Increased SPARC expression promotes U87 glioblastoma invasion in vitro

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Abstract
Our recent studies have focused on identifying invasion-promoting genes that are expressed early in brain tumor progression. We identified and characterized SPARC (secreted protein acidic and rich in cysteine) as a potential candidate. To determine whether increased SPARC expression functionally promotes brain tumor invasion, SPARC was transfected into U87MG glioblastoma cells using the tetracycline-off gene expression system. The parental cell line (U87MG), the parental transactivator-transfected clone (U87T2) and three selected U87T2–SPARC-transfected clones (A2bi, A2b2 and C2a4) were characterized for endogenous and transfected SPARC expression. In comparison to the parental or U87T2 cell lines, the SPARC-transfected clones demonstrated: (1) morphological changes, (2) increased SPARC transcript and protein abundances that were down-regulated by the tetracycline analog doxycycline, (3) perinuclear localization of the transfected SPARC (consistent with reported localization of SPARC in normal cells in culture) and (4) altered adhesion and increased invasion as assessed by the spheroid confrontation assay. These data indicate that increased SPARC expression contributes to U87 glioblastoma tumor invasion in vitro and that these cell lines will serve as useful reagents to investigate the mechanism(s) by which SPARC promotes this phenotype in vitro and in vivo.