High expression of TAM markers correlates with poor prognosis in ESCC patients

We evaluated the expression of the macrophage marker CD68 and the TAM marker CD204 in 117 ESCC tumors using an immunohistochemical (IHC) assay and found that these two markers were highly expressed in the stromal region (Fig. 1A). Importantly, increased levels of stromal CD68 and CD204 were most significantly associated with lymph node metastasis among the listed clinical parameters (Fig. 1B, C). Through Kaplan‒Meier analysis with the log-rank test, it was seen that high levels of stromal CD68 and CD204 were associated with poorer overall survival in ESCC patients (Fig. 1D, E).

Fig. 1

Immunohistochemical analysis of macrophages in clinical ESCC samples. A Representative IHC images of the expression of CD68 and CD204 in normal esophageal tissues or ESCC tissues with (LN+) or without (LN−) lymph node metastasis. B, C Percentages of ESCC patients with high expression of stromal CD68 (B) and CD204 (C) and low expression of stromal CD68 (B) and CD204 (C) according to different clinical parameters, as follows: tumor stage, tumor status and lymph node status. D, E Kaplan‒Meier curves of overall survival for ESCC patients stratified by low versus high expression of stromal CD68 (D) or stromal CD204 (E). Original magnification, ×5 or ×20

ESCC TAM-released CCL22 promotes tumor invasion

Cytokines are important mediators of the tumor-promoting functions of TAMs [4, 33, 34]. However, the secretion profile of cytokines in ESCC TAMs is still unclear. Thus, we performed an antibody array assay to screen a panel of cytokines in paired TAMs and peripheral blood monocytes (PBMs) isolated from the same patient with ESCC. Among the cytokines tested, CCL22 was the most abundantly expressed cytokine in TAMs compared with PBMs (Fig. 2A). Then, the secretion of selected cytokines, including CCL11, IL13, CCL2, CCL13, CCL22, CCL15, CXCL7, CCL5, TGF-β1, TNF-α, CXCL5, IL11, OPG, and HGF, in primary TAMs from human ESCC tissues (pri-TAMs), polarized TAMs (pol-TAMs) from human monocyte-derived macrophages (MDMs), and MDMs was evaluated using ELISAs. CCL22 was most evidently secreted from pri-TAMs and pol-TAMs but not MDMs (Fig. 2B). The IHC data showed that CCL22-positive TAMs were primarily distributed in regions surrounding tumor cells (Fig. 2C) and were most positively associated with lymph node metastasis among the various clinical parameters (Fig. 2D). Furthermore, CCL22 was colocalized with CD204 in the stromal region in ESCC samples (Fig. 2E). Kaplan‒Meier survival analysis indicated that patients with low numbers of CCL22 TAMs survived longer than those with high numbers of CCL22 TAMs (Fig. 2F). Multiplex staining of tissues from ESCC with lymph node metastasis showed the colocalization of CD204 and CCL22 in local tumors (Figure S1A-S1C). These data strongly suggest that CCL22 is produced and secreted by TAMs and might be a biomarker for evaluating ESCC progression.

Fig. 2

ESCC TAMs constitutively express CCL22. A The differential expression of cytokines in TAMs versus PBMs from the same ESCC patient, as evaluated by a cytokine antibody array assay. B The secretion of the indicated cytokines from MDMs, pol-TAMs, and pri-TAMs, as evaluated by ELISA. (C) Representative IHC images of the expression of CCL22 in normal esophageal tissues or ESCC tissues (LN+). D Percentages of ESCC patients with high expression of stromal CCL22 and low expression of stromal CCL22 according to different clinical parameters, as follows: tumor stage, tumor status and lymph node status. E Representative sequential IHC images of the expression of CD204 and CCL22 in ESCC tissues. Stromal CCL22 expression was positively associated with CD204 expression in 117 primary ESCC specimens. F Kaplan‒Meier curves of overall survival for ESCC patients stratified by low vs. high numbers of CCL22-positive TAMs. Original magnification, ×5, ×10 or ×20

A Transwell coculture system (8 μm pore size membranes) was applied to assess the invasion of ESCC cells by plating the indicated ESCC cells in the upper chamber and macrophages in the lower chamber. Coculture with pri-TAMs and pol-TAMs effectively induced the invasion of KYSE410 and KYSE510 cells compared with the invasion of these two ESCC cell lines cultured alone. However, little increase in invasion was observed in KYSE410 and KYSE510 cells cocultured with MDMs (Fig. 3A).

