Structural analysis of the mechanism of inhibition and allosteric activation of the kinase domain of HER2 protein

Aberrant signaling of ErbB family members human epidermal growth factor 2 (HER2) and epidermal growth factor receptor (EGFR) is implicated in many human cancers, and HER2 expression is predictive of human disease recurrence and prognosis. Small molecule kinase inhibitors of EGFR and of both HER2 and EGFR have received approval for the treatment of cancer. We present the first high resolution crystal structure of the kinase domain of HER2 in complex with a selective inhibitor to understand protein activation, inhibition, and function at the molecular level. HER2 kinase domain crystallizes as a dimer and suggests evidence for an allosteric mechanism of activation comparable with previously reported activation mechanisms for EGFR and HER4. A unique Gly-rich region in HER2 following the α-helix C is responsible for increased conformational flexibility within the active site and could explain the low intrinsic catalytic activity previously reported for HER2. In addition, we solved the crystal structure of the kinase domain of EGFR in complex with a HER2/EGFR dual inhibitor (TAK-285). Comparison with previously reported inactive and active EGFR kinase domain structures gave insight into the mechanism of HER2 and EGFR inhibition and may help guide the design and development of new cancer drugs with improved potency and selectivity.     

Pulmonary tumor thrombotic microangiopathy successfully treated with corticosteroids: a case report

Background

Pulmonary tumor thrombotic microangiopathy is a special type of tumor thromboembolism. We report the case of a patient who developed pulmonary tumor thrombotic microangiopathy with alveolar hemorrhage. Almost all patients with pulmonary tumor thrombotic microangiopathy die within 1 week of the onset of dyspnea; however, the prognosis in this case was better, with 10 weeks of survival from presentation.

Case presentation

A 62-year-old Japanese man was referred to our hospital with a 4-week history of dyspnea on exertion and severe pulmonary hypertension. Five years previously, he had undergone distal gastrectomy for gastric cancer. He was afebrile, normotensive, and hypoxemic. A physical examination was unremarkable except for purpura on his upper extremities and trunk. Blood tests showed anemia and disseminated intravascular coagulation. Chest computed tomography revealed diffuse ground-glass opacities with emphysema in his upper lungs, moderate pleural effusions, mediastinal lymphadenopathy, and enlargement of the right ventricle and main pulmonary artery. A computed tomography pulmonary angiogram showed no evidence of pulmonary embolism. Lung perfusion scintigraphy showed multiple segmental defects. Although recurrence of gastric cancer was confirmed from the results of bone marrow biopsy, bronchoscopy was not performed due to bleeding diathesis. He was treated with corticosteroids, antibiotics, and platelet transfusion, following which resolution of the abnormal lung shadows and right ventricular pressure overload along with partial alleviation of respiratory failure was observed. Because of his poor performance status, he was eventually transited to palliative care and died 6 weeks after admission. Necropsy of the lung confirmed the diagnosis of pulmonary tumor thrombotic microangiopathy with alveolar hemorrhage.

Conclusions

Pulmonary tumor thrombotic microangiopathy should be considered in the differential diagnosis of patients with cancer who present with severe pulmonary hypertension. In pulmonary tumor thrombotic microangiopathy, local inflammation in pulmonary microvasculature may contribute to pulmonary hypertension, and regulation of inflammation using corticosteroids may help improve the prognosis.

     

Isolation and Some Properties of Acid Phosphatase-11 from Tomato Leaves

An isozyme of acid phosphatase-1, acid phosphatase-1¹, was purified from the leaves of tomato (Lycopersicon esculentum) to homogeneity and characterized. The purified enzyme was homogeneous on polyacrylamide gel electrophoresis with or without sodium dodecyl sulfate. The gel filtration analysis showed that the native molecule had a relative molecular mass of about 61 kilodaltons (kDa). The relative molecular mass of the subunit on gel electrophoresis with sodium dodecyl sulfate was about 32 kDa, indicating that the native form of the enzyme was a homodimer. It was suggested by periodic acid-Schiff staining on the gel that the enzyme was a glycoprotein. The Km for p-nitrophenylphosphate was 2.9 × 10^?3 m. The enzyme had a pH optimum of 4.5 in 0.15 m potassium acetate buffer with p-nitrophenylphosphate as a substrate. This enzyme was activated by divalent metal ions, such as Zn²⁺, Mg²⁺, and Mn²⁺. The N-terminal amino acids were sequenced after the purified enzyme was treated with pyroglutamylpeptidase. It was suggested that the N-terminal amino acid was pyroglutamate.     

