AtaGenix’s Custom Phospho-USP8 Antibody Advances MDA5 Homeostasis Research, Unveiling a Novel Target for Autoimmune Therapy

Research Background

Melanoma differentiation-associated protein 5 (MDA5) is a key intracellular RNA sensor that mediates type I interferon (IFN-I) production — a critical component of antiviral innate immunity. Dysregulation of MDA5 activity is implicated in autoimmune diseases including systemic lupus erythematosus and Aicardi–Goutières syndrome. A 2025 study published in Advanced Science (DOI: 10.1002/advs.202503865) revealed that AKT-mediated phosphorylation of the deubiquitinase USP8 at Ser718 promotes USP8 interaction with MDA5, stabilizing MDA5 protein levels and enhancing IFN-I signaling. This identified a previously unknown post-translational regulatory mechanism linking AKT signaling to innate immune activation.

Client Needs

The research team required: (1) a phospho-specific antibody capable of distinguishing USP8 phosphorylated at Ser718 from the unmodified form; (2) validated performance in Western Blot for quantitative detection of phosphorylation levels in HEK293T and THP1 cell models; (3) compatibility with Co-immunoprecipitation (Co-IP) assays to confirm AKT–USP8 physical interaction; and (4) batch-to-batch consistency to ensure reproducibility across multiple experimental stages of a long-term study.

Technical Challenges

Developing a phospho-specific antibody against USP8 Ser718 presented several difficulties:

• USP8 is a large protein (~130 kDa) with multiple serine residues — the antibody had to recognize phospho-Ser718 exclusively without cross-reacting with other phosphorylated serines or the unmodified Ser718 site.
• The antibody needed to work under both denaturing conditions (WB) and near-native conditions (Co-IP), requiring robust epitope recognition across different experimental contexts.
• AKT-mediated phosphorylation of USP8 is stimulus-dependent and transient — the antibody required high sensitivity to detect dynamic phosphorylation changes in response to viral infection or AKT activation.
• No commercial phospho-USP8(S718) antibody was available, making a custom solution the only path forward.

Customized Solutions

AtaGenix designed a targeted phospho-antibody workflow:

• Phospho-Peptide Immunogen Design: A phosphorylated peptide spanning the Ser718 site (Cys-REPSKLKRSYS(p)SPDI) was synthesized and conjugated to KLH for immunization. The corresponding non-phosphorylated peptide was synthesized in parallel for use in negative depletion during purification.
• Rabbit Immunization & Two-Round Purification: New Zealand rabbits were immunized with the phospho-peptide conjugate. Serum was subjected to two-round affinity purification: positive selection on the phospho-peptide column followed by negative depletion against the non-phosphorylated peptide, ensuring exclusive phospho-Ser718 specificity.
• Cell-Based Validation: The anti-phospho-USP8(S718) antibody was validated in HEK293T cells (overexpression system with AKT co-transfection) and THP1 cells (endogenous expression under viral stimulation). Both WB and Co-IP applications confirmed specific detection of the phosphorylated form with clean background.
• Full Protocol & QC Support: AtaGenix provided optimized protocols for WB dilution, Co-IP lysis buffer conditions, and phosphatase inhibitor recommendations, along with batch consistency QC data to support the multi-stage study.

Research Outcomes and Impact

The custom phospho-USP8(S718) antibody enabled the research team to demonstrate that AKT phosphorylates USP8 at Ser718, which in turn promotes USP8-mediated deubiquitination and stabilization of MDA5. This mechanism amplifies type I interferon production during viral infection. Critically, the study showed that dysregulation of this AKT–USP8–MDA5 axis contributes to autoimmune pathology, identifying USP8 Ser718 phosphorylation as a potential therapeutic target for autoimmune diseases driven by excessive IFN-I signaling. The findings were published in Advanced Science, a top-tier interdisciplinary journal.

Figure 1. AKT–USP8–MDA5 signaling axis. AKT-mediated phosphorylation of USP8 at Ser718 promotes USP8 interaction with MDA5, stabilizing MDA5 and enhancing type I interferon production during viral infection.

This case study is based on a published research collaboration. Results may vary depending on target protein, phosphorylation site, and experimental conditions. All proprietary client information is subject to NDA. Reference: Advanced Science. 2025. DOI: 10.1002/advs.202503865