Fig. 3

TAM-derived CCL22 promotes the invasion of ESCC cells by inducing EMT and MMP secretion. A Boyden chamber assay of the indicated ESCC cells plated in the upper chambers of cell culture inserts, with culture medium alone, culture medium with MDMs, culture medium with pol-TAMs, or culture medium with pri-TAMs added to the lower chambers in the presence of the anti-CCL22 antibody (25 and 50 μg/ml) or the isotype-matched IgG control (IgG). ***P < 0.001 compared with cells incubated with medium alone; ###P < 0.001 compared with untreated cells cocultured with pol-TAMs or pri-TAMs. B Boyden chamber assay of the indicated ESCC cells, with culture medium containing rCCL22 at increasing concentrations (5, 25, and 50 ng/ml) added to the lower chambers. ***P < 0.001 compared with control cells. (C-D) KYSE410 and KYSE510 cells (lower chamber) were cocultured with control medium, MDMs, pol-TAMs, or pri-TAMs with or without the anti-CCL22 antibody (50 μg/ml) or CCL22 (50 ng/ml) (upper chamber) in a Transwell apparatus with a 0.4 μm pore size membrane for five days. C Morphologic changes in the indicated ESCC cells were evaluated using phase contrast microscopy. D Immunoblotting was used to evaluate the expression of E-cadherin, N-cadherin, and vimentin. GAPDH was used as the internal control. E–H After coculture with the indicated macrophages in a Transwell apparatus with a 0.4 μm pore size membrane for five days, macrophages cultured in the upper chamber were discarded, and the culture medium was replaced with fresh culture medium for 1 day. The concentrations of MMP2 (E), MMP3 (F), MMP9 (G), and MMP13 (H) in the CM of the indicated ESCC cells were measured using ELISA. ***P < 0.001 compared with control cells; ###P < 0.001 compared with untreated cells cocultured with pol-TAMs or pri-TAMs

We evaluated whether neutralization of CCL22 function contributes to the inhibition of TAM-mediated cancer cell invasion and found that treatment with a CCL22 neutralizing antibody (Ab) markedly decreased the number of invaded ESCC cells in cocultures with pol-TAMs or pri-TAMs. Furthermore, treatment of ESCC cells with recombinant CCL22 protein (rCCL22; 5, 25, and 50 ng/ml) for 24 h increased the invasive ability of ESCC cells in a dose-dependent manner (Fig. 3B). Two CCL22 siRNAs were transfected into pol-TAMs, and the transfection efficiency was assessed using ELISA. The CCL22 siRNAs effectively reduced the pol-TAM-induced invasion of KYSE410 and KYSE510 cells (Figure S2A and S2B).

CCL22 induces EMT and matrix metalloproteinase (MMP) secretion in ESCC cells

EMT is the initial step of tumor invasion and metastasis in cancers, including in ESCC [35, 36]. Thus, we evaluated whether TAMs can induce EMT in ESCC cells and found that KYSE410 and KYSE510 cells cocultured with pol-TAMs, pri-TAMs or CCL22 (50 ng/ml) underwent a transition from an epithelial-like phenotype to an elongated phenotype, with a decrease in E-cadherin expression and increases in vimentin and N-cadherin expression (Fig. 3C, D). the anti-CCL22 Ab (50 μg/ml) inhibited EMT in ESCC cells induced by coculture with pol-TAMs and pri-TAMs, indicating that CCL22 is the cytokine secreted by TAMs that is responsible for EMT in ESCC cells (Fig. 3C, D).

