Tomoko Izaki

Novel Human Homologues of p47phox and p67phox Participate in Activation of Superoxide-producing NADPH Oxidases

Abstract The catalytic core of a superoxide-producing NADPH oxidase (Nox) in phagocytes is gp91phox/Nox2, a membrane-integrated protein that forms a heterodimer with p22phox to constitute flavocytochrome b558. The cytochrome becomes activated by interacting with the adaptor proteins p47phox and p67phox as well as the small GTPase Rac. Here we describe the cloning of human cDNAs for novel proteins homologous to p47phox and p67phox, designated p41nox and p51nox, respectively; the former is encoded by NOXO1 (Nox organizer 1), and the latter is encoded by NOXA1 (Nox activator 1). The novel homologue p41nox interacts with p22phox via the two tandem SH3 domains, as does p47phox. The protein p51nox as well as p67phox can form a complex with p47phox and with p41nox via the C-terminal SH3 domain and binds to GTP-bound Rac via the N-terminal domain containing four tetratricopeptide repeat motifs. These bindings seem to play important roles, since p47phox and p67phox activate the phagocyte oxidase via the same interactions. Indeed, p41nox and p51nox are capable of replacing the corresponding classical homologue in activation of gp91phox. Nox1, a homologue of gp91phox, also can be activated in cells, when it is coexpressed with p41nox and p51nox, with p41nox and p67phox, or with p47phox and p51nox; in the former two cases, Nox1 is partially activated without any stimulants added, suggesting that p41nox is normally in an active state. Thus, the novel homologues p41nox and p51nox likely function together or in combination with a classical one, thereby activating the two Nox family oxidases.

Molecular Recognition in Dimerization between PB1 Domains

The PB1 (Phox and Bem 1) domain is a recently identified module that mediates formation of a heterodimeric complex with other PB1 domain, e.g. the complexes between the phagocyte oxidase activators p67phox and p40phox and between the yeast polarity proteins Bem1p and Cdc24p. These PB1 domains harbor either a conserved lysine residue on one side or an acidic OPCA (OPR/PC/AID) motif around the other side; the lysine of p67phox or Bem1p likely binds to the OPCA of p40phox or Cdc24p, respectively, via electrostatic interactions. To further understand molecular recognition by PB1 domains, here we investigate the interactions mediated by proteins presenting both the lysine and OPCA on a single PB1 domain, namely Par6, atypical protein kinase C (aPKC), and ZIP. Par6 and aPKC form a complex via the interaction of the Par6 lysine with aPKC-OPCA but not via that between the aPKC lysine and Par6-OPCA, thereby localizing to the tight junction of epithelial cells. aPKC also uses its OPCA to interact with ZIP, another protein that has a PB1 domain presenting both the lysine and OPCA, whereas aPKC binds via the conserved lysine to MEK5 in the same manner as ZIP interacts with MEK5. In addition, ZIP can form a homotypic complex via the conserved electrostatic interactions. Thus the PB1 domain appears to be a protein module that fully exploits its two mutually interacting elements in molecular recognition to expand its repertoire of protein-protein interactions.

The WD40 protein Morg1 facilitates Par6–aPKC binding to Crb3 for apical identity in epithelial cells

Par6–aPKC recruitment to the premature apical membrane through Morg1 interaction with Par6 is required for definition of apical identity of epithelial cells.

Association between the HER2 expression and histological differentiation in Wilms tumor

Human epidermal growth factor receptors (HER) play a critical role in the branching morphogenesis of renal tubules. In the current study, we analyzed the expression of HER2 in Wilms tumor and assessed the role of this gene in the tumorgenesis of Wilms tumor. During the period from 1960 to 2005, 40 patients with Wilms tumor were treated in our department. Twenty-four of those patients (except those with clear cell sarcoma of the kidney and malignant rhabdoid tumor of the kidney) were collected and assessed. The histological component of each Wilms tumor was divided into three categories (epithelial, blastemal, and mesenchymal) and the extent of HER2 protein expression was analyzed immunohistochemically. The normal kidney tissue accompanied with 12 cases of Wilms tumor was also examined. In the normal kidney, HER2 showed a strong immunoreactivity in the cell membranes of the collecting tubules and in the endothelial cells. Of 24 cases, 15 cases showed an epithelial component, while 24 cases had a blastemal component and 21 cases had a mesenchymal component, respectively. Among the 15 specimens with epithelial cell differentiation, eight (53.3%) showed HER2 immunoreactive epithelial cells. HER2 immunoreactive blastemal cells were present in 11 (45.8%) of 24 specimens with blastemal cells. On the other hand, only 3 (14.3%) of 21 specimens containing mesenchymal cells showed HER2 immunoreactivity. These results suggest that the extent of HER2 expression is associated with epithelial differentiation in Wilms tumor. These histological findings may therefore help to explain the development of Wilms tumor from the standpoint of histological differentiation.

