Lung cancer is the major cause of malignancy-related death worldwide. Mortality is 80% to 90%, which makes this disease the leading cause of cancer-related deaths.
1- Jemal A.
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Cancer statistics, 2009.
The high mortality rate of this disease is primarily due to the difficulty of early diagnosis, the high metastatic potential, and the poor responses to chemical therapy and radiotherapy. Because there is no established curative therapy for advanced lung cancer to date, clinical management is palliative in many cases. Therefore, it is crucial to investigate and understand the underlying biological and molecular mechanisms of lung cancer progression.
Surfactant protein A (SP-A) is a large multimeric protein found in the airways and alveoli of the lungs. SP-A is a member of the collectin family of proteins, characterized by NH
2-terminal collagen-like regions and COOH-terminal lectin domains. Although other SPs, such as SP-B, function to reduce surface tension in the lungs, SP-A (and SP-D) regulates the pulmonary immune response.
2Immunoregulatory functions of surfactant proteins.
Previous
in vivo studies have shown that SP-A regulates responses involved in initiation and potentiation of inflammation by regulating the production of proinflammatory cytokines, such as tumor necrosis factor α (TNF-α), in response to lipopolysaccharide
3- Borron P.
- McIntosh J.C.
- Korfhagen T.R.
- Whitsett J.A.
- Taylor J.
- Wright J.R.
Surfactant-associated protein A inhibits LPS-induced cytokine and nitric oxide production in vivo.
or by accelerating the clearance of a variety of pathogens.
4- LeVine A.M.
- Gwozdz J.
- Stark J.
- Bruno M.
- Whitsett J.
- Korfhagen T.
Surfactant protein-A enhances respiratory syncytial virus clearance in vivo.
, 5- Mariencheck W.I.
- Savov J.
- Dong Q.
- Tino M.J.
- Wright J.R.
Surfactant protein A enhances alveolar macrophage phagocytosis of a live, mucoid strain of P. aeruginosa.
, 6- Giannoni E.
- Sawa T.
- Allen L.
- Wiener-Kronish J.
- Hawgood S.
Surfactant proteins A and D enhance pulmonary clearance of Pseudomonas aeruginosa.
, 7- Atochina E.N.
- Beck J.M.
- Preston A.M.
- Haczku A.
- Tomer Y.
- Scanlon S.T.
- Fusaro T.
- Casey J.
- Hawgood S.
- Gow A.J.
- Beers M.F.
Enhanced lung injury and delayed clearance of Pneumocystis carinii in surfactant protein A-deficient mice: attenuation of cytokine responses and reactive oxygen-nitrogen species.
, 8- Kuronuma K.
- Sano H.
- Kato K.
- Kudo K.
- Hyakushima N.
- Yokota S.
- Takahashi H.
- Suzuki H.
- Kodama T.
- Abe S.
- Kuroki Y.
Pulmonary surfactant protein A augments the phagocytosis of Streptococcus pneumoniae by alveolar macrophages through a casein kinase 2-dependent increase of cell surface localization of scavenger receptor A.
Because SP-A has the ability to opsonize and enhance pathogen uptake by phagocytes, the immunoregulatory roles of SP-A have been studied mainly in the field of infectious diseases. Recently, we reported that SP-A has a role in regulating bleomycin-induced acute noninfectious lung injury by inhibiting lung epithelial cell apoptosis.
9- Goto H.
- Ledford J.G.
- Mukherjee S.
- Noble P.W.
- Williams K.L.
- Wright J.R.
The role of surfactant protein A in bleomycin-induced acute lung injury.
Pastva et al
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- Walker J.K.
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- Mukherjee S.
- Giamberardino C.
- Hsia B.
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- Zhu H.
- Degan S.
- Sunday M.E.
- Lawson B.L.
- Korfhagen T.R.
- Schwartz D.A.
- Eu J.P.
- Foster W.M.
- McMahon T.J.
- Que L.
- Wright J.R.
