Restoration of functional PAX3 transcriptional factor enhanced neuronal differentiation in PAX3b isoform depleted neuroblastoma cells

Abstract Reexpressed PAX3 transcription factor frequently found in neuroblastoma is believed to be responsible for their differentiation defects however the underlying mechanism remains unexplored. Here, we have analyzed how PAX3 is involved in neuroblastoma cell differentiation. Specifically, we have analyzed PAX3 expression, its functional status and its correlation with the neuronal marker expression in SH-SY5Y and its parental SK-N-SH cells. We have found that SH-SY5Y cells which expressed more PAX3 showed increased expression of neuronal marker genes (TUBB, MAP2, NEFL, NEUROG2, SYP) than the SK-N-SH cells with low levels of PAX3. The reported PAX3 targets (MET, TGFA and NCAM1) expression is also more in SH-SY5Y than in SK-N-SH cells which indicated PAX3 function. Retinoic acid treatment is unable to induce neuronal differentiation in cells (SK-N-SH) with low PAX3 level/activity. Moreover, ectopic expression of PAX3 in SK-N-SH cells neither induces neuronal marker genes nor its target genes. PAX3 isoform expression analysis revealed the expression of PAX3b isoform that contains only paired domain in SK-N-SH cells whereas in SH-SY5Y cells we could also observe PAX3c isoform that contains all functional domains. Further, PAX3b depletion in SK-N-SH cells is not induced by PAX3 target genes and the cells remain poorly differentiated. Interestingly, ectopic PAX3 expression enhanced neuronal outgrowth along with neuronal marker gene induction in PAX3b-depleted SK-N-SH cells. Collectively, these results showed that the PAX3b isoform may be responsible for the differentiation defect observed in SK-N-SH cells and restoration of functional PAX3 in the absence of PAX3b can induce neurogenesis in these cells.