Brain tumors, in particular glioblastomas, have a high morbidity and mortality, mainly due to their invasive nature. A prerequisite for this invasiveness is cell migration based on increased expression of proteases digesting the extracellular matrix. Brevican, an important extracellular proteoglycan that is upregulated in glioblastomas, can be degraded by certain proteases. We demonstrate that in human glioblastomas secretory proteases like ADAMTS4 and ADAMTS5 (aggrecanases 1 and 2; ADAMTS 5 a disintegrin and metalloproteinase with thrombospondin motifs) are expressed on the mRNA and protein levels in considerable amounts. Realtime RT-PCR shows a higher levels of ADAMTS4 and 5 expressions in glioblastomas in situ, compared to cultured human glioblastoma cells. The upregulation of these proteases in vivo by cytokines may explain this difference. In vitro, transforming growth factor-b induces ADAMTS4, but less ADAMTS5, and interleukin1b ADAMTS5, but not ADAMTS4. As demonstrated by immunohistochemistry and confocal microscopy in situ, ADAMTS5 expression is confined to proliferating glioblastoma cells of surgical tumor sections and with lower intensity to astroglial cells in normal brain sections, as opposed to brevican. In vitro, glioblastoma-derived ADAMTS5 degrades recombinant human brevican to several smaller fragments. Our results show that ADAMTS4 and 5 are upregulated on proliferating glioblastoma cells and these proteases may contribute to their invasive potential. ' 2005 Wiley-Liss, Inc.Key words: glioblastoma; invasion; proteases; extracellular matrix; degradation; cytokines High-grade glial tumors (anaplastic astrocytoma and glioblastoma multiforme) are the most frequent brain tumors in adults. 1,2 Despite multimodal therapeutic efforts, the mean survival time is only 9-12 months for glioblastoma multiforme (WHO Grade IV) and 2 years for anaplastic astrocytoma (WHO Grade III). The ability of individual tumor cells to infiltrate brain tissue is the primary reason for this poor prognosis. Individual tumor cells (''guerrilla cells'') can migrate more than 4.0-7.0 cm from the gross tumor into the surrounding normal brain tissue. 3 In part, the migratory and invasive behavior is a consequence of tumor cell interaction with specific components of the extracellular matrix (ECM). Brain ECM components include laminin, collagen IV, tenascin, fibronectin and proteoglycans. 4 The glycosaminoglycan hyaluronic acid (HA) plays a central role in cellular proliferation, differentiation and migration, and may be a key element in tumor spreading. 5 BEHAB (brain enriched hyaluronan binding)/brevican is a recently identified HA binding protein that belongs to the lectican family. 6-9 BEHAB/brevican expression is developmentally regulated in the central nervous system, in particular during periods of glial cell proliferation and migration. 9 Accordingly, BEHAB/brevican is upregulated in the vast majority of surgical glioblastomas, 9-11 and expression levels and proteolytic cleavage of BEHAB/brevican seem to correlate with tumo...