Metabolism of Aromatic Compounds by Microbes

The metabolic products of m-hydroxybenzoic acid formed by certain Pseudomonas, Micrococcus, and Bacterium strains which possess oxidizing ability of this acid were detected by paperchromatography. It was recognized that protocatechuic acid or gentisic acid are intermediary metabolites of m-hydroxybenzoic acid by these bacteria and the both acids are not detected in one cultural broth.     

Futile short-patch DNA base excision repair of adenine:8-oxoguanine mispair

8-Oxo-7, 8-dihydrodeoxyguanosine (8-oxo-dG), one of the representative oxidative DNA lesions, frequently mispairs with the incoming dAMP during mammalian DNA replication. Mispaired dA is removed by post-replicative base excision repair (BER) initiated by adenine DNA glycosylase, MYH, creating an apurinic (AP) site. The subsequent mechanism ensuring a dC:8-oxo-dG pair, a substrate for 8-oxoguanine DNA glycosylase (OGG1), remains to be elucidated. At the nucleotide insertion step, none of the mammalian DNA polymerases examined exclusively inserted dC opposite 8-oxo-dG that was located in a gap. AP endonuclease 1, which possesses 3′→5′ exonuclease activity and potentially serves as a proofreader, did not discriminate dA from dC that was located opposite 8-oxo-dG. However, human DNA ligases I and III joined 3′-dA terminus much more efficiently than 3′-dC terminus when paired to 8-oxo-dG. In reconstituted short-patch BER, repair products contained only dA opposite 8-oxo-dG. These results indicate that human DNA ligases discriminate dC from dA and that MYH-initiated short-patch BER is futile and hence this BER must proceed to long-patch repair, even if it is initiated as short-patch repair, through strand displacement synthesis from the ligation-resistant dC terminus to generate the OGG1 substrate, dC:8-oxo-dG pair.     

Direct Visualization of Lignifying Secondary Wall Thickenings in Zinnia elegansCells in Culture

The lignifying secondary wall thickenings of tracheary elementsthat were differentiating from Zinnia mesophyll cells in suspensionculture were examined by a freeze-etch replica technique. Cellulosemicrofibrils in primary and secondary wall thickenings differedin terms of both width and arrangement. The primary wall wasobserved as a randomly arranged network of microfibrils. Bycontrast to microfibrils in the secondary wall thickenings werehighly organized, with many pores and spaces between them. Numerousfilamentous and granular cross-links were observed in both primarywalls and secondary wall thickenings. As lignifica-tion proceeded,the cellulose microfibrils in secondary wall thickenings becameobscure as a result of the deposition of large numbers of sphericalbodies around and between the microfibrils. This material hadcompletely covered the fibrous matrix by the end of lignification.It might have been composed of the products of the dehydrogenationof monolignols. We also noted that the microfibrils appearedto be slightly irregular or wavy just after the start of lignificationbut were straighter and appeared to be more rigid when lignificationwas complete. (Received July 25, 1996; Accepted April 24, 1997)     

Study on the origin of apical tubules in ileal absorptive cells of suckling rats using concanavalin-A as a membrane-bound tracer

