Analysis of MVP and VPARP promoters indicates a role for chromatin remodeling in the regulation of MVP

The Vault Nanoparticle: A Gigantic Ribonucleoprotein Assembly Involved in Diverse Physiological and Pathological Phenomena and an Ideal Nanovector for Drug Delivery and Therapy

Simple Summary

In recent decades, a molecular complex referred to as vault nanoparticle has attracted much attention by the scientific community, due to its unique properties. At the molecular scale, it is a huge assembly consisting of 78 97-kDa polypeptide chains enclosing an internal cavity, wherein enzymes involved in DNA integrity maintenance and some small noncoding RNAs are accommodated. Basically, two reasons justify this interest. On the one hand, this complex represents an ideal tool for the targeted delivery of drugs, provided it is suitably engineered, either chemically or genetically; on the other hand, it has been shown to be involved in several cellular pathways and mechanisms that most often result in multidrug resistance. It is therefore expected that a better understanding of the physiological roles of this ribonucleoproteic complex may help develop new therapeutic strategies capable of coping with cancer progression. Here, we provide a comprehensive review of the current knowledge.

Abstract

The vault nanoparticle is a eukaryotic ribonucleoprotein complex consisting of 78 individual 97 kDa-“major vault protein” (MVP) molecules that form two symmetrical, cup-shaped, hollow halves. It has a huge size (72.5 × 41 × 41 nm) and an internal cavity, wherein the vault poly(ADP-ribose) polymerase (vPARP), telomerase-associated protein-1 (TEP1), and some small untranslated RNAs are accommodated. Plenty of literature reports on the biological role(s) of this nanocomplex, as well as its involvement in diseases, mostly oncological ones. Nevertheless, much has still to be understood as to how vault participates in normal and pathological mechanisms. In this comprehensive review, current understanding of its biological roles is discussed. By different mechanisms, vault’s individual components are involved in major cellular phenomena, which result in protection against cellular stresses, such as DNA-damaging agents, irradiation, hypoxia, hyperosmotic, and oxidative conditions. These diverse cellular functions are accomplished by different mechanisms, mainly gene expression reprogramming, activation of proliferative/prosurvival signaling pathways, export from the nucleus of DNA-damaging drugs, and import of specific proteins. The cellular functions of this nanocomplex may also result in the onset of pathological conditions, mainly (but not exclusively) tumor proliferation and multidrug resistance. The current understanding of its biological roles in physiological and pathological processes should also provide new hints to extend the scope of its exploitation as a nanocarrier for drug delivery.

Vault-poly-ADP-ribose polymerase in the Octopus vulgaris brain: a regulatory factor of actin polymerization dynamic

Our previous behavioural, biochemical and immunohistochemical analyses conducted in selected regions (supra/sub oesophageal masses) of the Octopus vulgaris brain detected a cytoplasmic poly-ADP-ribose polymerase (more than 90% of total enzyme activity). The protein was identified as the vault-free form of vault-poly-ADP-ribose polymerase. The present research extends and integrates the biochemical characterization of poly-ADP-ribosylation system, namely, reaction product, i.e., poly-ADP-ribose, and acceptor proteins, in the O. vulgaris brain. Immunochemical analyses evidenced that the sole poly-ADP-ribose acceptor was the octopus cytoskeleton 50-kDa actin. It was present in both free, endogenously poly-ADP-ribosylated form (70kDa) and in complex with V-poly-ADP-ribose polymerase and poly-ADP-ribose (260kDa). The components of this complex, alkali and high salt sensitive, were purified and characterized. The kind and the length of poly-ADP-ribose corresponded to linear chains of 30-35 ADP-ribose units, in accordance with the features of the polymer synthesized by the known vault-poly-ADP-ribose polymerase. In vitro experiments showed that V-poly-ADP-ribose polymerase activity of brain cytoplasmic fraction containing endogenous actin increased upon the addition of commercial actin and was highly reduced by ATP. Anti-actin immunoblot of the mixture in the presence and absence of ATP showed that the poly-ADP-ribosylation of octopus actin is a dynamic process balanced by the ATP-dependent polymerization of the cytoskeleton protein, a fundamental mechanism for synaptic plasticity.

Major vault protein may affect nonhomologous end-joining repair and apoptosis through Ku70/80 and bax downregulation in cervical carcinoma tumors

PURPOSE

We investigated the relationship between major vault protein (MVP) expression, the nonhomologous end-joining (NHEJ) repair gene Ku70/80, and related genes involved in the regulation of apoptosis and proliferation to shed light on the possible causes of genetic instability, tumor progression, and resistance to oncologic treatment in patients with clinical cervical cancer.

