Treatment with retinoic acid (RA) often promotes neuroblastoma differentiation and growth inhibition, including the suppression of the expression of the MYCN oncogene. However, RA also targets protumoral chemokines, such as CCL2, which may contribute to the development of resistance. The present study aimed to investigate the regulation and function of CCL2 and N-Myc in RA-treated neuroblastoma cells. Materials and

CCL2 and N-Myc promote the viability of RA-treated cells, although the levels of these mediators were not consistently correlated with cellular outcomes, especially during apoptotic signaling.

In Kelly or SH-SY5Y cells, viability was quantified by cell fitness assays. Expression was analyzed using quantitative PCR and the regulation of proteins using enzyme-linked immunoabsorbent assays (ELISA) or western blots.

In MYCN-amplified Kelly cells, endogenous CCL2 levels were significantly lower compared to MYCN non-amplified SH-SY5Y cells. Treatment with 5 μM RA increased CCL2 release in both cell lines, but reduced N-Myc levels and cell numbers in Kelly cells. Over-expression of MYCN enhanced viability in SH-SY5Y cells, but did not affect RA-induced CCL2 release, while supplementation of CCL2 in Kelly cells did not prevent RA-mediated growth reduction. Impaired N-Myc or CCL2 signaling reduced the survival of all RA-treated cells and inhibition of N-Myc also decreased CCL2 levels. However, attenuated survival signaling was not generally associated with reduced levels of N-Myc or CCL2. Co-application of RA and the growth factor receptor inhibitors cediranib or crizotinib decreased N-Myc levels only in Kelly cells, while CCL2 release was dependent on the cell type and stimulus.