Human VAP-C Negatively Regulates Hepatitis C Virus Propagation

Abstract

Human vesicle-associated membrane protein-associated protein (VAP) subtype A (VAP-AHepatitis C virus (HCV) is a major causative agent of chronic liver disease and thus a major public health problem, infecting at least 3% of the world population (47). HCV infection proceeds to the persistent stage in approximately 80% of patients, leading to the development of cirrhosis in 20% to 50% of patients, of whom approximately 5% eventually develop hepatocellular carcinoma (12). HCV encompasses a single-stranded positive-sense RNA genome of approximately 9.6 kb, which encodes a large precursor polyprotein comprising approximately 3,000 amino acids (26). The structural proteins are cleaved from the N-terminal one-fourth of the polyprotein by the host signal peptidase and signal peptide peptidase (23,32,33), resulting in the maturation of the capsid protein, two envelope proteins and viroporin p7. The NS2 protease cleaves after the carboxyl terminus, and then NS3 cleaves the appropriate downstream positions to produce NS4A, NS4B, NS5A, and NS5B (8, 42), all of which form the replication complex along with several host proteins (5, 21). NS5B is the RNAdependent RNA polymerase, which is a main enzymatic component of the replication complex of HCV (3), while NS5A is a membrane-anchored zinc-binding phosphoprotein that appears to possess diverse functions, including the suppression of host defense and the regulation of the virus's replication (1,4,6,41), although its biological function remains unclear.The NS5A protein has been shown to interact with several host proteins, including vesicle-associated membrane protein (VAMP)-associated protein (VAP) subtype A (VAP-A) (44) and subtype B (VAP-B) (9), FKBP8 (34), MyD88 (1), FBL2 (46), human butyrate-induced transcript 1 (hB-ind1) (40), and so on (25). VAP-A and VAP-B also bind to NS5B, although it remains unclear whether these interactions modulate HCV replication positively or negatively (9, 44). VAP-A and VAP-B have been shown to associate with the cytoplasmic face of the endoplasmic reticulum (ER) and the Golgi apparatus (38) and to consist of the major sperm protein (MSP) domain, the coiled-coil domain, and the transmembrane (TM) region, in that order (30,39), as shown in Fig. 1A. VAP was originally reported as a protein binding to VAMP, which is a synaptic vesicle SNARE protein required for synaptic-vesicle fusion in the nematode Aplysia californica, and was designated the 33-kDa VAMP-associated protein, VAP-33 (39). Two mammalian homologues, VAP-A and VAP-B, were subsequently identified (30,38). The transcription of VAP-A and VAP-B is ubiquitously detected in mammalian organs, including the heart, placenta, lung, liver, skeletal muscle, and pancreas (30), suggesting that VAP family proteins are involved in diverse cellular functions other than neurotransmitter release (30,38,49). Several VAP-interacting proteins share the FFAT motif (two phenylalanines in an acidic tract), which has the consensus amino acid sequence EFFDAXE, as determined by a comparison among oxysterol bind...

Prolactin Regulatory Element Binding Protein Is Involved in Hepatitis C Virus Replication by Interaction with NS4B

“…8A and B). It has been reported that several host cofactors involved in HCV replication, such as chaperonin TRiC/CCT, VAP-A, VAP-B, and PI4KIII␣, are recruited into the membranous HCV replication compartment by HCV replicase proteins (25,32,33,41,42). Taken together with our findings, the evidence to date emphasizes a common strategy in which HCV recruits host proteins into the membranous HCV replication compartment by replicase proteins to regulate its replication.…”

Hepatitis c virus and host cell lipids: An intimate connection

“…[146][147][148] This hypothesis is supported by the aberrant fractionation of NS5B in detergent soluble membranes and by the decreased HCV replication upon VAP-A and -B silencing or overexpression of dominant-negative VAPs. [146][147][148][149][150] Whether VAP-C also contributes to HCV replication remains to be confirmed, 149 as this protein is not expressed in liver tissue. The VAP-A-NS5A interaction appears to depend on the phosphorylation status of the viral protein.…”

Peripheral B Cells May Serve as a Reservoir for Persistent Hepatitis C Virus Infection

“…VAP-C is a splicing variant of VAP-B that lacks two thirds of the C terminus [36,37] ; therefore, it cannot interact with VAP-A, VAP-B or NS5A. A physiological role of VAP-C was recently demonstrated by Kukihara et al [38] , who found that VAP-C inhibited the association between VAP-A/B and NS5B, thereby reducing HCV replication efficiency. Interestingly, VAP-C expression in hepatocytes was found to be negligible, which may be advantageous for and CHC patients (n = 3) were subjected to SDS-PAGE and analyzed by immunoblotting using anti-IRF-3 and anti-ACTB antibodies.…”

“…VAP-B has been identified as another NS5A-binding protein by screening human libraries using the yeast two-hybrid system with NS5A as bait [35] . Both VAP-A and VAP-B are involved in HCV replication via interactions with NS5A and NS5B [35] , while VAP-C inhibits the association between VAP-A/B and NS5B, which results in reduced HCV replication efficiency [38] . Therefore, the absence of VAP-C expression in B cells, similar to hepatocytes, may be favorable for HCV replication.…”

“…Samples were subjected to SDS-PAGE and analyzed by immunoblotting using anti-IRF-3, anti-GAPDH (cytoplasmic marker protein) and anti-PARP-1 (nuclear marker protein) antibodies. HCV replication in the liver [38] . These results prompted us to examine VAP-C expression in B cells.…”