STING causes replication stress and nascent DNA degradation via SAMHD1

Keywords

• STING

• Replication Stress

• SAMHD1

• Noncanonical interferon response

Main Findings

While STING is classically known as an ER-anchored adaptor in the innate immune response, this study investigates its role during replication stress and aging. In their previous paper, the authors contradicted the conventional dogma by showing that aging cells progressively lose their ability to activate the canonical cGAS-STING response to cytosolic DNA (PMID: 40638086), begging the question of what drives their inflammatory state. In this preprint, they find that during replication stress (induced by progerin, HU, or ssDNA), STING accumulates in the nucleus and on chromatin. In the nucleus, STING acts as a genotoxic agent; it binds to nascent DNA and recruits SAMHD1. This leads to a depletion of dNTP pools and facilitates the recruitment of the nuclease MRE11, which degrades nascent DNA and stalls replication forks. Ultimately, this STING-SAMHD1-MRE11 axis drives genomic instability and inflammation by stalling replication, inhibiting proliferation, and enhancing the expression of Interferon-Stimulated Genes (ISGs).

Limitations & Suggestions

I.  Key experiments to strengthen this study (immediate limitations):

• The nuclear localization and function of STING should be consolidated and further explored:

  •  The rim-like localization of STING observed by immunofluorescence needs further clarification to determine which compartment STING is linked to:

    • Suggestion: co-stain with other organelles and nuclear markers

  • Validate the specificity of STING antibody:

    • Suggestion: use STING KO cells and/or alternative antibodies

  • Is nuclear STING sufficient to induce replication stress?

    • Suggestion: force the nuclear translocation of STING by using an NLS-fused STING and monitor change on replication and dNTP levels.

  •  Confirm localisation of STING to replication fork by using another readout:

    • Suggestion: iPOND is considered the "gold standard" to prove that a specific protein is localized at active replication forks (detection by WB or MS). It allows to physically isolate the proteins associated with newly synthesized DNA.

• DNA metabolism link to STING: The claim that STING impairs DNA metabolism through dNTP depletion requires direct measurement.

  • Suggestion: measure the levels of dNTP in STING-depleted cells

• Scarce evidence for IFN signalling: Only three ISGs were used to represent IFN activation, and one (ISG15) did not change upon SAMHD1 depletion (Figure 4F), which contradicts the overall claim.

  • Suggestion: perform whole transcriptomics to better understand the ISG subsets involved and also analyse interferon genes expression (RNA and protein) to determine the autocrine/paracrine contributions to the IFN pathway in this context.

• SAMHD1 activation: The activation of SAMHD1 by nuclear STING is not directly assessed.

  • Suggestion: analyse SAMHD1 phosphorylation levels and test if a phospho-mimetic (inactive) form of SAMHD1 can reproduce the protective phenotype seen with si-SAMHD1.

II.  The outstanding questions (next steps?):

1. How does replicative stress drive the accumulation of STING into the nucleus?

2. How does nuclear STING activate SAMHD1?

3. What are the signalling events downstream of STING activation following replication stress that culminate in an inflammatory response?

Significance/Novelty

This preprint introduces a compelling conceptual shift, uncovering an unexpected, non-canonical role for STING as a nuclear genotoxic agent. This mechanism likely applies to a wide range of conditions beyond rare progeroid syndromes, including natural aging and chemotherapy response.

For general immunologists, this research matters because it identifies a specific STING-SAMHD1 axis that drives dNTP depletion, fuelling chronic inflammation and genomic instability independent of the traditional cytosolic DNA-sensing pathway. This opens the door to exploring STING biology more deeply and across different cellular contexts, which is fundamental both to our basic research quest of deciphering biological complexity and to the therapeutic perspective, where STING inhibitors are currently of high interest in oncology and immunological disorders.

Credit

Reviewed by Marie-Therese El-Daher as part of a cross-institutional journal club between the Max-Delbrück Center Berlin, the Ragon Institute Boston (Mass General, MIT, Harvard), the University of Virginia, the Medical University of Vienna and other life science institutes in Vienna.