Association of increased phosphatidylinositol 3-kinase signaling with increased invasiveness and gelatinase activity in malignant gliomas

Object. Glioblastoma multiforme is the most malignant of the primary brain tumors and aggressively infiltrates surrounding brain tissue, resulting in distant foci within the central nervous system, thereby rendering this tumo r surgically incurable. The recent findings that both phosphatidylinositol 3-kinase (PI 3-K) and the phosphatase and tensin homolog PTEN) regulate tum or cell invasiveness have led the authors to surmise that these lipid signa ling molecules might play a role in regulating matrix metalloproteinases (M MPs), which are essential for tumor cell invasion. Methods. Using the C6 glioma cell line, which does not express measurable a mounts of PTEN protein and in which in vitro invasiveness is MMP dependent, the authors determined that in vitro glioma cell invasiveness was signific antly reduced when cells were preincubated overnight with LY294002 or wortm annin, two specific inhibitors of PI 3-K signaling. Next, using gelatin zym ography, it was noted that these compounds significantly inhibited MMP-2 an d MMP-9-activities. Moreover, the decrease in MMP activity correlated with the decrease in PI 3-K activity, as assessed by Akt phosphorylation. Finall y, using semiquantitative reverse transcriptase-polymerase chain reaction. the authors demonstrated that LY294002 decreased messenger (m)RNA levels fo r both MMPs. Thus, these in vitro data indicate that PI 3-K signaling modul ates gelatinase activity at the level of mRNA. Using immunostaining of phosphorylated Akt (p-Akt) as a measure of PI 3-K a ctivity, the authors next assessed rat brains implanted with C6 cells. Comp ared with surrounding brain, there was marked p-Akt staining in C6 glioma c ells and in neurons immediately adjacent to the tumor, but not in normal br ain. The p-Akt staining in rumors was especially intense in perivascular ar eas. Using double-labeling techniques, colocalization of p-Akt with MMP-2 a nd MMP-9 was also noted in perivascular tumor areas. Conclusions. The increase in p-Akt staining within these PTEN-deficient gli omas is consistent with what would be predicted from unchecked PI 3-K signa ling. Furthermore, the immunohistochemically detected colocalization of p-A kt and MMP-2 and MMP-9 supports the authors' in vitro studies and the propo sed linkage between PI 3-K signaling and MMP activity in gliomas.