ARTICLE

Synaptotagmin I Expression in Mast Cells of Normal Human Tissues, Systemic Mast Cell Disease, and a Human Mast Cell Leukemia Cell Line

Correspondence to: Noriko Kimura, Dept. of Pathology and Laboratory Medicine, Tohoku Rosai Hospital, 21-3-4 Dainohara, Aoba-ku, Sendai 981-8563, Japan. E-mail: nkimura-path@tohokuh.rofuku.go.jp

	Summary

Top Summary Introduction Materials and Methods Results Discussion Literature Cited

Synaptotagmin I (STG I) is a Ca²⁺ sensor and one of the synaptic vesicle proteins that mediate exocytosis. To determine the mechanism of release of large granules from mast cells, we studied by immunohistochemistry the presence of STG I in mast cells in normal human tissues simultaneously with the mast cell markers mast cell tryptase (tryptase) and c-kit. The tumor cells of systemic mast cell disease (SMCD) and a human mast cell leukemia cell line (HMC-1) were also examined. Human mast cells in normal tissues and the tumor cells of SMCD expressed STG I as well as mast cell tryptase (tryptase) and c-kit. STG I mRNA and its products in HMC-1 were examined by RT-PCR analysis and immunocytochemistry, respectively. STG I expression in HMC-1 cells was compared with that in cells stimulated and non-stimulated by phorbol 12-myristate 13-acetate and also with that in NB-1 and PC12 cells, known to express STG I. STG I mRNA was detected in both non-stimulated and stimulated HMC-1 cells and in NB-1 and PC12 cells. STG I immunoreactivity was weaker than NB-1 or PC12 immunoreactivity. However, it increased in the stimulated HMC-1 cells. Mast cells expressed STG I in various states. STG I may mediate exocytosis of large granules in mast cells. (J Histochem Cytochem 49:341–345, 2001)

Key Words: mast cell, synaptotagmin I, c-kit, mast cell tryptase, exocytosis, immunohistochemistry, RT-PCR, systemic mast cell disease, HMC-1, PC12

	Introduction

Top Summary Introduction Materials and Methods Results Discussion Literature Cited

Mast cells are multifunctional effector cells of the immune system and are distributed throughout the body. Mast cells have large granules containing histamine, many kinds of cytokines, prostaglandin D2, leukotriene C4 and proteases, trypsin-like enzyme (tryptase), and chymotrypsin-like enzyme (chymase). Tryptase is stored in all human mast cells, regardless of anatomic site, whereas chymase is restricted to connective tissue mast cells. (Gordon and Galli 1990 ; Holgate 1992 ; Bradding et al. 1994 ; Inoue et al. 1996 ). Many markers for identifying mast cells have been found. Of these, mast cell tryptase and c-kit (CD117) are recommended for detection of mast cells in mature and immature stages (Valent 1995 ). Intracellular signal transduction via IgE receptors has been clarified (Beaven and Metzger 1993 ). However, the mechanism of release of the large granules remains unknown.It was recently reported that mast cells express rab3a and rab3d proteins and interfere with a rate-limiting step in IgE receptor-stimulated exocytosis (Oberhauser et al. 1994 ; Smith et al. 1997 ). Rab3s are synaptic proteins postulated to regulate exocytotic vesicle traffic in neurons and many secretory cells (Sudhof 1995 ). Furthermore, Baram et al. 1998 demonstrated that rat peritoneal mast cells and rat basophilic leukemia cells express STG I by Western blotting and immunocytochemistry. STG-I localized almost exclusively to their secretory granules. This encouraged us to examine whether STG I mediates human mast cell exocytosis.