METHODS AND MATERIALS

One hundred sixteen consecutive patients with localized cervix carcinoma were prospectively included in this study from July 1997 to Dec 2003. Patients were staged according to the tumor, node, metastasis (TNM) classification. Forty patients had Stage I disease, 45 had Stage II, and 31 had Stage III/IVA. Most patients had squamous tumors (98 cases) and Grades II (52 cases) and III (45 cases) carcinomas. Expression of MVP, Ku70/80, Insulin-Like Growth Factor-1 receptor (IGF-1R), BCL2-associated X protein (BAX), B-cell CLL/lymphoma 2 (BCL-2), p53, and Ki67 was studied by using immunohistochemistry in paraffin-embedded tumor tissue.

RESULTS

Tumors overexpressing MVP (65 of 116 cases) showed low levels of Ku70/80 (p = 0.013) and BAX expression (p < 0.0001). Furthermore, low Ku70/80 expression was strongly related to suppressed BAX (p < 0.001) and, to a lesser extent, upregulated BCL-2 (p = 0.042), altered p53 (p = 0.038), and increased proliferation (p = 0.002).

CONCLUSION

We hypothesize that an early regulatory mechanism favors homologous or NHEJ repair at first, mediated by vaults along with other factors yet to be elucidated. If vaults are overexpressed, NHEJ repair may be suppressed by means of several mechanisms, with resultant genomic instability. These mechanisms may be associated with the decision of damaged cells to survive and proliferate, favoring tumor progression and reducing tumor response to oncologic treatment through the development of resistant cell phenotypes. Additional clinical studies are necessary to test this hypothesis.

The major vault protein is responsive to and interferes with interferon-γ-mediated STAT1 signals

The major vault protein (MVP) is the main component of vaults, large ribonucleoprotein particles implicated in the regulation of cellular signaling cascades and multidrug resistance. Here, we identify MVP as an interferon γ (IFN-γ)-inducible protein. Treatment with IFN-γ resulted in a significant upregulation of MVP promoter activity as well as mRNA and protein levels. Activation of MVP expression by IFN-γ involved transcriptional upregulation through the JAK/STAT pathway based on an interaction of STAT1 with an interferon-γ-activated site (GAS) within the proximal MVP promoter. Mutation of this site distinctly reduced basal as well as IFN-γ-stimulated MVP transcription. IFN-γ also significantly enhanced the translation rate of MVP. Ectopic MVP overexpression in the MVP-negative lung cancer cell model H65 led to a downregulation of three known IFN-γ-regulated genes, namely ICAM-1, CD13 and CD36. Additionally, presence of MVP in H65 cells blocked both basal and IFN-γ-induced ICAM-1 expression whereas downmodulation of endogenous MVP levels by shRNA enhanced IFN-γ-induced ICAM-1 expression in U373 glioblastoma cells. MVP-mediated IFN-γ insensitivity was accompanied by significantly reduced STAT1 phosphorylation at Y701 and diminished translocation of STAT1 into the nucleus. Summarizing, we identify MVP as an IFN-γ-responsive gene interfering with IFN-γ-activated JAK/STAT signals. These data further substantiate that the vault particle functions as a general interaction platform for cellular signaling cascades.

YB-1 facilitates basal and 5-fluorouracil-inducible expression of the human major vault protein (MVP) gene

Vaults have been suggested to play a direct role in multidrug resistance (MDR) to anticancer drugs. The human major vault protein (MVP) also known as lung resistance-related protein (LRP) represents the predominant component of vaults that may be involved in the defense against xenobiotics. Here, we demonstrate that besides MDR-related cytostatics, also the non-MDR-related drug 5-fluorouracil (5-FU) was able to induce MVP mRNA and protein expression. Treatment with 5-FU amplified the binding activity and interaction of the transcription factor Y-box binding protein-1 (YB-1) with the Y-box of the human MVP gene promoter in a time-dependent manner. 5-FU also induced reporter expressions driven by a panel of newly generated MVP promoter deletion mutants. Interestingly, stably YB-1 overexpressing cell clones showed enhanced binding of YB-1 to the Y-box motif, associated with enhanced basal as well as 5-FU-inducible MVP promoter-driven reporter expressions. Moreover, transduction of YB-1 cDNA led to increased expression of endogenous MVP protein. Under physiological conditions, we observed a strong coexpression of MVP and YB-1 in human colon carcinoma specimen. In summary, our data demonstrate a direct involvement of YB-1 in controlling basal and 5-FU-induced MVP promoter activity. Therefore, YB-1 is directly linked to MVP-mediated drug resistance.