Characterization of Autoantibodies against the E1α Subunit of Branched-Chain 2-Oxoacid Dehydrogenase in Patients with Primary Biliary Cirrhosis.

Primary biliary cirrhosis (PBC) is characterized by antimitochondrial antibodies (AMAs) that react with the lipoyl-containing E2 subunits of 2-oxoacid dehydrogenase complexes such as BCOADC and PDC. The lipoyl domains of E2 contain the major epitopes essential for immunopathology. However, the non-lipoyl-containing E1 subunits are also frequently targeted. Since anti-E1 antibodies always appear in combination with anti-E2 antibodies, the mechanisms underlying the autoimmunity against E1 may be linked to, but distinct from, those against E2. Here, we demonstrate that intermolecular and intramolecular determinant spreading underlies the autoimmunity against E1. We performed characterizations and epitope mapping for anti-BCOADC-E1α antibodies from both the intermolecular and intramolecular points of view. The antibody reactivities form a cluster against the BCOADC complex that is distinct from that against the PDC complex, and the anti-BCOADC-E1α antibodies arise as part of the cluster against the BCOADC complex. Multiple epitopes are present on the surface of the BCOADC-E1α molecule, and the major epitope overlaps with the active center. Sera with anti-BCOADC-E1α antibodies strongly inhibited the enzyme activity. These findings suggest that the E1α subunit as part of the native BCOADC complex is an immunogen, and that determinant spreading is involved in the pathogenesis of AMA production.

NIRF constitutes a nodal point in the cell cycle network and is a candidate tumor suppressor.

In biological networks, a small number of "hub" proteins play critical roles in the network integrity and functions. The cell cycle network orchestrates versatile cellular functions through interactions between many signaling modules, whose defects impair diverse cellular processes, often leading to cancer. However, the network architecture and molecular basis that ensure proper coordination between distinct modules are unclear. Here, we show that the ubiquitin ligase NIRF (also known as UHRF2), which induces G1 arrest, interacts with multiple cell cycle proteins including cyclins (A2, B1, D1 and E1), p53 and pRB, and ubiquitinates cyclins D1 and E1. Consistent with its versatility, a bioinformatic network analysis demonstrated that NIRF is an intermodular hub protein that is responsible for the coordination of multiple network modules. Notably, intermodular hubs are frequently associated with oncogenesis. Indeed, we detected loss of heterozygosity of the NIRF gene in several kinds of tumors. When a cancer outlier profile analysis was applied to the Oncomine database, loss of the NIRF gene was found at statistically significant levels in diverse tumors. Importantly, a recurrent microdeletion targeting NIRF was observed in non-small cell lung carcinoma. Furthermore, NIRF is immediately adjacent to the single nucleotide polymorphism rs719725, which is reportedly associated with the risk of colorectal cancer. These observations suggest that NIRF occupies a prominent position within the cell cycle network, and is a strong candidate for a tumor suppressor whose aberration contributes to the pathogenesis of diverse malignancies.

NIRF induces G1 arrest and associates with Cdk2.

NIRF is a RING finger protein with a ubiquitin-like domain, a PHD finger, a YDG/SRA domain, and a RING finger domain. Previous study showed that NIRF is a nuclear protein expressed in association with cell proliferation. In this study, we further characterized NIRF functions in cell cycle regulation. Flow cytometric analysis showed that overexpression of NIRF induced an increase in G1 phase cells. Immunoprecipitation and immunoblotting experiments showed that NIRF bound to the inactive Cdk2-cyclin E complex. There existed phosphorylated NIRF in cells, and dephosphorylated NIRF interacted with Cdk2. NIRF was phosphorylated by Cdk2 in vitro. These results suggest that NIRF may participate in the G1/S transition regulation.

NIRF is a ubiquitin ligase that is capable of ubiquitinating PCNP, a PEST-containing nuclear protein.

We previously reported the association of a novel Np95/ICBP90-like RING finger protein (NIRF) with a novel PEST-containing nuclear protein (PCNP). NIRF is a nuclear protein with a ubiquitin-like domain, a PHD finger, a YDG/SRA domain, Rb-binding motifs and a RING finger. In this study, we showed that NIRF has auto-ubiquitination activity, the hallmark of a ubiquitin ligase. PCNP was readily ubiquitinated in 293 and COS-7 cells, and NIRF ubiquitinated PCNP in vitro as well as in vivo. Considering that NIRF is implicated in cell cycle regulation, these findings suggest that NIRF and PCNP are a ubiquitin ligase and its substrate, respectively, and may constitute a novel signaling pathway with some relation to cell proliferation.

Phytoplankton gene detection in drowned rabbits.

We have developed a sensitive and specific polymerase chain reaction (PCR) method for identifying phytoplankton in cases of death by drowning, and we have designed four primer pairs, EG1, EG2, SK1 and SK2, for chlorophyll-related genes of Euglena gracilis and Skeletonema costatum, which are commonly distributed in all types of water. In order to evaluate the usefulness of this method for diagnosis of drowning, we have used this method for detection of plankton genes in non-drowned rabbits submerged after death and in decomposed drowned rabbits. Plankton DNA was identified in lung samples obtained from the non-drowned rabbits because of postmortem plankton penetration into the respiratory system, and plankton DNA was identified in liver and kidney samples obtained from the decomposed drown rabbits. The results show that our new PCR method is a useful method for diagnosing drowning.

