Synopsis

 

Glioblastoma multiforme (GBM) is the most aggressive and deadly CNS cancer. Its dismal prognosis is attributed to difficulty of resection, resistance to traditional chemotherapeutics, and invasion along the brain vasculature. Finding mechanisms by which GBM invades is critical for development of more effective surgical protocols and adjuvant therapies. Invasion of GBM involves alteration of non-cancerous cells, such as endothelial cells and astrocytes, in the tumor microenvironment toward a cancer-friendly phenotype. Evidence suggests post-transcriptional regulation by miRNAs may be the culprit.    

                Astrocytes express gap junction proteins Connexin 30 and Connexin 43. Here we present evidence that functional Cx43 homotypic gap junctions form between GBM and astrocytes in vitro, and presence or absence of Cx43 causes a shift in miRNA profile for cells cocultured with the GBM cell line U87-MG. Further, presence/absence and functionality of astrocyte-GBM Cx43 channels alter the invasion potential of GBM in vitro and ex vivo. Our data indicate that GBM-GBM Cx43 junctions limit invasion, while astrocyte-GBM junctions promote invasion. Previous studies have highlighted the potential transfer of miRNAs from GBM to astrocytes by means of gap junction channels, however it is widely accepted that gap junctions have a size exclusion of approximately 1 kDa, and miRNAs are on the order of 14 kDa. From here we seek to address the question of how gap junctions are implicated in the expression or transfer of miRNAs whether by direct passage through Cx43 junctions, exosomal release and uptake, or cell-cell endocytosis of Cx43 itself.