Altered in vitro spreading and cytoskeletal organization in human glioma cells by downregulation of urokinase receptor

Abstract

The interaction of urokinase-type plasminogen activator (uPA) with its cell-surface receptor (uPAR) is implicated in diverse biological processes such as cell migration, tissue remodeling, and tumor cell invasion. Recent studies indicated that uPAR can act as an extracellular matrix receptor during cell adhesion. Recently, we showed that transfection of the human glioma cell line SNB19 with antisense uPAR resulted in downregulation of uPAR at both the mRNA and protein levels. In this study, we used SNB19 to determine how the presence or absence of uPAR promotes cell spreading and associated changes in cell morphology. Microscopic analysis of cell spreading revealed that antisense uPAR-transfected cells were larger, remained round, and did not spread efficiently over extracellular matrix substrate type IV collagen and fibronectin, unlike parental SNB19 cells, which were smaller and spindle shaped. Biochemical studies showed that antisense uPAR-transfected cells, in addition to not spreading, exhibited increased expression of alpha 3 beta 1 integrin but not alpha 5 beta 1 integrin. However, we could not find a change in the expression of extracellular matrix components or altered growth rate in these cells. Furthermore, despite the increased alpha 3 beta 1 integrin expression, antisense uPAR-transfected cells failed to form an organized actin cytoskeleton when plated on type IV collagen or fibronectin, unlike parental SNB19 cells, which displayed an organized cytoskeleton. These findings show that the absence of uPAR in human glioma cells leads to morphological changes associated with decreased spreading and a disorganized cytoskeleton resulting in altered cell morphology, suggesting that coordinated expression of uPAR and integrin may be involved in spreading of antisense uPAR-transfected glioma cells.

Mitogenic Signaling of Urokinase Receptor–Deficient Kidney Fibroblasts

“…Whereas the mitogenic effects of uPA are widely known (25), the role of uPAR has not been as clearly delineated. In fact, some previous uPAR blocking studies using a specific monoclonal antibody or uPAR antisense reported no effect on uPA-induced proliferation, consistent with our current findings that uPA-induced kidney fibroblast proliferation is independent of uPAR expression (25,30,34). In fact, in the present study, the opposite response was observed, with either genetic uPAR deficiency or pretreatment with a uPAR-blocking antibody associated with higher rates of uPA-induced proliferation than with control wild-type fibroblasts.…”

Retracted: Knockdown of cathepsin B and uPAR inhibits CD151 and α3β1 integrin‐mediated cell adhesion and invasion in glioma

“…As uPAR plays a role in recruitment and organization of cytoskeletal proteins in glioma , we sought to investigate the effect of cathepsin B and uPAR downregulation on LN‐induced expression of talin and vinculin at both the protein and the mRNA levels. The expression levels of talin and vinculin proteins were significantly decreased with pU, pC, and pCU treatments in both U251 and 4910 cells, as evidenced by Western blotting and RT‐PCR analysis (Figure A).…”

“…Glioma, the most common type of brain tumor, is characterized by its highly invasive behavior . This invasive behavior is a consequence of the reaction of glioma cells to specific components of the ECM.…”

Doublecortin induces mitotic microtubule catastrophe and inhibits glioma cell invasion

“…Dynamic alterations in the organization of the actin cytoskeleton play a critical role in tumor‐associated progression such as invasion and metastasis (Chintala et al. 1997, 1999).…”

“…1997, 1999). Inhibition of phosphatase activities induces actin depolymerization, reduces invasion of glioma cells and decreases MMP expression (Chintala et al. 1997, 1999).…”