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. 2021 Apr 12;39(4):480-493.e6.
doi: 10.1016/j.ccell.2020.12.023. Epub 2021 Jan 28.

Stanniocalcin 1 is a phagocytosis checkpoint driving tumor immune resistance

Affiliations

Stanniocalcin 1 is a phagocytosis checkpoint driving tumor immune resistance

Heng Lin et al. Cancer Cell. .

Abstract

Immunotherapy induces durable clinical responses in a fraction of patients with cancer. However, therapeutic resistance poses a major challenge to current immunotherapies. Here, we identify that expression of tumor stanniocalcin 1 (STC1) correlates with immunotherapy efficacy and is negatively associated with patient survival across diverse cancer types. Gain- and loss-of-function experiments demonstrate that tumor STC1 supports tumor progression and enables tumor resistance to checkpoint blockade in murine tumor models. Mechanistically, tumor STC1 interacts with calreticulin (CRT), an "eat-me" signal, and minimizes CRT membrane exposure, thereby abrogating membrane CRT-directed phagocytosis by antigen-presenting cells (APCs), including macrophages and dendritic cells. Consequently, this impairs APC capacity of antigen presentation and T cell activation. Thus, tumor STC1 inhibits APC phagocytosis and contributes to tumor immune evasion and immunotherapy resistance. We suggest that STC1 is a previously unappreciated phagocytosis checkpoint and targeting STC1 and its interaction with CRT may sensitize to cancer immunotherapy.

Keywords: PD-1; T cell immunity; calreticulin; checkpoint; dendritic cell; eat-me signal; macrophages; phagocytosis; stanniocalcin 1; tumor.

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Conflict of interest statement

Declaration of interests The authors declare no conflict of interest.