Because EMT activates the secretion of MMPs from tumor cells to facilitate the degradation of the basement membrane and promote cell invasion [37], we further examined the secretion profiles of MMPs induced by TAM-derived CCL22 using ELISA and found that pol-TAMs, pri-TAMs, or CCL22 (50 ng/ml) effectively stimulated the secretion of MMP-2, MMP-3, MMP-9, or MMP-13 from the indicated ESCC cells. The anti-CCL22 Ab (50 μg/ml) inhibited pol-TAM- or pri-TAM-induced MMP secretion from ESCC cells (Fig. 3E–H). These results together indicate that TAM-derived CCL22 induces ESCC cell invasion by stimulating EMT and MMP secretion in tumor cells.

We further evaluated whether blockade of mesenchymal biomarkers, including N-cadherin and vimentin, or inhibition of MMP activity can suppress CCL22-mediated ESCC invasion. KYSE410 and KYSE510 cells were cocultured with CCL22 (50 ng/ml) for 5 days, and then these ESCC cells were transfected with N-cadherin or vimentin siRNAs. The transfection efficiency of the indicated siRNAs was evaluated by immunoblotting. Subsequently, these N-cadherin- or vimentin-depleted ESCC cells were subjected to an invasion assay, and the results showed that the N-cadherin and vimentin siRNAs effectively inhibited the invasion of the indicated KYSE410 and KYSE510 cells (Fig. S3A–S3C). Furthermore, KYSE410 or KYSE510 cells cocultured with CCL22 (50 ng/ml) were incubated with MMP inhibitors, including SB-3CT (25 μM; an inhibitor of MMP2 and MMP9 activity) or GM6001 (25 μM; a broad-spectrum MMP inhibitor), and then subjected to an invasion assay. As shown in Fig. S3D, these two MMP inhibitors reduced the invasive ability of CCL22-educated ESCC cells.

CCL22-treated ESCC cells are hypersensitive to FAK inhibition

We screened CCL22-regulated pathway kinases in ESCC cells using a phosphokinase array and found that several kinases were activated by CCL22 (50 ng/ml) in KYSE410 cells, especially those involved in FAK/AKT signaling (Fig. 4A). Quantitative ELISA showed that the phosphorylation of FAK and AKT in the indicated ESCC cells was significantly upregulated by conditioned medium (CM) from pol-TAMs or pri-TAMs and by CCL22 (50 ng/ml) but not by CM from MDMs (Fig. 4B, C). Furthermore, the anti-CCL22 Ab counteracted pol-TAM and pri-TAM CM-induced FAK and AKT activation in ESCC cells (Fig. 4B, C). We investigated whether inhibition of FAK can suppress AKT activation under stimulation with TAM-derived CCL22. Interestingly, the FAK inhibitor VS-6063 (0.5–10 μM) inhibited AKT activation in ESCC cells incubated with pol-TAMs or CCL22 (50 ng/ml) more significantly than in control ESCC cells (Fig. 4D). Clinically, the level of stromal CCL22 was positively correlated with the levels of intratumoral pFAK Tyr397 (P = 0.001) and pAKT Ser473 (P < 0.0001) in 25 ESCC tissue samples (Fig. 4E).

