Cell lines and reagents
Raw264.7 cells were cultured in complete DMEM (Gibco) medium. PY8119 cells were cultured in DMEM∶F12(1:1) (Gibco) supplemented with 10% FBS (Gibco). Macrophages were polarized in M1 macrophages with 100 ng/mL LPS (R&D Systems, USA) and 20 ng/mL IFN-γ (R&D Systems, USA); and macrophages were treated with 20 ng/mL IL-4 (R&D Systems, USA) to generate M2 macrophages.
Small interfering RNA (siRNA) (Invitrogen) for PGRN was transfected with R4000 (Engreen, China). Recombinant murine PGRN was purchased from RD (R&D Systems, USA). Stattic, LY294002 and U0126 were purchased from MCE (Shanghai, China).
Peritoneal macrophages isolation
Each mouse was injected intraperitoneally with 2 ml of 3% thioglycollate (Difco) on day 1. Mice were sacrificed 4 days after injection. Peritoneal macrophages were harvested from peritoneum, after being injected with 7ml cold PBS into peritoneal cavity. The peritoneal cells were centrifuged at 1500 RPM for 10 min then seeded into cell culture dishes. The suspension cells were discarded by washing with PBS after 2h. And the adherent cells were considered as peritoneal macrophages.
In vitro T cell activation assay and co-culture
Spleens were ground with syringes, washed with PBS, and then passed through 70 μm cell strainers to gain single-cell suspensions. Red blood cells were lysed by using Red Blood Cell Lysing Buffer (Biosharp, China). Splenocytes were further separated with mouse spleen lymphocyte separation solution (tbdscience, China) to obtain spleen lymphocytes. Obtained spleen lymphocytes were cultured in complete RPMI 1640 medium. For T-cell activation assays, anti-CD3e (5μg/ml; eBioscience) was pre-coated in 96 well plates overnight at 4°C. Subsequently anti-CD28 (1μg/ml; BD) was added to the plates.
For co-culture assay, peritoneal macrophages at indicated ratios were added to the medium after T cell activation. Moreover, cells were cocultured with or without neutralizing monoclonal antibodies against PD-L1, PD-1 or IgG isotype control (BioLegend). After 4 days, cells were detected by flow cytometry.
Immunohistochemistry
Sections from tumors were cut into 4 μm in thickness and deparaffinized in xylene for 10 min. The slides were immersed in 3% H2O2 for 20 min to block the endogenous peroxidase and were blocked in goat serum blocking solution for 30 min. After being incubated at 4 °C overnight with primary antibodies, the slides were incubated with secondary HRP-conjugated antibodies (Thermo Fisher Scientific) for 30 min at RT. The primary antibodies were as follows: F4/80 (Cell Signaling Technology), iNOS (Abcam), CD206 (proteintech), CD4 (Cell Signaling Technology), CD8 (Cell Signaling Technology), Granzyme B (NOVUS), and PD-1 (Abcam). IHC stainings were examined with microscopy.
Immunofluorescence
Slides from tumors were deparaffinized in xylene and dehydrated in graded ethanol solutions. The sections were blocked in goat serum blocking solution for 1h at room temperature. The slides were incubated overnight at 4 °C with the following antibodies for multicolor immunofluorescence staining: F4/80 (Cell Signaling Technology), PD-L1 (Abcam), CD206 (proteintech), Arg1 (Abcam), iNOS (Abcam), CD8 (Cell Signaling Technology), CD4 (Cell Signaling Technology), CK19 (Abcam), and PD-1 (Abcam). The next day, the slides were washed in PBS and stained with the secondary antibody for 1 h at room temperature. Multicolor immunofluorescence staining was detected with fluorescence microscope.
Western blot
The cells were lysed in RIPA lysis buffer (Beyotime, China) supplemented with protease inhibitors PMSF (Beyotime, China). Protein concentration were determined by using BCA protein assay kit (Beyotime, China). The primary antibodies included iNOS (Abcam), Arg1 (Abcam), PGRN (Abcam), PD-L1 (Abcam), STAT3 (Cell Signaling Technology), pSTAT3 (Cell Signaling Technology), AKT (Cell Signaling Technology), pAKT (Cell Signaling Technology), ERK1/2 (Cell Signaling Technology), pERK1/2 (Cell Signaling Technology), and β-actin (proteintech).
RNA extraction and real-time quantitative PCR
Total RNA was extracted with TRIzol reagent (TaKaRa, Japan), and cDNA was reverse transcribed subsequently with PrimeScript RT reagent kit (TaKaRa, Japan). qRT-PCR was then performed using a SYBR Premix Ex Taq II (TaKaRa, Japan) according to the manufacturer’s instructions. The sequences of primers were presented in Table 1.
Flow cytometry
The single-cell suspensions were first blocked with anti-CD16/32 (101302, BioLegend) for 10 min at 4 °C. Then the following antibodies were used: PE/Cy7-PD-L1, APC-CD206, PE-CD86, Brilliant Violet 421TM-CD86, APC-CD8a, PE-IFN-γ, PE-Ki-67, and PE-PD-1 from Biolegend.
Orthotopic breast tumor model
Wild-type (WT) C57BL/6 mice aged 6 to 8 weeks were obtained from Chongqing Medical University. PGRN knock out (KO) mice were a generous gift from Dr. Yibing Yin. A total of 5×106 PY8119 cells suspended in 100 μl of PBS were injected into the fourth right mammary fat pad of the mice. Tumor growth was evaluated by measuring tumor volume (TV=0.5×length×width2) every 3 days until they were sacrificed 3 weeks after treatment. Survival was determined by tumor size ≥1000 mm3 or animal death. All animal experiments were approved by the Institutional Animal Care and Use Committee of Chongqing Medical University.
Statistical analysis
Unpaired student t-test was used for mean difference comparison between two groups. One-way ANOVA followed by multiple comparison was used for multiple groups. All data were presented as mean±SEM or SD. P < 0.05 was considered as significant. All the experiments were performed independently for three times.