Mitochondrial control by DRP1 in brain tumor initiating cells

Abstract

Brain tumor initiating cells (BTICs) coopt the neuronal high affinity GLUT3 glucose transporter to withstand metabolic stress. Here, we investigated another mechanism critical to brain metabolism, mitochondrial morphology. BTICs displayed mitochondrial fragmentation relative to non-BTICs, suggesting that BTICs have increased mitochondrial fission. The essential mediator of mitochondrial fission, dynamin-related protein 1 (DRP1), was activated in BTICs and inhibited in non-BTICs. Targeting DRP1 using RNA interference or pharmacologic inhibition induced BTIC apoptosis and inhibited tumor growth. Downstream, DRP1 activity regulated the essential metabolic stress sensor, AMP-activated protein kinase (AMPK), and AMPK targeting rescued the effects of DRP1 disruption. Cyclin-dependent kinase 5 (CDK5) phosphorylated DRP1 to increase its activity in BTICs, whereas Ca2+–calmodulin-dependent protein kinase 2 (CAMK2) inhibited DRP1 in non-BTICs, suggesting tumor cell differentiation induces a regulatory switch in mitochondrial morphology. DRP1 activation correlates with poor prognosis in glioblastoma, suggesting mitochondrial dynamics may represent a therapeutic target for BTICs.

RBPJ maintains brain tumor–initiating cells through CDK9-mediated transcriptional elongation

“…Where indicated, BTICs and non-BTICs were derived immediately after dissociation or after transient xenograft passage in immunocompromised mice using prospective sorting followed by assays to confirm stem cell marker expression, sphere formation, and secondary tumor initiation. Although CD133 is controversial, in the models used in these studies, CD133 has previously identified functional BTICs (2,30). Therefore, in experiments with matched TIC and non-TIC cultures, we segregated AC133 marker-positive and marker-negative populations using an APC-conjugated anti-CD133/2 antibody (293C3, Miltenyi Biotech) by FACS or magnetic bead separation (Miltenyi Biotech), as previously described (2,30).…”

“…Although CD133 is controversial, in the models used in these studies, CD133 has previously identified functional BTICs (2,30). Therefore, in experiments with matched TIC and non-TIC cultures, we segregated AC133 marker-positive and marker-negative populations using an APC-conjugated anti-CD133/2 antibody (293C3, Miltenyi Biotech) by FACS or magnetic bead separation (Miltenyi Biotech), as previously described (2,30). The TIC phenotype of these cells was validated by stem cell marker expression (CD133, OLIG2, and SOX2), functional assays of self-renewal (serial tumorsphere passage), and tumor propagation by in vivo limiting dilution.…”

Cancer stem cells in glioblastoma

“…Moving forward, these studies demonstrate the importance of understanding the molecular alterations that are present in recurrent tumors and how these influence the structure of cells within the tumor hierarchy. In addition, it is necessary to consider that therapeutic resistance mechanisms may not be solely innate but may evolve from exposure to microenvironmental factors such as hypoxia and acidic and metabolic stress Li et al 2009b;Hjelmeland et al 2011;Flavahan et al 2013;Xie et al 2015).…”

Mitochondrial dynamics and cancer

“…Furthermore, while total DRP1 levels were similar in normal and neoplastic brain tissues, activating phosphorylation of DRP1 (DRP1 S616 ) was increased in glioblastomas, and a strong inverse correlation was found between DRP1 S616 and poor survival in glioblastoma patients. 69 In this work, the authors suggest that cyclin-dependent kinase 5 (CDK5) was responsible for DRP1 activation in brain TICs and that calcium-/calmodulin-dependent protein kinase type 2 (CAMK2) was responsible for inhibitory phosphorylation of DRP1 in Ser 637 in non-TICs. 69 Since glioblastomas rank among the most lethal cancers, it will be interesting to explore DRP1 inhibition as a therapeutic strategy for these tumors.…”