Carboxypeptidase E reduces Glioblastoma migration through modulation of motility-associated gene expression and signaling cascades

Abstract

Glioblastoma (GBM) is the most common and most malignant brain tumor in humans. The prognosis is poor since GBM is highly-resistant to therapy and possesses a strong migratory and invasive potential, making complete surgical resection impossible. Previous work demonstrated that Carboxypeptidase E (CPE), originally identified as a neuropeptide processing enzyme, is secreted by a subcohort of malignant glioma and, if overexpressed in glioma cells, exerts anti-migratory, but pro-proliferative activity, suggesting that CPE might be a ‘‘Go or Grow’’ switch factor. Here we describe CPE mainly as an anti-migratory protein in glioma cells and we aim in deciphering the mechanism by which CPE modulates glioma cell behavior. Using transcriptome analyses, followed by Ingenuity Pathway Analyses (IPA) and investigation of several signaling cascades, we found that in CPE-overexpressing cells a variety of motility-associated mRNAs and miRNAs were differentially regulated and connected to motility-associated networks including FAK, PAK, CDC42, integrin, STAT3, TGF-β as well as ERK1/2. In particular SNAI2/SLUG, a transcription factor known to induce tumor cell motility and metastasis, was downregulated. Matrix-Metallo-Proteases (MMP) as well as MMP-activity inducing factors, all necessary for glioma cell invasion, were reduced in CPE-overexpressing cells. SNAI2/SLUG expression was regulated via ERK1/2 since inhibition of ERK1/2 activation abolished CPE-mediated SLUG downregulation and reduction of cell migration. Moreover, we showed a synergistic effect of CPE overexpression in combination with standard glioma therapy (Temozolomide and radiation) in the clonogenic survival of GBM cells. In vivo, the anti-migratory capacity of CPE translated in prolonged survival of mice bearing CPE-overexpressing tumors. These data help to understand the role of migration in glioma aggressiveness and how CPE is involved in this process.