144 GPR133 Promotes Glioblastoma Growth in Hypoxia.

Microenvironmental diversity in glioblastoma (GBM) is exemplified by normoxic hypervascular areas and hypoxic necrotic regions. GBM stem cells (GSCs) play a central role in tumor growth and therapy resistance. How GSCs adapt to diverse GBM microenvironments remains an important and unanswered question. Using primary human GBM cultures, we discovered that CD133+ GSCs are metabolically adept at expanding in hypoxic conditions. Transcriptional analysis indicated that CD133+ GSCs have 17.8 ± 8.8-fold enriched expression of GPR133 (n = 3 biospecimens), a member of the adhesion family of G-protein-coupled receptors. We used genetic, biochemical, and computational assays to interrogate the role of GPR133 in GBM. Immunostaining of 12 human GBM biospecimens revealed that GPR133 expression is restricted to hypoxic regions of GBM and not present in normal brain. To test whether GPR133 expression is regulated by oxygen tension, we subjected GBM cultures to 1% O2 and found that GPR133 transcript was consistently upregulated (n = 5 cultures) in HIF1a-dependent manner. To elucidate GPR133's role in tumor growth, we used small hairpin RNA-mediated knockdown. GPR133 knockdown depleted CD133+ GSCs and inhibited tumor sphere formation under both normoxic and hypoxic conditions (P < .05). GPR133 knockdown also prevented in vivo tumor formation and increased survival of implanted mice (n = 4/group). CD133+ GSCs have 26.2% ± 12.53% higher cAMP levels than CD133- GBM cells (n = 3). GPR133 knockdown downregulated cAMP levels to 47.25% ± 27.27% of control (n = 3). Forskolin, which activates adenylate cyclase and boosts cAMP production, rescued the knockdown phenotype. These findings suggest that GPR133 canonical signaling is mediated by cAMP. Kaplan-Meier survival analysis of 160 The Cancer Genome Atlas (TCGA) patients indicated that increased GPR133 mRNA in GBM tumors correlated with poor survival (P = .002). Our results suggest that GPR133 acts promotes GBM growth in hypoxia. We propose that GPR133 represents an attractive novel therapeutic target in GBM.

Citation

Nermin Sumru Bayin, Joshua Frenster, J Robert Kane, Aram Modrek, Nadim Shohdy, Douglas J MacNeil, David Zagzag, Dimitris G Placantonakis. 144 GPR133 Promotes Glioblastoma Growth in Hypoxia. Neurosurgery. 2016 Aug;63 Suppl 1:158-9

PMID: 27399423

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