The CXCL12/CXCR4 axis in breast cancer-associated fibroblasts: a transcriptome analysis and systematic literature...

Cancer-associated fibroblasts (CAFs) represent a pivotal component of the breast cancer microenvironment. In a paracrine model, CAFs secreted the chemokine CXCL12 (SDF-1α), which bound to CXCR4 and activated the PI3K/AKT and MAPK signaling pathways, stimulating their migration and invasion. TGF-β1 induces myofibroblast differentiation of CAFs by acting through the TGFBR2/ALK5 receptor complex and phosphorylating SMAD2/3, thereby increasing the expression of ACTA2 and FAP. An autocrine loop has been demonstrated in CAF, whereby TGF-β1, via SMAD3, induces the transcription of CXCR4, and subsequently, CXCR4, by binding to the same cell, maintains the myofibroblast phenotype. However, a systematic comparison of paracrine and autocrine variants has not yet been conducted in the context of CAF subtypes.

A secondary analysis of 101 bulk RNA-seq samples was performed, with classification into healthNF, riskNF, cancerNF, and CAF S1-S4 using correlation analysis (Spearman), differential expression (DESeq, FDR <0.05), GSEA (FDR <0.25), and a systematic review of the literature (2005-2026).

The PCA and the contingency table analysis enabled the description of two patterns of Cancer-associated fibroblasts subtype distribution across clinical and morphological groups: healthNF → cancerNF → CAF and healthNF → riskNF → CAF. Elevated levels of CXCR4 were identified exclusively in CAF (22.7%, FDR = 5.98 × 10^-4) and were associated with the CAF-S3 and CAF-S4 fibroblast phenotypes. At CXCR4^High levels, the correlation between CXCL12 and TGFB1 became negative, while the correlation between CXCL12 and ITGAV, FAP, and ITGB1 remained positive. This finding suggests a possible shift from TGF-β-dependent to CXCR4-mediated regulation of CXCL12. GSEA revealed an association of CXCR4^High -CAF with enrichment of gene sets related to the interferon response, inflammation, and apoptosis, as well as with decreased enrichment of proliferation sets, EMT, and TGF-β signaling. A recent systematic review revealed that only 8.6% of publications contain experimental data supporting an autocrine loop, 17.1% describe a paracrine model, and 74.3% do not distinguish between the signaling types.

It is hypothesised that the CXCR4^High-CAF transcriptome profile is compatible with a biologically plausible theory of transition between paracrine and autocrine regulatory modes and inflammatory cell states. In vitro validation is a prerequisite for establishing a causal relationship.