Does soluble CD44 reflect the clinical behavior of human cancer?

Evaluation of CD44 and CD44v6 in colorectal carcinoma patients: soluble forms in relation to tumor tissue expression and metastasis

INTRODUCTION

It has been shown that CD44 may be associated with poor prognosis in various human malignancies. This study was designed to investigate and compare the prognostic relevance and clinical value of soluble forms of CD44 and its variant v6 (CD44v6) and their tissue expression in colorectal carcinoma.

MATERIALS AND METHODS

Serum levels of pre- and postoperative CD44 and CD44v6 molecules were evaluated in 37 colorectal cancer patients and compared to healthy individuals.

RESULTS AND DISCUSSION

The serum levels of soluble CD44 and CD44v6 showed no significant decrease after surgical resection of the tumor (p = 0.5). Both CD44 and CD44v6 serum levels either before or after surgery were significantly higher in patients than in normal individuals (p < 0.001). The serum level of CD44v6 molecule was higher in patients with lymph node metastasis than other patients (p = 0.05) implying the role of this molecule in tumor progression. Immunohistochemical staining showed expression of CD44 in 14.3% and CD44v6 in 42.9% of the tumor samples. The expression of CD44v6 was associated with metastatic involvement of lymph nodes (p = 0.03). CD44v6 expression was positively correlated with its level in the serum of patients (p = 0.04).

CONCLUSIONS

Results of this study showed that CD44v6 expression level either in the soluble form or in the cell membrane is associated with tumor metastasis indicating the importance of this molecule in progression of colorectal carcinoma. The serum levels of soluble CD44 as well as CD44v6 might be useful markers for tumor screening.

A PSP94-derived Peptide PCK3145 inhibits MMP-9 Secretion and Triggers CD44 Cell Surface Shedding: Implication in Tumor Metastasis

PURPOSE

PCK3145 is a synthetic peptide corresponding to amino acids 31-45 of prostate secretory protein 94, which can reduce experimental skeletal metastases and prostate tumor growth in vivo. Part of its biological action involves the reduction of circulating plasma matrix metalloproteinase (MMP)-9, a crucial mediator in extracellular matrix (ECM) degradation during tumor metastasis and cancer cell invasion. The antimetastatic mechanism of action of PCK3145 is however, not understood.

EXPERIMENTAL DESIGN

HT-1080 fibrosarcoma cells were treated with PCK3145, and cell lysates used for immunoblot analysis of small GTPase RhoA and membrane type (MT)1-MMP protein expression. Conditioned media was used to monitor soluble MMP-9 gelatinolytic activity by zymography and protein expression by immunoblotting. RT-PCR was used to assess RhoA, MT1-MMP, MMP-9, RECK, and CD44 gene expression. Flow cytometry was used to monitor cell surface expression of CD44 and of membrane-bound MMP-9. Cell adhesion was performed on different purified ECM proteins, while cell migration was specifically performed on hyaluronic acid (HA).

RESULTS

We found that PCK3145 inhibited HT-1080 cell adhesion onto HA, laminin-1, and type-I collagen suggesting the common implication of the cell surface receptor CD44. In fact, PCK3145 triggered the shedding of CD44 from the cell surface into the conditioned media. PCK3145 also inhibited MMP-9 secretion and binding to the cell surface. This effect was correlated to increased RhoA and MT1-MMP gene and protein expression.

CONCLUSIONS

Our data suggest that PCK3145 may antagonize tumor cell metastatic processes by inhibiting both MMP-9 secretion and its potential binding to its cell surface docking receptor CD44. Such mechanism may involve RhoA signaling and increase in MT1-MMP-mediated CD44 shedding. Together with its beneficial effects in clinical trials, this is the first demonstration of PCK3145 acting as a MMP secretion inhibitor.

