Inverse correlation between heparan sulfate composition and heparanase-1 gene expression in thyroid papillary carcinomas: a potential role in tumor metastasis.

PURPOSE

Heparanase-1 (HPR1) is an endoglycosidase that degrades the side chains of heparan sulfate proteoglycan (HSPG), a key component in cell surfaces, the extracellular matrix (ECM), and the basement membrane (BM). The purpose of this study was to evaluate HPR1 expression in thyroid neoplasms and its effect in degrading the HSPG substrates in the ECM and BM and to determine its role in thyroid tumor metastasis.

EXPERIMENTAL DESIGN

HPR1 mRNA expression was analyzed by using in situ hybridization with a digoxigenin-labeled antisense RNA probe on paraffin-embedded tumor sections and reverse transcription-PCR (RT-PCR) in fresh tumor tissues. HPR1 protein expression was analyzed by using immunohistochemical staining with an anti-HPR1 rabbit antiserum and immunofluorescence (IF) with an anti-HPR1 monoclonal antibody. The effect of HPR1 expression in thyroid neoplasms was analyzed by examining the presence and integrity of the HSPG substrates in the ECM and BM using IF staining with a specific monoclonal antibody against heparan sulfate. The relationship of HPR1 expression in papillary thyroid carcinomas (PTCs) with various clinicopathological parameters was analyzed statistically. The role of HPR1 in thyroid tumor metastasis was further examined by comparing HPR1 levels in 10 thyroid tumor cell lines to their invasive and metastatic potential.

RESULTS

In situ hybridization analysis of 81 tumor samples (62 papillary carcinomas and 19 follicular adenomas) revealed that HPR1 was expressed at a much higher frequency in PTCs than in follicular adenomas (P<0.05). RT-PCR analyses of fresh tumor tissues revealed that HPR1 mRNA could be detected in primary and metastatic thyroid papillary carcinomas. HPR1 expression was confirmed at the protein level by immunohistochemical staining and IF stainings. IF analysis of HSPG revealed that HS was deposited abundantly in the BM of normal thyroid follicles and benign follicular adenomas but was absent in most thyroid papillary carcinomas. A lack of heparan sulfate in PTCs inversely correlated with HPR1 expression. Clinicopathological data analyses revealed that PTCs with local and distant metastases scored HPR1 positive at a significantly higher frequency than nonmetastatic thyroid cancers (P=0.02). To further explore the role of HPR1 in tumor metastases, we characterized HPR1 expression in 10 thyroid tumor cell lines using RT-PCR and Western blot and measured HPR1 enzymatic activity using a novel ELISA. HPR1 was differentially expressed in different types of cell lines; overexpression of HPR1 in two tumor cell lines led to a dramatic increase of their invasive potential in vitro in an artificial BM.

CONCLUSIONS

Our study suggests that HPR1 expressed in papillary carcinomas is functional and that HPR1 expression is associated with thyroid tumor malignancy and may significantly contribute to thyroid tumor metastases.