O-GlcNAcylation Induced HMGB1 Signaling as a Molecular Switch for Immune Escape in Esophageal Carcinoma

Esophageal squamous cell carcinoma (ESCC): Esophageal cancer ranks 4th in mortality rates in all cancer types in Mainland China [1], with the Greater Bay Area showing above-than-average mortality rates. The Chaoshan area in the Guangdong province shows one of the most significant incidence and mortality rates worldwide [2]. In Hong Kong, it is one of the top 10 deadliest cancer types (Hong Kong Cancer Registry Cancer Statistics of 2019). ESCC is the prevalent subtype of esophageal cancer in these areas and most parts of Asia. It is highly aggressive, with a dismal five-year survival rate of 10~20%. Chemoradiotherapy (CRT) and chemotherapy (CT) remain the Standard of Care (SOC) treatment regimens in addition to surgery [3]. In brief, after imaging, endoscopic examination, and patient assessment, ESCC patients may undergo esophagectomy, neoadjuvant CRT/CT followed by esophagectomy, or palliative CT without surgery.

However, ESCC often resists therapy. Resistance to death is a hallmark of cancer, contributing to progression and treatment failure. Damage-associated molecular patterns (DAMPs) released by stressed or dying cells play dual roles: they can stimulate antitumor immunity during immunogenic cell death, but also promote tumour growth by sustaining inflammation and impairing immune surveillance. Among DAMPs, high mobility group box 1 (HMGB1) is a key regulator of cancer-related inflammation and immuneescape1. HMGB1's function is compartment-specific: nuclear HMGB1 maintains genomic integrity, cytoplasmic HMGB1 promotes autophagy and survival, and extracellular HMGB1 activates pro-inflammatory signal via receptors such as RAGE and TLRs, leading to tumour cell survival, proliferation, and angiogenesis [4]. Elevated HMGB1 levels correlate with poor prognosis in multiple cancers [5-8]. Despite its clinical relevance, the mechanisms regulating HMGB1 localisation and activity remain poorly understood, positioning it as an underexplored molecular switch in tumour-immune dynamics.

OGlcNAcylation is a type of intracellular glycosylation- a nutrient-sensitive post-translational modification (PTM) that regulates protein function, stability, localisation and interactions with other cellular proteins. Catalyzed by O-GlcNAc transferase (OGT) and reversed by OGlcNAcase (OGA) [9], this modification affects thousands of intracellular proteins and is elevated across multiple cancer types. HMGB1 activity is tightly controlled by PTMs. These PTMs act like molecular switches, regulating its translocation and secretion. Under basal conditions, Beclin1-a key autophagy regulator- is sequestered by Bcl-2 and remains inactive. Under stress, HMGB1 translocates to the cytoplasm and binds to Beclin, displacing Bcl-2 and triggers autophagy [10]-a survival mechanism often hijacked by tumour cells. Recent studies show HMGB1 can be modified by O-GlcNAcylation [11] and O-GlcNAcylated at serine 100, weakens its DNA-binding and enhance oligomerisation [12], potentially stabilising it in the cytoplasm and reinforcing autophagy. This autophagy-promoting axis known to intersect with TBK1, a key kinase involved in stress response and immune pathways. Therefore, how does HMGB1 O-GlcNAcylation influence its subcellular localization, protein-protein interactions (interactome), and does this modulation associate with changes in immune cell positioning or clustering within ESCC tumours? Can these features serve as clinically relevant biomarkers or be leveraged for therapeutic targeting? Blood based biomarkers that mirror TME biology would be practical tools for recurrence prediction and disease monitoring in ESCC, complementing tissue based features is clinically needed. We aim to evaluate whether baseline and early on treatment plasma cytokine signatures can predict recurrence in ESCC patients and to determine how these circulating immune mediators correspond to spatially resolved TIME features.