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Discrepancy between mRNA and protein expression of tumour suppressor maspin in synovial tissue may contribute to synovial hyperplasia in rheumatoid arthritis

J Schedel^1,2, O Distler², M Woenckhaus³, R E Gay², B Simmen⁴, B A Michel², U Müller-Ladner¹ and S Gay²

¹ Department of Internal Medicine I, Division of Rheumatology and Clinical Immunology, University Hospital of Regensburg, D-93053 Regensburg, Germany
² Centre of Experimental Rheumatology and WHO Collaborating Centre for Molecular Biology and Novel Therapeutic Strategies for Rheumatic Diseases, Department of Rheumatology, University Hospital of Zurich, CH-8091 Zurich, Switzerland
³ Department of Pathology, University Hospital of Regensburg, D-93053 Regensburg, Germany
⁴ Department of Orthopaedic Surgery, Schulthess Hospital, CH-8006 Zurich, Switzerland

Correspondence to:
Correspondence to:
Dr J Schedel
Department of Internal Medicine I, Division of Rheumatology and Clinical Immunology, University Hospital of Regensburg, D-93042 Regensburg, Germany; joerg.schedel{at}klinik.uni-regensburg.de

Objective: To investigate the expression of maspin in RA synovial tissue and compare it with the expression in osteoarthritis (OA) and normal synovial tissue (NS).

Methods: Using specific primers for maspin, a 237 bp fragment was amplified from cDNA obtained from cultured RA, OA, and normal synovial fibroblasts (SF) by RT-PCR. Additionally, mRNA expression levels were determined quantitatively by real time PCR. mRNA expression of maspin was investigated on snap frozen and paraffin embedded synovial tissue sections by in situ hybridisation. Immunohistochemistry was used to identify the cell type expressing maspin. SDS-PAGE and western blotting were performed to evaluate the protein expression in cultured SF. To confirm protein synthesis in situ, immunohistochemistry with specific anti-maspin antibodies was performed in synovial tissue sections of patients with RA.

Results: RT-PCR showed expression of maspin in all cDNA samples from cultured SF. Maspin mRNA was found to be decreased in RA SF twofold and 70-fold compared with OA SF and NS SF, respectively. Maspin mRNA was expressed in RA, OA, and normal synovial tissue. Importantly, maspin transcripts were also found at sites of invasion into cartilage and bone. At the protein level, maspin could be detected in RA and, less prominently, OA SF. In RA synovial tissue, maspin protein was detected in only a few synovial lining cells.

Conclusion: Maspin is expressed intensively in RA SF at the mRNA level, but only slightly at the protein level, possibly owing to down regulation of maspin; this may contribute to the hyperplasia of synovial tissue in RA.

Abbreviations: maspin, mammary serine protease inhibitor; NS, normal synovial tissue; OA, osteoarthritis; PAI, plasminogen activator inhibitor; RA, rheumatoid arthritis; RT-PCR, reverse transcriptase-polymerase chain reaction; SDS-PAGE, sodium dodecyl sulphate-polymerase gel electrophoresis; SF, synovial fibroblasts; uPA, urokinase plasminogen activator

Keywords: maspin; rheumatoid arthritis; synovial fibroblasts; synovial hyperplasia; tumour suppressor genes

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