Vault (organelle)

The vault or vault cytoplasmic ribonucleoprotein is a eukaryotic organelle whose function is not fully understood. Discovered and isolated by Nancy Kedersha and Leonard Rome in 1986,[2] vaults are cytoplasmic organelles which when negative-stained and viewed under an electron microscope resemble the arches of a cathedral vaulted ceiling, with 39-fold (Or D39d) symmetry.[1] They are present in many types of eukaryotic cells and appear to be highly conserved amongst eukaryotes.[3]

Vault Particle
Structure of the Vault complex from rat liver.[1]
Identifiers
SymbolVault
PfamPF01505
InterProIPR002499
PROSITEPDOC51224

Morphology

Vaults are large ribonucleoprotein particles. About 3 times the size of a ribosome and weighing approximately 13 MDa, they are found in most eukaryotic cells and all higher eukaryotes. They measure 34 nm by 60 nm from a negative stain, 26 nm by 49 nm from cryo-electron microscopy, and 35 nm by 59 nm from STEM.[4] The vaults consist primarily of proteins, making it difficult to stain with conventional techniques. The protein structure consists of an outer shell composed of 78 copies of the ~100 KDa major vault protein (MVP). Inside are two associated vault proteins, TEP1 and VPARP. TEP1, also known as the telomerase-associated protein 1,[5] is 290 KDa and VPARP (also known as PARP4) is related to poly-(ADP-ribose) polymerase (PARP) and is 193 KDa.[6] Vaults from higher eukaryotes also contain one or several small vault RNAs (vRNAs, also known as vtRNAs) of 86–141 bases within.[7]

Function

Despite not being fully elucidated, vaults have been associated with the nuclear pore complexes and their octagonal shape appears to support this.[8][9] Vaults have been implicated in a broad range of cellular functions including nuclear-cytoplasmic transport, mRNA localization, drug resistance, cell signaling, nuclear pore assembly, and innate immunity.[10] The three vault proteins (MVP, VPARP, and TEP1) have each been knocked out individually and in combination (VPARP and TEP1) in mice.[11][12][13] All of the knockout mice are viable and no major phenotypic alterations have been observed. Dictyostelium encode three different MVPs, two of which have been knocked out singly and in combination.[14] The only phenotype seen in the Dictyostelium double knockout was growth retardation under nutritional stress.[15] If vaults are involved in an essential cellular functions, it seems likely that redundant systems exist that can ameliorate their loss.

Association with cancer

In the late 1990s, researchers found that vaults (especially the MVP) were over-expressed in cancer patients who were diagnosed with multidrug resistance, that is the resistance against many chemotherapy treatments.[16] Although this does not prove that increased number of vaults led to drug resistance, it does hint at some sort of involvement. This has potential in discovering the mechanisms behind drug-resistance in tumor cells and improving anticancer drugs.[14]

Evolutionary conservation

Vaults have been identified in mammals, amphibians, avians and Dictyostelium discoideum.[3] The Vault model used by the Pfam database identifies homologues in Paramecium tetraurelia, Kinetoplastida, many vertebrates, a cnidarian (starlet sea anemone), molluscs, Trichoplax adhaerens, flatworms, Echinococcus granulosus and Choanoflagellate.[17]

Although vaults have been observed in many eukaryotic species, a few species do not appear to have the ribonucleoprotein. These include:[18]

These four species are model organisms for plants, nematodes, animal genetics and fungi respectively. Despite these exceptions, the high degree of similarity of vaults in organisms that do have them implies some sort of evolutionary importance.[3]

Vault engineering

The Rome lab at UCLA has collaborated with a number of groups to use the baculovirus system to produce large quantities of vaults. When the major vault protein (MVP) is expressed in insect cells, vault particles are assembled on polyribosomes in the cytoplasm.[19] By using molecular genetic techniques to modify the gene encoding the major vault protein, vault particles have been produced with chemically active peptides attached to their sequence. These modified proteins are incorporated into the inside of the vault particle without altering its basic structure. Proteins and peptides can also be packaged into vaults by attachment of a packaging domain derived from the VPARP protein.[15] A number of modified vault particles have been produced in order to test the concept that vaults can be bio-engineered to allow their use in a wide variety of biological applications including drug delivery, biological sensors, enzyme delivery, controlled release, and environmental remediation.

A vault has been packaged with a chemokine for potential use to activate the immune system to attack lung cancer, and this approach has undergone phase I trials.[20][21]

