RXR beta isoforms in neuroblastoma cells and evidence for a novel 3'-end transcript

RXR beta is predominantly involved in retinoid responses in neuroblastoma cells, in particular the N-type SH SY 5Y cells and the S-type SH S EP cells, both derivatives of a mixed phenotype neuroblastoma cell line. The aim of this study was to identify RXR beta isoforms expressed in neuroblastoma cells and to characterise a putative novel RXR beta transcript. RXR beta 1 and RXR beta 2 were expressed in these neuroblastoma cells. An isoform with an insertion into the ligand binding domain, RXR beta(SLSR) (referred to in previous studies as RXR beta 3), was expressed at a similar level to RXR beta. A novel RXR beta transcript was identified by RNase protection assays and was at least as abundant as the expected RXR beta transcript and expressed in other cell types. Evidence suggests that this novel transcript was transcribed from an internal promoter between exons 5 and 6, contained a retained intron (intron 6) and was alternatively spliced with and without the SLSR insertion. These data show that the pattern of RXR beta expression is complex. The relative abundance of the novel RXR beta transcript suggests that it may be an important aspect of RXR beta function or regulation in a range of cell types.