Changes in MYCN expression in human neuroblastoma cell lines following cisplatin treatment may not be related to MYCN copy numbers.

Neuroblastoma is a tumor accounting for approximately 10% of all childhood malignancies and 50% of all childhood cancer-related deaths. MYCN gene copy number variation represents the most important prognostic factor in neuroblastoma. Prognostic significance of MYCN gene expression is more complicated and may depend on other factors such as MYCN gene copy number status. In the present study, we assessed MYCN gene expression using real-time RT-PCR following cisplatin treatment in three human neuroblastoma cell lines (UKF-NB-3, UKF-NB-4 and SK-N-AS) and their cisplatin-resistant counterparts. We also examined MYCN gene status and copy number (gain and amplification) variations using interphase and metaphase fluorescent in situ hybridization (FISH) and multiplex ligation-dependent probe amplification (MLPA). Only cisplatin-sensitive UKF-NB-4 cells exhibited decreased MYCN expression following treatment with cisplatin. Other sensitive neuroblastoma cells did not exhibit a change in MYCN expression. In contrast, cisplatin-resistant UKF-NB-4 and SK-N-AS cells exhibited increased MYCN expression irrespective of the number of MYCN copies or concentration of cisplatin in the medium. In MYCN-amplified neuroblastoma cells we did not observe any significant change in the number of MYCN copies after cisplatin treatment, whereas MYCN-non-amplified SK-N-AS cells revealed during cisplatin treatment an increased number of MYCN gene copies caused by 2p gain in the majority of cells by FISH. We postulated that cisplatin treatment does not result directly in altered transcription of MYCN. A functional change in MYCN mRNA levels and increased MYCN expression in cisplatin-resistant neuroblastoma cells do not have a clear relationship to MYCN copy numbers. These findings may further contribute to the understanding of cisplatin chemotherapy in connection with MYCN expression, and the possible copy number variations in MYCN neuroblastoma cells may be of importance since targeting of MYCN is being tested as neuroblastoma therapy.