HTLV-1 Tax Transcriptionally Activates HMGB1 and Links Glycolytic Reprogramming to Immune-Evasion Phenotypes in Adult T-Cell Leukemia/Lymphoma

Abstract

Background: Adult T-cell leukemia/lymphoma (ATLL) is a human T-cell leukemia virus type 1 (HTLV-1)-associated T-cell malignancy marked by metabolic remodeling and immune escape. Whether the viral transactivator Tax directly engages host transcriptional regulators that connect these processes remains unclear. Objectives: This study tested whether Tax transcriptionally activates high mobility group box 1 (HMGB1) and whether the Tax-HMGB1 axis is associated with glycolytic and immune-evasion phenotypes in ATLL. Methods: Public Gene Expression Omnibus (GEO) cohorts were analyzed within cohort after dataset-specific preprocessing, probe-to-gene collapsing, and standardized signature scoring. Patient-cohort findings were interpreted as associations, whereas mechanistic ordering was examined in a Tax-inducible T-cell model by HMGB1 promoter luciferase assays, chromatin immunoprecipitation quantitative polymerase chain reaction (ChIP-qPCR), small interfering RNA (siRNA) knockdown/rescue, extracellular acidification rate (ECAR), lactate and glucose-uptake assays, flow cytometry, and donor-matched cytotoxic co-culture. Results: In ATLL samples, HMGB1 expression and predefined glycolysis and immune-inhibitory signature scores were higher than in normal CD4+ T-cell controls. Within ATLL, HMGB1 expression was positively associated with both scores and with programmed death-ligand 1 (PD-L1; CD274). Tax induction in a switch model increased HMGB1 expression together with glycolytic and checkpoint-related programs. In mechanistic assays, Tax increased HMGB1 promoter activity and enriched the HMGB1 promoter interval -1163 to -975 in ChIP-qPCR, whereas mutation of a C/EBP-like motif blunted reporter responsiveness. HMGB1 knockdown reduced lactate, ECAR, glucose uptake, PD-L1 and Galectin-9 surface expression, and resistance to cytotoxic killing; HMGB1 re-expression partially restored metabolic output. Lactate inhibition and PD-L1 blockade each partially rescued cytotoxic killing in donor-matched co-cultures. Conclusions: The experimental data support direct transcriptional activation of HMGB1 by Tax and place HMGB1 upstream of a lactate-associated immune-evasion phenotype in ATLL models. The public patient datasets provide complementary associative support but do not by themselves establish causality or resolve contributions from extracellular HMGB1 and tumor microenvironmental composition.