Journal News

How post-translational modifications affect the DNA sensor cGAS

John Arnst
June 18, 2020

When a pathogen finds its way inside the human body, the innate immune system springs into action, thanks to pattern-recognition receptors that pick up on molecular patterns associated with the pathogen’s genetic material and the damage that they cause. While one of these DNA sensors, cyclic GMP-AMP synthase, or cGAS, has been characterized in recent years as a key part of an immune signaling axis that upregulates the cytokine type I interferon, the role that factors including post-translational modifications play in its recruitment and activation have remained unclear.

To figure out how PTMs regulate cGAS, a laboratory at Princeton University led by Ileana Cristea has identified and functionally analyzed phosphorylations and acetylations of cGAS in various cell types. They published their findings in the journal Molecular & Cellular Proteomics.

“I am fascinated by our co-evolution with the diverse array of viral pathogens that are part of our ecosystem,” Cristea said. Her research involves the proteomics of host–virus interactions and has recently focused on understanding how proteins called DNA sensors distinguish between host DNA and viral DNA to induce immune signaling during infections with DNA viruses.

“A growing body of evidence points to post-translational modifications as modulators of DNA sensor functions,” Cristea said, “but this area of investigation is still in early stages, so we aimed to expand the understanding of the cGAS PTM landscape and of how these PTMs impact the ability of cGAS to induce immune responses and apoptosis.”

The researchers enriched cGAS by applying immunoaffinity purification to THP-1 macrophage-like cells, STING-HEK293T cells that had been immune-stimulated and human primary fibroblasts before and after the cells were infected with herpes simplex–type I virus, finding a total of six phosphorylations and eight acetylations. To assess the functional relevance of each of these PTMs, Cristea’s lab then generated a series of single-point cGAS mutations in stable cell lines constructed to express cGAS with amino acid substitutions that would either present phosphorylation and acetylation or that mimicked the modified states.

Herpes-simplex-virus-1-890x454.jpg
BERNARD HEYMANN /NIAMS & NIH
The image on the left is the outer protein shell of the herpes simplex virus type 1, the virus that causes cold sores. The image on the right is the mature capsid of the same virus, which Ileana Cristea and her colleagues at Princeton University have used to examine the effect of post-translational modifications on the DNA sensor cGAS.

They found that an acetyl-mimic mutation at Lys198, where lysine was swapped to glutamine, increased cGAS-dependent interferon signaling compared to a control, and they showed that two acetyl-mimic mutations at Lys384 and Lys414 can inhibit the ability of cGAS to induce apoptosis. The researchers also found, through parallel reaction–monitoring mass spectrometry, that acetylation of Lys198 decreases during infection with both HSV-1 and human cytomegalovirus, which highlights the residue as a regulatory point during virus infection.

“It was striking to find that cGAS is so richly modified,” said Bokai Song, the first author on the paper.  “Our findings add to growing evidence that PTMs on DNA sensors provide means through which host cells and viruses compete to regulate the functions of these important immune factors. Perhaps these PTMs also contribute to localization-dependent functions, but this remains to be discovered.”

Future work for the lab will involve investigating the functions and evolutionary role of different DNA sensors.

“This area of immunity has advanced significantly with the recent identification of different DNA sensors,” Cristea said. “Next we need to determine their unique and redundant functions and whether they evolved to recognize diverse pathogens in a biological state- or tissue-specific manner. This information is critical for understanding human immunity, autoimmune disorders and our ability to combat infections.”  

Enjoy reading ASBMB Today?

Become a member to receive the print edition monthly and the digital edition weekly.

Learn more
John Arnst

John Arnst was a science writer for ASBMB Today.

Get the latest from ASBMB Today

Enter your email address, and we’ll send you a weekly email with recent articles, interviews and more.

Latest in Science

Science highlights or most popular articles

A Nobel for biochemistry underlying COVID-19 vaccines
News

A Nobel for biochemistry underlying COVID-19 vaccines

Oct. 2, 2023

Katalin Karikó and Drew Weissman won the 2023 prize for medicine or physiology “for their discoveries concerning nucleoside base modifications that enabled the development of effective mRNA vaccines against COVID-19.”

Art imitates science
Announcement

Art imitates science

Oct. 2, 2023

Congratulations to the winners of the ASBMB's inaugural Molecular Motifs bioart competition.

Improvements in genome databases promising for cancer research
Journal News

Improvements in genome databases promising for cancer research

Oct. 1, 2023

Scientists expand the use of ribosome profiling, also known as Ribo-seq, to understand protein production in cells.

Flesh-eating bacteria infections are on the rise in the U.S.
News

Flesh-eating bacteria infections are on the rise in the U.S.

Sept. 30, 2023

ASBMB Today editorial advisory board chair Bill Sullivan explains how to protect yourself.

From the journals: JBC
Journal News

From the journals: JBC

Sept. 29, 2023

Creating the ideal PROTAC. A new player in mRNA polyadenylation. Improved inhibitors of human growth hormone signaling. Read about recent papers on these topics.

An unexpected component in retinal survival
Journal News

An unexpected component in retinal survival

Sept. 26, 2023

Researchers find that the lack of a specific membrane-linked receptor protein, PEDF-R, contributes to photoreceptor dysfunction.