Exploitation of Astrocytes by Glioma Cells to Facilitate Invasiveness: A Mechanism Involving Matrix Metalloproteinase-2 and the Urokinase-Type Plasminogen Activator–Plasmin Cascade

Abstract

The presence of reactive astrocytes around glioma cells in the CNS suggests the possibility that these two cell types could be interacting. We addressed whether glioma cells use the astrocyte environment to modulate matrix metalloproteinase-2 (MMP-2), a proteolytic enzyme implicated in the invasiveness of glioma cells. We found that astrocytes in culture produce significant amounts of the pro-form of MMP-2 but undetectable levels of active MMP-2. However, after coculture with the U251N glioma line, astrocyte pro-MMP-2 was converted to the active form. The mechanism of pro-MMP-2 activation in glioma-astrocyte coculture was investigated and was found to involve the urokinase-type plasminogen activator (uPA)-plasmin cascade whereby uPA bound to uPA receptor (uPAR), leading to the conversion of plasminogen to plasmin. The latter cleaved pro-MMP-2 to generate its active form. Furthermore, key components (i.e., uPAR, uPA, and pro-MMP-2) were contributed principally by astrocytes, whereas the U251N glioma cells provided plasminogen. In correspondence with this biochemical cascade, the transmigration of U251N cells through Boyden invasion chambers coated with an extracellular matrix barrier was increased significantly in the presence of astrocytes, and this was inhibited by agents that disrupted the uPA-plasmin cascade. Finally, using resected human glioblastoma specimens, we found that tumor cells, but not astrocytes, expressed plasminogen in situ. We conclude that glioma cells exploit their astrocyte environment to activate MMP-2 and that this leads to the increased invasiveness of glioma cells.

Tenascin-C Stimulates Glioma Cell Invasion through Matrix Metalloproteinase-12

“…Transwell migration chambers (Costar 3422, polycarbonate membrane, 24-well format, 8-Am pore size, Corning, Inc., Corning, NY) were used (30,31). Following polymerization of the collagen I droplet in the top compartment, 100 AL of DMEM/F-12 medium with N2 supplement were added to the upper chamber and 1 mL of 10% FBS-containing glioma medium was applied to the lower well.…”

“…Cells were then allowed to invade out of the three-dimensional collagen I matrix, across the membrane, at 37jC for 24 hours. Noninvasive cells were then removed from the top compartment of the transwell with a cotton swab and the invasive cells present on the underside of the membrane were fixed and stained with hematoxylin (30). The number of invasive cells was counted per field (Â40 microscope objective) from four random fields of each membrane.…”

The brain tumor microenvironment

“…Reactive astrocytes are frequently associated with glioma cells in the CNS (Le et al, 2003). Tumor-associated astrocytes have been demonstrated to mediate glioblastoma cell invasion via activation of proMMP2 (Le et al, 2003), a metalloproteinase that plays a critical role in glioma invasion (Uhm et al, 1996).…”

“…For example, one study found marked increases in MMP2 production following cross-communication between astrocytes and glioblastoma cells. This study utilized co-cultures of glioblastoma cells with astrocytes to demonstrate enhancement of the invasive capacities of glioblastoma cells through production of proMMP (Le et al, 2003). This effect was mediated by the urokinase-type plasminogen activator (uPA)-plasmin cascade.…”

Standard of care therapy for malignant glioma and its effect on tumor and stromal cells

“…Another signaling pathway associated with tumor invasiveness involves the plasminogen/plasmin pathway. Glioma cells can secrete plasminogen, which interacts with the astrocyte products urokinase-type plasminogen activator (uPA)/uPA receptor resulting in plasmin production (Le et al, 2003). The inactive matrix metalloprotease-2, also secreted by astrocytes, can then be converted to active MMP-2 by plasmin-promoting tumor invasion.…”