Objective To investigate the expression characteristics of RAB1A in the breast tumor microenvironment (TME) and its mechanism of promoting tumor metastasis, with the aim of identifying potential targets for TME-targeted antimetastatic therapy.

Methods Proteomic sequencing was performed on tumor and adjacent tissues from 16 patients with triple-negative breast cancer (TNBC) or HER2-overexpressing breast cancer. Single-cell RNA sequencing was conducted on biopsy samples from four patients with TNBC or HER2-overexpressing breast cancer. TME cell heterogeneity and RAB1A expression patterns were analyzed at the proteomic and single-cell transcriptomic levels. ELISA and wound healing assays were utilized to verify the mechanism by which RAB1A regulates the function of cancer-associated fibroblasts (CAFs), thereby promoting the metastasis of TNBC cells.

Results RAB1A was specifically highly expressed in CAFs. Functional module analysis indicated an association with the prometastatic secretion pathway and matrix remodeling modules. Human mammary fibroblasts (HMFs), CAFs, and RAB1A-overexpressing CAFs (CAF-OE-RAB1A) were cocultured with MDA-MB-231 cells for 24 h. The wound healing assay revealed that after 24 h of coculture with MDA-MB-231 cells, the CAF coculture group exhibited a significantly higher migration rate (38.86%) than the negative control (25.07%, P<0.01) and HMF coculture groups (30.56%, P<0.05). Notably, the migration rate in the CAF-OE-RAB1A coculture group further enhanced to 47.21% relative to that in the CAF coculture group (P<0.05). Additionally, TGF-β1 secretion in the CAF-OE-RAB1A coculture group (1030.56 pg/ml) was markedly elevated relative to that in the CAF (417.62 pg/ml, P<0.001) and HMF coculture groups (29.52 pg/ml, P<0.0001).

Conclusion RAB1A is specifically highly expressed in CAFs within the breast cancer TME. It may be involved in the metastatic process of breast cancer. Furthermore, RAB1A can promote TNBC cell migration by regulating the secretory function of CAFs.