Tumor-associated macrophages (TAMs) are a major component of innate immunity supporting primary tumor growth and metastasis. Chemotherapy is one of the main treatment strategies for solid tumors, while chemoresistance is the major limitation of the chemotherapy for patients with various types of cancer. A number of evidence indicate that TAMs can accumulate in tumors after chemotherapy and contribute to chemoresistance.
For the endocytic uptake of EGF we used flow cytometry analysis. Confocal microscopy was used for the analysis of stabilin-1-mediated internalization and endocytic trafficking of EGF in CHO cells and in modeled TAMs differentiated in the presence of conditioned supernatants of breast cancer (MCF-7) and colorectal cancer (Colo206F) cell lines. We performed next-generation sequencing of RNA samples obtained from our modeled TAMs. Validation of sequencing data by real-time PCR was performed for selected genes implicated in the endocytic uptake: DNM3, STX8, DENND1A and EHD1.
For the first time we demonstrated that stabilin-1 ectopically expressed in CHO cells mediates endocytic uptake of EGF, key growth factor stimulating progression of breast and colorectal cancer. In the model of primary human TAMs, we have demonstrated that cisplatin decreases stabilin-1-mediated internalization and endocytic trafficking of EGF, without affecting gene expression of scavenger receptor stabilin-1. Molecular mechanisms of cisplatin effect on TAMs were uncovered using high throughput RNA sequencing. Gene set enrichment analysis identified that cisplatin contributes to defects in endocyting machinery reducing membrane biogenesis and vesicular transport. Significant suppression of DNM3, STX8, DENND1A and EHD1 genes expression by cisplatin was confirmed by RT-PCR.
We suggested that suppression of receptor-mediated clearance of tumor-supportive factors, such as EGF, by chemotherapeutic drugs may potentially lead to the tumor progression and/or relapse as a mechanism of macrophage-mediated chemoresistance. This study was supported by grand RSF №19-15-00151.
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National Research Tomsk State University.
All authors have declared no conflicts of interest.