GNAS knockout potentiates HDAC3 inhibition through viral mimicry-related interferon responses in lymphoma

In cancer research, the quest to understand and overcome treatment resistance is a perpetual journey1. Our new study, recently published in Leukemia, investigates the intricate mechanisms by which GNAS knockout (KO) sensitizes resistant lymphoma cells to HDAC3 inhibition2. This discovery not only sheds light on potential new clinical applications but also uncovers unexpected biological interactions that could optimize lymphoma treatment strategies.
The Challenge of HDAC3 Inhibition in CREBBP Wild-Type Tumors
Histone deacetylase 3 (HDAC3) inhibitors have shown promise in treating lymphomas, particularly those with CREBBP mutations3. However, the resistance exhibited by CREBBP wild-type tumors limits the clinical potential of HDAC3 inhibitors. It is therefore important to define strategies for overcoming this resistance to enhance the efficacy of HDAC3 inhibition across a wider range of lymphoma cases.
Uncovering the Novel Roles of GNAS in Lymphoma
Through unbiased genome-wide CRISPR screening, we identified GNAS KO as a sensitizer of resistant lymphoma cells to HDAC3 inhibition. GNAS, a gene encoding the G-protein α subunit, typically activates the cyclic AMP signaling. Interestingly, our findings indicate that the sensitizing effect of GNAS KO is independent of the canonical G-protein activities, suggesting novel functions of GNAS in lymphoma other than its GTPase activity.
Viral Mimicry and Interferon Responses: An Unexpected Mechanism
What sets our study apart is the discovery that GNAS KO-induced sensitization is mediated by viral mimicry-related interferon (IFN) responses, validated by functional rescue experiments for a causal rather than merely correlative relationship. This phenotype is characterized by the activation of TBK1 and IRF3, double-stranded RNA formation, and the expression of transposable elements (TEs). Essentially, GNAS KO plus HDAC3 inhibition triggers a cellular state that mimics a viral infection, leading to activated anti-viral IFN signaling. The induced IFN responses create a cellular environment that disrupts the tumor’s resistance mechanisms, allowing HDAC3 inhibitors to exert their therapeutic effects more effectively.

Proposed model: GNAS KO sensitizes resistant DLBCL cells to HDAC3 inhibition via viral mimicry-related IFN receptor signaling. GNAS KO plus HDAC3 inhibition upregulates transposable element expression which results in the formation of double-stranded RNA (dsRNA) or cytosolic DNA. These cytosolic nucleic acids are detected by the RNA or DNA sensors to activate MAVS or STING, respectively. Consequently, a phosphorylation cascade involving TBK1 and IRF3 is initiated, further leading to the activated IFN receptor signaling through JAK and STAT to induce sensitization. IFN, interferon; LINE, long interspersed nuclear elements; LTR, long-terminal repeat; P, phosphorylation; SINE, short interspersed nuclear element. 
Enhancing Immune-Mediated Cytotoxicity
Our research further demonstrates that GNAS KO synergizes with HDAC3 inhibition to boost CD8+ T cell-induced cytotoxicity. This synergistic effect extends the anti-tumor effects by GNAS KO and HDAC3 inhibition from cell-intrinsic IFN responses to immune interactions, suggesting the potential to enhance the body’s anti-tumor immunity and concurrent immunotherapy.
Clinical Implications and Biomarker Potential
Beyond the laboratory, our findings have potential clinical implications. In human lymphoma patients, we observed that low GNAS expression correlates with high baseline TE expression and upregulated IFN signaling, indicating a viral mimicry-primed condition. Strikingly, the tumor samples from two independent lymphoma patient cohorts (n > 800 in total) exhibit similar disrupted biological activities as those seen in our GNAS KO cell-line models, particularly in histone modification, mRNA processing, and transcriptional regulation, providing potential biological insights into how GNAS induces viral mimicry and interacts with HDAC3 inhibition. 
This correlation suggests that low GNAS expression could serve as a biomarker for identifying patients who might benefit from HDAC3 inhibition. By leveraging this biomarker, clinicians could better tailor treatments to individual patients, improving outcomes for those with resistant lymphomas.
A New Perspective in Lymphoma Treatment
Our study establishes an unprecedented link between HDAC3 inhibition and viral mimicry in lymphoma. This connection not only enhances our understanding of the underlying biology but also opens up new avenues for therapeutic intervention. By targeting the viral mimicry-related pathways induced by GNAS KO or integrating GNAS PROTAC degraders instead of inhibitors, we can potentially overcome resistance to HDAC3 inhibitors and provide more effective treatment options for lymphoma patients.
For those interested in the detailed findings and implications of our study, we invite you to read our full paper titled “GNAS knockout potentiates HDAC3 inhibition through viral mimicry-related interferon responses in lymphoma” in Leukemia. 

Study summary. GNAS knockout sensitizes resistant diffuse large B-cell lymphoma (DLBCL) cells to HDAC3 inhibition by inducing cell-intrinsic anti-tumor effects via viral mimicry-related interferon responses and potentiating CD8+ T-cell-induced cytotoxicity. In DLBCL patients, low GNAS expression (“GNAS low”) is associated with viral mimicry priming characterized by high baseline transposable element expression and a pro-interferon state, which is proposed to enhance epigenetic therapy. GNAS low DLBCL samples share commonly disrupted signaling pathways in histone modification, mRNA processing, and transcriptional regulation with GNAS knockout DLBCL cells, further indicating novel functions of GNAS in lymphoma.
References
1. He MY, Kridel R. Treatment resistance in diffuse large B-cell lymphoma. Leukemia. 2021;35:2151–65.
2. He MY, Tong KI, Liu T, Whittaker Hawkins R, Shelton V, Zeng Y, et al. GNAS knockout potentiates HDAC3 inhibition through viral mimicry-related interferon responses in lymphoma. Leukemia. 2024.

3. Mondello P, Tadros S, Teater M, Fontan L, Chang AY, Jain N, et al. Selective inhibition of HDAC3 targets synthetic vulnerabilities and activates immune surveillance in lymphoma. Cancer Discov. 2020;10:440–59.
Preparation of the figures was aided by BioRender.com.