We conducted an immunohistochemical study of STG I in mast cells of various normal and neoplastic human tissues and in systemic mast cell disease (SMCD). SMCD is a rare disease characterized by a generalized abnormal infiltration of mast cells, most notably involving the bone marrow, lymph node, liver, spleen, and other parenchymal organs, with or without cutaneous involvement. There are four forms of SMCD: (a) an indolent form limited to the skin, with a favorable prognosis; (b) a form with associated hematological disorders; (c) an aggressive form with a poor prognosis, which exhibits visceral and bone involvement that may or may not be associated with skin lesions; and (d) mast cell leukemia (Warnke et al. 1995 ). C-kit is also a useful marker in the differential diagnosis of SMCD involving the bone marrow (Natkunam and Rouse 2000 ). Furthermore, we verified the expression of STG I mRNA and its products in HMC-1 cells that were established from the peripheral blood of a patient with mast cell leukemia by Butterfield et al. 1990 with or without stimulation by phorbol 12-myristate 13-acetate (PMA).

	Materials and Methods

Top Summary Introduction Materials and Methods Results Discussion Literature Cited

Histochemistry and Immunohistochemistry
Ten normal human tissues, including stomach, colon, pancreas, adrenal medulla, skin, salivary gland, and uterine cervix obtained by surgery, were fixed in 10% buffered formalin and embedded in paraffin. To avoid nonspecific staining, the histochemistry and immunohistochemistry were based on Shiltz et al. (1993). Mast cells in these tissues were identified by immunohistochemistry of tryptase and c-kit. In a case of SMCD, Dr. Maruyama (Hirakata, Japan) kindly supplied paraffin-embedded tissues of the kidney and stomach with lymph node. This case was of Type c, with an elevated plasma histamine level of 3.59 ng/ml (normal <0.8 ng/ml). An autopsy had revealed mast cell infiltration mainly in the spleen, liver, kidney, lymph nodes, and bone marrow. This case has been previously reported by Maruyama et al. 1998 .

A human mast cell line (HMC-1) was cultured in Dulbecco's medium (IMDM) with 10% heat-inactivated fetal bovine serum. A rat pheochromocytoma cell line (PC12) and a human neuroblastoma cell line (NB-1), both known to contain STG-I (Shoji-Kasai et al. 1992 ), were used for positive controls. PC12 and NB-1 cells were cultured in RPMI 1640. These cells were stimulated with PMA 10 ng/mL for 2, 5, and 8 hr and the expression of STG I was compared with that of non-stimulated cells by immunocytochemistry and RT-PCR analysis.

Immunohistochemical Staining
Mast cells contain heparin, which is a proteoglycan. Proteoglycans contain many sulfate and carboxyl groups that impart a highly negative charge to molecules such as avidin and immunoglobulins. Furthermore, nonspecific labeling of mast cells results from an ionic interaction between the (Fab')₂ segments of antibodies and the heparin constituent of the mast cell secretory granules (Schiltz et al. 1993 ). Thus, histochemistry and immunohistochemistry in mast cells have been carefully performed.

We used the Histofine SAB-PO(M) kit (Nichirei, Tokyo), and Simple Stain Max (M) kit (Nichirei), which is an amino acid polymer labeled by peroxidase and rabbit anti-mouse IgG Fab' for immunohistochemistry. Sections were dewaxed in xylene, washed in ethanol, and incubated in a 0.06% hydrogen peroxide–methanol solution to block endogenous peroxidase activity. For the SAB-PO kit, but not the Simple Stain kit, nonspecific staining was blocked with 10% normal rabbit serum. Then the sections were incubated with the primary antibodies at the appropriate dilution for 18 hr at 4C. After a wash in PBS, the sections were incubated in biotin-labeled rabbit anti-mouse IgG + IgA + IgM antibody (10 µg/ml) for 30 min at room temperature (RT). After another wash in PBS, the sections were incubated in peroxidase-labeled streptavidin for 30 min at RT.

For the Simple Stain kit, the procedure was the same as for the SAB-PO kit until the first antibodies were applied. The sections were incubated in the solutions containing amino acid polymer labeled by peroxidase and rabbit anti-mouse IgG for 60 min. After a wash with PBS, the sections were washed and colorized with diaminobenzidine solution (Wako Chemicals; Tokyo, Japan). Methyl green or hematoxylin was used for counterstaining of nuclei.

