Recombinant major vault protein is targeted to neuritic tips of PC12 cells

The major vault protein (MVP) is the predominant constituent of ubiquitous, evolutionarily conserved large cytoplasmic ribonucleoprotein particles of unknown function, Vaults are multimeric protein complexes with several copi es of an untranslated RNA. Double labeling employing laser-assisted confoca l microscopy and indirect immunofluorescence demonstrates partial colocaliz ation of vaults with cytoskeletal elements in Chinese hamster ovary (CHO) a nd nerve growth factor (NGF)-treated neuronlike PC12 cells. Transfection of CHO and PC12 cells with a cDNA encoding the rat major vault protein contai ning a vesicular stomatitis virus glycoprotein epitope tag demonstrates tha t the recombinant protein is sorted into vault particles and targeted like endogenous MVPs. In neuritic extensions of differentiated PC12 cells, there is an almost complete overlap of the distribution of microtubules and vaul ts. A pronounced colocalization of vaults with filamentous actin can be see n in the tips of neurites. Moreover, in NGF-treated PC12 cells the location of vaults partially coincides with vesicular markers. Within the terminal tips of neurites vaults are located near secretory organelles. Our observat ions suggest that the vault particles are transported along cytoskeletal-ba sed cellular tracks.