The enzyme L-isoaspartyl (D-aspartyl) methyltransferase promotes migration and invasion in human U-87 MG and U-251 MG glioblastoma cell lines

The protein L-isoaspartyl (D-aspartyl) methyltransferase (PIMT) recognizes abnormal L-isoaspartyl and Daspartyl residues in proteins. Among examined tissues, PIMT shows the highest level in the brain. The U-87 MG cell line is a commonly used cellular model to study the most frequent brain tumor, glioblastoma. Previously, we reported that PIMT amount increased when U-87 MG cells were detached from the extracellular matrix. Recently, we also showed that PIMT possessed pro-angiogenic properties. Together, these PIMT features led us to postulate that PIMT could play a critical role in glioblastoma growth. Here, we investigate PIMT role in U-87 MG cell viability, adhesion, migration, invasion, and colony formation and in the reorganization of the actin and tubulin cytoskeleton. PIMT inhibition by siRNA significantly reduced in vitro cell migration and invasion in various assays, including wound-healing assay, Boyden chambers coated with gelatin and Matrigel invasion assay. Conversely, in stably transfected U-87 MG cells overexpressing wild-type PIMT, cell migration, invasive capacity and colony formation significantly increased. However, in stably transfected cells with the gene encoding for mutated PIMT(D83V), despite of its overexpression, migration and invasion remained similar to those observed in control cells. In all these conditions, cell viability was unaffected. Importantly, overexpressed wild-type PIMT and mutated PIMT(D83V) have opposite effects on the organization of microtubules and actin cytoskeleton and thus on morphology of U-87 cells. These data highlighted the importance of PIMT level and its catalytic activity in migration and invasion of U-87 glioma cells and its possible contribution in cancer invasion during glioma growth.