Fig. 4

TAM-derived CCL22 activates FAK/AKT signaling in ESCC cells. A Total protein lysates from KYSE410 cells treated with PBS or CCL22 (50 ng/ml) were analyzed using an array of antibodies against phosphorylation sites in 43 signaling kinases (left panel). Representative sites of upregulated phosphorylation in protein kinases in CCL22-treated KYSE410 cells are listed (right panel). B, C The indicated ESCC cells were incubated with CM from MDMs, pol-TAMs, or pri-TAMs with or without the anti-CCL22 antibody (50 μg/ml) or CCL22 (50 ng/ml). The activity of FAK and AKT was assayed by a FAK Tyr397 (B) or an AKT Ser473 (C) activation quantitative ELISA. ***P < 0.001 compared with control cells; ###P < 0.001 compared with untreated cells cocultured with pol-TAMs or pri-TAMs. D KYSE410 or KYSE510 cells (lower chamber) were cocultured with control medium, pol-TAMs, or CCL22 (50 ng/ml) (upper chamber) in a Transwell apparatus with a 0.4 μm pore size membrane for five days and then treated with different concentrations of VS-6063 (0.5–10 μM). AKT activity was assayed by an AKT Ser473 activation quantitative ELISA. ***P < 0.001 compared with the indicated ESCC cells treated with 0.5 μM VS-6063 in the absence of pol-TAMs or CCL22 (50 ng/ml); ###P < 0.001 compared with the indicated ESCC cells treated with 1 μM VS-6063 in the absence of pol-TAMs or CCL22 (50 ng/ml); $$$ P < 0.001 compared with the indicated ESCC cells treated with 2.5 μM VS-6063 in the absence of pol-TAMs or CCL22 (50 ng/ml). E Stromal CCL22 expression was associated with FAK Tyr397 and AKT Ser473 phosphorylation in 25 primary human ESCC specimens. Two representative specimens with low and high levels of CCL22 are shown. Magnification, ×10 as indicated. Percentages of specimens showing low or high CCL22 expression relative to the level of pFAK or pAKT. Statistical differences were evaluated using the chi-square test. F, G KYSE410 and KYSE510 cells (lower chamber) were cocultured with control medium, pol-TAMs, or CCL22 (50 ng/ml) (upper chamber) in a Transwell apparatus with a 0.4 μm pore size membrane for five days and then treated with different concentrations of VS-6063 (0.5–10 μM). F The invasion ability of the indicated ESCC cells was assessed using a quantitative 96-well Boyden chamber assay. G The growth ability of the indicated ESCC cells was evaluated using a 3D MTS assay. ***P < 0.001 compared with the indicated ESCC cells treated with 0.5 μM VS-6063 in the absence of pol-TAMs or CCL22 (50 ng/ml); ###P < 0.001 compared with the indicated ESCC cells treated with 1 μM VS-6063 in the absence of pol-TAMs or CCL22 (50 ng/ml); $$$ P < 0.001 compared with the indicated ESCC cells treated with 2.5 μM VS-6063 in the absence of pol-TAMs or CCL22 (50 ng/ml)

We further evaluated whether inhibition of FAK potentially abrogated TAM-induced malignancy in ESCC cells. The indicated ESCC cells were cocultured with CCL22 (50 ng/ml) or pol-TAMs for five days, and these ESCC cells were collected and incubated with VS-6063 (0.5–10 μM). Then, the invasion index (Fig. 4F) and proliferative ability (Fig. 4G) of these ESCC cells treated with different concentrations of VS-6063 was evaluated using a 96-well cell invasion assay and a Matrigel-based proliferation assay. Unexpectedly, the reductions in ESCC invasion (Fig. 4F) and growth (Fig. 4G) upon VS-6063 treatment were more statistically significant in ESCC cells incubated with CCL22 or pol-TAMs than in ESCC cells cultured alone.

TAM-derived CCL22 enhances the antitumor effect of FAK inhibitor treatment in vivo

The hypersensitivity of TAM-stimulated ESCC cells to FAK suppression is associated with “oncogene addiction”, a biological event in which inhibition of driver oncogenes is sufficient to induce rapid and persistent tumor regression [38, 39]. We investigated whether inhibition of FAK activity in TAM-driven “FAK-addicted” cells might be therapeutically significant for blocking ESCC cell malignancy using a preclinical xenograft animal model. KYSE410 and KYSE510 cells were subcutaneously injected into the right flanks of nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. When the xenograft volumes reached approximately 100:mm3, we intravenously injected CCL22 (0.1 μg/kg; twice/week) and treated the animals with VS-6063 for approximately three consecutive weeks and observed tumor growth, AKT activity, and the expression of various markers of malignant tumor progression, including Ki67 (a marker of proliferation), LYVE-1 (a marker of lymphatic vessels), and CD31 (an endothelial marker). The results in Fig. 5A, C show that intravenous injection of CCL22 into KYSE410 and KYSE510 xenografts increased the tumor size (Fig. 5A) and enhanced the activation of AKT (Fig. 5B) and the expression of Ki67, CD31, and LYVE-1 (Fig. 5C), as evaluated by quantitative ELISAs. Importantly, VS-6063 more effectively inhibited tumor malignancy in the CCL22-treated group than in the PBS-treated group (Fig. 5A, C). We compared the survival time between the different groups and found that CCL22 treatment shortened the survival time of tumor-bearing animals compared with control animals, whereas FAK inhibition caused a more statistically significant extension of survival in CCL22-treated animals than in PBS-treated animals (Figure S4A). We evaluated whether VS-6063 suppresses CCL22-induced ESCC progression using a lung colonization model. The results in Fig. 5D show that the number of tumor nests in the lungs in the CCL22 treatment group was significantly higher than that in the control group. Treatment with VS-6063 more significantly weakened the lung colonization ability of CCL22-stimulated ESCC tumors than of PBS-treated tumors (Fig. 5D).

