Tumor metastasis is a hallmark of colorectal cancer (CRC), in which exosome plays a crucial role with its function in intercellular communication. Plasma exosomes were collected from healthy control (HC) donors, localized primary CRC and liver-metastatic CRC patients. Researchers at Shandong University performed proximity barcoding assay (PBA) for single-exosome analysis, which enabled them to identify the alteration in exosome subpopulations associated with CRC progression. By in vitro and in vivo experiments, the biological impact of these subpopulations on cancer proliferation, migration, invasion, and metastasis was investigated. The potential application of exosomes as diagnostic biomarkers was evaluated in 2 independent validation cohorts by PBA. Twelve distinct exosome subpopulations were determined. The researchers found 2 distinctly abundant subpopulations: one ITGB3-positive and the other ITGAM-positive. The ITGB3-positive cluster is rich in liver-metastatic CRC, compared to both HC group and primary CRC group. On the contrary, ITGAM-positive exosomes show a large-scale increase in plasma of HC group, compared to both primary CRC and metastatic CRC groups. Notably, both discovery cohort and validation cohort verified ITGB3+ exosomes as potential diagnostic biomarker. ITGB3+ exosomes promote proliferation, migration, and invasion capability of CRC. In contrast, ITGAM+ exosomes suppress CRC development. Moreover, the researchers also provide evidence that one of the sources of ITGAM+ exosomes is macrophage. ITGB3+ exosomes and ITGAM+ exosomes are proven 2 potential diagnostic, prognostic, and therapeutic biomarkers for management of CRC.
ITGB3-rich exosomes promote migration and invasion of colon cancer cell lines
(A) Quantitative RT-PCR analysis of ITGB3 expression in Caco-2, HT29, HCT116, SW480, and SW620 cell lines. Relative mRNA levels were determined by normalization to the housekeeping gene GAPDH. (B) Quantitative RT-PCR analysis of ITGB3 expression in SW480 with (ITGB3 LV) or without (CON335), where data of CON335 served as a control after normalization to GAPDH. (C to E) NTA analysis, transmission electron microscopic image and immunoblot of ITGB3 expression of SW480-derived exosomes from (B). (F and H) Representative images of migration assay and invasion assay of HCT116 treated with SW480-derived exosomes from (B) with quantification. (G and I) Representative images of migration assay and invasion assay of SW480 treated with SW480-derived exosomes from (B) and quantifications. Statistical analyses were performed using the paired t test. Data were calculated as means ± SD from at least 3 independent experiments. ***P < 0.001; ****P < 0.0001.