IL-3/STAT5/miR-155-5p axis supports stem-related pathway reprogramming in TNBC

Background Triple negative breast cancer (TNBC) remains one of the most aggressive subtypes of cancer with a poor prognosis and limited treatment options. Building on our previous findings of elevated Interleukin-3-Receptor-alpha (IL-3R alpha) expression in TNBC, this study investigates the mechanisms underpinning IL-3-mediated actions in TNBC. Methods GEO database (GSE25066) was interrogated to evaluate the expression of IL-3. RNAseq data were acquired from the TCGA-BRCA (Breast Carcinoma) project. Seven TNBC cell lines were used to validate the expression of IL-3 by ELISA assay. Chromatin immunoprecipitation assay was performed to evaluate the binding of STAT5A to the miR-155-5p promoter in TNBC cells. FACS analysis and ALDH activity were performed to evaluate the expansion of ALDH-1A1 + and CD44(high)/CD24(low) subpopulations. Mammosphere formation efficiency (MFE) was evaluated using the standard assay, while chemoresistance by applying the incucyte cell viability assay. miR155-5p silencing served to validate the expression of all target proteins both in vitro and in vivo. Results Bioinformatic analysis of breast cancer patient gene datasets revealed significant upregulation of the IL-3 gene in TNBC patient samples compared to the non-TNBC group (GEO: p = 0.004: TCGA p = 2.7e-30 respectively). We also found that TNBC cells secrete IL-3, which activates STAT5A promoting miR-155-5p expression by binding to its promoter in TNBC cells. Correlation analysis based on TCGA-BRCA confirmed elevated miR-155-5p levels in TNBC compared to non-tumoral tissues (p = 2.1e-33) and non-TNBC (p = 6.5e-30), with positive correlations between the IL-3 and miR-155-5p (r = 0.157, p < 0.001), as well as between miR-155-5p and miR-155-3p and STAT5A (r = 0.250, p = 0.002; r = 0.245, p < 0.005 respectively). Functional studies demonstrated that miR-155-5p downregulates programmed cell death 4, APC, and GSK-3 beta, enhancing beta-catenin nuclear translocation and c-myc expression. Silencing miR-155-5p reversed all these effects. IL-3, via miR-155-5p, also drives ALDH-1A1 + and CD44(high)/CD24(low) subpopulation expansion and ALDH activity, enhances MFE and chemoresistance. Notably, blocking IL-3 impaired MFE, suggesting an autocrine loop sustaining IL-3 action in TNBC. In vivo, IL-3 promoted tumour growth, beta-catenin activity, and metastasis, while miR-155-5p silencing mitigated these effects. Conclusions Overall, our results underscore the crucial role of IL-3 in tumour progression, thereby advocating IL-3/IL-3R alpha axis targeting as a promising therapeutic approach for TNBC.