ABSTRACT
Heparan sulphate proteoglycans are major components of the liver extracellular matrix. Their cleavage by heparanase (endo-beta-glucuronidase) may thus be involved in liver-specific normal and pathological processes. Heparanase mRNA and protein were expressed during liver development but not in the mature healthy liver. A biphasic gain of heparanase expression, detected by immunostaining, western blotting, and real-time RT-PCR, was clearly noted following partial hepatectomy, peaking at 12 and 96-168 h and subsiding 2 weeks post-surgery. Expression of heparan sulphate gradually increased throughout the regeneration process. Unlike heparanase, baseline levels of matrix metalloproteinase-2 (MMP-2) were detected in the intact liver, increasing up to 4 days following partial hepatectomy and subsiding at day 10. Bands matching MMP-9 were absent prior to hepatectomy, but visible 2 h post-hepatectomy. Thioacetamide-induced liver fibrosis was associated with increased levels of MMP-9 and MMP-2, correlating with the severity of the disease. Elevated heparanase levels were noted in the early stages of fibrosis, with no further increase evident in rats exhibiting higher fibrotic grades. Taken together, these data suggest a role for heparanase during liver development and remodelling.
Subject(s)
Heparin Lyase/analysis , Hepatectomy/methods , Liver/embryology , Animals , Blotting, Western/methods , Electrophoresis, Polyacrylamide Gel/methods , Immunohistochemistry/methods , In Situ Hybridization/methods , Liver/enzymology , Liver Cirrhosis, Experimental/metabolism , Liver Regeneration/physiology , Male , Matrix Metalloproteinase 2/metabolism , Matrix Metalloproteinase 9/metabolism , RNA, Messenger/analysis , Rats , Rats, Sprague-Dawley , Reverse Transcriptase Polymerase Chain Reaction/methodsABSTRACT
The lysyl oxidase gene family members function as extracellular matrix modulating enzymes. We have found that another member of this family, lysyl oxidase related protein-1 (LOR-1), is highly expressed in metastatic breast cancer-derived cell lines but not in the nonmetastatic estrogen-dependent MCF-7 cells. Furthermore, LOR-1 expression in periductal tumor cells of breast carcinomas is significantly correlated with increased tumor malignancy. MCF-7 cells expressing recombinant LOR-1 formed estrogen-dependent tumors that developed much slower than tumors derived from empty vector-transfected MCF-7 cells. The cells of these LOR-1-expressing tumors were surrounded by a high concentration of dense collagen fibers, and the tumors contained many fibrotic foci. Induction of fibrosis in vivo by lysyl oxidase-like enzymes has never been observed before and suggests that LOR-1 may function as an autonomous inducer of fibrosis. The appearance of fibrotic foci in spontaneous breast cancer tumors is correlated with poor prognosis and metastasis, and we, therefore, examined the invasiveness of the LOR-1-expressing tumors. LOR-1-expressing MCF-7 cells invaded the pseudocapsules surrounding the tumors. In contrast, vector-transfected MCF-7 cells did not invade the pseudocapsules. This observation suggests that LOR-1 enhances the malignancy of the tumors. Furthermore, the LOR-1-expressing tumor cells invaded blood vessels, nerves, and muscles adjacent to the tumor, indicating that the LOR-1-expressing MCF-7 cells acquired metastatic properties. We conclude that LOR-1 promotes tumor fibrosis and tumor invasiveness simultaneously, which indicates that these two processes may be associated.