To avoid nonspecific binding of the antibodies to the heparin contained in mast cells, the specificity of immunostaining was checked. PBS for washing and dilution of the antibodies was acidified to pH 6.0. Preadsorption of the STG I antibody with 1000 U/ml heparin (Sigma; St Louis, MO) for 60 min at RT before use was carried out to avoid nonspecific binding of immunoglobulins and heparin. The specificity of the immunohistochemistry was confirmed with negative controls: absence of primary or secondary antibody and avidin-labeled peroxidase. Normal non-immune mouse serum was also used instead of the primary antibody. The tissues of rat brain, human brain, and pheochromocytoma that contain abundant synaptic vesicle proteins were fixed in 10% buffered formalin and simultaneously stained as positive controls. The specificity of the antibody for STG I has been confirmed by Western blotting using rat brain.

The sources and characteristics of the antibodies used are as follows: mast cell tryptase mouse, monoclonal, 1:3000, Chemicon (Temecula CA), against human lung mast cell tryptase; c-kit rabbit, polyclonal, 1 µg/ml, IBL (Fujioka, Japan), against the C-terminus of synthesized c-kit peptide (k963); synaptotagmin I mouse, monoclonal, 1:100, Wako Chemicals (Osaka, Japan), against rat brain synaptosome.

Cultured HMC-1 cells were autosmeared by a cytocentrifuge at 1000 rpm for 3 min and fixed with Bouin's solution for 1 hr. The smears were frozen and thawed. After that, immunocytochemical staining was performed the same as was done in the tissues. The cells cytocentrifuged and fixed with 10% buffered formalin easily peeled off from the glass and were not suitable for immunostaining. Therefore, the smears were fixed with Bouin's solution.

RT-PCR
Trizol, Superscript II reverse transcriptase, and Taq DNA polymerase were obtained from GIBCO BRL (Gaithersburg, MD). Total RNA was isolated from PMA-treated or non-treated cells by a modified acid–guanidine thiocyanate–phenol–chloroform method using Trizol. RNA was quantified by spectrophotometry at 260 nm. Total RNA (5 µg) was reverse-transcribed with 200 U of Superscript II reverse transcriptase in the presence of 0.5 µg of oligo-dT anchor primer and 0.5 µM of each dNTP. The mixture was incubated at 37C for 60 min. One tenth of the total reverse-transcribed single-stranded cDNA was then subjected to PCR with 25 pmol each of the forward and reverse primers, 0.2 mM of each dNTP, and 1 U of Taq DNA polymerase in a final volume of 20 µl in PCR buffer. The sense primer for rat or human STG I was 5'-GTGAGTGCCAGTCATCCTGAG-3' or 5'-GTGAGCGAGAGTCACCATGAG-3', and the antisense primer for rat and human STG I was 5'-CCTTCATGGTCTTCCCTAAGTC-3'. The predicted size of the amplified product was 340 base pairs (Xi et al. 1999 ). To confirm the integrity of the total RNA samples and RT activity, the -actin sequence was detected by PCR on the same RT reactions with sense primer, 5'-TTCTACAATGAGCTGCGTGTGG-3', and antisense primer, 5'-ATACCCAGGAAGGAAGGCTGGAAG-3', for rat and human -actin. Amplification was performed for 30 cycles with each cycle consisting of denaturation for 45 sec at 94C, 30-sec annealing at 55C, and 1-min extension at 72C. An additional 10 min at 72C was added at the end of the 30 cycles. The PCR amplification products were resolved on a 1.5% Agarose–Tris acetate–EDTA gel and visualized with ethidium bromide. DNA molecular weight markers were included on each gel to confirm PCR product sizes.

	Results

Top Summary Introduction Materials and Methods Results Discussion Literature Cited

Detection of Mast Cells in Normal Tissues
We detected many mast cells in all the tissues examined, showing cytoplasmic staining by mast cell tryptase and cell membrane staining by c-kit (Fig 1a and Fig 1b).

