Heparanase Influences Expression and Shedding of Syndecan-1, and Its Expression by the Bone Marrow Environment Is a Bad Prognostic Factor in Multiple Myeloma.

The heparan sulfate (HS) proteoglycan (PG) syndecan-1 plays a major role in multiple myeloma (MM), in part by concentrating HS-binding growth factors on the surface of MM cells (MMC). The function of HSPG is regulated by extracellular enzymes that modulate the structure of HS-chains. One such enzyme is heparanase (HPSE), an endo-glucuronidase that cleaves HS chains at only a few sites, resulting in fragments of 10–20 sugar units long that are biologically active.

Using Affymetrix microarrays and real-time RT-PCR, we showed that the gene encoding HPSE was expressed by 11/19 myeloma cell lines (HMCLs). In HSPE-positive HMCLs, syndecan-1 mRNA expression and production of soluble syndecan-1, unlike expression of membrane syndecan-1, were significantly increased. Downregulation of HPSE by HPSE-siRNA resulted in a decrease of syndecan-1 mRNA expression and soluble syndecan-1 production, without affecting membrane syndecan-1. Contrary to HMCLs, HPSE was expressed in only 4/39 primary MMC samples at a low level, whereas it was highly expressed in 36/39 whole bone marrow (WBM) microenvironment samples. In the latter, HPSE was expressed at a median level in polynuclear cells and T cells, at high level in monocytes and osteoclasts, and it was not expressed in BM stromal cells. In order to investigate the connection of clinical parameters with HPSE gene expression, 30/39 myeloma patients treated with high dose chemotherapy and autologous stem cell transplantation where classified into two groups: 15 patients with the lowest or the highest HPSE expression in the WBM. The HPSE^high group had an increased percentage of patients with elevated C-reactive protein and β2-microglobulin. According to the international staging system (ISS), the HPSE^high group included a significant higher frequency of patients with stage III MM and a lower frequency of patients with stage I MM. HPSE^high patients had a shorter event free survival (EFS) (p=.017) and overall survival (OAS) (p=.023) than HPSE^low patients. Classifying these 30 patients into two groups according to HPSE expression in MMC did not yield to any EFS or OAS significant differences between the two groups.

Altogether, those data provide evidence that HPSE not only modulate syndecan-1 activity through the cleavage of HS chains but also regulates syndecan-1 mRNA expression and shedding. We report for the first time that the expression of a gene in the BM, i.e. HSPE, is an indicator of poor prognostic for MM patients. Therefore, HPSE inhibitors like PI-88, which is currently in clinical trial, will be of interest for the treatment of patients with MM.