S100 protein in oral biology and pathology

Plasmacytoid cells in salivary pleomorphic adenoma: an alternative interpretation of their immunohistochemical characteristics highlights function and capability for epithelial-mesenchymal transition

OBJECTIVES

Plasmacytoid cells (PLCs) in salivary pleomorphic adenoma (SPA) are regarded as modified neoplastic myoepithelia and define plasmacytoid myoepithelioma (pMYO). However, histochemically, immunohistochemically and ultrastructurally, PLCs fail to demonstrate frank myogenous properties. Epithelial-mesenchymal transition (EMT) may explain the phenotypes in SPA. Our aim was to evaluate (1) PLCs with accepted or purported myoepithelial and EMT-related markers; and (2) pMYOs for PLAG1 aberrations by using fluorescence in situ hybridization.

STUDY DESIGN

Eight SPAs with or without PLC-predominance and 3 pMYOs were immunohistochemically studied.

RESULTS

PLCs in SPA and pMYO exhibited strong, scattered to diffuse positivity for K7, rare K14 positivity and were mostly negative for α-smooth muscle actin, h-caldesmon, and p63/p40. S100 staining was strong and diffuse, whereas calponin was variable. DOG1 was negative. PLCs in pMYO and PLC-rich SPA exhibited selective or diffuse WT1 and D2-40 immunoreactivity. EMT markers SNAIL/SLUG exhibited strong and variable immunoreactivity in PLCs in contrast to weak or absent E-cadherin expression. SOX10 was diffusely and strongly positive. PLAG1 rearrangement was present in 1 pMYO.

CONCLUSIONS

PLCs mostly fail to express myoepithelial markers; PLCs are neoplastic cells adapting to microenvironmental changes and capable of EMT; and tumors composed solely of PLCs are apparently SPAs depleted of a ductal component.

Certainty of S100 from Physiology to Pathology

S100 exists in wide variety of tissues and cell types, originally isolated from brain tissue and they are of low molecular weight proteins. S100 is evenly distributed in cytoplasm and also in nucleoplasm and is involved in both intercellular and extracellular functions. S100 protein is generally expressed in normal and also in pathological conditions. In current review, we discuss: a) update nomenclature of the various S100 proteins, b) expression of S100 in oral diseases (different soft tissue tumors, odontogenic cyst and tumor) for diagnostic value and also to know their histogenesis, c) role of S100 and RAGE receptor in oral squamous cell carcinoma.

S100A6 expression and function in human osteosarcoma

There is a critical need to identify markers that can accurately identify existing or predict future metastatic disease in patients with osteosarcoma since the majority of patients present with undetectable micrometastatic disease. We previously reported S100A6 is overexpressed in human osteosarcoma and increased expression of S100A6 by immunohistochemistry correlated with decreased clinical metastasis. We have established 11 primary cultures from biopsies of patients with osteosarcoma and ten of the 11 primary cultures have increased expression of S100A6 relative to normal human osteoblasts. To further explore possible mechanisms for metastasis suppression previously reported, we used in this report siRNA-mediated knockdown of S100A6 in four commonly used human osteosarcoma lines, then examined their cell adhesion, migration, and invasion properties. Knockdown of S100A6 expression inhibited cell adhesion and promoted cell migration and invasion in these lines. Conversely, S100A6 overexpression enhanced cell adhesion and inhibited cell invasion. Our data demonstrate S100A6 is commonly overexpressed in human osteosarcoma. S100A6 may inhibit osteosarcoma metastasis by promoting cell adhesion and inhibiting cell motility and invasion. Thus, S100A6 may be considered a potential marker for human osteosarcoma with prognostic value for identifying patients without metastases.

Increased expression of S100A6 is associated with decreased metastasis and inhibition of cell migration and anchorage independent growth in human osteosarcoma

While most osteosarcoma patients have metastatic or micrometastatic lesions, less than 15% of them have clinically detectable metastatic diseases at presentation. To identify potential markers that may predict osteosarcoma metastasis, we analyzed the expression of S100A6 in 50 osteosarcoma cases and found that 84% of the analyzed specimens stained positive for S100A6. There is a trend towards decreased clinically evident metastasis with increased S100A6 staining. Overexpression of S100A6 in osteosarcoma cells decreases cell motility and anchorage independent growth on collagen gels. Our findings provide evidence that, while S100A6 is commonly overexpressed in human osteosarcoma, loss of its expression correlates with a metastatic phenotype.

Heterocomplex formation between metastasis-related protein S100A4 (Mts1) and S100A1 as revealed by the yeast two-hybrid system

S100A4 (Mts1) is a Ca(2+)-binding protein of the S100 family. This protein plays an important role in promoting tumor metastasis. In order to identify S100A4 interacting proteins, we have applied the yeast two-hybrid system as an in vivo approach. By screening a mouse mammary adenocarcinoma library, we have demonstrated that S100A4 forms a heterocomplex with S100A1, another member of the S100 family. The non-covalent heterodimerization was confirmed by fluorescence spectroscopy and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Mutational analysis revealed that replacement of Cys(76) and/or Cys(81) of S100A4 by Ser abolishes the S100A4/S100A1 heterodimerization, but does not affect the S100A4 homodimerization in vivo.