Fig. 5

Pharmacological inhibition of FAK activity blocks CCL22-mediated ESCC malignancy in vivo. A The indicated ESCC cells were intravenously injected along with rCCL22 at a dosage of 0.1 μg/kg biweekly for approximately three consecutive weeks alone or with VS-6063 (25 mg/kg/day, p.o.). Tumor growth curves are shown. The ratio of pAKT/AKT in the indicated ESCC tumors from the above different groups was evaluated using ELISA. C The expression of Ki-67, CD31, and LYVE1 in the indicated ESCC tumor tissues was evaluated using ELISA. D A lung colonization model was established in mice by intravenous injection of the indicated cells via the lateral tail vein (n = 5 biologically independent mice per group). Representative H&E staining of lungs and the number of metastatic nodules on the surface of the lungs are shown. Magnification, ×1 as indicated. *P < 0.05, **P < 0.01, ***P < 0.001; two-tailed unpaired Student’s t test. Error bars, mean ± SD of five independent experiments

We inoculated the indicated ESCC cells along with pol-TAMs into the flanks of NOD/SCID mice. Coinjection of pol-TAMs and tumor cells resulted in larger tumor sizes, higher AKT activity and higher Ki67, CD31, and LYVE-1 expression in tumor tissues (Fig. S5A–S5C). However, treatment with the anti-CCL22 Ab substantially reduced TAM-induced ESCC malignancy (Fig. S5A–S5C). VS-6063 significantly decreased tumor growth and the expression of the above ESCC tumor biomarkers, especially in the presence of TAMs, indicating that the FAK inhibitor exhibited a stronger antitumor effect in TAM-coinjected ESCC tumors than in non-TAM-coinjected ESCC tumors (Fig. S5A–S5C). Additionally, TAMs shortened the survival time of tumor-bearing animals (Fig. S4B), whereas the anti-CCL22 Ab was able to attenuate this effect. Importantly, FAK inhibition more effectively prolonged the survival of tumor-bearing animals in the TAM-injected group than in the non-TAM-injected group (Fig. S4B).

An in vivo lymph node metastasis model was established to evaluate the effect of TAMs on the metastatic ability of ESCC cells. The results in Figure S6 show that the lymph nodes in mice bearing tumors formed after coinoculation of pol-TAMs had larger volumes than those in mice not coinjected with pol-TAMs. In addition, VS-6063 substantially decreased the volume of lymph nodes in the ESCC cell/pol-TAM coinjection group compared with the group injected with ESCC cells alone (Fig. S6). Collectively, our results suggest that TAM-derived CCL22 induces hypersensitivity to FAK inhibition due to the addiction to hyperactive FAK.

CCL22 induces FAK activation via CCR4/PLC-γ1 axis-mediated DGKα membrane recruitment

Because CCR4 is the receptor for CCL22 [27], we further evaluated whether intratumoral CCR4 is critical for mediating CCL22-induced FAK activation. The immunoprecipitation assay showed that CM from pol-TAMs, CM from pri-TAMs, and CCL22 (50 ng/ml) induced a physical interaction between CCR4 and the FAK C-terminus but not the FAK N-terminus, PI3K p85α, p110α, or AKT, whereas the anti-CCL22 Ab (50 μg/ml) disrupted the pol-TAM- or pri-TAM-induced interaction between CCR4 and the FAK C-terminus (Fig. 6A).

