Abstract 24P
Background
Tumor associated myeloid cells are major promoters of progression and metastasis. Monocytic and granulocytic myeloid-derived suppressor cells (M-MDSC and G-MDSC) together with tumor associated macrophages (TAM) are among the main contributors to tumor-induced immunosuppression. The influence of the tumor microenvironment on their differentiation is well-accepted but the specific molecular changes leading towards MDSC subsets and TAM are not well-characterized. Here, we describe the main differences between MDSC subsets and TAMs, focused on differential pathways by high-throughput proteomics.
Methods
We used an ex vivo differentiation system for MDSCs and TAM by modelling the tumor microenvironment from C57BL/6J mouse bone marrow cells in conditioning medium (1). We also differentiated resting macrophages (M0) as controls using standard techniques. Flow cytometry and microscopy confirmed their phenotype by assessing their morphology and presence of characteristic lineage markers. Three global experiment of mass spectrometry-based quantitative (shotgun) proteomics were performed. Construction of functional interactomes from up- or down-regulated proteins was conducted with the Ingenuity Pathway Analysis (IPA) Tool from Quiagen. Targeted proteins were evaluated using western blot. Bibliography: 1) Liechtenstein T, Perez-Janices N, Gato M, et al. Oncotarget. 2014;5(17):7843-7857.
Results
We observed morphological differences in ex vivo differentiated myeloid populations. High-throughput proteomics uncovered protein expression patterns characteristic of populations modelling tumor-infiltrating subsets, result of the tumor microenvironment pressure. MAPK1 was identified as upstream regulator using IPA tool. We identified upregulation of STAT3 phosphorylation in all tumor-associated subsets. Both TAM and MDSC have strongly upregulated phosphorylation on S727. Moreover, strong increase in STAT3 Y705 phosphorylation was observed in TAM versus both monocytic and granulocytic MDSC.
Conclusions
In the present study, we identified differences in proteomic signatures between myeloid cells modelling M-MDSCs, G-MDSC and TAMs related to lineage, and cancer-driven polarization.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.