Stimulatory effects of pleural fluids from mesothelioma patients on CD44 expression, hyaluronan production and cell proliferation in primary cultures of normal mesothelial and transformed cells

CD44 and its ligand hyaluronan as potential biomarkers in malignant pleural mesothelioma: evidence and perspectives

Malignant pleural mesothelioma (MPM) is a rare and highly drug resistant tumor arising from the mesothelial surfaces of the lung pleura. The standard method to confirm MPM is the tedious, time-consuming cytological examination of cancer biopsy. Biomarkers that are detectable in pleural effusion or patient serum are reasonable options to provide a faster and noninvasive diagnostic approach. As yet, the current biomarkers for MPM lack specificity and sensitivity to discriminate this neoplasm from other lung tumors. CD44, a multifunctional surface receptor has been implicated in tumor progression in different cancers including MPM. The interaction of CD44 with its ligand, hyaluronan (HA) has demonstrated an important role in modulating cell proliferation and invasiveness in MPM. In particular, the high expression levels of these molecules have shown diagnostic relevance in MPM. This review will summarize the biology and diagnostic implication of CD44 and HA as well as the interaction of both molecules in MPM that will demonstrate their potential as biomarkers. Augmentation of the current markers in MPM may lead to an earlier diagnosis and management of this disease.

EMT induced by EGF and wounding activates hyaluronan synthesis machinery and EV shedding in rat primary mesothelial cells

The mesothelium is a membrane that forms the lining of several body cavities. It is composed of simple squamous mesothelial cells that secrete a glycosaminoglycan-rich lubricating fluid between inner organs. One of the most abundant glycosaminoglycans of those fluids is hyaluronan, which is synthesized on a plasma membrane and especially on apical filopodia of cultured cells. Our recent study showed that similar hyaluronan-rich protrusions are found in mesothelial lining in vivo, which suggests that hyaluronan synthesis in plasma membrane protrusions is a general process. However, the mesothelial lining was negative for the hyaluronan receptor CD44 while in many previous studies cultured mesothelial cells have been shown to express CD44. To further explore these findings we induced epithelial to mesenchymal transition in primary rat mesothelial cells by EGF-treatment and scratch wounding. Surprisingly, the results showed that at a normal epithelial, confluent stage the mesothelial cells are negative for CD44, but EMT induced by EGF or wounding activates CD44 expression and the whole hyaluronan synthesis machinery. In addition to typical EMT-like morphological changes, the growth of apical filopodia and budding of extracellular vesicles (EVs) were induced. In summary, the results of this study show that the activation of hyaluronan synthesis machinery, especially the expression of CD44 is strongly associated with EMT induced by EGF and wounding in mesothelial cells. Moreover, EMT enhances the secretion of EVs that carry CD44 and hyaluronan, which may be important regulators in EV interactions with their targets and ECM remodeling. The results of the present study also suggest that CD44 is a potential marker for EVs, especially those secreted from cells during tissue repair and pathological processes.

Genetics of malignant pleural mesothelioma: molecular markers and biologic targets

MPM is a poorly understood lethal malignancy. Although the pathobiology of MPM is not completely elucidated, new genomic technology is likely to help shed light on the mechanisms of carcinogenesis through genome-wide screening of tumor-specific gene expression. Related efforts to identify the molecular markers of mesothelioma are pursued with the aim of refining current diagnostic capabilities, predicting prognosis, and designing appropriate trimodality programs. These new genomic tools also will assist efforts to tailor current adjuvant and neoadjuvant therapies, optimizing their effect and furthering research that may lead to new therapeutic options.

Hyaluronan content in pleural fluid as a prognostic factor in patients with malignant pleural mesothelioma

BACKGROUND

Regardless of the modality of therapy used, malignant pleural mesothelioma is a highly treatment-resistant and invariably fatal disease. Identification of prognostic variables are important for future investigational therapeutic studies.

