Xanthohumol impairs autophagosome maturation through direct inhibition of valosin-containing protein.
ABSTRACT Autophagy is a bulk, nonspecific protein degradation pathway that is involved in the pathogenesis of cancer and neurodegenerative disease. Here, we observed that xanthohumol (XN), a prenylated chalcone present in hops (Humulus lupulus L.) and beer, modulates autophagy. By using XN-immobilized beads, valosin-containing protein (VCP) was identified as a XN-binding protein. VCP has been reported to be an essential protein for autophagosome maturation. Using an in vitro pull down assay, we showed that XN bound directly to the N domain, which is known to mediate cofactor and substrate binding to VCP. These data indicated that XN inhibited the function of VCP, thereby allowing the impairment of autophagosome maturation and resulting in the accumulation of microtubule-associated protein 1 light chain 3-II (LC3-II). This is the first report demonstrating XN as a VCP inhibitor that binds directly to the N domain of VCP. Our finding that XN bound to and inactivated VCP not only reveals the molecular mechanism of XN-modulated autophagy but may also explain how XN exhibits various biological activities that have been reported previously.
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ABSTRACT: Genomic alterations may make cancer cells more dependent than normal cells on mechanisms of proteostasis, including protein folding and degradation. This proposition is the basis for the clinical use of proteasome inhibitors to treat multiple myeloma and mantle cell lymphoma. However, proteasome inhibitors have not proved effective in treating other cancers, and this has called into question the general applicability of this approach. Here, I consider possible explanations for this apparently limited applicability, and discuss whether inhibiting other broadly acting components of the ubiquitin-proteasome system - including ubiquitin-activating enzyme and the AAA-ATPase p97/VCP - might be more generally effective in cancer therapy.BMC biology. 01/2014; 12(1):94.
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ABSTRACT: Studies on anti-picornavirus compounds revealed an essential role of a novel cellular pathway via host phosphatidylinositol-4 kinase III beta (PI4KB) and oxysterol-binding protein (OSBP) family I in poliovirus (PV) replication. However, the molecular basis of this pathway in PV replication has yet to be determined. Here, I analyzed viral and host proteins modulating production of phosphatidylinositol 4-phosphate (PI4P) and accumulation of unesterified cholesterol (UC) in the cells, and characterize the role of a PI4KB/OSBP pathway in PV replication. Virus protein 2BC was identified as a novel interactant of PI4KB. PI4KB and VCP/p97 bind to a partially overlapped region of 2BC with different sensitivity to a 2C inhibitor. Production of PI4P and accumulation of UC were enhanced by virus protein 2BC, but suppressed by virus proteins 3A and 3AB. In PV-infected cells, a PI4KB inhibitor suppressed production of PI4P, and both a PI4KB inhibitor and an OSBP ligand suppressed accumulation of UC on virus-induced membrane structure. Inhibition of PI4KB activity caused dissociation of OSBP from virus-induced membrane structure in PV-infected cells. Synthesis of viral nascent RNA (nsRNA) in PV-infected cells was not affected in the presence of PI4KB inhibitor and OSBP ligand, but transient pre-treatment of PV-infected cells with these inhibitors suppressed viral RNA synthesis. These results suggested that virus proteins modulate PI4KB activity and provide PI4P for recruitment of OSBP to accumulate UC on virus-induced membrane structure for formation of a virus replication complex.Microbiology and Immunology 02/2014; · 1.31 Impact Factor
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ABSTRACT: Tissue inhibitor of metalloproteinases (TIMPs) are endogenous inhibitor proteins of matrix metalloproteinases and contain 12 cysteine residues that are conserved among TIMPs, and which are important for their activity and structure. In the present study, three tryptophan residues conserved among TIMPs were revealed to be important for the secretion of TIMP-2. Replacement of conserved tryptophan residues in TIMP-2 with alanine led to a decrease in extracellular TIMP-2 levels and an increase in intracellular TIMP-2 levels. Furthermore, wild-type TIMP-2 and TIMP-2 mutated at unconserved tryptophan residues mainly localized in the Golgi apparatus, while TIMP-2 proteins mutated at conserved tryptophan were mainly observed in the endoplasmic reticulum (ER). This indicated that conserved tryptophan is essential for transporting TIMP-2 from the ER to Golgi apparatus. These observations suggested that conserved tryptophan residues among the TIMP family of proteins have critical roles for ER-Golgi transport and subsequent secretion of TIMP-2.Oncology letters 03/2014; 7(3):631-634. · 0.99 Impact Factor