TGF-beta PROMOTES MEMBRANE TUBE FORMATION IN GLIOBLASTOMA THAT CONTRIBUTES TO INVASION AND THERAPY RESISTANCE

AbstractTransforming growth factor-β (TGF-β) is a cytokine with a key role in tissue homeostasis and cancer. TGF-β signalling is highly active in glioblastomas (GBM) and elevated TGF-β activity has been associated with poor clinical outcome. Here we report the role of TGF-β in mediating the formation of membrane tubes (MTs), which are tubular cytoplasmic extensions forming important communication structures. We observed that TGF-β stimulation promotes enhanced MT formation both in vitro and in vivo. Blockade of the TGF-β pathway using a selective inhibitor (A8301) or the administration of Cytochalasin-D, a potent inhibitor of actin polymerization could significantly reduce the MT formation and associated invasion. Further we found that the cells connected through MTs sustained lesser amount of DNA double strand breaks post administration of TMZ in comparison to the non-connected cells. We also observed shuttling of mitochondria through the MTs and an elevation of mitochondrial biogenesis post TGF-β administration. The role of TGF-β in MT formation was further evident in a TGF-β responsive and non-responsive patient derived cell lines. The non-responsive cell line was found to lack the TGF-β receptor 2 and stimulation of this cell line with TGF-β did not show an elevation in MT formation. Interestingly the non-responsive cell line generated a small and well circumscribed tumour upon intracranial implantation that remained confined to the site of injection and showed poor MT formation and weak pSMAD2 staining. However, the responsive cell line on the other hand presented a highly invasive tumour with intense pSMAD2 staining and abundant MTs connecting the cells inside the tumour. Similar observation was also made on the corresponding patient samples from which these cell lines where derived. Taken together it is compelling to speculate that targeting TGF-β pathway or its downstream components could potentially break the complex MT driven invasion/ resistance network in GBM.