View larger version (121K): [in this window] [in a new window]   Figure 1. (a) C-kit in mast cells of human gastric mucosa. (b) The immunoreactivity of c-kit is observed mainly on the cell membrane. Figure 2. (a) STG I in mast cells of human gastric mucosa. (b) The immunoreactivity of STG I is observed mainly in the cytoplasm of mast cells. Figure 3. The infiltrating tumor cells of systemic mast cell disease in the stroma of the kidney are immunoreactive to the antibodies for human mast cell tryptase (a) and STG I (b). The tubules show no immunoreactivity to both antibodies. Figure 4. (a) Non-stimulated HMC-1 cells show fewer granules immunoreactive to STG I. (b) HMC-1 cells stimulated by PMA and incubated for 5 hr show an increased number of granules positive for STG-I. Figure 5. Non-stimulated NB-1 cells (a) and PC12 cells (b) show strong STG I immunoreactivity.

STG I in Mast Cells of Normal Tissues
Both the SAB-PO kit and the Simple Stain kit showed specific immunoreactivity compared to the control studies. STG I immunoreactivity was observed as rough granules in mast cells locating in the mucosal tissues and connective tissues of all the specimens examined (Fig 2a and Fig 2b).

Negative Controls
Non-immune serum, omission of the primary and the secondary antibody, and avidin complex produced no specific immunostaining.

Positive Controls for STG I
The tissues of rat brain, human brain, and pheochromocytoma stained simultaneously showed strong immunoreactivity in the cytoplasm.

STG I in Mast Cells of SMCD
Infiltrating abnormal mast cells in the stomach, lymph node, and kidney of the patient with SMCD showed immunoreactivity for tryptase (Fig 3a), c-kit, and STG I (Fig 3b).

STG I in HMC-1, PC12, and NB-1 Cells
STG I was detected as a rough granular pattern in the HMC-1 cells. The majority of non-stimulated HMC-1 cells had fewer granules immunoreactive for STG I (Fig 4a). In contrast, HMC-1 cells stimulated with PMA contained many granules immunoreactive for STG I (Fig 4b). The number of STG I-positive cytoplasmic granules increased after PMA stimulation, reaching a maximum at 5 hr after stimulation. The cells stimulated for 8 hr showed fragmented nuclei compatible with apoptotic death. NB-1 cells (Fig 5a) and PC12 cells (Fig 5b) demonstrated strong immunoreactivity in the entire cytoplasm regardless of PMA stimulation. The results are summarized in Table 1.

RT-PCR
Expression of STG I mRNA in Cultured Cell Lines. RT-PCR analysis revealed STG I mRNA expression in HMC-1 cells before and after PMA treatment as well as in PC12 cells and NB-1 cells. Both non-stimulated and stimulated HMC-1 cells expressed mRNA showing the same sized PCR product as that from NB1 and PC12 cells. (Fig 6).

View larger version (37K): [in this window] [in a new window]   Figure 6. RT-PCR products of STG I and -actin. From left to right: DNA size marker, HMC-1 non-stimulated (Lane 1), HMC-1 treated with PMA 10 ng/ml and incubated for 2 hr (Lane 2) and 5 hr (Lane 3) after treatment, NB1 (Lane 4) and PC12 (Lane 5) in order. STG I transcripts are observed in all lanes. Lanes 6–10 are -actin in HMC-1, NB1, and PC12, the same order as above.

	Discussion

Top Summary Introduction Materials and Methods Results Discussion Literature Cited

Because mast cells are well known for their nonspecific binding with immunoglobulin, we have carefully carried out immunohistochemical studies using heparin preadsorbed antibody for STG I and two different detection kits for immunohistochemistry: streptavidin–biotin complex, and an amino acid polymer-linked with IgG and peroxidase. We confirmed that both kits gave the same immunoreactivity.

STG I was detected in human mast cells in the mucosal and connective tissues of various normal tissues examined. Mast cells were immunoreactive for STG I tryptase, and c-kit. The tumor cells of SMCD also demonstrated immunoreactivity for STG I as well as tryptase and c-kit.

