The N-terminal domain of precursor IL-1α enhances IL-6 expression via an intracrine mechanism in oral squamous cell carcinoma

Introduction: Interleukin-1α (IL-1α) is a pleiotropic cytokine that functions both extracellularly and intracellularly; however, the mechanisms by which precursor IL-1α (pIL-1α) contributes to cytokine regulation in oral squamous cell carcinoma (OSCC) remain unclear. Methods: To elucidate the intracellular role of pIL-1α, IL-1α knockout (KO) cells (designated α7) were established from HSC-3 OSCC cells. Reconstitution experiments were performed using constructs expressing pIL-1α, mature IL-1α (mIL-1α), or an N-terminal propiece (ppIL-1α). The Δ nuclear localization sequence (NLS) mutant was used to evaluate the functional relevance of nuclear localization. Results: α7 cells exhibited significantly diminished secretion of IL-6, IL-8, and IL-1β relative to the parental cells. Reexpression of full-length pIL-1α selectively restored IL-6 expression, whereas neither mIL-1α nor ppIL-1α alone had this effect. The ΔNLS mutant was retained in the cytoplasm and failed to upregulate IL-6, indicating its necessity for its nuclear localization. Exogenous recombinant IL-1α did not induce IL-6 expression in HSC-3 cells, suggesting a receptor-independent regulation. Conclusion: These findings delineate a non-canonical intracrine mechanism by which pIL-1α, via its N-terminal NLS-containing domain, translocates to the nucleus and regulates IL-6 gene expression independent of IL-1 receptor signaling. This study provides new insights into the intracellular functions of IL-1α in inflammatory and tumorigenic processes and suggests potential therapeutic avenues targeting its nuclear trafficking.