenesis.
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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...

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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Updated: Apr 15, 2026

A Quantitative Measurement of Reactive Oxygen Species and Senescence-associated Secretory Phenotype in Normal Human Fibroblasts During Oncogene-induced Senescence

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Published on: August 12, 2018

RPA hyperphosphorylation hinders the resolution of R-loops and G-quadruplex-associated R-loops during RAS-driven

Ylenia Cortolezzis¹, Vanessa Tolotto¹, Luca Triboli¹

¹Laboratory of Biochemistry, Department of Medicine, University of Udine, Piazzale M. Kolbe 4, 33100 Udine, Italy.

Nucleic Acids Research

|April 14, 2026

Summary

This summary is machine-generated.

RAS oncogenes trigger cell cycle arrest (senescence) by creating R-loops and G-loops. Resolving these structures via RPA and RNase H1 activity is key to bypassing senescence and preventing tumor formation.

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A Quantitative Measurement of Reactive Oxygen Species and Senescence-associated Secretory Phenotype in Normal Human Fibroblasts During Oncogene-induced Senescence

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Quantifying Tissue-Specific Proteostatic Decline in Caenorhabditis elegans

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Published on: September 7, 2021

Area of Science:

Molecular Biology
Cell Biology
Genomics

Background:

RAS oncogene activation induces RAS-induced senescence (RIS), a stable cell cycle arrest.
RIS is characterized by DNA damage and epigenetic alterations, but mechanisms for bypassing it are unclear.
Understanding RIS bypass is crucial as it promotes tumorigenesis.

Purpose of the Study:

To investigate the molecular mechanisms underlying the bypass of RAS-induced senescence (RIS).
To identify key molecular players and pathways involved in genome maintenance during oncogene-induced stress.

Main Methods:

Analysis of R-loop and DNA G-quadruplex structures in RIS cells.
Investigating the role of the RPA complex and RNase H1 activity in resolving these structures.
Assessing the impact of RPA32 phosphorylation on RNase H1 activity and DNA damage.

Main Results:

RIS cells accumulate R-loops and G-quadruplexes, forming G-loop-like structures.
The heterotrimeric RPA complex facilitates RNase H1-mediated R-loop processing.
Hyperphosphorylation of RPA32 impairs RPA's enhancement of RNase H1, leading to unresolved R-loops/G-loops and DNA damage (γH2AX).
Restoring RPA-regulated RNase H1 activity reduces DNA damage and allows cell cycle re-entry, bypassing senescence.

Conclusions:

A regulatory axis involving RPA phosphorylation and RNase H1 activity controls R-loop and G-loop resolution.
This axis acts as a critical genome maintenance mechanism during oncogene-induced stress.
Targeting this pathway could offer strategies to manage oncogene-driven cancers.