STG I immunoreactivity increased in HMC-1 cells stimulated by PMA. HMC-1 is an immature mast cell line and c-kit receptors are constitutively activated in these cells (Butterfield et al. 1989 ). In the stimulated HMC-1 cells, the rough granular immunoreactivity to STG I antibody increased remarkably. PMA is believed to induce cell maturation and secretion of the large granules via protein kinase C. It has been reported that PMA increased the expression of histidine decarboxylase in mast cells (Maeda et al. 1998 ).

STG is a calcium sensor on the surface of synaptic vesicles (Brose et al. 1992 ). The microinjection of monoclonal and polyclonal antibodies raised against STG decreased the K⁺/Ca²⁺-mediated dopamine -hydroxylase surface staining, which supports the hypothesis that STG is important in regulation of exocytosis in neurons (Elferink et al. 1993 ). STG I has been detected not only in synaptic vesicles but also in anterior and intermediate pituitary and in adrenal medullary cells (Marqueze et al. 1995 ). Baram et al. 1998 found that STG I mediated rat mast cell exocytosis using immunocytochemistry and Western blotting analysis. These authors also reported that STG I was localized almost exclusively to the secretory granules of the mast cells. Furthermore, the present study demonstrated the presence of mRNA of STG I in HMC-1 by RT-PCR. We therefore propose that STG I plays an important role in exocytosis in large granules of mast cells, especially mature cell types.

In conclusion, the present study confirms that STG I mRNA and STG I protein are present in human mast cells, the tumor cells of SMCD, and HMC-1 cells, especially cells stimulated by PMA. STG I may play important roles in mast cell exocytosis.

	Acknowledgments

We thank Dr J.H. Butterfield (Mayo Medical School, Mayo Clinic, and Mayo Foundation; Rochester, MN) for supplying the HMC-1 cells and Dr H. Maruyama (Hoshigaoka Koseinenkin Hospital; Hirakata, Japan) for supplying tissues from a patient with SMCD.

Received for publication September 5, 2000; accepted November 1, 2000.

	Literature Cited

Top Summary Introduction Materials and Methods Results Discussion Literature Cited

Baram D, Linial M, Mekori YA, Sagi-Eisenberg R (1998) Cutting edge: Ca²⁺-dependent exocytosis in mast cells is stimulated by the Ca²⁺-sensor, synaptotagimin I. J Immunol 161:5120-5123[Abstract/Free Full Text]

Beaven MA, Metzger H (1993) Signal transduction by Fc receptors: the Fc epsilon RI case. Immunol Today 14:222-226[Medline]

Bradding P, Roberts JA, Britten KM, Montefort S, Djukanovic R, Mueller R, Heusser CH, Havarth PH, Holgate ST (1994) Interleukin-4, 5, and 6 and tumor necrosis factor in normal and asthmatic airways: evidence for the human mast cell as a source of these cytokines. Am J Respir Cell Mol Biol 10:471-480[Abstract]

Brose N, Petrenko AG, Sudhof TC, Jahn T (1992) Synaptotagmin: a calcium sensor on the synaptic vesicle surface. Science 256:1021-1025[Abstract/Free Full Text]

Butterfield JH, Weiler D, Dewald G, Gleich GJ (1989) Establishment of an immature mast cell line from a patient with mast cell leukemia. Leukemia Res 12:345-355[Medline]

Butterfield JH, Weiler DA, Hunt LW, Wynn SR, Roche PC (1990) Purification of tryptase from a human mast cell line. J Leukocyte Biol 47:409-419[Abstract]

Elferink LA, Peterson MR, Scheller RH (1993) A role for synaptotagmin (p65) in regulated exocytosis. Cell 72:153-159[Medline]

Gordon JR, Galli SJ (1990) Mast cells as a source of both preformed and immunological inducible TNF-/cachectin. Nature 346:274-276[Medline]

Holgate ST (1992) Basophil polymorph and mast cells. In McGee JOD, Isaacson PG, Wright NA, eds. Oxford Textbook of Pathology. Vol I. Oxford, Oxford University Press, 332-336

Inoue Y, King TE, Jr, Tinkle SS, Dockstader K, Newman LS (1996) Human mast cell basic fibroblast growth factor in pulmonary fibrotic disorders. Am J Pathol 149:2037-2054[Abstract]

