Ultrastructural immunolocalization of a cartilage-specific proteoglycan, aggrecan, in salivary pleomorphic adenomas

Heterogeneity and versatility of the extracellular matrix during the transition from pleomorphic adenoma to carcinoma ex pleomorphic adenoma: cumulative findings from basic research and new insights

Pleomorphic adenoma (PA) is the most common salivary gland tumor, accounting for 50%-60% of these neoplasms. If untreated, 6.2% of PA may undergo malignant transformation to carcinoma ex-pleomorphic adenoma (CXPA). CXPA is a rare and aggressive malignant tumor, whose prevalence represents approximately 3%-6% of all salivary gland tumors. Although the pathogenesis of the PA-CXPA transition remains unclear, CXPA development requires the participation of cellular components and the tumor microenvironment for its progression. The extracellular matrix (ECM) comprises a heterogeneous and versatile network of macromolecules synthesized and secreted by embryonic cells. In the PA-CXPA sequence, ECM is formed by a variety of components including collagen, elastin, fibronectin, laminins, glycosaminoglycans, proteoglycans, and other glycoproteins, mainly secreted by epithelial cells, myoepithelial cells, cancer-associated fibroblasts, immune cells, and endothelial cells. Like in other tumors including breast cancer, ECM changes play an important role in the PA-CXPA sequence. This review summarizes what is currently known about the role of ECM during CXPA development.

Effect of Xylosyltransferase-I Silencing on Implanting Growth of Salivary Pleomorphic Adenoma

BACKGROUND Salivary pleomorphic adenoma is one of the most common salivary gland tumors. It has a relatively high tendency to recur and a high risk of malignant transformation. The present study aimed to study the effect of XT-I gene silencing on the implanting growth of salivary pleomorphic adenoma. MATERIAL AND METHODS Primary cultures of SPA cells and fibroblasts from the same patient were assessed. The adenovirus vector Ad-shRNA-XT-I was constructed and transfected into SPA cells. The expression of XT-I gene and XT-I protein was detected by real-time PCR and Western blot. The contents of proteoglycans were detected. The SPA cells transfected with Ad-shRNA-XT-I (group SPA-XT-I) and Ad-shRNA-HK (group SPA-HK), as well as without transfection (group SPA), were implanted into ADM scaffold with fibroblasts and then transferred into 18 BALB/C-nu nude mice for 3 months. RESULTS Primary cultures showed SPA cells were positive for human CK and S-100 protein and the fibroblasts were positive for human vimentin. The expressions of XT-I gene and protein were decreased by 51% and 51.31%, respectively. The content of proteoglycans was reduced by 48.45%. The results of the implanting growth in vitro and in vivo of nude mice indicated that no tumors grew in the SPA-XT-I group, whereas SPA grew in groups SPA-HK and SPA positive for human a-SMA, S-100 protein, and calponin. CONCLUSIONS XT-I gene silencing effectively inhibited the implanting growth of SPA.

Characteristic Formation of Hyaluronan-Cartilage Link Protein-Proteoglycan Complex in Salivary Gland Tumors

Hyaluronan (HA) and its binding molecules, cartilage link protein (LP) and proteoglycan (PG), are structural components of the hydrated extracellular matrix. Because these molecules play important roles in the tumor microenvironment, we examined the distribution of HA, LP, versican, and aggrecan in salivary gland tumors using histochemical and immunohistochemical methods, including double staining. LP was present in pleomorphic adenoma (PA) and adenoid cystic carcinoma (ACC) tissues, and aggrecan was absent in the malignant tumors that we investigated. LP colocalized with both HA and aggrecan in the chondromyxoid matrix of PA, suggesting the presence of a HA-LP-aggrecan complex. Furthermore, the HA-LP-versican complex could be observed in the pseudocystic space of the cribriform structures in ACC. The characteristic HA-LP-PG complex in PA and ACC might play a role in the behavior of tumors, and immunohistochemical analysis of these molecules could represent a diagnostic adjunct for salivary gland tumors.

Antithetic roles of proteoglycans in cancer

Proteoglycans (PGs), a family of complex post-translationally sculptured macromolecules, are fundamental regulators of most normal and aberrant cellular functions. The unparalleled structural-functional diversity of PGs endows them with the ability to serve as critical mediators of the tumor cells' interaction with the host microenvironment, while directly contributing to the organization and dynamic remodeling of this milieu. Despite their indisputable importance during embryonic development and in the adult organism, and their frequent dysregulation in tumor lesions, their precise involvement in tumorigenesis awaits a more decisive demonstration. Particularly challenging is to ascertain to what extent selected PGs may catalyze tumor progression and to what extent they may inhibit it, implying antithetic functions of individual PGs. Integrated efforts are needed to consolidate the routine use of PGs in the clinical monitoring of cancer patients and to broaden the exploitation of these macromolecules as therapeutic targets. Several PGs have the required attributes to be contemplated as effective antigens for immunotherapeutic approaches, while the tangible results obtained in recent clinical trials targeting the NG2/CSPG4 transmembrane PG urge further development of PG-based cancer treatment modalities.