Endothelial SMAD1-MCAM axis facilitates sunitinib resistance and progression of clear cell renal cell carcinoma via LAMB1-ITGB1 signaling.

Clear cell renal cell carcinoma (ccRCC) is characterized by high metastatic potential and frequent resistance to conventional therapies, highlighting the need for a deeper understanding of its tumor microenvironment. Here, we integrated single-cell RNA sequencing and spatial transcriptomics from large ccRCC cohorts to map the cellular landscape of ccRCC. We identified a distinct stromal cell subpopulation, Melanoma Cell Adhesion Molecule, MCAM+ endothelial cells (MCAM+ ECs), which spatially associates with EMT-like tumor cells and promotes disease progression. Mechanistically, our findings suggest that MCAM+ ECs facilitate metastatic features via a LAMB1-ITGB1-RhoA signaling axis, contributing to epithelial-mesenchymal transition (EMT) and extracellular matrix remodeling. Furthermore, transcriptional analysis and experimental validation revealed that SMAD1 acts as a pivotal regulator of MCAM+ EC reprogramming by modulating MCAM and LAMB1 expression. To assess clinical relevance, we applied an integrative machine learning framework to develop an MCAM+ EC-based Risk Score (MERS). This model effectively stratified patients by overall survival and metastatic risk, demonstrating superior prognostic accuracy compared to standard clinicopathological features. Collectively, our study elucidates a critical tumor-stroma crosstalk mechanism governed by the SMAD1-MCAM-LAMB1-ITGB1-RhoA axis, providing novel mechanistic insights into the metastatic process and identifying potential candidates for therapeutic intervention in ccRCC.