Histamine H1 Receptor-Mediated JNK Phosphorylation Is Regulated by Gq Protein-Dependent but Arrestin-Independent Pathways

Arrestins are known to be involved not only in the desensitization and internalization of G protein-coupled receptors but also in the G protein-independent activation of mitogen-activated protein (MAP) kinases, such as extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK), to regulate cell proliferation and inflammation. Our previous study revealed that the histamine H1 receptor-mediated activation of ERK is dually regulated by Gq proteins and arrestins. In this study, we investigated the roles of Gq proteins and arrestins in the H1 receptor-mediated activation of JNK in Chinese hamster ovary (CHO) cells expressing wild-type (WT) human H1 receptors, the Gq protein-biased mutant S487TR, and the arrestin-biased mutant S487A. In these mutants, the Ser487 residue in the C-terminus region of the WT was truncated (S487TR) or mutated to alanine (S487A). Histamine significantly stimulated JNK phosphorylation in CHO cells expressing WT and S487TR but not S487A. Histamine-induced JNK phosphorylation in CHO cells expressing WT and S487TR was suppressed by inhibitors against H1 receptors (ketotifen and diphenhydramine), Gq proteins (YM-254890), and protein kinase C (PKC) (GF109203X) as well as an intracellular Ca2+ chelator (BAPTA-AM) but not by inhibitors against G protein-coupled receptor kinases (GRK2/3) (cmpd101), β-arrestin2 (β-arrestin2 siRNA), and clathrin (hypertonic sucrose). These results suggest that the H1 receptor-mediated phosphorylation of JNK is regulated by Gq-protein/Ca2+/PKC-dependent but GRK/arrestin/clathrin-independent pathways.

Differential regulation of histamine H1 receptor-mediated ERK phosphorylation by Gq proteins and arrestins

Gq protein-coupled histamine H1 receptors play crucial roles in allergic and inflammatory reactions, in which the phosphorylation of extracellular signal-regulated kinase (ERK) appears to mediate the production of inflammatory cytokines. ERK phosphorylation is regulated by G protein- and arrestin-mediated signal transduction pathways. Here, we aimed to explore how H1 receptor-mediated processes of ERK phosphorylation might be differentially regulated by Gq proteins and arrestins. For this purpose, we evaluated the regulatory mechanism(s) of H1 receptor-mediated ERK phosphorylation in Chinese hamster ovary cells expressing Gq protein- and arrestin-biased mutants of human H1 receptors, S487TR and S487A, in which the Ser487 residue in the C-terminal was truncated and mutated to alanine, respectively. Immunoblotting analysis indicated that histamine-induced ERK phosphorylation was prompt and transient in cells expressing Gq protein-biased S487TR, whereas it was slow and sustained in cells expressing arrestin-biased S487A. Inhibitors of Gq proteins (YM-254890) and protein kinase C (PKC) (GF109203X), and an intracellular Ca2+ chelator (BAPTA-AM) suppressed histamine-induced ERK phosphorylation in cells expressing S487TR, but not those expressing S487A. Conversely, inhibitors of G protein-coupled receptor kinases (GRK2/3) (cmpd101), β-arrestin2 (β-arrestin2 siRNA), clathrin (hypertonic sucrose), Raf (LY3009120), and MEK (U0126) suppressed histamine-induced ERK phosphorylation in cells expressing S487A, but not those expressing S487TR. These results suggest that H1 receptor-mediated ERK phosphorylation might be differentially regulated by the Gq protein/Ca2+/PKC and GRK/arrestin/clathrin/Raf/MEK pathways to potentially determine the early and late phases of histamine-induced allergic and inflammatory responses, respectively.

[Diagnosis of acute phase of venous infarction by diffusion-weighted image: case report and review of the literature]

Diffusion-weighted imaging (DWI) can diagnose early stage not only of the arterial infarction but also of venous infarction. We successfully diagnosed a case as acute venous infarction by DWI. The patient, an infant of one year and ten months, presented disturbance of consciousness and left hemiparesis two weeks after dehydration and infections. Computed tomographic scan revealed a cerebral hemorrhage in the right parietal lobe. Cerebral angiography revealed no contrast filling of the posterior side of superior sagittal sinus, straight sinus and transverse sinus. DWI demonstrated a large hyperintensity lesion around the hematoma, suggesting venous infarction in the early stage. We thought that venous infarction was caused by secondary extension of thrombus to cerebral cortical veins and deep cerebral veins. External decompression and postoperative hypothermia therapy were performed because of rapidly deteriorating intracranial hypertension. Intracranial hypertension was, however, uncontrollable. The patient died four days after the onset. Diagnosis of the venous infarction by DWI was discussed along with other recent reports. Diffusion hyperintensity was displayed in almost all subjects with acute venous infarction. DWI pattern of venous infarction is more heterogeneous than that of arterial one because pathway from venous obstruction to infarction is complicated.

Sigmoid sinus thrombosis after mild closed head injury in an infant: diagnosis by magnetic resonance imaging in the acute phase--case report

Intracranial sinus thrombosis following a mild closed head injury without a skull fracture or intracranial hematoma is extremely rare. A 23-month-old girl presented with vomiting and gait ataxia 1 day after occipital trauma. Computed tomography revealed a slightly increased density area in the region of the left sigmoid sinus. T1-weighted magnetic resonance (MR) imaging demonstrated an isointense area in the left sigmoid sinus and T2-weighted imaging showed a hyperintense area reflecting the characteristics of oxyhemoglobin. MR angiography and cerebral angiography indicated occlusion of the left sigmoid sinus. After 4 days of conservative treatment, her symptoms subsided completely. Follow-up MR angiography and cerebral angiography showed recanalization of the sigmoid sinus. The MR images and MR angiograms were useful for both early diagnosis and follow-up. Treatment should reflect the severity of individual cases, and early diagnosis will help achieve a good outcome.