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.”  

John Arnst

John Arnst is a science writer for ASBMB Today.

Join the ASBMB Today mailing list

Sign up to get updates on articles, interviews and events.

Latest in Science

Science highlights or most popular articles

Gut microbiome shaped by dietary sphingolipids
Journal News

Gut microbiome shaped by dietary sphingolipids

September 22, 2020

A new tracing method described in the Journal of Lipid Research offers clues on how a macronutrient interacts with the microbes that live inside us.

From the journals: JBC
Journal News

From the journals: JBC

September 21, 2020

Proteases that fire up the flu. A sulfate pocket to take out MRSA. Proteins that prompt cancer protrusions. Read about recent papers on these topics and more.

AeroNabs promise powerful, inhalable protection against COVID-19
News

AeroNabs promise powerful, inhalable protection against COVID-19

September 20, 2020

As the world awaits vaccines to bring the COVID-19 pandemic under control, UC San Francisco scientists have devised a novel approach to halting the spread of SARS-CoV-2, the virus that causes the disease.

Keeping bone and muscle strong on the ISS
News

Keeping bone and muscle strong on the ISS

September 19, 2020

Researchers helped mice stay mighty with an experiment to counter the effects of microgravity. The gene treatment might also enhance muscle and bone health on Earth — and in humans.

Understanding the impact of Type 1 diabetes susceptibility genes
Research Spotlight

Understanding the impact of Type 1 diabetes susceptibility genes

September 17, 2020

Starting in eighth grade, a series of mentors who saw something special in Sharifa Love–Rutledge helped her stay on the path to being a researcher — and becoming a mentor to others.

Re-creating coagulation in a lab
Journal News

Re-creating coagulation in a lab

September 15, 2020

Threatened arthropods are in the crossfire of medical and conservation efforts, but new research could benefit horseshoe crabs and humans alike.