PtdIns 4-kinasebeta and neuronal calcium sensor-1 co-localize but may not directly associate in mammalian neurons

It was recently demonstrated that the yeast homologue of phosphatidylinositol 4-kinasebeta PIK1 is directly associated with frq1, the yeast homologue of mammalian neuronal calcium sensor-1 (NCS-1) (Hendricks et al., [1999] Nat. Cell Biol. 1:234- 241). This was a novel finding and suggests that a calcium binding protein activates and regulates PtdIns 4-kinasebeta. This finding had not been shown in mammalian cells and both PtdIns 4-kinasebeta and NCS-1 have been shown to have important roles in the regulation of exocytotic release associated with neurotransmission. The aims of this study were to determine if PtdIns 4-kinasebeta and NCS-1 directly associate in mammalian neural tissues. We show that the immunostaining pattern for PtdIns 4-kinasebeta and NCS-1 is co-localized throughout the neurites of newborn cultured dorsal root ganglia (DRG) neurons but not in E13 DRG neurons. We then provide biochemical evidence that PtdIns 4-kinasebeta may not be in physical association with NCS-1 in mammalian nervous tissue unlike that previously reported in yeast.