Proteomic Pathway Analysis Reveals Inflammation Increases Myeloid-Derived Suppressor Cell Resistance to Apoptosis

Olesya Chornoguz,Lydia Grmai,Pratima Sinha,Konstantin A Artemenko,Roman A Zubarev,Suzanne Ostrand-Rosenberg

doi:10.1074/mcp.m110.002980

Abstract

Myeloid-derived suppressor cells (MDSC) accumulate in patients and animals with cancer where they mediate systemic immune suppression and obstruct immune-based cancer therapies. We have previously demonstrated that inflammation, which frequently accompanies tumor onset and progression, increases the rate of accumulation and the suppressive potency of MDSC. To determine how inflammation enhances MDSC levels and activity we used mass spectrometry to identify proteins produced by MDSC induced in highly inflammatory settings. Proteomic pathway analysis identified the Fas pathway and caspase network proteins, leading us to hypothesize that inflammation enhances MDSC accumulation by increasing MDSC resistance to Fas-mediated apoptosis. The MS findings were validated and extended by biological studies. Using activated caspase 3 and caspase 8 as indicators of apoptosis, flow cytometry, confocal microscopy, and Western blot analyses demonstrated that inflammation-induced MDSC treated with a Fas agonist contain lower levels of activated caspases, suggesting that inflammation enhances resistance to Fas-mediated apoptosis. Resistance to Fas-mediated apoptosis was confirmed by viability studies of MDSC treated with a Fas agonist. These results suggest that an inflammatory environment, which is frequently present in tumor-bearing individuals, protects MDSC against extrinsic-induced apoptosis resulting in MDSC with a longer in vivo half-life, and may explain why MDSC accumulate more rapidly and to higher levels in inflammatory settings.

Highlights

Immunotherapies aimed at activating the host’s immune system are promising strategies for the treatment of cancer because of their potential for minimal toxicity to healthy cells
Inflammation Increases Myeloid-derived suppressor cells (MDSC) Resistance to Apoptosis inoculated into the mammary fat pad of syngeneic BALB/c mice, wild type 4T1 and 4T1/IL-1␤ tumor cells form a primary tumor at the site of injection and spontaneously metastasize to the lungs, liver, brain, lymph nodes [16], and bone marrow [17]
MDSC Accumulate in Tumor-bearing Mice and Suppress T-cell Activation—BALB/c and TLR4Ϫ/Ϫ mice were inoculated in the mammary fat pad with 4T1 or 4T1/IL-1␤ cells on day 0 and bled on day 21–24 when primary and metastatic tumors were established (Fig. 1A)

Summary

Introduction

Immunotherapies aimed at activating the host’s immune system are promising strategies for the treatment of cancer because of their potential for minimal toxicity to healthy cells. We have used mass spectrometry based quantitative proteomic analysis followed by pathway analysis to identify activated pathways and proteins of inflammatory MDSC induced by 4T1/IL-1␤ tumor versus conventional MDSC induced by 4T1 tumor.

Results

Conclusion