Functional roles of S100 proteins, calcium-binding proteins of the EF-hand type

A multigenic family of Ca2+-binding proteins of the EF-hand type known as S100 comprises 19 members that are differentially expressed in a large number of cell types. Members of this protein family have been implicated in the Ca2+-dependent (and, in some cases, Zn2+- or Cu2+-dependent) regulation of a variety of intracellular activities such as protein phosphorylation, enzyme activities, cell proliferation (including neoplastic transformation) and differentiation, the dynamics of cytoskeleton constituents, the structural organization of membranes, intracellular Ca2+ homeostasis, inflammation, and in protection from oxidative cell damage. Some S100 members are released or secreted into the extracellular space and exert trophic or toxic effects depending on their concentration, act as chemoattractants for leukocytes, modulate cell proliferation, or regulate macrophage activation. Structural data suggest that many S100 members exist within cells as dimers in which the two monomers are related by a two-fold axis of rotation and that Ca2+ binding induces in individual monomers the exposure of a binding surface with which S100 dimers are believed to interact with their target proteins. Thus, any S100 dimer is suggested to expose two binding surfaces on opposite sides, which renders homodimeric S100 proteins ideal for crossbridging two homologous or heterologous target proteins. Although in some cases different S100 proteins share their target proteins, in most cases a high degree of target specificity has been described, suggesting that individual S100 members might be implicated in the regulation of specific activities. On the other hand, the relatively large number of target proteins identified for a single S100 protein might depend on the specific role played by the individual regions that in an S100 molecule contribute to the formation of the binding surface. The pleiotropic roles played by S100 members, the identification of S100 target proteins, the analysis of functional correlates of S100-target protein interactions, and the elucidation of the three-dimensional structure of some S100 members have greatly increased the interest in S100 proteins and our knowledge of S100 protein biology in the last few years. S100 proteins probably are an example of calcium-modulated, regulatory proteins that intervene in the fine tuning of a relatively large number of specific intracellular and (in the case of some members) extracellular activities. Systems, including knock-out animal models, should be now used with the aim of defining the correspondence between the in vitro regulatory role(s) attributed to individual members of this protein family and the in vivo function(s) of each S100 protein.

Oral granular cell tumours: a histological and immunocytochemical study

In a series of nine cases of intra-oral granular cell tumors (GCTs) an attempt was made, using both histochemical and immunocytochemical methods, to determine whether these tumours show Schwann-cell or neuroendocrine differentiation. Positive immunostaining with protein gene product 9.5 (PGP 9.5), neurone-specific enolase (NSE) and S-100, in contrast to predominantly negative immunostaining in 12 cases of neurilemmoma of the head and neck, and a similar pattern of staining with luxol fast blue to five known neuroendocrine tumours, strongly suggests that granular cell tumors may be neuroendocrine in nature.

Expression pattern of S100 calcium-binding proteins in human tumors

The S100 Ca(2+)-binding proteins recently became of major interest because of their differential expression in neoplastic tissues, their involvement in metastatic processes, and the clustered organization of at least 10 S100 genes on human chromosome 1q21, a region frequently rearranged in several tumors. As a first attempt towards a specific and differentiated immunohistochemical classification of human tumors, we produced, purified and characterized a number of human recombinant S100 proteins and raised specific polyclonal antibodies. Their distinct cellular and intracellular localization was examined by immunohistochemical methods in normal and cancerogenic human tissues and cell lines. S100A1 and S100A2 can be detected in a few normal tissues only, whereas S100A4, S100A6, and S100B are expressed at higher levels in cancer tissues. In the future, these S100 antibodies will potentially be of great value in cancer diagnosis and therapy.

A histological, lectin and S-100 histochemical study of the developing prenatal human sublingual salivary gland

Lectin and S-100 protein histochemistry during fetal growth and development (10-38th gestational weeks) of these glands was studied. The histological development of glandular structures followed the known pattern for other salivary glands. Using biotinylated lectins Ulex europeus-I, Dolichos biflorus, Glycine maximus (soyabean), Helix pomatia, Arachis hypogaea (peanut) and Triticum vulgare (wheatgerm), the binding level and, by implication, the concentration of associated specific oligosaccharide available for binding was low at 10 to 19 weeks and generally higher as maturity increased through the middle and late stages of development. S-100 protein reactivity was demonstrated in the cytoplasm of basophil acinar cells of the gland primordia from their origin. Stereological analysis of these developing salivary glands showed a highly significant progressive increase in proportional gland volume occupied by acini from 25% at 20 weeks to 60% at 38 weeks (p < 0.0001), and a comparable halving of the relative gland volume occupied by connective tissue in the same period (p < 0.0001). The extent of these changes depended upon the stage of differentiation and maturation of the glands but by the late stage of fetal development, histochemical reactions were similar to known adult patterns.

A clinicopathological and immunohistochemical analysis of primary oral mucosal melanoma

Nine cases of primary oral mucosal melanoma in Caucasian patients were reviewed and the tumours analysed for expression of S100, HMB45, NKI/C3, HLA-DR, PCNA, cytokeratin and von Willebrand factor. The clinical, histopathological and immunohistochemical features were quite distinctive and our findings support previous suggestions that oral melanoma should be classified as a separate entity rather than as a sub-type of cutaneous melanoma.