Nitric oxide mediates relative airway hyperresponsiveness to lipopolysaccharide in surfactant protein A-deficient mice.
reported that SP-A regulates T
H2 cytokine production in a mouse asthma model. These results suggest that SP-A has diverse functions to control various lung diseases. Considering that SP-A contributes to multiple aspects of pulmonary host defense, we hypothesized that SP-A might have a role in lung cancer progression.
In a lung cancer study, SP-A was expressed in approximately 49% of primary non–small cell lung carcinomas
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- Baughman R.P.
- Biddinger P.W.
- Miller M.A.
- Fenoglio-Preiser C.
- al-Kafaji B.
- Di Lauro R.
- Whitsett J.A.
Surfactant proteins and thyroid transcription factor-1 in pulmonary and breast carcinomas.
and is used as a specific marker of carcinoma that originates in type II pneumocytes. In addition, a previous study demonstrated that deletion of the
SFTPA1 (alias,
SPA) gene in non–small cell lung cancer cells was associated with tumor progression.
12- Jiang F.
- Caraway N.P.
- Nebiyou Bekele B.
- Zhang H.Z.
- Khanna A.
- Wang H.
- Li R.
- Fernandez R.L.
- Zaidi T.M.
- Johnston D.A.
- Katz R.L.
Surfactant protein A gene deletion and prognostics for patients with stage I non-small cell lung cancer.
Tsutsumida et al
13- Tsutsumida H.
- Goto M.
- Kitajima S.
- Kubota I.
- Hirotsu Y.
- Yonezawa S.
Combined status of MUC1 mucin and surfactant apoprotein A expression can predict the outcome of patients with small-size lung adenocarcinoma.
found that patients with lung adenocarcinoma with relatively high MUC1 mucin expression and low SP-A expression in cancer cells had a poor outcome. These clinical studies demonstrate that in addition to use as a diagnostic marker, SP-A expression in lung cancer cells could be a useful biomarker of good prognosis. Although these studies suggested that SP-A might have a role in suppressing lung cancer progression, the role of SP-A in lung cancer has not been extensively studied, and the mechanisms by which SP-A controls lung cancer progression remain unknown.
In this study, we generated SP-A–overexpressing human lung adenocarcinoma cells and evaluated the role of SP-A in lung cancer progression using experimental mouse models.
Materials and Methods
Cell Lines
The human lung adenocarcinoma cell line PC14PE6 was a gift from Dr. Isaiah J. Fidler (The University of Texas MD Anderson Cancer Center, Houston TX). The human lung adenocarcinoma cell line A549 was purchased from ATCC (Manassas, VA). These cell lines were authenticated by BEX Co. Ltd. (Tokyo, Japan) using a multiplex short tandem repeat assay. Both cell lines were maintained in RPMI 1640 medium supplemented with 10% heat-inactivated fetal bovine serum, 100 U/mL of penicillin, and 50 μg/mL of streptomycin and were cultured at 37°C in a humidified atmosphere of 5% CO2 in air.
Reagents
An anti-mouse IL-2 receptor β-chain monoclonal antibody, TM-β1 (IgG2b), was a gift from Drs. Masayuki Miyasaka and Toshio Tanaka (Osaka University, Osaka, Japan).
SP-A Purification
SP-A was purified from the lung lavage fluid of patients with alveolar proteinosis as previously described
14- McIntosh J.C.
- Swyers A.H.
- Fisher J.H.
- Wright J.R.
Surfactant proteins A and D increase in response to intratracheal lipopolysaccharide.
and was routinely tested to reduce endotoxin contamination.
14- McIntosh J.C.
- Swyers A.H.
- Fisher J.H.
- Wright J.R.
Surfactant proteins A and D increase in response to intratracheal lipopolysaccharide.
Briefly, SP-A was suspended in 100 mmol/L octylglucoside and 5 mmol/L Tris, pH 7.4, after butanol extraction. Polymyxin-agarose (Sigma-Aldrich, St. Louis, MO) was added 1:5 (v/v) and allowed to incubate at room temperature for 30 minutes. The mixture was then dialyzed (14,000 molecular weight cutoff value) for four changes ≥4 hours each against autoclaved 5 mmol/L Tris, pH 7.4. The mixture was then centrifuged, and the supernatant, containing SP-A, was removed by gentle aspiration. SP-A preparations had final endotoxin concentrations of <0.1 pg/μg of SP-A as determined by the Limulus amoebocyte lysate assay (QCL-1000; BioWhittaker, Walkersville, MD).
