Plexin-B2 promotes invasive growth of malignant glioma.

Invasive growth is a major determinant of the high lethality of malignant gliomas. Plexin-B2, an axon guidance receptor important for mediating neural progenitor cell migration during development, is upregulated in gliomas, but its function therein remains poorly understood. Combining bioinformatic analyses, immunoblotting and immunohistochemistry of patient samples, we demonstrate that Plexin-B2 is consistently upregulated in all types of human gliomas and that its expression levels correlate with glioma grade and poor survival. Activation of Plexin-B2 by Sema4C ligand in glioblastoma cells induced actin-based cytoskeletal dynamics and invasive migration in vitro. This proinvasive effect was associated with activation of the cell motility mediators RhoA and Rac1. Furthermore, costimulation of Plexin-B2 and the receptor tyrosine kinase Met led to synergistic Met phosphorylation. In intracranial glioblastoma transplants, Plexin-B2 knockdown hindered invasive growth and perivascular spreading, and resulted in decreased tumor vascularity. Our results demonstrate that Plexin-B2 promotes glioma invasion and vascularization, and they identify Plexin-B2 as a potential novel prognostic marker for glioma malignancy. Targeting the Plexin-B2 pathway may represent a novel therapeutic approach to curtail invasive growth of glioblastoma.

Matrix metalloproteinase-7 regulates cleavage of pro-nerve growth factor and is neuroprotective following kainic acid-induced seizures.

The neurotrophin nerve growth factor (NGF) regulates neuronal growth, differentiation, and survival during development. However, the precursor of NGF, proNGF, is a potent apoptotic ligand for the p75 neurotrophin receptor (p75(NTR))-sortilin complex. The mechanisms that regulate cleavage of proNGF, therefore, are critical determinants of whether this factor promotes neuronal survival or death. In this study, we demonstrate that, following kainic acid-induced seizures, the proNGF processing enzyme matrix metalloproteinase 7 (MMP-7) and its inhibitor TIMP-1 (tissue inhibitor of matrix metalloproteinase 1) are regulated in a manner that prevents proneurotrophin cleavage and leads to increased proNGF in the extracellular milieu. Furthermore, we demonstrate both in vitro and in vivo that exogenous MMP-7 enhances proNGF cleavage and provides neuroprotection following kainic acid treatment. These data demonstrate that increased extracellular proNGF levels following seizures are stabilized by altered MMP-7 enzymatic activity, leading to increased neuronal death via activation of p75(NTR).