Targeting engulfment and cell motility 1 protein methylation attenuates M2 macrophage infiltration and boosts anti-PD-1 efficacy in colorectal cancer
Guanman Li, Zexian Chen, Kai Wang, Junguo Chen, Xiao Yue, Tianze Huang, Bin Zhang, Danling Liu, Shuang Guo, Jiong Bi, Ping Lan, Xiaosheng HeAbstract
Background
Immunotherapy has been very successful in the field of cancer treatment. However, some patients exhibit unresponsive to PD-1 blockade, even for microsatellite instability-high (MSI-H) colorectal cancer (CRC).
Methods
Engulfment and cell motility 1 (ELMO1) expression and macrophage infiltration in clinical samples and mouse models were detected by using quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemistry staining. Western blotting, qRT-PCR, and enzyme-linked immunosorbent assay (ELISA) were used to evaluate ELMO1, C-C chemokine ligand 18 (CCL18), and transforming growth factor-β (TGF-β) expression in tumor cells. Macrophage phenotypes were determined using qRT-PCR, flow cytometry, and RNA sequencing. Tumor viability was investigated using XTT assays and foci formation assays.
Results
ELMO1 was significantly overexpressed in MSI-H CRC and associated with poor clinical outcomes. ELMO1 depletion suppressed the growth of MSI-H cancer cells but exerted minimal effects on microsatellite stable (MSS) CRC cells. Tumor cell-shed ELMO1 recruited M2 macrophages and facilitated M0-to-M2 polarization by signal transducer and activator of transcription 6 (STAT6) activation. Accumulated M2 macrophages further promoted the proliferation of ELMO1-positive tumor cells. Mechanistically, CCL18 secreted by M2 macrophages strengthened the binding between protein arginine methyltransferase 5 (PRMT5) and ELMO1. Pharmacological inhibition of PRMT5 reduced ELMO1 methylation, thereby decreasing the level of extracellular ELMO1. Moreover, PRMT5 blockade diminished M2 macrophage infiltration, inhibited tumor growth, and improved the responsiveness of ELMO1-overexpressing MSI-H CRC to anti-PD-1 immunotherapy.
Conclusions
Our findings demonstrate that ELMO1 acts as a novel biomarker to classify the MSI-H group into distinct subtypes and provides a promising therapeutic target for the treatment of ELMO1-overexpressing MSI-H CRC.