SPA Gene Transduction
The human
SPA gene–expressed region [SFTPA1 (
NM_005411)] (OriGene Technologies, Rockville, MD) was introduced into the pMIG vector (a gift from Dr. Alana L. Welm, University of Utah, Salt Lake City). The Platinum-E packaging cell line (a gift from Dr. Toshio Kitamura, Tokyo University, Tokyo, Japan)
15- Morita S.
- Kojima T.
- Kitamura T.
Plat-E: an efficient and stable system for transient packaging of retroviruses.
was transfected with pMIG or derivative vector DNA by using FuGENE 6 transfection reagent (Roche Applied Science, Indianapolis, IN). PC14PE6 or A549 cells were infected using the viral supernatant as described previously.
16- Maekawa S.
- Tsukumo S.
- Chiba S.
- Hirai S.
- Hayashi Y.
- Okada H.
- Kishihara K.
- Yasutomo K.
Delta1-Notch3 interactions bias the functional differentiation of activated CD4+ T cells.
The proportion of green fluorescent protein–positive cells was >90% in the entire population.
Animals
Male athymic BALB/c nude mice and SCID mice were obtained from Charles River Laboratories Japan (Yokohama) and CLEA Japan (Tokyo), respectively, and were maintained under specific pathogen-free conditions throughout the study. All the experiments were performed in accordance with the guidelines established by The University of Tokushima Committee on Animal Care and Use, Tokushima, Japan. At the end of each in vivo experiment, the mice were anesthetized with isoflurane and euthanized humanely by cutting the subclavian artery. All the experiment protocols were reviewed and approved by the Animal Research Committee of The University of Tokushima.
In Vivo Subcutaneous Xenograft Model
PC14PE6 cells (1.0 × 106 per mouse) or A549 cells (3.0 × 106 per mouse) suspended in 0.1 mL of PBS were subcutaneously inoculated into the right flank of nude mice. Tumor size was measured using a vernier caliper three times a week (volume = ab2/2, where a indicates long diameter; b, short diameter). The mice were euthanized humanely on day 21, and the tumors were resected for further analyses.
In Vivo Lung Metastasis Model
To establish lung metastasis, nude mice were intravenously inoculated via the tail vein with 1.0 × 10
6 tumor cells per mouse.
17- Yano S.
- Nokihara H.
- Yamamoto A.
- Goto H.
- Ogawa H.
- Kanematsu T.
- Miki T.
- Uehara H.
- Saijo Y.
- Nukiwa T.
- Sone S.
Multifunctional interleukin-1β promotes metastasis of human lung cancer cells in SCID mice via enhanced expression of adhesion-, invasion- and angiogenesis-related molecules.
The mice were euthanized humanely on either day 28 (PC14PE6) or day 42 (A549). The lungs were weighed, and the number of metastatic colonies on the surface of the lungs was determined by visual examination. Because PC14PE6 cells produce large amounts of pleural effusion,
18- Yano S.
- Shinohara H.
- Herbst R.S.
- Kuniyasu H.
- Bucana C.D.
- Ellis L.M.
- Fidler I.J.
Production of experimental malignant pleural effusions is dependent on invasion of the pleura and expression of vascular endothelial growth factor/vascular permeability factor by human lung cancer cells.
the volume of the effusion was also evaluated. In some experiments, natural killer (NK) cells were depleted by treating nude mice with TM-β1 5 days after inoculation of PC14PE6 cells.
19- Yano S.
- Nishioka Y.
- Izumi K.
- Tsuruo T.
- Tanaka T.
- Miyasaka M.
- Sone S.
Novel metastasis model of human lung cancer in SCID mice depleted of NK cells.
