A transcriptomic signature mediated by HOXA9 promotes human glioblastoma initiation, aggressiveness and resistance to temozolomide

Glioblastoma is the most malignant brain tumor, exhibiting remarkable resistance to treatment. Here we investigated the oncogenic potential of HOXA9 in gliomagenesis, the molecular and cellular mechanisms by which HOXA9 renders glioblastoma more aggressive, and how HOXA9 affects response to chemotherapy and survival. The prognostic value of HOXA9 in glioblastoma patients was validated in two large datasets from TCGA and Rembrandt, where high HOXA9 levels were associated with shorter survival. Transcriptomic analyses identified novel HOXA9-target genes with key roles in cancer-related processes, including cell proliferation, DNA repair, and stem cell maintenance. Functional studies with HOXA9-overexpressing and HOXA9-silenced glioblastoma cell models revealed that HOXA9 promotes cell viability, stemness and invasion, and inhibits apoptosis. Additionally, HOXA9 promoted the malignant transformation of human immortalized astrocytes in an orthotopic in vivo model, and caused tumor-associated death. HOXA9 also mediated resistance to temozolomide treatment in vitro and in vivo via upregulation of BCL2. Importantly, the pharmacological inhibition of BCL2 with the BH3 mimetic ABT-737 reverted temozolomide resistance in HOXA9-positive cells. These data establish HOXA9 as a driver of glioma initiation, aggressiveness and resistance to therapy. In the future, the combination of BH3 mimetics with temozolomide should be further explored as an alternative treatment for glioblastoma.
The authors would like to acknowledge the funding agencies that supported this work: Fundação para a Ciência e Tecnologia (PTDC/SAU-GMG/113795/2009 and SFRH/ BPD/33612/2009 to B.M.C.; SFRH/BD/81042/2011 to M.P.; SFRH/BD/88220/2012 to A.X.M.; PTDC/SAUGMG/ 113795/2009 to A.I.O. and C.S.G.), Fundação Calouste Gulbenkian (B.M.C.), and Liga Portuguesa Contra o Cancro (B.M.C.), and Schering-Plough Farma (R.M.R), Portugal. Project co-financed by Programa Operacional Regional do Norte (ON.2—O Novo Norte), Quadro de Referência Estratégico Nacional (QREN), Fundo Europeu de Desenvolvimento Regional (FEDER). The authors would like to extend their appreciation to Dr. Chris Jones and Dr. Sergey Popov (ICR, UK) for helpful assistance regarding histopathological analysis of xenograft tumors, Dr. Russell Pieper for sharing the hTERT/E6/E7 cell line (UCSF, USA), and Dr. Joseph Costello (UCSF, USA) for critical review of the manuscript.