CBIO-03ALTERNATIVE SPLICING IN GLIOBLASTOMA MULTIFORME: CHARACTERIZATION OF Baf45d ABERRANT SPLICING IN THE PATHOGENESIS OF GLIOBLASTOMA

We performed, for the first time, an alternative splicing global analyses (AS) in Glioblastoma (GBM) using specific splicing arrays with paired samples (tumor/non tumor). We identified 51 genes with a significantly different AS and we chose BAF45d as one of the best candidates. BAF45d AS occurs by the exclusion of exon 7 (exon 6a). This exclusion results in a Zinc finger protein domain with the ability to bind specific DNA sequences. The predominant isoform in GBM is one that presents the exclusion of exon 6a (BAF45d-T) and therefore it harbours the zinc finger domain suggesting a possible role in transcription regulation. The inhibition of BAF45d-T in vitro results in a decrease in cell proliferation, in the capacity to self-renew and in the downregulation of markers related with an undifferentiated phenotype. In this line of thinking, we demonstrated that BAF45d-T isoform is present in murine neural progenitor and its expression is reduced during the differentiation toward mature neurons. The inhibition of BAF45d in vivo increases significantly animal survival in a GBM orthotopic model. Moreover, our work revealed that BAF45d splicing was mediated by PTBP1. Interestingly, we also found that BAF45d regulated positively the expression of PTBP1, uncovering a link between splicing regulation and chromatin remodelling. In summary, our results suggest that the AS of BAF45d AS participates in the GBM pathogenesis through the maintenance of an undifferentiated cellular state. In addition, our data suggest that alternative splicing is a mechanism that could be central to GBM development.