CD44 cell adhesion molecules

The CD44 proteins form a ubiquitously expressed family of cell surface adhesion molecules involved in cell-cell and cell-matrix interactions. The multiple protein isoforms are encoded by a single gene by alternative splicing and are further modified by a range of post-translational modifications. CD44 proteins are single chain molecules comprising an N-terminal extracellular domain, a membrane proximal region, a transmembrane domain, and a cytoplasmic tail. The CD44 gene has only been detected in higher organisms and the amino acid sequence of most of the molecule is highly conserved between mammalian species. The principal ligand of CD44 is hyaluronic acid, an integral component of the extracellular matrix. Other CD44 ligands include osteopontin, serglycin, collagens, fibronectin, and laminin. The major physiological role of CD44 is to maintain organ and tissue structure via cell-cell and cell-matrix adhesion, but certain variant isoforms can also mediate lymphocyte activation and homing, and the presentation of chemical factors and hormones. Increased interest has been directed at the characterisation of this molecule since it was observed that expression of multiple CD44 isoforms is greatly upregulated in neoplasia. CD44, particularly its variants, may be useful as a diagnostic or prognostic marker of malignancy and, in at least some human cancers, it may be a potential target for cancer therapy. This review describes the structure of the CD44 gene and discusses some of its roles in physiological and pathological processes.

In vitro expression of soluble and cell surface-associated CD44 on endometrial cells from women with and without endometriosis

BACKGROUND

Endometriosis is one of the most common benign gynaecological diseases, and attachment of retrogradely shed viable endometrial cells is considered to be important in its development. CD44 is a multifunctional adhesion molecule that undergoes alternative splicing, giving rise to different isoforms.

METHODS

The expression of cell surface-associated CD44 std, v4, v5, v6 and v10 variants before and after cytokine treatment was investigated in endometrial cultures derived from 10 endometriosis patients and 22 women without the disease using immunocytochemistry. The immunoreactivity of soluble CD44 std, v5 and v6 variants was measured in culture medium using an enzyme immunoassay kit.

RESULTS

We report on the presence of soluble CD44 in endometrial culture supernatants. In particular, circulating CD44 standard form levels were significantly higher than levels of splice variants. We also found that both epithelial and stromal cells express surface-associated CD44 molecules in a distinct pattern and that this expression is not modulated by tumour necrosis factor (TNF)-alpha or/and interleukin 1 (IL-1) alpha/beta. Finally, cell surface-associated as well as soluble CD44 expression was similar in the two groups.

CONCLUSION

Our results indicate that endometrial cells can serve as a source of circulating CD44, but a direct role in the pathogenesis of endometriosis is rather improbable.

CD44 isoform expression in the diffuse neuroendocrine system. II. Benign and malignant tumors

The membrane glycoprotein CD44 may be associated with aggressive behavior, dissemination, and poor prognosis of a variety of human tumors. In order to extend our knowledge on the expression and significance of CD44 in cells of the dispersed neuroendocrine system we investigated a spectrum of 134 neuroendocrine tumors, including pituitary adenomas, medullary thyroid carcinomas, parathyroid adenomas, pheochromocytomas, neuroblastomas, small-cell lung carcinomas, and bronchopulmonary, pancreatic, and gastrointestinal neuroendocrine tumors immunohistochemically for CD44 standard and variant exon-encoded gene products (CD44v3, -v4, -v5, -v6, -v9). Furthermore, we compared protein expression with that of CD44 mRNA by reverse-transcriptase PCR and Southern blot hybridization in a subset of tumors. Our results show that CD44 expression is correlated with the "histogenetic origin" of the appropriate neuroendocrine neoplasm. Endoderm-derived tumors generally express 3'-end CD44 variant exon-containing isoforms, whereas neural crest-derived tumors rarely are positive for CD44. Furthermore, we provide evidence that CD44 expression is not correlated with metastatic disease or a particular hormonal phenotype but exhibits an association with the degree of cellular differentiation. Thus, CD44 is not useful as marker for malignancy or prognosis. The number of patients with clinical follow-up data in our study was too small to allow definite conclusions about a possible correlation between CD44 expression and prognosis. But CD44 may help to better classify neoplasms with an unclear neuroendocrine phenotype.