Recombinant Major Vault Protein Is Targeted to Neuritic Tips of PC12 Cells

Abstract

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 copies of an untranslated RNA. Double labeling employing laser-assisted confocal microscopy and indirect immunofluorescence demonstrates partial colocalization of vaults with cytoskeletal elements in Chinese hamster ovary (CHO) and nerve growth factor (NGF)-treated neuronlike PC12 cells. Transfection of CHO and PC12 cells with a cDNA encoding the rat major vault protein containing a vesicular stomatitis virus glycoprotein epitope tag demonstrates that 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 vaults. A pronounced colocalization of vaults with filamentous actin can be seen 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 observations suggest that the vault particles are transported along cytoskeletal-based cellular tracks.

Depletion of major vault protein increases doxorubicin sensitivity and nuclear accumulation and disrupts its sequestration in lysosomes

“…In UMUC-3 bladder tumor cells, there is a clear organization of the lysosomal compartments to one side of the nucleus and this level of higher organization is clearly disrupted by MVP siRNA. As mentioned earlier, there are several observations that would argue that the vault complex is associated with the microtubular network, and perhaps vesicles along it, such as colocalization of MVP and secretory vesicles in neuron-like PC-12 cells (38) and the lysosomal marker CD63 (Lamp-3) in dendritic cells (40). An interesting finding by Eichenmuller et al (37) shows that vaults not only colocalize to microtubules but seem to directly interact with these structures via their structurally more complex cap regions.…”

The Vault Exterior Shell Is a Dynamic Structure that Allows Incorporation of Vault-Associated Proteins into Its Interior

“…It will be interesting to study the factors that control opening/closing of vaults or "breathing" of the vault structure, and to determine whether breathing is a important factor, not just in vault assembly, but in vault function. Vaults have been suggested to be carriers or transporters in the cell due to both their highly conserved capsule shape and their localization at such diverse regions including the nuclear pore complex, the leading edges of lamellapodia, adhesion plaques, the tips of neurites, and along microtubules (7,40,41). They have also been proposed to function as assembly scaffolds for signaling complexes (8,9,42).…”

The formation of vault-tubes: a dynamic interaction between vaults and vault PARP

“…Nevertheless, a small part (~5%) of major vault protein (MVP) is consistently associated with the nucleus (Abbondanza et al, 1998;Chugani et al, 1993). Although the cellular function of vaults is still unknown, their subcellular localization and distinct morphology point to a role for vaults in intracellular, particularly nucleo-cytoplasmic, transport (Abbondanza et al, 1998;Chugani et al, 1993;Hamill and Suprenant, 1997;Herrmann et al, 1999;Herrmann et al, 1996;Kitazono et al, 2001;Kitazono et al, 1999;Li et al, 1999). Vaults are frequently upregulated in multidrug-resistant cell lines and tumors of different histogenetic origin.…”