Diagnostic value of lectin reactive alpha-fetoprotein for neoinfantile hepatic tumors and malignant germ cell tumors: Preliminary study

Background and Purpose The serum alpha-fetoprotein (AFP) level has been used as a tumor marker for hepatoblastoma, and malignant germ cell tumors in pediatric patients. The AFP has 3 isoforms (L1, L2, L3), and the usefulness of the L3 fraction as a diagnostic marker for the adult hepatocellular carcinoma is well known. However, there are few reports dealing with various pediatric malignant tumors. In the current study, we analyzed the diagnostic value of AFP fractions for pediatric diseases, in particular, those occurring in the neoinfantile period. Materials and Methods From 2003 to 2006, two cases of hepatoblastoma, and 5 cases of germ cell tumor, all of which were neoinfantile, were treated in our department. In our analytical system (LiBASys), the level of the L3 fraction contains the majority of the L2 fraction. The total AFP (ng/mL) level and the L3 fraction (%) were measured to assess the usefulness of the L3 fraction as a diagnostic marker. Results In all cases of hepatoblastoma and yolk sac tumor, both the total AFP and the L3 fraction were high, either before treatment or in the presence of malignant tumors. Most of the cases of neonatal immature teratoma showed a high total AFP level during the neoinfantile period, however, the L3 fraction was around 10%, and decreased after surgical treatment. Only 1 case of the immature teratoma demonstrated malignant transformation, when the patient was 8 months old. As the total AFP and the AFP-L3 fraction were proportionally elevated, the patient was treated with additional surgical resection and chemotherapy. In the case of neonatal mature teratoma, the L3 fraction was below 0.5%, even when the total AFP level was high. Discussion Our results indicated that the level of the L3 fraction accurately confirmed the existence, or the malignant potential of hepatic tumor or germ cell tumor. The L3 fraction is useful as a tumor marker during the neoinfantile period.

Ondine's curse associated with Hirschsprung disease and ganglioneuroblastoma.

Ondine’s curse, also called congenital central alveolar hypoventilation (CCAH), is a rare condition involving failed automatic respiration in the absence of cardiopulmonary disease, resulting in inadequate ventilation with progressive hypercapnia and hypoxia during sleep (1). The prognosis of this syndrome is poor and its cause is not fully known. However, it probably is a disorder of the central chemoreceptor that originates from the neural crest cells (2). This syndrome is often reported in association with Hirschsprung disease (HD) because of an abnormal distribution and/or migration of neural crest cells and neurogenic tumors that originate from the neural crest cells. Therefore, these diseases are often described as “neurocristopathy,” first reported in 1974 by Bolande (3), and characterized by lesions related to neural cell growth, migration, or differentiation. Several cases have been reported of CCAH and HD (1,2), CCAH and neurogenic tumors (4), or HD and neurogenic tumors (5). However, it is extremely rare to find patients who simultaneously have all three diseases (1,6–11). We report a 0 day-old Japanese girl with Ondine’s curse associated with HD involving aganglionosis from the proximal jejunum to the rectum and right retroperitoneal ganglioneuroblastoma. Mutation analyses of the receptor tyrosine kinase (RET) proto-oncogene, glial cell-derived neurotrophic factor gene, and neuturin were also made for this patient.

Extensive spinal epidural immature teratoma in an infant: case report

Here, the authors present an extremely rare case of an extensive spinal epidural teratoma (SET) in an infant and provide a review of the cases in the literature. In this report, the authors focused on the clinical manifestation and management of extensive SET. A 64-day-old girl presented with severe dyspnea and paraparesis caused by a large thoracic mass. Imaging studies revealed that the mass originated from the epidural space of the thoracic spine and extended from C7 to L1. The tumor extended bilaterally through the intervertebral foramina and formed a large posterior mediastinal mass. The tumor was partially resected via laminotomy after an emergency thoracotomy. The remnant grade I immature teratoma grew rapidly. After a re-laminotomy and bilateral thoracotomy, the residual tumor stopped growing. However, the patients paraparesis improved very little, and her scoliosis progressed gradually. Therefore, SET should be included in the differential diagnosis when an infant patient with paraparesis of the lower extremities is encountered. Timely diagnosis, aggressive treatment, and close monitoring are of critical importance to successful recovery in such patients.