Immunofluorescence
The excised tumor tissue was placed into OCT compound (Sakura Finetechnical Co., Tokyo, Japan) and snap frozen. Eight-micrometer-thick frozen tissue sections were fixed with 4% paraformaldehyde solution in PBS and were used for identification of macrophages using 1:150 rat anti-mouse CD68 monoclonal antibody (Serotec, Oxford, UK) and of NK cells using 1:100 goat anti-mouse NKp46/NCR1 monoclonal antibody (R&D Systems, Minneapolis, MN). Alexa Fluor 488–labeled secondary antibodies (dilution 1:250; Invitrogen, Carlsbad, CA) were used for immunofluorescence (IF) detection. To identify M1 or M2 macrophages, the sections were stained with 1:150 fluorescein isothiocyanate–conjugated rat anti-mouse TNF-α antibody (BD Pharmingen, Franklin Lakes, NJ) or 1:150 fluorescein isothiocyanate–conjugated rat anti-mouse CD206 [mannose receptor C type 1 (MRC-1)] antibody (BioLegend, San Diego, CA) after CD68 staining. Alexa Fluor 594–labeled anti-rat secondary antibodies (dilution 1:250; Invitrogen) were used for CD68 IF detection. M1 or M2 macrophages were identified as CD68-positive/TNF-α-–positive or CD68-positive/MRC-1–positive cells, respectively. Nuclei were counterstained with DAPI (blue). In each slide, the number of positive cells was counted in five areas under fluorescent microscopy at ×100 (single staining) or ×200 (double staining) magnification.
RT-qPCR
Total RNA was extracted from the tumors using the RNeasy mini kit (Qiagen, Valencia, CA) and reverse transcribed to cDNA using a high-capacity cDNA Reverse Transcription kit (Applied Biosystems, Carlsbad, CA) according to the manufacturer’s instructions. RT-PCR was performed using the CFX96 real-time PCR system (Bio-Rad Laboratories, Hercules, CA) using SYBR Premix Ex Taq (Takara, Kyoto, Japan). Human RPL27
20- de Jonge H.J.
- Fehrmann R.S.
- de Bont E.S.
- Hofstra R.M.
- Gerbens F.
- Kamps W.A.
- de Vries E.G.
- van der Zee A.G.
- te Meerman G.J.
- ter Elst A.
Evidence based selection of housekeeping genes.
and mouse β2m mRNA were used as housekeeping genes, and quantification was determined by using the ΔΔC
T method. Specific PCR primer pairs for each studied gene are shown in
Table 1.
Table 1Primer Sequences Used in Quantitative PCR
SP-A Stimulation of Monocytes, Macrophages, and NK Cells
Human monocytes were separated from the peripheral blood of healthy volunteers as described previously.
21Comparative analysis of the priming effect of human interferon-gamma, -alpha, and -beta on synergism with muramyl dipeptide analog for anti-tumor expression of human blood monocytes.
The purity and viability of the monocytes was confirmed to be >98% by staining with Diff-Quik (Baxter Diagnostics, Deerfield, IL) and trypan blue, respectively. Mouse alveolar macrophages (AMs) were collected by using bronchoalveolar lavage as described previously.
9- Goto H.
- Ledford J.G.
- Mukherjee S.
- Noble P.W.
- Williams K.L.
- Wright J.R.
The role of surfactant protein A in bleomycin-induced acute lung injury.
More than 95% of the cells were confirmed to be AMs. For eliciting mouse peritoneal macrophages (PMs), 2 mL of thioglycollate (BD Biosciences, San Jose, CA) was injected into the peritoneal cavity of SCID mice. After 3 days, peritoneal exudative cells were harvested by intraperitoneal lavage with ice-cold PBS. Approximately 80% of isolated cells were macrophages. NK cells from SCID mice were isolated as previously described.
22- Hyodo Y.
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- Yamauchi H.
- Hiroishi K.
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- Iwakura Y.
- Kayagaki N.
- Kurimoto M.
- Okamura H.
- Hada T.
- Yagita H.
- Akira S.
