INCREASE IN CYTOPLASMIC CASEIN KINASE-II-TYPE ACTIVITY ACCOMPANIES NEURITE OUTGROWTH AFTER DNA-SYNTHESIS INHIBITION IN NIA-103 NEUROBLASTOMA-CELLS

Whereas cells from most clonal lines derived from the murine neuroblastoma C1300 tumor can be induced to differentiate by serum withdrawal from culture medium, the NIA-103 clonal cell line has been considered unable to extend axon-like processes (neurites). Neurite growth depends on microtubule protein assembly, and although NIA-103 cells have essentially the same amounts of microtubule-associated protein (MAP)-1B and the neuronal-specific class beta-3-tubulin isoform as other neuroblastoma cell lines, these proteins are not phosphorylated in NIA-103 cells on serum withdrawal. The lack of microtubule protein phosphorylation may be due to the different sorting between the nucleus and the cytoplasm of the casein kinase II-related enzyme that is possibly involved in the modification of microtubule proteins. It is interesting that addition of DNA synthesis inhibitors to serum-starved NIA-103 cell cultures induces an increase in the level of cytosolic casein kinase II, an augmented in situ phosphorylation of MAP-1B, and the extension of neurites. Thus, the level of cytoplasmic casein kinase II appears to be controlled by the growth status of neuroblastoma cells. The shift to an increased cytoplasmic concentration of casein kinase II in nonproliferating, differentiating neuroblastoma cells is consistent with its putative role in the regulation of the cytoskeletal rearrangements underlying neuronal morphogenesis and plasticity.