Summary The ileal absorptive cells of suckling rats exhibit high levels of endocytic activity being engaged in nonselective uptake of macromolecules from the intestinal lumen. The apical cytoplasm usually contains an extensive network of small, membrane-limited tubules (apical tubules: AT), in addition to newly formed endocytic vesicles and large endocytic vacuoles. To determine whether the AT are directly involved in the endocytic process by carrying the tracer into the cell, we have analysed movements of the apical cell membrane of the ileal absorptive cells by using a membrane-bound tracer (horseradish peroxidase-labelled cancanavalin-A: Con-A HRP). The ileal absorptive cells were exposed in vitro to Con-A HRP for 10 min at 4° C, incubated for different times in Con-A free medium at 37° C, and prepared for electron microscopy. After 1 min incubation at 37° C, invaginations of the apical cell membrane, including coated pits, and endocytic vesicles were labelled with HRP-reaction product, whereas the AT and large endocytic vacuoles were negative. After 2.5 min, almost all the large endocytic vacuoles were labelled with reaction product, which was seen in their vacuolar lumen and along the luminal surface of their limiting membrane. A few AT with reaction product were seen in the apical cytoplasm; they were in frequent connection with the reaction-positive large endocytic vacuoles. With increasing incubation time, the number of the labelled AT increased. Thus, after 15 min at 37° C, the apical cytoplasm was fully occupied by the reaction-positive AT. The ends of these AT were often continuous with small spherical coated vesicles. No reaction product was detected in the Golgi complex at any time after incubation. These observations indicate that the AT located in the apical cytoplasm probably originate by budding off from the large endocytic vacuoles, rather than being involved in the process of endocytosis.     

Discovery of novel 2-(3-phenylpiperazin-1-yl)-pyrimidin-4-ones as glycogen synthase kinase-3β inhibitors

We herein describe the results of further evolution of glycogen synthase kinase (GSK)-3β inhibitors from our promising compounds containing a 2-phenylmorpholine moiety. Transformation of the morpholine moiety into a piperazine moiety resulted in potent GSK-3β inhibitors. SAR studies focused on the phenyl moiety revealed that a 4-fluoro-2-methoxy group afforded potent inhibitory activity toward GSK-3β. Based on docking studies, new hydrogen bonding between the nitrogen atom of the piperazine moiety and the oxygen atom of the main chain of Gln185 has been indicated, which may contribute to increased activity compared with that of the corresponding phenylmorpholine analogues. Effect of the stereochemistry of the phenylpiperazine moiety is also discussed.     

The Melatonin Agonist Ramelteon Induces Duration-Dependent Clock Gene Expression through cAMP Signaling in Pancreatic INS-1 β-Cells

Prolonged exposure to melatonin improves glycemic control in animals. Although glucose metabolism is controlled by circadian clock genes, little is known about the role of melatonin signaling and its duration in the regulation of clock gene expression in pancreatic β-cells. Activation of MT₁ and MT₂ melatonin receptors inhibits cAMP signaling, which mediates clock gene expression. Therefore, this study investigated exposure duration-dependent alterations in cAMP element-binding protein (CREB) phosphorylation and clock gene expression that occur during and after exposure to ramelteon, a selective melatonin agonist used to treat insomnia. In rat INS-1 cells, a pancreatic β-cell line endogenously expressing melatonin receptors, ramelteon persistently decreased CREB phosphorylation during the treatment period (2–14 h), whereas the subsequent washout induced an enhancement of forskolin-stimulated CREB phosphorylation in a duration- and concentration-dependent manner. This augmentation was blocked by forskolin or the melatonin receptor antagonist luzindole. Similarly, gene expression analyses of 7 clock genes revealed the duration dependency of the effects of ramelteon on Rev-erbα and Bmal1 expression through melatonin receptor-mediated cAMP signaling; longer exposure times (14 h) resulted in greater increases in the expression and signaling of Rev-erbα, which is related to β-cell functions. Interestingly, this led to amplified oscillatory Rev-erbα and Bmal1 expression after agonist washout and forskolin stimulation. These results provide new insights into the duration-dependent effects of ramelteon on clock gene expression in INS-1 cells and may improve the understanding of its effect in vivo. The applicability of these results to pancreatic islets awaits further investigation.