Fig. 6

CCL22 induces the assembly of the CCR4/DGKα/FAK complex in ESCC cells. A Immunoprecipitation-immunoblotting showed that CCR4 interacted with only the FAK C-terminal and not the FAK N-terminal, PI3K catalytic subunit p110α, PI3K regulatory subunit p85, or AKT in KYSE410 and KYSE510 cells with the indicated treatment. B Silencing of DGKα in ESCC cells transduced with the two indicated short hairpin (sh) RNAs was analyzed by immunoblotting. GAPDH was used as the loading control. C The indicated control shRNA- and DGKα shRNA-transduced ESCC cells were treated with PBS or CCL22 (50 ng/ml). The activity of FAK and AKT was assayed by a FAK Tyr397 (left panel) or an AKT Ser473 (right panel) activation quantitative ELISA. D–F Control and CCR4-depleted ESCC cells were treated with or without CCL22 (50 ng/ml). D Silencing of CCR4 in ESCC cells transfected with the two indicated small interfering (si) RNAs was analyzed by immunoblotting. GAPDH was used as the loading control. E The Intracellular Ca2+ concentration was evaluated using a calcium detection assay kit. F Protein lysates were immunoprecipitated with an anti-PLC-γ1 or anti-DGKα antibody and then subjected to immunoblotting to evaluate the protein levels of pPLC-γ1 Tyr783 and pDGKα Tyr335. G KYSE410 and KYSE510 cells were pretreated with the Ca2+ chelator BAPTA-AM (10 μM) for 90 minutes and then incubated with CCL22 (50 ng/ml). Lysates were collected to evaluate the expression of pPLC-γ1 Tyr783 and PLC-γ1 using immunoblotting. H Immunoprecipitation-immunoblotting showed that PLC-γ1 interacted with DGKα but not FAK, CCR4, or AKT in KYSE410 or KYSE510 cells treated with CCL22 (50 ng/ml)

Although CCL22 stimulates the CCR4/FAK axis, there is no evidence that CCR4 has a direct effect on the phosphorylation of FAK at Tyr397 (the phosphorylation site for FAK-mediated PI3K/AKT activation in the N-terminus of FAK). We thus speculated that at least one other factor mediates CCL22-induced FAK Tyr397 phosphorylation. DGKα has been proposed to directly interact with the N-terminus of FAK to mediate the phosphorylation of FAK at Tyr397 [40]. We depleted DGKα in KYSE410 and KYSE510 cells using shRNA and then treated these ESCC cells with CCL22 (50 ng/ml) to observe the activation of intratumoral FAK and AKT (Figs. 6B, C). The ELISA results showed that DGKα shRNA markedly inhibited CCL22-mediated FAK/AKT activation in ESCC cells (Figs. 6B, C).

We assessed the concentration of intracellular calcium ([Ca2+]i) upon CCL22 treatment using a calcium detection assay, which has been extensively applied to evaluate the activation of chemokine receptors [41]. The results in Fig. 6D, E show that CCL22 (50 ng/ml) induced an increase in the intracellular Ca2+ concentration in control ESCC cells but not in CCR4 siRNA-transfected ESCC cells. Correspondingly, the results of immunoblotting showed that CCL22 (50 ng/ml) induced the phosphorylation of PLC-γ1, which is known to be a mediator in the Ca2+i pathway (Fig. 6F). However, transfection of CCR4 siRNA inhibited CCL22-induced phosphorylation of PLC-γ1 (Fig. 6F). The Ca2+ chelator BAPTA-AM (10 μM) effectively inhibited CCL22-induced phosphorylation of PLC-γ1 in KYSE410 and KYSE510 cells (Fig. 6G). A previous study found that PLC-γ1 directly phosphorylated Tyr335 of DGKα in an in vitro system, and activation via phosphorylation of this site is critical for membrane recruitment of DGKα [42]. The results in Fig. 6H show that PLC-γ1 interacted with DGKα but not with CCR4, FAK or AKT in the indicated ESCC cells treated with CCL22 (50 ng/ml). Furthermore, the change in the DGKα Tyr335 phosphorylation status was positively correlated with the change in the PLC-γ1 phosphorylation status in the indicated ESCC cells (Fig. 6F). Blockade of the CCR4/Ca2+/PLC-γ1 axis with the Ca2+ chelator BAPTA-AM (10 μM), CCR4 siRNA or PLC-γ1 siRNA effectively inhibited CCL22-mediated phosphorylation of DGKα at Tyr335 (Fig. 7A). Stable depletion of intratumoral PLC-γ1 by shRNA effectively inhibited CCL22-induced lymphatic metastasis of ESCC cells in vivo (Fig. S7A and S7B).

