The transcriptome of the Oncogenic HOXA9 homeoprotein in human glioblastoma : functional and clinical relevance

Dissertação de mestrado em Genética Molecular ; Gliomas are a heterogeneous group of neoplasias that account for the majority of primary tumors of the central nervous system, of which glioblastoma (GBM) is the most common and malignant subtype. These are dramatic diseases for which no curative therapies are yet available. The clinical responses of GBM patients are particularly poor and vary greatly among individuals, especially due to the heterogeneity of their molecular alterations. Regardless, these patients are equally treated with a standardized therapeutic approach, mainly due to the lack of wellestablished molecular prognostic markers. Recently, the reactivation of HOXA9 expression in GBM has been implicated as a poor prognostic marker. As HOXA9 is a transcription factor, we hypothesized that a set of HOXA9-transcriptionally regulated genes may be its true biological effectors. In this sense, we aimed to characterize the HOXA9 transcriptome in GBM to identify novel prognostic biomarkers and putative therapeutic targets. By analyzing expression microarrays in HOXA9-negative and positive U87MG and hTERT/E6/E7 cells, we found a vast number of genes regulated by HOXA9 that are involved in important hallmarks of cancer as proliferation, invasion, and therapy resistance. Interestingly, we found high expression of the long non-coding RNA HOTAIR (HOX transcript antisense intergenic RNA) in HOXA9-positive GBM cell lines, consistent with a significant co-expression between HOTAIR and HOXA9 in highgrade gliomas, particularly GBMs. Mechanistically, using chromatin immunoprecipitation and quantitative PCR analysis in GBM cell lines, we found that HOXA9 directly interacts with the promoter region of HOTAIR and induces its transcription. Importantly, GBM patients with high expression of HOTAIR had a relatively shorter overall survival, independently of other putative prognostic factors. Using in silico analysis we found other putative direct targets of HOXA9, and ChIP analysis proved the direct regulation of WNT6 ...