STAT1β modulates the tumor immune microenvironment to improve prognosis in ovarian cancer: a comprehensive study of transcriptional and protein expression differences.

OBJECTIVES: As a central regulator of the JAK/STAT signaling pathway, STAT1 generates functionally distinct α and β protein isoforms through alternative splicing. We systematically investigated the expression patterns and prognostic relevance of STAT1 isoform-specific transcripts across pan-cancer tissues, with a particular focus on ovarian cancer (OV), and elucidated their potential mechanisms in modulating the tumor immune microenvironment (TIME) to influence patient prognosis. METHODS: Integrated analysis of the GTEx and TCGA databases was conducted to systematically evaluate the transcript expression profiles of STAT1 isoforms across 32 cancer types and 29 normal tissues. Clinical prognostic significance was analyzed using Cox proportional hazards regression models, complemented by multi-omics approaches including functional enrichment analysis, Tumor immune dysfunction and exclusion (TIDE) immune signature evaluation, and mediation effect models. At the experimental validation level, protein expression differences were assessed by Western blotting, while dynamic changes in immune cell infiltration were examined via immunohistochemistry (IHC) and multiplex immunofluorescence. RESULTS: In the GTEx/TCGA combined dataset, the transcriptional level of the STAT1α isoform was significantly higher than that of the β isoform in most tissues. However, Western blot revealed elevated expression of the STAT1β isoform in OV tissues and cell lines-a phenomenon that may reflect isoform-specific variations in mRNA translation efficiency and/or protein stability. IHC and multiplex immunofluorescence analyses demonstrated that STAT1 expression promoted CD8(+) T-cell infiltration, suppressed M2 tumor-associated macrophages (M2-TAMs), and remodeled the immune microenvironment. Multivariate Cox regression analysis identified the β isoform as an independent protective prognostic factor in OV (HR = 0.74, 95%CI: 0.55-0.99, p < 0.05), and correlation analysis with TIDE immune scores showed higher absolute correlation coefficients for STAT1β. Mediation analysis indicated that STAT1β improved prognosis by reducing T-cell dysfunction (mediation: 26.53%) and inhibiting M2-TAMs infiltration (mediation: 48.07%). These effects may stem from underlying molecular mechanisms involving modulation of PD-L1/PD-1 signaling and transcriptional interference with CSF1-dependent differentiation signals. CONCLUSION: The STAT1β isoform plays a more critical role in OV progression and immunomodulation, with its prognostic protective effect closely linked to the regulation of the immune microenvironment. These findings underscore the functional heterogeneity of STAT1 isoforms and their distinct roles in tumor immunology. Future research should prioritize the development of subtype-specific diagnostic tools and targeted therapeutic strategies to advance the development of precision immunotherapies.