SC-04 * NON-UNIFORM NOTCH SIGNALING UNDERLIES HETEROGENEITY WITHIN THE GLIOBLASTOMA STEM CELL POPULATION

Glioblastoma stem cells (GSCs) have the ability to self-renew, differentiate into tumor lineages, and give rise to tumors in immunodeficient animal models. More importantly, GSCs are resistant to current therapies, leading to tumor recurrence. Glioblastoma (GBM) is highly heterogeneous at the molecular and cellular level. This heterogeneity also exhibits itself within the stem cell compartment, further impairing the development of effective therapies. CD133+ GSCs cells have increased tumorigenicity. However, the facts that CD133- cells also give rise to tumors in animal models and that some tumors do not have a CD133+ cell population suggest that CD133 is not a universal GSC marker. The Notch signaling pathway, previously believed to be activated in CD133+ GSCs, is important for GSC self-renewal and therapy resistance. To study GSC heterogeneity, we used genetic reporters for Notch activation and made the surprising observation that Notch signaling is active in small populations of cells that do not express CD133 (CD133-/Notch + ; n = 3 primary GBM cultures). Our in vitro tumorsphere formation and in vivo tumor formation assays showed that both CD133 + /Notch- and CD133-/Notch+ cells have stem cell properties. Global transcriptome analysis revealed that CD133 + /Notch- and CD133-/Notch+ GSCs utilize differential transcriptional programs, which prime CD133 + /Notch- GSCs to rely on anaerobic glycolysis. Furthermore, CD133/-Notch+ cells are able to give rise to CD133 + /Notch- cells, although the converse does not occur. This finding suggests that the two cell types have distinct differentiation potentials. Finally, preliminary data suggest that these two GSC subtypes behave differentially in response to temozolomide and radiation treatment, which are the standard of care for GBM. We are currently testing the contribution of distinct GSCs to tumor heterogeneity in vivo, using lineage-tracing systems. Understanding the biology of GSCs and the functional importance of heterogeneity within GSC populations is critical for the design of novel therapies.