PO-291 A cell-penetrating peptide based on the connexin43-Src interacting sequence reduces glioma stem cell migration and proliferation by recruiting Src, Csk and PTEN

Introduction The expression of connexin43 (Cx43), the main gap junction channel-forming protein, is down-regulated in glioma stem cells (GSC). Our previous studies showed that a cell-penetrating peptide containing the region of Cx43 that interacts with the oncoprotein c-Src (TAT-Cx43266–283), inhibits its oncogenic activity and up-regulates the tumour suppressor PTEN. Through this pathway, TAT-Cx43266–283 reduces glioma cell proliferation and reverses the GSC phenotype. Our next goal was to uncover the mechanism of action and the effects of TAT-Cx43266–283 on the migration and invasion of human GSCs. Material and methods Human primary GSCs (G9, G12, G13, G15 and G16) were obtained from glioblastoma patients’ biopsies from the Neurosurgery Service of the Hospital Universitario de Salamanca, Spain. The migration was analysed in these primary GSCs by tracking individual cell trajectories in cultures recorded by Time-Lapse Live-cell Imaging and the invasion with Matrigel-treated transwell inserts. The same tumour biopsies were used to study the effect of TAT-Cx43266–283 on fresh undissociated tumour blocks by time-lapse microscopy. The molecular interactions were studied in G166 GSCs by pull-down assays of biotinylated TAT-Cx43266–283 (TAT-Cx43266–283-B) and Western blot analysis. Results and discussions Our results confirmed that TAT-Cx43266–283 strongly reduces the migration and invasion of human primary GSCs by inhibiting c-Src activity and up-regulating PTEN that consequently, lowers the levels of phosphorylation of focal adhesion kinase tyrosines 397, 576 and 577. In addition, fresh undissociated tumour blocks revealed a dramatic reduction on the survival of these glioblastoma cells when exposed to TAT-Cx43266–283. By pull-down assays, we showed that TAT-Cx43266–283-B recruits c-Src together with its inhibitors PTEN and Csk, confirming the proposed mechanism for Cx43. Conclusion In conclusion, TAT-Cx43266–283 exerts an important antitumor effect by inhibiting c-Src and up-regulating PTEN with the subsequent reduction in FAK phosphorylation required to establish appropriate focal adhesions for migration, proliferation and survival. This inhibition is mediated by the recruitment of the c-Src intrinsic inhibitors, PTEN and Csk. All together, these results reinforce the relevance of this sequence of Cx43 that interacts with c-Src for the development of new therapies against glioblastoma.