Figures

Figure 1.
Figure 1.. STC1 correlates to cancer resistance to immunotherapy
(A) Transcriptome analysis in patients treated with checkpoint blockade. Upregulated genes in non-responders treated with checkpoint blockade were determined in cohorts 1 (Hugo et al., 2016) and 2 (Riaz et al., 2017). The overlapping upregulated genes in 2 cohorts are shown. Cohort 1, n = 15 (responders), 13 (non-responders); Cohort 2, n = 26 (responders), 25 (non-responders). (B-C) Expression of STC1 transcripts in Responders (R) and Non-Responders (NR) in cohort 1 (B) n = 14 (R), 13 (NR), p = 0.0287; and cohort 2 (C) n = 26 (R), 25 (NR), p = 0.0301. The dash line represents the median value, the bottom and top of the boxes are the 25th and 75th percentiles (interquartile range). Whiskers encompass 1.5 times the inter-quartile range. (D) Association of STC1 expression levels with cancer patient survival analyzed on combined cohorts 1 and 2, STC1 high (n = 22) and low (n = 27) expression, p = 0.0385. (E-G) Relationship of STC1 expression with cancer patient survival in 18 cancer types in TCGA data set. Results are shown as individual cancer survival curves with top 15% high and low STC1 expression (E); living status (F) Forest plot represents the adjust value of Cox proportional hazard ratio (HR) and 95% confidential interval (CI) of overall survival; and p-values (G) (STAD n = 56, p = 0.00475; HNSC n = 74, p = 0.00272; KIRP n = 42, p= 0.00698; LUAD n = 73, p = 0.0145; CESC n = 39, p = 0.00762; LGG n = 76, p = 0.00521; GBM n = 22, p = 0.00421; BLCA n = 60, p= 0.000765) See also Figure S1.
Figure 2.
Figure 2.. Tumor STC1 is critical for intrinsic resistance to tumor immunity
(A-B) Tumor growth curves of control MC38 and Stc1OE MC38 in (A) C57BL/6J mice and (B) NSG mice (n = 8). (C-F) Tumor growth curves of Stc1+/+ and Stc1−/− LLC, and Stc1+/+ and Stc1−/− B16-F10 in (C, D) C57BL/6J mice and (E, F) NSG mice (n = 5–8). (G-H) Tumor growth curves of control LLC and shStc1 LLC in (G) C57BL/6J mice and (H) NSG mice (n = 4–5). (I) Tumor growth curves of Stc1+/+ and Stc1−/− LLC tumors in (I) C57BL/6J mice with anti-PD-L1 or isotype control antibodies treatments every 3 days starting day 3 (n = 4–7). Data are shown as mean ± SEM, 2 tail t-test was used for two-way comparisons (A-I) (*p < 0.05, **p < 0.01). See also Figure S2.
Figure 3.
Figure 3.. Tumor STC1 impairs anti-tumor CD8+ T cell responses
(A-B) Percentages of Ki67+CD8+ T cells in tumor drained lymph nodes (TdLNs) and tumor tissues in mice bearing Stc1+/+ and Stc1−/− LLC tumors determined by FACS. (C-F) Percentages of IFNγ+, granzyme B+, and TNFα+CD8+ T cells in Stc1+/+ and Stc1−/− LLC tumor tissues (C, D) and B16-F10 tumor tissues (E, F) determined by FACS. (G-H) Percentages of IFNγ+ and TNFα+ CD8 T cells in control and Stc1OE B16-F10 tumor tissues determined by FACS. Data are shown as mean ± SEM, 2 tail T-test was used for two-way comparisons (n = 4–5, *p < 0.05; **p<0.01) (A-H). See also Figure S3.
Figure 4.
Figure 4.. STC1 abrogates tumor immunogenicity via targeting APCs
(A-L) Effect of Stc1 on OT-I cell activation in vitro. Stc1+/+ or Stc1−/− LLC cells were loaded with OVA and killed with UV-irradiation. CFSE-labeled OT-I cells were cultured with different numbers of dead LLC cells in the presence of macrophages (A-F) or DCs (G-L) for 3 days. CSFE dilution (A-B; G-H), IFNγ+ (C-D; I-J), and granzyme B+ (E-F; K-L) OT-I cells determined by FACS. Data are presented as mean ± SEM, 2 tail T-test was used for two-way comparisons (n = 3–5, *p < 0.05, **p < 0.01). (M-O) Effect of Stc1 on OT-I cell activation in vivo. B16-F10 tumor bearing mice initially received intratumoral injection of dead tumor cells from OVA loaded-B16-F10 cells and OVA loaded-Stc1OE-B16-F10 cells, and were subsequently intravenously transfused with CSFE labeled OT-I cells (M). CFSE dilution and OT-I cell divisions in TdLNs (N, O) were determined by FACS. Data are presented as mean ± SEM, 2 tail T-test was used for two-way comparisons (n = 3, *p < 0.05). (P-S) Effect of APCs on tumor growth curves. Stc1+/+ and Stc1−/− LLC cells were inoculated into Batf3+/+ or Batf3−/− mice. Starting 3 days before tumor inoculation, anti-CSF1R or isotype control antibodies were given every 3 days (n = 8). Data are shown as mean ± SEM, 2 tail t-test was used for two-way comparisons (P-R) (*p < 0.05, **p < 0.01). (T) Percentages of Ki67+ and granzyme B+ CD8+ T cells in Stc1+/+ and Stc1−/− LLC tumor tissues from wild type or Batf3/− mice under anti-CSF1R or isotype control antibody treatment (***p < 0.001, Stc1+/+ vs. Stc1−/− LLC tumor; p < 0.05, wild type vs Batf3−/− mice; p < 0.001, anti-CSF1R vs. isotype control antibodies). See also Figure S4.
Figure 5.
Figure 5.. Tumor STC1 traps CRT to inhibit macrophage function
(A) Effect of Stc1 on macrophage-mediated phagocytosis. Macrophages were incubated with dead cells from fluor-647 labeled B16-F10 cells and fluor-647 labeled Stc1OE B16-F10 cells. Mean fluorescence intensity (MFI) of fluorescence 647 in macrophages, gated on CD11b+ cells, determined by FACS. Data are presented as mean ± SEM, 2 tail T-test was used for two-way comparisons (n = 6, *p < 0.05, **p < 0.01). (B-C) Effect of Stc1 on macrophage-mediated bead up-taking. Macrophages were incubated with dead cells from B16-F10 cells and Stc1OE B16-F10 cells (B) or Stc1+/+ and Stc1+/+ LLC cells (C) for 20 hours. pHrodo-SE labeled 3 μm latex beads were added for 1 hour. Red pHrodo signals in macrophages were determined by FACS. Data are shown as mean ± SEM (n = 4, *p < 0.05, **p < 0.01). (D) Effect of Stc1 on antigen presentation. Macrophages were incubated with dead cells from OVA-loaded B16-F10 cells (control) and OVA-loaded Stc1OE B16-F10 cells for 48 hours. Surface OVA-binding-H2b complex expression (MFI) in macrophages were determined by FACS (n = 3, **p < 0.01). (E) Mass spectrum showing STC1 interactive proteins. FLAG-IP was conducted in dead cells from STC1-FLAG expressing B16-F10 cells. Mass spectrum was subsequently performed in the FLAG-IP proteins. Control, cell lysates from B16-F10 cells without STC1-FLAG. Top 5 hits are shown. (F) Interaction between endogenous CRT and STC1. Co-IP of STC1-FLAG was conducted with endogenous CRT, ERp57, and IRE1α in B16-F10 cells. One of 2 representative experiments is shown. (G) Interaction between exogenous CRT and STC1. Co-IPs of CRT-FLAG with STC1-GFP and ERp57 were performed in cell lysates from UV-treated or non-treated B16-F10 cells. One of 2 representative experiments is shown. (H) Duo-link showing the interactions (Red) of CRT and STC1-GFP, co-localizing with mito-tracker (white) in B16-F10 cells transfected with GFP or STC1-GFP with or without UV-treatment. Scale bars: 10 μm. Duo-link dots per cell merged or unmerged with mito-tracker were counted from over 20 images, mean ± SEM (n = 20, ***p < 0.001, STC1-GFP vs. GFP; # p <0.05, UV vs. No UV treatment). (I) Membrane CRT in B16-F10 cells. UV-treated B16-F10 and Stc1OE B16-F10 cells were labeled with biotin. Western blot showed cell membrane CRT and Na+, K+-ATPase α1 in biotin-labeled proteins. One of 2 representative experiments is shown. (J) Membrane CRT in UV-treated Stc1+/+ and Stc1−/− LLC cells. Confocal images showed membrane CRT expression. Scale bars: 10 μm. The intensity of CRT expression was analyzed through ImageJ software. Data are shown as mean ± SEM (n = 12, **p < 0.01). (K) Western blots showing CRT distribution in mitochondria (TOM20) and cytosol (GAPDH) from UV-treated B16-F10 cells and Stc1OE B16-F10 cells. Mito, mitochondria; Cyto, cytosol. One of 2 experiments is shown. (L-M) Effect of Stc1 on T cell activation in the context of Calr. Calr+/+ or Calr−/− vehicle control and Stc1OE B16-F10 cells were loaded with OVA and killed by UV-irradiation. CFSE-labeled OT-I cells were cultured with different numbers of dead B16-F10 cells with macrophages for 3–4 days. CSFE dilution (L), and granzyme B+ and IFNγ+ (M) OT-I cells were determined by FACS. Data are presented as mean ± SEM, 2 tail T-test was used for two-way comparisons (n = 3–5, **p < 0.01). See also Figure S5.

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