Fig. 7

CCL22 induces membrane recruitment of DGKα via the Ca2+/PLC-γ1 axis. A Silencing of PLC-γ1 in ESCC cells transfected with the two indicated siRNAs was analyzed by immunoblotting. GAPDH was used as the loading control (upper panel). Control or CCR4-treated PLC-γ1 siRNA-transfected KYSE410 and KYSE510 cells were pretreated with the Ca2+ chelator BAPTA-AM (10 μM) for 90 min and then incubated with CCL22 (50 ng/ml). Protein lysates were immunoprecipitated with an anti-DGKα antibody and then subjected to immunoblotting to assess the level of pDGKα Tyr335. B–D Control or CCR4-treated PLC-γ1 siRNA-transfected KYSE410 and KYSE510 cells were pretreated with the Ca2+ chelator BAPTA-AM (10 μM) for 90 min and then incubated with CCL22 (50 ng/ml). B Cell membrane and cytosolic proteins were extracted, and immunoblotting was used to detect the expression of DGKα, α1-ATPase (a membrane marker) and TUBA1A (a cytoplasmic marker). C Immunoprecipitation-immunoblotting was used to evaluate the interaction between DGKα and FAK at the plasma membrane. D FAK activity was assessed by ELISA. E The transfection efficiency of the DGKα Y335F plasmid in the indicated ESCC cells was evaluated. GAPDH was used as the loading control. F–H Vector or DGKα Y335F mutant KYSE410 and KYSE510 cells were treated with CCL22 (50 ng/ml). F Cell membrane and cytosolic proteins were extracted, and immunoblotting was used to detect the expression of DGKα, α1-ATPase (a membrane marker) and TUBA1A (a cytoplasmic marker). G Immunoprecipitation-immunoblotting was used to evaluate the interaction between DGKα and FAK at the plasma membrane. H FAK activity was assessed by ELISA. ***P < 0.001, two-tailed unpaired Student’s t test. Error bars, mean ± SD of five independent experiments

Disruption of the CCR4/Ca2+/PLC-γ1 axis effectively blocked CCL22-induced membrane recruitment of DGKα (Fig. 7B), the interaction between DGKα and FAK (Fig. 7C), and FAK activation (Fig. 7D). After the catalytically inactive DGKα Y335F mutant was transfected into ESCC cells (Fig. 7E), the CCL22-facilitated membrane recruitment of DGKα, the DGKα/FAK interaction, and subsequent FAK activation were blocked (Fig. 7F–H). We further evaluated whether inhibition of DGKα/FAK activity can reduce the secretion of MMPs from ESCC cells; to this end, we treated CCL22-treated KYSE410 and KYSE510 cells with VS-6063 (2.5 μM). After FAK inhibition, the secretion of MMP2, MMP3, MMP9, and MMP13 from CCL22-treated KYSE410 and KYSE510 cells was significantly decreased (Fig. S8A–S8D). Similarly, expression of the DGKα Y335F mutant effectively inhibited CCL22-induced MMP secretion from KYSE410 and KYSE510 cells (Fig. S8E–S8H). These observations strongly suggest that the CCL22/CCR4 axis is the driving force for the direct interaction between FAK and DGKα and for FAK activation in tumor cells.