Maeda K, Taniguchi H, Ohno I, Ohtsu H, Yamauchi K, Sakurai E, Tanno Y, Butterfield JH, Watanabe T, Shirato K (1998) Induction of L-histidine decarboxylase in a human mast cell line, HMC-1. Exp Hematol 26:325-331[Medline]

Marqueze B, Bkoudier JA, Mizuta M, Inagaki N, Seino S, Seagar M (1995) Cellular localization of synaptotagmin I, II, and III mRNAs in the central nervous system and pituitary and adrenal glands of the rat. J Neurosci 15:4906-4917[Abstract]

Maruyama H, Sugihara S, Ishihara K, Sada K, Tsutsumi M, Tsujiuchi T, Nakae D, Konishi Y (1998) Systemic mast cell disease with splenic infarction: a case report. Pathol Int 48:403-411[Medline]

Natkunam Y, Rouse RV (2000) Utility of paraffin section immunohistochemistry for C-KIT (CD117) in the differential diagnosis of systemic mast cell disease involving the bone marrow. Am J Surg Pathol 24:81-91[Medline]

Oberhauser AF, Balan V, Fernandez–Badilla CL, Fernandez JM (1994) RT-PCR cloning of Rab3 isoforms expressed in peritoneal mast cells. FEBS Lett 339:171-174[Medline]

Schiltz PM, Lieber J, Giorno RC, Claman HN (1993) Mast cell immunohistochemistry: non-immunological immunostaining mediated by non-specific F(ab')₂-mast cell secretory granule interaction. Histochem J 25:642-647[Medline]

Shoji–Kasai Y, Yoshida A, Sato K, Hoshino T, Ogura A, Kondo S, Fujimoto Y, Kuwahoca R, Kato R, Takahashi M (1992) Neurotransmitter release from synaptotagmin-deficient clonal variants of PC 12 cells. Science 256:1820-1823[Abstract/Free Full Text]

Smith J, Thompson N, Thompson J, Armstrong J, Hayes B, Crofts A, Squire J, Teahan C, Upton L, Solari R (1997) Rat basophilic leukaemia (RBL) cells overexpressing Rab3a have a reversible block in antigen-stimulated exocytosis. Biochem J 323:321-328

Sudhof TC (1995) The synaptic vesicle cycle: a cascade of protein-protein interactions. Nature 375:645-653[Medline]

Valent P (1995) Mast cell differentiation antigens: expression in normal and malignant cells and use for diagnostic purposes. Eur J Clin Invest 25:715-720[Medline]

Warnke RA, Weiss LM, Chan JC (1995) Systemic mastocytosis. In Tumors of the lymph nodes and spleen. Atlas of Tumor Pathology. Fasc 14. Ser 3. Washington, DC, Armed Forces Institute of Pathology, 398–410

Xi D, Chi H, Gainer H (1999) Analysis of synaptotagmin I-IV messenger RNA expression and developmental regulation in the rat hypothalamus and pituitary. Neuroscience 88:425-435[Medline]

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				B. Textor, A. H. Licht, J. P. Tuckermann, R. Jessberger, E. Razin, P. Angel, M. Schorpp-Kistner, and B. Hartenstein JunB Is Required for IgE-Mediated Degranulation and Cytokine Release of Mast Cells J. Immunol., November 15, 2007; 179(10): 6873 - 6880. [Abstract] [Full Text] [PDF]

				Y.-N. Lee, J. Tuckerman, H. Nechushtan, G. Schutz, E. Razin, and P. Angel c-Fos as a Regulator of Degranulation and Cytokine Production in Fc{epsilon}RI-Activated Mast Cells J. Immunol., August 15, 2004; 173(4): 2571 - 2577. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kimura, N. Articles by Kimura, I. Search for Related Content PubMed PubMed Citation Articles by Kimura, N. Articles by Kimura, I. Social Bookmarking                      What's this?

Guidelines | Subscriptions | About | exPRESS - Current - Archive | Business Information | Contact