METHODS

The prognostic significance of various clinical variables, including hyaluronan levels in pleural fluid, was evaluated in a retrospective analysis in 100 patients with histologically confirmed malignant pleural mesothelioma.

RESULTS

The overall median survival was 11.5 months. Univariate analyses identified histologic subtype, i.e., epithelial or mixed, and elevated content of hyaluronan in the pleural effusion as significant prognostic variables. A multivariate analysis confirmed the independent predictive power of histologic subtype, and an elevated concentration of hyaluronan in the pleural fluid also indicated longer survival in older patients and in patients receiving therapy other than supportive.

CONCLUSIONS

The prognostic value of histologic subtype and the concentration of hyaluronan in pleural effusions should be considered when designing and evaluating treatment trials for patients with malignant pleural mesothelioma.

Hyaluronan production increases the malignant properties of mesothelioma cells

Malignant pleural mesotheliomas is in most cases associated with elevated amounts of hyaluronan. To investigate the importance of hyaluronan for the malignant properties of mesotheliomas, we have expressed murine hyaluronan synthase 2 (HAS2) in the non-hyaluronan producing mesothelioma cell line, Mero-25. We found that upon hyaluronan overproduction the mesothelioma cells changed their epitheloid character to a fibroblastic phenotype and were surrounded by pericellular matrices, the size of which correlated to the amount of synthesized hyaluronan. HAS2-transfected cells with the ability to synthesize about 520 ng hyaluronan/5 x 10(4)cells/24 h exhibited about a 2-fold increase in the expression of the cell surface hyaluronan receptor CD44 and their locomotion increased compared to that of mock-transfected Mero-25 cells. Furthermore, the malignant properties of mesothelioma cell clones as determined by the ability to grow in a soft agar assay correlated to their hyaluronan production. These results provide evidence for an important role of hyaluronan in the aggressive spread of mesotheliomas in adjacent non-cancerous stromal tissues.

Use of E-cadherin and CD44 aids in the differentiation between reactive mesothelial cells and carcinoma cells in pelvic washings

BACKGROUND

The presence of malignant cells in peritoneal washings is an independent prognostic factor in the evaluation of gynecologic malignancies. The differentiation between reactive mesothelial cells and carcinoma cells can be a diagnostic challenge based on morphology alone. The expression of some cell adhesion molecules may be helpful in the differential diagnosis.

METHODS

To evaluate the specificity of 2 transmembrane cell adhesion proteins (E-cadherin and CD44) in the differentiation of mesothelial cells from carcinoma cells in pelvic washings, formalin fixed, paraffin embedded cell blocks of pelvic washings from 19 cases of metastatic ovarian adenocarcinoma and 16 cases of benign peritoneal washings were immunostained with monoclonal antibodies to E-cadherin and CD44. The staining patterns were evaluated blindly by three observers. Positive staining was defined as uniform membranous staining for each marker.

RESULTS

Fourteen benign peritoneal washings (87.5%) demonstrated immunoreactivity with anti-CD44. On the contrary, only four adenocarcinomas (21.1%) demonstrated anti-CD44 immunoreactivity. E-cadherin expression was identified in only 2 benign peritoneal washings (12.5%) whereas 16 adenocarcinomas (84.2%) strongly expressed E-cadherin. The differences in immunostaining for both CD44 and E-cadherin between benign and malignant peritoneal washings were statistically significant. The combination of positive staining for E-cadherin and negative staining for CD44 was 100% specific for metastatic adenocarcinoma, whereas a combination of negative staining for E-cadherin and positive staining for CD44 was 100% specific for reactive mesothelial cells.

CONCLUSIONS

Both E-cadherin and CD44 reliably distinguish reactive mesothelial cells from adenocarcinoma. The combination of E-cadherin/CD44 is highly specific and is a useful diagnostic adjunct with which to distinguish benign reactive mesothelial cells from adenocarcinoma in pelvic washings.