- Nakanishi K.
- Higashino K.
IL-18 up-regulates perforin-mediated NK activity without increasing perforin messenger RNA expression by binding to constitutively expressed IL-18 receptor.
These immune cells were stimulated with 20 μg/mL of human SP-A for 4 hours in RPMI 1640 medium containing 1% fetal bovine serum. Total RNA was extracted for quantitative RT-PCR.
Cell Migration Assay
The migration assay was performed using 8-μm pore size cell culture inserts (BD Biosciences). After 24 hours of serum starvation, PMs in serum-free media were added to the inner chamber in the presence or absence of 20 μg/mL of SP-A. RPMI 1640 medium containing 10% fetal bovine serum was added to the lower chamber. After 17 hours of incubation, the cells that had migrated to the bottom surface of the filter were counted in six randomly selected fields on each filter under a microscope at ×200 magnification.
Western Blot Analysis
Twenty micrograms of total protein extracted from tumor cell lines was resolved by SDS-PAGE (Invitrogen) and was transferred to polyvinylidene difluoride membrane (Atto Corp., Tokyo, Japan), and Western blot was performed as described previously.
9- Goto H.
- Ledford J.G.
- Mukherjee S.
- Noble P.W.
- Williams K.L.
- Wright J.R.
The role of surfactant protein A in bleomycin-induced acute lung injury.
Immunoreactive bands were visualized using SuperSignal west femto maximum sensitivity substrate (Thermo Scientific, Waltham, MA).
Statistical Analysis
Data are given as means ± SEM. Statistical analysis was performed using the Student’s t-test of unpaired samples or the U-test. Values of P < 0.05 were considered statistically significant.
Discussion
In this study, we demonstrated that i) SP-A expression in cancer cells suppresses progression of lung adenocarcinoma in xenograft and lung metastasis models; ii) SP-A inhibits lung cancer progression not by its direct effect on tumor cells but by regulating the host microenvironment, including macrophages and NK cells; and iii) SP-A increases the number of M1 TAMs in the tumor microenvironment, resulting in NK cell recruitment and activation in tumor tissue. These results suggest new immunoregulatory functions of SP-A, which is frequently expressed in pulmonary adenocarcinoma.
Tumors comprise not only malignant cells but also many other nonmalignant cell types, and they produce a unique microenvironment that can modify the neoplastic properties of the tumor cells. Among the cells recruited in the tumor microenvironment, TAMs are one of the major players known to have pivotal roles in the progression and metastasis of tumors.
23Tumour-educated macrophages promote tumour progression and metastasis.
, 24- Solinas G.
- Germano G.
- Mantovani A.
- Allavena P.
Tumor-associated macrophages (TAM) as major players of the cancer-related inflammation.
Although partially contradictive, high numbers of TAMs often correlate with poor prognosis in various types of cancer.
28- Bingle L.
- Brown N.J.
- Lewis C.E.
The role of tumour-associated macrophages in tumour progression: implications for new anticancer therapies.
Therefore, a better understanding of the role of TAMs seems crucial to control cancer progression.
Considering the character of TAMs, it is now generally accepted that TAMs usually polarize to M2 and represent protumoral functions.
23Tumour-educated macrophages promote tumour progression and metastasis.
Indeed, we have seen in this study that approximately 60% of TAMs had the M2 phenotype in PC14PE6 and A549 control (vector-transduced) tumors (
Figures 2B and
5C). However, when tumor cells expressed SP-A, this M1/M2 balance was reversed, and M1 macrophages became dominant in both tumors. As far as we have investigated, the expression of multiple M1 markers was up-regulated in SP-A–expressing tumors, whereas the expression of M2 markers was not altered in xenograft and metastatic lung tumors. Together with the fact that the number of M1 TAMs was increased in SP-A–expressing tumors, these results indicate that SP-A aided in making the TAMs M1 dominant by increasing the number of recruited M1 macrophages rather than shifting the M2 TAMs into the M1 phenotype in the tumor microenvironment.
