Background Early-stage myeloid-derived suppressor cells (eMDSCs) are a newly defined subset of myeloid-derived suppressor cells (MDSCs) that accumulate densely in tumors and potently promote tumor growth and metastasis by suppressing antitumor immune responses in vitro and in vivo. We previously identified a subset of eMDSCs in human breast cancer with a characteristic phenotype of Lin-HLA-DR-CD33+. We also found that SOCS3 deficiency and sustained activation of the JAK/STAT signaling pathway are critical molecular events coordinating the differentiation of eMDSCs, although the distinct molecular regulation has not been fully elucidated.
Methods Herein, we genetically constructed conditional SOCS3 knockout mice with SOCS3 deficiency specifically in the myeloid linage (SOCS3MyeKO). We analyzed the number of eMDSCs in SOCS3MyeKO mice (eMDSCsSOCS3KO). To explore which pathways participated in dysfunctional eMDSC differentiation, we performed whole-genome RNA sequencing and miRNA microarray on CD11b+Gr-1+ cells, eMDSCsfl/fl and eMDSCsSOCS3KO to screen the potential regulatory ceRNA network in eMDSCsSOCS3KO. CD11b+Gr-1+ cells isolated from SOCS3fl/fl mouse spleens were used as mature myeloid cell controls. Furthermore, we applied a specific miR-155 antagonist and the autophagy agonist rapamycin to suppress tumor growth and eMDSC infiltration.
Results The transcriptome results and corresponding intervention experiment revealed that the differentiation block in eMDSCsSOCS3KO was caused by SOCS3 deficiency-mediated limited autophagy activation in an AMPK-independent manner. The results of miRNA microarray and RNA sequencing demonstrated that miR-155 overexpression and Wnt/ß-catenin pathway activation were involved in the SOCS3 knockout-mediated myeloid differentiation block and autophagy repression. Further experiments revealed that miR-155 was induced by activation of the STAT3/NK-?B pathway upon SOCS3 deficiency, which consequently activated the Wnt/ß-catenin pathway via targeting C/EBPß. Furthermore, applying a specific miR-155 antagonist or the autophagy agonist rapamycin efficiently suppressed tumor growth and eMDSC infiltration in vivo.
Conclusions Overall, these findings indicated that SOCS3 deficiency blocked autophagy-dependent myeloid differentiation of e-MDSCs via the miR-155/C/EBPß/Wnt axis, and thus targeted therapy against this pathway could be a potential therapeutic target in breast cancer.
This is an open access article distributed in accordance with the Creative Commons Attribution 4.0 Unported (CC BY 4.0) license, which permits others to copy, redistribute, remix, transform and build upon this work for any purpose, provided the original work is properly cited, a link to the licence is given, and indication of whether changes were made. See: https://creativecommons.org/licenses/by/4.0/.