L1-CAM knock-down radiosensitizes neuroblastoma IMR-32 cells by simultaneously decreasing MycN, but increasing PTEN protein expression

Childhood neuroblastoma is one of the most malignant types of cancers leading to a high mortality rate. These cancerous cells can be highly metastatic and malignant giving rise to disease recurrence and poor prognosis. The protooncogene myelocytomatosis neuroblastoma (MycN) is known to be amplified in this type of cancer, thus, promoting high malignancy and resistance. The L1 cell adhesion molecule (L1-CAM) cleavage has been found upregulated in many types of malignant cancers. In the present study, we explored the interplay between L1-CAM, MycN and PTEN as well as the role played by PDGFR and VEGFR on tumorigenicity in neuroblastoma cells. We investigated the effect of L1-CAM knock-down (KD) and PDGFR/VEGFR inhibition with sunitinib malate (Sutent (R)) treatment on subsequent tumor sphere formation and cellular proliferation and migration in the MycN-amplified IMR-32 neuroblastoma cells. We further examined the effect of combined L1-CAM KD with Sutent treatment or radiotherapy on these cellular functions in our cells. Tumorsphere formation is one of the indicators of aggressiveness in malignant cancers, which was significantly inhibited in IMR-32 cells after L1-CAM KD or Sutent treatment, however, no synergistic effect was observed with dual treatments, rather L1-CAM KD alone showed a greater inhibition on tumorsphere formation compared to Sutent treatment alone. In addition, cellular proliferation and migration were significantly inhibited after L1-CAM KD in the IMR-32 cells with no synergistic effect observed on the rate of cell proliferation when combined with Sutent treatment. Again, L1-CAM KD alone exhibited greater inhibitory effect than Sutent treatment on cell proliferation. L1-CAM KD led to the simultaneous downregulation of MycN, but the upregulation of PTEN protein expression. Notably, radiotherapy (2 Gy) of the IMR-32 cells led to significant upregulation of both L1-CAM and MycN, which was abrogated with L1-CAM KD in our cells. In addition, L1-CAM KD radiosensitized the cells as exhibited by the synergistic effect on the reduction in cell proliferation compared to radiotherapy alone. Taken together, our data show the importance of L1-CAM interplay with MycN and PTEN on the MycN amplified neuroblastoma cell radioresistance, proliferation and motility.