Numerous studies have shown that macrophages could be a target cell type that SP-A interacts with to regulate infectious inflammation, and, to date, diverse and contradictive functions of SP-A against monocytes/macrophages are reported.
29Surfactant protein A stimulation of inflammatory cytokine and immunoglobulin production.
, 30- Kremlev S.G.
- Umstead T.M.
- Phelps D.S.
Surfactant protein A regulates cytokine production in the monocytic cell line THP-1.
, 31- McIntosh J.C.
- Mervin-Blake S.
- Conner E.
- Wright J.R.
Surfactant protein A protects growing cells and reduces TNF-alpha activity from LPS-stimulated macrophages.
, 32- Stamme C.
- Walsh E.
- Wright J.R.
Surfactant protein A differentially regulates IFN-gamma- and LPS-induced nitrite production by rat alveolar macrophages.
These studies all indicate that SP-A has various effects on inflammation induced by different agonists. Indeed, we also observed that the cytokine/chemokine expression profiles of PMs and human monocytes were different in response to SP-A (
Figure 4), suggesting that SP-A may exert cell- and agonist-specific effects that contribute to the inflammation state of the host.
In addition to the observations investigating the role of SP-A during infection, we showed that SP-A activates and increases M1 macrophages in the tumor microenvironment and induces the production of inflammatory cytokines, suggesting that SP-A facilitates inflammation in the tumor to reduce tumor progression. The precise molecular mechanism by which SP-A activates M1 macrophages in the tumor remains unclear with the current observation; however, several mechanisms should be considered. First, SP-A may enhance the binding of cytokines to their respective receptors. SP-A is reported to bind to several receptors, including Toll-like receptors 2 and 4, and to regulate inflammatory responses induced by pathogen-derived products, such as peptidoglycan and lipopolysaccharide via Toll-like receptors.
33- Sano H.
- Sohma H.
- Muta T.
- Nomura S.
- Voelker D.R.
- Kuroki Y.
Pulmonary surfactant protein A modulates the cellular response to smooth and rough lipopolysaccharides by interaction with CD14.
, 34- Sato M.
- Sano H.
- Iwaki D.
- Kudo K.
- Konishi M.
- Takahashi H.
- Takahashi T.
- Imaizumi H.
- Asai Y.
- Kuroki Y.
Direct binding of Toll-like receptor 2 to zymosan, and zymosan-induced NF-kappa B activation and TNF-alpha secretion are down-regulated by lung collectin surfactant protein A.
, 35- Henning L.N.
- Azad A.K.
- Parsa K.V.
- Crowther J.E.
- Tridandapani S.
- Schlesinger L.S.
Pulmonary surfactant protein A regulates TLR expression and activity in human macrophages.
In addition to its role in Toll-like receptor–mediated cellular responses induced by infectious challenges, it is very possible that SP-A regulates the function of TAMs in the tumor microenvironment through the interaction with Toll-like receptors. Second, signal transduction in the TAMs could be regulated by SP-A. SP-A has been shown to trigger rapid tyrosine, but not serine or threonine, phosphorylation
36- Schagat T.L.
- Tino M.J.
- Wright J.R.
Regulation of protein phosphorylation and pathogen phagocytosis by surfactant protein A.
of macrophage proteins and could possibly enhance/accelerate the initial phosphorylation steps of the signal transduction pathway, which leads to the regulation of inflammation in the tumor. It was also possible that SP-A directly affects tumor cells and regulates cytokine expression. Thus, we compared the chemokine expression of SP-A–expressing PC14PE6 and control (vector-transduced) cells using the PCR array system. Of 92 chemokine and chemokine-related genes tested, none were altered by SP-A overexpression (data not shown), suggesting that SP-A did not directly affect chemokine expression of tumor cells.