See also

References
  1. Tanaka H, Kato K, Yamashita E, Sumizawa T, Zhou Y, Yao M, Iwasaki K, Yoshimura M, Tsukihara T (January 2009). "The structure of rat liver vault at 3.5 angstrom resolution". Science. 323 (5912): 384–8. Bibcode:2009Sci...323..384T. doi:10.1126/science.1164975. PMID 19150846.
  2. Kedersha NL, Rome LH (September 1986). "Isolation and characterization of a novel ribonucleoprotein particle: large structures contain a single species of small RNA". The Journal of Cell Biology. 103 (3): 699–709. doi:10.1083/jcb.103.3.699. PMC 2114306. PMID 2943744.
  3. Kedersha NL, Miquel MC, Bittner D, Rome LH (April 1990). "Vaults. II. Ribonucleoprotein structures are highly conserved among higher and lower eukaryotes". The Journal of Cell Biology. 110 (4): 895–901. doi:10.1083/jcb.110.4.895. PMC 2116106. PMID 1691193.
  4. Kedersha NL, Heuser JE, Chugani DC, Rome LH (January 1991). "Vaults. III. Vault ribonucleoprotein particles open into flower-like structures with octagonal symmetry". The Journal of Cell Biology. 112 (2): 225–35. doi:10.1083/jcb.112.2.225. PMC 2288824. PMID 1988458.
  5. Kickhoefer VA, Stephen AG, Harrington L, Robinson MO, Rome LH (November 1999). "Vaults and telomerase share a common subunit, TEP1". The Journal of Biological Chemistry. 274 (46): 32712–7. doi:10.1074/jbc.274.46.32712. PMID 10551828.
  6. Kickhoefer VA, Siva AC, Kedersha NL, Inman EM, Ruland C, Streuli M, Rome LH (September 1999). "The 193-kD vault protein, VPARP, is a novel poly(ADP-ribose) polymerase". The Journal of Cell Biology. 146 (5): 917–28. doi:10.1083/jcb.146.5.917. PMC 2169495. PMID 10477748.
  7. van Zon A, Mossink MH, Scheper RJ, Sonneveld P, Wiemer EA (September 2003). "The vault complex". Cellular and Molecular Life Sciences. 60 (9): 1828–37. doi:10.1007/s00018-003-3030-y. PMID 14523546.
  8. Chugani DC, Rome LH, Kedersha NL (September 1993). "Evidence that vault ribonucleoprotein particles localize to the nuclear pore complex". Journal of Cell Science. 106 ( Pt 1): 23–9. PMID 8270627.
  9. Unwin PN, Milligan RA (April 1982). "A large particle associated with the perimeter of the nuclear pore complex". The Journal of Cell Biology. 93 (1): 63–75. doi:10.1083/jcb.93.1.63. PMC 2112107. PMID 7068761.
  10. Berger W, Steiner E, Grusch M, Elbling L, Micksche M (January 2009). "Vaults and the major vault protein: novel roles in signal pathway regulation and immunity". Cellular and Molecular Life Sciences. 66 (1): 43–61. doi:10.1007/s00018-008-8364-z. PMID 18759128.
  11. Kickhoefer VA, Liu Y, Kong LB, Snow BE, Stewart PL, Harrington L, Rome LH (January 2001). "The Telomerase/vault-associated protein TEP1 is required for vault RNA stability and its association with the vault particle". The Journal of Cell Biology. 152 (1): 157–64. doi:10.1083/jcb.152.1.157. PMC 2193651. PMID 11149928.
  12. Liu Y, Snow BE, Hande MP, Baerlocher G, Kickhoefer VA, Yeung D, Wakeham A, Itie A, Siderovski DP, Lansdorp PM, Robinson MO, Harrington L (November 2000). "Telomerase-associated protein TEP1 is not essential for telomerase activity or telomere length maintenance in vivo". Molecular and Cellular Biology. 20 (21): 8178–84. doi:10.1128/mcb.20.21.8178-8184.2000. PMC 86427. PMID 11027287.
  13. Mossink MH, van Zon A, Fränzel-Luiten E, Schoester M, Kickhoefer VA, Scheffer GL, Scheper RJ, Sonneveld P, Wiemer EA (December 2002). "Disruption of the murine major vault protein (MVP/LRP) gene does not induce hypersensitivity to cytostatics". Cancer Research. 62 (24): 7298–304. PMID 12499273.
  14. Kickhoefer VA, Vasu SK, Rome LH (May 1996). "Vaults are the answer, what is the question?". Trends in Cell Biology. 6 (5): 174–8. doi:10.1016/0962-8924(96)10014-3. PMID 15157468.
  15. Rome LH, Kickhoefer VA (February 2013). "Development of the vault particle as a platform technology". ACS Nano. 7 (2): 889–902. doi:10.1021/nn3052082. PMID 23267674.
  16. Mossink MH, van Zon A, Scheper RJ, Sonneveld P, Wiemer EA (October 2003). "Vaults: a ribonucleoprotein particle involved in drug resistance?". Oncogene. 22 (47): 7458–67. doi:10.1038/sj.onc.1206947. PMID 14576851.
  17. http://pfam.xfam.org/family/PF01505 Major Vault Protein repeat Pfam family
  18. Rome L, Kedersha N, Chugani D (August 1991). "Unlocking vaults: organelles in search of a function". Trends in Cell Biology. 1 (2–3): 47–50. doi:10.1016/0962-8924(91)90088-Q. PMID 14731565.
  19. Mrazek J, Toso D, Ryazantsev S, Zhang X, Zhou ZH, Fernandez BC, Kickhoefer VA, Rome LH (November 2014). "Polyribosomes are molecular 3D nanoprinters that orchestrate the assembly of vault particles". ACS Nano. 8 (11): 11552–9. doi:10.1021/nn504778h. PMC 4245718. PMID 25354757.
  20. Sharma S, Zhu L, Srivastava MK, Harris-White M, Huang M, Lee JM, Rosen F, Lee G, Wang G, Kickhoefer V, Rome LH, Baratelli F, St John M, Reckamp K, Chul-Yang S, Hillinger S, Strieter R, Dubinett S (January 2013). "CCL21 Chemokine Therapy for Lung Cancer". International Trends in Immunity. 1 (1): 10–15. PMC 4175527. PMID 25264541.
  21. Kar UK, Srivastava MK, Andersson A, Baratelli F, Huang M, Kickhoefer VA, Dubinett SM, Rome LH, Sharma S (May 2011). "Novel CCL21-vault nanocapsule intratumoral delivery inhibits lung cancer growth". PLOS ONE. 6 (5): e18758. Bibcode:2011PLoSO...618758K. doi:10.1371/journal.pone.0018758. PMC 3086906. PMID 21559281.
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