A novel PCR method for identifying plankton in cases of death by drowning.

We present a new PCR method for identifying plankton in cases of death by drowning. We designed four primer pairs for chlorophyll-related genes of Euglena gracilis (EG) and Skeletonema costatum (SK), which are commonly distributed in water. The primers were selected from sequences coding chloroplast/chlorophyll apoprotein of EG (EG1 and EG2) and fucoxanthin-chlorophyll a/c harvesting protein of SK (SK1 and SK2). With EG1 or EG2, up to 2 fg of EG-DNA was identified, and 0.2 pg of SK-DNA was detectable with SK1 or SK2. No PCR products were amplified from green vegetables (komatsuna, spinach, parsley) or human DNA with the four primer pairs. Regardless of the origin, seawater or fresh water, most diatoms were detectable with primer pairs of EG1 and EG2. With SK1, only Centrales diatoms were identified, and five diatom strains originating from seawater were detectable with SK2. EG1 and EG2 gave rise to PCR products from most water samples. By using Percoll, plankton was easily isolated from human tissue or blood samples and good results of PCR analysis were obtained in cases of death by drowning.

Epitope mapping on E1alpha subunit of pyruvate dehydrogenase complex with autoantibodies of patients with primary biliary cirrhosis.

BACKGROUND: A major mitochondrial autoantigen recognized by sera of patients with primary biliary cirrhosis (PBC) is dihydrolipoamide acetyltransferase (E2) of the pyruvate dehydrogenase complex (PDH). The alpha subunit of pyruvate decarboxylase (E1alpha) of PDH is also recognized in some E2-reactive PBC sera, suggesting that the occurrence of autoimmunity against Elalpha is subsequent to that against E2. METHODS. To investigate the mechanism inducing autoimmunity against E1alpha, we surveyed immunoreactive sequences of E1alpha by ELISA with synthesized oligopeptides, and determined minimum amino acid residues for each determinant. RESULTS: The major determinants of E1alpha appeared to reside in its N-terminal region, apparently forming 'nested epitopes', and all E1alpha-reactive PBC sera tested recognized these regions. Minor epitopes were also found scattered throughout the entire sequence. The reactivities of these minor epitopes to individual PBC sera were proportional to those of the major epitopes. All the epitopes were located in hydrophilic regions of E1alpha, and many of them were out of the known functional domains (TPP-binding domain, subunit interaction site, and phosphorylation sites) whose structures are phylogenically well conserved. Furthermore, the sequences of many epitopes appeared to be specific to humans. CONCLUSION: These observations suggest that determinant spreading might underlie the autoimmunity against Elalpha.

NIRF, a novel RING finger protein, is involved in cell-cycle regulation.

Through database mining, we found a novel PEST-containing nuclear protein (PCNP). To characterize PCNP, we carried out yeast two-hybrid screening for PCNP-interacting factors. A novel Np95/ICBP90-like RING finger protein (NIRF), which possessed a ubiquitin-like domain, a PHD finger, a YDG/SRA domain and a RING finger, was identified. Interaction between PCNP and NIRF was clarified by mammalian two-hybrid system, GST pull-down assay, and nuclear co-localization. RT-PCR showed that NIRF expression is high in proliferating phase but significantly low in G0/G1 phase in normal TIG-7 and WI-38 cells, while consistently high in tumoral HT-1080 and HepG2 cells, suggesting that NIRF is involved in cell-cycle regulation. The NIRF gene resides in 9p23-24.1 that is altered in numerous types of tumors at the top of frequency. Furthermore, the NIRF gene is just within small amplicons in some tumors, suggesting that PCNP and NIRF might be involved in some aspects of tumorigenesis.

Characterization of rainbow trout branched-chain alpha-keto acid dehydrogenase complex: inter-domain segments of the E2 component affect the overall activity.

Branched-chain alpha-keto acid dehydrogenase complex (BCKADH) contains decarboxylase (E1), dihydrolipoyl transacylase (E2), and dihydrolipoyl dehydrogenase (E3) as catalytic components. BCKADH purified from rainbow trout (Oncorhynchus mykiss) liver was comparable with mammalian BCKADH in various enzymatic characteristics, but less efficient in catalyzing the overall reaction. The trout E2 subunit was larger than the mammalian subunit and rather similar to the chicken one in relative molecular mass on SDS-PAGE, whereas the E1 component was similar between trout and mammalian both in relative molecular mass of its alpha and beta subunits and in the catalytic activity. Trout E2 cDNA cloning and nucleotide sequencing revealed that the mature trout E2 subunit consists of 435 residues, and possesses 14 additional residues compared with mammalian E2. Eleven of these are localized in two interdomain segments as two sequences with two and nine residues, respectively. Trout E2 was inferior to rat E2 in the capacity for binding the E1 component, similar to chicken E2. Thus, it appears that non-mammalian BCKADH E2 is distinct from that in mammals in the structure of interdomain segments, resulting in reduction of overall activity of the enzyme complex.