Of note, we showed the effect of SP-A on M1 macrophage recruitment and tumor suppression in xenograft and lung metastasis models. This result indicated two important aspects of SP-A. First, the lung tumor–specific expression of SP-A is more important than the host SP-A in the lung to suppress lung cancer progression. Second, the recruited M1 TAMs by tumor-derived SP-A could be originated from circulating monocytes. This possibility was supported by the result that SP-A activated only circulating monocytes/macrophages (mouse PMs or human monocytes) and showed no effect on resident AMs in cytokine expression. In the lung, the sensitivity of resident AMs against SP-A is thought to be suppressed as they are continuously contacted by SP-A, which could be a plausible explanation because the host needs to be protected from the overzealous inflammation in the resting, normal, noninflamed lungs. The molecular mechanism of different SP-A sensitivities in different cells is not still clearly understood. However, as stated previously herein, the expression of inflammatory signaling molecules that might be regulated by SP-A could be different between AMs and other type of monocytes/macrophages. In addition, there could be an unknown SP-A receptor(s) that might be critical in regulating inflammation in macrophages, as SP-A is reported to bind to multiple receptors.
2Immunoregulatory functions of surfactant proteins.
Further studies are needed to understand the precise molecular mechanisms of the diverse and cell-specific function of SP-A against macrophages in the context of SP-A and lung cancer.
These results indicate that NK cell activation was the main mechanism by which SP-A lead to the reduction in tumor burden. The production of Prf1 and GzmB was strongly increased (15- to 30-fold), whereas the number of NK cells was increased only twofold to threefold in the SP-A–expressing tumor, suggesting the multiple pathways regulated by SP-A to recruit and activate NK cells. Because cytokines produced by M1 macrophages, such as interferon-γ and CCL2, are known to activate NK cells,
37- Rolny C.
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HRG inhibits tumor growth and metastasis by inducing macrophage polarization and vessel normalization through downregulation of PlGF.
, 38- Schroder K.
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Interferon-gamma: an overview of signals, mechanisms and functions.
, 39- Morrison B.E.
- Park S.J.
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Chemokine-mediated recruitment of NK cells is a crucial host defense mechanisms in invasive aspergillosis.
it is likely that SP-A implicitly induces NK cell killing via activating M1 TAMs and increasing various inflammatory cytokines in the tumor microenvironment.
Two functional genes of SP-A were detected in a previous report
40- White R.T.
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Isolation and characterization of the human pulmonary surfactant apoprotein gene.
: SP-A1 and SP-A2. These genes were differentially regulated by development
41- McCormick S.M.
- Mendelson C.R.
Human SP-A1 and SP-A2 genes are differentially regulated during development and by cAMP and glucocorticoids.
and have a minor difference in carbohydrate-binding activity.
42Recombinant human SP-A1 and SP-A2 proteins have different carbohydrate-binding characteristics.
However, SP-A protein derived from SP-A1 and SP-A2 genes are reported to be functional and to enhance TNF-α secretion by the monocytic cell line.
43- Wang G.
- Phelps D.S.
- Umstead T.M.
- Floros J.
Human SP-A protein variants derived from one or both genes stimulate TNF-alpha production in the THP-1 cell line.
Thus, although we have transduced only the SP-A1 gene, we suspect that SP-A protein from the SP-A2 gene could also contribute to activation of the innate immune system and suppress tumor progression.
In conclusion, these findings demonstrate that SP-A regulates the tumor microenvironment by controlling the polarization of TAMs. SP-A expression by tumor cells leads to increased numbers and the activation of M1 TAMs. These activated M1 TAMs then recruit and activate NK cells that function in tumor suppression. These results indicate that SP-A plays an important protective role in the progression of lung cancer. Specifically targeting M1 TAMs (not bulk TAMs) to induce the activation of a proinflammatory program in the tumor, generating the pharmacologic modulators of SP-A for example, could be the therapeutic approach to improve the effect of anticancer therapy.
Article Info
Publication History
Published online: March 15, 2013
Accepted:
January 10,
2013
Footnotes
Supported by the Ministry of Education, Culture, Sports, Science and Technology Grants-in Aid for Scientific Research (MEXT KAKENHI) grant 22790759 (H.G.) and NIH grants AI-81672 and HL-111151 (J.G.L.).
A.M. and H.G. contributed equally to this work.
Copyright
© 2013 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.