Functional investigation of the potential therapeutic target gene DLG2 in an11q-deleted neuroblastoma cell line and effects of 1,25 vitamin D3 and retinoic acid combination treatments

Sammanfattning: Neuroblastoma as a pediatric tumor develops in the sympathetic nervous system. DLG2 is a gene that encodes a member of the membrane-associated guanylate kinase (MAGUK) family and it resides in the chromosome region 11q. SK-N-AS is a neuroblastoma cell line with 11q deletion and consequently only one copy of the potential tumor suppressor gene DLG2. This study investigated synergistic effect by a combination treatment with 1,25(OH)2D3 and the vitamin A metabolite, retinoic acid.  Separately, SK-N-AS cells was transfected with expression vector pcDNA3.1+‐DYK that contained the DLG2-gene, followed by monitoring cell proliferation and qPCR, investigating the expression of the genes DLG2, DLG3, DLG4, VDR and PDIA3. Simultaneously, effects of knocked-down of DLG2, by siRNA transfection was monitored.  Transfection of expression plasmid with the DLG2 gene increased significantly gene expression in SK-N-AS cells with significant inhibition of the proliferation rate. Furthermore, silencing of DLG2 gene had no effect on the cell growth as well. Slower cell growth showed in combination treatment with 1,25(OH)2D3 (1nM) and 9-cis RA after 48 hours of treatment. Down-regulated VDR and possible missing RARRES3 could be the reason why SK-N-AS cell line showed resistance to the combination treatment with vitamin metabolites. All these results raised the question if another vitamin D synthetic analog could be a better choice for the future study of SK-N-AS cells. Moreover, overexpression of NAIP, large amounts of IGF-II, or not responsive RXR-VDR heterodimer to 1,25(OH)2D3 could be a potential explanation for the SK-N-AS cell unresponsiveness to the treatment.