No abstract

Dopamine D2 receptors (D2Rs; short form, which is one of the alternative splicing variants) expressed in COS-7 cells are internalized in an agonist-dependent manner only when G protein-coupled receptor kinase 2 (GRK2) is coexpressed [Ito, K., Haga, T., Lameh, J. & Sade Âe, W., (1999) Eur. J. Biochem. 260, 112±119]. We have examined the effects of coexpression of dynamin, a small molecular mass GTP-binding protein, rab5A, and their mutants on the internalization of D2Rs in the presence of both dopamine (10 or 100 mm) and GRK2. The rate and extent of D2R internalization was increased or decreased by coexpression of dynamin I or a dominant-negative form of dynamin I (dynamin I K44E), respectively. The effects of coexpressing these two dynamins were more prominent at 10 mm dopamine than at 100 mm. In the presence of 10 mm dopamine, internalization of D2R was completely suppressed when dynamin I K44E was coexpressed, and the half-life (t1 2 ) of D2R internalization decreased relative to cells not expressing dynamin from 82 to 29 min when dynamin I was coexpressed. Internalization of D2Rs was facilitated or suppressed by coexpression of a constitutively active form of rab5A (rab5A Q79L) or a dominant-negative form of rab5A (rab5A S34N), respectively. The t1 2 of D2R internalization at 10 mm dopamine decreased from 82 to 16 min in cells coexpressing rab5A Q79L. The effect of coexpression of rab5A S34N was more apparent at 100 mm dopamine than at 10 mm; the t1 2 of D2R internalization at 100 mm dopamine increased from 20 to 56 min and the proportion of internalized D2Rs after 120 min decreased from 53 to 28%. These results indicate that the internalization of D2Rs is dependent on the action of dynamin as well as GRK2, and is regulated by the action of rab5A.Keywords: G protein-coupled-receptor kinase 2; dopamine D2 receptor; rab5; dynamin; internalization.Many kinds of G protein-coupled receptors (GPCRs) are transferred to intracellular compartments from the plasma membrane within minutes of stimulation by agonists, a process that is termed sequestration, or internalization of receptors. This internalization serves to clear receptors from the cell surface, thereby modulating the responsiveness of the cell to further stimulation and/or resensitizing desensitized receptors [1±3]. The molecular mechanism of receptor internalization has not yet been fully elucidated, but several lines of evidence indicate that G protein-coupled receptor kinases (GRKs), arrestin, clathrin, and dynamin, are involved in the internalization of GPCRs, particularly of b 2 adrenergic and muscarinic acetylcholine receptors. Muscarinic m2 receptors expressed in COS-7 and the chemokine receptor CCR-5 expressed in HEK293 cells have been shown to be phosphorylated in an agonist-induced manner by GRK2, and their consequent internalization is facilitated by coexpression of GRK2 [4,5]. In addition, coexpression of a dominant-negative mutant of GRK2 (DN-GRK2) has been reported to inhibit agonist-dependent internalization and phosphorylation of b 2 adrenerg...

These data suggest that TGF-beta1 may contribute to the interstitial fibrosis found in the human kidney with ureteral obstruction, mainly because of an increase in the expression of this cytokine without significant changes to its receptors.

The chromosomal inversion (16)(p13q22), which is associated with the M4-eosinophilia subtype of human acute myeloid leukemia, causes the fusion of two distinct genes

Background: A retrospective study was conducted to examine the host factors of 240 testicular germ cell tumor patients. This study was performed to address a new theory proposed by Skakkebaek called testicular dysgenesis syndrome which claims that cryptorchism, hypospadias, poor semen quality and testicular germ cell tumors are symptoms of an underlying testicular dysgenesis in uterus. Methods:The past health histories and familial episodes of 240 testicular germ cell tumor patients were examined. The past health histories included cryptorchism, hypospadias, infertility, atrophic testis and inguinal hernia. Results: Of the 240 patients, 13 (5.4%) had a history of cryptorchism or orchidopexy. Two (0.8%) showed existence of hypospadias or had experienced urethroplasty. Among 129 married couples, 104 (80.6%) couples were fertile. Three (1.3%) patients developed testicular tumors after they were diagnosed as infertile or came to the hospital with the complaints of infertility. Four (1.7%) had contralateral atrophic testis. 19 (7.9%) had experienced inguinal herniorrhaphy before age 15. Three (1.3%) had testicular germ cell tumor patients among their family or relatives. Conclusions:The testicular germ cell tumor patients showed a considerable incidence of complications such as cryptorchism, hypospadias and incomplete closure of processus vaginalis. Cryptorchism, perinatal factors and familial factors could be risks for developing testicular germ cell tumors.